XLIV Ibero-Latin American Congress on Computational Methods in Engineering

Isogeometric analysis with interactive modeling of multi-patches NURBS

2024-04-26T19:08:34+00:00

Isogeometric analysis (IGA) is an innovative method of numerical analysis of structures that seeks to
unite design and simulation, allowing the creation of computational models that preserve the exact geometry of
the problem. This approach uses mathematical functions known as NURBS (Non-Uniform Rational B-Splines),
widely used in CAD systems to model curves and surfaces. In the context of the IGA, these same functions that
define the geometry are used to approximate the field variables. This work aims to provide a computational tool
for two-dimensional isogeometric analysis, covering the stages of modeling, analysis, and visualization of the
results. It is worth mentioning that the visualization of results is still a prototype under development. The system
consists of two software: FEMEP (Finite Element Method Educational Computer Program), developed in Python,
responsible for geometric modeling, and FEMOOLab (Finite Element Method Object-Oriented Laboratory), a
MATLAB software used for analysis and display of results. The proposed tool presents an intuitive graphical user
interface (GUI) to facilitate the visualization and manipulation of NURBS curves, providing advanced modeling
features. The device also includes features for the automatic intersection of curves and region recognition to
simplify and streamline the modeling process. In addition, the modeling software is also responsible for managing
attributes such as material properties and natural and essential boundary conditions. A relevant aspect of this work
is to provide open-source code, allowing the user and developer community to collaborate and contribute to the
continuous development of the tool. This open-source approach encourages innovation and shared growth,
fostering an environment for collaboration and mutual learning. This tool aims to make isogeometric analysis
accessible even to users with basic programming knowledge, expanding its scope and enabling its application in
various projects and engineering studies.

LESM: An interactive-graphics open-source educational software in MATLAB for static and dynamic structural analysis

2024-04-26T19:15:57+00:00

This paper highlights the latest advancements in LESM (Linear Elements Structure Model), an educational software designed to analyze frames, trusses, and grillages. Developed as an open-source project using MAT- LAB, LESM boasts a user-friendly Graphical User Interface (GUI) that facilitates modeling and post-processing. The primary focus of the latest version of LESM centers around dynamic analysis, which necessitated substantial modifications to the program’s analysis module. The notable enhancements encompass integrating inertial and damping effects, robust support for time-dependent load conditions, and introducing a transient analysis solver that accommodates multiple time integration schemes. The upgraded GUI is one of the most significant improvements, empowering users to leverage the dynamic analysis features interactively. This development holds immense po-
tential in academic applications, offering students and researchers a valuable tool for exploring and understanding structural dynamics.

Tri-objective optimization of 3d Steel Frames Considering Columns Ori- entation and Bracing System Configuration as Design Variables

2024-04-26T19:21:12+00:00

In the field of steel structural design, particularly in the context of tall buildings, there is a need to minimize costs while enhancing performance with regards to dynamic behavior, and structural stability. Furthermore, determining the most suitable geometric configuration for the bracing system and the optimal orientation of the principal axes of inertia for the columns is not readily apparent. Typically, such decisions are based on the expertise of the designer. Consequently, solving this complex problem, which involves simultaneously considering three objectives, is far from straightforward. Hence, this paper focuses on the tri-objective optimization of spatial steel frames, considering both the configuration of the bracing system and the orientation of the columns as design variables. To accomplish this, four differential evolution algorithms have been employed: the third evolution step of generalized differential evolution (GDE3), the success history-based adaptive multi-objective differential evolution (SHAMODE), the SHAMODE with whale optimization (SHAMODE-WO), and the multi-objective meta-heuristic with iterative parameter distribution estimation (MM-IPDE). Additionally, a multi-criteria tournament method is utilized to extract desired solutions from the Pareto front, aligning with the preferences of the decision-maker.

A phase-field model to simulate hydraulic fracture propagation

2024-04-26T19:27:18+00:00

The term hydraulic fracturing is used in problems where the fracture starts and propagates due to the hydraulic load of the fluid inside the fracture. In petroleum engineering, hydraulic fracturing is mainly used to re-cover oil and gas from reservoirs. For structural engineering, a great interest is in the analysis of concrete structures that are exposed to hydraulic environments, such as dams, offshore platforms, and bridges. Given the relevance of the subject, the aim is to study the hydraulic fracturing process using a phase-field model. Phase-field models have been intensively studied in the last decade regarding their application in hydraulic fracturing problems, with emphasis on its variational formulation that allows the detection of the initiation, propagation, and nucleation of any number of cracks without the need for additional techniques. The adopted model has been studied and extended by several researchers over the years, who have shown its robustness and efficiency. It is considered a homogeneous and impermeable reservoir and an incompressible fluid, which is not explicitly modeled, only its effect on the crack is considered, indirectly, from the phase-field model. All implementation and numerical simulations were carried out in the INSANE (INteractive Structural ANalysis Environment), an open-source software developed at the Structural Engineering Department of the Federal University of Minas Gerais.

Modeling in digital rock analysis: an image segmentation tutorial

2024-04-26T18:59:08+00:00

Image-based simulations are fundamental to assist in rock characterizations using a fully digital envi-
ronment. The basic workflow in digital rock physics or petrophysics comprises three general phases: 1) 3-D scan:

image acquisition and reconstruction, 2) 3-D modeling: image processing and segmentation, and 3) 3-D analysis:

image simulation and characterization. In this work, we focus in the modeling phase, by presenting two educa-
tional approaches to perform image segmentation of rock samples. The first approach relies completely in the use

of software with user interfaces, whereas the second one is a fully script-based approach relying in open source

packages with Python APIs. Although we describe educational approaches, which adopt compact sets of dedi-
cated strategies, they can also be combined to achieve the best performance and learning process. We assume here

that the images were acquired by high-resolution X-ray micro-computed tomography (micro-CT), and that they
will be employed to perform rock characterizations, such as determination of the effective absolute permeability
of porous materials based on the concepts of numerical homogenization. Therefore, step-by-step procedures and
implementations to achieve high quality segmented images are described.

NUMERICAL SIMULATION OF THE VAGINAL WALL REINFORCE- MENT USING COG THREADS

2024-04-29T14:09:58+00:00

Pelvic floor disorders (PFD), including Pelvic Organ Prolapse (POP), can significantly negatively impact a woman’s daily activities and quality of life. POP is a complex and challenging topic in the medical field. The number of cases of genital prolapse has been on the rise each year, with one in ten women requiring at least one surgical procedure and one in four women in midlife having asymptomatic prolapse. The use of mesh implants to correct prolapses requires knowledge of the mechanical properties of the mesh and vaginal and surrounding tissues so that the type of mesh can be chosen to match the actual resistance of the tissue as closely as possible. Using mesh implants to correct POP has proven less effective, often requiring hospital readmission and further surgery;
an alternative surgical intervention technique using injectable biodegradable cog threads was proposed. Typically used for face-lifting procedures, these threads will be applied to reinforce and correct vaginal wall defects. The application of Finite element analysis (FEA) to this research allows us to personalize and select suitable POP correction techniques and study the effect of alternative reinforcement techniques, pointing to areas experiencing critical levels of stress and strain. The 3D computational model of the vagina will be used to simulate defect repair using cog threads. Through using different vaginal wall properties (i.e., early-stage prolapsed tissue), various conditions of its repair could be simulated: reinforcement with a different number of threads (the density could be adjusted, depending on tissue conditions), different thread geometries (thread diameter, cog type), angle of thread
insertion. The threads we will use in our investigation are commercially available and made of polycaprolactone (PCL).

Development of Data-driven Constitutive Models: Applications in the Fi- nite Element Simulation of Hyperelastic Materials

2024-04-29T14:27:32+00:00

When subjected to large deformations, hyperelastic materials present a highly nonlinear behaviour, which makes their constitutive description complex and computationally expensive. Surrogate models can replace these traditional and costly models and overcome some computational limitations by learning directly from acquired data. Currently, the usage of surrogate models in commercial finite element (FE) software, such as Abaqus, is nonexistent. In this work, surrogate models, able to describe the constitutive behaviour of different materials, were developed and were then incorporated into Abaqus, using a user defined material, programmed in Fortran
Language. Artificial neural networks were trained to predict the isochoric part of the Cauchy stress tensor and the spatial elasticity tensor from the existing data. With the parameters of the trained neural networks, a user defined material was developed. The present method was validated using classical benchmark problems, and the results obtained using the developed constitutive models were compared with the ones obtained with the conventional approach. The correctness of the obtained results highlights the possibility of using data-driven constitutive models to describe the behaviour of hyperelastic materials. The proposed approach can be a viable alternative, avoiding the need to express a given material constitutive equation directly.

Isogeometric Analysis For The Platelets Role On Shear Stress Effect Over The Cancer Cells Into The Blood Vessel

2024-04-29T14:43:34+00:00

The spread of cancer cells from the original place to another part of the body is known by metastasis. During this processes, cancer cells leave from primary tumor, travel through the blood or lymph system, and form a new tumor in other organs or tissues of the body. Before arrive to new tissues, the cancer cell are subject to the natural body defenses. Once inside the blood vessel, the cancer cells are subject to the shear forces and immune defenses. Recent works induce that platelets play a relevant role in the protection of the cancer cell clusters while in circulation, protecting them from the effects of shear force by forming clumps with the cancer cells.
Using Isogeometric analysis, for modelling complex geometries, we numerical study the shear stress effect over the cancer cells on interstitial medium on later works. With the present work we pretend continue the numerical investigation, through the development and analysis of a mathematical model, for the shear stress effect over the cancer cells into the blood vessel and quantify the platelets protection effect.

Characterization of biodegradable PCL cog threads for pelvic organ prolapse treatment

2024-04-29T14:52:40+00:00

Pelvic organ prolapse (POP) is a disease that progressively affects women,
creating a growing demand for the development of new techniques and methods to treat this type
of disorders. The correction of POP is complex, where the mainstay of treatment for these
problems continues to be surgical correction, which is presented, in most cases, as a highly
invasive procedure in the pelvic area with several associated risks and a relatively high failure
rate. With this, our multidisciplinary team studies the potential of providing to healthcare
professionals a novel and beneficial solution to correct pelvic organ prolapse (POP). Our
proposal is based on the application and proof of concept of novel minimally invasive technique,
using biodegradable PCL (polycaprolactone) cog threads for vaginal tissue reinforcement and
prolapse correction. At the moment, the provisional results obtained from the in vitro controlled
degradation and mechanical tests carried out on the cog threads demonstrate that they have the
desired properties for the formulation of a new technique for prolapse correction. These results
are encouraging and suggest the need for additional testing to better understand mechanical and
biological properties of the PCL cog threads.

Simplified vehicle model validation through test track experimental data - An SUV case study analysis

2024-05-01T23:12:26+00:00

The vehicle development process benefits from modeling as a tool for investigating ways to improve
performance and efficiency. Vehicle modeling also enables virtualization of vehicle development, aiming to reduce
costs through virtual simulation of use cases. However, the process of conceiving a vehicle requires a systematic
and structured approach that encompasses validation. Complex models can result in increased development costs

and reduced computational efficiency. In this study, a modified three-degree-of-freedom (bicycle) model is pro-
posed to describe vehicle’s lateral dynamics. As important as the vehicle model, a good representation of tire

dynamic through tire models also play an essential role in representing general vehicle dynamics. In this work, tire
force generation is described by Paceijka’s Magic Formula. The reliability of the model proposed is ensured by
comparing it with test track data from a real SUV vehicle, with estimated inertia data. The model output exhibited
correlation with the actual data.

Design and Implementation of PID-Based Longitudinal and Lateral Con- trol for Small-Scale Vehicle

2024-05-03T11:11:35+00:00

The rapid advancement of technology has brought about significant transformations in various domains.
Electronics and embedded software reached a high-efficiency level, highlighting the need for their implementation
in vehicles. The automotive industry is increasingly recognizing the importance of integrating high-tech control
systems and driver assistance features to ensure safety and comfort. This study will present the development
of an electronic architecture for a small vehicle, comprising an integrated acceleration and braking system and
a steering system which will be controlled by two Electronic Control Units (ECUs). These ECUs will include
control algorithms based on PID (Proportional Integrative Derivative) controllers and the communication between
these units will be performed through the CAN (Controller Area Network) protocol. Virtual tools will be used for
accurate modeling and simulation of control systems, allowing the evaluation of subsystem behavior under various
input conditions. Furthermore, validation tests will be carried out on a small-scale vehicle equipped with embedded
systems. In this way, the use of PID controllers should present satisfactory results, reaching a harmonious balance
between performance and stability.

MODELLING MR DAMPERS UNDER NON-HARMONIC EXCITATIONS THROUGH LOGISTIC CURVE MODELS

2024-05-03T11:16:15+00:00

The present work proposes modifications for a MR damper Sigmoid-curve-based mathematical model
in the literature to expand the range of conditions in which it can be employed, such as white noise excitations,
as well as increase its accuracy. The proposed formulation is compared to Bingham and Bouc-wen models, two

formulations with widespread use for MR dampers. The Sigmoid model addressed some issues with prior mod-
els, such as their inaccuracy in situations where the current or excitation were continuously varied. However, this

articles demonstrates that the model has stability issues, including instances of numerical divergence. This article
proposes tweaks that eliminate the issue. It also further proposes an expanded model with more parameters based

on the generalized logistic curve, evaluating if a better agreement between the numerical model and the experi-
mental data is possible. The results are compared according to the sum of the absolute difference between the

experimental and predicted force on steady-state conditions, where a lower value means a better agreement. The
new model decreased the disagreement between the theoretical and numerical models by 8,6%. The modifications
to address the numerical divergence were a success.

Lateral dynamic identification of a hatchback vehicle

2024-05-03T11:19:20+00:00

Vehicle dynamics identification plays a critical role in understanding and modeling the complex behavior of

vehicles during maneuvers and it is fundamental to the design of Electronic Stability Control (ESC) once a mathe-
matical vehicle model needs to be embedded into the brake ECU to calculate the desired yaw rate. This calculated

value is subsequently compared to the measured yaw rate to define ESC actuation during the maneuver. This
paper discusses linear methods for vehicle dynamics system identification, encompassing both model-based and
data-driven approaches. Model-based methods rely on physical principles and mathematical models to describe the
dynamics, while data-driven methods leverage experimental data to identify system parameters and behaviors. The
focus of this study is the identification of a 2-DOF (Degree-of-Freedom) vehicle model based on real data acquired
from a hatchback vehicle. The hatchback vehicle was instrumented and several maneuvers were performed on a
test track to generate data for identification purposes. Furthermore, different speeds of the vehicle were considered
for the identification, followed by a comparison between all the identified models.

Development of a test bench for lithium-ion battery evaluation: Towards high-performance battery management

2024-05-03T11:24:00+00:00

Developing efficient, high-performance battery management systems requires an experimental bench
capable of real-time data acquisition for various battery parameters. This paper details the development of an
experimental bench, designed for efficient and safe testing of individual cells or cell sets. Notably, this proposed
configuration is more cost-effective than existing market options. The bench facilitates real-time data acquisition
of battery parameters by utilizing the PCI-DAS6013 analog acquisition board from Measurement Computing and
integrated with Simulink Desktop’s real-time environment. Furthermore, it incorporates power resistors, relay
modules, and a controlled bench power supply for precise battery charging and discharge control. The setup’s

versatility extends to testing diverse battery operating conditions by applying varying current profiles during dis-
charge.

Analysis of a Semi-Active Suspension Model with an Attached Inerter Device

2024-05-03T11:28:16+00:00

This study employs computational numerical analysis to investigate a semi-active suspension system
featuring an integrated inerter device within a 1/4 vehicle model. The study aims to assess suspension performance
and the impact of the inerter on vehicle dynamics. Semi-active suspension offers adaptable parameter adjustments
based on current conditions. Incorporating an inerter in suspension, a recent focus, adds inertia without increasing
mass. A quarter car vehicle model was employed for analysis, representing vertical dynamics and passenger
comfort. Numerical simulations encompassed a step road profile, comparing semi-active suspension versus passive
suspension. Results, including body displacement, highlighted improved performance with the inerter. Vertical
displacement and accelerations were significantly reduced, enhancing comfort. This underscores the inerter's
potential to enhance semi-active suspension performance effectively.

Improving the vibration control performance of metamaterial structures by the inclusion of nonlinear local resonators

2024-05-04T01:12:37+00:00

The use of periodicity has become an exciting solution for structural noise and vibration reduction in many engineering applications. Acoustic metamaterials are structures built using repetitive assemblies of identical elements to explore either Bragg-scattering or internal resonance to control mechanical waves. They present frequency bands in which waves do not freely propagate, named bandgaps, allowing acoustic and vibration attenuation at various frequency ranges. If properly designed and implemented, nonlinear stiffness can result in resonance frequency shifts that broaden the attenuation frequency band and better isolate subsystems that could be sensitive to higher excitation levels. This work investigates the effects of geometrically nonlinear local resonators on the low frequency bandgap formation of a metamaterial beam. Attention is paid to the realization of lightweight non linear resonators via additive manufacturing of compliant mechanisms as the nonlinear resonant unit. The proposed model is validated through simulations and experimental analysis. This investigation contributes to understanding improvements provided by nonlinear elements for vibration control of a metastructure.

LOW-FREQUENCY PASSIVE NOISE CONTROL USING PERIODIC HELMHOLTZ RESONATOR ARRAYS

2024-05-04T01:26:47+00:00

Passive noise control in specific frequency ranges can be achieved using Helmholtz resonators (HR), which are reactive devices that exhibit distinctive geometry, resulting in impedance variations within the enclosing system. Due to the acoustic resonance in the HR, such variations enable the attenuation of propagating waves within a narrow frequency range. When multiple HRs are periodically arranged in an acoustic system, they produce an acoustic metamaterial that greatly expands the frequency range known as a stop band or band gap, which are band structures where sound waves are not allowed to propagate or attenuated. The aim of this paper is to analyze sound wave attenuation in an acoustic metamaterial consisting of HRs arranged in parallel and in series configurations. For this purpose, methods such as the transfer matrix and conventional finite elements will be employed. Parameter sensitivity analysis of HR geometry will be conducted to maximize the attenuation bandwidth of band gaps through Differential Evolution. An optimization process is also conducted to obtain the best sound attenuation using metrics such as sound transmission loss through the amplitude of the incident and reflected wave. Simulated examples are presented to demonstrate the efficiency and validation of the proposed methods.

Stability and Performance Analysis of Active Topological Non-hermitian Metastructures

2024-05-04T01:32:55+00:00

Metamaterials can be divided into passive and active types, with the latter incorporating programmable devices in their design. While active metamaterials promise resilience against manufacturing inconsistencies and defects, a notable gap exists in the current literature regarding metastructure stability and performance. Historically, the phenomena linked to non-Hermitian systems were investigated in quantum mechanics, but recent breakthroughs have translated them into classical mechanics. This research investigates the stability of active metamaterials through numerical simulations of a one-dimensional structure, wherein each unit cell showcases periodic feedback interactions. Stability limits for different feedback laws are determined. Central to this investigation is the relationship between closed-loop stability and directional propagation driven by the topological skin effect. This analysis entails exploring how distinct control law strategies affect stability and performance.

Investigation of Band Structures for Different Lattice Types in Sierpinski Phononic Fractal Crystals with Local ResonanceInvestigation of Band Structures for Different Lattice Types in Sierpinski Phononic Fractal Crystals with Local Resonance

2024-05-04T01:38:19+00:00

This article presents an analysis of the band properties and forced response in phononic crystals that use fractal structures, focusing on square and triangular Brillouin lattices. Initially, we describe the construction of phononic crystals based on fractals, using fractal patterns such as the Sierpinski set or quasi-Sierpinski. Thesefractal structures allow the creation of complex and branched arrangements at different scales, resulting in different properties. Different types of Brillouin networks will be used to analyze and verify the influences on the band structures of phononic crystals. Furthermore, we examine the forced response of phononic crystals, analyzing how these structures react when subjected to external excitations. Using the finite element method, we obtained
the forced responses, revealing the resonance modes and attenuation characteristics at different frequencies. This study highlights the importance of fractal structures in manipulating the acoustic properties of phononic crystals. The analysis of the band structures and forced response offers valuable insights for the development of phononic devices with applications in acoustic insulation, frequency selective transmission and other related areas. These results contribute to the understanding and advancement of fractal phononic crystals, paving the way for future research and promising technological applications, both in terms of frequency and attenuation, depending on the complexity and hierarchy of the fractal structures used.

Combining acoustic black hole and phononic crystal to attenuate structural vibrations

2024-05-04T01:44:23+00:00

In the last decades, phononic crystals (PCs) have been investigated extensively and proposed for noise and vibration attenuation, due to the bandgap generated by a destructive wave propagation interference. However, PCs are limited by the characteristic of anisotropy and the periodic cell size that must be of the same order of magnitude as the wavelength in the direction of wave propagation, which are determinants for the band gap width and attenuation. The Acoustic Black Hole (ABH) effect has also been used to attenuate structural vibrations by slowing the waves in a thin-walled structure with a power-law thickness variation. The aim of this paper is to establish reliable numerical approaches for designing and modeling an effective passive structural device combining periodicity and ABH effects to attenuate vibrations efficiently. This structural PC-ABH device is modeled by the Spectral Element (SE) method and verified by the Wave Spectral Element (WSE) method. Simulated examples are performed and the results are compared between the methods and their efficiency to extended band gap widths and to attenuate the structural vibrations are evaluated.

A New Method For Sub-resolution Porosity Modelling On Rock Samples Using X-ray Microtomography And Pore Network Modelling Techniques

2024-05-01T16:31:11+00:00

The heterogeneity of carbonate rocks at multiple scales presents challenges in terms of estimating their
petrophysical properties and predicting the full capacity of oil and gas reservoirs. Digital analyses are increasingly
used to study the complex pore structure of carbonate rocks by means of such techniques as X-ray tomography.
With this approach, one usually needs to find a compromise between the field of view (i.e., the volume dimension)
and the resolution (i.e. the smallest size of distinguishable structures). For large volumes, this usually means that
a fraction of the pore space, whose size is below the resolution, is not visible (i.e., the sub-resolution porosity or
unresolved porosity). In this work, X-ray microtomography images of a carbonate rock with a significant fraction
of porosity below the image resolution will be used to estimate flow properties. The presence of unresolved
porosity is supported by mercury intrusion capillary pressure (MICP) and nuclear magnetic resonance (NMR)
data. A new method is proposed for modeling the sub-resolution porosity of the images in which the topology of
unresolved pores bodies/throats is correlated with the CT values of regions below the imaging resolution. Within
these regions, preferential paths between visible pores will be determined using the minimal distance weighted by
a probability function. Connections between visible pores are then created by assigning pore bodies and throats
along these paths, whose dimensions are compatible with MICP measurements. Finally, results of numerical flow
simulation with obtained pore network model are shown, demonstrating the improvement in the permeability and
the potential of the proposed methodology.

Pore-scale experimental simulation of water flow in acidified carbonate rock based on tomographic imaging

2024-05-01T22:04:38+00:00

It presents a pore-scale experimental simulation of water flow in acidified carbonate rock based on
tomographic images with the aim of investigating the variations in the rock petrophysical properties because of
the acidizing as well as the efficiency of the wormhole pattern. The experimental configuration allows an
understanding of the behavior of the acidified reservoir by means of comparisons between the experimental
petrophysical analysis and the digital analysis of an acidified sample. Digital analysis accounts for mathematical
models of reconstructing images by using computerized X-rays. The validation of the simulation is done by
comparing the experimental petrophysical results with the digital petrophysical analysis before and after the
acidizing. This research is motivated by the need to evaluate the permeability and porosity characteristics of the
rock and the digital rock derived from the simulation. Moreover, the simulation is used to evaluate the efficiency
of the wormhole pattern (dissolution channels structure) and, consequently, validate the acidification process.

Effects Of Permeability and Pore Connectivity On Gas Trapping In Carbonate Rocks

2024-05-01T22:08:50+00:00

Trapped gas is a significant factor affecting the hydraulic properties of oil reservoirs, including re-
coverable oil reserves. The degree of trapped gas in oil fields is a crucial aspect that affects the convergence of

recoverable reserves, which has been evaluated in different experimental and simulation studies. These studies
aim to assess the impact of trapped gas on different rock properties, as it is crucial for the Advanced Oil Recovery
(EOR) and Carbon Capture, Use and Storage (CCUS) scenarios. several studies show that air or gas entrapment is
a function of many parameters, including the prevailing wetting rate, wettability, and especially grain texture and

pore structure. Understanding and quantifying the effects of trapped gas in oil reservoirs is challenging, partic-
ularly for carbonate rocks that have an unusually complex multiscale heterogeneous pore structure, causing fluid

retention and unique flow properties. the same is not observed for carbonate rocks. This study examined how

permeability and pore connectivity interact to influence saturation levels of trapped gas in 47 representative sam-
ples of carbonate rock formations. The 3D characterization of the pore space was made possible through microCT

images, obtained for the silurian dolomite and coquina samples. It has been observed that larger pore radii and
better connectivity lead to increased gas trapping, even in cases where pore connectivity may be more pronounced.
This contrasted with previous assumptions emphasizing the influence of pore structure on gas trapping.

Dynamic buckling of slender variable section members to self-weight

2024-04-19T19:01:28+00:00

We present a study of the dynamic buckling of variable section very slender members due to their self-weight. Modern materials and powerful new analysis methods are leading to the design of very slender aerospace structures that may be prone to instability issues. Elastic stability of such structural systems is a problem inside the
scope of Non-Linear Dynamics Analysis Methods. An indicator of instability is when the structure's free vibration frequency tends to zero. Two factors affect these frequency results. First the stiffness, composed of elastic stiffness, always positive and non-zero, that diminishes rapidly with height, and the geometric stiffness, negative for compressive forces, whose absolute value grows as the structure gets taller and heavier. Second, the mass, that also grows with the height of the structures, and is always positive. To access this behavior, we present a one-
degree-of-freedom mathematical model of a cantilever vertical member via Rayleigh's Method, adopting a cubic polynomial as shape function. Closed form formulas are obtained for elastic and geometric equivalent stiffness, as
well as for equivalent mass, dependent on the member length and transverse section variable characteristics. For some adopted numerical geometric and material properties we use an optimization algorithm to maximize the member length. Check of the formulation is possible for the prismatic member case.

QUAD LAMINATES AEROELASTIC INSTABILITY'

2024-04-23T18:32:14+00:00

The flutter in panels of rockets, missiles, and vehicles was identified when technological advances al-
lowed these vehicles to reach supersonic and hypersonic speeds. The phenomenon was first noticed and recognized during World War II, when the German V2 rockets were being developed. The initial studies used the Ritz and Galerkin approach based on a linear aerodynamic and structural model intended to determine the critical dynamic pressure. Researchers started using nonlinear structural models with a nonlinear aerodynamic model and obtain-ing the limits cycle oscillation (LCO) due to computer advances and the growing use of matrix techniques, such as finite elements. In the last ten years of the previous century, structural components and aircraft wings began to utilize composite materials like carbon and glass fiber on a large scale. Thus, the researchers began to verify the impact of using these materials on structures subject to this instability. This paper investigates the aeroelastic stability of laminate panels in supersonic flow. It is optimized to obtain the best fiber direction and number of layers to increase the critical dynamic pressure. The researchers discovered that quadriaxial laminates with prede-termined directions have several advantages over others. In order to reduce flutter, the impact of employing quad laminate sets will be examined and contrasted with that of alternative configurations. The analysis is performed using a specially customized program. Finally, the results are compared with the literature, and the differences are
analyzed.

Energy Harvesting Using a Piezoelectric Nonlinear Energy Sink (PNES) to an Aeroelastic System

2024-04-26T18:11:46+00:00

The influence of piezoelectric nonlinear energy sink (PNES) on the dynamic behaviour of an energy harvesting system applied to an aeroelastic structure in flutter condition is studied. NES is often used in aeroelastic systems to decrease the amplitude of vibration, possibly attenuating , controlling or delaying typical aeroleastic phenomena, such as flutter, galloping and VIV (vortex-induced vibrations). It is also able to harvest energy and distribute this energy to electric devices available in the system. The dynamic response of the PNES with en-ergy harvesting was analysed for four cases: linear case, only cubic nonlinear stiffness, only quadratic nonlinear piezoelctrical coupling and both nonlinear terms combined. The inclusion of nonlinear terms increased flutter speed, and the combination of both nonlinear terms have the greatest increase. The cubic nonlinear stiffness is responsible for increasing the equivalent stiffness of the system, which causes a decrease in the amplitude of the system response, while quadratic nonlinear piezoelectrical coupling increases the energy harvest of the system, which also decrease the amplitude and increase the electric energy harvested. The influence of electric parameters in flutter speed and power were also studied. The variation of these parameters is able to maximize flutter speed and electrical power.

TMD's Optimization for Dynamic Analysis of Walkways Excited by Pseudorandom Pedestrian’s Load

2024-04-26T12:39:17+00:00

In this work, optimization of vibration absorbers (TMD) will be presented for dynamic analysis of walkways in aerospace structures excited by pedestrians. The dynamic loading used to excite the walkway will be a pseudorandom model. Using this type of loading, it is possible to cover a band of frequencies and amplitudes of possible excitation to the structure, similar to a PSD. The deterministic dynamic loading used as a basis is the Schulze loading. First, a simply supported beam representing a walkway will be modeled via a commercial FEM software to obtain modal mass, modal stiffness and frequency. Next, a two-degree-of-freedom model of the critical vibration mode of the structure close to the excitation frequency is presented, with a vertical TMD and a horizontal TMD, the latter modeled as a pendulum. Using MATLAB tools, the TMD mass ratio is optimized using as
objective function the minimization of the difference between the maximum acceleration of the system and limit
accelerations recommended by standards of human comfort. These optimal parameters will be carried back to the
FEM model for comparisons.

Nonlinear dynamic analysis of guyed mast under random aerodynamic loading

2024-04-26T12:53:09+00:00

In this research, a guyed mast with non-linear behavior under random aerodynamic loading is modeled. It is a slender lattice metal structure, articulated at the base, stabilized by cables. An equivalent mass of the system concentrated at its upper end is admitted, whose displacements are the generalized coordinates of the system. The model admits large displacements, leading to the need to consider geometric nonlinearity, that is, dynamic equilibrium is always imposed on the displaced position. The non-linear equations of motion are derived via direct
dynamic equilibrium. The numerical algorithm for simulating the response is based on step-by-step time integration using Runge-Kutta’s Method. The random aerodynamic loading is simulated by a Monte Carlo-type
procedure with superposition of harmonic series whose amplitudes are obtained from Power Spectrum Density Functions with randomly chosen phases. For application to the model under study, an equivalent point load is applied to the mass at the top of the mast. This procedure is inspired by the well-known Synthetic Wind Method.

Satellite ACS Design during Orbit Injection using the SDRE Method

2024-04-26T13:00:23+00:00

The performance of the Satellite Attitude Control System (ACS) during the orbit injection phase is of fundamental importance for the success of the mission. In this phase the satellite leaves the launcher with high angular velocity and then the ACS needs to manoeuvre the satellite to its normal mode of operation, which is characterized by an attitude of small angles. One way to achieve this transition between these two phases is using gas jets followed by reaction wheels. In this paper one investigates and develops by simulation the ACS algorithm to minimize space mission costs by reducing the number of errors transmitted to laboratory prototypes project. The high angular velocities of the satellite in the injection phase makes its dynamics highly nonlinear introducing some level of perturbation into the system. As a result, application of linear control technique cannot be able to design the ACS with adequate performance to reach the required level of appointment. To mitigate this problem, one will use the State-Dependent Riccati Equation (SDRE) method which can deal with nonlinear system. The SDRE controller design algorithm is based on gas jets and reaction wheel torques to perform large angle manoeuvre to reduce the high angular velocities to attitude with small angles. The criterion for the transition between the two operating modes is based on the decrease of the system energy. This investigation serves to validate the numerical simulator model and to verify the functionality of the control algorithm designed by the SDRE method. It is intended to use in the next phase of this research the Federal University of ABC (UFABC) 3D simulator which supplies the conditions for implementing and testing the SDRE algorithm in terms of hardware and software.

Study of the effect of pressurization on the vibration frequencies of fuselages

2024-04-26T13:03:38+00:00

In this research, an aerospace vehicle fuselage was modeled as a long-pressurized cylinder. The
investigation assessed the presence of high tensile stresses in the structure and their correlation with the values of
the undamped free vibration frequencies of the system, which vary according to its geometric stiffness. The
modeling was conducted utilizing the Finite Element Method, employing thin shell elements accounting for
geometric nonlinearity, as offered in commercial and academic software. Generally, such programs can address
the eigenvalue problem associated with this model, using a stiffness matrix considering application of the load,
i.e., pressurization. This can originate from the conditioning of the internal atmosphere of commercial aircraft or
the presence of large loads of fuel and oxidant in space vehicles (rockets). Another aspect to consider in this
analysis is the fact that these vehicles do not have supports, leading to the existence of so-called rigid body modes,
with zero vibration frequencies. Ultimately, a maximum variation of 45.29% in the natural frequency value of the
investigated structure was observed.

Analysis of a Hydrogen Flying Airplane

2024-04-26T14:05:53+00:00

Present aircrafts make use of fossil fuels in combustion processes that create large amounts of emissions.
Pollution and climate changes are perceived as related to this type of emissions. These worries have led to worldwide efforts towards reduction in the use of combustion engines. Clean airplanes with zero direct emissions require technological developments some yet in exploratory phase. Hydrogen propelled airplanes promise large reductions in CO2 emissions. Design, testing and evaluation of power type modified airplanes is quite challenging, as a whole new system of components is required to work with the fuel cell. To this endeavor a method is presented here, with parameters from a conceptual plane chosen as reference airplane, so as to avoid unnecessary and costly changes. Once verified the main premises, structural response of the hydrogen powered airplane is developed with due consideration of powertrain components. For the plane, the same mission requirements are set. Balance of the plant is undertaken, before specifications are done. A first order structural analysis of the plane, for cruise conditions, shows redundancy enough to accept the modifications. Discussion and comparisons are presented.

Dynamic analysis of transversal response due to moving mass in a continuous beam

2024-04-26T16:41:29+00:00

This paper presents a computational analysis of the dynamic responses of a continuous beam subjected
to a moving mass and corresponding load that travels along its entire length. It aims to understand the behavior of the structure and to determine its transversal response. Here, a discretized dynamic finite element algorithm was developed, using numerical integration by Newmark’s Method for the solution of ordinary differential equations and obtain the transversal displacements of the structure in the time domain, in order to evaluate its behavior due to moving masses and loads. The analysis is made in different velocities, damping ratios, with and without the contribution of the moving mass in the inertia of the system and comparing the effects of these parameters in the responses. The main objective is to apply the results obtained with the method to obtain displacements due to moving loads in structures such as bridges and viaducts, among other applications, and to obtain the critical velocities, where the greatest deflections of the structure are found.

Numerical analysis of pressure gradients in piping due to hydraulic transients to determine critical axial loads

2024-04-29T12:43:46+00:00

Hydraulic transient or “water hammer” is the sudden pressure variation in a fluid system. In pipelines, it is often associated with closing valves and starting and stopping pumps. In aerial installations, it may produce great axial forces due to the steep pressure differentials that may occur. To correctly dimension pipe supports, stress analysis studies must consider these loads, which, in turn, require hydraulic simulations. Often this data is unavailable given the required deadlines. The work presented here aims to provide data on dynamic forces generated in hydraulic transients in a wide range of cases found in the oil industry. Hydraulic simulations were performed considering various pipeline diameters, flow velocities, and different fluids, analyzing the rapid closure of a ball valve. These simulations provided the pressure gradients that occur across multiple pipe lengths. Quadratic interpolations were then performed with the data obtained by the simulations, and it was verified that they were adequate to get pressure gradients for scenarios of flow velocities and density values intermediate to those of the simulated cases without the need to carry out new simulations. It was also verified that a fifth-order polynomial could perfectly describe the pressure gradient curves of each scenario, allowing the results to be obtained by simple equations.

The influence of different projection operators in the Virtual Element Method applied to bi-dimensional elastic problem

2024-04-29T12:51:50+00:00

The Virtual Element Method (VEM) generalized the Finite Element Method (FEM) in terms of mesh discretization since any simple polygon can be used as elements in the mesh. By working with more general polygons, the shape functions are not always low-order polynomials, meaning that the VEM must compute these functions implicitly by using projection operators, which responsible to map functions from the virtual element space to polynomial spaces. The choice of different projection operators requires some adaptation of the VEM formulation but the general implementation pipeline still the same. In this way, this work shows those adjustments in the formulation and proposes to investigate how the choice of the operators influences the method convergence. For that, two numerical models are presented: a patch test in a unitary square and a static analysis regarding a zeta-profile (commonly used in pressure armors of risers). All the formulation is restricted to the Virtual Element Method linear two-dimensional case taking in consideration the Theory of Elasticity.

Numerical Validation Of The Imerspec Methodology in Flow Over Jumps

2024-04-29T12:56:35+00:00

For a long time, the movement of fluids has been a subject of interest for society. Whether it’s the transposition of tributaries, the extraction, and transportation of oil and derivatives, or the behavior of winds in the atmosphere, the study of flows proves essential for the development of these activities and others that sustain and drive humanity. In light of this, and considering the obstacles to conducting experiments in the field of fluid dynamics, this study consists of applying the IMERSPEC2D methodology, which combines the immersed bound- ary and pseudo-spectral Fourier methods to computationally simulate boundary conditions for a two-dimensional laminar flow over a rectangular cross-sectional obstacle positioned between two plates. The objective is to validate
the IMERSPEC2D methodology under these conditions and assess its independence from the number of points in the physical domain. The presented velocity field data obtained from four simulations with different placement point numbers are compared to the results of Onur and Baydar [1], a reference work under similar conditions. It was possible to conclude that the methodology provides a satisfactory approximation to real experiments with the same purpose and demonstrates good accuracy.

Stability Analysis of Shells Using a NURBS-based Isogeometric Approach

2024-04-29T13:02:16+00:00

Shells are structures sensitive to buckling due to their characteristic high slenderness. Thus, the evaluation of buckling loads and the study of the post-buckling behavior are essential. Isogeometric analysis has been widely used in analysis of shells, due to its ability to accurately represent the geometry of the structure regardless of the discretization level and the simplicity of model refinement procedures. The aim of this work is to evaluate the stability of shells through an isogeometric approach, considering large displacements and moderate rotations. This formulation is based on the Reissner-Mindlin theory for thick shells and the degenerated continuum approach using NURBS as basis functions. The proposed formulation is applied in the stability analysis of plates and shells,
where critical loads and equilibrium paths are evaluated and compared to solutions available in the literature or obtained by the Finite Element Method.

A study of axisymmetric Stokes flows using a Hybrid-Mixed Finite Element formulation

2024-04-29T13:09:32+00:00

We propose a hybrid-mixed finite element formulation based on H(div)-conforming velocity and discontinuous pressure approximations for axisymmetric Stokes flows. This scheme is locally conservative, which means that mass conservation is strongly satisfied at element level resulting in exact divergence-free solutions for incompressible flows. The normal component continuity of vector quantities over the element interfaces is automatically guaranteed, while the tangential conformity is weakly imposed by a traction that acts as a Lagrange multiplier. For stability purposes, there must be a compatibility between the approximation spaces used for velocity and traction that fulfills the inf-sup condition. The developed numerical method is verified against classical bench-
marks that have analytical solutions available in the literature, and its convergence properties are also investigated in different scenarios. The resulting code is implemented in an open source C++ object-oriented computational environment called NeoPZ.

An Adaptive Generalized/eXtended FEM For Linear Elastic Fracture Me- chanics

2024-04-29T13:14:44+00:00

The Generalized/eXtended Finite Element Method (G/XFEM) has been recognized as a method able to accurately and efficiently solve problems that face difficulties when treated by standard methodologies, such as those from three-dimensional (3-D) Linear Elastic Fracture Mechanics (LEFM). The main advantages of G/XFEM for this class of problems are the fact that the finite element mesh does not need to fit the crack surface andthat optimal convergence rates in the energy norm are attained. This last advantage has been demonstrated for two dimensional (2-D) problems even when uniform meshes are adopted. For 3-D, however, in addition to using
enrichment functions, it has been shown that mesh refinement must be performed to obtain optimal convergence rates. In this case, since the level of refinement to be adopted is problem-dependent and difficult to be defined a priori, this work proposes an h-adaptive strategy, based on a posteriori error estimation, able to find optimal non uniform meshes that recover optimal convergence rates for 3-D LEFM problems. This is shown herein for a LEFM problem that exhibits 3-D effects.

Modelling vibrations of a moderate amplitude in piezoelectric nanoplates using nonlocal elasticity and G/XFEM

2024-04-29T13:20:39+00:00

In this paper, we address the problem of free and unforced vibration of nanoplates immersed in a transverse electric field using the theory of non-local elasticity. The numerical model was obtained using the first-order plate kinematic theory, which included the shear deformation (FSDT) and the approximation spaces in accordance with the homogeneous “p” version of the G/XFEM method with regularity C k, k = 2, 4. The scale effect is approached using the non-local elasticity theory, and moderate amplitude waves are taken into consideration using the von Karmann geometric non-linearity. In this study an electric stationary field is obtained from a potential function that satisfies Maxwell’s law for moving current and the electric potential boundary conditions on the free surface
of the plate. Investigations on the estimation of the first nonlinear frequency, as well as the stiffness-softening and stiffness-hardening phenomena, are carried out for a simply supported nanoplate. The findings for the proposed numerical models are contrasted with those attained using Lagrange C 0 finite elements, a semi-analytical solution attained using Navier biharmonic modes, and results acquired using the Generalized Differential Quadrature Method (GDQM) from published results. The GFEM approximation space demonstrated its ability to describe all features of the problem at hand.

Analysis of the local domain size and the number of enriched nodes in a global-local GFEM approach simulating damage propagation in an L- shaped concrete panel

2024-04-29T13:27:04+00:00

The Generalized Finite Element Method (GFEM) has been developed to overcome some limitations inherent to the FEM by using some knowledge about the expected solution behavior to improve the analysis. The GFEM enriches the space of the polynomial FEM solution with a priori known information based on the concept of Partition of Unit. In this context, the GFEM global-local approach to the nonlinear analysis of quasi-brittle media is investigated here. The kernel concern is the impact on the structural global response of expanding the local domain and the number of nodes enriched with the global-local numerically obtained functions. Such analysis has been encouraged by observations that the quality of the global solution transferred to the boundary of the local problem can indeed impact the problem solution in media with linear elastic behavior. The importance of this is grounded by the interest in having a reasonably coarse global mesh to justify a global-local analysis with the local problem discretized by a fine mesh. It is suggested, for example, the polynomial enrichment of the initial global approximation and the increase in the size of the local domain, enlarging the so-called buffer zone. Here, this strategy is evaluated to solve nonlinear problems induced by the degradation of the continuous medium. Thereby,a Smeared Crack Model of fixed direction with the stress-strain laws of Carreira and Chu is applied in the local
domain to simulate the damage propagation experimentally obtained in an L-shaped concrete panel. The resulting global-local responses are compared with experimental findings from the literature and numerical results obtained by standard GFEM.

The Modified Local Green's Function Method for the solution of the anoma- lous diffusion equation

2024-04-29T13:33:32+00:00

The field of fractional calculus is currently gaining momentum in mathematics and has extensive practical applications across several scientific and engineering problems, particularly those that involve nonlocality. This study aims to enhance the discourse surrounding the utilization of numerical techniques for solving problems governed by partial differential equations with fractional time derivatives. To this end, the present work employs an enriched formulation of the Modified Local Green's Function Method (MLGFM) to solve the anomalous diffusion equation in two dimensions. The anomalous, or fractional, diffusion equation presents a time-derivative of

non-integer order, in the interval (0,1]. When the order of the time-derivative is equal to 1, the classical diffusion equation is recovered, which means that it can be treated as the simplest case of the fractional diffusion equation. To represent the fractional time derivative, the Caputo representation is chosen based on the authors’ previous work. The MLGFM is an integral method hybrid of the Finite Element Method (FEM) and the Boundary Element Method (BEM). The method uses the FEM to create discrete projections of the Green's functions and use them as fundamental solutions in BEM formulation. The MLGFM presents high convergence for the potential in the domain, inherited from the FEM, and for the normal flux in the boundary, inherited from the BEM. This paper proposes a trigonometric enrichment based on the Generalized Finite Element technique for the solution of the anomalous diffusion equation. The results are compared with analytical solutions available in the literature.

On the Parameters Investigation of a Non-Intrusive Multiscale Framework for Structural Analysis

2024-04-29T13:39:38+00:00

IGL-GFEMgl is a multiscale framework proposed by H. Li, P. O’Hara, and C. A. Duarte in 2021 that combines the IGL strategy with the GFEMgl. In the Iterative Global-Local method (IGL), two different meshes are adopted. The global mesh is used to describe the global behavior of the structure. Local features are represented in the local mesh. The solution of the two meshes is coupled through an non-intrusive iterative algorithm that exchanges displacements and enforces the equilibrium between them. The GFEMgl considers two scales of representations, but the coupling is provided by the GFEM’s enrichment strategy. Finally, in the IGL-GFEMgl
framework, a third problem is defined, named mesoscale. The mesoscale works as a bridge between the two methods (IGL and IGL-GFEMgl), allowing a non-intrusive coupling of the global problem FEM solution and the meso-local scale solution provided by the GFEMgl. In this work, the commercial software Abaqus solves the global problem and is coupled with an in-house computational platform where GFEMgl is already implemented. A thorough investigation is performed over some IGL-GFEMgl parameters, such as the size of the mesoscale and the use of acceleration techniques to improve the convergence of the method.

Numerical analysis of a reinforced concrete railway bridge considering soil-structure interaction

2024-04-30T01:04:49+00:00

The integrity and performance of bridges are crucial for railway infrastructure. Consequently,
evaluating their condition and dynamic response remains a top priority for infrastructure operators. This paper
delves into the study of dynamic structural responses of bridges in the presence of railway-type trains. We focus
on the soil-structure interaction process, considering local soil characteristics and foundation types. A six-span
reinforced concrete bridge served as our case study. We developed a computational finite element model
employing finite shell elements, augmented with calibrated springs to represent the foundations, temporary steel
supports, and neoprene bearing supports. The study sheds light on the natural frequencies of vibration,
accelerations, and velocities within the railway bridge components. These results were juxtaposed with
monitoring data to gauge the bridge's structural response to dynamic loads. The numerical findings closely
aligned with the monitoring data, reinforcing the validity of our modeling approach. This model stands as a
robust tool to appraise structural conditions and predict bridge behavior throughout its lifespan. Furthermore, it
has potential applications in forecasting failures, bolstering monitoring efforts, guiding inspection campaigns,
and even merging into a digital twin framework for comprehensive bridge integrity management.

Analysis of the performance of a ballasted track in a transition zone

2024-04-30T01:10:33+00:00

The transition zones are characterized by an abrupt change in track support stiffness, which increases
dynamic wheel loads and leads to the acceleration of differential settlement and track degradation. Inefficient
performance of the transition zones is a major concern of the Railway Infrastructures Managers since the
degradation of the track in these areas is the cause of the generation of noise, vibration, poor ride comfort, higher
risks of derailment, and a decrease of the train speed. Since the performance of the ballasted track decreases
significantly in a transition zone, this work aims to study its short and long-term behaviour with a focus on a
transition between a ballasted and slab track. The analysis uses a hybrid methodology, combining an iterative
procedure between a 3D finite element modelling with empirical settlement equations. The FEM is capable of
simulating train-track interaction. At each iteration, the track-ground stress fields are calculated using a 3D model.
The stress results are the main inputs of an empirical equation capable of computing settlement across the
transition. The model is used to analyse settlement and stresses for a transition zone case study, which is crucial
to understand the response of the ballasted track in such areas.

Dynamic Analysis of a Prestressed Concrete Railway Bridge Considering Cyclic Fatigue Load due to Railway Traffic

2024-04-30T01:13:59+00:00

The dynamic interaction between railway train composition, track, and bridge considering increased
deflections under fatigue loading is realized through computational analyses. The twenty five equations of
motion of three dimensional railway vehicle are obtained through dynamic equilibrium. The railway train
composition model is obtained by the eight vehicle’s association. The railway track irregularities are represented
by harmonic functions. The mechanic contact between wheels and rails model is based on Hertz, Kalker,
Coulomb, Vermeulen and Johnson’s theories. The rails are modeled with Euler-Bernoulli beam’s. The sleepers
and the ballast are modeled with spring-damper systems. The railway bridge structure in prestressed concrete is
mainly composed by two simply supported I-beams, which are represented with three-dimensional frame
elements based on the Euler-Bernoulli assumption. The Rayleigh’s method is used in structural damping. The
equations of motion of structural systems are implemented in Matlab software. Static analyses are presented
considering vertical deflections due to permanent load and prestress effects. Dynamic analyses are presented
considering the displacements of the sleepers, the ballast and the bridge. Results of vertical deflections
considering cyclic load fatigue influences at the reinforced concrete beams are presented and analyzed.

Indirect Analysis of Railway Infrastructure Anomalies Using Passenger Comfort Criteria

2024-04-30T01:16:07+00:00

Railways are one of the most efficient and widely used public transport systems for medium distances.
To improve the attractiveness of this type of transport, it is necessary to improve comfort, which is greatly affected
by vibrations caused by the train motion and wheel-track interaction, making railway track infrastructure condition
and maintenance a main concern. Based on the passenger’s discomfort level, a new methodology capable of
detecting railway track infrastructure maintenance requirements is proposed. While performing regular passenger
service, acceleration and GPS measurements were performed on Alfa Pendular and Intercity trains between Porto
(Campanhã) and Lisbon (Oriente) stations. Following ISO 2631 methodology, instantaneous floor discomfort
levels were calculated. Matching the results for both trains, twelve track section locations were identified as
requiring preventive maintenance actions. The developed methodology was validated by comparing these results
with those obtained by the EM 120 track inspection vehicle for which similar locations were found. The developed
system can identify critical maintenance sections but does not distinguish the type of defect.

Enhanced Fatigue Life Prediction in Ancient Riveted Metallic Railway Bridges

2024-04-30T01:20:20+00:00

The majority of transport investments funded by the European Union are aimed at improving the
capacity of railway infrastructure in order to meet challenging environmental targets, which will culminate in
achieving carbon neutrality by 2050. In this framework, existing railway bridges are relevant and should be
preserved in service for as long as possible according to a sustainability perspective. In this paper, fatigue damage
assessment is addressed, as this phenomenon has been proven to threaten the structural integrity of metallic railway
bridges, affecting severely riveted details in particular. For this type of connection, very limited guidance is given
in standards and codes concerning global methods based on S-N curves for nominal stresses, and unreliable results
may be obtained, limiting the accurate fatigue check. Thus, a multiscale approach using submodelling techniques
leveraged by modal superposition principles can be considered to calculate local fatigue parameters, allowing to
compute the remaining life for the crack initiation and crack propagation phases, in line with the properties of the
load transfer mechanism. From global to local assessment, relevant differences in results are found.

Prediction of vibrations induced by railway traffic using a surrogate model

2024-04-30T01:24:48+00:00

Over the latter years has been a demand for the development of advanced numerical techniques for the
prediction of ground-borne vibrations induced by railway traffic which can provide the desired level of accuracy,
despite of structural complexity of the entire system. Despite the suitability of these models in dealing with such
phenomena, their applicability to cases where it is intended to have a general assessment of the potential impacts
of a new/updated railway project is difficult to achieve. In such cases, the development of expedited prediction
methods is desired, allowing the delimitation of cases that require a deeper analysis, using advanced numerical
models, and of those that can be immediately discarded, with all the benefits of cost and time associated. Thus, it
is the intention to develop an innovative prediction tool, powered by an efficient and intelligent calculation engine
based on surrogate modelling, that allows an efficient assessment of ground-borne vibrations at the free-field
surface due to railway operation.

Enhancing Thermal Comfort Analysis and Optimization of HVAC Systems Using Open-Source Software

2024-05-01T13:00:53+00:00

Ventilation, cooling, and heating systems play a crucial role in providing thermal comfort within occu-
pied environments, influencing productivity, well-being, health, and energy consumption. This research focuses on

leveraging Computational Fluid Dynamics (CFD) as a tool for studying fluid flows and optimizing heating, ven-
tilation, and air conditioning (HVAC) systems to achieve ideal room temperatures efficiently. Initially, a thermal

comfort study is conducted using the OpenFOAM software, aiming to compare and validate its algorithm against

a reference article that utilized proprietary software. By demonstrating the capabilities of OpenFOAM as an open-
source alternative, this research opens opportunities for analyzing HVAC systems using an accessible program,

facilitating the optimization of climatization strategies. Subsequently, an optimization analysis of ventilation sys-
tems is performed through a factorial design that involves altering the positions of air inlets and outlets, as well as

adjusting the insufflation velocity. The findings reveal that superior positions of air inlets lead to improved thermal
comfort results, as measured by the Air Diffusion Performance Index (ADPI). This research provides an insights
into optimizing the configuration of ventilation systems to enhance occupant’s thermal comfort. By utilizing CFD
simulations and exploring several parameters affecting thermal comfort, this research contributes to advancing
HVAC system optimization.

Analysis of the Effects of Soil Thermal Properties on the Performance of an Earth-Air Heat Exchanger

2024-05-01T13:05:11+00:00

Among the ways to obtain good thermo-energetic performance in buildings, passive air conditioning
stands out. These systems use the potential of the local climate and the characteristics of the building envelope to
promote thermal comfort for the occupants, using low energy costs, as is the case with Earth-Air Heat Exchangers
(EAHE). In this system, ambient air circulates through a pipe buried at a certain depth in the ground, causing it to
heat up or cool down, depending on weather conditions. These effects are possible due to the high thermal inertia
that keeps the soil at an almost constant temperature, at specific depths, even with high external temperature
amplitudes. In this context, the performance of EAHE depends directly on the thermal properties of the soil. Thus,
numerical simulations will be performed using the Ansys/Fluent software. The effects of the thermal properties of
different types of soils will be verified on the thermal performance of these exchangers. An EAHE prototype was
installed at the Federal University of Technology – Paraná (UTFPR) to validate the numerical model.

Accuracy Assessment of the 2D Laminar Boundary Layer on a Flat Plate in an Immersed Boundary-Fourier Pseudospectral Simulations

2024-05-01T13:08:50+00:00

We investigate the accuracy of the laminar boundary layer over a flat plate in the simulation by an

immersed boundary – Fourier pseudospectral methods (IMERSPEC). In this study, we use the The Fourier pseu-
dospectral method (FPM) combined with the Multi-Direct Forcing Method, can enforce the boundary conditions

accurately by determining the body force iteratively. The IMERSPEC solves the continuity equation and linear
momentum equations numerically implementing the Pseudospectral Fourier Method (PFM) with the use of the

Discrete Fourier Transform (DFT), specifically the Fast Fourier Transform (FFT) algorithm. The reduced com-
putational cost is achieved by the use of FFT as well as the pseudospectral approach which does not solve the

convolution product of the advective term found in momentum linear equations. Furthermore, the mathematical
process of pressure projection replaces the solution of Poisson Equation simultaneously ensures mass balance and
decouples the pressure from the computational solution. The simulations of the laminar boundary layer on a flat
plate at the Reynolds number of 104

are performed by using IMERSPEC and modelling the behaviour of the flow
after the flat’s leading edge to eliminate any undesirable Gibbs phenomenon. To obtain reasonably accurate results
such that the maximum error from the friction coefficient distribution obtained is less than 4% over the useful
domain we use at least a uniform mesh with 1024x256 collocation points. The rightness showed in these results
indicates far improvement from the usual finite volume method’s modelling which needs a local refinement mesh
with far more volumes to present comparable results.

Computation of Deformable Interface Two-Phase Flows: A Semi-Lagrangian Finite Element Approach

2024-05-01T13:12:12+00:00

This work aims at presenting a computational approach to study two-phase flows and the coalescence
phenomenon using direct numerical simulation. The flows are modeled by the incompressible Navier-Stokes
equations, which are approximated by the Finite Element Method. The Galerkin formulation is used to discretize
the Navier-Stokes equations in the spatial domain and the semi-Lagrangian method is used to discretize the material
derivative backward in time. In order to satisfy the Ladyzhenskaya–Babuska–Brezzi condition, high-order pair of ˇ
elements are used, with pressure and velocity fields being calculated on different sets of the unstructured mesh
nodes. The interface is modeled by an uncoupled adaptive moving mesh, where interface nodes are tracked in
a Lagrangian fashion and moved with the velocity solution of the motion equations. The interface tension is
computed using the interface curvature and the gradient of a Heaviside function, and added in the momentum
equations as a volume force. In order to stabilize the simulation, a smooth transition between fluid properties is
defined on the interface region. Several benchmark tests have been carried out to validate the proposed approach,
and the obtained results have demonstrated agreement with analytical solutions and results reported in the literature.
A coalescence modeling is also proposed considering geometric parameters and results show interesting dynamics.

ANALYSIS OF THE FLUID DYNAMIC BEHAVIOR OF THE REVERSE OSMOSIS DESALINATION PROCESS FOR DIFFERENT GEOMETRIES OF SPACERS

2024-05-01T13:15:26+00:00

Water scarcity is a problem that has affected humanity for decades and, in recent years, has been getting
worse, even more so with global warming, population growth, and droughts. Therefore, desalination processes
have been seen as essential alternatives for producing drinking water around the world. Finally, several
technologies are used for the desalination of brackish water; among these techniques, desalination by membrane
separation processes via reverse osmosis (RO) stands out, a promising technology, considering that it is a simple
process and presents low investment. However, the disadvantage that there is in its use is the sensitivity of the
membrane to fouling. In this context, this work aimed to define computational modeling capable of understanding
the behavior of the reverse osmosis process from different spacer geometries. The mathematical model used to
carry out the simulations was based on mass conservation equations, movement, species transport, and Spiegler
and Kedem's model. All simulations were performed using the ANSYS FLUENT software and ICEM CFD to
create the geometry and the mesh. The simulation results showed a good representation of the transfer phenomena
involved in the reverse osmosis separation process; moreover, these results enabled a detailed analysis of fluid
behavior under the effects of turbulence promoters in the flow channel to be permeated. Finally, when analyzing
these parameters, it was observed that the lozenge-type spacers had better process performances in the geometries
studied.

Numerical Modeling of the 1-D Two-Phase Flow in Pipelines by Using the Two-Fluid Model and a Very High Order (VHO) Flux Reconstruction (FR) Scheme

2024-05-01T13:19:20+00:00

Flow models for 1-D two-phase flows in pipelines are commonly implemented using first-order
schemes. Despite being simple and robust, these schemes introduce a large amount of numerical diffusion due to
low order truncation errors, causing a high loss of accuracy. In the present work, for the first time in literature, we
propose the use of the very high-order (VHO) flux-reconstruction (FR) method to improve the accuracy and
efficiency of one-dimensional two-phase flow simulations in pipelines. The FR is implemented to solve the mass
and momentum conservation equations of the isentropic four-equation single-pressure two-fluid model. The
pressure correction equation is obtained through the mass conservation and a semi-implicit pressure-based method
SIMPLE-like is used to perform the coupling. The pressure equation is solved through the Two-Point Flux
Approximation (TPFA) finite volume technique. To test and numerically validate our formulation, we present two
benchmark problems. For the problems we have solved, our results are very promising.

Evaluating the Impact of Boundary Conditions on the MR-LBM

2024-05-01T13:23:35+00:00

The fluid flow investigation in heterogeneous porous media has several applications, such as in the oil
and gas industry. One of the problems is determining the permeability of the porous media. However, numerical
studies often employed simple geometric forms (spheres, cubes, cylinders) to represent the porous media. Complex
meshes are usually required when scans are employed to describe the porous media. The Lattice Boltzmann
Method (LBM) can address this problem without complicated meshes. Recently, the moment representation of the
LBM has gained interest due to its reduced memory requirements and increased speed. The reduced memory usage
is achieved by storing moments from 0th to 2nd order instead of the mesoscopic populations. This change also
reduces the bandwidth usage between the memory and the processor, which is a bottleneck for the LBM, thereby
increasing performance. However, boundary lattices will require additional arithmetic operations when conditions
other than a periodic need to be applied, leading to speed degradation. In simulations of a heterogeneous porous
media, many lattices are subjected to boundary conditions, and the probability of having a neighbor lattice affected
by it increases with a reduction in porosity. Additionally, cases with the same solid volume fraction can exhibit
different performances. This discrepancy arises because the effect of the boundary condition in the processing is
associated with the wet surface area. To investigate these parameters (solid volume fraction and wet surface area),
we build heterogeneous porous media using a Gaussian blur over a randomly generated domain. We varied the
porosity by tuning the threshold value while the standard deviation changed the surface area. The results
demonstrate that as the porosity decreases, the computational performance also decreases. However, once the
porosity reaches a certain threshold, the execution time decreases due to reduced total wet surface area, and the
number of fluid nodes reduces. Additionally, there is a direct correlation between the computational speed and the
standard deviation of the Gaussian blur for the wet surface area. With more lattices neighboring other solid lattices,
there is a reduction of boundary conditions being applied as well as the number of collision-streaming steps being
performed, resulting in improved performance.

Firsts steps for a fully exact thin-walled rod model incorporating generic cross-sectional distortion

2024-04-29T23:38:14+00:00

Thin-walled frame structures consisted of profiles or rod members are often subject to loadings that induce local effects on the profiles ́ webs and flanges. For some elements, local instability is the main design constraint. This work aims to present the first steps towards a thin-walled kinematically-exact rod formulation with cross-sectional local effects on its kinematical assumptions. The model ́s displacement field allows for the traditional cross-sectional rigid body motion, along with wall ́s mid-line in- and out-of-plane deformations (first-order in-plane distortion and out-of-plane warping, respectively, herein called primary deformations) and a kinematically-exact rotation for out-of-mid-line points (herein called secondary deformation). Accordingly, rigid body motion is parametrized as usual for geometrically exact models, whilst primary deformations are described by means of the Generalized Beam Theory (GBT) concept. The (shell-like) rotation that defines the secondary deformation, in turn, is obtained as a function of the walls ́ mid-line displacement field and is parametrized using Kirchhoff-Love shell assumptions. This is an ongoing research, and only the kinematical description, the related weak form (for future FEM discretization) are presented. Its linearization is only conceptually briefed by now. Neither constitutive equations nor numerical implementation are addressed here.

A Simple Geometrically Exact Finite Element for Thin Shells

2024-04-30T00:16:38+00:00

In this Article, we present a shell finite element, with 6 nodes, and a special non-conforming rotational field constructed from an incremental scalar rotation variable and displacement field. This approach eliminates the need for any numerical techniques such as penalties or Lagrange multipliers to address C1 continuity, a kinematic requirement for Kirchhoff-Love shell theory. The quadratic displacement field of the mid-plane is represented by the standard degree-of-freedom at the element’s 6 nodes. The element has been tested under very different simulations scenarios ans has proved to be a reliable element for simulation of thin shells even for large displacements, rotations and strains.

Study of the Inclusion of Heterogeneity in the Determination of Constitu- tive Relations for Micromorphic Media through Homogenization

2024-04-30T00:20:25+00:00

The behavior of quasi-brittle materials, such as concrete, is closely tied to their heterogeneous structure, leading to complex responses to applied loads, including the formation of localized zones of damage. Traditional continuum mechanics models fail to adequately consider the influence of microstructure. To address this limitation, generalized continuum theories have emerged, such as the micromorphic theory, which incorporates additional degrees of freedom to capture the material’s microstructure. Additionally, these theories can effectively handle localization issues in quasi-brittle materials represented as elastic-degrading media due to their nonlocal nature. In this study, we investigate the influence of heterogeneity on determining constitutive relations for micro-
morphic media using a homogenization approach, with a particular focus on quasi-brittle materials. By employing a homogenization technique, the effective constitutive relations for the micromorphic continuum are obtained considering the heterogeneity in a finer-scale. This miscrostructure formed by aggregates and matrix considered in the finer-scale is generated by the take-and-place algorithm and its behavior is described by a classical continuum. Furthermore, an important challenge when modeling with the micromorphic theory is the determination of the 18 elastic parameters required for an elastic isotropic medium. To overcome this obstacle, through this homogenization framework, only classical parameters for the microstructure components are required for the analysis. An analysis is here conducted in order to understand the effect of different characteristics of the finer-scale, as mesh, microcontinuum size, and heterogeneity distribution, on the resulting macroscopic micromorphic constitutive relations. This work could lead to models that are able to capture the microstructure influence, often disregarded when modeling quasi-brittle media, associated to a generalized continuum theory.

Numerical investigation of orthotropic finite elasticity problem with discontinuous deformation gradient

2024-04-30T00:24:43+00:00

We consider the problem of an elastic annular disk in equilibrium in the absence of body force. The disk is fixed on its inner surface and compressed by a uniform pressure on its outer surface. The disk is made of a cylindrically orthotropic material that is stiffer in the radial direction than in the tangential direction. Such material properties are found in certain types of wood and carbon fibers with radial microstructure. We consider that the disk is made of a cylindrically orthotropic St Venant-Kirchhoff material, which is a natural constitutive extension from the linear to the nonlinear elasticity theory. The solution of this problem predicts material overlapping,
which is unphysical if either the pressure is large enough or the inner radius is small enough. A way to prevent this anomalous behavior consists of imposing the local injectivity constraint through a constrained minimization problem of the energy functional. We use both a penalty and an augmented Lagrangian formulation to obtain convergent sequences of finite element approximations. Our results indicate that, to impose the local injectivity constraint accurately, it is preferable to increase the degree of the finite element approximation than to increase the number of finite elements in the mesh.

A simple triangular multilayer Kirchhoff-Love shell element

2024-04-30T00:37:08+00:00

This paper presents a new triangular multi-layer nonlinear shell finite element suitable for simulation with large displacements and rotations. This is a nonconforming element with 6 nodes, a quadratic displacement and a linear rotation field based on Rodrigues incremental rotation parameters, having in total 21 degrees of freedom. The novelty of this element concerns the extension to a multilayer situation of the T6-3iKL element, a kinematical model with properties from Kirchhoff-Love theory, approximating the shell director across the layers as constant and the rotation-continuity between adjacent elements, allowing multiple branches connections in the mesh. These kinematical assumptions make the element extremely simple, without need of artificial parameters such as penalties. The element allows implementation of different material constitutive equations. The model is numerically implemented and displacement results are compared to different references in multiple examples, showing the consistency and robustness of the formulation. It is believed that the multilayer extension conserving all the desirable properties of the T6-3iKL (such as no necessity of penalty, simple kinematic, a relatively small number of DoFs, geometric exact, possibility to use 3D material models, easily connected with multiple branched shells and beams) and including possibly the simplest multilayer model, create a simple yet powerful shell element.

Topological derivative-based multi-material structural optimization with adaptive mesh refinement

2024-04-30T00:41:22+00:00

Topology optimization of structures has been a topic great interest and intense research in the last decades. In simple terms, topology optimization aims at finding a material distribution within a given design domain which minimizes a shape functional. Typically, most works in this area mainly focus on considering the problem of obtaining optimal topologies composed of a single material. However, recent efforts and developments allowed for the incorporation of more than one material in the optimization problem. More specifically, we adopt here a topology optimization algorithm based on the topological derivative together with a domain representation on a fixed mesh with the help of multiple level-set functions. The topological derivative measures the sensitivity
of a given shape functional with respect to an infinitesimal singular domain perturbation, such as holes, inclusions, source terms or cracks. In this work, the topological derivative is used in the optimization procedure as a steepest descent direction, like in any method based on the gradient of the cost functional. In addition, adaptive mesh refinement procedures are performed as a part of the optimization scheme for an enhanced boundary resolution of the final topology. Finally, numerical experiments of classical benchmarks in structural optimization are performed into two and three spaces dimensions to show the effectiveness of the proposed approach.

On the numerical modeling of laser powder bed fusion additive manufacturing of Ti-6Al-4V

2024-04-30T00:44:24+00:00

Laser Powder Bed Fusion (LPBF) represents an additive manufacturing methodology employed to produce intricately designed components. Residual stresses, stemming from the swift thermal transitions inherent in this process, can give rise to defects like cracks, distortions, and delamination. This research endeavors to comprehensively examine the dynamics governing the progression of residual stresses and temperatures during the LPBF of Ti-6Al-4V. A three-dimensional finite element model was developed to investigate the influence of various process parameters on the intricate variations of temperature and stresses throughout multi-layer LPBF procedure, as well as the resultant residual stress post-cooling. The outcomes reveal a substantial influence of process parameters on the temperature gradients and final stress distributions. Notably, higher input energy to the layer led to elevated induced residual stresses. The transition from 50 W to 400 W in laser power resulted in a pronounced shift in residual stress, effecting a transformation from -56 MPa (i.e., compressive) to 148 MPa (i.e.,tensile).

Dissipation analysis on a large strain thermo-elasto-viscoplastic model us- ing the Finite Element Method

2024-04-30T00:48:18+00:00

We present a phenomenological large strain thermo-elasto-viscoplastic constitutive model using the multiplicative decomposition of the thermal, elastic and plastic deformation gradients. The laws of thermodynamics are used as basis to formulate the model and to obtain the heat equation, including the dissipation from the viscoplastic component. An isotropic expansion law in exponential form is used for the thermal part of the deformation, and a neo-Hookean model is used for the elastic part. Plasticity is considered based on the von Mises yield criterion with Perzyna model to account for the viscous behavior of the plastic component, Norton’s law for the
overstress function, and the Armstrong-Frederick model of kinematic hardening. For the numerical integration of the evolution laws, we employ an exponential map method that ensures the property of plastic incompressibility. The resulting constitutive model is applied in a position-based Finite Element framework to solve the mechanical problem. The thermal problem is also solved by the Finite Element Method, using temperatures as nodal parameters, and the thermo-mechanical coupling is performed as an iterative partitioned method. Finally, a representative numerical example is selected to show the characteristics of the constitutive model, with special focus on the heat generated due to plastic dissipation over different strain and stress rates.

Analytical Techniques for Calculating the Work of a Plate

2024-04-30T00:51:12+00:00

The article analyzes the selection of the deflection function for calculating the functional of the work and presents a matrix approach to simplify this functionality. The problem requiring such a careful approach grew out of the problem of the loss of stability of an infinite plate with an elliptical hole (inclusion) during stretching, where, with an ill-considered choice of deflection functions and irrational calculations, the accumulated error of machine counting ruined the results obtained. The authors have carefully approached the study of this problem and show techniques that allow us to consider the work analytically. These functions and the general approach are
also suitable for analytical calculation of potential energy, but this is the topic of a separate article.

A triangular virtual element for thin shells

2024-04-30T00:56:47+00:00

We propose a low-order triangular element for Kirchhoff-Love shells by the virtual element method, for use in the kinematically linear range. The shell domain discretization by flat triangles enables no use of a predefined mapping approach and curvilinear coordinates system. The displacements and deflection gradient locally defined at the triangle vertices are the local degrees of freedom, corresponding to the lowest-order cases for conforming in-plane and out-of-plane displacement approximations. Accordingly, their respective projections from the finite-dimensional space to linear and quadratic polynomials over the element, supplied by a stabilization, allow defining a (projected) constant strain and curvature virtual element. Numerical examples including stabilization and element geometry extension to quadrilateral for cylindrical shells are used as an illustration of our results.

Logarithmic strain tensor in the positional formulation of FEM

2024-04-30T01:00:07+00:00

Besides structural engineering, rubber-like materials have been used in several fields such as bioengineering and medicine. Usually, these materials undergo, not only large displacements, but large deformations as well, and this requires a special attention to write a formulation both mathematically and physically consistent. To this end, one must choose a strain measure that, preferably, depends on the initial configuration of the body and that results in the null tensor for a given arbitrary rigid body motion. One of the most used strain measures in this context is the Green strain. However, this measure does not show a physical coherence for the one-dimensional case, as it is known. Thus, this work formulates the problem by using another strain measure, namely, lnU, where U is the right stretch tensor. The positional formulation of the finite element method together with the Newton-Raphson procedure are applied for solid analysis. The constitutive equation is supposed to be linear. At the end, a comparison between the numerical results obtained by the Green strain and by lnU is performed.

An Artificial Intelligence Approach for Predicting Hydropower Production in the Nordic Power Market

2024-05-01T14:21:38+00:00

Hydropower has historically had an important role in the Nordic power market. In the Nordic power
market, hydropower accounts for around 60% of the electricity generated (2010–2019). The share of variable
renewable energy sources (VRES) has grown considerably in recent years. Because of the growing awareness
about climate change, this tendency is likely to continue in the future. In this paper, an artificial intelligence-based
model to forecast hydropower production in different bidding areas in the Nordic power market was developed.
Furthermore, the effects of spatial characteristics of VRES production on short-term hydropower production
planning are analysed at bidding area level. As predicted, the AI model revealed that inflow and reservoir level
are critical for the model's performance prediction. The findings showed that residual demand within the bidding
region alone is insufficient to estimate hydropower generation. The model's forecast can be greatly improved by
including residual demand for the other bidding areas as an input parameter. The forecast performance of the AI
model for hydropower deteriorated as the percentage of non-dispatchable generation increased. However, the
model demonstrated its ability to estimate hydropower in the face of the growing amount of variable renewable
energy generation in the Nordic power market.

Online Learning of Data Streams: Evolving Fuzzy Predictor with Multi- variable Gaussian Participatory Learning and Recursive Weighted Total Least Squares

2024-05-01T14:25:21+00:00

This paper introduces an evolving fuzzy system called eFTLS (evolving Fuzzy with Multivariable Gaus-
sian Participatory Learning and Recursive Weighted Total Least Squares) constructed based on a non-supervised

recursive clustering algorithm with participatory learning and multivariate Gaussian membership functions. The

eFTLS uses a clustering algorithm to extract the first-order Takagi-Sugeno functional rules. The clustering algo-
rithm can add a new cluster, delete, merge, or update existing clusters. The clusters are created using a compatibility

measure and an alert mechanism. The compatibility measure is computed by Euclidian or Mahalanobis distance

according to the number of samples in the cluster. An age and population based-method excludes inactive clus-
ters. Redundant clusters are merged whenever there is a noticeable overlap between two clusters. An algorithm

of recursive weighted total least squares updates the consequent parameters. The performance of the eFTLS is
evaluated and compared with alternative state-of-the-art models in forecasting tasks. Computational experiments
and comparisons suggest that the eFTLS perform better or are similar to alternative models.

SIGNAL POWER LOSS PREDICTION USING ARTIFICIAL INTELLIGENCE

2024-05-01T14:27:53+00:00

In this study, we conducted a machine learning approach to propose a mobile telephony signal propa-
gation model using regression. The acquisition of signal propagation models provides relevant indicators about

the network signal quality offered to users. Although the most advanced technology is 5G, a study was developed
using 3G and 4G data, since the implementation of 5G in Brazil is still a distant scenario. Signal power loss
data from a single operator were collected through the G-Net Track application and processed using Haversine.
This enabled the application of linear regression technique to obtain a model representing signal power loss. The
regression-generated result was compared to nine literature models, including Rappaport, Okumura-Hata, ECC33,
Modified Cost231-Hata, SUI, Extended SUI, Walfish-Ikegami, and Ericson999. The results from the sampled data
indicate that the literature models do not adequately represent the signal behavior, and that the application of linear

regression produces a solution capable of representing, in a more realistic manner, the behavior of 3G and 4G sig-
nal power loss concerning the transmitting antenna. Through this study, we aim to comprehend the heterogeneity

of the network infrastructure and contribute by providing research that aids in the formulation of public policies to
enhance the Brazilian telecommunications system.

Acquisition, processing and data analysis of piezoelectric sensors for training musical robots in a didactic model

2024-05-01T14:36:32+00:00

This paper introduces a developed system tailored for processing and analyzing data acquired from
piezoelectric sensors. The system’s objective is to detect rhythmic patterns in percussive music, generating a
database to train musical robots. This training enables collaborative interaction among musical robots, thereby
nurturing human musical advancement. The proposed approach involves assessing the musician’s performance
by installing piezoelectric cells affixed to rubber pads corresponding to each instrument. Processing techniques
applied to the piezoelectric sensor signals facilitate system implementation through accessible didactic hardware,

which is more user-friendly compared to alternatives such as frequency spectrum processing. Analyzing param-
eters based on rhythmic beat intensity and timing leads to the establishment of a precise database characterizing

musician dynamics. The progression from a simplified to a more intricate data model explores intensity and

data structure within the database. Testing employed well-known basic rhythms to construct a rhythm reposi-
tory, demonstrating the system’s adeptness in microcontroller-based data processing and analysis. The system

showcases benefits like compactness, energy efficiency, and reduced space and weight, favorable for constructing
robotic frameworks. The proposed approach supports real-time and embedded system applications, extending a
multitude of possibilities and applications within the realm of music and robotics.

Database with information on the electric grid of the national interconnected system for application in short term operation planning in Brazil

2024-05-01T14:41:02+00:00

In Brazil, the operation planning of the hydro-thermal-wind power system and subsequent power
dispatch is carried out by the National Electric System Operator (ONS) using a hierarchical chain of software
tools, which includes medium, short, and very short-term time horizon models. Currently, only the latest software
in the chain provides a more detailed representation of data regarding the transmission lines of the National
Interconnected System (SIN). However, studies indicate that a more detailed consideration of the electrical grid in
medium or short-term horizons can bring the operation closer to planning. Therefore, the Laboratory of
Technologies and Bioinspired Solutions of the Federal University of ABC of the Federal University of ABC
(LabBITS) seeks to implement the transmission system data of SIN, available through the Expansion and
Reinforcement Plan (PAR). Consequently, the objective of this work is to identify and process the PAR
information using JAVA programming, registering and managing the database with MySQL, so that this data can
be intuitively utilized to support the development of modules for the studies of the Brazilian electrical system
operation within a bioinspired computational platform called Energ.IA.

Data Aggregator for Physics Informed Neural Networks in NVIDIA Modulus Framework

2024-05-01T14:44:08+00:00

The development of Physics Informed Neural Networks (PINNs) has been receiving considerable atten-
tion lately. PINNs incorporate the partial derivative equations that describe the physical behavior of a natural or

engineered system in the loss functions of neural networks. This model family represents a new paradigm for the

solutions of PDEs for both forward and inverse problems. Different frameworks that aim to facilitate the produc-
tion and training of such models are currently being provided, and Modulus is one of the available frameworks that

has been gaining ground recently. In any case, despite the capability of these packages to assist the construction of

PINNs, it is important to consider a viable data analysis strategy for the experiments. This work presents the Mod-
ulus Aggregator tool, which is developed to support the data analysis expert in the hyperparameter configuration

of multiple models produced, with a strategy for the aggregation of results. The aggregation tool complements the
TensorBoard visualization toolkit and takes advantage of the native directory structure of a Modulus experiment.
The experiment of a wave propagation shows the potential to assist the analysis of results and the possibility of
automating the extraction and filtering activities of trained models in a scenario of a significant amount of data.

Certification and characterization of technical production registered on the Lattes Platform

2024-05-01T14:48:28+00:00

The Lattes Platform is a valuable source of information, however, due to the large volume of data and
filling in the information being the responsibility of the individual, it may eventually cause inconsistencies in the
entered data, which emphasizes the need for validation mechanisms. Methodology: The methodological process
was divided into two parts, in which the first is characterized by the collection and construction of the local
database with data from patents filed in Brazil and curricula from the Lattes Platform, and the second part is the
description of the patent certification process informed in the CVs of the Lattes Platform. Results: A local database
was built, consisting of 903,979 patent records from Espacenet and 76,619 patent records distributed in 28,581
CVs collected on the Lattes Platform, organized in a relational database. It was possible to certify approximately
58% of the patents reported on the Lattes Platform. Conclusion: About 1% of the CVs on the Lattes Platform
contain information on patents, a base composed of more than 7 million CVs (2022). Of this amount, not all could
be validated and certified on Espacenet due to inconsistency in the recorded data, highlighting the need for
validation and certification mechanisms for patent data.

Influence of roughness filters in the analysis of elastohydrodynamic and dry circular contact

2024-05-01T22:13:15+00:00

Surface finishing and roughness parameters can directly affect the system’s efficiency and components’
useful life of several mechanical applications. In order to evaluate these parameters’ influence, one can employ
numerical methods that predict the pressure field and maximum contact pressure. The problem assessed in this
study is that, despite surface roughness being an “intrinsic” surface property, measured roughness is “extrinsic”
meaning that instruments using different sampling intervals and filters produce different asperities distribution,
which can affect the pressure field predicted by numerical modelling. Therefore, this study employs two numerical
models, a Dry Circular Contact (DCC) model and an Elastohydrodynamic lubrication (EHL) model to investigate
filtering influence over the maximum contact pressure. The results show that the same surface filtered with
different cut-off lengths presents distinct pressure fields and maximum pressure values. Also, the simulations
indicate that smaller cut-offs tend to produce higher pressures.

An adaptive implicit-explicit time-marching technique for elastodynamic analysis

2024-04-29T13:57:10+00:00

In this work, we discuss an implicit-explicit time-marching procedure with adaptive time integration parameters for the analysis of hyperbolic models. This methodology utilizes two locally evaluated time integration parameters, allowing for their different spatial and temporal distributions. The first parameter defines implicit/explicit subdomains within the model, ensuring stability and reducing errors related to period elongation.
The second parameter controls the dissipative properties of the methodology, effectively eliminating the influence of spurious high-frequency modes and reducing amplitude decay errors. Moreover, this implicit-explicit approach reduces computational effort by obtaining reduced systems of equations and serves as an efficient non-iterative single-step procedure. The key features of this novel methodology can be summarized as follows: it is simple, locally defined, guarantees stability, provides enhanced accuracy, enables advanced controllable algorithmic dissipation in higher modes, establishes a connection between temporal and spatial discretizations, operates as a single-solve framework based on reduced systems of equations, is self-starting, and fully automated. The paper concludes with the presentation and comparison of numerical results with those obtained using standard techniques, illustrating the remarkable effectiveness of the discussed approach.

A Posteriori Error Estimation For Linear Elasticity With Weak Stress Sym- metry

2024-04-29T01:09:58+00:00

This work focuses on the development of a posteriori error estimation for linear elasticity with weak stress symmetry [1]. The procedure is based on the post-processing of the enriched displacement field computed by a mixed finite element formulation, as in [2]. Inspired by [3], the estimation involves two post-processing techniques: averaging the numerical displacement over element interfaces and solving a set of local problems. By applying the Prager-Synge theorem in the context of linear elasticity [4], we are able to develop an estimator with known constants.

Numerical simulation of gas lift systems using the Volume of Fluid method

2024-04-29T01:14:09+00:00

Oil production in reservoirs declines over time as pressure decreases, presenting a challenge in maintaining economically desired production rates. Artificial lift methods can be used to address this issue, considering the characteristics of the production system, such as reservoir and fluid properties, as well as facility constraints. Gas lift involves injecting gas into lower sections of the tubing through strategically placed valves along the pipeline, effectively reducing the density of the fluid mixture and facilitating its upward flow. This lifting method is applicable to offshore operations and is not limited by well depth, allowing for different types of operations, including continuous or intermittent lift. In the present work, a gas lift flow is numerically studied using the volume of fluid method and a fluid mixture of water-air. The method is based on defining the liquid volume fraction and employing a transport equation to capture the interface. The interFoam solver from OpenFOAM-10 is used to simulate a three-dimensional two-phase gas lift scenario. The setup consists of vertical water flow in a 44 mm pipe diameter, while air is injected through a 2 mm diameter orifice in the ortoghonal-flow direction. The total pressure drop is evaluated and compared with experimental data. The phase fraction and mean velocity profile are also obtained.

Fully computable a posteriori error estimates for the primal hybrid variational formulation of Poisson’s equation

2024-04-29T01:23:26+00:00

We present a new fully computable a posteriori error estimates for the primal hybrid formulation applied to Poisson’s problem. The estimates are based on the reconstruction of a continuous potential field and an equilibrated flux, which are computed using the potential and Lagrange multipliers solutions. The potential reconstruction is the result of orthogonally projecting the potential solution onto a function over the mesh skeleton, smoothing this function into a continuous trace, and solving local pure Dirchlet problems. This procedure for reconstructing the potential were used to develop error estimates for the mixed formulation in [1, 2]. The equilibrated flux is obtained from solving local mixed problems using Lagrange multipliers at a pure Neumann boundary condition. This technique is similar to the flux recovery strategy based on the Arnold–Boffi–Falk spaces described in [3], but for the divergent compatible pair of spaces described in [4]. An adaptive refinement strategy is developed, and numerical results illustrate the efficiency of the error estimates.

CFD open-source code validation for fluid-structure interaction in building analysis

2024-04-29T21:27:30+00:00

With the advancement of computational technology and numerical techniques, Computational Fluid Dynamics (CFD) has been playing a fundamental role in solving problems of wind-structure interaction. Aiming at the optimization of the structural design from the reduction of the costs of experimental tests directed with computer simulations, this article presents an analysis of the feasibility in the use of an open access CFD tool, OpenFOAM, for the calculation of the dynamic pressures due to the action of the wind in buildings. CFD simulation was coupled in conjunction with the structural analysis model to evaluate the efforts and displacements by using the Finite Element Method.

A locally-adaptive truly-explicit time-marching formulation for acoustic analyses

2024-04-29T21:33:19+00:00

This study discusses a novel explicit time-marching procedure for solving acoustic problems in the time domain. The procedure is designed to adapt to the characteristics of the spatially discretized model, providing a fully automated and highly effective solution. The approach is second-order accurate, explicitly formulated, and self-starting, offering the advantages of adaptive algorithmic dissipation and extended stability limits. Furthermore, the paper discusses automated subdomain/sub-cycling splitting procedures that enhance the performance of the proposed formulation. By partitioning the model domain into multiple subdomains based on
the discretization properties, different time-step values can be utilized to ensure stability and enable more precise and efficient analyses. The method incorporates adaptive values for the time integration parameters, which are determined based on the characteristics of the spatial discretization. This locally-defined self-adjustable formulation establishes a link between the spatial and temporal solution procedures, better compensating for their errors. The paper presents and discusses expressions for the adaptive time integration parameters and the limiting time-step values of the discretized domain elements. Finally, numerical results are presented at the end of the paper, comparing them to those obtained using standard techniques, thereby illustrating the performance of the discussed approach.

An adaptive implicit-explicit time-marching technique for elastodynamic analysis

2024-04-29T21:38:43+00:00

In this work, we discuss an implicit-explicit time-marching procedure with adaptive time integration parameters for the analysis of hyperbolic models. This methodology utilizes two locally evaluated time integration parameters, allowing for their different spatial and temporal distributions. The first parameter defines implicit/explicit subdomains within the model, ensuring stability and reducing errors related to period elongation. The second parameter controls the dissipative properties of the methodology, effectively eliminating the influence of spurious high-frequency modes and reducing amplitude decay errors. Moreover, this implicit-explicit approach reduces computational effort by obtaining reduced systems of equations and serves as an efficient non-iterative single-step procedure. The key features of this novel methodology can be summarized as follows: it is simple, locally defined, guarantees stability, provides enhanced accuracy, enables advanced controllable algorithmic dissipation in higher modes, establishes a connection between temporal and spatial discretizations, operates as a single-solve framework based on reduced systems of equations, is self-starting, and fully automated. The paper concludes with the presentation and comparison of numerical results with those obtained using standard techniques, illustrating the remarkable effectiveness of the discussed approach.

OpenFOAM validation for indoor ventilation applications

2024-04-29T21:44:23+00:00

The use of Computational Fluid Dynamics (CFD) to study ventilation strategies in indoor spaces is an crucial tool for energy consumption reduction and sustainability. In this study, the application of several turbulence models for indoor ventilation modelling were validated using the OpenFOAM software. These validations were based on two experimental benchmark cases available in the literature. In the first case, an isothermal quasi 2-dimensional flow in a room with one inlet and one outlet was studied. Comparisons of URaNS simulations using the pimpleFoam solver together with the high-Reynolds number k − ε, RNG k − ε and the low-Reynolds
number LaunderSharma k − ε and k − ωSST turbulence models are presented. The second benchmark case is a three-dimensional non-isothermal flow in a room with one inlet (cold jet) and four outlets placed in a vertical opposite wall, where a heat flux is applied. The flow has an Archimedes number of 0.016. For the second case URaNS simulations were performed using the buoyantPimpleFoam solver with k − ε turbulence model with buoyant production term, and the isothermal k − ε and RNG k − ε turbulence models. In the first benchmark case all turbulence models produced a good description of the experimental flow with exception of k − ωSST that
overestimated the size of the recirculating zone and was then discarded from further tests. The second benchmark case, performed only with high-Reynolds number turbulence models, showed an overall good agreement with the experimental results, and, as almost expected, the buoyant k − ε model had the best performance pointing the importance of the buoyant term inclusion on other popular turbulence models of the OpenFOAM library.

A discontinuous and nonlinear multiscale method for solving convection- dominated problems

2024-04-29T21:49:54+00:00

This work presents a discontinuous and nonlinear multiscale method for solving problems dominated by convection. The method introduces a nonlinear artificial diffusion term at both scales of discretization while employing a discontinuous framework solely at the coarse scale. The micro scale is approximated using bubble functions, enabling efficient and accurate representation of the solution behavior. This approach aims to improve the accuracy and stability of numerical simulations for convection-dominated phenomena. Convection-dominated problems pose challenges in accurately resolving steep gradients and rapid variations in the solution. Conventional numerical methods often encounter problems related to numerical stability when solving this type of problem. In order to overcome these limitations, the proposed numerical scheme combines the benefits of nonlinear artificial diffusion, the discontinuous framework, and the use of bubble functions. To validate the effectiveness of the new method, some numerical experiments were conducted on convection-dominated problems of varying complexity. The results demonstrate that the multiscale method outperforms traditional approaches in accurately capturing the solution behavior, particularly in regions with sharp gradients.

Simulation of turbulent flow around a bridge deck in OpenFOAM: com- parison with wind tunnel test results

2024-04-29T21:54:20+00:00

This work presents a two-dimensional simulation of a turbulent flow around a bridge deck using the software OpenFOAM and Large-Eddy Simulation turbulence model. It is a cable-stayed bridge, which has already been built and is located in the city of Guarulhos, Brazil. We sought to validate the results of this simulation through an experiment previously carried out in a wind tunnel, by comparing the aerodynamic coefficients results. OpenFOAM as well as Smagorinsky LES turbulence model proved to be effective tools to simulate this type of problem.

FEM Simulation of Orthogonal Machining of Al 6101-T6 and Inconel 718 Using Johnson-Cook Constitutive Model

2024-05-01T12:51:32+00:00

Traditional machining processes such as milling and turning consist in using a cutting tool with defined
geometry to give shape to a workpiece by removing material in the form of chips. The Finite Element Method
(FEM) can be used to simulate the metal cutting procedure and predict output variables such as chip morphology
and cutting forces, facilitating the optimization of machining parameters and reducing experimental costs. Thus,
the present work aims to simulate machining operations to conduct a numerical analysis of chip morphology and
cutting forces in different materials. The nickel superalloy Inconel 718, which is considered a hard-to-cut material,
was chosen for a comparative study with the aluminum alloy Al 6101-T6, considered a material of good
machinability. The mechanical properties of both materials were characterized using the Johnson-Cook
constitutive model in the simulations, whereas the cutting tool was modelled as a rigid body. The results show that
machining of Inconel 718 leads to worse chip formation, higher residual stresses, and higher cutting forces than
Al 6101-T6, which is expected from literature.

Numerical investigation on the fire resistance of load bearing LSF walls: the effect of the load level

2024-05-01T16:12:11+00:00

This article investigates the fire performance of Light Steel Frame (LSF) walls commonly used in
buildings. Six full-scale LSF tests with different layouts are validated through numerical simulations using
uncoupled thermal and mechanical analyses. The hybrid numerical model incorporates experimental data to
accurately predict the LSF wall temperature, solving the non-linear transient thermal analysis. Three mechanical
simulations are developed: elastic buckling analysis for instability mode, Geometric and Material Non-Linear
Imperfection Analysis (GMNIA) for load-bearing capacity at room temperature, and thermo-mechanical analysis
considering temperature effects under constant load. Model validation compares six experimental tests under room
temperature and fire conditions. The Root Mean Square Error is used for each comparison. Results show that the
fire resistance (R) of LSF walls decreases with the load level. The impact of the cavity insulation is examined,

revealing potential improvements in fire resistance for cavity-insulated LSF hollow stud walls compared to non-
insulated ones. Notably, hollow section studs generally exhibit higher fire resistance than corresponding lipped

section studs when void cavities are used. The investigation proposes a new approach to determine the fire
resistance based on the relationship between the critical temperature of steel studs (Hot flange) and load levels.
This relationship allows us to predict the fire resistance time through a preliminary thermal analysis of LSF walls.

Evaluation of the Cross-Section of Support Construction Elements in Wood with Gypsum Submitted to Fire on One Side

2024-05-01T16:15:43+00:00

In this work, different numerical tests are presented, for the assessment of the thermal and transient
analysis, of different constructive elements in wood, with gypsum protection, in fire conditions. This type of
constructive element presents cavities, making the numerical analysis in the study complex in the approximation
to real models. The analysis was carried out considering the nonlinearity of the materials. The objectives were to
investigate which is the best numerical model, using the finite element method, which addresses experimental
tests carried out by other authors and to be used in different parametric models that can be used by designers to
prevent fire resistance in these components.

ANALYSIS OF THE FLUID DYNAMIC BEHAVIOR OF AN ENCLOSED STAIRCASE UNDER FIRE

2024-05-01T16:18:33+00:00

The analysis of fire through computer modeling allows the improvement of current legislation, as well
as fire protection and fighting techniques. This work presents an analysis of the fluidodynamic behavior of a
cloistered staircase (EP) under fire through a computational modeling using the commercial software Fire
Dynamics Simulator (FDS), developed by NIST (National Institute of Standards and Technology). The Enclosed
Ladder (EP) was dimensioned according to the specifications of the NBR 9077 standard(1). Through the
simulation, it is possible to understand the fluidodynamic behavior of (PE) in relation to the aspects of smoke
behavior in fire situations and develop mitigating measures for buildings already built. The results showed that the
use of (PE) with the dimensions provided for by NBR 9077 (1) is not effective, since it confines the smoke inside
the staircase and does not provide the complete escape of the smoke from its interior, being proposed in this worka
larger opening dimension dthe windows for smoke escape, as well as the creation of a gap that provides the entry
of air inside the staircase in a natural way, providing a better distance of visibility.

Buckling and Post-Buckling Behavior of Lipped-Channel Columns Undergoing Distortional-Global Interaction at Elevated Temperatures

2024-05-01T16:21:38+00:00

This study investigates the behavior of cold-formed steel fixed-ended lipped-channel columns
undergoing distortional-global (D-G) interaction at high temperatures. It extends the scope of previous works by

including columns exposed to temperatures up to 800o C due to fire conditions with a different temperature-
dependent material model. The columns' dimensions and lengths were chosen to provide true D-G interaction.

ABAQUS shell finite element analyses were conducted to obtain elastic-plastic post-buckling equilibrium paths,
failure loads, and collapse modes for these columns. The AZ/NZS 4600 (2018) constitutive model was employed
to account for the steel behavior at high temperatures. Several room-temperature yield stresses were considered to
cover a wide slenderness range. The numerical failure loads provided insights for further studies, including
remarks to be taken into account in the future proposals of DSM-based curves, more specifically in the sense of
considering the effects caused by the variation of the non-linearity of the steel stress-strain curves with temperature.

Energy balance for restrained steel columns in fire

2024-05-01T16:25:14+00:00

The behavior of restrained steel columns in fire is analyzed in the paper, by quantifying the evolution
of the mechanical and thermal energies from ignition until collapse. An appropriate structural model is adopted,
to simulate real columns in buildings, and is analyzed by means of the voxels-based Rayleigh-Ritz method. This
numerical method accounts for stability effects, spread of plasticity, degradation of the steel’s mechanical
properties with heating and non-uniform temperatures distributions at any stage of heating. The column’s behavior
in fire consists of thermal buckling followed by plastic collapse. From a Thermodynamics point of view, the heat
given to the column is transformed into thermal and mechanical forms of energy stored in the column, and in
energy conducted to the surrounding frame. The energy transformations during this process must respect all
principles of Thermodynamics. To this end, a new energy balance expression is proposed, and the most relevant
energy parts related to the mechanical problem are computed for an illustrative example. A new quantity – the
thermal absorption capacity denoted by H – is proposed to quantify the resistance of columns in fire.

Numerical modeling of the fire behavior of composite steel and concrete joints after earthquake

2024-05-01T16:27:58+00:00

This paper presents a numerical model for analyzing the fire behavior of composite steel and concrete
end-plate joints after earthquake. The model was developed and validated with experimental results. The obtained
moment-rotation results showed that cyclic loading damage affects the performance of the joint in case of fire.

A 3-D Extension of the Multiscale Control Volume Method for the Simula- tion of the Steady-State Diffusion Equation

2024-04-23T20:24:36+00:00

The level of detail on modern geological models requires higher resolution grids that may render the simulation of multiphase flow in porous media intractable. Moreover, these models may comprise highly heteroge-neous media with phenomena taking place in different scales. The Multiscale Finite Volume (MsFV) method can tackle such issues by constructing a set of numerical operators that map quantities from the fine-scale domain to a coarser one where the initial problem can be solved at a lower computational cost and the solution mapped back to the original scale. Unlike more traditional techniques like homogenization and upscaling, the MsFV has the advantage of maintaining the coupling between the scales even when there is no clear scale separation. However, the MsFV formulation is limited to k-orthogonal grids since it uses a Two-point Flux Approximation (TPFA) method and employs an algorithm to generate the coarse meshes that is not capable of handling general geometries. The Multiscale Restriction Smoothed-Basis method (MsRSB) improves on the MsFV by introducing a new iterative procedure to find the multiscale operators and modifying the algorithm for the generation of the multiscale geometric entities to accommodate unstructured coarse grids, but is still limited to structured fine grids due to the TPFA discretization. Finally, the Multiscale Control Volume method (MsCV) replaces the TPFA by the Multipoint Flux
Approximation with a Diamond stencil (MPFA-D) scheme on the fine-scale while further enhancing the generation of the geometric entities to allow truly unstructured grids on the fine and coarse scales for two-dimensional simulation. In this work we propose an extension to three-dimensional geometries of both the MsCV and the algorithm to obtain the multiscale geometric entities based on the concept of background grid. We also modify the MPFA-D to use the very robust Generalised Least Squares (GLS) interpolation technique to obtain the required auxiliary nodal unknowns. We show that the 3-D MsCV method produces satisfactory results even for heterogeneous and highly anisotropic media, employing true unstructured grids on both scales to handle the simulation of the steady-state diffusion equation.

A multiscale finite element method for simulating flow in fractured porous media

2024-04-23T21:00:36+00:00

This work extends on Duran et al. [1] to propose a multiscale locally conservative finite element method ́
for the simulation of flow in fractured porous media. The method employs H(div)-confirming flux approximations
that carry advantages such as the ability to solve problems with nearly incompressible materials, better accuracy
for the velocity field approximation, fewer requirements on the regularity of the solution, and continuity of the
normal velocity between elements. The last of these leads to locally conservative approximations of the velocity
field, which is considered paramount in the area of reservoir simulation. The flow in the porous media is modeled
using traditional Darcy’s law, and the coupling with the fracture flow is modeled with the Discrete-Fracture-Matrix
representation, where the fractures are idealized as lower-dimensional elements at the interface of matrix elements. The method is applied to a benchmark problem of a complex reservoir with several fractures.

A Multipoint Flux Approximation Method Based Of Harmonic Points (MPFA- H) For The Numerical Simulation Of Coupled Poroelastic Problems

2024-04-24T16:43:01+00:00

Reservoir simulation is an important tool for the prediction of oil and gas production. However, some
physical phenomena were either neglected or oversimplified in the simulations, in order to facilitate the process
of developing a simulation tool to analyze the fluid flow within the rock reservoir. One such phenomenon is the
mechanical behavior of the reservoir and surrounding rocks, and how it affects rock properties, and consequently,
the fluid flow behavior through the porous media, which, in turn, influences its mechanical behavior, since fluid
pressure contributes to the rock deformation. These effects are well observed in wellbore stability and reservoir
subsidence, as both can severally change the production behavior, if not considered. In this work, Biot’s theory of
consolidation is used to derive the governing equations of both the process of rock deformation and fluid flow in
the porous rock and their coupling. In the petroleum reservoir community, usually, these problems are solved using different numerical methods: The Finite Element Method (FEM) is used for the geomechanics problem while the Finite Volume Method (FVM) is employed for the fluid flow problem. However, in the present paper, we propose a full finite volume formulation for both problems based on the use of the Multi-Point Flux Approximation using Harmonic Points (MPFA-H), which was extended to handle the geomechanical problem. The MPFA-H method is very robust and flexible. Using the same basic strategy for both problems has the advantage of producing a locally conservative formulation, which is important for multiphase flow modeling, and the use of the same data structure which eases the simulation tool development, is expected to increase numerical stability, accuracy, and simulation speed. We use a sequential solution method in which the equations for solid deformation and fluid flow are solved separately and the solutions of each problem exchange information in all time steps, using the fixed-strain split. The solutions obtained with the strategy described are verified using benchmarks found in literature.

Numerical assessment of pressure, velocity, and stress post-processing strate- gies for the Biot’s problem

2024-04-24T16:49:36+00:00

In the context of the displacement-pressure formulation for the Biot’s problem, the present work ex-plores some possibilities of Finite Element post-processings to improve the accuracy of the pressure field, the Darcy velocity, and the effective stress. Numerical experiments illustrate the performance of the different strategies and compare their results with the native approximations obtained through the use of the lowest-order Taylor-Hood space in the displacement-pressure Galerkin method. Our results indicate that the post-processing strategies pre- sented significantly improve the approximation of the velocity and effective stress fields. The pressure field, on the other hand, does not benefit as much from the strategies considered here.

A methodology to evaluate fluid-dynamic forces on immersed bodies in 3D fluid flow problems

2024-04-24T16:54:03+00:00

This work presents first results on a methodology to evaluate fluid-dynamic forces on immersed bodies
in three-dimensional fluid flows resolved through the finite element method (FEM). A classical Eulerian approach
is followed to describe the fluid (assumed incompressible through the Navier-Stokes equations). The fluid-body
interface is treated through Nitsche’s method, which is an immersed boundary technique with which we
consistently impose the Dirichlet boundary conditions in a weak form. In order to assess the accuracy and
efficiency of the developed scheme, a numerical simulation of a 3D benchmark stationary flow of an
incompressible fluid is performed. This work refers to an intermediate stage of a doctoral research that aims to
model fluid flows with immersed particles with consistent fluid-particle interaction and particle-to-particle
contacts, as observed in many particle-laden fluid applications.

An improved embedded finite element formulation for investigating fluid flow behavior in fractured porous media

2024-04-24T16:58:52+00:00

Discontinuities, such as fractures and geological faults, are present in several geological models where a fluid flow analysis is performed. In cases where the discontinuity filling material has a lower permeability than the matrix, this discontinuity will act as a barrier to fluid flow in the porous media. On the other hand, fluid flow is enhanced in the absence of filling material or in the highly porous case. Embedded formulations have become attractive to model discontinuities over the last decades since they do not require mesh conformity. However, the literature lacks a formulation fully developed in the context of the Finite Element Method capable of modeling discontinuities that act like barriers to fluid flow in transient problems. This paper presents an improved embedded finite element formulation to investigate fluid flow behavior in fractured porous media. The proposed approach includes additional degrees-of-freedom representing the pressure drop between fracture surfaces and the fluid pressure within the fracture. Single-phase flow is considered. Darcy’s law governs fluid flow through the porous media, while the cubic law of parallel plates controls the fluid flow inside the fracture channel. A numerical
example comparing the results with a model with interface elements modeling the discontinuity is compared to
the embedded formulation. The numerical results demonstrate the capability and limitations of the proposed
approach to capture the influence of discontinuities on fluid flow behavior in porous media.

A Multipoint Flux Approximation Method based on Harmonic Points to Simulate Highly Heterogeneous and Anisotropic Aquifers

2024-04-24T17:08:13+00:00

Currently, groundwater has become an essential natural resource for human consumption, particularly in arid regions. It is well-known that aquifers have very complex geological characteristics due to the presence of zones of low permeability, vugs and fractures. The geological complexity and the presence of strongly coupled terms in the mathematical models make it difficult, if not impossible, to obtain an analytical solution, and solving this class of problem is a challenge for the hydraulic engineer. In this sense, computer simulators supported by numerical methods have become a fundamental tool for dealing with these mathematical models. Currently, in the context of numerical simulation of fluid flow in aquifers, several classical numerical methods are used in most commercial simulators such as FEFLOW, MODFLOW, and HydroGeoSphere. However, it is well known that these classical methods cannot deal with complex physical phenomena and can lead to inconsistent approximate solutions. In this sense, in the present work, the hydraulic head equation of the aquifer is solved for the first time using a cell-centered finite volume method, where the spatial and temporal terms are solved using the multi-point flux approximation method based on harmonic points (MPFA-H) and the backward Euler or Crank-Nicolson schemes, respectively. In this context, the MPFA-H method is characterized by being globally and locally conservative, piecewise-linear, and able to deal with highly heterogeneous and anisotropic porous media. Moreover, the harmonic points are calculated from physical and geometrical parameters, which allows a piecewise-linear solution and guarantees the positivity of the interpolation weights of the hydraulic head on the control surface of the computational mesh. The results show that the proposed method provides high accuracy and efficiency in groundwater simulation.

Computational Model for the Optimization of the Generation of Thermal Power Plants in Brazil

2024-04-26T19:34:09+00:00

An organized infrastructure and available energy resources are fundamental for the development of a country to be continuous and effective. Although Brazil has many natural resources and a large water structure, other types of energy generation sources are required to contribute to the country's energy demand. Given this, thermoelectric generation has characteristics that make it capable of guaranteeing the necessary complementation, making the reliable system. For this, the planning of the hydrothermal operation is necessary to determine the optimal generation to guarantee the supply with efficiency, safety and economy. Given the complexity of the system, computational models help in decision-making on determining the optimal generation. Therefore, this research work seeks to explore a methodology that aims to determine the optimal generation of thermoelectric plants in part of the Brazilian system, based on the necessary complementation determined by the optimal generation of hydroelectric plants. In this study, the real data from the Brazilian system, available on the NEWAVE deck, were modeling and processed by Linear Optimization Toolbox of MATLAB® program. After the performance of tests, satisfactory results were presented and demonstrated that the proposed methodology is efficient for determining the generation of the thermoelectric system.

Solution of bound constrained nonlinear least squares problems with ap- plication to backcalculation of asphalt pavements

2024-04-26T19:38:33+00:00

Backcalculation is a procedure used to estimate the material properties of pavement layers from results of non destructive tests, as the Falling Weight Deflectometer. It is important to assess the quality of a pavement construction and/or to monitor its condition during its lifespan. The Finite Element Method can be used to evaluate pavement deflections, provided that the loading and the properties of each layer are known. Assuming linear elastic behavior and known Poisson’s ratios, the backcalculation procedure consists in the determination of the elastic moduli that minimize the differences between the simulated and measured deflections. Thus, pavement backcalculation corresponds to the solution of a Nonlinear Least Squares problem, where the unknown parameters (elastic moduli) are strictly positive. This paper presents a simply approach to include bound constraints in the Gauss-Newton and the Levenberg–Marquardt methods to ensure convergence to physically meaningful solutions. The accuracy, robustness, and computational efficiency of the modified algorithms are compared in the backcalculation of asphalt pavements.

Metamodel-assisted metaheuristic for structural optimization problems

2024-04-26T19:46:21+00:00

Optimization problems are common in many different areas, especially engineering. The complexity of modern problems has led to the development of increasingly complex mathematical models, resulting in expensive simulation models. An alternative for solving these problems is population-based metaheuristics, especially those of natural inspiration. However, they usually require many evaluations to obtain a feasible or even satisfactory solution. In this context, the application of metamodels, or surrogate models, together with metaheuristics, has received the growing attention of researchers in several areas. The metamodels generate a simpler computational model to be used in parts of the optimization process, replacing the original model. This work presents an application strategy of metamodels within metaheuristics, which allows for computational cost reduction. The methodology is applied to structural optimization problems, demonstrating its applicability and establishing it as an alternative to improving solutions in the context of fixed-budget simulations.

Sensitivity analysis of flexible multibody systems with nonlinear beams

2024-04-26T19:56:28+00:00

Optimization of the dynamics of multibody systems is an active area of research with many important applications in different fields. Among many available optimization techniques, gradient methods are very versatile and popular; and one of its main ingredients is the computation of sensitivities. Sensitivities provides information about how the coordinates of the system change with time when the parameters change. Since multibody systems are typically represented by systems of nonlinear differential equations (or algebraic-differential systems), sensitivities are computed evaluating the corresponding derivatives respect the parameters around the reference movement. These derivatives (sensitivities) depends on time and are the solutions of a system of linear differential
equations (with variable coefficients). Their computation may be performed after the solution for the dynamics, or simultaneously with it. Sensitivity analysis of mechanisms exclusively composed by rigid bodies has been studied in many works of the literature. However, analysis dealing with flexible mechanisms are rarer. In this work we show the results of a sensitivity analysis of special systems, where the flexible parts are slender beams represented by a nonlinear beam model. Their sensitivity contributions are computed analytically improving the efficiency and accuracy of the computations. What is more, a robust and physically intuitive approach based on a finite-difference method is presented for obtaining preliminary sensitivity results, that provide a valuable tool for developing and validate the previously described analytical approach. Some simple numerical examples are presented showing the performance of the proposed approach.

Analysis of CO2 Emissions in the Topological Optimization of Floor Systems Composed by Composite Trusses

2024-04-26T20:09:06+00:00

The use of composite floor systems in steel buildings has been growing over the last few decades. However, this application usually takes place with full web composite beams and composite slabs with incorporated steel formwork, although there are other possibilities, such as, for example, trusses composite beams. The objective of this work is to present the formulation of the topological and sizing optimization problem for floor systems composed of composite trusses with tubular steel profiles and composite slabs. A structure for the floor, secondary trusses are proposed that directly support the slabs and main trusses that serve as support for the
secondary trusses. The trusses are simply supported and the upper compressed chord may or may not be filled with concrete. The objective function minimizes CO2 emissions from the manufacture of materials used in the floor. The optimization problem solution was obtained via Genetic Algorithm (GA) and the Particle Swarm Optimization (PSO). The algorithm selects, in addition to the topology of the truss (height and number of truss panels), the ideal number of secondary trusses, the compressive strength of the concrete slab and the filling of the upper chord, and finally, it selects the profiles of the chords, diagonals and verticals and composite slab formwork from manufacturers' catalogues. The results indicate that, when compared with composite floor systems composed of
full web beams, a reduction in CO2 emissions of over 20% can be obtained depending on the spans of the analyzed floors. In addition, tubular trusses with a concrete-filled upper chord provide better solutions than trusses with an unfilled tube.

Multi-Objective Harmony Search applied to minimize cost and displacement of steel-concrete composite beams

2024-04-26T20:21:34+00:00

During the design of structures, it is common for the engineer to come across situations in which different and conflicting objectives must be assessed, where the multi-objective or multicriteria optimization provides subsidies to assist in decision-making by designers. In this sense, this paper aims to present the cost and displacement minimization of steel-concrete composite beams, applying the Multi-objective Harmony Search (MOHS) algorithm. The steel-concrete beam is represented by nine design variables, namely the concrete strength of the slab, the slab thickness, the dimensions of the welded steel beam, and the interaction degree. Solutions are
verified in terms of ultimate and serviceability limit states according to Brazilian standards. With the optimization results, a Pareto front is generated, and the efficiency of the MOHS is evaluated from the comparison with results of another multiobjective optimization algorithm already consolidated in the literature, the Nondominated Sorting Genetic Algorithm II (NSGA-II).

Optimal Reconfiguration of the Eletric Power Distribution Network with High Photovoltaic Generation and Overvoltage

2024-04-26T20:50:35+00:00

Distribution Network Reconfiguration (DNR) is the most common method employed by distribution network operators to achieve optimal system operation. The proliferation of Renewable Energy Sources (RES), particularly photovoltaic (PV) energy generation, in modern distribution networks has introduced novel challenges in network planning and operation. In this context, this paper introduces a DNR strategy involving the manipulation of network topology through switch opening and closing, integrated with a Modified Flower Pollination Algorithm (FPA-M). The primary aim is to minimize active power losses and regulate voltage levels at distribution system buses, particularly under high PV generation. The problem formulation takes the form of a Mixed Integer
Nonlinear Programming (MINLP), encompassing continuous and discrete variables. The FPA-M method is an efficient meta-heuristic algorithm inspired by flower pollination processes. Compared to alternative methods, the FPA-M boasts a single control parameter and proves highly effective in optimization problems. The study’s central contribution lies in enhancing algorithm performance and reducing computational effort through a refined determination of the search space. The proposed approach is evaluated across diverse operational scenarios, including load curves and PV data collected from the Federal University of ABC. Tests are conducted on a 33 bus distribution system, and results are benchmarked against other methodologies from the literature. The findings underscore that the amalgamation of FPA-M with DNR yields substantial energy loss reductions, effectively maintaining voltage levels within acceptable bounds throughout the evaluation period.

Automated Approach For Multi-objective Optimization Of Steel Trusses Using Genetic Algorithms and Reliability

2024-06-13T14:21:34+00:00

Optimization is a valuable tool in structural engineering, enabling the achieve of optimal solutions that meet design constraints and objectives. The application of multi-objective optimization in steel trusses can bring significant benefits in terms of structural efficiency and economy. In this article, an automated approach was developed to obtain parametric and multi-objective optimal settings for flat truss structures. The methodology was developed based on the utilization of the finite element method for structural analysis and the integration of evolutionary computing techniques, employing Genetic Algorithms (GAs) via MATLAB. Furthermore, to address the uncertainties inherent in the optimization process, a reliability analysis was conducted using the First-Order Reliability Method (FORM). This analysis took into consideration the variability of key parameters such as area, density, diameters, thicknesses and displacement, treating them as random variables. The results demonstrated good accuracy when compared to benchmark trusses from the literature, highlighting the potential of applying multi-objective optimization in steel trusses to improve efficiency and quality of these structures.

LAETA, INEGI, Faculdade de Engenharia, Universidade do Porto, Porto, Portugal

2024-04-29T14:58:21+00:00

In the present paper assessment of corroded pipelines taking into account uncertainties are considered. The possibilities for pipelines assessment, after inspection, are standards, and numerical simulations. Here, a computational tool to perform the reliability analysis of corroded pipelines is created. The tool combine together an efficient mesh generator, an in-house finite element (FE) based plasticity software and four different options for reliability computations. The corroded pipelines are modeled by axisymmetric finite elements. Deterministic validation studies are conducted considering eleven specimens from literature. Then, reliability analysis (RA) studies to assess the sensitivity of the reliability index against the geometry of corrosion-related defects are performed. This later is also accomplished with the purpose to find out the most efficient RA procedure from different methodologies such as traditional crude Monte Carlo (MC), Importance sampling (IS), selective Monte Carlo (SMC) and the first-order reliability method (FORM). To conduct this comparison, initially, semi-empirical equation from the ASME B31G standard are used. As typical, large number of function evaluations were needed for MC simulation method. Big reductions were achieved for both IS and SMC. However, SMC prove to be as accurate as CMC and simpler than IS. FORM method has demonstrated to be very computationally efficient when compared to the other approaches, slightly less accurate than MC based methods. Due to this observed behavior, FE studies were performed on SMC and FORM only. Good comparison was found. Recommendation is the use of the SMC in the assessment of corroded pipelines as it provided the best accuracy-speed compromise.

Dimensional reduction of probability spaces via Sobol’ indices applied to composite laminates optimal design

2024-04-29T15:05:23+00:00

It is proposed the application of Sobol’ indices as importance measures for the dimensionality reduction of probability spaces, in probabilistic reliability assessment. The indices are computed approximately using a local approximation of the response functionals, via an adjoint method. As a numerical example, it is considered the Reliability-based Robust Design Optimization (RBRDO) of a composite shell structure. The problem is defined as the bi-objective minimization problem of the total weight and the determinant of the variance-covariance matrix of the structural response functionals, subject to a deterministic displacement constraint and a probabilistic stress constraint. The goal is to study how the dimensionality reduction in reliability assessment affects the RBRDO of
composite laminate structures. The results show that, from a total of 16 random mechanical properties, only 5 to 8 are important, while explaining at least 99.7% of the uncertainty. It is achieved a drastic reduction in computing times between 2 to 12 times faster, in reliability assessment, and 2 times faster in the overall RBDO of composite laminate structures.

Performance Comparison between Multiple-Output Artificial Neural Net- works and Classic Surrogate Models for System Reliability Problems

2024-04-29T15:10:07+00:00

Artificial neural networks (ANNs) have been successfully used as a surrogate model in structural reliability analysis due to their ability to model complex, nonlinear relationships between input and output variables. In this context, the ANN model is usually trained using input variables such as material and geometrical properties to learn the relationship between the inputs and the output variable, which is the probability of failure. Despite their potential, ANNs are often overlooked in favor of more robust and easier-to-train models, such as Polynomial Chaos Expansions and Kriging. However, in system reliability problems with multiple outputs, ANNs offer an advantage as they can handle multiple outputs in their default formulations, avoiding the need for multiple surrogates or complex formulations, thus reducing computational costs. This paper aims to compare the performance of ANNs with other surrogate models in this context. Two examples are addressed comparing ANNs, Kriging and Polynomial Chaos Expansions surrogate models. Results suggest that using multiple-output ANNs for surrogating all limit states at once is more efficient than training separate networks for each limit state, but more studies are required in order to propose a comprehensive strategy.

Probabilistic Assessment of Cement Sheath Integrity in Oil and Gas Wells

2024-04-29T15:14:02+00:00

Cementing is one of the most important stages of oil and gas well construction. It consists of displacing cement paste to the annular space between the casing and wellbore, after laying the casing string of each drilled phase. The objective is to guarantee hydraulic isolation in permeable zones and ensure the borehole structural stability. Given its importance and complexity, the cement sheath demands a robust integrity assessment, considering that if it is poorly designed or executed, it causes operational problems such as unwanted influx, so-called kick, or it can even lead to a critical event like a blowout. This work proposes a probabilistic analysis of the analytical models that quantify the interaction of the casing-cement-formation system, to evaluate the displacements and stresses acting on the interfaces between these components. The classical Mohr-Coulomb criterion is applied, which pro- vides the limiting stress for shear failure in the cement sheath. The probability of failure is estimated using the First Order Reliability Method (FORM). Some design variables such as material and geometrical parameters of tubulars, cement and formation are randomly described, and their influence on the probabilistic response is investigated. Case studies are presented to illustrate the application of the proposed methodology in the reliability-based analysis of the cement sheath integrity, contributing to the decision-making process in well structure design.

In structural optimization, for both Deterministic Design Optimization (DDO) or Reliability-Based De- sign Optimization (RBDO) approaches, the nature of the objective function remains the same, as minimizing the weight, for example. However, RBDO formula

2024-04-29T17:06:33+00:00

In structural optimization, for both Deterministic Design Optimization (DDO) or Reliability-Based Design Optimization (RBDO) approaches, the nature of the objective function remains the same, as minimizing the weight, for example. However, RBDO formulation differs from DDO by the possibility of finding the optimal solution considering failure probabilities limits or target reliability indices as design constraints. Classical methods found in the literature can do reliability assessment. Nonetheless, due to convergence problems and the considerable computational effort required, it is interesting to employ other techniques like surrogate models in order to reduce the processing time. Thus, this work intents to compare a traditional double-loop RBDO analysis and a
machine learning based RBDO model, by using Artificial Neural Networks (ANNs), in a single floor steel frame example. First order structural analysis is considered, and Genetic Algorithms perform the optimization. The First Order Reliability Method (FORM) calculates the reliability index. The numerical example shows how the ANN performance and accuracy are quite dependent on its architecture and on the available number of training samples.

Optimal risk-based design of a RC frame under different column loss scenarios

2024-04-29T17:16:56+00:00

The sudden loss of a single supporting element in a reinforced concrete (RC) frame can result in disproportionate structural collapse if its design fails to confine the initial damage through resistance mechanisms. Given the significant impact of uncertainties related to material properties and geometric parameters on the behavior of these resisting mechanisms, and considering the high stakes involved in such failure events, risk optimization provides a practical approach to striking the right balance between cost-efficiency and safety. This is demonstrated herein through the optimization of a two-story, four-bay RC frame under two scenarios of column
removal at the first floor: middle column and corner column. Design variables include cross-sectional depth, steel rebar areas, and concrete strength of beams and columns. Failure consequences are assessed for both the intact structure (considering beam serviceability, beam bending, shear failure of beams, and flexo-compression failure for the columns) and for both column removal scenarios (involving steel rupture of the top rebar layer at the interface between the beam and adjacent column, shear failure of beams, and flexo-compression failure of the columns). A physical and geometrical nonlinear static analysis is conducted, with sample points subjected to bay pushdown analysis. Material behavior is characterized by an elastoplastic model with isotropic hardening for the steel rebars and the Mazars μ model for the concrete (using the modified Park-Kent model for calibration reference). Failure probabilities are assessed using the Weighted Average Simulation Method, and risk optimization is performed using the Firefly Algorithm. To mitigate the computational cost arising from the nonlinearities and the high number of required sample points, Kriging is employed to generate an accurate metamodel for the limit states and reliability indexes. The optimal conventional design prioritizes resistance against bending failure at the beam ends rather than serviceability failure. Beyond a certain threshold value of local
damage probability, an increase in the overall frame robustness is observed for both column loss scenarios, with the most significant improvement occurring for corner column removal. This is attributed to this scenario leading to lower resistance against steel rupture and to keep bending moments at the adjacent column close to zero.

Numerical analysis of Daguangbao slope failure in China induced by Wenchuan earthquake

2024-04-29T18:14:44+00:00

The 2008 Wenchuan earthquake resulted in a large number of fatalities and caused significant economic losses, in China. Thousands of landslides, many of which are very large, were triggered by the earthquake. Most of these catastrophes were distributed along the Longmenshan fault system, on the edge of the Tibetan plate. Some of these landslides blocked rivers, causing flooding that in turn triggered secondary landslides. Among the most significant landslides, the Daguangbao landslide had the highest volume. To analyze the Daguangbao landslide, two-dimensional and three-dimensional numerical models based on the Material Point Method (MPM) were developed to simulate failure and post failure behavior of the slope, taking into account large deformations. The numerical results were compared with the post-earthquake profile and with the affected area by the event. As a consequence of the landslide, an almost vertical rockwall of more than 500m was generated. This situation is considered high risk, requiring ongoing monitoring and evaluation.

Experimentally estimated bipedal model parameters to simulate human- induced vibrations on footbridges

2024-05-01T12:06:51+00:00

The human-structure interaction in slender structures has received increasing attention from civil
engineers and researchers lately. For this reason, several pedestrian models that take into account the biodynamic
parameters of the human body have been widely studied. In this paper, results from a series of experimental
tests are used to obtain parameters for a bipedal walking model. The ground reaction forces (GRF) induced by
different people during walking on a test footbridge were measured using force platforms. The bipedal model is
then adjusted to match the measured pedestrian forces. Thus, a set of non-linear regression equations are proposed
to estimate the fundamental model parameters as functions of the pedestrian’s mass, height, and walking speed.
The new set of empirical equations resulted in improvements in the parameter expressions with a higher R-squared
compared to linear regression. Then, the numerical model is used to reproduce the experimental situations of
walking people on the structure, and the predicted vertical accelerations of the structure are compared with those
measured experimentally. The results show the suitability of the proposed numerical model to reproduce the
vibrations induced by people on pedestrian structures.

Nonlinear dynamic analysis of non-ideal motor foundations

2024-05-01T12:09:59+00:00

This paper addresses the electromechanical coupled response of interconnected foundations of non-
ideal motors, identifying the relevant parameters for the phenomenon of machine synchronization. DC electric motors are considered in the model, using a linear approximation of the characteristic curve (angular velocity x
torque), delineating the electromechanical coupling. To obtain the 2D projections of the basins of attractions of
stable solutions, the (ψ2 − ψ1) x (ψ′2 − ψ′1) plane was chosen at different voltages. These planes were divided
into several square cells and, for each one of them being obtained the self-synchronization attractor. To obtain the
projections of the basins of attraction, the electrical voltage was kept constant over time.
It was identified that synchronizations occur for unbalanced rotors angle differences of zero or π radians. It
was observed that there is a gradual change of attractors between dimensionless voltages 0.66 and 0.74 (6.70 V and 7.50 V), in addition to another change of attractors between dimensionless voltages 1.25 and 1.39 (12.7 V and 14.5 V).

On the effect of manufacturing imperfections and internal damage on the collapse strength of tubes: a nonlinear perspective

2024-05-01T12:13:31+00:00

The estimation of critical external pressure of tubes is a nontrivial problem, particularly when
considering the presence of damage, such as mechanical or chemical, and, manufacturing imperfections, such as
cross-section ovality and eccentricity. This study presents the findings obtained from a nonlinear finite element
analysis of 2-D tube cross-sections subjected to collapse pressures. The collapse strength of the tubes can vary
significantly with modifications to the parameters related to the geometric disposition of the damage and
imperfections. The study is carried out adopting configurations that are commonly observed in casing tubulars of
oil and gas wells. Therefore, the results can support the design and integrity analysis of casing strings, improving
knowledge about their behavior under well service conditions. The study is performed using Abaqus software with
a Python scripting interface, enabling efficient evaluation of various geometric inputs. The nonlinear solver
employs a load increment approach, causing the system to become unstable upon reaching the critical load. The
load increments and displacements were carefully adjusted to maintain equilibrium using the arc length
methodology (known as the Riks Method in the software). Different equilibrium trajectory shapes can arise
depending on the initial geometric configuration, leading to diverse conclusions. For example, an increase in the
separation angle between the ovality reference location and eccentricity reference location can decrease the
collapse strength of thick tubes but increase it for thin tubes. Several other insights can be drawn from this study.
Finally, a brief case study is presented, comparing the results with widely used equations in the well casing design
practice.

Study on the use of passive control systems in the dynamic response of coupled buildings

2024-05-01T12:20:29+00:00

Based on the increasing knowledge in the field of engineering and construction, driven by the rapid
expansion of urban centers, building designs have prioritized optimizing physical spaces and maximizing housing
potential. This approach has led to structures being built closer together and becoming slenderer, which has raised
concerns about excessive oscillations and the risk of pounding between adjacent structures. To address these
challenges, the technique of structural coupling has emerged as a promising solution. This technique involves
using connecting elements, often achieved through vibration control devices, to link the adjacent structures.
However, despite the positive results observed with this approach, further studies are still required to enhance its
effectiveness. In this context, the present study explores the utilization of passive control devices for coupling,
which can dissipate the energy of the main system and/or transfer it to secondary auxiliary systems. The study
proposes a numerical approach in a multiple degrees of freedom (MDOF) system, incorporating passive dampers,
to simulate and analyze the behavior of a reduced-scale model consisting of two coupled buildings. The results are
presented, demonstrating the influence of control parameters on the proposed structural system in effectively
controlling the dynamic responses of the buildings.

Simple equation to account for the human-structure interaction effects on the modal damping of footbridges

2024-05-01T12:24:15+00:00

Footbridges dynamic properties may be affected by the presence of pedestrians, especially the modal
damping of the occupied structure which is greater than that of the isolated one. To account for this increase,
particularly in lightweight and slender footbridges, which are susceptible to the human-structure dynamic
interaction (HSI), the pedestrians are modelled as a mechanical system coupled to the footbridge model. In this
paper, an equation is proposed to add the damping contribution provided by persons walking on footbridges to the
isolated structure damping ratio. The presented equation is based on numerical results obtained from a
computational tool especially developed to address the effects of HSI. A comparison of the damping ratio obtained
with the proposed equation and the experimental measurements in a slender footbridge from the literature is
favorable. The estimated damping ratio of the coupled system (footbridge plus pedestrians) could then be used to
include the HSI effects to existing design methodologies based on the live load approach to simulate pedestrian
forces.

Stable high order space-time finite element formulation for large displace- ment elastodynamics

2024-05-01T12:27:42+00:00

Direct time integration methods have been widely used in structural and solid dynamics simulations,
specially in nonlinear problems. Time-marching methods have been applied to discrete systems of differential

equations obtained from different spatial discretization techniques, like finite differences, finite volume, bound-
ary elements and finite elements, with finite elements being currently the most applied method for structural and

solid mechanics. On the other hand, space-time formulations consider time as a dimension of the finite element
discretization, so that the precision in time integration can be increased by using higher order shape functions
in time direction. In this context, this work presents a position-based total Lagrangian space-time finite element
formulation for the solution of two-dimensional elasticity problems with large displacements. By using structured
space-time mesh in time direction, it is possible to divide the space-time domain into space-time slabs, so that such
slabs can be solved progressively with the final nodal positions and velocities from previous slab being applied as

initial conditions to the current one. The adopted space-finite elements are prismatic with a triangular basis corre-
sponding to the spatial discretization and height corresponding to the temporal discretization, so that the space-time

shape functions are given by the product of the Lagrange polynomial shape functions adopted for the triangular
elements of spatial discretization, with Hermite polynomials based shape functions defined along the height of
the prism, for time discretization. The test functions in time direction are modified so that different stability and
precision can be achieved. Through the simulation of selected examples, and the comparison with solutions from
known time-marching methods, the robustness and stability of the proposed formulation is demonstrated.

Structural Dynamic Analysis Considering a Locally-defined Time Integration Procedure

2024-05-01T12:31:26+00:00

This paper addresses the use of a locally-defined time-marching methodology for the dynamic analysis
of frame structures. The discussed formulation allows specifying time integration parameters at an element level,
enabling intended numerical features, such as numerical damping, to be locally applied, providing a much more
versatile approach. Additionally, these locally-defined time integration parameters may also be established
following the inherent properties of each element of the discretized model, allowing optimized definitions to be
carried out and enhanced accuracy to be provided. The presented technique is unconditionally stable, second-order
accurate, and truly self-starting, and it allows adaptive controllable algorithm dissipation. At the end of the
manuscript, numerical examples are presented, illustrating the effectiveness of the discussed methodology.

Nonlinear Dynamics in Graded Waterbomb Origami Tubes

2024-05-01T12:34:21+00:00

The graded Waterbomb origami tube, an extension of the classic Waterbomb pattern, offers a versatile
platform with potential applications in diverse fields. This periodic 3D structure can exhibit wave-like behavior
along its longitudinal axis, making it intriguing for applications ranging from metamaterials to medical implants.
Recent work has connected its wave properties to a discrete 2D dynamical system. We extend this concept by

investigating the impact of introducing gradation into unit cells along tessellation lines. This introduces a non-
autonomous nonlinear iterated map that generates ordered and disordered origami tubes based on deterministic

and stochastic rules. In this study, we explore these dynamics and report their distinctive properties.

Vulnerability Assessment of Reinforced Concrete (RC) Structures based on Modal Parameters

2024-05-01T12:39:38+00:00

During an earthquake, the gradual deterioration of structural components in a building decreases its
stiffness. As a result, the overall period of vibration of the entire structure progressively increases. The extent of
damage to these components, commonly termed as a Damage Limit State (DLS), can be assessed either through
visual inspection or by using numerical analyses that correlate the exceeding of a certain Engineering Demand
Parameter (EDP) threshold with the attainment of a specific DLS for a specific earthquake scenario. Evaluating
the DLS in a building after an earthquake serves as the basis for determining its serviceability. This study
conducted numerical time history and pushover analyses on reinforced concrete buildings. The pushover analysis
was used to determine the thresholds for a set of DLS of infilled RC structures. The main objective of this study
is to establish a preliminary relationship between two factors: a) the damages that a building experiences due to a
specific earthquake scenario, which determines its serviceability, and b) its period elongation, which can be
analytically measured using finite elements methods. The aim is to determine whether the building's period
elongation can be a reliable indicator for assessing its damage state after an earthquake.

Regularization of complex flexibility of layered models of railway track

2024-05-01T12:46:06+00:00

In this contribution, a regularization technique of the function representing the complex flexibility of
layered models of ballasted railway track is proposed in a way that allows one to keep the general steps from the
one-layer model and analyze in depth other models that are inherently more realistic. With this regularization, it
is also possible to more precisely analyze how damping can negatively affect the instability of two or more moving
proximate masses. The results are presented in a dimensionless form, and it is demonstrated that the proposed
technique works reasonably well.

Elastic Buckling Load Prediction of Tapered Steel Columns Via Artificial Neural Networks

2024-05-01T12:48:04+00:00

This study presents a novel approach for predicting the critical buckling load of slender, cylindrical,
tapered steel towers commonly used in wind turbines and telecommunications equipment. These towers are prone
to instability issues caused by buckling loads, which necessitates accurate evaluation. To overcome the limitations
of existing instability load formulations and regulatory codes, we developed an artificial neural network (ANN)
model. The ANN model utilizes a comprehensive database of 1,440 finite element models to accurately predict
the critical buckling loads. An MLPRegressor model instantiated with the 'adam' solver and the 'tanh' activation
function in the hidden layers demonstrated a significant alignment with the data, as the model accounted for
approximately 97% of the variance in the dependent variable. Furthermore, the outcomes obtained from the ANN
model closely aligned with the original values, surpassing the predictive precision of the classical shell and beam
formulations, and offering insights into the complexities associated with transformed data.

Fatigue life estimate in metallic chains links of mooring system

2024-05-01T12:55:00+00:00

This contribution proposes the application of the Finite Element Method (FEM) for the study and
analysis of chain links of the Floating Production Storage and Offloading (FPSO) ship anchoring system, regarding
the level of stress at the hotspots. Besides that, cyclical flexion occurred outside the main plane of the links, known
as Out of Plane Bending (OPB) was considered. The loads increase the resulting friction allocated in the contact
between the links, making it behave like a bezel, so transverse forces result in bending out of the plane. The
loadings come due to the platforms operating under various factors of nature, such as variations in waves and sea
currents, in addition to the operating conditions of the platform. Thus, FPSO ships, designed to last more than
twenty years, recorded cases of failure in the anchoring system in less than two years. The material used in the
model of the links was offshore steel belonging to grade R4. The simulations were carried out with winding angles
of 60°, with loads in the range of 200 and 400 ton being applied. With the result of this analysis, it is possible to
validate the hotspots in the links of the moorings, identifying the influence of the winding angle. Thus, it is possible
to validate the equations that describe the behavior of the mooring-fairlead set taking in consideration the
transverse and axial loads. Finally, the fatigue life of the links was calculated using the Smith-Watson-Toper
(SWT) fatigue criterion, considering a loading with variable amplitude.

Model Mixing with Frequency Based Substructuring: 4 DoF Half-Vehicle Analysis

2024-06-27T17:25:24+00:00

This paper reviews the system equivalent model mixing (SEMM) technique. This method is applied to obtain hybrid dynamic models, primarily by using a numerical model in order to expand the degree of freedom space of an experimental model. The formulation of this method is based on coupling and decoupling of substruc-tures, by means of the Lagrange multiplier frequency-based substructuring (LM-FBS) technique. Therefore, the SEMM technique will be applied in a half-vehicle model, where the dynamics of a parent model will be updated with the dynamics of an overlay model of an equivalent system, but with lower density of degrees of freedom (DoFs). This procedure aims to create a hybrid model, which expands the dynamics of the overlay model to the denser DoFs of the parent model. The influence of the interface size, damping and signal noise on the final hybrid model will be evaluated in this paper.

Evaluation of the redistribution of loads in the foundations of reinforced concrete structures from the computational modeling of the construction sequence

2024-04-29T18:46:46+00:00

The aim is to analyze the loads on columns on a reinforced concrete building considering elastic
behavior with instantaneous loading and gradual loading (construction in 3 stages). The finite element commercial
program SAP2000 (version 15) with staged construction module was used. Time analysis is carried out
subsequently, considering instantaneous loading and construction in 3 stages. Staged construction allows the
consideration of creep and shrinkage of concrete. Concerning elastic analysis with instantaneous loading in 3
stages, it was found that a redistribution of loads on columns took place even when normal stress value is low.
Therefore, the significant influence of the construction sequence on the redistribution of loads on reinforced
concrete structures is highlighted. Further research is required to investigate the influence of masonry, coatings,
occupancy overload and structural elements (especially beams and columns) of variable stiffness. No redistribution
of loads was observed in the analysis carried out over time (creep and shrinkage). This result may be related to
structural simplicity.

Numerical analysis of large-diameter bored piles in sandy soil

2024-04-29T18:59:18+00:00

The paper presents a numerical model to analyze the load transfer mechanisms and load-displacement
patterns of large-diameter bored piles in sandy soil. The model is calibrated using a seven-layer soil profile,
encompassing dense to loose sand layers and a silty-sandy clay layer located between depths of 18 m to 22 m. The
pile and soil materials are represented with elastic model and Mohr-Coulomb elasto-plastic model, respectively.
Discrepancies between experimental and numerical load-displacement curves are evident, particularly when
calibrating the model with reference experimental and lab-derived soil parameters. Adjusting interface friction
angles and reducing soil elastic moduli aligns the pile's behavior with numerical predictions for bentonite cases.
However, polymer-modified cases display higher values and require more extensive parameter modifications.
Discussing the effects of polymers and bentonite on lateral resistance, coupled with a comparison of the β
coefficient, coefficient of lateral earth pressure (K), and frictional coefficient (μ) between numerical and
experimental data, deepens the comprehension of bored pile behavior in sandy soils.

Probabilistic Analysis of Embankment Stability on Soft Soils using Random Fields

2024-04-29T19:08:21+00:00

It is widely recognized that geotechnical properties vary spatially due to mineralogical composition, stress history and deposition processes, even within soil layers that appear to be homogeneous. Recently, there are studies that capture the spatial variability from input variables and random fields to create models. These models can be integrated with finite element methods (FEM) to calculate slope stability. In the present study, the objective was to conduct a probabilistic analysis using random fields applied to the stability of embankments on soft soils. The Local Average Subdivision (LAS) method was employed to generate random fields of undrained shear
strength (Su) which were incorporated into the finite element analysis using Abaqus software. To validate the implementation of random fields, modeling experiments on two literature slopes were developed and compared the obtained results with the original data. The comparison revealed acceptable agreement, indicating the effectiveness of the random field implementation approach.

Numerical simulation of flooding process of a collapsible soil with raft foundation

2024-04-29T19:14:23+00:00

Collapsible soils are those that suffer a considerable reduction in volume when exposed to an increase in water content, even without the addition of external loading. Numerical and experimental simulation of this phenomenon to understand the behavior of shallow and deep foundations is relatively complex, since it involves phenomena related to unsaturated soils and transient flow. In view of this, the present study aims to present the numerical simulation of the flooding process of a collapsible soil in the Federal District of Brazil (Geotechnical Experimental Field of the University of Brasilia), where was built a physical reference model consisting of a raft
and a system of vertical drains. The simulation was carried out using the Finite Element Method in the Plaxis software, with the implementation of the Costa and Cavalcante hydraulic model, proposed in 2021. After comparing the results of the numerical analysis with those obtained in the field, it was observed that the model used managed to properly reproduce the flooding process carried out, in such a way that it can also be used to simulate numerically, together with an adequate mechanical model, the phenomenon of collapse and the behavior of more complex foundation systems in such a situation.

Stabilization of Filtered Tailings Dry Stacking with Cemented Tailings Berms: A Parametric and Limit Equilibrium Analysis

2024-04-29T19:21:21+00:00

This work addresses the urgent need for secure and sustainable tailings management, after several
Tailings Storage Facility (TSF) failures. This research proposes a stabilization solution for iron ore filtered tailings
dry stacking using cemented tailings berms. Despite being a safer alternative to dam deposition, dry-stacked
tailings face several vulnerabilities, especially during heavy rainfall or with inadequate drainage systems. For that
purpose, limit equilibrium analysis using the Plaxis LE geotechnical software were performed to evaluate the effect
of berm width and strength of cemented material, on the stability of these slopes. This process pinpointed the
required berm width for a specified dry stacking height and width of cemented tailings, even considering the
potential for increased saturation under unfavorable conditions. The conducted analyses aimed to perform a
parametric evaluation of the cemented tailings parameters necessary to enhance the structure's stability. The results
emphasize the efficacy of the benefits of the computational method in improving the stability and safety of TSFs.

Influence of Soil Spatial Variability on Embankment Deformation Reliability Analysis Using the Random Finite Element Method

2024-04-29T19:26:09+00:00

When dealing with practical engineering problems, the uncertainties associated with soil are a major limiting factor in terms of defining the subsurface characterization and the input parameters used for design considerations in computational analysis. These uncertainties are mostly associated with the fact that soil is a natural material, formed by different geological processes that entail inherent variability. The increasing use o CPTu for site investigations allows geotechnical engineers to obtain reliable data to describe the spatial variability of soil. In this study, a geotechnical engineering situation is presented, in which the deformation of an embankment section is analyzed. On-site investigations are provided by CPT profile data, which are used to estimate soil
parameters using well-known correlations from the literature. The inherent spatial variabilities in soil geotechnical properties along the profile are described using the decomposition method by a smoothly varying trend function and residuals components. Then, the random finite element method (RFEM) is applied to compare the results with homogeneous layer probabilistic analysis. The results obtained show that consideration of spatial variability can lead to almost identical average displacement values compared to homogeneous layer probabilistic analysis, but with tighter distribution of the findings.

Comparison between PLAXIS 2D and CYPE to simulate an anchored wall

2024-04-29T20:25:09+00:00

This paper presents a specific case study where a retaining wall necessary to support the construction of a residential building with 4 floors below the ground level and 10 floors above ground was numerically evaluated. The design solution comprised a reinforced concrete diaphragm wall with four levels of ground anchors. Two different commercial software were used to model this case study: PLAXIS 2D ®, and the Cype - StruBIM Embedded walls, v.2023. PLAXIS 2D ® uses the Finite Element Method, allowing the simulation of the soil deformation and comprising the soil-structure interaction. Cype models the soil behaviour by the Winkler theory representing it by fictious springs with a given stiffness related to the soil properties. The results are compared in terms of the deformation of the wall and surrounding soil, as well as the bending moments on the wall. The comparison between the two numerical tools highlights their different assumptions. PLAXIS 2D ® provides the deformation of the surrounding soil, while Cype is more devoted to the estimation of the stresses and bending moments on the wall.

Effect of permeability on the stability conditions of a slope through hydromechanical numerical analyses

2024-05-03T22:41:34+00:00

In this work, data from laboratory tests on an iron tailing was used to calibrate the Clay and Sand Model
(CASM), a critical state constitutive model able to reproduce the undrained softening behavior that can occur in
loose soils. After defining a set of parameters that could reproduce the soil behavior in triaxial compression tests,
a simple slope was simulated with the finite element program PLAXIS 2D to evaluate its hydromechanical
behavior as a function of the imposed flow conditions. For this purpose, different permeability coefficients were
used to evaluate its effect in fully coupled flow deformation analyses. Furthermore, in the case of stratified soil
masses, or in the presence of intercalations of materials with different properties, vertical and horizontal
permeabilities can vary significantly. Therefore, another objective of the work was to evaluate the effect of the
relationship between vertical and horizontal permeabilities on the behavior of the slope, as well as the existence
of materials with different permeabilities.

Implicit numerical integration of an advanced subloading surface clay and sand model

2024-05-03T23:07:57+00:00

This paper focuses on the algorithmic and computational aspects of implementing the clay and sand model (CASM) using a fully implicit numerical scheme. CASM is a unified critical state model that relies on the state parameter concept and incorporates a non associated flow rule. Within this framework, the subloading enhancement is introduced, which enables a smooth elastic-plastic transition through an isotropic modification. The addition of just one extra parameter significantly enhances the calibration process. Subsequently, the modified version of CASM is implemented into a finite element procedure. The demonstrate the efficiency and good performance of the proposed algorithm, including the subloading modification, simulations of triaxial compression tests

under undrained conditions are conducted.

Influence of track and vehicle wheel damages in the train running safety

2024-05-01T22:23:07+00:00

Train running safety is an important concern because although many derailments are minor in terms of
fatalities, all result in temporary rail operation disruption and they are a potentially serious hazard. Running safety
is evaluated by three safety criteria based on factors related to the vehicle contact forces: the Nadal criterion, the
Prud’Homme criterion and the Unloading criterion. Several research studies have focused on the assessment of
the derailment risk based on monitoring measurements but as it is influenced by the existence of various conditions
and environments in which the train is running, it is important to identify the factors that most influence derailment
risk. In this research, the unloading criterion is used to analyze the influence of track irregularities and wheel
defects such as flats, polygonization in the train running safety. The research relies on train-track dynamic
responses obtained by numerical simulations. A freight train and a ballasted track are considered. A 3D wheel–
rail contact model couples the train to the track by using the Hertzian theory to compute normal contact forces and
tangential forces caused by rolling friction creep. The results are promising for the research purposes.

Drive-by damage detection in railway bridges subject to operational vari- abilities using deep autoencoder

2024-05-01T22:58:50+00:00

One of the major challenges in the design and management of railway bridges is ensuring their safety and
structural integrity throughout their lifespan. This is due to the fact that the loss of structural function and eventual
failure of these structures have catastrophic consequences. Additionally, climate change projection which permeate
the present show a tendency towards an increase in the frequency and intensity of extreme events, accelerating the
deterioration process of railway infrastructure. In this context, there is a demand to define strategies in structural
health monitoring (SHM) in order to minimize disruptions in railway operations and maximize its profitability
through the safe operation of the system. There are two approaches to acquiring structural data for evaluating
integrity: the direct monitoring approach and the indirect monitoring approach, or drive-by. In direct monitoring
of railway bridges, sensors are installed directly on the bridge to capture responses caused by train excitations on
the structure. On the other hand, in the drive-by monitoring approach, sensors are installed on the train to capture
vibrational responses from the dynamic interaction of the train-bridge system during its passage. The advantages
of the indirect approach over the direct approach involve the ability to obtain spatial information along the entire
length of the bridge without the need to interrupt train operation, in addition to a substantial decrease in the cost
associated with monitoring an entire railway line. However, one of the main challenges of indirect monitoring is
dealing with the variability of operational and environmental conditions which affect monitoring data and result
in false negatives or false positives in damage identification process. This study focuses on the indirect structural
health monitoring of railway bridges using deep autoencoder model. For this purpose, numerical simulations of
the dynamic train-via-structure interaction (TTBI) are performed. These simulations aimed to gather acceleration
responses as trains crossed the target bridge under different levels of bridge foundation scour damage. Operational
variability involving train speed and track irregularity, and measurement data noise are considered to simulate
conditions closer to reality. The results show that the applied methodology is highly effective for detecting the
scour damage of railway bridge foundations.

Envelope Spectrum Analysis With Algorithm Simulations To Detect Railway Wheel Out-of-roundness Defects

2024-05-01T23:06:20+00:00

The objective of this work is to identify defects in railway vehicle wheels using an envelope spectrum
analysis technique combined with spectral kurtosis analysis. The analysis is performed on data collected by a
simulated wayside monitoring system situated on the track. A dynamic 3D interaction model is implemented using
the in-house software VSI-Vehicle-Structure Interaction Analysis to simulate the dynamic interactions between a
passing train and the track. In this work, an Alfa Pendular passenger vehicle and a section of the Portuguese
Northern Line serve as the basis for the numerical models of the train and track, respectively. In the simulations,
three types of wheel flat profiles and three periodic polygonal wheel profiles are analysed, along with results
obtained from dynamic analyses conducted on wheels that do not exhibit any type of damage. Additionally, the
simulation considers track irregularity profiles generated based on the Federal Railroad Administration (FRA)
standards. The dynamic responses of several strain gauges and accelerometer sensors located on the rail between
sleepers are then evaluated through numerical calculations. To further validate the methodology, the influence of
different train speeds, track unevenness profiles, and wheel fault severity are considered. For validation purposes,
the right wheel of the first wheelset is modelled with a defect, but the detection methodology is effective for
damaged wheels modelled in any position. The application of the methodology demonstrates that envelope
spectrum analysis can successfully differentiate between healthy and defective wheels.

Explainability analysis of a machine learning-based constitutive model for concrete

2024-04-30T01:29:38+00:00

Concrete, like other quasi-brittle materials, exhibits intricate mechanical behavior that defies simple mathe-
matical description and remains partially elusive. Limited comprehension of the governing mechanisms hampers

the development of a comprehensive theory and broader constitutive models. This limitation suggests that more

encompassing models could emerge through advanced techniques, like Machine Learning (ML) algorithms, capa-
ble of capturing material behaviors effectively. While various studies endorse ML-based constitutive models and

validate the proposed hypothesis, skepticism persists within academia due to concerns about ML models being
“black boxes” devoid of interpretable physical consistency. To challenge this perception, this paper introduces the
SHAP tool, employed to validate the physical coherence of an ML-based constitutive model focused on concrete
representation. The SHAP tool’s methodology is outlined, accompanied by illustrative applications showcasing
the correlation between input variables and model outputs. Clear demonstrations of physical consistency debunk

the notion of ML models as opaque “black boxes.” Ultimately, this study debunks skepticism, offering new per-
spectives on the utilization of ML-based constitutive models, thus fostering broader acceptance and integration in

the structural engineering community.

A HYBRID LEARNING MODEL FOR ASSESSMENT BEAM DAMAGE DETECTION

2024-04-30T09:38:29+00:00

Structural damage induces local flexibility into the structure generating undesirable displacements and
vibrations. Such changes in the dynamic response can be used as a resource allowing us to discriminate the
current structural condition and to predict its useful life for short or long periods. Early damage detection and
periodic structural integrity assessment are the keys for the system to operate correctly and prolong its lifespan.
Many structural health monitoring techniques have been used in technologies that combine modern sensors and
intelligent computational algorithms. This study focuses on applying machine learning (ML) algorithms within a
multiclass framework to monitor structural integrity, enabling the identification and quantification of damage. In
this context, this paper proposes a strategy to damage detection in a beam structure based on an artificial neural
network machine learning algorithm. A damage index calculated from the natural frequency builds the input
dataset for the ML algorithms. The methodology combines supervised learning classification (artificial neural
networks) and unsupervised (cluster k-means) methods for constructing a hybrid classifier. The results show that
the hybrid classifier can correctly classify the integrity condition of the structure compared to the artificial neural
network algorithm.

Evaluating the influence of loss function on performance of a neural net- work for particle 3D shape reconstruction from 2D projections

2024-04-30T09:43:15+00:00

Abstract. In recent years, Supervised Neural Networks have been used to solve different tasks due to their ability
to extract and predict patterns. This kind of algorithm has in its development a first step known as the training
phase, where it tries to find the best values for the weights and biases, making the neural net predictions as close
as possible to some expected outputs. In each training iteration, updating weights and biases is realized like an
optimization problem. When developing a Neural Network that uses Spherical Harmonics Functions (SPH) for
reconstructing the 3D shape of a particle from its 2D projections, one can choose as objective function different
parameters, e.g., the volume, radius, the SPH coefficients, etc. In this paper, we discuss the performance of a
Neural Network trained with different loss functions in a 3D shape reconstruction problem context.

Combining neural networks with multiscale techniques for lattice unit cell design

2024-04-30T09:45:58+00:00

Complex non-linear mapping between the input and output data is one of the advantages of neural net-
works. The aim of this work is to train a neural network to generate the optimum unit cell topology for a given

constitutive elastic matrix. In order to reverse homogenization, the neural network maps the correlation between

the shape of the unit cell and the constitutive elastic characteristics. With data produced from a collection of var-
ious geometries, a dataset of elastic properties and respective geometries was developed. All of these geometries

underwent homogenization using periodic boundary conditions. To lessen their impact on the homogenized consti-
tutive matrix, the lattice was modeled as a biphasic material, with the solid phase having the material’s properties

and the remaining area of the representative volume element (RVE) being treated as the void phase. To make it
possible to directly impose the periodic boundary conditions, a uniform mesh of square 2D elements was used.

The dataset includes truss-like unit cells based on the FCC and BCC systems, as well as gyroid-like unit-cells, sim-
plified to a 2D representation. In order to increase the dataset, operations between basic unit cell geometries were

applied as well as rotations of the unit cell. The neural network is capable of suggesting unit cells. The non-linear
mapping between the unit cell elastic properties and geometry reduces the computational cost of running structural
optimization to create a unit cell which presents the required properties, for example.

THE APPLICATION OF BOOSTING ALGORITHMS IN THE PREDICTION OF BOND STRENGTH BETWEEN THIN STEEL BARS AND CONCRETE

2024-04-30T09:48:46+00:00

The current study discusses the application of intelligent algorithms and machine learning techniques
to predict the bond strength between steel and concrete. The paper focuses on three boosting algorithms employed
for this prediction task. The research exploited a database derived from pull-out tests conducted on thin steel bars
to assess the bond between steel and concrete. The experimental program involved the use of three different classes
of concrete and two types of steel bars. The goal was to analyze the steel-concrete bond strength, which is
influenced by various factors. For the computational simulations, the input variables considered in this study were
the bar surface, bar diameter (φ), concrete compressive strength (fc), and anchorage length (Ld). The output was
the pull-out strength at the steel-concrete interface. It is important to highlight that most previous studies in this
field have mainly focused on bars with diameters greater than 10.0 mm, while there is limited research available
to evaluate the performance of bars with diameters smaller than 10.0 mm. The paper describes the computational
experiments conducted using different boosting algorithms: Adaptive Boosting (AdaBoost), Gradient Boosting
(GB), and Extreme Gradient Boosting (XGB). These machine learning-based models achieved highly accurate
predictions, applying specific hyperparameters. The following metrics were used to compare the performance of
the different methods: Root Mean Squared Error (RMSE), the coefficient of variation (CV), and the error. These
metrics were used to evaluate the reliability of each algorithm in predicting the bond strength in the samples. The
results indicate the accuracy and goodness of fit of the model's predictions. Based on them, it can be concluded
that the presented model can satisfactorily predict the bond strength of samples between thin steel bars and
concrete.

An approach for displacement prediction in truss structures combining the Finite Element Method and Deep Learning Techniques

2024-04-30T09:54:24+00:00

Recent advancements in machine learning have facilitated groundbreaking applications across various
knowledge domains. This paper introduces a promising application of Deep Learning Techniques (DL) in
conjunction with the Finite Element Method (FEM). The aim of this study is to evaluate a convolutional neural
networks ́s (CNN) ability to predict 2D truss displacement fields. This assessment leverages prior knowledge of
the structure's global stiffness matrix (K) and applied external load vector (f). The technique's advantage lies in
circumventing complex numerical approaches for solving linear and nonlinear systems, which often entails
extended processing times and substantial computational effort depending on model complexity. The employed
methodology involves constructing a dataset comprising varied structural configurations, processed through a
finite element solver. This dataset then trains a CNN composed of residual, dense, and fully connected blocks. The
outcomes underscore the significance of this approach; the proposed model demonstrates commendable
performance in this task, exhibiting a maximum absolute mean error of approximately 2% and a maximum mean
squared error of 0.2%, when contrasted with classical FEM solutions.

Advancing Structural Design with Machine Learning: Stress Field Predic- tion in Plates with Cutouts

2024-04-30T09:56:48+00:00

Machine learning techniques are creating disruptive approaches in diverse engineering fields, including
in engineering and structural design, pushing the boundaries of performance and reliability. This presentation
delves into the development of a machine learning model that accurately predicts stress fields in complex structures.
By leveraging the SimuStruct dataset, encompassing diverse geometries and configurations, valuable insights are
gained into the challenges faced in structural engineering.
Complex structures, especially those with holes, introduce complexities that affect structural behavior and

integrity. Accurately predicting stress distribution in these configurations is crucial for ensuring safety and perfor-
mance. The incorporation of hole-containing structures into the SimuStruct dataset enables training and evaluating

machine learning models specifically tailored to address this critical aspect of structural design. This resource
facilitates optimization and informed decision-making.
The application of machine learning in predicting stress fields in structures with holes holds promise for
enhanced design and performance. By precisely capturing stress distribution, engineers can identify regions of

heightened stress concentration, enabling informed choices in material selection, reinforcement, and weight reduc-
tion. These advancements lead to improved efficiency, reliability, and safety in structural operations. The focus on

structures with holes in the SimuStruct dataset, alongside the development of machine learning models for stress
prediction, significantly impacts the engineering industry, fostering innovation and optimization while ensuring
structural integrity under complex loading conditions.

In conclusion, the integration of structures with holes or other discontinuities into the SimuStruct dataset di-
rectly addresses ongoing challenges in structural design. The remarkable development of machine learning models

for stress prediction represents a significant leap forward, empowering researchers and engineers to optimize de-
sign and achieve substantial improvements in efficiency, reliability, and safety. With a focus on complex structures,

machine learning techniques revolutionize the industry, paving the way for innovative advancements in structural
integrity and performance.

Aircraft Structures Life-cycle Simulation through Digital Twins and Model Updating Techniques

2024-04-30T10:01:33+00:00

Numerical modeling tools have become essential in the realm of aircraft structural design and assess-
ment. These tools allow for the analysis of intricate structural parts, incorporating diverse material properties and

loading scenarios while minimizing the need for extensive experimental testing. However, the current models face
limitations in accurately capturing the nuanced real-world behavior of aircraft structures. Challenges arise due
to factors such as material property scatter, manufacturing-induced geometric deviations and residual stress, and
other effects that can only be estimated or fully captured during service.
This work aims to evaluate and discuss the potential impact of digital twins on addressing these limitations

and enhancing the reliability of numerical models through model updating techniques. Digital twins, virtual repli-
cas of physical assets or systems, can improve the solutions to overcome the gaps between numerical models and

real-world behavior. By integrating and processing data from sensors, operational inputs and historical data, digital
twins provide a more comprehensive understanding of the structural behavior throughout an aircraft’s life cycle.

With the exploitation of machine learning techniques, new methods for model calibration and validation are possi-
ble, combining experimental inputs with simulation models. By leveraging these techniques, digital twins can be

continuously updated and refined, allowing for more accurate predictions of structural behavior and performance.
These models can enable real-time monitoring and more precise damage assessment, supporting the decision
making in diverse contexts. In addition, integrating sensor data and model updating techniques, digital twins
have the potential to improve the design and maintenance operations. They can provide valuable insights into the
structural health, safety, and reliability of aircraft structures, leading to more efficient and safer operations.

Assessment of Physics-Informed Neural Networks for the mechanical char- acterization of viscoplastic materials

2024-05-01T22:16:19+00:00

Recent works have introduced the concept of Physics-Informed Neural Networks (PINN), which are
trained to solve supervised learning tasks while fulfilling laws of physics described by nonlinear partial differential
equations. In this work, this approach is compared to established constitutive models that address viscoplastic
material behaviour. The materials analysed are the Poly-lactic acid (PLA) and the Acrylonitrile Butadiene Styrene
(ABS). Two constitutive models are studied: Mulliken-Boyce, and an enhanced Zapas’ model for viscoplasticity.
The finite element method is employed for the discretization of solids under frictional contact and large strains.
The output of the numerical model is coupled to a PINN, which is trained to replicate the experimental data and
to be compared to the results provided by the constitutive models. The objective of this assessment is to verify
the benefits and liabilities of each method. The focus is given to the accurate representation of stress-strain and/or
force-displacement relationships. Other features such as computational time and memory bandwidth are also
assessed.

Analysis on 3D fretting contact stresses along thickness under fatigue load

2024-05-01T22:19:40+00:00

This work aims to analyse the effect of filleted edges in the stress distribution on a 3D cylinder-plane
fretting fatigue problem. The 3D configuration is required since the stresses are distributed along the thickness of

the contact interface differently from the common analytical 2D contact stresses solution which consider the plane-
strain state to be critical. More recent studies showed results of 3D numerical simulations for different

configurations of pad and specimen, but they did not consider the effect of the fatigue load. Herein, focus is given
to specimen and pad with the same thickness and both having a small fillet at their edges. This geometry represents
well the milling process when fabricating the test specimens employed in fretting fatigue tests. The effect on the
filleted edge of each one of the three loads (i.e., contact pressure, fretting load, and fatigue load) are analysed and
discussed.

Topology optimization of a solar-powered boat

2024-04-30T11:52:59+00:00

To reduce climate change effects caused by the marine industry’s uncontrolled emissions, the proposal
of a technique that implements topology optimization to boat design can help boatyards and governments to reduce
CO2 emissions. Boats are responsible for approximately 3% of the world’s total CO2 emissions and making lighter
boats is a great way to reduce this contribution. Until now, the works that use topology optimization do not take
into account some specifications of marine design, such as balance. This work solves the compliance minimization
problem subject to a volume constraint and a new COG (center of gravity) constraint to respect the primary boat
equilibrium project to avoid rework. A reference solar-powered boat is considered as a baseline design. The power
required by the boat is used as a measure of CO2 reduction for comparing the baseline and the optimized designs.
This is done via hydrodynamic analyses before and after optimization.

Topology Optimization fiber reinforced materials considering Tsai-Wu yield criterion

2024-04-30T13:22:36+00:00

The utilization of fiber-reinforced materials has experienced a significant surge due to their notable advantages, particularly their high strength-to-mass ratio. As a result, new additive manufacturing technologies have emerged to accommodate these materials, offering capabilities for tailoring fiber orientation and creating opportunities for optimization techniques. Consequently, a growing body of literature has focused on optimizing fiber orientation. However, a crucial consideration in this context is the stress yield criteria. This study addresses the Topology Optimization problem by minimizing the structure volume while considering local stress constraints using Tsai-Wu yield criteria. To achieve this, we use the method NDFO-adapt, which determines the material distribution and fiber orientation. Our approach optimizes the penalization fields, material distribution, and fiber angles. Additionally, we extend a similar approach to optimize the threshold projection parameter. By adopting this strategy, we modify the solution space, enabling the exploration of previously unattainable local minima. To handle the local stress constraint, we employ the Augmented Lagrangian method. The efficacy of the proposed method is demonstrated through numerical examples.

Reliability-based optimization of evolutionary topology and automated generation of strut-and-tie models for 3D structures

2024-05-03T23:15:15+00:00

This paper addresses reliability-based topology optimization (RBTO) coupled with the Smoothing-ESO (SESO) method for automated generation of optimal strut-and-tie models. The proposed approach handles with the generation of truss-like designs for three-dimensional problem, addressing the design of a single corbel and a deep beam with two openings. The reliability analysis is performed using the Reliability Index Approach (RIA) via First-Order Reliability Method (FORM) by inserting into the Topology Optimization (TO) approach the follow random variables geometry, volume, strength and compliance, considering the limit state functions maximum displacement and maximum von Mises stress imposed in the optimization procedure. The automatic generation of optimal 3D strut-and-tie models was obtained through the derivatives of the von Mises stress fields by finding the force paths where compression and tensil predominate, respectively, in the direction of the struts and ties for reinforcement insertion.

Topology optimization of a solar-powered boat

2024-05-03T23:55:04+00:00

To reduce climate change effects caused by the marine industry’s uncontrolled emissions, the proposal of a technique that implements topology optimization to boat design can help boatyards and governments to reduce CO2 emissions. Boats are responsible for approximately 3% of the world’s total CO2 emissions and making lighter boats is a great way to reduce this contribution. Until now, the works that use topology optimization do not take into account some specifications of marine design, such as balance. This work solves the compliance minimization problem subject to a volume constraint and a new COG (center of gravity) constraint to respect the primary boat equilibrium project to avoid rework. A reference solar-powered boat is considered as a baseline design. The power required by the boat is used as a measure of CO2 reduction for comparing the baseline and the optimized designs.
This is done via hydrodynamic analyses before and after optimization.

A smooth boundary extraction technique for topology optimization with binary design variables and a geometry trimming procedure

2024-05-04T00:01:55+00:00

One important step for topology optimization methods is to obtain representative smooth boundaries of the design. This is a step mostly used as a post-processing tool to facilitate manufacturing. However, smooth boundaries become also relevant during optimization in problems where the information at the boundaries is crucial, e.g., in stress-based design or fluid-structure interaction problems. This work investigates a boundary smoothing procedure to be used at every iteration of the topology optimization procedure. The present technique is proposed for binary-based topology optimization methods, such as the BESO (Bi-directional Evolutionary Structural Optimization) or the TOBS (Topology Optimization of Binary Structures) algorithms. In this context, a nodal numerical filter is applied to the binary design, and a smooth level set boundary is extracted from the design. The idea is further discussed in the context of the TOBS-GT (TOBS with geometry trimming) method, where the optimization and finite element meshes are separated. In this method, the void regions are trimmed out of the analysis domain and a new finite element mesh is generated at every optimization step. In this procedure, smooth boundaries are fundamental to guarantee a reasonably cheap and convergent finite element mesh. The smoothing procedure has the potential to improve the performance of the resulting structural surface as well as its appearance. 3D Numerical examples are investigated to evaluate the smoother robustness.

Topology Optimization fiber reinforced materials considering Tsai-Wu yield criterion

2024-05-04T00:30:27+00:00

The utilization of fiber-reinforced materials has experienced a significant surge due to their notabl advantages, particularly their high strength-to-mass ratio. As a result, new additive manufacturing technologies have emerged to accommodate these materials, offering capabilities for tailoring fiber orientation and creatingopportunities for optimization techniques. Consequently, a growing body of literature has focused on optimizing fiber orientation. However, a crucial consideration in this context is the stress yield criteria. This study addresses the Topology Optimization problem by minimizing the structure volume while considering local stress constraints using Tsai-Wu yield criteria. To achieve this, we use the method NDFO-adapt, which determines the material distribution and fiber orientation. Our approach optimizes the penalization fields, material distribution, and fiber angles. Additionally, we extend a similar approach to optimize the threshold projection parameter. By adopting this strategy, we modify the solution space, enabling the exploration of previously unattainable local minima. To handle the local stress constraint, we employ the Augmented Lagrangian method. The efficacy of the proposed method is demonstrated through numerical examples.

Labyrinth Diode Designed by Topology Optimization of Binary Structures using Laminar Flow and Real Gas Properties with Experimental Validation

2024-05-04T00:37:52+00:00

One of the most pressing issues that require attention is the reduction of CO2 emissions, and one approach to mitigate this problem is by enhancing the performance of diodes used for sealing and minimizing leakage in turbomachinery. This study focuses on the design of a labyrinth diode using the Topology Optimization of Binary Structures (TOBS) method, which incorporates laminar flow and real gas properties. The labyrinth diode design is obtained through TOBS, considering energy dissipation and vorticity magnitude as a multi-objective framework within a specified volume fraction. The optimization problem takes into account the dimensions of
the test bench and the properties of real CO2 gas in a two-dimensional axisymmetric model. The labyrinth diode design is optimized for laminar fluid flow governed by the Navier-Stokes equations, with the inclusion of the standard Darcy term to penalize solid domain infiltration. Computational Fluid Dynamics (CFD) is employed to numerically assess the diode’s performance and compare it with experimental measurements, evaluating its effectiveness in reducing leakage. The optimized topology is transformed into a solid model and fabricated using UV-photosensitive resin through 3D printing. The fabricated prototype is then tested on a test bench (TB) equippedwith a chamber capable of evaluating two seals with a middle entry, utilizing a 40 mm rotor. The TB can reach a maximum rotational speed of 10,000 rpm and generate a pressure drop of up to 5 bar. The leakage rate is measured in kg/s using instrumentation that adjusts the mass flow rate based on pressure/temperature analysis. The results indicate the need for further improvements to accommodate turbulent flow and higher Mach numbers in compressible flow during Topology Optimization. Nonetheless, the current findings offer promising insights into reducing leakage in turbomachinery seals.

Conceptual Design of Steam Turbine Labyrinth Seals Considering Thermal Compensation and Topology Optimization

2024-05-04T00:46:47+00:00

Labyrinth seals (LS) are used in gas and steam turbines. These seals usually present thermal expansion in their fins, which can generate damages in the component with a subsequent increase of leakage. This problem can be explored and solved from the conceptual design stage in order to increase and optimize the seal performance. This work shows a methodology for the analysis and conceptual design of steam turbine labyrinth seals, considering thermal compensation and the topology optimization method (TOM). In this work, the TOM is applied as a tool for improving the seal thermal performance and it is implemented in the COMSOL CAE
software. As result, several conceptual designs of optimized labyrinth seals for steam turbines are obtained and compared with a non-optimized seal. For the steam turbine optimized seal, designs with 44%, 76% and 50% reduction in the average radial displacement of the fins were obtained. In addition, it was determined that, due to thermal expansion wear, in a non-optimized steam turbine seal a 42% increase in leakage through the seal can occur.

Lattice Structures Design Based on Topology Optimization: Modeling, Ad- ditive Manufacturing and Experimental Analysis

2024-05-04T01:07:38+00:00

Materials made with architected microstructures present tunable mechanical properties and can be used to obtain lightweight structures and, at the same time, with high strength. In lattice structures, for example, topology and truss diameter can be varied so that the material is efficiently distributed in the design domain. Due to the complex geometries of these structures, designing them using computer-aided design tools is a challenging task.

In this work, a parametric modeling was developed in the Rhinoceros program using the Grasshopper extension to assist in the construction of models of lattice structures with varying truss diameters. The developed parametric modeling allows defining the topology and the diameter of the truss bars, which greatly simplifies the generation of models of porous solids. Microstructure models were generated and manufactured in polyamide 12 through selective laser sintering to assess whether it is feasible to print the trusses from the established parameters. The problem of a simply supported beam with a concentrated load at the center was solved using the topology optimization method and the density field was used to generate the variable density models. Both regular and variable density beam models have been designed to have the same mass and additively manufactured with the use of the selective laser sintering technique. Experimental analyzes were carried out using three-point bending tests and the results show that the solution using variable density has a large increase in stiffness when compared to solutions with uniform density.

Numerical Analysis of the Stresses and Behavior of Composite Castellated Beams

2024-04-23T19:22:33+00:00

This work has as main objective to analyze, through numerical modeling, the structural behavior of Composite Castellated Beams (CCB), with steel profile and reinforced concrete slab, in order to map the performance of the beams and the stress distribution for hexagonal castellated holes. For this, a detailed study of the CCB behavior will be done, then, based on the data obtained, a numerical modeling through the Finite Element Method (FEM) using the ABAQUS/CAE software was elaborated, and finalized with an extensive analysis of the behavior of the stresses in each type of beam modeled. This study is important because composite castellated beams are structural elements that have high strengths because they are the result of the application of various construction techniques. First, composite beams with steel profile and reinforced concrete slab increase the bending stiffness and resistance to stresses of the beam. Also, castellated beams have higher bending stiffness due to the height gain after their construction process. Therefore, the union of these techniques needs to be studied and analyze the stresses generated in the beam.

Optimum Design of continuous composite slab using Particle Swarm Optimization

2024-04-23T19:30:49+00:00

Civil construction is one of the main contributors to the emission of CO2 in the atmosphere. In the pursuit of more environmentally friendly structures, evaluating the emission of gases generated by civil construction, particularly in the manufacturing process of composite slabs, is of paramount importance. Composite slabs are typically analyzed as a succession of simply supported spans; however, due to the construction method, these structures are actually built as continuous. Considering the continuity of the slabs in composite steel and concrete systems can lead to a more optimized structural design. The aim of this paper is to determine optimal solutions for continuous composite slabs in terms of CO2 emissions. The constraints of the optimization problem are based on the design criteria of Brazilian Standards, and the solution to the optimization problem was obtained using Particle Swarm Optimization. As result, the algorithm selected slabs with thinner steel formwork, lower concrete cover, and lower rates of negative and additional positive reinforcement. Additionally, it chosen concrete with intermediate compressive strength and a rate of negative reinforcement close to lower bound. The CO2 emissions resulting from steel formwork and concrete were the most influential variables in the final problem solution.

Advanced Parametric Modelling of Pyramidal Trusses

2024-04-23T19:33:21+00:00

Trusses are an affordable and easy solution for engineers, especially when spanning large distances. It is notorious that several aspects of trusses influence their behavior. By accounting for material and geometric non-linearities, this study examines the behavior of pyramid trusses under vertical load. Practical applications make these structures valuable as either a primary or secondary component. This study looks at how elastic and inelastic
stability of pyramidal trusses are influenced by factors like focus height, base radius and number of bars. Therefore, it will be possible to identify the ideal stability and strength configurations for pyramidal trusses. The advanced nonlinear analyzes intend to use results from the literature or obtained via other softwares in the calibration of the proposed numerical models. It will be possible to perceive under what conditions the pyramidal truss presents gain and loss of rigidity, indicating alternatives for designers that envisage such structure shape.

Path following strategies for non-linear analysis of steel-concrete composite sections: a bi-axial bending evaluation

2024-04-23T19:57:40+00:00

The present study aims at the non-linear analysis of steel-concrete composite cross-sections. The strain compatibility method (SCM) is used to describe the sections deformed shape in each step of the incremental-iterative solution process. For the full analysis of the moment-curvature relationship, the SCM is coupled to path-following strategies (adapted generalized displacement technique and adapted minimum residual displacement method) to go beyond the critical bending moment points in the construction of the relations that describe the complete cross-section mechanical behavior. Concomitantly, the strain-control strategy is implemented as an alternative numerical approach and used for comparison, since the bending moment limit points do not prevent the complete construction of the cross-section equilibrium path. The constitutive relationships are addressed explicitly, as well as the residual stresses present in the steel sections. To validate the proposed numerical formulation, the results obtained are compared with the numerical and experimental data available in the literature. To validate the proposed numerical formulation, the results obtained here are compared with the numerical data available in the literature. Additionally, the softening effect on the concrete was increased to induce descending stretches in the moment-curvature relationship, and this condition was correctly evaluated.

In recent decades, the increasing of slenderness in buildings structural design has been relevant leading to the reduction of the natural frequencies values and the damping levels, resulting in excessive vibrations and human discomfort, in some situations

2024-04-24T11:44:02+00:00

In recent decades, the increasing of slenderness in buildings structural design has been relevant
leading to the reduction of the natural frequencies values and the damping levels, resulting in excessive
vibrations and human discomfort, in some situations. Having in mind the current day-to-day project practice
aiming to determine the dynamic structural response of tall buildings, two aspects are generally disregarded,
associated to the effect of the geometric nonlinearity and the aerodynamic damping. Therefore, this research
work aims to assess the dynamic structural behaviour of a steel-concrete composite building with 48 floors and
172.8 m height, when subjected to wind nondeterministic actions, including in the dynamic analysis the effects
of the geometric nonlinearity and the aerodynamic damping. The building numerical model was developed to
obtain a realistic representation of the analysed structural system, based on the Finite Element Method (FEM),
through the use of the ANSYS software. The conclusions of this study, obtained based on the displacements and
accelerations values, pointed out to the fact that the effect of the geometric nonlinearity led to relevant
differences on the dynamic structural response of the investigated building. On the other hand, the contribution
of the aerodynamic damping was not significant.

Generalized direct strength design approach: steel cold-formed columns under buckling mode interaction

2024-04-26T14:29:28+00:00

Thin-walled steel cold-formed members exhibit local (L), distortional (D), and global (G) buckling modes. These modes can interact in various ways, depending on the relationship between the corresponding buckling loads (PcrL, PcrD, and PcrG). The direct strength method (DSM) provides equations for designing columns experiencing global, local, distortional, and local-global buckling interaction (LG). This study focuses on the most general buckling mode interaction (LDG), building upon a recent approach by the authors that covers local-distortional buckling (LD). To develop the design equations, extensive numerical (FEM) and experimental databases were utilized, covering the relevant ranges of slenderness factors (λL, λD, and λG) associated with L, D, and G buckling modes, respectively. The proposed approach combines the existing DSM equations from the Brazilian code NBR 14762:2010 and the design equations for LD buckling interaction, recently proposed by the authors. After identifying the main variables and calibrating the design equations using FEM and literature-based experimental results, the contribution of the global mode is incorporated. The resulting set of design equations takes into account all the possible buckling modes, L, D and G, and the buckling interactions (LG, LD, and LDG)
for axial compression of steel cold-formed members.

Vibration analysis and human comfort assessment of composite floors subjected to dynamic loads induced by groups of people

2024-04-26T14:49:41+00:00

This research works aims to assess the human comfort and study the structural behaviour of steel-concrete composite floors subjected to dynamic loadings induced by rhythmic human activities. In this paper, the analysed structural system corresponds to a steel-concrete composite floor with dimensions of 40m x 40m and total area of 1600m2. The structure represents a typical interior floor of a commercial building commonly used for aerobics. The dynamic loadings were obtained through the use of traditional “only force” mathematical models, and also based on the consideration of biodynamic systems, in order to incorporate the human-structure interaction dynamic effect to assess the floor dynamic response. This way, the finite element model of the floor was developed based on the use of modelling techniques, adopting the mesh refinement present in the Finite Element Method (FEM) and implemented in the ANSYS software. The floor dynamic response, analysed based on the displacements and accelerations values, was determined through the investigation of several dynamic load models considering groups of people practicing rhythmic activities on the concrete slabs. Finally, it was concluded that the displacements and accelerations values have surpassed the design criteria recommended limits indicating that the floor human comfort was violated, inducing excessive vibrations and human discomfort.

Influence of the geometric nonlinearity and the aerodynamic damping on the dynamic response of tall buildings

2024-04-26T14:53:56+00:00

In recent decades, the increasing of slenderness in buildings structural design has been relevant leading to the reduction of the natural frequencies values and the damping levels, resulting in excessive vibrations and human discomfort, in some situations. Having in mind the current day-to-day project practice aiming to determine the dynamic structural response of tall buildings, two aspects are generally disregarded, associated to the effect of the geometric nonlinearity and the aerodynamic damping. Therefore, this research work aims to assess the dynamic structural behaviour of a steel-concrete composite building with 48 floors and 172.8 m height, when subjected to wind nondeterministic actions, including in the dynamic analysis the effects of the geometric nonlinearity and the aerodynamic damping. The building numerical model was developed to obtain a realistic representation of the analysed structural system, based on the Finite Element Method (FEM), through the use of the ANSYS software. The conclusions of this study, obtained based on the displacements and accelerations values, pointed out to the fact that the effect of the geometric nonlinearity led to relevant differences on the dynamic structural response of the investigated building. On the other hand, the contribution of the aerodynamic damping was not significant.

Dynamic structural analysis of transmission lines steel towers subjected to nondeterministic wind loadings

2024-04-26T14:57:58+00:00

In the current design practise of steel latticed towers used to support electrical transmission lines, the structure’s dynamic behaviour is not considered. However, the main loading to be taken into account in the structural analysis of electrical transmission lines steel towers is produced by the wind loads, which acts dynamically over the structural system composed by towers and cables. In addition, it’s not uncommon for slender towers to present disadvantageous dynamic properties, making them vulnerable to the wind action. Considering that many accidents associated to this kind of structure occur even for wind velocities below that specified in project, it’s possible that most of these accidents have been produced by dynamic actions. This research work proposes an analysis methodology that can accurately simulate the coupled behaviour between the transmission line cables and the suspension structures, when subjected to wind nondeterministic actions, including in the dynamic analysis the effects of the geometric nonlinearity and the aerodynamic damping. The results obtained in this work indicated that the dynamic response can be relevant to the system structural behaviour, and in this scenario the use of a static analysis can lead to a non-trustable design of the towers.

Numerical Simulation Of FPCB Shear Connectors For Thin Sheets

2024-04-26T19:53:43+00:00

In this work, experimental investigations were conducted, and a numerical model was proposed to analyze the behavior of circular openings with transverse bars as steel-concrete shear connectors (FPCB).
Although the effectiveness of these connectors for thick plates has already been proven by previous works, the application of circular openings with transverse rebar shear connectors to thin sheets has not been widely evaluated yet. This paper presented the development of the numerical model for the analysis of circular openings with transverse bars as steel-concrete shear connectors. The three-dimensional model of the plug-in test adapted for the analysis of these connectors was performed in the finite element program ABAQUS. The C3D8R solid element was used to simulate the concrete block, the steel sheet, and the steel rebar. For the steel stirrups, T3D2 truss elements were used. To simulate the concrete the Concrete Damaged Plasticity (CDP) model was adopted and for the steel elements the bilinear simplified curve was implemented. The aim of this paper was to compare it with experimental tests performed by the author and to demonstrate its capacity to efficiently represent the behavior of the circular openings with transverse rebar shear connectors to thin sheets observed in the experimental test.

Timber Cross-Section Verification in Fire Situation

2024-04-26T20:46:06+00:00

Temperature has a significant influence on the timber structural elements behavior. Such material, anisotropic, with irregular fibers and the presence of knots, and flammable, when exposed to high temperatures (fire situation), has its physical and resistance properties deteriorated. This deterioration leads to a considerable loss of stiffness and strength of timber structural systems. During a fire, the thermal analysis of the structural element cross-section becomes dominant, since the behavior of the beam, column, truss or frame under high temperature depends directly on this phase. This thermal analysis allows for determining the temperature field
variation through the boundary conditions adopted for the timber cross-section model. Therefore, the objective of this study is to carry out transient thermal analysis, via FEM, of a timber cross-section widely used in civil construction. Such numerical analysis will be carried out through the CS-ASA/FA module with additions of graphical interfaces via GiD platform. Thus, a more complete and accurate visualization of the temperature field variation in the timber cross-section is expected. Finally, comparisons are made with other literature or software results, as SAFIR, to prove the capability of the CS-ASA/FA module and GiD graphical interfaces.

Crack detection in 2D structures using wavelet transform and the boundary element method

2024-04-23T20:08:55+00:00

Detecting damages in structures is of paramount importance as they can lead to the collapse of structural
elements. In the current scenario, two reliable techniques for non-destructive testing of structures, namely
ultrasound and X-rays, are practically applicable for precise localization of hidden damages. However, such
techniques are costly, time-consuming, and require special procedures to be performed. Currently, research
suggests the possibility of using numerical methods to assist in damage detection in structures. Generally,
numerical methods for damage detection, such as cracks, are based on finite element modeling and comparisons
between the signatures or responses of the structures before and after the occurrence of damage. This article
proposes a new approach to damage identification based on the Wavelet Transform (WT) and the Boundary
Element Method (BEM), making the numerical modeling of structures more accurate, straightforward, and without
requiring the structure's signature before the damage occurs. To validate the adopted methodology, a cantilever
beam containing a crack with different orientations will be modeled using the in-house programs BEMLAB and
BEMCRACKER2D, as well as the algorithms implemented in MATLAB for handling wavelet coefficients and
damage localization. The obtained results indicate that WT is a useful tool for identifying and monitoring damages
in structures.

BemLab2D & BemCracker2D: A computational package for modeling and analyzing fracture mechanics problems with boundary elements

2024-04-23T20:16:36+00:00

The stress analysis in structures with complex geometry as in aircraft fuselages, where geometry is
continuously altered by crack growth, usually requires the use of numerical methods, since the presence of
cracks in the structure raises difficulties related to the modeling and, consequently, to the calculation of the stress
intensity factors (SIF). In this aspect, the dual boundary element method (DBEM) has been applied in this type
of analysis, taking advantage over the FEM considered, since there is no need for continuous remeshing at each
crack increment. Therefore, this work introduces a software written in C ++ and based on Object Oriented
Programming, called BemCracker2D, for two-dimensional analysis by DBEM for crack propagation problems in
the field of linear elastic fracture mechanics, as well as its BemLab2D GUI. Parameters as SIF, crack-growth,
number of load cycles and others, will be computed and compared with examples from the open literature in
order to attest to the program's efficiency and robustness.

Towards a general multiscale methodology for the simulation of thermal behavior of granular media

2024-04-24T17:16:02+00:00

This work presents a continuum-discrete hierarchical multiscale methodology based on data-driven
computations of the microscale response to simulate heat conduction in static granular materials. The effective
thermal conductivity tensors of the continuous method at the macroscale is obtained from a database of microscale results. The microscale database is created by generating and homogenizing several Representative Volume Elements (RVEs) in order to relate the thermal conductivity of the granular material to its microstructural
properties. In this study, these properties are the local porosities and anisotropies, which are inputs of the database to obtain the conductivity. An easy yet efficient protocol for RVE generation and homogenization is also presented.

Simulation of fresh concrete slump test with the Material Point Method

2024-04-24T18:22:32+00:00

The exponential growth in computational power in recent years has increasingly made numerical simulations a go-to tool for studying the behavior of structures and materials. A pertinent application is the simulation of the fresh concrete slump test, a laboratory test used to study the consistency and mobility of the concrete mixture. However, this simulation presents a challenge, as concrete — composed of a varied mixture of materials like water, cement, sand, and gravel — exhibits viscoplastic behavior. Therefore, a robust numerical method that models this physical nonlinearity is necessary. Previous works have successfully simulated the fresh concrete slump test as a Herschel-Bulkley fluid, utilizing the lattice Boltzmann method. Meanwhile, the Generalized Interpolation Material Point (GIMP) method is gaining traction in the industry. GIMP unites the best traits of mesh-based methods with the best traits of particle-based methods, by combining a fixed background grid of finite elements (i.e., a grid that remains still throughout the simulation) with material points where the kinematic data is stored. This approach favors the simulation of large displacements and deformations. In this work, GIMP is adopted to numerically simulate the fresh concrete slump test with the Herschel-Bulkley model.

An Analysis of water hammer pipe flow with unsteady friction model using the SPH Method

2024-04-24T18:39:00+00:00

Two methods used for simulating flow problems in engineering are Method of Characteristics (MOC)
and Smoothed Particle Hydrodynamics (SPH). This paper compares the results obtained using these two methods
for hydraulic transient in forced conduits. Both steady and unsteady friction losses are considered using the
unsteady model proposed by Vardy et al. [1]. The study findings obtained by in-house codes are compared with
the experimental results of Martins et al.

Discrete element modeling for predicting 3D-printed concrete process parameters

2024-04-24T18:43:15+00:00

This work presents a computational model for the simulation of the rheological behavior of 3D-printed
fresh concrete. Our approach is based on the discrete element method (DEM) for description of the particles’
overall dynamics, combined with the Discrete Fresh Concrete (DFC) model [1] to account for particle-particle
and particle-wall interactions at the level of the (contact) constitutive equation. Using the DFC model, we hope
to be able to represent the interaction among coarse aggregate particles within a fine mortar matrix. This is an
on-going research that is part of a master’s dissertation, and only the theoretical framework will be presented by
now. Numerical results shall appear soon.

Gas-lift simulation using Smoothed Particle Hydrodynamics

2024-04-30T19:23:41+00:00

Oil reservoir production reduces over time as the pressure decreases, posing a challenge to maintaining economically desired production rates. We can use artificial lift methods to address this issue, considering the characteristics of the production system, such as reservoir and fluid properties or surface facility constraints. Here, we focus on the gas lift technique, which involves injecting compressed gas into lower sections of the tubing through valves installed along the pipeline. As the gas aerates the oil, it decreases the effective density of the fluid, making it easier to reach the surface. It is suitable for offshore installations and not limited by the well depth, allowing continuous or intermittent lift to restore productivity. However, fewer studies use particle-based methods such as the Smoothed Particle Hydrodynamics method (SPH). It is a Lagrangian mesh-free method, and we can use this method to simulate multiphase flows. Therefore, we chose it to reproduce a simplified gas lift test case that involves a two-dimensional two-phase flow within a vertical pipe that contains oil, and we inject high-pressure gas into the system through a horizontal valve. The main objective is to verify if the SPH method can reproduce the phenomena associated with gas lift operations.

Numerical Simulation of the Stress-strain Behavior of Polymeric Fibers for Mooring Offshore Structures

2024-04-24T18:51:01+00:00

Polyester fibers have been used in offshore mooring due to their excellent mechanical properties,
resistance to marine environments, and relatively low cost. However, its mechanical behavior still needs further
investigation since its working environment is subject to adverse conditions that can magnify inelastic behaviors.
Thus, this work focuses on the characterization of components of this material according to different levels of
construction. Multifilaments and sub-ropes were numerically simulated based on the Modified Yeoh strain energy
model. The simulation parameters were adjusted using experimental data from cyclic tests, and the results were
then compared with the experimental data. The numerical simulations demonstrated good agreement, with an
average error of approximately 1.3% for both multifilaments and sub-ropes. Furthermore, the study identified
dissimilarities in constitutive behavior between them due to the twisting and braiding involved in sub-rope
construction. These findings suggest the possibility of developing a formation law that can predict the constitutive
behavior of sub-ropes based on the numerical simulation results obtained for multifilaments. Such correlation
could prove advantageous in optimizing material performance and construction methods for offshore moorings
utilizing polyester fibers. However, it's important to conduct further studies to establish the precise correlation
between both behaviors under different manufacturing conditions.

Towards a methodology to estimate environmental loadings from time history motions of offshore platform by using Artificial Neural Networks

2024-04-24T18:58:25+00:00

Floating production systems (FPS) for offshore oil exploration are subject to environmental loads such
as waves, wind and current in different directions of incidence and varying intensities that result in dynamic
movements of this same system. Nowadays, FPS has several sensors, in this particular case, its position is
monitored by GPS and accelerometers. On the other hand, it is hard to monitor environmental loadings in a deep
water that depends on oceanographic buoys. Therefore, this paper presents the first steps to estimate the parameters
of wave loading from a time history motions of an offshore platform by using Artificial Neural Networks (ANN).
From this, it may be possible to verify oceanographic forecast models and to know the environmental conditions
at the moment of an event, such as, line break or equipment breakdown. In addition to this, we can estimate real
environmental data for the generation of digital twins, which is a digital replica of the real system. In the case
study, ANN training process is performed from data of a rigorous Finite Element (FE) analysis. From the results,
we can observe that ANN presents a high level of accuracy in this kind of application, which allows to move
forward with research in this area.

Finite Element Analysis of a NORSOK L005 Ball Valve for Oil & Gas Applications

2024-04-24T20:01:28+00:00

The oil and gas sector is one of the main consumers of industrial valves, which are essential devices for
managing liquid, gas, or mixed fluids, ensuring safety and production in this industry. Designed according to
international standards, valves undergo structural analyses with calculations to ensure reliability and safety,
considering the pipeline's pressure class. In this study, a NPS 6 trunnion-mounted split-body ball valve was
analyzed, with flanged connections between the body and the cover designed according to NORSOK L005 [5]
standard. Using the finite element method and ANSYS software, three analyses were applied: linear-elastic with
stress linearization, elastoplastic, and elastoplastic for localized deformations, following the guidelines of ASME
VIII, Division II code [7]. The study resulted in an optimized valve geometry concerning mass concentration in
the body-to-cover connection, meeting the strength criteria defined in the design by analysis methodology of
ASME VIII, Division II [7].

Sensitivity analysis of production parameters in multiphase flow simulations

2024-04-24T20:05:11+00:00

With the development of oil fields in ever deeper water depths, the costs involved in exploration and
production have grown drastically. Thus, to make projects more economically attractive, it is necessary to
understand the factors that contribute to maximize production. In hydrocarbon production management, there are
several parameters that involve fluid flow through the production system that can significantly impact field
productivity. The value of these parameters may contain uncertainties that interfere in the platform's short-term
decisions, such as: well opening and closing strategies, choke valve opening, injection parameters, among others.
In this context, the proposed paper aims to evaluate the well test parameters and perform a sensitivity analysis to
verify which parameters have the most impact on the well productivity, through a correlation matrix. The analyzed
parameters are reservoir pressure, productivity index, gas-oil ratio, water cut and gas lift injection rate.

Using metamaterial to control offshore wind turbine vibrations

2024-04-24T20:10:33+00:00

Wind energy is one of the renewable sources in fast development and implementation worldwide.
Developing competitive renewable energies and energy supply networks, e.g. offshore wind turbines (OWT), is
essential to guarantee a sustainable power supply in cities and megacities. In these scenarios, a reliable energy
supply is crucial. These large and flexible structures are vulnerable to external vibration sources such as wind, sea
waves and earthquake excitation. It is necessary to mitigate the dynamic responses of offshore wind turbines to
ensure the safety of these structures. The OWT selected is a National Renewable Energy Lab (NREL) monopile

5 MW baseline wind turbine. This OWT is a conventional three-bladed variable-speed, pitch-to-pitch, upwind-
controlled turbine. This paper explores using metamaterial to control vibrations from offshore wind turbine tower

modes. The effectiveness of the proposed control is numerically investigated. The outcomes reveal the benefit of
using the metamaterial compared to conventional tuned damped mass passive controls.

Evaluation of Extreme Conditions for Transportation of Offshore Drilling Equipment Using Riser Column

2024-04-24T20:14:45+00:00

Considering the increase in offshore production activities taking place in deep water depths, the
operations related to well drilling and oil production are becoming more complex and expensive and demands
detailed analysis to assess the safety of the procedures. An example is the transportation of equipment with large
dimensions such as the Blow-Out Preventer (BOP) and Lower Marine Riser Package (LMRP) pack, which is a
procedure that needs attention since it is costly and demands a lot of time due to deep water depths at which this
equipment is being installed. In addition, the pack can reach resonance zones during the installation procedure,
increasing the relevance of dynamic analyses. In this context, the objective of this paper is to study the feasibility
of transporting the BOP/LMRP without the need to withdraw the equipment to the drilling rig, which, in some
cases, should considerably reduce the time and cost of the operation. In addition, the work addresses the main
forces acting on the drilling riser during this procedure and the need to perform specific analyses. Typical
equipment will be studied at three different depths considering different navigation speeds and wave heights.
Criteria such as maximum stress and limit angle of the lower flexjoint are evaluated. Although the wave and Vortex
Induced Vibration (VIV) fatigue phenomena have not been studied, the main goal is to assess whether extreme
efforts are points of attention in transport operations with the BOP/LMRP set suspended.

Nonlinear dynamic structural optimization of offshore structures using equiv- alent static models

2024-04-24T20:19:11+00:00

Nonlinear dynamic analyses of offshore structures are well-known for their often expensive computa-
tional cost. Optimizing such models is an even more complex task because it requires many nonlinear dynamic

analyses in sequence. On the other hand, nonlinear static analyses of offshore structures have significant lower
computational cost, and can be used to approximate the nonlinear dynamic nature of the original problem and
come up with a valid optimized solution. This work proposes the use of an equivalent static model to perform
structural optimization applied to anchor systems of offshore structures. The equivalent static model is built based

on the field of displacement of the original model, using a penalization factor to approximate the static displace-
ments field to the dynamic one. To encompass more of the dynamic nature of the problem into the static model,

not only the field of displacement is used, but also its convex hull. This strategy allows minor differences between
the models to be taken into consideration. This penalization factor, chosen at the start of the optimization, as well
as the use of the convex hull of the displacement fields were shown to create a fair correspondence between the
models, allowing the problem to be solved in a fraction of the original time, and resulting in valid, optimized
results.

TOWARDS THE GLOBAL ANALYSIS OF SOIL AND RISER INTERACTION USING A DEGRADATION SOIL MODEL

2024-04-24T20:27:44+00:00

In offshore industry as water depth gets deeper, the prediction of riser loads gets more complex, due to
issues such as its interaction with seabed. The touchdown point (TDP) – where the riser touches the seabed for the
first time – is a hot spot where the interaction is intense, and good predictions of TDP response is critical to the
assessment of steel catenary riser (SCR) fatigue life. Therefore, the soil model plays an important role, because
simplified models can overestimate the SCR curvature at TDP. Different types of soil have been studied from
linear to nonlinear springs to represent the seabed. Nonetheless, linear springs cannot represent the real soil
behavior, thus research focuses on P-y curves based in pipe-soil experimental results. Two models became widely
studied: the non-degradation and degradation models. The former has been applied in general software analysis,
but the degradation model has not. The degradation model is based on plastic soil deformation under cyclic loads,
and it has other features such as consideration of soil- water mixing, erosion, and soil consolidation, which can
drive the riser-soil separation and trench formation. The purpose of this article is to describe the implementation
of a soil-riser interaction model considering degradation effects [1] on the in-house time domain global analysis
software SITUA-Prosim. Two case studies are presented to validate the model and the proposed algorithm.

Streamlining nonlinear blast analysis for efficient structural design of off- shore platforms

2024-04-24T20:32:23+00:00

The design of offshore platforms requires comprehensive blast analyses to ensure safety and structural

integrity. However, creating dedicated structural models for nonlinear blast analyses can be complex and time-
consuming. This paper describes the development of an innovative application that simplifies and automates steps

of the model preparation process for nonlinear blast analyses, by taking advantage of existing structural models
used for in-place operational structural analyses. Engineers can use wizards within the application to automate

steps, reducing manual work and potential errors. Developed with a Java Spring Boot backend and a React fron-
tend, this tool not only simplifies but also streamlines the model preparation process, ultimately enhancing the

efficiency of offshore platform design. As a result, the application has demonstrated substantial efficiency gains,
significantly reducing the time required for nonlinear blast analysis model preparation when compared to manual
methods for a single structure. This application represents a significant advancement in nonlinear blast analysis
workflow, boosting productivity, accuracy, and reliability in the development of offshore structures.

Dynamic Model Updating of Al-Al Honeycomb Sandwich Panels for Aerospace Applications

2024-04-24T20:40:41+00:00

In aerospace environment, it is crucial to develop reliable dynamic models to accurately predict the
structural behavior of aircraft. The established approach involves constructing numerical models using the Finite
Element Method and utilizing experimental data for model updates and improvements. This paper focuses on the
construction and updating process of dynamic models applied to Al-Al honeycomb sandwich panels, which serve
as the main structure of the Brazilian Geostationary Satellite. Two numerical models are proposed to replicate the
honeycomb plate's geometry, including a simple equivalent laminated plate, and a face plate-equivalent solid core
model. Experimentally obtained parameters are utilized to update the numerical models using a Bayesian

optimization algorithm, which finds equivalent values for physical parameters enhancing the numerical-
experimental correlation of natural frequencies. Since this process is probabilistic, Monte Carlo simulations are

performed to ensure convergence of the obtained values. The results demonstrate that even the lower complexity
equivalent plate model can adequately represent the panel, making it suitable for preliminary analysis and saving
computational time compared to the higher complexity model. Overall, this paper presents a comprehensive
approach to constructing and updating dynamic models of honeycomb sandwich panels, demonstrating their
effectiveness in accurately capturing the dynamical behavior of aerospace structures.

Contribution of the eccentricity of unbonded tendons to the punching shear resistance of prestressed flat slabs

2024-04-25T01:05:28+00:00

With the increasing use of prestressed flat slabs in floor construction, studies are needed to assess the
high shear stresses generated in the slab-column connection, which is a vulnerable point to punching failure and
crucial for the design of this constructive system. Together with experimental studies, the use of computational
tools has allowed the analysis of the influence of prestressing on the ultimate resistance and thus the understanding
of the puncture phenomenon through numerical simulations. In this study, experimental tests were simulated
through nonlinear three-dimensional analysis using the computational program ATENA. The nonlinear behavior

of cracked concrete and the yielding of steel in passive and active reinforcement was considered. The load-
displacement and load-strain curves were compared between the experimental and numerical results obtained, with

the aim of validating the constitutive models adopted for concrete and steel. From the adequate calibration of
models, a parametric study was carried out with variations in the spacing and eccentricity of the tendons in the
slab, thus allowing to identify the influence of these parameters on the punching shear resistance.

Parametric structural computational study of flat slabs under punching shear stress

2024-04-25T01:17:30+00:00

The system composed of flat slabs and columns offers advantages compared to the traditional system
of slab-beam system such as increased internal space and reduced formwork usage. This structural system has
been the object of study over the last few decades due to the complexity of its structural behavior, particularly the
punching shear phenomenon. It is a brittle failure mechanism that occurs in the slab-column connection, induced
by high shear forces. Thereby, the study of punching shear is crucial due to structural sudden failure characteristic.
Over the last decades, the relevance of parameters that influence the performance of flat slabs has been
investigated, such as slab thickness, longitudinal reinforcement ratio and column size. The use of parametric
computational analyses allows the use of optimization procedures to improve the efficiency of the system and

further investigate the relevant parameters affecting punching shear. Therefore, this research employs three-
dimensional parametric structural computational models to analyze the impact of slab thickness and column size

in the phenomenon of punching shear. The models are based on a centrally located column in a slab panel
measuring 250 x 250 mm. The space of solutions for the parameters under analysis are examined to find the optimal
range for their use.

Remote inventory and inspection of the truss bridge elements and connections using STS and UAV

2024-04-25T01:22:50+00:00

The traditional visual inspections, along with the remote Structural Health Monitoring (SHM) methods
are very valuable tools to keep the existing bridges safely in service. In the case of old structures with incomplete
documentation, verification of dimensions is also an essential aspect. Traditional on-foot or on-boat visual
inspections have many limiting factors. For large or tall structures, there is little to no possibility of visually
inspecting the entire structure without using lifts or other heavy machinery. This paper presents an attempt to use
a Scanning Total Station (STS) for the inspection and inventory of the dimensions of a truss railway bridge over
the largest river in Poland. Measurements were conducted using two methods: the direct method with the use of a
total station and the use of advanced geometric analyses of the collected point cloud. The field tests on the bridge
were preceded by tests in the laboratory, where the accuracy of the method was assessed. During the tests on the
bridge, a deviation from the actual geometry of the selected truss connection in relation to the old documentation
was detected. The credibility and scale of this deviation throughout the bridge span were confirmed by Unmanned
Aerial Vehicle (UAV) inspections.

A study on temperature rise in heterogeneous cement materials using the FE2 method

2024-04-25T14:31:02+00:00

The hydration reaction of ordinary Portland cement (OPC) is a complex process that initiates as soon as
the OPC meets water. During this process, hydration products are formed, changing the thermal and mechanical
properties and releasing heat. Massive structures of cement-based materials (CBMs) such as damns, bridges or
foundations of large buildings, tend to present a substantial increase of temperature due the great amount of heat
generated by the hydration reaction which together with the mechanisms of heat transfer trough the boundaries
can cause significative high temperature gradients and nonhomogeneous dilation/shrinkage, leading to cracking

during the early ages. To prevent these damages, the hydration process can be numerical predicted using multi-
scale models, once that the thermochemical response and increasing of temperature of the macroscale depends on

the microstructural changes due the hydration reaction. In this paper, the recent computational homogenization
approach direct FE2 method (dFE2) is applied to predict the adiabatic and semi-adiabatic temperature rising in
mortars, assuming a simple chemical kinetics law to describe the hydration of the OPC and several sand fractions.
The dFE2 method is a monolithic method in which the passage information macro to micro and micro to macro
is not required as in the usual FE2. Instead, by using the concepts of multipoint constrains the macro and micro

discretization are linked allowing the imposition of the boundary conditions (linear, periodic, etc.) to the represen-
tative volume element (RVE). The implementation was made on ABAQUS finite element software by developing

particular user-subroutines used to determine state of cure of cement-based materials. A example of macrostructure
under semi-adiabatic conditions, exchanging heat with its surroundings by convection, is presented. The results
show the adequacy of the proposed approach.

Numerical and Analytical Study of Reinforced Concrete Beams with Ultra-High Performance Fiber Reinforced Concrete (UHPFRC)

2024-04-25T14:39:19+00:00

Ultra-High Fiber Reinforced Concrete (UHPFRC) has recently been used to retrofit structures,
presenting great mechanical behavior under flexural loads. This work used the data of a developed numerical study
to develop a numerical and analytical methodology to obtain the ultimate bending moment (Mu) of a reinforced
concrete (RC) beam retrofitted with UHPFRC subjected to monotonic load. The numerical model was developed
in the commercial program ATENA 3D, using the Finite Elements Method (FEM). The numerical analysis
considered the nonlinear material behavior to obtain closer values to the experimental test. The analytical
methodology was based on the previous equations developed by other authors, with the modification of the tensile
diagram of the UHPFRC. The results obtained from both methods presented good accuracy in the ultimate bending
moment compared to the experimental one. Regarding the case study, the analytical and numerical models showed
differences of 7.1% and 2.9%, respectively, and similarity in the load-displacement curve of the retrofit beam with
UHPFRC. This work demonstrated the ability of the ATENA program to simulate the structural behavior of RC
beams retrofitted with UHPFRC. Finally, it is possible to conclude that both methodologies could determine the
ultimate bending moment for beams strengthened with UHPFRC.

Bond Behavior between helically wrapped FRP rebars and concrete

2024-04-25T14:57:52+00:00

The bond behavior of FRP rebar embedded in concrete structures is influenced by many factors, such
as fiber type, fiber content, the diameter of the rebar, and concrete strength. The bond behavior of FRP rebars is
one of the major concerns in FRP applications as reinforcement in concrete structures. There are many studies in
this area because there is no standardization for the surface treatment of these rebars. Besides the experimental
analysis of the behavior of the rebars through pullout tests, numerical analyses are extremely necessary so that
more of the parameters that influence bond behavior can be varied and their influence analyzed. The aim of this
paper is to analyze the bond behavior of new FRP rebars developed. The numerical analysis will be carried out on
the finite element analyses program ABAQUS. The material of both the concrete block and the FRP rebar was
implemented as linear elastic until failure. For the interaction between the concrete block and the FRP rebars was
used the cohesive surface solution and the results obtained by the simulation were compared with experimental
results obtained by the authors.

Analysis of transition variables in a continuous-discontinuous model to describe the crack process in concrete structures

2024-04-25T17:18:00+00:00

The complete characterization of fracture in quasi-brittle materials such as concrete remains a chal-
lenge in computational modeling because of the complexity of this phenomenon and the material constitution.

Continuous-discontinuous approaches have been developed to fill this gap, embracing the continuous degradation
process related to smeared cracks and the discontinuity representation when discrete cracks emerge. Besides the
efforts, there is no consensus about the transition procedure between continuous and discontinuous. The literature
indicates that many parameters can be monitored to annunciate the transition, such as energy, historical variables,
crack length, crack opening, etc. But the most frequently used variable is damage. More recently, the phase-field
models have shown an ability to connect Continuum Damage Mechanics and Fracture Mechanics, acting as a crack

enunciator and tracker. Considering the context, an analysis of the transition variable and the value it assumes dur-
ing the evolution of smeared degradation to an explicit crack is proposed. A combined strategy that associates

nonlocal damage models with a mesh redefinition model based on nodal duplication is adopted. Two parameters

are compared in the transition function: the damage variable and the phase-field variable. Some numerical simula-
tions were performed, admitting different limit values. The results are analyzed to establish the optimal value that

characterizes crack nucleation and which parameter works better as a transition variable.

Numerical analysis of two pile caps reinforced concrete with partially embedded and shear key interface

2024-04-25T17:23:57+00:00

On Precast concrete structures the column foundation connections can occur through the socket
foundation, which can be embedded, partially embedded or external, with socket walls over the pile caps. This
paper presents an experimental study about two pile caps reinforced concrete with partially embedded socket
submitted to central load, using 1:2 scaled models. In the analyzed models, the shear key interface between the
socket walls and column was considered. Additionally, a numerical analysis in the Abaqus software was
performed, considering the physical non-linearity of the materials. The results are compared to a reference model
that presents monolithic connections between the column and pile caps. It is observed that the ultimate load of
pile caps with partially embedded socket present less magnitude than the reference model, and that the presence
of additional reinforcement does not significantly change the behavior of pile caps.

Advancing Cement Paste Shrinkage Modeling: Investigating The Normalized Ultrasonic Pulse Transit Time Evolution And Its Impact On Stress Analysis In Oil Wells

2024-04-25T18:45:01+00:00

This study presents a new modeling approach for predicting cement paste shrinkage evolution, with a
specific focus on its relationship with transit time, and consequently with the hydration of the cement paste. Cement
plays a crucial role in well integrity, and therefore, cement shrinkage is a critical factor in stress analysis within
oil wells. By developing a proper modeling technique, it becomes possible to numerically calculate the residual
capacity of the cement sheath, accounting for thermal and pressure loads throughout the well's lifespan. In this
research, a new modeling approach is proposed for the evolution of shrinkage based on cement slurry cured under
temperature 60 °C and pressure of 1.0 kpsi. The development of the cement was analyzed using ultrasonic pulse
velocity and volumetric shrinkage tests over a period of 90 hours. The newly developed shrinkage evolution model
is compared to the traditional linear adjustment method, considering the degree of hydration.

A discrete and explicit representation of tendons based on coupling finite elements for numerical analysis of prestressed concrete structures

2024-04-25T19:12:11+00:00

This work presents a new strategy for representing tendons with a discrete and explicit approach to
numerical analysis of prestressed concrete structures via finite element method. The prestressing tendons are
represented by one-dimensional truss finite elements with the behavior described through a bilinear elastoplastic
model with a prescription for initial deformations. The concrete and prestressing tendons are inititally discretized in
finite elements in a totally independent way. Then, coupling finite elements are inserted to describe the interaction
between tendons and concrete. A damage constitutive model is used for modeling unbonded postensioned cases.
The proposed approach is validated through the numerical simulation of benchmarks available in the literature and
a good agreement between them can be observed.

An algorithm to compute the parameters of a Generalized Kelvin Chain model to represent aging creep of concrete

2024-11-09T10:16:13+00:00

The numerical modelling of viscoelastic behavior of large concrete structures can be optimized by representing the compliance function in terms of series of exponentials, usually termed Dirichlet series, Prony series, or Generalized Kelvin Chain mechanical model. The viscoelastic behavior of concrete is usually described
in terms of a compliance function obtained from classical creep tests or design codes, being, thus, necessary to devise a workflow to derive the set of retardation times and moduli that completely describe the correspondent Generalized Kelvin Chain model. Direct fitting of the Generalized Kelvin Chain model to a given compliance function is usually not feasible, as the problem becomes ill-posed if the chain contains a reasonable number of units, which is necessary for correct representing the viscoelastic behavior. The present work presents an open-
source Python algorithm to compute the parameters of a Generalized Kelvin Chain model associated to a set of aging compliance functions. The use of the algorithm is exemplified by computing the Generalized Kelvin Chain model associated to compliance functions obtained from Eurocode 2 and fib Model Code 2010, which are common viscoelastic models used in engineering practice.

1D Nonlinear Acoustic Wave Equation In Heterogeneous Fluid

2024-04-25T20:21:38+00:00

In this work, the one-dimensional nonlinear equation of acoustic wave propagation in non-homogeneous fluid was developed using the physical laws of fluid mechanics and thermodynamics for a compressible fluid, including a source term for pressure wave generation. The solution of the 1D Acoustic Wave equation is performed in the time domain using the Petrov-Galerkin Finite Element Method (FEM), and the linear and parabolic approximation basis functions. In wave generation, two different types of pressure source term were implemented, the Ricker type (Chacaltana [1]; Picolli [2]) and the sinusoidal type. The boundary conditions of Neumann (natural reflection) and Reynolds [3] (Absorbing Boundary Condition - ABC) were also implemented and tested. To test the model, a Fortran code was written and a graphical interface in Octave was used to visualize and analyze the numerical results. Simulations were performed in a discrete domain of points representing the one-dimensional mesh. The non-uniform distribution of discrete points was obtained by the GMSH mesh generator. Numerical results were compared with those found in the literature. And, there was a good agreement between them.

Analysis of the conditioning of the inertia matrix in acoustic models of the Boundary Element Method with Direct Interpolation

2024-04-25T20:34:41+00:00

After to be solved problems given by Helmholtz, Diffusion-Advection, and Poisson equations, this work presents the results of the Direct Interpolation Method concerning acoustic wave cases to homogeneous media. The main objective is to establish a link between the stability of the discrete model with the conditioning level of the dynamic matrix, which is generated through a sequential of radial basis functions. Several conditioning norms were verified and applied to several linear boundary element meshes. A classical problem of wave propagation in scalar fields was chosen for the numerical analysis.

Application of a Relevance Matrix to Thermal Unit Commitment in the Presence of Renewable Energy Sources

2024-04-25T22:44:39+00:00

The short-term unit commitment problem is considered hard to optimally solve given the combinatorial
explosion of the operation decisions regarding the generating units involved in the daily operation planning. The
problem’s complexity further increases when introducing renewable energy sources, e.g., solar and wind, to the
planning. This paper applies a recently proposed search space reduction method to thermal unit commitment
systems penetrated by solar and wind power generation.

Utilization of Artificial Intelligence techniques in the development of City Information Models (CIM)

2024-04-25T22:57:16+00:00

This paper presents an investigation into the application of computational intelligence techniques, optimization, and data modeling in the development of CIM models. CIM is a concept that seeks to integrate information and data related to a city into a three-dimensional digital model, allowing for a detailed and dynamic representation of the urban environment. However, dealing with large volumes of data and optimizing the efficiency of urban operations is a complex challenge. To address this challenge, this article proposes the use of artificial intelligence techniques, such as machine learning algorithms and artificial neural networks. These techniques are capable of handling large-scale problems, finding optimal or approximate solutions, and dealing with uncertain or imprecise data. The article explores the different applications of computational intelligence techniques in the optimization and data modeling of CIM through the development of a systematic literature review (SLR) and the application of the Design Science Research (DSR) method to discuss the relationship between these technologies and CIM.

Map Fusion for Precise Yet Efficient Collaborative SLAM

2024-04-25T23:01:35+00:00

Collaborative Simultaneous Localization and Mapping (C-SLAM) is an active research area in robotics that aims to enable the collaboration of multiple robots in constructing a shared map and simultaneously estimating their positions. However, Map fusion poses a significant challenge, especially when involving a large group of robots. It aims at obtaining an accurate global representation of the environment. This paper proposes an novel approach using the Fourier Transform, the Pearson correlation coefficient and Particle Swam Optimization to address the map fusion problem. Efficiently merging maps into a global representation requires careful consideration of spatial relationships and alignment of these maps. The Fourier Transform analyzes spectral features in each robot’s measurements, extracting insights about spatial distribution. The Pearson correlation coefficient evaluates
spectral similarity between different map sections, facilitating region pairing for successful fusion. The search for
optimal fusion parameters is performed using the Particle Swarm Optimization Algorithm. These distinct regions
guide the fusion process, optimizing global map creation. Instead of a complete map fusion, selective fusion of sections increases the likelihood of success. Experiments involving five robots in a simulated environment validate the proposed approach, demonstrating the capability of optimized map fusion to provide a more accurate and comprehensive representation of the environment. This enhancement should contribute to refine further the
C-SLAM.

Optimization of Load Frequency Control parameters In hydro-wind sys- tems using Manta Ray Foraging Optimization

2024-04-26T11:20:12+00:00

This work proposes a novel hybrid optimization approach combining nonlinear programming and the Manta Ray Foraging Optimization (MRFO) metaheuristic to optimize the controller parameters of the hydro-wind interconnected power system to improve the Load Frequency Control (LFC). The optimization process addresses challenges posed by integrating wind power into power grids due to its limited inertia, which hampers natural inertial response. The research focuses on incorporating wind generation into Load Frequency Control (LFC) utilizing the Virtual Synchronous Generator (VSG) technique and operational adjustments. In this way, this work contributes to improving LFC efficiency in mixed power generation setups by introducing a hybrid method that surpasses the limitations of traditional controllers, enhancing the equilibrium between power generation and demand.

Parallel Implementation of the Particle Swarm Optimization Algorithm on a Multiprocessor Embedded System with Network-on-Chip

2024-04-26T11:28:27+00:00

In recent years, with technological advancements, the need to solve complex problems has emerged in various areas of knowledge, such as data mining, combinatorial optimization, power systems, signal processing, pattern recognition, machine learning, and robotics. The key characteristic of these problems is their computational intensity, particularly in terms of execution time. In order to accelerate the problem-solving process, bio-inspired
algorithms have been developed, which aim to simulate the behavior found in biological systems, such as living organisms and ecosystems, to efficiently solve complex problems. Examples of these algorithms include Particle
Swarm Optimization, Ant Colony Optimization, Artificial Bee Colony, and Cuckoo Search. This work aims to obtain a parallel implementation of the Particle Swarm Optimization algorithm using a Multiprocessor Embedded System with Network-on-Chip. The parallelization strategies we employ are based on the Parallel Particle Swarm Optimization and Cooperative Parallel Particle Swarm Optimization algorithms, using master-slave, ring, and 2D
grid topologies. Based on the execution time obtained by each parallel algorithm and each employed topology
during the simulations, it will be possible to identify which parallelization strategy provides the best performance,
as well as the number of processors required. Currently, the results, when compared to the serial version of the
Particle Swarm Optimization algorithm, are promising.

Collective transport by caging in swarm robotics

2024-04-26T11:44:02+00:00

Collective transport, in swarm robotics, is based on the transportation of objects by swarms of robots characterized by having significantly smaller dimensions compared to the object to be transported. The set of robots of the swarm generally have the same architecture. Individually, the robots are able to perform simple functions, such as sensing, locomotion, and basic communication. However, cooperatively, they can perform complex task. Collective transport has diverse applications that encompass the transportation of both large-scale objects and nanoscale objects. Consequently, numerous studies have been driven by this topic, highlighting three transport strategies: pushing, grasping, and caging. In this work, the caging strategy is adopted. It can be defined as the complete enclosure of the object. Allowing it a certain degree of freedom but preventing it from escaping the formation of robots around it. The main advantage of this strategy is the coordinated and cohesive progression of the transport since the forces applied to the object by the swarm complement each other and prevent significant deviations in its trajectory towards the planned destination. This work proposes a method to approach collective transport by caging, which operates in three stages: the search for the object by the swarm, the recruitment of swarm robots, aiming to position the robots around the object and enclose it, and the transport stage. The implementation of the proposed strategy is carried out in the CoppeliaSim platform, wherein the swarm is composed of Khepera III-type robots. This robot is chosen due to the arrangement of its sensors along its perimeter, which allows for a wide view of the environment. The arena, which is the scenario where the simulations are conducted is discretized into different configurations. This space discretization has a significant impact on the performance of the search and transport stages. The performance evaluation of the search and recruitment stages are based on the execution time, while for the transport stage, in addition to the execution time, the normalized error of the object’s trajectory is evaluated for different arena discretization configurations and path lengths. The proposed method proves to be effective, as the caging is maintained throughout the entire path, thus ensuring the uniform transport of the object.

Estimating geomechanical parameters from hydraulic fracturing tests using a soft computing-based methodology

2024-04-26T19:59:57+00:00

The discovery of naturally fractured reservoirs in the Brazilian pre-salt has attracted considerable attention for a better understanding of reservoir characterization and fluid flow inside fracture channels. Predicting the hydromechanical behavior of these reservoirs is a cumbersome task, which requires the identification of their geomechanical parameters. In this scenario, a soft computing-based methodology is implemented to estimate geomechanical parameters from borehole injection pressure in hydraulic fracturing tests. Based on artificial intelligence techniques, this approach integrates a proxy model and an optimization algorithm to match the field measurements and the borehole pressure curve predicted by a finite element model. Considering a multistep-ahead strategy to predict time series, a multilayer perceptron-based proxy model computes the borehole pressure curves, substituting the numerical simulation of a minifrac test. The adoption of a proxy model substantially reduces the computational effort of the parameter identification task. Therefore, a genetic algorithm can efficiently estimate the reservoir geomechanical parameters by solving a nonlinear least squares problem. The application to field-measured data from a minifrac test confirms the capability of the proposed methodology to estimate geomechanical parameters from hydraulic fracturing tests.

Enhancing public transportation planning through travel data analysis: a data mining application in the inference of passenger trip purpose in the Metropolitan Region of Belo Horizonte, Brazil

2024-06-24T20:16:23+00:00

Planning an efficient transport system begins with the collection of demand data. Traditionally, this data has been gathered through travel surveys conducted by interviews. These surveys involve questioning people about their trip’s starting and ending points, purpose, mode of transportation, travel duration, and other relevant details. However, this method is costly and can be somewhat inaccurate since it relies on respondents’ ability to accurately describe their journeys. With technological advancements in the transportation sector, Big Data sources have emerged as a new possibility to studying urban mobility patterns. In the public transport sector, since the 2000s the data collected by automatic fare collection systems provide a quick, accurate, and cost-effective means to estimate Origin and Destination (OD) matrices. However, a significant challenge arises when using this data source for OD matrix estimation—the lack of trip purpose information. To address this, researchers have turned to data mining techniques to inference this trip atribute. This paper contributes to the field by applying these emerging data mining approaches to infer the trip purposes of public transport passengers in the Metropolitan Region of Belo Horizonte (RMBH).

Architecture-Structure Conception in the Design of the CCBB Building in Brasilia

2024-04-26T16:55:05+00:00

The Presidente Tancredo Neves building, which has housed the Banco do Brasil Cultural Center in Brasilia since 2000, is one of the iconic works by architect Oscar Niemeyer, designed in 1992. In the architecture of the building stand out the facades composed of long longitudinal walls in reinforced concrete with large openings that allow ventilation and natural lighting of the upper floors. These structures, with minimal thickness compared to their grandiose dimensions, have the appearance of vierendeel beams, although the structural system does not function as such. This work presents a structural design analysis of the building, seeking to show the designer’s elements of creativity to balance the structure, maintaining the formal characteristics provided by the architecture. A numerical analysis of the structural solution is made with the available computational tools, describing the adopted structural system.

Numerical Safety and Performance Analysis of a Multipurpose Building’s Structure – Case Study

2024-04-26T17:20:43+00:00

The present work shows the case study of a multi-use building located in Brasília-DF. The analyzed
building has a structural model formed by elements of a spatial portico and four-knot plate, with dimensions of
25.75 by 25.75 m and a height of 11.65 m. It is supported on the foundations by rotating pillars at the base. It has
a ceiling height of 3.25 m on the ground floor and 2.80 m on the other floors. The closures are in bored brick
masonry. The article presents numerical analyses through the three-dimensional model of the building, using the
SAP2000 structural software. These analyses were executed to verify the displacements and deformations and the
efforts developed by the structure. The ultimate and in-use limit state criteria for the Brazilian standard of
reinforced concrete (NBR 6118) were observed for the study. In addition, the records and analyses of the
structure’s pathologies, found in the building, are presented. The main structural elements with their respective
pathologies are described, detected by visual inspection, and then the numerical tests performed are shown. Due
to the presence of several cracks among other pathologies in the building, an elastic instability analysis of the
structure was performed to verify the collapse load factor, using the Rankine-Marchant analysis model.

Phase-Field modelling of ramdomly representative volume elements

2024-04-26T17:26:32+00:00

Real-world engineering materials are usually heterogeneous in nature. Taking concrete as an example,
it is composed of sand, gravel, a cementitious matrix, in addition to various voids and imperfections caused by
chemical hardening reactions inherent of the material itself. To model those kinds of materials, the Phase-Field
Modelling has been widely used by the scientific community due to the advantages presented by it like the ability
to detect crack nucleation and to obtain its full path. For that, this model considers the smeared variational form
of Griffith’s sharp crack that spreads over a portion of the domain according to a length scale parameter. The
Phase-Field is inserted into the problem through an additional equation that solves, for each degree of freedom,
its variable that varies from 0 to 1 and indicates the damage. The purpose of this article is to use the Phase-Field
Models with heterogeneous material to study the behaviour of RVE for different sizes and grading curves. All the
implementation was done in INSANE, an open-source software, developed in Java at the Structural Engineering
Department of the Federal University of Minas Gerais. Numerical results will be presented.

Analysis of the Battistero di San Giovanni’s behavior subjected to seismic events

2024-04-26T17:37:36+00:00

The analysis behavior of historical structures over the years constitute a fundamental research’s field to
perpetuate the constructive methods and the cultural heritage of civilizations. Such analyzes involve not only the
static aspect but also the seismic action, present in a large part of the world territory and which subjects several
structures to vibrations. Evaluating the historic masonry construction’s vulnerability against earthquakes, many
studies are carried out to guarantee the protection of structures and consequently the cultural heritage. With the
ease of access to computational means, a large part of the historic building’s studies has been carried out using the
finite element method, with the aid of computational tools made available by commercial software. In this context,
the Italian municipality of Florence, which has the highest concentration of universally renowned works of art, is
in a seismic zone, presenting episodes of earthquakes in the month of June 2023, with 4.0 Mw of magnitude. Thus,
the present work aims to numerically analyze the dynamic behavior of the Battistero di San Giovanni, from the
4th-5th centuries, located in Florence. Its behavior against seismic events is evaluated from the structural analysis
by the finite element method, using the ABAQUS software.

Comparative analysis of the structural systems of blocks A and B of the architectural set of the Attorney General of the Republic of Brazil, Brasília, DF

2024-04-26T17:57:08+00:00

Oscar Niemeyer's work, recognized in the landscape of international architecture, has always attracted
the attention of architects and engineers to discover the dichotomy and paradigm that exists between structure and
architecture. Among the Works of Oscar Niemeyer of the 2000 ́s, symbol of the juridical order and the democratic
regime, the “Attorney General’s Office” stands out for being constituted by an architectural complex of six
buildings. The geometric forms of this complex are defining a monumental space represented by two main
buildings, realized by two constructive technologies and different structural solutions. The block “A”, supported
by a cable-stayed system, and the block “B”, supported by reinforced concrete pillars, demonstrates how the
structure is strongly linked to the design of architectural morphology. Through a structural analysis carried out by
the SAP2000 program, it was possible to identify the structural models that constitute the Attorney ́s project to
obtain numerical data that represent the innovation of constructing the same architectural object through two
antithetical conceptions. This study of the work in question allowed to understand the patterns that characterize
the formal aspects of the structural technology used by the genius of the Brazilian architect and the relative
constructive methods adopted.

Structural Degradation Assessment of RC Buildings: Application via Software of the method of assessment by integrity and safety - MAIS Method - in a Heritage Case Study in Brasilia

2024-04-26T18:19:49+00:00

The assessment of an existing structure is a complex task that necessitates a thorough understanding of
the materials involved, the applied loads, environmental aggressiveness, and various other factors to accurately
evaluate its functionality and predict structural safety levels. This process is challenging due to the numerous
uncertainties inherent in it, as buildings do not always reveal the condition of their internal components and
materials. In response to these challenges, the Method of Assessment by Integrity and Safety - MAIS Method - has been developed over the past five years. One of the modes that the MAIS Method can be employed involves
the utilization of a structural software. Through on-site surveys, data is collected, enabling the quantification of
the integrity of each constituent element within the system. Subsequently, structural modeling is carried out using
dedicated software for both the intact structure and the degraded structure, incorporating the integrity index directly
into the elasticity index of each structural element. The software is then executed, and a comparative analysis is
conducted between the two structural representations. The study focused on a building located in the Asa Sul
region of Brasília, Brazil, recognized as a UNESCO World Heritage Site. The present research concludes that the
MAIS Method is efficacious, facilitating visual identification of the structural condition. Furthermore, it
establishes the feasibility of conducting both global and local analyses of the structure.

Numerical analysis of vibrations of cable and tower of electric power transmission lines

2024-04-26T18:41:02+00:00

This article presents preliminary results on the behavior of towers and cables in power transmission
lines using a three-dimensional numerical model. Computational analyses were performed considering the plastic
behavior of ASTM-A36 and ASTM-A242 steels used in the tower. The mechanical model included rigid
connections and fixings, and four vibration modes of the metal tower were obtained: transverse, longitudinal,
torsional, and flexural. To validate the dynamic behavior of the cable, the classical problem of the violin string
was used, verifying that natural frequencies increased with cable tension. Receptance analysis allowed obtaining
displacement curves as a function of wind excitation frequency for different orientations. Critical wind excitation
frequencies were related to the vibration modes of the structure. The geometry and dynamic behavior of the
transmission tower and cable were explored, providing information on vibration frequencies and dynamic response
of the structure under different wind orientations. Four vibration modes were found: transverse, longitudinal,
torsional, and beam bending.

Python Program for 3D Linear Static Reticular Structural Analysis Based on Finite Element Method

2024-04-26T18:49:33+00:00

Structural analysis in civil engineering is the method, in which, the response of a real-world structure
before its design and construction is predicted. For any non-simplistic structure, it's hard to conceive the analysis
by hand without relying on simplifications, that by themselves, sacrifices precision of the analytical solutions.
Therefore, to solve these structures quickly and accurately, a computational tool is needed. These computational
tools, usually available in commercial version, come at a high monetary cost, causing inaccessibility for students
to have access, even for confirming and/or learning purposes. In this regard, this paper proposes to develop a free
and open-source computational tool, able to make structural analysis of reticular structures in 3D linear-static
regime. To make it possible, the Finite Element Method for structural discretization and the Python programming
language were used. Analytical and numerical examples available in the literature were exhaustively tested. The
differences between the solutions obtained with the numerical tool and the reference solutions are in the range of
10-7 to 10-5 showing the good performance of the implemented tool for the tested examples.

Study of the importance of mesh refinement in the IMERSPEC methodology

2024-05-03T11:32:02+00:00

The development of new computational methodologies (Computational Fluid Dynamics) aiming for
higher accuracy and lower computational cost is something that aids technological advancement, allowing for
investigation and understanding of physical phenomena with low cost and precision. This study investigates the
importance and necessity of correctly utilizing mesh refinement for modeling immersed bodies. For this purpose,
the pseudospectral Fourier method coupled with the Immersed Boundary method (IMERSPEC metodology) was
employed to model the flow over a pair of spaced and side-by-side cylinders. The mathematical methodology was
based on mass conservation and the Navier-Stokes equations for a Reynolds number of 100. The results, addressing
drag coefficient, lift, and vortex patterns, are analyzed and discussed for three different mesh refinement numbers:
256x128, 512x256, and 1024x512. This study concludes which mesh refinement number yields the lowest error
when compared to the reference. The authors would like to thank FURNAS Centrais Eletricas and the “Programa ́
de Pesquisa e Desenvolvimento Tecnologico” (P& D) of the ANEEL for the financial support. ́

A Comparative Study on the Fatigue Life of Mooring Lines under Combined Stresses

2024-05-03T11:35:58+00:00

Mooring lines are essential for offshore floating platforms, but accurately assessing their integrity and
fatigue poses a challenge. Traditionally, fatigue calculations only considered tension loads, neglecting out-of-plane
bending (OPB) stresses caused by plastic strains during the proof loading process in chain links. This oversight
may lead to early failures. Bureau Veritas guidelines BV NI604 propose a fatigue analysis method that considers
combined stresses for fatigue crack initiation. This study presents a comparative analysis of mooring line fatigue
life, comparing traditional methods with BV NI604's approach. Two case studies are examined: one focuses on an
FPSO vessel with a turret mooring system, experiencing significant out-of-plane bending due to turret rotation,
while the other explores an FPSO vessel with a spread mooring system. The analysis highlights the importance of
considering combined stresses and bending effects to ensure the safety of offshore installations.

Optimization of plane frames using the search group algorithm for economically efficient structural design

2024-05-03T11:39:30+00:00

This paper presents a design procedure that leverages the Search Group Algorithm (SGA) to optimize
discrete planar steel frames. SGA, a robust global optimization heuristic, orchestrates search groups to
systematically explore the design space on a global scale, subsequently fine-tuning their exploration in localized
optimal regions. The algorithm's application revolves around solving a structural optimization problem focused on
obtaining steel frames with minimum weight, all while meeting requirements for both strength and displacement
of the set. This is achieved through the selection of appropriate sections from a standardized set of steel sections
as outlined by ABNT NBR 8800. Demonstrating the procedure's efficacy, a steel frame example is transformed
into two distinct designs, maintaining consistent spatial arrangements. By conducting a comparative analysis, they
are examined to verify the effectiveness of the SGA for similar problems, and compared to see which design
performed better.

Modal Identification of Damage in the Dowling Hall Pedestrian Footbridge

2024-05-03T11:41:55+00:00

The methods that stand out in damage identification are those rooted in vibration response analysis,
known as Vibration-based Damage Identification (VBD). This arises from the direct influence of deterioration on
the global and local dynamic responses of structural elements, leading to alterations in dynamic parameters. Modal
indices, such as modal curvature (MC) and modal strain energy (MSE), were evaluated for the Dowling Hall
pedestrian walkway using a finite element model that extracted three-dimensional vibration modes. Additionally,
a newly introduced index known as the resultant vector, which incorporates three-dimensional modal coordinates,
was also examined and compared with the other indices. The results showed that there is a strong correlation
between the location of the actual damage and the location predicted by the indices. The study further investigates
the influence of damage magnitude on the accuracy of the indices and analyzes how damages impact adjacent
beams. The objective is to minimize ambiguities in determining damage locations and to provide guidance for
inspection and structural integrity monitoring programs. In conclusion, the methods of MC and MSE presented
more satisfactory results in identifying the introduced damages, whereas the resultant vector method exhibited
certain inconsistencies. The study also observed minimal variations when applying damages of different
intensities, indicating heightened sensitivity primarily in lower intensities.

MEAT TENDERNESS PREDICTION USING MACHINE LEARNING: DISTRIBUTION APPLIED TO VARIABLES

2024-05-03T11:45:21+00:00

Beef tenderness is an attribute of great prestige for consumers. Several factors, such as genetics, food,
and environment, influence meat tenderness, which can be objectively evaluated after the animal is slaughtered.

Typically, sensitivity measurement involves mechanical testing, in which the shear force required to break mus-
cle fibers is quantified. This study aims to validate a more comprehensive and robust database, incorporating

hyperspectral imaging, to help predict meat tenderness non-destructively. In this new approach, computational

techniques, such as machine learning with the use of artificial neural networks, are employed to explore the depen-
dence of transmitted variables without the need to control the response. Hyperspectral images provide information

about specific wavelengths, allowing for a more detailed analysis of the sample. To assess tenderness parameters,

measures such as pH, sample color, hot carcass weight, ribeye area, breed, and sex, as well as hyperspectral im-
ages, along with fillet shear force. The objective is to identify the relationship between these variables and the

shear force required to break the muscle fibers. The use of normal and gamma mathematical distributions as tools
for more comprehensive training in Machine Learning was used. The analysis showed that the statistical model
adequately adjusted the data, confirming the reliability and accuracy of the forecasts obtained. This additional
validation reinforces the robustness of the proposed model, which can handle the variability of beef tenderness
data. With these new arrangements, it was possible to study the behavior of these distributions through validation
from a robust database in which Random Forest algorithms were implemented in Machine Learning and Neural
Network. Based on the data presented, a Coefficient of Determination (R2) of 0.4494 was obtained, demonstrating
the effectiveness of the Machine Learning model in predicting the shear force in relation to the values obtained in
the mechanical tests. This innovative approach, using hyperspectral imaging in conjunction with machine learning
techniques, provides a broader and more robust database for predicting beef tenderness. These scientific advances
have the potential to improve end-product quality and meet consumer expectations for beef tenderness.

Numerical Modeling of a Vibration Test Platform with Imbalance CILAMCE-2023

2024-05-03T11:57:02+00:00

The study of vibrations caused by imbalances is crucial in industry and engineering, as imbalance can
cause vibrations and material fatigue. Motors exhibit vibrations due to imbalance, which can be caused by
imperfections in manufacturing, design flaws and maintenance. This study analyzes the vibratory behavior of a
sliding bearing on a rotating shaft with rotary imbalance through Finite Element simulations. The numerical results
were compared to experimental results obtained on a bench using an accelerometer. The analyses were performed
using MATLAB and Ansys software. The study aims to contribute to the understanding of vibrations in rotating
systems and the development of prevention and correction techniques for imbalance. The comparison between
experimental and numerical results enabled the calibration of the model in terms of its boundary conditions,
particularly with regard to the supports of the piece. Initially, it was believed that a perfect fixed support would be
sufficient, but the numerical results showed discrepancies in relation to the experimental results. Therefore, the
system was modeled with the introduction of an elastic support, and through manual adjustments in stiffness, it
was possible to obtain good correspondence between the numerical and experimental results, adapting the model
of the bearing to its real counterpart.

Database structured model for energy planning applications

2024-05-03T12:01:02+00:00

Actual updated data from the hydroelectric and thermoelectric energy system in Brazil is provided by
the National System Operator (ONS). It is made available as a package of digital files (text and binaries).
Researchers at the Laboratory of Bio-Inspired Technologies and Solutions from Federal University of ABC
(LabBITS - UFABC) implemented a platform for accessing the information of this Brazilian electric power
generation system from a SQL (Structured Query Language) database, regularly updated from the ONS’s provided
package of files. The database is accessed by the laboratory researchers via a REST (Representational State
Transfer) API (Application Programming Interface) which is used to supply the parameters of the energy system
models used in the energy planning calculations for the Energ.IA platform. This paper presents the recent
achievements of the team of under-graduate students, guided by seniors’ researchers of the LabBITS. Students
have developed a Java library which connects with the remote database and pulls the updated power system
parameters to instantiate Java object models and parametrized calculation methods of the Brazilian electricity
generation system. Those models are then used to simulate system operation or in optimization routines within the
Energ.IA platform. A simplified case study is presented to demonstrate its use.

Drive-by Damage Detection In Railway Bridges Using 1d Convolutional Neural Networks

2024-05-03T12:05:36+00:00

The aging of civil engineering infrastructure emphasizes the importance of structural health monitoring
(SHM) in railway bridges. Data-driven models are a prominent approach in this field. However, network-wide

bridge instrumentation is logistically difficult and expensive, leading to the development of the drive-by or indi-
rect monitoring method. In the drive-by approach, the instrumented vehicle acts as the SHM system’s actuator

and receiver. Environmental and operational conditions can affect structure properties and measured acceleration
signals, making it challenging to infer the real condition of the structure. To address this, we propose a drive-by

damage detection method using a classification model with a Convolutional Neural Network (CNN). CNNs under-
stand connectivity patterns between neurons, inspired by the animal visual cortex. The 1D CNN identifies damage

from raw acceleration signals at the front boogie of a train. Training data generated by a finite element method

considers healthy and damaged bridge conditions. The paper focuses on identifying scour-induced damage, result-
ing from the loss of stiffness in the bridge support due to erosion. Extensive numerical experiments evaluate the

effectiveness and robustness of the 1D CNN approach.

Python Program for 3D Linear Dynamic Reticular Structural Analysis Based on Finite Element Method

2024-05-03T12:22:19+00:00

Dynamic structural analysis in civil engineering is the method, in which, the vibrations response, modes,
frequencies, displacements, velocities and accelerations, of a real-world structure caused by arbitrary external
excitements is predicted, before its design and construction. But even for simple structures, to conceive the analysis
by hand, without relying on simplifications, for which, by themselves, sacrifices precision of the analytical
solutions, is hard. Therefore, a computational method to solve these structures is needed. But these softwares come
at a high monetary cost, causing an inaccessibility for students to have access to, even for confirming and/or
learning purposes. For such, a computational tool development, capable of linear structural analysis, both in 2D
and 3D, in dynamic regime, open-source for all, were proposed. To make it possible, the Finite Element Method
(FEM), for structural discretization, the Rayleigh damping model, for viscous approximation, the Newmark's
numerical method, for vibration analysis, and the Eigen-vectors and values, for modal analysis, and Python, for
the programming language, were used. And to a reticular structures, they were applied. Then, with examples found
in the available literature in the subject of dynamic structural analysis, were tested and compared. The results from
examples tested, errors ranging from 10-5 to 10-2 were shown by the tool, in the same unit as the mesh and properties
and time discretization, inputted in the program, compared to examples available in the literature.

Finite Element Modeling of Heat Transfer Modes in Local Gap Formation During Solidification of Cast Components CILAMCE-2023

2024-05-03T12:25:39+00:00

In the casting process, there is the casting and the mold. Due to the temperature difference between
these two parts and the fact that materials present physical deformations due to this temperature variation, there is
the phenomenon of the appearance of gaps between the components. This work then aims to analyze the influence
of how the development of these gaps occurs during solidification, on the resulting local cooling curves of the
casting. Using a finite element software, different simulations were performed that show different approaches to
the evolution of the process, considering different plots and behaviors of the heat transfer phenomena - conduction,
radiation, convection. Through the study and correct definition of the model parameters, the outputs generated by
the program were observed and evaluated in graphic and tabular form, confirming the possibility of analyzing the
piece locally, with satisfactory results regarding the general aspect of the heat exchange phenomena and gap
formation involved in the process.

Implementation of the Euler-Rodrigues formula to define the initial configuration of offshore systems lines

2024-05-03T12:28:00+00:00

During the construction of structural models for computational analysis, various pieces of information
concerning the structure, including the initial spatial configuration, are provided. This configuration represents the
spatial arrangement of the structure at the beginning of the simulation. In DOOLINES, an object-oriented
framework that performs nonlinear dynamic analysis of mooring lines and offshore production systems in the time
domain, the initial configurations of risers, hoses, and mooring lines are generated using the catenary equation,
which considers only axial stiffness, despite the presence of other stiffnesses such as bending and torsional
stiffness, as observed in risers. Because the initial configuration may differ from the relaxed configuration, it can
lead to the development of internal loads, even at time zero of the simulation. Therefore, the algorithm must discern
the difference between the initial and relaxed configurations and compute the corresponding loads. One possible
strategy, known as the "assembly" approach, involves considering the line in its relaxed position and prescribing
movement at one of the supports to bring it to its actual position in the initial configuration. However, this approach

requires computational effort before the actual simulation of interest. In this study, we implement the Euler-
Rodrigues formula of rigid body rotation to calculate the internal forces resulting from the initial configuration,

thus replacing the "assembly" approach. Through analysis of reference examples, we demonstrate that the results

obtained by the two strategies are similar. Consequently, due to its lower computational requirements, the Euler-
Rodrigues formula serves as a suitable replacement for the "assembly" approach.

Spatial transformer-based Machine learning architecture for bridge damage detection via car-mounted sensors

2024-05-03T12:31:06+00:00

Bridge infrastructure plays a vital role in facilitating transportation networks and is subject to various

types of damage that can compromise its structural integrity. Early detection of bridge damage is crucial for en-
suring public safety and minimizing maintenance costs. The present work proposes a spatial transformer-based

machine learning architecture for the detection of bridge damage through computational simulation of vibration
data. Traditional methods for bridge damage detection predominantly rely on visual inspections or expensive

sensor networks deployed on bridges. These methods are time-consuming, expensive, and often suffer from lim-
itations such as human subjectivity and limited coverage. To overcome these challenges, the proposed solution

leverages the advancements in machine learning that allow the detection of damages that can be easily overlooked
during the inspection process. Spatial Transformers are a type of neural network module that can learn to perform

spatial transformations on the input data. These transformations help the network align and focus on relevant re-
gions of the input data, which can be particularly useful in tasks that involve object recognition, image alignment,

and other spatially related problems. The advantages of the proposed system include its non-intrusive nature,
cost-effectiveness, and scalability.

Comprehensive aeroservoelastic evaluation of a simplified rectangular wing subjected to parametric control analysis

2024-05-03T12:34:37+00:00

The quality of aircraft flight control systems plays important role in terms of aircraft guidance, but especially
in safety, integrity and stability. Furthermore, such systems enable the response when an external load, such as
gust, reaches the aircraft. The control strategies have become increasingly important in the aeronautical context,
especially in the aeroelastic field when, in addition to inertial, elastic and aerodynamic interaction, control surfaces
can be excited in such a way as to impair aircraft performance or even prevent undesirable aeroelastic phenomena.
With the increase in geometric complexity, availability of lighter materials with high equivalent stiffness, it is also
necessary to update and implement computational tools for aeroservoelastic analysis to ensure not only efficiency
and cost reduction in testing and certification processes but also enable the advent of new technologies. Thus,
this work aims to perform an aeroservoelastic analysis in open and closed loop in a pre-defined geometry related
to a simplified wing in order to compare the control laws usually applied aircraft’s control. The model will be
represented numerically as a cantilever, untapered and unswept wing, with equations of motion obtained from
Lagrange energy methods for various assumed modes of vibrations. The material used in the wing will be linear and
orthotropic. The aerodynamics considered will be equivalent to the non-stationary Theodorsen model, including
Hanckock simplifications. The control laws will be variations of the PID method, under which various parametric
combinations will be involved. The results will be presented in terms of the classic Vgf diagrams, where it is
possible to identify the critical flutter speed. For gust behavior, temporal displacement graphs and spectral density
functions will be studied. Still through ASeS, it will be possible to perform parametric comparisons, highlighting
which factors influence the most in aeroservoelastic stability, making the poper initiative consolidate as an excellent
preliminary aeroelastic design tool.

APPLICATION OF COMPUTATIONAL MODELING AND NUMERICAL SIMULATION FOR THE DEVELOPMENT OF NEW WHEELCHAIR SEAT-BACK SYSTEMS TO IMPROVE POSTURAL ADEQUACY OF CHILDREN WITH MOTOR DISABILITIES

2024-05-03T12:37:02+00:00

One of the most compromised abilities in individuals who have neuromotor dysfunction is posture,
requiring that most of them need to use some type of Assistive Technology equipment, for instance a wheelchair.
This disorder can interfere with the insertion of the individual into society and impact his or her quality of life.
The present work intends to develop low-cost seat-back systems focused on the children population with some
kind of motor disability in the context of postural adequacy, and the numeric tools were used to give support for
the development of new technologies. The thermography technique was used to create maps according to specific
deformities of every child volunteer in this project. The temperature maps were converted into pressure maps and
implemented as input data to perform numerical simulations in the Finite Element software COMSOL
Multiphysics®. The computational analysis of different geometry cuts of polyester foams and their strategic
positioning on the seat-back systems are also being studied to provide better distribution of the child body pressure
on the system. Simulations show the potential of using octagon shapes of several foam densities to accommodate
the deformations and to decrease the stress concentrations in the system.

Fatigue life prediction on steel plates under variable range stress from 2D FEM models

2024-05-03T12:42:44+00:00

Structural and component metallic materials usually undergo strict quality control at the manufacturing
stage. However, they are inevitably subject to non-homogeneity and, consequently, to crack nucleation under
fatigue loads. Fatigue failures occur in a wide sort of engineering applications, such as platforms, bridges, ships,
and aircraft. These structures are constantly being subjected to variable amplitude loadings. Therefore, increasing
demands arise for studies to better understand the phenomenon of crack growth under variable amplitude loading
conditions. In this paper, the fatigue life under these conditions is evaluated. For this purpose, two-dimensional
simulations using finite elements are performed for different initial crack geometries. The models are subject to
mode I fracture and combinations of modes I and II. The crack propagation is performed incrementally through
the software FRANC2D. At each step, the stress intensity factor (SIF) is determined. All results of the SIF obtained
are then initialized in a Python language algorithm to calculate the fatigue life using the crack retardation and
acceleration model. Then, the fatigue life is evaluated for the different variable amplitude loading histories.

Application of the two-dimensional Cartesian Finite-Volume Theory in problems of solid mechanics

2024-05-03T12:45:32+00:00

This paper presents the development of a Python software with a simple and intuitive graphical interface
that allows for the computational modeling of solid mechanics problems (simple beams) using Two-Dimensional
Cartesian Finite-Volume Theory (FVT). The numerical approach based on FVT has gained prominence in the
computational modeling of structures due to its mathematically simple formulation compared to other classical
methods, as well as its low computational cost. Therefore, the main objective is to demonstrate the importance
of FVT in the education of engineering undergraduates, highlighting the advantages of its use as a substitute for

traditional methods that have long been used in solid mechanics, such as the Finite Element Method (FEM). Ad-
ditionally, it is important to emphasize the power of Python programming and its practical applications in the

daily life of an engineer. Lastly, the aim is to encourage the inclusion of Finite-Volume Theory as a mandatory

subject in engineering curricula, facilitating the understanding and development of simulation programs and struc-
tural analysis, enabling comparison with other numerical methods and analytical solutions of material strength.

This provides a differentiated education for undergraduate students in the areas of computational modeling and
structural mechanics to cope with an increasingly competitive job market.

Non Newtonian transport in OpenFOAM: validation and applications

2024-05-03T12:48:55+00:00

Most of the fluids used in all industries nowadays can be classified as non-newtonian. In numerical
simulations conducted via Computational Fluid Dynamics (CFD) techniques, as a consequence of its highly
non-linear behavior, this kind of material is usually described by a mathematical model. The way this model
represents the fluid affects immensely the manner it flows in a domain, and the correct transport model can
increase precision and detail capturing of a simulation. The purpose of this work is to validate the
Herschel-Bulkley rheology model, implemented in the CFD open source tool OpenFOAM, reproducing
experimental conditions and comparing results with benchmark data. To this end, the cases chosen for study all
involved non-newtonian fluids, and are extensively researched problems in civil engineering. Furthermore, it is
presented an application of rheology in CFD in the investigation of blood flow in the aortic arch. Four different
rheology models are used to simulate blood behavior, Carreau, Casson, Cross and Power Law.

Analysis of one-vs-all versus one-vs-one approaches in lithofacies classification

2024-04-28T22:17:41+00:00

The lithofacies classification provides valuable information about the geological history and the depositional environment. For multiclass classification tasks, as is usually the case with lithofacies classification, there are two basic approaches for building the models: the One-vs-One (OvO) and the One-vs-All (OvA) approaches. In general, when building models, default settings are typically employed, without conducting a detailed study to determine the most suitable approach for each scenario. In this study, we evaluated the performance of the OvA and OvO in the lithofacies classification task. The results indicate that the OvA model has lower computational cost and consistently outperforms the OvO model across almost cross-validation folds. Results on test data indicate that OvA can be a good alternative in scenarios with imbalanced classes or when there is a limited amount of data for training and testing. The OvO model can be an interesting alternative when the imbalance between classes is an important factor for the problem.

Model constrained empirical Bayesian neural networks for inverse problems

2024-04-28T23:00:32+00:00

Principled Uncertainty quantification (UQ) in deep learning is still an unsolved problem. Numerous methods have been developed so far, with Bayesian neural networks (BNNs) as the popular approach. BNNs, while inherently UQ-enabled and resistant to over-fitting, suffer from unnatural and artificial priors over their parameters. This paper develops a model-constrained framework for quantifying the uncertainty in deep neural network inverse solutions. At the heart of our approach is an interpretable and physically-meaningful prior over neural network parameters trained through use of Stein variational gradient descent (SVGD). We provide comprehensive numerical results for a 2D inverse heat conductivity problem and a 2D inverse initial conditions problems for both the time-dependent Burgers’ and Navier-Stokes equations.

Spectral Method and Machine Learning approach to Wind Turbine damage detection

2024-04-28T23:07:54+00:00

Wind energy is one of the cleanest energy source currently used in the world, an energy source that interferes least with the environment. It is important to locate Wind Farms (WF) in such a way as not to limit the living space and not to reduce the comfort of people in the area. Due to the intensity of the wind and minimal human impact, offshore farms seem to be the required solution. Another aspect important from the point of operational reliability, is ensuring continuous working conditions due to the design and material solutions. Wind Turbine (WT) structures are exposed to the dynamic action of wind and waves from the sea, as well as to the corrosive environment, causing accelerated damage to WT. The action ensuring safe use of structural elements of WT is monitoring the technical condition of the structure based on the analysis of frequency response functions (FRF). At the design, as well the operational stage, it is important to predict the failure of the element. The paper presents the simulation results of the monitoring and prediction of damage of IEA 15-Megawatt offshore wind turbine using the analysis of changes in resonant frequencies in the FRF and the Machine Learning technique.

Model constrained empirical Bayesian neural networks for inverse prob- lems

2024-04-29T13:03:30+00:00

Principled Uncertainty quantification (UQ) in deep learning is still an unsolved problem. Numerous methods have been developed so far, with Bayesian neural networks (BNNs) as the popular approach. BNNs, while inherently UQ-enabled and resistant to over-fitting, suffer from unnatural and artificial priors over their parameters.
This paper develops a model-constrained framework for quantifying the uncertainty in deep neural network inverse solutions. At the heart of our approach is an interpretable and physically-meaningful prior over neural network parameters trained through use of Stein variational gradient descent (SVGD). We provide comprehensive numerical results for a 2D inverse heat conductivity problem and a 2D inverse initial conditions problems for both the time-dependent Burgers’ and Navier-Stokes equations.

Using a Radial Point Interpolation Meshless Method for the numerical simulation of the viscoplastic extrusion process

2024-04-28T23:18:33+00:00

In this work, an accurate and efficient meshless technique - the Radial Point Interpolation Method (RPIM) – is used to address the numerical simulation of the viscoplastic extrusion process, which is the initial phase of the Fused Filament Fabrication (FFF), an extrusion-based additive manufacturing (AM) process. Unlike the FEM, in meshless methods, there is no preestablished relationship between the nodes in the nodal mesh. Thus, the concept of ‘element’ is inexistent. In meshless methods, nodal discretization can be straightforwardly modified since nodes can be added or removed from the initial nodal mesh. Hence, mesh-free techniques show a particular relevance if associated with AM processes since the nodes can be distributed to match the layer-by-layer deposition of the printing process. Additionally, meshless methods have shape functions with virtually a higher order, allowing a higher continuity and reproducibility. This work combines, for the first time, the flow formulation and the heat transfer formulation in an RPIM algorithm to simulate the extrusion process of viscoplastic materials like the ones used in the FFF. The proposed algorithm is developed, implemented, and then validated for benchmark examples. The accuracy of the obtained numerical results highlights the importance of using meshless techniques in this field.

A novel SPH algorithm to simulate tumour angiogenesis

2024-04-28T23:40:00+00:00

Nowadays, cancer is one of the foremost causes of death worldwide. As a tumor grows, it requires an increased supply of oxygen and nutrients to sustain its progression. However, once it reaches a critical size, the transportation of these molecules to the center of the tumor becomes challenging. In such circumstances, tumor cells initiate the process of angiogenesis to generate new blood vessels and so, a new nutrient source. Understanding the impact of angiogenesis on tumor progression is crucial for comprehending cancer. In recent decades, computational models have been extensively employed to investigate various biological problems, including tumor progression. The objective of this study was to develop a 3D algorithm to simulate the process of cell proliferation combined with angiogenesis. The algorithm utilizes the Smoothed Particle Hydrodynamics method and takes into account the concentration of Vascular Endothelial Growth Factor. To validate the algorithm, various high-concentration points were selected to observe whether the generated blood vessels followed appropriate paths. The proliferation process was assumed to follow an exponential pattern, and its reliance on the created blood vessels was analyzed. The results demonstrated that in all cases, the process of angiogenesis was
successfully integrated with the process of cell proliferation.

Radial Point Interpolation Meshless Methods for applications in Mechan- ics and Biomechanics

2024-04-28T23:46:56+00:00

Computational mechanics emerged alongside the advent of the first computers and has undergone significant development since then. Presently, the literature describes numerous advanced numerical techniques for discretization that are capable of efficiently conducting structural analyses. The finite element method (FEM) was one of the earliest discrete numerical methods to be developed and remains the most popular technique among the computational mechanics research community. FEM is known for its ease of programming, robustness, and ability to provide reasonable approximations. However, despite its efficiency and success, the last decade of the previous century witnessed the emergence of new, mature advanced discretization techniques known as meshless methods. In contrast to FEM, which discretizes the problem domain using a structured element mesh comprising a grid of nodes, meshless methods discretize the domain with an unstructured nodal distribution. Consequently, meshless methods enable the creation of discrete geometric models directly from medical images or CAD geometries. This advantage in meshing is a valuable asset in the fields of computational mechanics and biomechanics. This work presents a brief description of the evolution of advanced discretization meshless techniques in computational mechanics and biomechanics, highlighting the most significant ones and their formulations. Furthermore, it presents several demanding numerical applications in computational mechanics and biomechanics developed by the author and his research team. These applications encompass the analysis of transient behavior in bone tissue, the study of elastoplastic behavior in metallic and biological tissues, examination of blood fluid flow, and investigation of the structural response of implants and bio-structures. The results obtained using meshless methods are compared with FEM solutions to provide insights into the efficiency and accuracy of meshless techniques.

Structural analysis of adhesive joints using meshless methods

2024-04-28T23:52:07+00:00

Adhesive bonding is a joining method that presents several advantages in comparison to other commonly used techniques, such as bolting or riveting. One notable advantage is the relative lightweight nature of adhesive joints, which holds significant relevance in the pursuit of more efficient transportation vehicles. It is well-known that lighter vehicles consume less energy, making this a desirable characteristic. Given the growing interest in adhesive joints, it becomes crucial to thoroughly investigate their behaviour under various conditions. Currently, the literature contains several documents describing the structural behaviour of adhesive joints, with
numerous research numerical studies using as numerical discretization method the finite element method (FEM). However, other mature advanced discretization techniques are also available to the computational mechanic’s research community, such as meshless methods. This work proposes to show several numerical applications of adhesive joints using meshless methods. Static and dynamic demanding examples are addressed, and the results are compared with solutions obtained with the FEM. The results show the efficiency of meshless methods, proving that such discretization techniques are valid alternatives to the FEM. Additionally, this work provides valuable insights and knowledge that are currently lacking, ultimately enhancing our understanding of adhesive joints and
their behaviour under static and varying dynamic conditions.

Subclinical Gender-specific Differences in Arterial Carotid Stiffness - A Review

2024-04-29T00:01:54+00:00

Arterial stiffness is a complex and inevitable physiological process that affects the entire cardiovascular system. Among the various arterial structures, the carotid arteries play a pivotal role in supplying oxygenated blood to the brain. The aging process impacts both men and women differently, and recent research has shed light on the gender-specific differences in arterial carotid stiffness. This article aims to explore published reports on the underlying mechanisms and clinical implications of these disparities, providing valuable insights for future research.

Modelling the hemodynamics in a realistic cerebral aneurysm with clot through transient FSI simulations

2024-04-29T00:04:33+00:00

Modelling the hemodynamics of a patient-specific cerebral aneurysm with a clot in the most realistic conditions possible is still a challenge. The present work focus on the validation of the numerical procedure, implemented in ANSYS® software, for further accurate results. The 3D geometry used for simulations is a real patient cerebral artery with an aneurysm. The aneurysm is an Internal Carotid Artery (ICA) and is a saccular type. A Womersley velocity profile at the inlet boundary condition was used and blood was considered as a non-Newtonian fluid. These conditions were implemented in User-Defined Functions (UDFs) of ANSYS®. Moreover, an isotropic linear elastic model was used for the arterial walls and a hyperelastic Ogden model for the clot. The Fluid-Structure Interaction (FSI) model was also implemented in ANSYS® in order to really mimic the deformability of the artery during the pulsatile blood flow. In this patient case, the maximum WSS was 38 Pa and the TAWSS on the sac surface was 0.1 Pa. These values are within the expected since the results are similar to previous research. Thus, this numerical procedure can be considered valid for further hemodynamic studies of the aneurysm clot migration process in a realistic cerebral aneurysm.

Exploring XNAT to Foster Development and Testing of Image Processing Methods for Clinical Settings: Preliminary Results

2024-04-29T00:10:00+00:00

Medical imaging has evolved greatly in the past two decades and provides a rich set of data on the anatomy and function of important organs such as the heart. In this regard, medical image processing has also evolved to take advantage of these data and provide clinicians with methods supporting, for instance, (semi-)automatic identification of regions of interest and objective measures that can inform diagnosis. Recently, methods have also been proposed to perform haemodynamic simulations based on anatomic structures extracted from this data, which consubstantiate a noninvasive alternative to obtain important descriptors, such as the fractional flow
reserve (FFR). The development of such methods is best served by working closely with clinicians, and, after a first validation, if these methods can be experimented with in a wide range of cases, they can more closely inform their evolution and an assessment of their performance. Clinicians often have their diagnosis workflow supported on dedicated workstations, often proprietary, that not only integrate the processing and analysis of the imaging data but also provide visualization features that allow, for instance, visualizing the data from specific angles so as to conform with standard practice. Therefore, when developing new methods, it is important to comply with these basic features to promote easier use and evaluation. However, integrating novel methods in existing workstations is mostly out of question and developing a new framework from scratch to support all the workflow is a major effort. In this work, we argue for a novel approach to supporting the research workflow in image processing and analysis methos and explored the XNAT framework, designed to support clinical studies pipelines, to assess how it can be used to deploy these methods, particularly by its integration with image viewers such as the one provided by the Open Health Image Foundation (OHIF). After its deployment in a virtualized environment and exploration of its main features, a proof-of-concept pipeline developed in Python was successfully integrated to smooth the images and return the processing results to the framework. Overall, mastering the integration with XNAT is complex at
first, but the framework provided a promising response to the intended use.

Computational Methods to Predict the Fractional Flow Reserve in Coronary Arteries - a Literature Review

2024-04-29T00:15:04+00:00

Coronary artery disease (CAD), characterized by the buildup of plaque in arteries restricting blood flow to the heart, requires an accurate diagnosis with the Fractional Flow Reserve (FFR) assessment. Traditional FFR measurement involves invasive procedures, but non-invasive computational methods have been explored to mitigate risks and costs. This study reviews recent literature on computational approaches to predict FFR in coronary arteries. Researchers have investigated the use of advanced hemodynamic simulations considering patient-specific real conditions in the non-invasive prediction of the FFR. This approach aims to deliver accurate FFR results for on-site diagnosis in hospitals. The integration of these non-invasive tools could improve the effectiveness of FFR assessment and diagnosis.

Exploring a Python-based Semi-Automatic Approach for Coronary Artery Segmentation

2024-04-29T00:22:26+00:00

The segmentation of coronary arteries from Computed Tomography (CT) images is vital for coronary artery diseases (CADs) diagnosis and treatment. Combining thresholding, region growing, and several entity properties, we have implemented an in-house semi-automated method using Python, circumventing commercial software dependence in hospitals. Our technique swiftly isolates coronary arteries in under 2 minutes, enhancing efficiency, accuracy, and reproducibility compared to manual MIMICS® segmentation. Moreover, it is able to detect coronary branches that surge upstream severe stenosis which is usually a major limitation due to lack of
contrasted blood. In sum, our proposed method stands as a transformative stride toward the efficient and accurate segmentation of coronary arteries in the clinical landscape. Anchored in the marriage of computational prowess and clinical imperatives, it emerges as a potent beacon, poised to illuminate a path toward enhanced diagnostic insight and treatment efficacy.

Comparative study of homogenization techniques in masonry

2024-04-29T00:29:22+00:00

Masonry is a composite material widely used in construction, consisting of individual units, such as bricks or blocks, and mortar joints. This combination results in a highly anisotropic material, which means that its properties can vary significantly in different directions. However, adequately characterizing masonry represents a significant challenge. Due to its composite and anisotropic nature, determining the mechanical properties and structural behavior of masonry requires a careful and precise approach. One of the main difficulties in characterizing masonry is dealing with the variation in the properties of individual components, such as bricks and mortar, as well as the influence of mortar joints on the overall response of the structure. In addition, the presence of imperfections, such as cracks and discontinuities in units and joints, can significantly affect the structural performance of masonry. The analysis and homogenization of masonry have been approached through several techniques, including the Finite Element Method (FEM), which has been widely applied. However, more recent techniques, suchas Mechanics of Structure Genome (MSG) and Finite-Volume Direct Averaging Micromechanics (FVDAM), have also shown promise in this field. FEM has been employed for the analysis of masonry, both for unreinforced masonry cases and for those reinforced with fiber reinforced polymer (FRP). However, MSG emerges as an interesting alternative for masonry homogenization, as it considerably reduces the computational cost compared to FEM. In addition, FVDAM, a relatively new technique, has been used to analyze composite materials and obtain their effective properties. Although it is a technique under development, FVDAM has shown excellent results compared to other numerical approaches. In a pioneering study, FVDAM was applied for the first time to the numerical study of FRP-reinforced masonry. The results obtained were compared with MSG and FEM, demonstrating the good performance of FVDAM with respect to the methods used in the comparison.

Preliminary studies of homogenization of NFRCM reinforcement and re- inforced masonry

2024-04-29T13:37:30+00:00

Masonry is a heterogeneous material formed by the manual and individual arrangement of units con-nected by joints, being one of the first construction materials, and that can have a partition or structural function.

Despite apparently being a simple material, masonry is a composite material with a complex characterization. For various reasons, masonry often needs some type of reinforcement. Currently, one of the most used materials as reinforcement are the composites known as FRP (fiber reinforced polymer), which consist of fibers (usually car-bon, glass, or aramid) embedded in a polymer matrix (epoxy resin, for example). This type of reinforcement is already well characterized in the literature. However, FRPs have some disadvantages, such as high cost, use of synthetic materials, and in the case of masonry, adhesion problems between the reinforcement and the substrate.
Recently, fabric reinforced cementitious matrix (FRCM) with natural fibers (NFRCM) have been studied as an alternative to FRPs. There are already works that show the potential of using NFRCM as structural reinforcement, where Brazil appears in a prominent position as one of the largest producers of natural fibers in the world, as is the case of sisal and pineapple leaf fiber. For the numerical characterization of these and other composite materials, the Finite Element Method (FEM) is commonly used. In the present work, an alternative numerical technique is used: Mechanics of Structure Genome (MSG), which has been successfully employed in the homogenization of unreinforced and FRP-reinforced masonry. Thus, this work deals with a preliminary numerical study for the characterization of NFRCMs and masonry reinforced with this type of reinforcement.

Failure criteria characterization of orthotropic beams under combined loads for stiffness and strength assessment

2024-04-29T00:33:54+00:00

Composites are no longer promising materials in the industry and have already become a reality in several applications. Their valuable properties such as high strength/weight ratio, durability, and corrosion resistance make them suitable for a vast range of applications. Looking for composites manufacturing, pultrusion is a technique that can produce closed and open-section profiles with a broad range of fiber orientation distribution throughout different areas of the cross-section. The process involves pulling reinforcement fibers through guides, immersing them in resin material, and placing them in a heated chamber to cure, all in a continuous process.
Various applications, including bridge construction, marine construction, transportation, and energy systems, have adopted these techniques. Typically, structural components can be simplified into beam-like components. These components can be exposed to different loading conditions in each application, usually in a combination of torsion, flexure, and traction, which have varying contributions to the total load. In this situation, creating new composite parts can be a difficult and time-consuming task because of the many variables involved. To address this issue, a previous investigation of this research focused on using the constant cross-section of extruded parts to analyse their free vibrational modes and frequencies. This analysis provided information on the stiffness distribution. However, this information alone does not provide all the necessary collection of data to draw robust conclusions. In this
sense, this work aims to investigate structures under combined loads in attempt to extract information about their static behavior. Along with this information a static analysis is also employed to generate failure curves, which are collections of points that characterizes the resistance of each cross section studied under different load contributions of bending and torsion. Thus, stiffness and resistance of different types of cross-sections, with multiple fiber angle distributions, can give valuable insights to the designer.

Textile Modeling with Beams and Contact: A Biaxial Tension Study

2024-04-29T00:41:46+00:00

The mechanical response of textile composite materials depends substantially on the configuration of fibers that compose a given textile material pattern. The fibers’ configuration is, however, difficult to be predicted due to several factors such as their large deformability and nonlinear mechanical response. The large deformability of textiles results from the characteristics of these materials, in which the axial stiffness of yarns is predominant. The overall nonlinear response is a complex phenomenon that includes, but is not limited to, complex yarns’ contact interactions. As a possibility to overcome these difficulties, in this work, the textile’s mechanical behavior is modeled with beam elements and contact formulations. A geometrically-exact structural formulation that can handle large displacements and finite rotations is adopted for the beam elements. Moreover, two contact formulations including nonlinear compliance laws are employed. The former contact formulation considers surface-to-surface interaction while the latter uses a beam-to-beam smooth approach. This textile modeling strategy, including both contact formulations, is verified with biaxial tension experimental results. The advantages and disadvantages of each contact formulation when compared to the experimental results are discussed.

Preliminary studies of homogenization of NFRCM reinforcement and reinforced masonry

2024-04-29T00:46:52+00:00

Masonry is a heterogeneous material formed by the manual and individual arrangement of units connected by joints, being one of the first construction materials, and that can have a partition or structural function. Despite apparently being a simple material, masonry is a composite material with a complex characterization. For various reasons, masonry often needs some type of reinforcement. Currently, one of the most used materials as reinforcement are the composites known as FRP (fiber reinforced polymer), which consist of fibers (usually carbon, glass, or aramid) embedded in a polymer matrix (epoxy resin, for example). This type of reinforcement is already well characterized in the literature. However, FRPs have some disadvantages, such as high cost, use of synthetic materials, and in the case of masonry, adhesion problems between the reinforcement and the substrate. Recently, fabric reinforced cementitious matrix (FRCM) with natural fibers (NFRCM) have been studied as an alternative to FRPs. There are already works that show the potential of using NFRCM as structural reinforcement, where Brazil appears in a prominent position as one of the largest producers of natural fibers in the world, as is the case of sisal and pineapple leaf fiber. For the numerical characterization of these and other composite materials, the Finite Element Method (FEM) is commonly used. In the present work, an alternative numerical technique
is used: Mechanics of Structure Genome (MSG), which has been successfully employed in the homogenization of unreinforced and FRP-reinforced masonry. Thus, this work deals with a preliminary numerical study for the characterization of NFRCMs and masonry reinforced with this type of reinforcement.

Computational modelling of the crushing behaviour of pultruded glass-fibre reinforced polymer stub columns

2024-04-29T00:52:00+00:00

The popularity of pultruded glass-fibre reinforced polymer (pGFRP) profiles in construction stems from their lightness, strength, and durability. However, gaps remain in understanding their mechanics, notably the "true" material crushing failure. Current methodologies to estimate the compressive resistance of pGFRP profiles rely on small-scale tests on coupons, but there is evidence that the full-section compressive strength diverges considerably from that estimated from laminate testing. This study addresses that gap, investigating the crushing behaviour of pGFRP I-section profiles. To that end, computational models were developed, considering second-order effects due to imperfections and displacements. The model includes Gonilha’s damage initiation and progression criteria and also end surface irregularities. The study investigates the amplification of the end surface imperfection compared to a perfect flat end surface, providing insights into stress and deformations resulting from those geometrical defects, envisioning the enhancement of design guidelines for safer and more reliable pGFRP structures.

Multiscale homogenization model for wood and the variables influence over the mechanical properties

2024-04-29T00:58:49+00:00

Wood has great potential as a structural material with excellent strength, lightweight, thermal insulation, and acoustical properties. However, its hierarchical nature and complexity represent a challenge in wood structure’s design and manufacture. Homogenization can be a helpful tool for understanding wood behavior, encouraging wood usage as a structural material for new applications. The homogenization method calculates the effective properties of a material with many heterogeneities, represented as a base cell that repeats itself over the continuum. This base cell is called Representative Element volume (RVE), a volume with all the information necessary to describe the geometry of the different phases and the local material properties. This work uses a displacement- based approach with Finite Element Method (FEM) to calculate six boundary conditions applied over the RVE, where each boundary condition relates to a different stiffness matrix component. The result is a homogenized material at the macroscale, considering the mechanical properties of each phase and its distribution over the RVE. This work identifies the most important variables for each scale and discusses its influence over the effective properties. The homogenization method allows for a better understanding of the different variables that influence the mechanical properties of wood at each scale.