Topology optimization of vortex-induced vibrations using a geometry projection approach

Resumo

Fluid-structure interactions are present in many engineering applications, occasionally as a desired effect for energy haversting and, more often, as a non-desired effect, for structures that are subjected to fluid flow. Within this field there are several different phenomena, due to the type of structure, type of flow and dynamics involved. One of the most studied topics is vortex-induced vibrations, in which the natural frequency of a structure under crossflow is similar to the natural frequency of vortex shedding, which excites the structure due to resonance and leads to instability. One of the most established methods for controlling this instability is with passive controls, where the presence of strakes or control rods changes the flow characteristics and makes the system stable. These methods have been extensively studied experimentally and computationally, although there is still a lack of gradient-based optimizations of passive control parameters that deal with both solid and fluid equations coupled. Therefore, the present work proposes a topology optimization study of passive control systems for vortex-induced vibrations using the geometry projection method, considering vortex-induced vibrations for straight and bent structures, where the latter approaches the instability as rotation. The optimization algorithm combines the numerical simulations performed in Nektar++ with a Python script that performs the geometry projection and the optimization with SciPy. The sensitivities are determined in a continuum formulation. Preliminary results for a fixed set of Reynolds and reduced velocities show that for the vertical analysis,the optimized points lies within the experimental studies for control rods, which validates the methodology. For both transverse and rotational analysis, considering a wider range of Reynolds, reduced velocities and mass ratios, it is observed that the optimized parameters vary greatly, which indicates that these points are closely related to the fluid and structural parameters.