Finite Element-Based Dynamic Analysis of a Hybrid Sounding Rocket During Key Flight Stages

Resumo

This work presents a computational structural dynamic analysis of a hybrid sounding rocket developed at University of Brasília (UnB), aiming to investigate the vibrational response of the structure at different stages of launch. The analysis focuses on the region connected to the base of the payload section, an area particularly sensitive to dynamic excitations due to the presence of onboard instruments and critical structural connections. The rocket’s structure was modeled in three dimensions using the finite element method within the ANSYS environment, incorporating geometric details and the actual material properties employed in the prototype.
Three distinct scenarios were simulated, representing different flight stages with significant variations in the remaining propellant mass. This approach seeks to capture the effects of mass variation on the system’s dynamic behavior, particularly regarding the shift in natural frequencies and the amplification of structural responses. The thrust force applied to the models was obtained from experimental data collected during a hybrid rocket motor burn test conducted by the project’s supervising professor at the university’s facilities, ensuring a more realistic representation of external excitation.
The methodology involved the application of modal analysis to identify the vibration modes and their respective frequencies, as well as transient analysis under realistic time-varying loads simulating the thrust profile over time. The acceleration associated solely with the rigid body modes and the acceleration response corresponding to the structure’s elastic frequencies were considered separately. The values of the damping factor was also considered in the analysis, aiming to reproduce a more reliable result. The direct integration of the equations of motion was also performed in ANSYS, using the same configuration as in the modal analysis, allowing for a consistent comparison between methods and the evolution of the structural response over time. The combined use of these techniques provided a robust characterization of the rocket’s dynamic behavior, enabling an assessment of vibrations under different operational conditions, with a focus on structural integrity and the functional performance of the payload. This study contributes to the ongoing effort to strengthen the national scientific and technical foundation dedicated to the development of academic aerospace vehicles.