Vibro-acoustic analysis of a satellite reflector antenna using FEM

University essay from Umeå universitet/Institutionen för fysik

Abstract:

The acoustic environment generated during launch is the most demanding structural load case for large, lightweight satellite reflector antennas. The reflector is exposed to extremely high sound pressure levels originating from the structural excitation of the rocket engines and exterior air flow turbulence. This thesis aims to predict the structural responses in the reflector due to the acoustic pressure load with a model based on Finite Element Modelling (FEM). The FE-model is validated against a previously performed Boundary Element Method (BEM) analysis. An approach called Split Loading together with a combination of BEM and FEM will be utilized to handle the surrounding air mass and the applied sound pressures. The idea of Split Loading is to divide the structure into several patches and apply a unit pressure load to each patch separately. In the last step the unit pressure is scaled and correlated by a power spectral density calculated from the acoustic pressures. Split Loading will be implemented in software packages MSC.NASTRAN/PATRAN. The model developed in this thesis handles both the added mass of the surrounding air and the sound pressure applied to the reflector. The model can qualitatively well reproduce the results of the BEM-analysis and the test data. However, the model tends to overestimate responses at low frequencies and underestimate them at high frequencies. The end results is that the model becomes too conservative at low frequencies to be used without further development.

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