Coupled finite element and boundary element analysis of 3-dimensional payload effect in launcher payload compartment structures

Predicting the response of a spacecraft in a launcher payload compartment structure for the acoustic excitation during lift-off requires sophisticated analysis tools as well as a high amount of computational effort. This is particularly true if complete 3-dimensional models are used. Such a task was solved in a study under an ESA contract. Complete coupling between infinite external domain with a diffuse acoustic field, fairing structure, cavity and satellite was performed by linking a Finite Element structure-acoustic code (ASKA) with a Boundary Element code (Rayon-3D). For this purpose advanced modal synthesis techniques have been developed by FFA. To evaluated the results special procedures were used which were based on the space-average properties. In this paper the space-averaged response of the coupled system is studied for selected parts of the models. The aspects of the interaction between payload and launcher is discussed and a comparison of diffuse field results between the two models is shown. Finally, the evaluation in terms of modal participation factors of the uncoupled modes is presented for some selected cases. A further objective of the study was to investigate the possibility of applying axisymmetric modelling techniques to geometries which only partly are axisymmetric. Therefore, the results of the 3D FEM-BEM analysis will be compared with those of equivalent axisymmetric models.