NUMERICAL COMPUTATION OF NOISE TRANSMITTED INSIDE A PAYLOAD FAIRING DUE TO EXTERNAL REVERBERANT FIELD EXCITATION

摘要

In launch vehicle applications one of the important areas during the design phase is to determine the acoustic environment inside the fairing. Traditionally this objective has been achieved by performing testing in a reverberant chamber. The reverberant field is utilized to simulate the launch environment outside the fairing. Acoustic pressure and acceleration measurements are obtained during testing. They serve to identify the acoustic environment inside the fairing and the noise transmitted through the walls of a fairing. In this work, a numerical approach combining the structural finite element and the acoustic boundary element methods is utilized to compute the noise transmitted in the interior of a fairing due to an external reverberant acoustic excitation. Two key issues which are successfully adressed in this work are the ability to have unequal mesh density between the structural finite element and the acoustic boundary element model, and the ability to simulate numerically the reverberant field as excitation for the coupled structural - acoustic analysis. Computations are performed for a composite payload fairing. A finite element model is utilized to compute the modal basis of the composite fairing. This information is imported to the coupled structural - acoustic boundary element analysis to represent the structure. In the coupled computation an external reverberant field is prescribed as excitation. The acoustic response in the interior of the fairing is computed. The numerical results are compared successfully with test data available for the particular design.