Improved accuracy for radiation damping in coupled finite element/equivalent source computations.

Abstract

In coupled structural-acoustic computations, radiation damping is due to the resistive component of the surface pressure created by structural vibrations. Equivalent sources using tripole sources as basis functions can be used to compute the surface pressure forces for exterior radiation problems. This technique is similar to the Burton and Miller method for eliminating numerical difficulties due to interior acoustic resonances in boundary element computations and has been proven to yield unique solutions. However, numerical computations presented here will show that for the specific equivalent source formulation under investigation, tripole sources overpredict the resistive component of the surface impedance, especially in the mid-to-high frequency range. It will also be shown that for frequency domain calculations, an accurate representation for the resistive component of the pressure forces can be derived from an analytical representation for the source radiation resistance. Unfortunately, this technique is not applicable to time domain computations. It is also shown that more accurate results can be obtained by allowing both the simple and dipole source amplitudes to be independent variables and enforcing boundary conditions in both the exterior and interior directions simultaneously to reduce the magnitude of the interior acoustic field.