ASA 124th Meeting New Orleans 1992 October

3aSA12. The effect of substructures on the acoustic radiation from axisymmetric shells of finite length.

J. Bjarnason

T. Igusa

J. D. Achenbach

Robert R. McCormick School of Eng. and Appl. Sci., Dept. of Civil Eng., Northwestern Univ., Evanston, IL 60208-3109

A modal-based method is developed to analyze the acoustic radiation of shells of finite length with internal substructures subjected to time-harmonic loads. In this method, variational analysis is used to solve for the shell surface velocity and pressure, and Lagrange multipliers are used to determine the substructure motion. To gain insight into the physical characteristics of the fluid/shell/substructure system, a singularity decomposition is introduced. This decomposition is based on the response singularities of the system in complex wave-number space that are closest to the real axis. It is then shown how the decomposition leads to a frequency window method to reduce computational effort. The method is demonstrated for a cylindrical shell with hemispherical endcaps and an internal circular panel. The effects of the substructure are illustrated by comparing the response of the shell/substructure system with corresponding quantities for an empty shell. [Work supported by ONR.]