### ASA 124th Meeting New Orleans 1992 October

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

**J. Bjarnason
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T. Igusa
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J. D. Achenbach
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*Robert R. McCormick School of Eng. and Appl. Sci., Dept. of Civil Eng.,
Northwestern Univ., Evanston, IL 60208-3109
*

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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.]