ASA 127th Meeting M.I.T. 1994 June 6-10

2pSA3. Response of submerged finite-length cylindrical shells with internals to an impulse load.

S.-H. Choi

T. Igusa

J. D. Achenbach

Dept. of Civil Eng., Northwestern Univ., Evanston, IL 60208

A finite-length, submerged cylindrical shell with elastic endcaps containing internal substructures is excited by a short-duration load. A recently developed modal-based analysis method is used to generate the responses on the shell surface and in the near and far fields. The method was developed specifically for analyzing the acoustic effects of substructures in an efficient manner. Nearly all of the computational effort is in determining the impedance relations between the pressure and the velocity along the shell surface. This analysis requires the evaluation of a twofold integral over the shell surface for each pair of pressure and velocity shape functions [Ginsberg et al. (1986)]. Once the impedance relations are determined, the analysis of the radiation problem for a given set of internal substructures and applied loads is solved with relatively little computational effort. The efficiency of the method stems from the fact that the same set of impedance relations can be used for any configuration of internal substructures and applied loads. In addition, the method can be combined with a frequency window method when analyzing responses for a wide range of excitation frequencies. Such analysis is useful when going into the time domain using the fast Fourier transform. The study shows that substructures interact with the in-plane and flexural waves propagating in the shell, causing wave conversion and subsequent radiation into the surrounding fluid. [Work supported by ONR.]