### 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.]