ASA 125th Meeting Ottawa 1993 May

3aSA12. Time-domain fluid--solid interaction and the proliferation of response frequencies.

Janet B. Jones-Oliveira

LLNL, L-84, P.O. Box 808, Livermore, CA 94551

Leo P. Harten

Paradigm Assoc., Inc., Cambridge, MA 02138

Exact modal solutions for the shell displacements and fluid pressure field resulting from the transient loading of a submerged, spherical shell are well-known [H. Huang, J. Acoust. Soc. Am. 45, 661--670 (1969)]. Comparisons of the shell deformation time histories with experimental data have been published previously [J. B. Jones-Oliveira and P. J. Wender, 55th Shock & Vib. Bull., Suppl. 3, 59--76 (1986)]. Herein, the analysis of the unloaded versus fluid-loaded frequencies reveals the effect of the fluid on the structual response to be more complex than simple damping and/or added mass. The fluid introduces a proliferation of frequencies in the structural response which is independent of the loading. The additional frequencies, which are introduced as a function of the expansion mode number via the fluid coupling, are associated with additional roots of an ever increasing higher-order system. The relative influence of the low, intermediate, and high frequencies are investigated. It is shown that while the proliferant frequencies are strongly damped and contribute little to the late time behavior in the far field, they can dominate the early time behavior. [This work was performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.]