ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

4pPAb1. Geometrical theory of acoustic scattering by thin elastic shells.

Jin-Meng Ho

SFA, Inc., 1401 McCormick Dr., Landover, MD 20785

Naval Res. Lab., Washington, DC 20375

The sound field scattered by a smooth thin elastic shell immersed in fluid arises largely from specular reflection and acoustic--membrane coupling, unless both source and observer are located near or on the shell. These two contributions have been found to be well described by ray fields for canonical shells in the mid-frequency regime, and hence may be generalized by the principle of localization to accommodate more general geometries. By examining the excitation, propagation, and radiation processes of the supersonic membrane waves on the shell, this paper defines the excitation and radiation coefficients associated with these shell-guided leaky waves as well as the divergence coefficients of the ray tubes characterizing the variation of the wave amplitudes. It extends the concepts of Keller and Karal's geometrical theory for surface waves [J. B. Keller and F. C. Karal, Jr., J. Appl. Phys. 31, 1039--1046 (1960)]. The explicit evaluation of these coefficients, and therefore the leaky fields, is demonstrated for two classes of shells---cylindrical shells of arbitrary cross section and shells of revolution---based on the knowledge of cylindrical and spherical shell prototypes and differential geometry. The reflected waves are more straightforward and the related coefficients are readily determined. [Work supported by ONR.]