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

5aUW12. High-frequency scattering from a spherical shell: Thickness quasiresonance.

Gary Steven Sammelmann

Code 130B, Coastal Systems Sta., Panama City, FL 32407

Steven Kargl

Univ. of Washington, Seattle, WA

Douglas G. Todoroff

Coastal Systems Sta., Panama City, FL 32407

Theoretical calculations have shown that the high-frequency scattering from a thin spherical shell is dominated by a single peak that occurs near the opening of the first symmetric Lamb wave. This peak is associated with a region of strong negative group velocity surrounding the opening of the first symmetric Lamb wave. Experimental verification of the existence of the thickness quasiresonance on a 2% stainless steel shell is given. In addition an analysis of the thickness quasiresonance in the complex-ka plane is presented for shells of different material parameters. It is shown that the thickness quasiresonance bifurcates as a function of Poisson's ratio in such a manner that the region of negative group velocity remains close to the opening of the first symmetric Lamb wave. [Work supported by ONR.]