ASA 125th Meeting Ottawa 1993 May

5aSA2. Scattering from a thin spherical shell: Higher-order Lamb waves.

Gary Steven Sammelmann

Coastal Syst. Station, Dahlgren Div., NSWC, Code 130B, Panama City, FL 32407-5000

Roger H. Hackman

Lockheed, Res. & Develop. Div., Palo Alto, CA 94304

M. F. Werby

NRL Stennis Space Center, Stennis, MS

The acoustic scattering from thin spherical shells is marked by the existence of the thickness quasiresonance in the high-frequency regime. This quasiresonance is due to the existence of a region of negative group velocity surrounding the first symmetric Lamb wave. This article presents results on the existence of higher-order quasiresonancelike phenomena, and it considers the effects of Poisson's ratio on the quasiresonance. Pole trajectories in the complex ka plane are exhibited for the first dozen modes on a spherical shell. This analysis reveals the existence of regions of negative group velocity surrounding higher-order Lamb waves. A time domain representation of the contributions of higher-order Lamb waves to the scattered field is presented. This analysis reveals the early time arrival nature of the thickness quasiresonance as reconstructed from the poles in the complex ka plane.