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

4aPAa4. Implementation of a ray tracing algorithm to calculate the acoustic scattering from fluid loaded, doubly curved shells.

Douglas A. Rebinsky

Andrew N. Norris

Dept. of Mech. and Aerosp. Eng., Rutgers Univ., P.O. Box 909, Piscataway, NJ 08855-0909

Yang par

SFA, Inc., Landover, MD 20785

Ray tracing is used to calculate the acoustical and structural response of smooth, elastic shells of nonseparable shape. The frequency range of interest is below flexural coincidence but still high enough that asymptotic methods are applicable. The structure and development of ray-like solutions on arbitrarily doubly curved shells is reviewed with a discussion of two mechanisms: (1) a ``background'' response determined by the local inertial impedance, and (2) phase matching to longitudinal and shear waves. The background response can be approximated by specular reflection, but the membrane waves require global treatment over the whole structure. After first calculating the coupling curves, which are the closed loci defined by phase matching with the incident wavefield, ``pressure'' rays are then sent out over the shell with each ray and its amplitude evolving according to a ray equation and a transport equation. Illustrative examples of ray paths and ray-tube areas will be presented for ellipsoidal and quasicylindrical shells. The use of the Gaussian beam summation method to describe the wavefields will be discussed. Numerical comparisons are made with the exact results for the canonical geometries, and extensions to nonseparable shapes and discontinuous shells will be shown and discussed. [Work supported by ONR.]