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

4pPAb3. Acoustic scattering from fluid-loaded elastic shells: A Gaussian beam approach.

Yang par

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

Andrew N. Norris

Rutgers Univ., Piscataway, NJ 08855-0909

Luise S. Couchman

Naval Res. Lab., Washington, DC 20375-5000

Acoustic scattering problems from fluid-loaded elastic shells are usually formulated in terms of surface Helmholtz integrals. The numerical evaluation of these integrals is very time consuming, especially at high frequencies. A new method is proposed here for the computation of the scattered fields. The basic idea is to use ray methods to first represent the supersonic surface fields. The surface integral is then represented as a summation of individual integrals along Gaussian beams. Each integral is approximated as a line integral along the center ray of the beam, and finally, the acoustic far field is obtained by asymptotically evaluating each line integral at its stationary points. The asymptotic expression for the membrane wave part is uniform and valid at all the observation angles. The difficulties of dealing with caustics and infinite sets of rays do not arise in the present formalism. This approach allows the acoustic response to be easily calculated without resorting to two-point ray tracing or surface Helmholtz integrals. It is therefore numerically fast. The numerical results agree well with the available exact solution and the pure ray results on a spherical shell for k[sub f]a>10, where k[sub f] is the fluid wave number. [Work supported by ONR and NRL.]