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

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

**Yang par
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*SFA, Inc., 1401 McCormick Dr., Landover, MD 20785
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**Andrew N. Norris
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*Rutgers Univ., Piscataway, NJ 08855-0909
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**Luise S. Couchman
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*Naval Res. Lab., Washington, DC 20375-5000
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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.]