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

## 4aSA8. Targets in nonuniform acoustic environments.

**E. P. McDaid
**

**
D. Gillette
**

**
D. Barach
**

**
**
*Code 787, RDT/&E Div., Naval Command, Control, and Ocean Surveillance
Ctr., San Diego, CA 92152-5000
*

*
*
The capability to numerically model the sound scattered from a target in a
dispersive environment has been developed. The target has been rigorously
coupled to its environment by combining a finite element formulation of the
target shell dynamics with a Helmholtz Integral Equation formulation of fluid
loading and a normal mode formulation of sound propagation. While the
computational cost of obtaining numerical solutions to this problem are
awesome, some simple approximations can result in significant savings. In
particular, neglect of Fresnel diffraction and boundary-induced multiple
scattering permits a particularly simple and tractable reformulation of the
problem. The reported work makes the following contribution to solving the
problem of target-environment interaction: the errors caused by neglecting
Fresnel diffraction terms and multiple scattering are numerically evaluated.
The significance of this contribution is that it will provide guidance as to
when these useful approximations can be applied to speed calculations while
still maintaining satisfactory fidelity.