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.