ASA 126th Meeting Denver 1993 October 4-8

2aUW3. A sparse boundary-element method for scattering from a rigid body of revolution.

Erik M. Rosen

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

Luise S. Couchman

Naval Res. Lab., Washington, DC 20375

Francis X. Canning

Rockwell Sci. Ctr., Thousand Oaks, CA 91360

A sparse boundary-element method is used to calculate the scattered acoustic field of a rigid body of revolution. The NxN full matrix resulting from the discretization of the Helmholtz integral is transformed to a sparse NxN matrix using the impedance matrix localization (IML) method. When applied to integral equations for wave phenomena, the IML method produces a sparse matrix by partitioning the scatterer into several regions, over which the response is represented by basis functions with directional radiation patterns. The number of important physical interactions is reduced to a small number over each region, leaving a large number of matrix elements with relative magnitudes less than 10[sup -4] which can be approximated by zero. Used in conjunction with existing BEM codes, the IML method reduces the memory and storage requirements from N[sup 2] to approximately 100N, while the solution time is O(N) compared to O(N[sup 3]) for the full untransformed case. The resulting sparse matrix can be approximately inverted leading to a convergent solution in less than five iterations. Results are given for scattering from a hemispherically endcapped cylinder of L/a=110 for ka=1 to ka=17.