ASA 124th Meeting New Orleans 1992 October

3aSA7. Numerical studies on the effectiveness of the CHIEF method in the medium frequency range.

Michael J. Butler

John A. Wilder

Dept. 452 M.S. J-47, Gen. Dynam./Elec. Boat Div., 75 Eastern Point Rd., Groton, CT 06340

It is well known that the boundary element method implementation of the Helmholtz integral equation produces nonunique solutions at certain frequencies in the medium frequency range. The spurious solutions can be eliminated by a straightforward application of the interior Helmholtz equation, a procedure often referred to as the combined Helmholtz integral equation formulation (CHIEF). This method has been in existence for 21/2 decades, and has seen increasing use over the years. However, its application has been limited, and speculation concerning its effectiveness persists. This study reports numerical investigations that have been conducted to further verify implementation of the technique, and to develop practical experience regarding its use. Radiation and scattering from finite cylinders and spheres have been examined up to ka=20. Automated selection of several interior point patterns has provided a measure of the method's robustness, and comparisons with closed-form solutions serve to validate the technique.