A BOUNDARY ELEMENT PACKAGE CONTAINING APPROXIMATE SOLVERS FOR TREATING HIGH FREQUENCY ACOUSTIC SCATTERING

The target strength of objects submerged in water, located on the sea bottom or partially buried in the sediment can be calculated by means of a boundary element solver. For this reason, a boundary element code with suitable pre-/postprocessor and parallel working solvers is developed. The scattering objects within the transition range between fluid and sediment can be modeled by the preprocessor. It can manage large and complex meshes (more than 100,000 elements) and is able to import mesh-files in different standard formats (e. g. NASTRAN-, ANSYS- or CDB-format) or to generate meshes with closed surfaces. Combined with material parameters, this information is used as a database for the following high frequency scattering calculations. In the high frequency range, the computing time can be reduced drastically by using approximations instead of solving the complete system of BEM equations. For this reason, a so-called plane wave approximation (PWA) has been implemented in the BEM-package for evaluating the scattered sound pressure. As an alternative high-frequency approximation the Kirchhoff approach, in order to compare and validate the results of both high frequency approximations, is also used. The theory of these and additional high frequency approximations for scattering problems based on boundary integral equations is presented in another paper written by the authors [1]. Results will be given for the scattering of plane waves from cylindrical shells located in the free space up to 100 kHz