A finite element-modal technique for scattering by complex 3-D cavity terminations and code parallelization

The simulation of radar scattering from 3D cavities with complex terminations is an important step towards the characterization of many aircraft structures. The authors describe the FEM-modal method, and the role of the modal scattering matrix for interfacing the FEM and ray/modal fields at a connection boundary in a 3D cavity configuration. The authors discuss implementation issues of the FEM technique including shape functions, application of boundary conditions and truncation of the FEM mesh at the open end through the use of an optimized, fictitious, material absorber. Computational gains from parallelization of the FEM code are emphasized, and the authors discuss a parallel sparse iterative linear system solver. The extension of this parallel solver to fully exploit the geometric symmetry in angularly periodic fan-like terminations (such as a jet engine face) is also addressed. Results are presented which validate the proposed hybrid FEM-modal method and show the utility of an artificial absorber for terminating the FEM mesh.