A flexible and efficient higher order FE-BI-MLFMA for scattering by a large body with deep cavities

The hybrid finite element-boundary integral-multilevel fast multipole algorithm (FE-BI-MLFMA) is applied to solve the challenge problem of scattering by a large body with deep cavities in this paper. The hierarchical higher order curvilinear vector finite element (HCVFE) is employed to reduce the numerical dispersion error in the FEM and to efficiently model the geometry of the cavity. The coupling approaches are investigated at the interface between the FE region and the BI region for handling the problem of the different order basis functions and meshes used in the FE and BI region. The problems encountered with the previous decomposition algorithm of FE-BI-MLFMA are pointed out and analyzed in this paper. A special algorithm of FE-BI-MLFMA is designed based on the distinct geometry characteristics of deep cavity. Numerical results are presented to demonstrate the accuracy, efficiency and flexibility of the higher order FE-BI-MLFMA for scattering by a large body with big and deep cavities.