A fast multipole accelerated indirect boundary element method for broadband scattering of elastic waves in a fluid-saturated poroelastic domain

A fast multipole accelerated indirect boundary element method is developed to efficiently solve the scattering of broadband waves by inhomogeneity in a fluid-saturated 3D poroelastic space. Based on the single layer potential theory, poroelastic free-space Green's functions of point force and fluid source are distributed on the scatterer surface at fictitious densities to construct the scattered waves. By using the plane wave expansion of 3D potential functions of compressional and shear waves, the multipole expansion and the local expansion coefficients are derived. Numerical results demonstrated that this proposed method can greatly improve the efficiency of traditional indirect boundary element method and reduce the memory requirement for 3D broadband wave scattering problems in an unbounded poroelastic medium. Problems of wave scattering by a spherical cavity, a group of cavities, and a canyon in a semiinfinite poroelastic space are investigated. Several notable scattering characteristics are revealed.