A HYBRID 3-D, TWO-WAY IFD PE MODEL FOR 3-D ACOUSTIC BACKSCATTERING

A hybrid three-dimensional (3-D), two-way sound propagation model (FDHB3D) is developed for solving 3-D backscattering problems. The FDHB3D model is based on a 3-D Radius-Marching Algorithm (RMA) incorporating a 2-D Two-way Coupling Approach (TCA) by means of a N×2-D procedure. Within a radius-independent space, a 3-D wave field is marched in the radial direction using the 3-D RMA. At the vertical boundaries, a 3-D reflected field is obtained by solving a 2-D Vertical Boundary Equation (VBE) using the 2-D TCA combined with a N×2-D procedure. Different approximations for the 3-D square root operator are compared. Errors arising from the azimuth discretization are analyzed. Numerical studies are performed to demonstrate the superior performance of the FDHB3D model, and to preliminarily reveal 3-D backscattering mechanisms. Studies show that the FDHB3D model can partly handle the azimuth coupling. It is also demonstrated that the diffraction mechanism dominates the backscattered field when the azimuth coupling is significant, while, the reflection mechanism dominates the backscattered field when the azimuth coupling is weak. It is concluded that the FDHB3D model may be applicable to solve specific 3-D backscattering problems in which the azimuth coupling is weak.