An improved hybrid absorbing boundary condition for wave equation modeling

A recently developed hybrid absorbing boundary condition (ABC) can significantly suppress artificial boundary reflections by inserting a transition area between the boundary and the inner area. The wavefield in the transition area is computed by linearly weighting the wavefield from one-way wave equation (OWWE) and that from two-way wave equation. This leads to a smooth variation from the computational area to the boundary via the transition area and thus greatly reduces boundary reflections. In this paper, we propose two techniques to further enhance the absorbing effect. First, we widen the boundary from one point to several points. Second, we adopt nonlinear weighting coefficients instead of linear ones. Numerical simulations with 2D acoustic finite-difference modeling, combined with Clayton-Engquist OWWE, demonstrate that the proposed techniques can significantly improve the absorption effect without increasing computational cost. Tests using Higdon OWWE-based ABC suggest that the second technique can greatly enhance the absorption effect. Experiments with frequency-domain finite-difference modeling demonstrate similar improvement in absorption effect.