Efficient absorbing boundary conditions for Biot's equations in time-harmonic finite element applications.

Absorbing boundary conditions for two phase media previously presented by Zerfa and Loret [Earthquake Eng. Struct. Dyn. 33, 89-110 (2004)] have been improved by considering additionally absorbing waves with auxiliary angles of incidence. These angles are defined at each point on the boundaries, so one can easily implement tensor impedances as analogous to those defined by Krenk and Kirkegaard for isotropic, nonporous media [J. Sound Vib. 247, 875-896 (2001)]. The boundary conditions have been tested and validated in two-dimensional frequency domain simulations.