LOCAL TENSOR RADIATION CONDITIONS FOR ELASTIC WAVES

A local boundary condition is formulated, representing radiation of elastic waves from an arbitrary point source. The boundary condition takes the form of a tensor relation between the stress at a point on an arbitrarily oriented section and the velocity and displacement vectors at the point. The tensor relation generalizes the traditional normal incidence impedance condition by accounting for the angle between wave propagation and the surface normal and by including a generalized stiffness term due to spreading of the waves. The effectiveness of the local tensor radiation condition is demonstrated by detailed finite element time and frequency analysis of a concentrated force in infinite three-dimensional space, and by a time analysis of a pulse load in a two-dimensional underground gallery.