DOUBLY ASYMPTOTIC APPROXIMATIONS FOR TRANSIENT POROELASTODYNAMICS

A doubly asymptotic approximation (DAA) is an approximate temporal imp edance relation at the boundary of a continuous medium. Here, first-an d second-order DAAs are formulated for an infinite external poroelasti c medium described by Blot's equations. As with their acoustic, elasto dynamic, and electromagnetic predecessors, the poroelastodynamic DAAs approach exactness in both the early-time (high-frequency) and late-ti me (low-frequency) limits, effecting a smooth transition between. They also lend themselves to straightforward boundary-element discretizati on, producing matrix ordinary differential equations in time that are readily solved by numerical integration. An initial examination of por oelastodynamic DAA accuracy is presented for two problems with spheric al symmetry. (C) 1997 Acoustical Society of America.