Hybrid BEM for the early stage of unsteady transport process

This paper presents a new approach for solving the early stage of 3D time-dependent transport problems in non-homogeneous fractured porous media in which the initial distribution of concentration presents discontinuous jump at the interface of two regions of transport properties differing in several orders of magnitude. The goal of this formulation is to overcome the problems of different scales and apparent large flux during early time by combining the 3D dual reciprocity boundary element method and a semi-analytical solution of the time-dependent advection–diffusion equation, employing a two-level finite difference time integration scheme. Theoretical background, validation results and practical applications for the advection–diffusion equation in fractured and continuous porous media are reported. The results show advantages for relatively large-scale models and complex geometries. Copyright q 2006 John Wiley & Sons, Ltd.