NUMERICAL MODELING OF TRANSIENT CONTAMINANT MIGRATION PROBLEMS IN INFINITE POROUS FRACTURED MEDIA USING FINITE INFINITE ELEMENT TECHNIQUE .1. THEORY

The leakage effect in porous fissured media has been considered in a g eneral sense by introducing a new expression of the leakage term in th is paper. The double porosity concept is employed and the related expr essions are formulated using the upwind finite element approach. Consi dering the infinite extension of the problem domain, a mapped transien t infinite element has been presented to simulate the far field of the infinite medium. Since the mass transfer function of the present mapp ed transient infinite element is dependent on both space and time vari ables, the mechanism of transient contaminant migration problems in in finite porous fractured media can be rigorously simulated because the property matrices of the element are evaluated at any time of interest . By comparing the current numerical results with the analytical ones, the accuracy, correctness and effectiveness of the present method hav e been established. Three different time discretization schemes were e xamined and it was found that either the central difference or the bac kward difference approximation is suitable for the upwind finite eleme nt simulation of transient contaminant migration problems.