AN ADAPTING FINITE ELEMENT MODEL FOR UNSATURATED POROUS MEDIA

A TWO-DIMENSIONAL NUMERICAL MODEL BASED ON A HYBRID FINITE ELEMENT METHOD WITH MESH ADAPTATION IS PROPOSED TO CALCULATE GROUNDWATER FLOW AND POLLUTANT TRANSPORT IN UNSATURATED POROUS MEDIA. THE ALGORITHM IS MODIFIED TO ENHANCE COMPUTATIONAL SPEED AND STORAGE, AND INCORPORATES PETROV-GALERKIN WEIGHTING FOR THE ADVECTION TERMS. NONLINEARITIES ASSOCIATED WITH UNSATURATED SOIL PROPERTIES, ATMOSPHERIC BOUNDARY CONDITIONS, AND PLANT UPTAKE ARE HANDLED IN THE SOLUTION ALGORITHM. BY UTILIZING UNSTRUCTURED MESH ADAPTATION, THE TRANSPORT OF GROUNDWATER AND SPECIES CONCENTRATION CAN BE ACCURATELY CALCULATED, AND THE LOCATION OF STEEP CONCENTRATION FRONTS PRECISELY PREDICTED. CONVENTIONAL FINITE DIFFERENCE AND FINITE ELEMENT METHODS REQUIRE GLOBALLY FINE MESHES, SIGNIFICANT STORAGE, AND EXCESSIVE COMPUTER TIME WHEN MODELING FLOW IN UNSATURATED MEDIA. ALTHOUGH THE ALGORITHM CAN BE RUN ON ENHANCED PCS OR WORKSTATION CLASS COMPUTERS, PORTING OF THE PROPOSED MODEL TO PARALLEL PROCESSING COMPUTERS APPEARS PARTICULARLY ATTRACTIVE.