Abstract:
A multi-dimensional finite element model, known as GWADAPT, was developed to calculate groundwater flow and the subsurface transport of contaminants under saturated and unsaturated conditions. The model employs local mesh adaptation to handle complex problems with a minimal number of nodal points, which increases accuracy, reduces storage requirements, and minimizes computational time. This adaptive mesh algorithm alleviates the burden of mesh generation from the user by refining and unrefining the mesh based on refinement indicators such as concentration gradients. The model uses simple modifications, such as local formulations per time step and reduced integration, to increase computational speed and allow it to run efficiently on PCs and workstations. GWADAPT also includes Petrov-Galerkin weighting to stabilize the advection-dispersion transport equation and a lumped mass approximation to diagonalize the mass matrix. The governing equations for both saturated and unsaturated conditions are cast into integral form using the Galerkin weighted residual technique and solved with an explicit second-order Runge-Kutta method. The research demonstrates the model's effectiveness by simulating a contaminant plume from a leaking deposit in both saturated and unsaturated conditions, with results showing good agreement when compared to another commercial finite element code called FEFLOW. For large-scale problems, a parallel version of GWADAPT was developed for the SGI Origin 2000 parallel computer, showing significant improvements in computing speed.
