daptive finite - element modeling using unstructured grids : he 2

Existing numerical modeling techniques commonly used for electromagnetic EM exploration are bound by the limitations of approximating complex structures using a rectangular grid. A more flexible tool is the adaptive finite-element FE method using unstructured grids. Composed of irregular triangles, an unstructured grid can readily conform to complicated structural boundaries. To ensure numerical accuracy, adaptive refinement using an a posteriori error estimator is performed iteratively to refine the grid where solution accuracy is insufficient. Two recently developed asymptotically exact a posteriori error estimators are based on a superconvergent gradient recovery operator. The first relies solely on the normed difference between the recovered gradients and the piecewise constant FE gradients and is effective for lowering the global error in the FE solution. For many problems, an accurate solution is required only in a few discrete