On the interplay between meshing and discretization in three-dimensional diffusion simulation

The maximum principle is the most important property of solutions to diffus ion equations. Violation of the maximum principle by the applied discretiza tion scheme is the cause for severe numerical instabilities: the emergence of negative concentrations and, in the nonlinear case, the deterioration of the convergence of the Newton iteration. We compare finite volumes (FV) an d finite elements (FE) in three dimensions with respect to the constraints they impose on the mesh to achieve a discrete maximum principle. Distinctiv e mesh examples and simulations are presented to clarify the mutual relatio nship of the resulting constraints: Delaunay meshes guarantee a maximum pri nciple for FV, while the recently introduced dihedral angle criterion is th e natural constraint for FE. By constructing a mesh which fulfills the dihe dral angle criterion but is not Delaunay,ve illustrate the different scope of both criteria, Due to the lack of meshing strategies tuned for the dihed ral angle criterion we argue for the use of FV schemes in three-dimensional diffusion modeling.