HR: 0800h
AN: H11D-1286    [Abstracts]
TI: A Particle Tracking Method on Partially Structured Grids for Modeling Solute Transport in Ground Water
AU: * Kelkar, S M
EM: kelkar@lanl.gov
AF: Los Alamos National Laboratory, LANL, EES-6, MS T003 , Los Alamos, NM 87545 United States
AU: Dash, Z V
EM: zvd@lanl.gov
AF: Los Alamos National Laboratory, LANL, EES-6, MS T003 , Los Alamos, NM 87545 United States
AU: Gable, C W
EM: gable@lanl.gov
AF: Los Alamos National Laboratory, LANL, EES-6, MS T003 , Los Alamos, NM 87545 United States
AU: Andrew, W V
EM: awolf@lanl.gov
AF: Los Alamos National Laboratory, LANL, EES-6, MS T003 , Los Alamos, NM 87545 United States
AB: With increasing accuracy, groundwater transport models seek to represent large, complex three-dimensional geological domains while resolving finer scale geometric features such as faults, pinchouts, and hydrostratigraphic units with varying properties. These models have to be efficient for repeated use in performance assessment calculations, often employing Monte Carlo techniques. Particle tracking is a popular method of computing solute transport offering many advantages over finite-difference approaches, especially for fractured porous media. One particularly efficient implementation of this method uses a semi-analytical approach, permitting time steps to be large. However, a serious limitation of this method is that it requires finite difference type regular, orthogonal grids, with brick-shaped control volumes. The combined requirements of geometrical complexity and computational efficiency make it attractive to use grids with local refinement using non-orthogonal, non-uniform spacing. For such problems, Octahedral Mesh Refinement (OMR) allows for the efficient placement of high grid resolution where needed while maintaining relatively coarse spacing elsewhere. However, the existing particle tracking models place severe restrictions on use of such grids to model solute transport. Therefore, we have developed an extension of the semi-analytical method of particle tracking for use on OMR grids. Each of the non-orthogonal control volumes is approximated locally by an orthogonal brick shape. Velocities are interpolated onto the approximated volume faces so as to minimize mass balance errors, allowing the use of semi-analytical time integration for computing path lines. This method has been implemented in a finite-element, finite-volume flow and transport code called FEHM, including the capabilities to model three dimensional dispersion, dual-porosity fractured media with multiple matrix diffusion models and linear sorption in fractures as well as the rock. Several verification examples comparing breakthrough curves with semi-analytical analysis, as well as results on uniform grids are presented. Comparison of particle paths obtained using Runge-Kutta integration is presented. Examples are shown of path-lines through complicated 3-dimensional grids incorporating faults with local mesh refinement.
DE: 1805 Computational hydrology
DE: 1832 Groundwater transport
DE: 1847 Modeling
DE: 1849 Numerical approximations and analysis
SC: Hydrology [H]
MN: Fall Meeting 2005