Walkabout

Designed to work within the FEHM code system and accept groundwater flow solutions from FEHM and computational mesh descriptions from LaGrit

Version 1 performs random walk particle tracking simulations of solute transport based on groundwater flow solutions that use fully unstructured control volume grids

A typical workflow for Walkabout within the FEHM system would use LaGrit to generate unstructured grids. FEHM then provides a discretized representation of the steady-state flow field to Walkabout. Given this discrete solution, Walkabout then reconstructs a groundwater flow field, and performs the random walk particle tracking calculation. Output is provided in a form compatible with the PLUMECALC software. PLUMECALC may be used to efficiently post-process the particle tracking results from Walkabout to add effects of retention/retardation and arbitrary source histories. An option exists to also record particle positions versus time, thus allowing other post-processing codes or visualization systems to be used. 

Walkabout Features and Limitations

• Walkabout works on fully unstructured tetrahedral meshes in three spatial dimensions. Two-dimensional meshes and meshes other than tetrahedral meshes are not supported in Version 1.0.
• A control-volume solution for steady groundwater flow is required. Finite-element solutions are not supported. Transient flow is not supported in Version 1.0.
• All particles are launched at time zero. The PlumeCalc (plumecalc.lanl.gov) software maybe used to postprocess the resulting particle tracks to obtain concentration for an arbitrary source history.
• Particles are moved through the system without decay or retardation. The PlumeCalc (plumecalc.lanl.gov) system may be used to postprocess the particle tracks to obtain concentration with decay and matrix diffusion or other retardation/retention processes.
• The Burnett and Frind (1987) model for dispersion coefficient is presumed.
• Full heterogeneity in porosity, liquid density, liquid saturation index, and dispersivity is supported.

This User Manual summarizes the technical basis for the Walkabout code, describes the input and output formats, documents verification testing, and provides example test cases that exercise the full range of capabilities.

Walkabout LANL LA-CC-11-033, Copyright No. C11063

Copyright (c) 2016. Triad National Security, LLC. All rights reserved. This program was produced under U.S. Government contract 89233218CNA000001 for Los Alamos National Laboratory (LANL), which is operated by Triad National Security, LLC  for the U.S. Department of Energy/National Nuclear Security Administration. All rights in the program are reserved by Triad National Security, LLC, and the U.S. Department of Energy/National Nuclear Security Administration. The Government is granted for itself and others acting on its behalf a nonexclusive, paid-up, irrevocable worldwide license in this material to reproduce, prepare derivative works, distribute copies to the public, perform publicly and display publicly, and to permit others to do so. If software is modified to produce derivative works, such modified software should be clearly marked, so as not to confuse it with the version available from LANL.

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