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Walkabout Version 1.0 (LA-CC-11-033) performs random walk particle tracking simulations of solute transport based on groundwater flow solutions that use fully unstructured control volume grids. Walkabout 1.0 is designed to work within the FEHM (Zyvoloski, 2007) code system, and accepts groundwater flow solutions from FEHM and computational mesh descriptions from LaGrit (Los Alamos Grid Toolbox,
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.

Walkabout Documentation

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.

  "User Manual for Walkabout Version 1.0 (PDF) "

Walkabout Distribution

Executable files for Walkabout Version 1.2 are available for the Apple Snow Leopard operating system and for 64bit versions of the Linux operating system.
Contact Scott Painter, spainter@lanl.gov

• Version 1.2 (November 2011)

"Walkabout Release Notice (PDF)"

Includes a slightly modified algorithm that eliminated a problem with numerical roundoff that caused the code to enter an infinite loop on rare occasions when searching for the computational cell containing the current particle.

Includes a new time step control algorithm that eliminates spurious steps in situations of a very large contrast in velocity.

Copyright 2011 Software titled "Walkabout Version 1.0beta" has been assigned LA-CC-11-033. The software is unclassified and does not contain Unclassified Controlled Nuclear Information (UCNI). You have indicated that the software will not be made publicly available; thus, the software falls under export control regulations. We have made an in-house determination that this software is controlled by the Department of Commerce under the Export Control Classification Number (ECCN) of EAR99. This determination establishes the requirements for exporting the software (including providing the source code to a foreign national in the United States). Any export of the software must be coordinated with the Customs Team in ASM-PM. Information on this process may be found at http://supply.lanl.gov/property/customs/default.shtml

Any distribution of the software outside the Laboratory should be in accordance with LANL's Industrial Business Development's Intellectual Property Management (IPM) procedures, which may be found at http://www.lanl.gov/source/orgs/tt/intellectual_prop/software.shtml

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