UMT (Unstructured Mesh Transport) is an LLNL ASC proxy application (mini-app) that solves a thermal radiative transport equation using discrete ordinates (Sn). It utilizes an upstream corner balance method to compute the solution to the Boltzmann transport equation on unstructured spatial grids.
This class of problems is characterized by tens of thousands of unknowns per zone and upwards of millions of zones, thus requiring large, scalable, parallel computing platforms with tens of processors per node.
To achieve scalability, the application exploits both spatial decomposition using message passing between nodes and a threading algorithm across angles and energy groups across processors within the node. More recent versions of UMT are also capable of utilizing both CPUs and GPUs on heterogenous platforms.
The code is primarily written in Fortran 2003 with some C++ and Cuda.
UMT uses the CMake build system. A MPI compiler is required.
More information on building UMT can be found in BUILDING.md
UMT depends on several libraries, some of them optionally. See the DEPENDENCIES.md file for more information.
The test driver also supports reading in MFEM meshes. These meshes can be refined using MFEM at runtime to provide larger problems.
A MFEM NURBs 2D mesh is provided here modeling a bent/crooked pipe problem. This mesh was produced using the LLNL mesh generator code PMesh.
Building UMT with MFEM mesh support requires several additional libraries and CMake options. For assistance on this build configuration, contact a team member on github.
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Nemanic, M K, and Nowak, P. "Radiation transport calculations on unstructured grids using a spatially decomposed and threaded algorithm". United States: N. p., 1999. https://www.osti.gov/servlets/purl/14136
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Nowak, P. "Deterministic Methods for Radiation Transport: Lessons Learned and Future Directions." United States: N. p., 2004. https://www.osti.gov/servlets/purl/15014024
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Howell, Louis H., Gunney, Brian T., and Bhatele, Abhinav. "Characterization of Proxy Application Performance on Advanced Architectures. UMT2013, MCB, AMG2013." United States: N. p., 2015. Web. doi:10.2172/1224409.
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Maginot, P G, Nowak, P F, and Adams, M L. "A Review of the Upstream Corner Balance Spatial Discretization". United States: N. p., 2017, https://www.osti.gov/servlets/purl/1357379
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Thomas A. Brunner, Terry S. Haut & Paul F. Nowak "Nonlinear Elimination Applied to Radiation Diffusion", Nuclear Science and Engineering, 2020, 194:11, 939-951, DOI: 10.1080/00295639.2020.1747262
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P. Nowak, A. Black, S. Rennich, D. Appelhans, R. Chen, T. Haut, P. Maginot, T. Bailey, P. Brown, A. Kunen, J. Loffeld, B. Tagani, "Porting Teton, a Discrete-Ordinates Thermal Radiative Transfer Code, to Sierra", Proceedings, M&C 2019, Portland, OR, August 25-29, 2019, Pages 2128-2137
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Steven J. Plimpton, Bruce Hendrickson, Shawn P. Burns, William McLendon III & Lawrence Rauchwerger (2005) "Parallel Sn Sweeps on Unstructured Grids: Algorithms for Prioritization, Grid Partitioning, and Cycle Detection", Nuclear Science and Engineering, 150:3, 267-283, DOI: 10.13182/NSE150-267
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Nowak, P. "Unstructured-Mesh Deterministic Radiation Transport. Single Physics Package Code". Computer software. Vers. 01. USDOE. 1 May. 2013. LLNL-CODE-638452, https://github.com/LLNL/UMT
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