UMT Introduction

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 heterogeneous platforms.

The code is primarily written in Fortran 2003 with some C++ and Cuda.

Building

UMT uses the CMake build system. A MPI compiler is required.

More information on building UMT can be found in BUILDING.md

Third party libraries

UMT depends on several libraries, some of them optionally. See the DEPENDENCIES.md file for more information.

Test problems

UMT includes an unstructured mesh 3d test problem using a MFEM mesh This mesh can be refined using MFEM at run time to provide larger problems.

To run this problem:

Build UMT. This will produce a test_driver and makeUnstructuredBox executable.
Run the makeUnstructuredBox to produce the 3d test mesh.

srun -n1 /path/to/install/bin/makeUnstructuredBox

Run the test driver. In the below example the problem will run for 10 cycles and the mesh will be refined. Run 'test_driver -h' for more info on the arguments.

srun -n2 path/to/install/bin/test_driver -i ./unstructBox3D.mesh -c 10 -r 1 -R 6

References

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
Nowak, P. "Deterministic Methods for Radiation Transport: Lessons Learned and Future Directions." United States: N. p., 2004. https://www.osti.gov/servlets/purl/15014024
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.
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
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
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
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
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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