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    High-order Lagrangian Hydrodynamics Miniapp

                   AMR version

Overview

This directory contains the automatic mesh refinement (AMR) version of Laghos (LAGrangian High-Order Solver), which is currently considered experimental and is NOT the official benchmark version of the miniapp.

For more details about Laghos see the README file in the top-level directory.

The Laghos miniapp is part of the CEED software suite, a collection of software benchmarks, miniapps, libraries and APIs for efficient exascale discretizations based on high-order finite element and spectral element methods. See http://github.com/ceed for more information and source code availability.

The CEED research is supported by the Exascale Computing Project (17-SC-20-SC), a collaborative effort of two U.S. Department of Energy organizations (Office of Science and the National Nuclear Security Administration) responsible for the planning and preparation of a capable exascale ecosystem, including software, applications, hardware, advanced system engineering and early testbed platforms, in support of the nation’s exascale computing imperative.

Differences from the official benchmark version

The AMR version differs from the official benchmark version of Laghos (in the top-level directory) in the following ways:

  1. The -amr parameter turns on dynamic AMR.
  2. The code includes functionality to change the mesh and the hydro operator on the fly.
  3. Parallel partitioning and load balancing is based on MFEM's non-conforming mesh algorithm that partitions a space-filling curve. METIS is not required.

Limitations

  • The current AMR implementation is just a demonstration.
  • Only the Sedov problem is supported, as the refinement/derefinement decisions are very simple and tailored specifically to Sedov.
  • Partial assembly is currently not supported in AMR mode. Also, the hydro operator update is currently not efficient (e.g., the whole mass matrix is reassembled on each mesh change).
  • MFEM currently does not support derefinement interpolation for non-nodal bases. The AMR version therefore does not use BasisType::Positive for the L2 space.

Building

The AMR version can be built following the same instructions as for the top-level directory.

Running

The AMR version only runs with problem 1 (Sedov blast). New parameters are:

  • -amr: turn on AMR mode
  • -rt or --ref-threshold: tweak the refinement threshold
  • -dt or --deref-threshold: tweak the derefinement threshold

One of the sample runs is:

mpirun -np 8 laghos -p 1 -m ../data/cube01_hex.mesh -rs 4 -tf 0.6 -rt 1e-3 -amr

This produces the following plots at steps 900 and 2463:

Verification of Results

To make sure the results are correct, we tabulate reference final iterations (step), time steps (dt) and energies (|e|) for the runs listed below:

  1. mpirun -np 8 laghos -p 1 -m ../data/square01_quad.mesh -rs 4 -tf 0.8 -amr
  2. mpirun -np 8 laghos -p 1 -m ../data/square01_quad.mesh -rs 4 -tf 0.8 -ok 3 -ot 2 -amr
  3. mpirun -np 8 laghos -p 1 -m ../data/cube01_hex.mesh -rs 3 -tf 0.6 -amr
  4. mpirun -np 8 laghos -p 1 -m ../data/cube01_hex.mesh -rs 4 -tf 0.6 -rt 1e-3 -amr
run step dt e
1. 2374 0.000308 90.9397751791
2. 2727 0.000458 168.0063715464
3. 998 0.001262 388.6322346715
4. 2463 0.000113 1703.2772575684

An implementation is considered valid if the final energy values are all within round-off distance from the above reference values.

Contact

You can reach the Laghos team by emailing laghos@llnl.gov or by leaving a comment in the issue tracker.

Copyright

The following copyright applies to each file in the CEED software suite, unless otherwise stated in the file:

Copyright (c) 2017, Lawrence Livermore National Security, LLC. Produced at the Lawrence Livermore National Laboratory. LLNL-CODE-734707. All Rights reserved.

See files LICENSE and NOTICE in the top-level directory for details.