Elmer Parallel Demo input files (elmer_parallel_demo)

Elmer demo to do parallel runs (input files for YouTube video). Mind, that the numerical setup is incorrect in the sense that the Navier-Stokes equation is not resolving the non-linearity of the advection term. You can change that (but needs longer runtimes) by setting the Nonlinear System Max Iterations to a value large enough for the system to converge on that level (e.g., 50). All input files are provided without any warranty.

Prerequisites

You need a big enough computer (min 6GB) with Gmsh and Elmer installed, the latter with both, OpenMP and MPI enabled. Recommended: ParaView for post processing

Instructions

First create the serial mesh-file using Gmsh and ElmerGrid

$ gmsh -3 elmer_flow.geo && ElmerGrid 14 2 elmer_flow.msh -autoclean

Then try running the serial run (NB: run needs about 6 GB RAM)

$ ElmerSolver elmer_flow_gcr.sif

In order to partition the mesh into N-partitions (replace N with the number of available CPU cores)

$ ElmerGrid 2 2 elmer_flow -partdual -metiskway N

To run the previous case in parallel using MPI, launch with (replace N with the number of available CPU cores)

$ mpirun -np N ElmerSolver elmer_flow_gcr.sif

To run with OMP multi-threading instead on serial mesh (replace N with the number of available CPU cores)

$ OMP_NUM_THREAD=N ElmerSolver elmer_flow_gcr.sif

Further things to try

elmer_flow_mumps.sif contains a setup solving with MUMPS (needs to be included in Elmer installation), a parallel direct solver. elmer_flow_BPC.sif is a setup that utilizes the block pre-conditioner (BPC) for solution in parallel, using GCR as the outer iteration solver. If you have a special Elmer version including AMGX compiled (naturally, needs a NVIDIA GPU in your computer), you may try elmer_flow_amgx.sif