OpenFOAM

OpenFOAM (Open Field Operation And Manipulation) is a open-source C++ toolbox maintained by the OpenFOAM foundation and ESI Group. Although primarily used for CFD (Computational Fluid Dynamics) OpenFOAM can be used in a wide range of fields from solid mechanics to chemistry.

The lack of licence limitations and native parallelisation makes OpenFOAM well suited for a HPC environment. OpenFOAM is an incredibly powerful tool, but does require a moderate degree of computer literacy to use effectively.

OpenFOAM can be loaded using;

module load OpenFOAM
source $FOAM_BASH

Versions

We maintain multiple different versions of OpenFOAM, an up to date list can be found here or by running module show OpenFOAM.

Care should be taken when choosing what version to use as execution may vary, especially between the OFF and ESI branches. The two can be told apart as OFF uses incremental version notation (5.0,6.0, etc), while the ESI uses YY-MM (1706, 1812, etc).

We highly recommend specifying the version in your scripts. e.g. 
module load OpenFOAM/v1812-gimkl-2017a as opposed to just module load OpenFOAM.

Example Script

#!/bin/bash -e
#=================================================#
#title          OpenFoamTest.sl
#description    Run simpleFoam in paralell.
#author         NeSI
#=================================================#
#SBATCH --time			    04:00:00
#SBATCH --job-name		    OF_16CORES
#SBATCH --output		    %x.output   #set output to job name
#SBATCH --ntasks		    16
#SBATCH --mem-per-cpu	            1500        #Standard memory for one cpu (/MB).
#=================================================#

#Working directory always needs to contain 'system', 'constant', and '0' DIR_WORKING="/nesi/nobackup/nesi99999/OpenFOAM/testRun"
#Add this script to start of output
cat ${0}
cd ${DIR_WORKING} module load OpenFOAM/v1712-gimkl-2017a source ${FOAM_BASH} decomposePar #Break domain into pieces for parallel execution. srun simpleFoam -parallel reconstructPar -latestTime #Collect

Filesystem Limitations

OpenFOAM generates a large number of files during run-time. In addition to the I/O load there is also the danger of using up available inodes.

Filesystems in excess of their allocation will cause any job trying to write there to crash.

There are a few ways to mitigate this

  • Use /nesi/nobackup
    The nobackup directory has a significantly higher inode count and no disk space limits.
  • ControlDict Settings
    • WriteInterval
      Using a high write interval reduce number of output files and I/O load.
    • deltaT
      Consider carefully an appropriate time-step, use adjustTimeStep if suitable.
    • purgeWrite
      Not applicable for many jobs, this keeps only the last n steps, e.g. purgeWrite 5 will keep the last 5 time-steps, with the directories being constantly overwritten.
    • runTimeModifiable
      When true, dictionaries will be re-read at the start of every time step. Setting this to false will decrease I/O load.
    • writeFormat
      Setting this to binary as opposed to ascii will decrease disk use and I/O load.
  • Monitor Filesystem 
    The command nn_check_quota should be used to track filesystem usage. There is a delay between making changes to a filesystem and seeing it on nn_check_quota.
    Filesystem         Available      Used     Use%     Inodes     IUsed     IUse%
    home_cwal219 20G 1.957G 9.79% 92160 21052 22.84%
    project_nesi99999 2T 798G 38.96% 100000 66951 66.95%
    nobackup_nesi99999 6.833T 10000000 2691383 26.91%
  • Contact Support
    If you are following the recommendations here yet are still concerned about indoes, open a support ticket and we can raise the limit for you.

Environment Variables

You may find it useful to use environment variables in your dictionaries e.g.

numberOfSubdomains ${SLURM_NTASKS};

Or create your variables to be set in your Slurm script.

startFrom ${START_TIME};

 This is essential when running parameter sweeps.

Recommended Resources   

Generally, using 16 or less tasks will keep your job reasonably efficient. However this is highly dependant on the type of simulation and how the model was decomposed.

 

 

 

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