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ANSYS / Fluent	software, ansys, fluent, slurm, interactive, rsm, batch job	07 September 2022	This document describes how to run ANSYS/Fluent in the Merlin6 cluster	merlin6_sidebar	/merlin6/ansys-fluent.html

This document describes the different ways for running ANSYS/Fluent

ANSYS/Fluent

Is always recommended to check which parameters are available in Fluent and adapt the below example according to your needs. For that, run fluent -help for getting a list of options. However, as when running Fluent one must specify one of the following flags:

• 2d: This is a 2D solver with single point precision.
• 3d: This is a 3D solver with single point precision.
• 2dpp: This is a 2D solver with double point precision.
• 3dpp: This is a 3D solver with double point precision.

Running Fluent jobs

PModules

Is strongly recommended the use of the latest ANSYS software available in PModules.

module use unstable
module load Pmodules/1.1.6
module use overlay_merlin
module load ANSYS/2022R1

Interactive: RSM from remote PSI Workstations

Is possible to run Fluent through RSM from remote PSI (Linux or Windows) Workstation having a local installation of ANSYS Fluent and RSM client. For that, please refer to the [ANSYS RSM](/merlin6/ansys-rsm.html) in the Merlin documentation for further information of how to setup a RSM client for submitting jobs to Merlin.

Non-interactive: sbatch

Running jobs with sbatch is always the recommended method. This makes the use of the resources more efficient. For running it as a job, one needs to run in no graphical mode (-g option).

Serial example

This example shows a very basic serial job.

#!/bin/bash
#SBATCH --job-name=Fluent    # Job Name
#SBATCH --partition=hourly   # Using 'daily' will grant higher priority than 'general'
#SBATCH --time=0-01:00:00    # Time needed for running the job. Must match with 'partition' limits.
#SBATCH --cpus-per-task=1    # Double if hyperthreading enabled
#SBATCH --hint=nomultithread # Disable Hyperthreading
#SBATCH --error=slurm-%j.err # Define your error file

module use unstable
module load ANSYS/2020R1-1

# [Optional:BEGIN] Specify your license server if this is not 'lic-ansys.psi.ch'
LICENSE_SERVER=<your_license_server>
export ANSYSLMD_LICENSE_FILE=1055@$LICENSE_SERVER
export ANSYSLI_SERVERS=2325@$LICENSE_SERVER
# [Optional:END]

JOURNAL_FILE=/data/user/caubet_m/Fluent/myjournal.in
fluent 3ddp -g -i ${JOURNAL_FILE}

One can enable hypertheading by defining --hint=multithread, --cpus-per-task=2 and --ntasks-per-core=2. However, this is in general not recommended, unless one can ensure that can be beneficial.

MPI-based example

An example for running Fluent using a Slurm batch script is the following:

#!/bin/bash
#SBATCH --job-name=Fluent    # Job Name
#SBATCH --partition=hourly   # Using 'daily' will grant higher priority than 'general'
#SBATCH --time=0-01:00:00    # Time needed for running the job. Must match with 'partition' limits.
#SBATCH --nodes=1            # Number of nodes
#SBATCH --ntasks=44          # Number of tasks
#SBATCH --cpus-per-task=1    # Double if hyperthreading enabled
#SBATCH --ntasks-per-core=1  # Run one task per core
#SBATCH --hint=nomultithread # Disable Hyperthreading
#SBATCH --error=slurm-%j.err # Define a file for standard error messages
##SBATCH --exclusive         # Uncomment if you want exclusive usage of the nodes

module use unstable
module load ANSYS/2020R1-1

# [Optional:BEGIN] Specify your license server if this is not 'lic-ansys.psi.ch'
LICENSE_SERVER=<your_license_server>
export ANSYSLMD_LICENSE_FILE=1055@$LICENSE_SERVER
export ANSYSLI_SERVERS=2325@$LICENSE_SERVER
# [Optional:END]

JOURNAL_FILE=/data/user/caubet_m/Fluent/myjournal.in
fluent 3ddp -g -t ${SLURM_NTASKS} -i ${JOURNAL_FILE}

In the above example, one can increase the number of nodes and/or ntasks if needed. One can remove --nodes for running on multiple nodes, but may lead to communication overhead. In general, no hyperthreading is recommended for MPI based jobs. Also, one can combine it with --exclusive when necessary.

Interactive: salloc

Running Fluent interactively is strongly not recommended and one should whenever possible use sbatch. However, sometimes interactive runs are needed. For jobs requiring only few CPUs (in example, 2 CPUs) and for a short period of time, one can use the login nodes. Otherwise, one must use the Slurm batch system using allocations:

• For short jobs requiring more CPUs, one can use the Merlin shortest partitions (hourly).
• For longer jobs, one can use longer partitions, however, interactive access is not always possible (depending on the usage of the cluster).

Please refer to the documentation Running Interactive Jobs for firther information about different ways for running interactive jobs in the Merlin6 cluster.

Requirements

SSH Keys

Running Fluent interactively requires the use of SSH Keys. This is the way of communication between the GUI and the different nodes. For doing that, one must have a passphrase protected SSH Key. If the user does not have SSH Keys yet (simply run ls $HOME/.ssh/ to check whether id_rsa files exist or not). For deploying SSH Keys for running Fluent interactively, one should follow this documentation: Configuring SSH Keys

List of hosts

For running Fluent using Slurm computing nodes, one needs to get the list of the reserved nodes. For getting that list, once you have the allocation, one can run the following command:

scontrol show hostname

This list must be included in the settings as the list of hosts where to run Fluent. Alternatively, one can give that list as parameter (-cnf option) when running fluent, as follows:

[Running Fluent with 'salloc' example]

(base) [caubet_m@merlin-l-001 caubet_m]$ salloc --nodes=2 --ntasks=88 --hint=nomultithread --time=0-01:00:00 --partition=test $SHELL
salloc: Pending job allocation 135030174
salloc: job 135030174 queued and waiting for resources
salloc: job 135030174 has been allocated resources
salloc: Granted job allocation 135030174
(base) [caubet_m@merlin-l-001 caubet_m]$ module use unstable
(
base) [caubet_m@merlin-l-001 caubet_m]$ module load ANSYS/2020R1-1
module load: unstable module has been loaded -- ANSYS/2020R1-1
(base) [caubet_m@merlin-l-001 caubet_m]$ fluent 3ddp -t$SLURM_NPROCS -cnf=$(scontrol show hostname | tr '\n' ',')
(base) [caubet_m@merlin-l-001 caubet_m]$ exit
exit
salloc: Relinquishing job allocation 135030174
salloc: Job allocation 135030174 has been revoked.