Difference between revisions of "HowTo:ansys"
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Revision as of 17:48, 12 March 2018
This is a help file on using the Mechanical Engineering structural code "ANSYS Mechanical" on our systems. This software is only licensed for academic researchers who have prior training. The software is only made available to persons who belong to a specific Unix group. See details below.
What is ANSYS Mechanical ?
ANSYS Mechanical is a Mechanical Engineering software that uses finite element analysis (FEA) for structural analysis. It covers a large range of applications ranging from geometry preparation to optimization. You can model advanced materials, complex environmental loadings and industry-specific requirements in areas such as offshore hydrodynamics and layered composite materials.
It can be used interactively and supplies a graphical user interface. It can also run in batch mode, if the required time for solving a problem is too long for interactive use. The latter situation is the standard if you are using it on CAC machines.
The most current version on our systems is Ansys-18.
Location and Access
ANSYS Mechanical runs under the Linux operating system.
The program is located in /opt/fluent/ on swlogin1 ("SW cluster") and in /global/software/ansys on caclogin01 ("Frontenac").
To use it, you have to be a trained University User. It is furthermore required that you read our licensing terms, and sign a statement. We will confirm your statement, and you will then be made a member of a Unix group fluent (so called for "historical" reasons), which enables you to run the software. Contact us if you are in doubt of whether you qualify to run ANSYS on our system.
The ANSYS license is "seat limited" and "process limited". At present, there are the following licensing limits on our systems:
25 program runs plus 512 parallel processes
i.e. at most 25 separate sessions can be run simultaneously (serial or parallel). Each of these sessions can run up to 4 processes for a total of 100. In addition, it is possible to run up to 512 "parallel only" processes in total. One scenario would be 24 users have 24 process parallel jobs running, and another one with 36, thus using up all available resources. Not that the seats are shared with the CFD software Fluent.
On the SW cluster
The setup for ANSYS on the SW cluster is done via usepackage. Simply type:
on the workup node (swlogin1) or include this command in your setup (.bash_profile) file. This will set up the default (Ansys 18) version. Other versions can be setup through specification of the proper version, for instance
to set up the "Ansys 17.0" version.
The setup for ANSYS on Frontenac is done via module. Type:
module purge --force module load ansys
on the workup node (caclogin01) or include these commands in your setup (.bash_profile) file. Note that this is "purging" the present setup which may make the shell in which this done unusable for running other software.
You have to be in the fluent Unix group for this to work on either system, as access permissions prevent general users from accessing ANSYS software.
ANSYS can (and usually must) be run in batch mode. Since you likely have access to ANSYS on your local machines, most interactive work should be done there, whereas the computationally intensive runs can be executed on a parallel system such as ours. For this, data and commands are written into a text file written in ANSYS Parametric Design Language (APDL) which is used to specify the system and describe the Analysis to be performed. Here is the top of an input file (the full file is too long to be displayed here):
/prep7 ET,1,SOLID185, ,2 MP,EX,1,70e09 MP,EY,1,70e09 MP,EZ,1,60e09 MP,NUXY,1,0.33 MP,NUYZ,1,0.30 MP,NUXZ,1,0.30 MP,GXY,1,26.5e09 MP,GYZ,1,22e09 MP,GXZ,1,22e09 *AFUN,DEG thetax=0.000000 thetay=0.000000 fx= 0 fy= -1000 fz= 0 fxp= fx fyp= fy*(cos(thetax)) - fz*(sin(thetax)) fzp= fy*(sin(thetax)) + fz*(cos(thetax)) [...]
Let's call this file "testsys.txt". The analysis can now be performed by calling ANSYS directly from the command line
ansys181 -b -i testsys.txt
In this case, output is sent to the screen, and output files are given the default name "file.*". No further input from the user is required. Once everything works you could submit this job into the background (using bash) by typing
ansys181 -b -i testsys.txt > test.out 2>&1 &
This would redirect standard output and standard error to test.out. The point is that ANSYS is run non-interactively this way, i.e. we can use the same technique to submit a production job to the scheduler, as shown in the next section.
To submit a production job on our clusters, you must use the scheduler. To obtain details, read through Sun Grid Engine (SW cluster) or SLURM (Frontenac). Production jobs that are run without scheduler will be terminated by the system administrator.
On Frontenac, the scheduler in use is SLURM. Here is a SLURM example script of an ANSYS production job:
#!/bin/bash #SBATCH --job-name=ANSYS_test #SBATCH --mail-type=ALL #SBATCH --mail-user=myEmail@whatever.com #SBATCH --output=STD.out #SBATCH --error=STD.err #SBATCH --nodes=1 #SBATCH --ntasks=1 #SBATCH --cpus-per-task=8 #SBATCH --time=00:30 #SBATCH --mem=1000 module purge --force module load ansys ansys181 -np $SLURM_CPUS_PER_TASK -b -i testsys.txt -o test.out -j test
Here we are running the file "testsys.txt" using 8 processors on a parallel machine. The output and any error messages from the system are re-directed to a file called "slurm-XXXXX.out" (where XXXXX is the job number).
The --time option is used to specify a time limit. If it is omitted you are assigned a default limit. It is best to specify this limit, and choose it to be slightly longer than the largest expected execution time. This will make the job harder to schedule, but it will ensure that the job is not terminated before it finishes. Note that time limits are "hard", i.e. the job will be stopped when it exceeds its limit. This is necessary to make efficient scheduling possible.
The --mem option is used to specify a memory limit. If it is omitted you are assigned a default limit. It is best to specify this limit, and choose it to be slightly larger than the largest expected memory usage. This will make the job harder to schedule, but it will ensure that the job is not for exceeding its memory allocation. Note that memory limits are "hard", i.e. the job will be stopped if it exceeds its allocated memory. This enable efficient memory allocation.
Parallel jobs of longer runtime should only be run in batch using SLURM. The number of processors "8" specified in our example script appears only once, in
which is where you let SLURM know how many processors to allocate to run the program. The internal environment variable SLURM_CPUS_PER_TASK will automatically be set to this value and can then be used in the ansys command line.
All processes are allocated within a single node. This means that the size of the job is restricted by the number of cores on a node. Once the script has been adapted (let's call it "ansys.sh"), it can be submitted to SLURM by
from the login node. Note that the job will appear as a parallel job on the "squeue" command.
ANSYS Mechanical is a complex software, and requires some practice to be used efficiently. We can not explain it use in any detail here.
The documentation for ANSYS can be access from inside the program GUI (WorkBench).
The documentation is subject to the same license terms as the software itself, i.e. you have to be signed up as a user in order to access it.
If you are experiencing trouble running a batch command script, check carefully if the sequence of commands is exactly in sync with the program. This might mean typing them in interactively as a test. If you have problems that you cannot resolve through the documentation, contact user support by sending email to firstname.lastname@example.org.