How do I set up and run a Fluent batch job?

How do I set up and run a Fluent batch job?

In most cases, you will run Fluent on the Sun Fire's in batch mode. Since you have to have access to Fluent outside of the HPCVL license, most interactive work can be done elsewhere, whereas the computationally intensive runs can be executed on the Sun Fire cluster.

For this, you have to set up a batch command file that consists of a sequence of commands that you would normally issue to "Fluent" in an interactive session. To get an idea how such a batch command file looks, you can produce a journal file during an interactive session, and edit it later to eliminate unnecessary commands. Note that this needs to be done using the command line inside Fluent, not the menu buttons of the GUI. In fact, it is best to generate journal files in sessions that have been started with the -g option, i.e. that do not use the GUI at all. You also can have a look at a simple . The example file will read in a case-file from the working directory directory, initialize the flow, and run 10 iterations. It then writes out the data on a file "fan.dat" and exits. Note that every command has to be included in the batch command file, including the answer "yes" to the question if you really want to exit the program without saving the case file.

Once you have produced a working command file, you can test it by calling

fluent 3d -g -i example.flin

where example.flin is the name of your command file, and we have assumed you are running a three-dimensional solver in single precision. You will have to alter those entries in different cases. Make sure that the output file for the data (in this case, fan_1.dat) does not exist before you start the job, otherwise the system will query if you want to over-write it and the answer is not in your command file.

Once everything works you can submit this job into the background by typing

fluent 3d -g -i example.flin>example.flout 2>&1 & (for ksh)

This will catch standard output and standard error in a file example.flout.

Production jobs are submitted on the Sun Fire systems via the GridEngine, which is a load-balancing software. To obtain details, read our . For a Fluent batch job, this means that rather than issuing the above command directly, you wrap it into a GridEngine batch script. For an example for such a batch script . This script needs to be altered by replacing all the relevant items enclosed in {} by the right values.

The batch script is submitted to the GridEngine by typing

	qsub batch_file_name

The advantage to submit jobs via a load balancing software is that the software will automatically find the resources required and put the job onto a set of processors that have a low load. This will help executing the job faster. Note that the usage of Gridengine for all production jobs on the Sun Fire cluster is mandatory. Production jobs with a running time of more than 3 hours that are submitted outside of the load balancing software will be terminated by the system administrator.