Learning Forum

[grayg34]

I have been periodically encountering a memmory allocation error when running Fluent through the gui on a compute server. I will be running a simulation and everything is working fine then the solver will stop and i get the following message:

fluent_mpi.22.2.0: malloc.c:4106: _int_malloc: Assertion `(unsigned long) (size) >= (unsigned long) (nb)' failed.

It seems more likely to occur on longer simulations. I reran a case where it happened and the same error occured after a different but similar number of iterations. It seems to me Fluent is running out of memmory somewhere but I am not sure how to go about fixing it

 

 

[grayg34]

I just encountered a different but seemingly related memory issue while using a different version of Fluent. The program crashed the the following error was sent to the command line where I had launched Fluent.

 

/usr/local/Ansys-2023/v232/fluent/fluent23.2.0/bin/fluent: line 2973: 3202720 Segmentation fault      (core dumped) $NO_RUN $CORTEX_PRE $EXE -f $FLUENT_PROD $CX_FLAGS "$CX_FUNCTION"
 

[Rob]

Depending on monitors, animations, image processing, expressions and parallel setting you may have found a memory leak. Check RAM usage as these typically slow the solution rather than cause an error. 

[grayg34]

After doing some more runs it appears the error only occurs when using the gui, I have not experience any memmory allocation errors running in batch.

The RAM usage is typically very low on the servers, over 800gb free. I am skeptical that total RAM usage is the issue.

 

Geoff

[MangeshANSYS]

If multiple machines are being used (Fluent GUI on one node and cores from different machine etc, then please check memory on all machines involved in the solve. 

Does this happen for all models or a specific model? Does a simple flow-through-pipe type test model run without issues? 

Are UDFs being used?

 

[grayg34]

I have only been running on a single machine. 

I have been working with a few different versions of the same model. The cell count is relatively low, about 600k cells. I am using udfs, I have a udf flux for a uds equation and a few udf reports which I have monitor plots for. 

I have not tried a simple test without udfs but I can add it to my list of things to do.