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151

PyroSim / Re: parallel run error - forrtl: severe (157): Program Exception - access violation

« on: September 07, 2010, 03:29:25 pm »

I looked at the screenshots, but my questions still remain.
10 processes/meshes does not equal 10 computers, 10 processors (cores) or 10GB of RAM (minimum).

For a simulation like this, you would probably need to be running FDS on a 64bit computer with at least 16GB of RAM.
Or, you would need to have distributed it over a few separate computers each with enough RAM to handle the number of cells distributed to it.

As a rough estimate you will need about 1GB of RAM for each million grid cells.  As the number of millions increase, so does the overhead above the 1GB per million cell estimate.

Could you please give a bit more information about the computer(s) you are trying to run this on?

-Bryan

152

PyroSim / Re: parallel run error - forrtl: severe (157): Program Exception - access violation

« on: September 07, 2010, 02:09:24 pm »

Access violation 157 is usually due to some kind of memory read/write error.
With almost 10 million mesh cells, you may be running into out of bounds or overflow errors.

How many computers are you using to run the simulation?
How much memory is available on each computer?
How many meshes are you allocating to each computer?

-Bryan Klein

153

PyroSim / Re: nozzle

« on: August 13, 2010, 12:23:14 pm »

This is an area of active research at NIST.
http://www.nist.gov/bfrl/fire_protection/fireservice/hose_stream_charact_effect_modeling.cfm

The key would be Validating that the nozzle in your model has some basis in reality.

Also, there are some physics of water suppression that are not accounted for by FDS, it is fairly complex from a physics and chemistry point of view.

The best approach is to put together a simple model of your nozzle spray and test various parameters related to how it operates.

Best Regards,
-Bryan Klein

154

PyroSim / Re: Mesh Sensitivity Testing

« on: July 15, 2010, 10:58:39 am »

This is a very important topic to consider when running models like FDS.  The answer is not simple, but I will do my best to point you in the right direction and hopefully give you some information and tools to determine for yourself if your FDS solutions are adequate for your needs. Note: This information may require an updated version of FDS and some will not be in the User Guide until FDS_6 is released.  But, I think it is important to answer your questions.

There was an extensive discussion on the FDS Discussion Group on a very similar topic that will be informative to review.
http://groups.google.com/group/fds-smv/browse_thread/thread/bcc91ccdd404022e

Since then, Randy McDermott at NIST has worked to develop quality assessment tools for LES calculations, specifically for FDS.  You can read about this in more detail in a paper he wrote entitled "TOWARD FDS 6: COMPLEX GEOMETRY, EMBEDDED MESHES, AND QUALITY ASSESSMENT" for presentation at V European Conference on Computational Fluid Dynamics (ECCOMAS CFD 2010) in June of 2010.
http://www2.bfrl.nist.gov/userpages/wmell/PUBLIC/TALKS_PAPERS/mcdermott_etal_FDS6_CFD2010.pdf

Pay particular attention to section 5 (page 10), where Randy covers metrics in that can be used in FDS to determine quality of the FDS mesh resolution.

To use MTR you must set CHECK_KINETIC_ENERGY -- (LOGICAL) to .TRUE. on the MISC line, which will estimate the subgrid kinetic energy after the corrector step and calculate MTR(x,t) -- the "measure of turbulence resolution".  This quantity may be output to a Slice through the area of interest by using QUANTITY=''TURBULENCE RESOLUTION'' on a SLCF line.

To do quick comparisons of SLCF output, Glenn Forney has developed a tool called SmokeDiff.  You can read more about how to use it in the Smokeview User Guide, Chapter 18. http://fds-smv.googlecode.com/svn/trunk/FDS/trunk/Manuals/All_PDF_Files/SMV_5_User_Guide.pdf
SmokeDiff is also mentioned in Randy''s paper linked above.

In the upcoming version of the FDS User Guide, there will be new information about how to use these metrics.  This version of the FDS User Guide is available in the FDS-SMV Subversion repository as a .tex file.  I have attached it to this message.  Please, keep in mind that it is not an official release of the manual, and should be taken as it is in draft form.

I hope this helps,
-Bryan Klein
Old Guy from NIST/New Guy at Thunderhead Eng.