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Topics - Dapke36

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PyroSim / OpenMP Threads and Threads MPI
« on: March 10, 2020, 08:20:13 am »
I'm still trying to wrap my brain around when to use OpenMP and when to use OpenMP Threads MPI (~"MPI) in FDS/Pyrosim.  I read the FDS users guide section 3.3.1, but still struggling on application...and i'm hoping someone can help!

The current machine I am utilizing for smaller runs is 12 GB ram with a Xeon e5 with 4 physical cores reported in that 1 cpu. When I read the user's guide, I am getting confused when they are talking about mapping to cores.

Using that hardware above, lets say I have a model with 4 meshes.  Should I be doing an MPI thread per core, i.e.:

Open MP Threads: 1
Open MP Threads MPI: 4
Open MP Stack: 200M


Or should I be doing 1 mpi thread per physical CPU and 1 OpenMP thread per core of that cpu? i.e.:

Open MP Threads: 4
Open MP Threads MPI: 1
Open MP Stack: 200M


Is MPI supposed to be per core available (parallel or cluster, whatever's linked), or per CPU? 

If there's one MPI per core, I should try to get my # of meshes to match the # of cores available, right? (with exceptions for dense meshes and distribution, understandably) Or is the OpenMP Thread supposed to match the # of cores?


If I double the CPU's on the machine to 2 physical CPU's, each with 4 cores (8 cores total), would it then be 8 MPI processes?

Any insight that can be offered is appreciated!

2
PyroSim / Quantifying HRR & Air Intake Flowrates
« on: July 02, 2015, 06:24:17 am »
I am modeling an Atrium smoke exhaust system, but using an irregular fuel composition & geometry.  I've gotten myself a little confused on what the total HRR is that I'm putting out, and I'm wondering what is the best device I can use to measure the HRR of the total fire over time.

I'm running a 1x1x1 mesh at the atrium floor, so I have a Flow Measuring Device at Z=0 and Z=1, both LxW the size of the burner vent.  Z=0 is recording a negative value (not surprising, as it's on the burner), but my Z=1 is recording a total output about 400 kW lower than I was expecting.

Is there another measurement device that might better quantify my total HRR over time from the fire?  I see the "Heat Release Rate" device, but I am not sure how to best apply that if appropriate (the fact it is a volume vs a plane gives me pause).

Fire is t2, and I know there is more growth coming, but the curve is not as steep as expected and is leveling off already.

Any suggestions?

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