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Messages - elchanan

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1
PyroSim / Re: OpenMP Threads and Threads MPI
« on: January 03, 2021, 05:43:56 am »
MPI uses parallel computing between physical cores (virtual are not advisable). the speed up is in relation to the number of cores used. so theoretically you could have 10 meshes on 10 different cores and the simulation would run much faster than one mesh one one core.
Open MP on the other hand, does parallel computations by dividing the task between a few threads. so the speedup is much more limited.
If you use 2 MPI processes, you will get almost double the speed. If you use 2 OMP, you will get about 20-30% speedup. if you jump to 8, MPI will give about 6-7 times faster simulation and OMP will only double the speed.
So in conclusion, use MPI according to available physical cores. you can try to add OMP if you have available virtual cores. experiment a little with both of them to better understand.

2
PyroSim / Re: Thermocouple vs. Gas phase device
« on: December 06, 2020, 01:16:52 am »
Hello Nikol,

the device you use depends on your needs.
for example, if we are talking about a door opening after a smoke detector goes off, you should use a smoke detector.
if you are interested in a window breaking due to temperature, use a solid phase device for the window (don't forget materials).
as a rule, start by defining the actual fire scenario and build your model accordingly.

for the steel beams you can use a solid phase device. also, in ooutput-boundary condotions, you can define visualization of the wall (or beam) temperature.

3
PyroSim / Re: Thermocouple vs. Gas phase device
« on: December 03, 2020, 06:31:43 am »
Hello Nikol,
A gas phase device records the actual quantity (temperature in your case) calculated in a mesh cell.
A thermocouple is a device that measures temperature by changes in electrical current that is passed through a metal bead. FDS calculates the temperature of a thermocouple with heat transfer equations.
that is why a thermocouple does not give the same values as a gas phase device.
in steady state, the two curves should be close.
In your case, a difference of 80 degrees is significant. the only way I can see that happening is if the fire ramps up very quickly and the thermocouple is lagging at the beginning due to the dampening and delaying effect of the heat transfer through the bead.

4
PyroSim / Re: Isosufrace
« on: November 08, 2020, 12:41:59 am »
an isosurface is a surface that moves with changes in the measured quantity.
in your caes, when you view results you can activate the isosurface and it will show you in 3D where a value of 10m visibility distance is met.
you can browse youtube for examples.

5
Pathfinder / Re: EVACUATION WITH CARS
« on: November 02, 2020, 12:43:34 am »
Just trying to be creative here:
if you define all people as being in wheelchairs with a certain velocity and group them so that they move together in groups according to cars (lets say 4 or 5 people group). that might give you a rough estimate of egress time (since you anyway need about 50% higher ASET than RSET, rough should be good enough).
you will have to see how you keep a certain distance between groups (simulating the distance between cars).
of course, visualization will not be cars...

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