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Old   April 24, 2009, 08:13
Default Lagrangian particle
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michel elsner
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Hello all,

can someone explain me what the number after the lagrangian position (x y z) n means, please. I have tried to find out the meaning but I come to no solution .

Thanks

Michél
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Old   April 24, 2009, 12:59
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Niklas Nordin
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It is the normal of the plane that the parcel moves in for 2D wedge simlations.
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Old   April 27, 2009, 02:55
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thank you for the answer
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Old   April 27, 2009, 07:11
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actually, i was wrong.

its the cell number of the cell it is currently in.
the vectors are all written last.
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Old   April 27, 2009, 08:51
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well. are you sure? because i played with the number and the particles start every time at the same position but has different movements properties.
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Old   April 27, 2009, 10:35
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ok. you are right.
but where can i found the function for this?
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Old   April 28, 2009, 05:49
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Quote:
Originally Posted by holzmichel View Post
ok. you are right.
but where can i found the function for this?
src/lagrangian/basic/Particle/Particle.H
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Old   April 28, 2009, 06:40
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thank you again
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Old   May 4, 2009, 04:43
Default kinematicCloud, a different question on lagrangian particles
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Hi,

I want to trace passive particles through a steady state RANS-solution, and have written a simple code using kinemaitcCloud. Seems to work well at first, but as the time steps march on, the clock time for each time step increases immensely. What might be the reason to this behaviour? Sure, as the particles enter further into the solution the flow speed increases, but not tremendously so. See the attached graph showing how clock time increases with time steps. Number of parcels are ~1e4 and the case size is about 2M cells from snappyHexMesh.

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Niklas
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Old   May 5, 2009, 05:39
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Hi Niklas!

Quote:
Originally Posted by wikstrom View Post
I want to trace passive particles through a steady state RANS-solution, and have written a simple code using kinemaitcCloud. Seems to work well at first, but as the time steps march on, the clock time for each time step increases immensely. What might be the reason to this behaviour? Sure, as the particles enter further into the solution the flow speed increases, but not tremendously so. See the attached graph showing how clock time increases with time steps. Number of parcels are ~1e4 and the case size is about 2M cells from snappyHexMesh.
First question: does the number of particles stay constant during the simulation? (I guess you already checked for that). If for instance injected particles get trapped in some cavity and won't leave the system that would explain the increase

Does the time spent in the lagrangian solver increase or in the other parts? To find an answer to things like that I use this extension:
Feature proposal: Application level profiling
If you prefer to use valgrind (like Henry suggested in that thread) I'd suggest that you restart from one of the later timesteps (where the calculation-time already exploded) because callgrind multiplies the time a run needs(at least for me, but maybe I'm using it wrong).

If the number of particles in the system doesn't increase and the lagrangian part is the one that eats up the CPU-time then I guess the reason is that the time-step during the lagrangian calculation becomes very small (either because particles have to travel through very small cells or because particles often pass zones were the velocity relative to the gas is high) but that is just a guess

Bernhard
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Old   May 5, 2009, 09:07
Default kinematicCloud
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Thank you Bernhard for the answer!

The answer probably lies in small local time steps as the particles enter the 'interesting region'. To be realistic, sadly, I will not have the time to profile the solver; It was years since I used Valgrind I'm afraid...

again, Thank you.

N.
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Old   May 5, 2009, 09:47
Default Callgrind
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Oh, it does not look that hard to use :-) I'll try it.

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