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Old   September 1, 2011, 11:20
Default manual decomposition for topological changes
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kshitij neroorkar
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I have read some posts that 1.7-ext might have topological changes implemented in parallel. I am currently using 1.6-ext and
I was wondering if there was a way in which I could manually decompose the mesh so that all the topological changes were handled by one processor and the rest of the mesh is handled by other processors.
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Old   September 1, 2011, 13:44
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1.6-ext already has topo-changes in parallel. Nevertheless, you can always partition a mesh in specific ways by supplying a processor addressing list during decomposePar (i.e., processor ID for each cell in the mesh - like an output from Metis). However, even if topo-changes occur on a single processor, the processor patch addressing can (and usually does) change, which requires a global sync prior to solution restart. Keeping all topo-changes specific to a single processor is also a bad idea from a load-balancing stand-point.
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Old   September 1, 2011, 14:11
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Thanks Sandeep for that information. Based on the thread
engine simulation with mesh motion and topological changes

I thought that parallel topo changes were going to be in the next release.
I do agree that what I am suggesting will be bad from load balancing point of view, but I am trying to run a pretty big case, and I wanted to know if there was any way of running it in parallel.
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Old   September 6, 2011, 15:40
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Hi, I ve followed this thread am I am also interested in parallel computing with topochanger. How can we remedy the issue with the addressing?
I ve noticed that after a topological change the mesh has not anymore the same cell and face zones as the initial one. I am doing engine simulations as well and by using for instance the engineTopoChangerMesh class, each time folder during a run contains a folder with the new mesh. Unfortunately, it does not anymore contain the nicely created zones of my initial mesh. I am aware of it that this will cause problems if I wanna simulate in parallel.
So, is there a way to get back the cell and face zones on the fly?

thx
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Old   September 6, 2011, 15:46
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Not really sure what you're talking about - what issues with addressing? If there's an error generated, please post that, so that we have an idea about what you're referring to. If the zone addressing is not being preserved after topo-changes, and you feel that something is wrong, please refer the problem to Hrv, who's written the relevant bits of code.
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Old   September 6, 2011, 16:12
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Hi Peter
I am using sliding interfaces and layering in my simulation. And the zones seem to be being tracked correctly during the serial simulation. When I do foamToVTK, I can see these zones in paraview too.

Is it possible that there is something else wrong in your simulation?
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Old   September 7, 2011, 08:34
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Sorry I expressed myself a little bit unclear.
Everything works fine. I just want to know if there are already some ways to decompose the mesh nicely to use topochanger in parallel.
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Old   September 7, 2011, 10:06
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Define "nicely"
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Old   September 7, 2011, 14:13
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Hi Sandeep

I don t know how I can decompose the mesh from my existing zones.
Considering an engine, I would like to have the ports and the cylinder seperated. You may have heard about enginescotch.
http://www.openfoamworkshop.org/6th_...sak_slides.pdf -> slide 15
I would like to decompose my case that way.
Thanks in advance
Peter
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Old   September 9, 2011, 11:02
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Hi Peter
This looks really nice, thanks for sending this presentation. I also would be interested in this. If you find out anything more, please let me know. my email address is kneroork@engin.umass.edu
Thanks
Kshitij
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Old   September 10, 2011, 08:41
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Unfortunately not. I was thinking of writing my own decomposition method like the engineScotch.
Any suggestions how to start?
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Old   September 12, 2011, 18:10
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As far as I can tell, it looks like a situation where CPU id's are specifically assigned based on mesh connectivity (or even geometry). Once this assignment is done, fvMeshDistribute can do the re-distribution bit quite easily. It wouldn't hold much water from a load-balancing point of view, but it gets the job done.
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Old   September 13, 2011, 03:34
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Thx, for the hints. I ll give it a try.
Peter
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Old   December 9, 2011, 10:42
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Hi Peter
I found out with Kalle's help that if the processor boundaries are perpendicular to the face where layerAR is working, then the topochanger will work in parallel (look at the picture on page 15 of the presentation). To do this you need to do a manual decomposition of the domain.
Hope this helps
Kshitij
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Old   December 10, 2011, 05:28
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Hi,
thank you for the answer. Indeed, it runs
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Old   December 10, 2011, 07:28
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I was using scotch for the decomposition of the mesh. How do you decompose manually?
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