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[Gmsh] problem converting mesh from gmsh

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Old   October 17, 2011, 06:28
Default problem converting mesh from gmsh
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Hello everyone,
as a OpenFoam user, I always build my mesh with gmsh and then export it with gmshToFoam.
Now, I have a problem I cannot solve. My geometry is a squared horizontal channel on which some vertical channels for inlet and outflow are placed. These channels are not aligned and they are cylindrical. I want to run a 3D simulation.
On gmsh everything is fine, all displayed and with correctly groups (boundaries) assigned. When I export to OpenFoam one of the channels disappears, a defaulfaces region is crated on the face of its intersection with the horizontal channels and in the output file I get this message:

Could not match gmsh face 4(27013 27044 27035 27052) to any of the interior or exterior faces that share the same 0th point

As I said, I checked more than once with gmsh and there everything looks fine. Changing mesh refinement on the sides does not change anything. I also have to say that if I try draw every single vertical channel alone it works.
Please, does anyone have an idea or a tip for that?
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Old   October 17, 2011, 17:29
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Hisham Elsafti
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Hi Fried

I have no clear idea (actually no clue). But maybe you could try the following:
2. Generate the parts separately import them to different cases then merge and stitch them with OF utilities (e.g. http://www.cfd-online.com/Forums/ope...titchmesh.html)
1. Try rebuilding your Gmsh model in a strictly incremental way "commenting blocks of the .geo file" and exporting the mesh (after each change) to have a better idea of what went wrong
3. Maybe provide the .geo file

Good luck!
Hisham
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Old   October 18, 2011, 04:36
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Hello Hisham,
thanks for the answer, I am going to look how the utilities you mentioned work (I guess the stitchMesh, if I want to make the vertexes coincide).
I post here the .geo file I use to build my geometry. Maybe this will give some inspiration? I already tried to make piece by piece and in that case it works; the problem is when I put all the channels at the same time.
Thanks again,
F.
Attached Files
File Type: txt TestChannels.txt (6.5 KB, 12 views)
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Old   October 18, 2011, 05:27
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Hi Fried,

I ran gmshToFoam on the mesh. I guess maybe some external patches are not defined as physical surface. I would try to carefully review that, but I am sure you did! But why not do that again.

I found all volumes are defined as a physical vol. and I can't spot a bug really.

You may want to re-select your physical surfaces using the GUI and compare them to the ones you did before (just unbiased check)

You may also separate the extrude for the missing vol.

Regards
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Old   October 18, 2011, 05:38
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Hello Hisha,
thanks again for the tips. unluckily I already tried all the options you mentioned. I only have one doubt, concerning surface 3, since i define it using many loop lines: do I need to give them a -/+ direction? (actually I tried also this, then I don't think so...)
But from your answer, should I guess the problem is in gmsh?
Couldn't it be related to the gmshToFoam utility?
Any other idea looking to the geo file?
Thanks again,
Fried
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Old   October 18, 2011, 06:02
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It is obvious that there is no problem with gmsh. The error is either in the gmshToFoam or just an input error. It is always a good idea to eliminate the second possibility first.

Looking at gmshToFoam.C near line 954, there is a comment about internal faces and faceZones. What I understood is maybe you need to define some extra internal surfaces as physical surfaces and see if it works. They will not appear as patches (in boundary file) rather a faceZone.

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Old   October 18, 2011, 08:52
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Hallo again Hisham,
I tried adding internal faces but again it didn't give the result I hope.
Then, I would like to try with stitchMesh, but I am not familiar enough to use it properly, I am afraid.
Please, could you drive me step by step (I mean, with the command lines for stitchMesh)?
I already created the two different meshes. Then, I don't know if I did correctly, I put them in two different directories and built them separately but now?
Thanks a lot in advance!
Regards,
Fried
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Old   October 18, 2011, 09:30
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Sorry! I have not used these utilities before. Maybe search the forum or Google it. If results are not helpful, try starting a new thread on the topic to attract their users.

I would also suggest trying to play with gmshToFoam switches (gmshToFoam -help).

If all is not working, maybe use blockMesh with #codeStream (OF 2.x) support like the potentialFoam cylinder tutorial (better than typical blockMesh). Or else maybe draw a CAD model and import it to gmsh before meshing!

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Hisham
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Old   October 18, 2011, 09:53
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Ok, I will try with a new tread about merge/stitchMesh
Thanks for the help
F.
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