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[snappyHexMesh] snappyHexMesh: problem meshing baffle (surface with zero thickness) |
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May 26, 2012, 09:40 |
snappyHexMesh: problem meshing baffle (surface with zero thickness)
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#1 |
Senior Member
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Hi,
I am trying to use snappyHexMesh to mesh a thin wall/baffle. The aim is to model a sail on a small sailing boat (i.e I want the sail to be zero thickness). I have some problem at the edge of the mesh generated by snappyHexMesh - it does not snap to the edges. I have replicated the problem with a simple 1x1 square STL surface. It is titled to be not aligned with the mesh in order to reproduce the problem (see attached picture). I have a nagging feeling that the issue is with the eMesh file (generated by surfaceFeatureExtract). When surfaceFeatureExtract is used without specifying an includedAngle, it reports the following error message (my concern is highlighted in bold as the surface is definitively not a closed manifold). It works as soon as includedAngle is specified: Feature line extraction is only valid on closed manifold surfaces.Also attached are: - snappyHexMeshDict; - blockMeshDict (in case it is relevant). I use blueCFD (Windows port of openFoam). I tried v2.0 and v2.1 without success. Also I am trying to use "surfaceFeatureConvert" but get the following problem (emesh file attached): --> FOAM FATAL IO ERROR:Any help/tips will be very appreciated. Kind regards, Julien
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--- Julien de Charentenay |
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May 26, 2012, 11:33 |
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#2 |
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,981
Blog Entries: 45
Rep Power: 128 |
Hi Julien,
About the conversion: apparently it's a bug in OpenFOAM, because I just tested this on Linux and it gave me the same error when converting eMesh to obj. The problem is that the converter isn't handling properly the eMesh file in binary format. Attached are the two scenarios ascii vs binary, but both give badly formed meshes, so it's not a strict eMesh. This conversion bug should be reported in the bug tracker: http://www.openfoam.org/mantisbt/my_view_page.php - if you want, I can report this. The reason for the bad mesh around the shape seems to be a visibility issue provided by the base mesh. Sometime ago I had a very similar problem, but it was with meshing inside very thin walls. A solution was to do the meshing process in two steps, so that certain cells would not be discarded: http://www.openfoam.org/mantisbt/view.php?id=295 I haven't tested the two stage mesh generation... I can test this later today. Another bug report that might be useful: http://www.openfoam.org/mantisbt/view.php?id=518 Best regards, Bruno
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May 26, 2012, 13:23 |
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#3 |
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,981
Blog Entries: 45
Rep Power: 128 |
OK, after looking a bit further into this, here's what I can figure out:
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May 27, 2012, 08:09 |
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#4 |
Senior Member
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Hi Bruno,
Thanks for looking into it for me. I had a long hard look at the problem today and I am still stuck... I tried to do a 3 step snappyHexMesh process: - SHM step 1: Refine the mesh at the edges (eMesh file); - SHM step 2: Casttelate; - SHM step 3: Snap. Did not really improve the problem (the jaggering was a little less as edges were refined at level 2). I noted a few strange things in step 1: 1) The initial eMesh has an entry: // edges:With this entry, there was no refinement at step 1. I had to manually edit it and change to: // edges:This seems very similar to the issue notified in http://www.cfd-online.com/Forums/ope...ain-edges.html 2) The final mesh is refined on three out of four edges. I also tried refining the initial block mesh (x 3 in all direction) - did not improve. My problem looks awfully similar to http://www.cfd-online.com/Forums/ope...t-surface.html. Let me know if you get any idea.
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--- Julien de Charentenay |
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May 27, 2012, 11:04 |
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#5 |
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,981
Blog Entries: 45
Rep Power: 128 |
Hi Julien,
Well, I've got several ideas, but haven't managed to implement any of them. My head isn't agreeing with the idea of wanting to work today... I did manage to do a little test if the old snapEdge utility would help, but it didn't do anything at first try, so I gave up on it. You should be able to build it directly with blueCFD in an MSys terminal. The ideas are:
By the way, I've already reported the bug about converting the binary eMesh to obj: http://www.openfoam.org/mantisbt/view.php?id=541 Best regards, Bruno
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May 29, 2012, 02:28 |
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#6 |
Senior Member
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Hi Bruno,
Thanks a lot for the inputs. I hoped for a quick fix. I will move on to other problems for the moment. If you find a solution, I would love to hear but do not get out of your way for it. Thanks again. Julien
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--- Julien de Charentenay |
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June 13, 2012, 18:14 |
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#7 |
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,981
Blog Entries: 45
Rep Power: 128 |
Hi Julien,
FYI: http://www.cfd-online.com/Forums/ope...tml#post366242 It looks like I'll have to check if your model is working with the latest 2.1.x I'll try looking at it this weekend. Best regards, Bruno
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June 16, 2012, 09:12 |
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#8 |
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,981
Blog Entries: 45
Rep Power: 128 |
Hi Julien,
Well, after compiling the latest 2.1.x, ran both the ASCII and binary cases and:
Best regards, Bruno
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Tags |
baffle, snappyhexmesh, surfacefeatureconvert |
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