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[snappyHexMesh] Edge/Surface snapping on thin geometry

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Old   May 14, 2012, 05:06
Default Edge/Surface snapping on thin geometry
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Tom
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I am trying to mesh a simple diffuser using SHM. I created the diffuser geometry as an STL file and used the surfaceFeatureExtract command. However, I am struggling to get SHM to snap to my geometry. See attached image of the diffuser surface mesh, and with the STL file showing corner edges it has missed. I have also attached the SHM dict and stl file.

Previously I have used Gmsh so am unfamiliar with the settings I need in SHM to achieve suitable snapping.

Any help/advice would be much appreciated.

Regards
Tom
Attached Images
File Type: jpg diffuser_Mesh.jpg (97.7 KB, 54 views)
File Type: jpg diffuser_Mesh_STL.jpg (97.5 KB, 55 views)
Attached Files
File Type: txt snappyHexMeshDict.txt (10.6 KB, 12 views)
File Type: txt blockMeshDict.txt (1.4 KB, 5 views)
File Type: zip diffuser.zip (78.5 KB, 3 views)
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Old   May 14, 2012, 05:30
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Hi Tom;
have you run surfaceFeatureExtract?
If you did, with which flags?

Should be something like this:

Quote:
surfaceFeatureExtract -includedAngle 150 -writeObj constant/triSurface/diffuser.stl diffuser
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Old   May 14, 2012, 05:36
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Wow, thank you for your quick reply.

Yes I used that exact command and checked the resulting object file to see the edges that were extracted were correct, which they were.

The problem seems to be with SHM in getting the mesh to snap to those edges.
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Old   May 14, 2012, 06:23
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Don't know exactly what's causing the issue here. I started sHM with the motorbike dictionary and I managed to get it working ok. If compared to your dictionary a lot of stuff is different…
To speed up the process I removed the layers and decreased the mesh refinement on the diffuser…

You may want to run

Quote:
diff my_sHMDict your_sHMDict
to find the differences between the two.


Hope this helps…

Regards
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File Type: zip snappyHexMeshDict.zip (4.2 KB, 17 views)
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Old   May 14, 2012, 07:32
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Brilliant, thank you very much.

After increasing the refinement 1 more level all edges are snapped and well defined.

After some playing I think the parameter that had the biggest effect was the 'resolveFeatureAngle'. Previously I had 90, but in your dictionary 30 and this improved the snapping a lot.

Thanks again for your help,

Tom
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