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-   -   Defective snapping produced deviation (http://www.cfd-online.com/Forums/openfoam-meshing-snappyhexmesh/122108-defective-snapping-produced-deviation.html)

skeptik August 12, 2013 10:00

Defective snapping produced deviation
 
1 Attachment(s)
I think the problem has principle character.
I've tried a lot of modifications of some basic sHM dictionaries but if somebody need my source files i will attach it.
The problem:
Attachment 24331

Questions:
1. Did somebody met similar problem with snapping procedure?

2. What did you do with it to eliminate deviation from stl surface or feature edge?

Thanks.

skeptik August 13, 2013 04:50

Done!
 
I've analyzed the problem successfully!

1. To prevent such behavior of sHM the mesh should not have 'empty' patches. So if you need prism layer at the symmetryPlane, you should change patch type only on final stage of your meshing process.

2. So when you have 'empty' patches you will get such messages:

Code:

Correcting 2-D mesh motion--> FOAM Warning :
    From function twoDPointCorrector::twoDPointCorrector(const polyMesh& mesh, const vector& n)
    in file twoDPointCorrector/twoDPointCorrector.C at line 152
    the number of vertices in the geometry is odd - this should not be the case for a 2-D case. Please check the geometry.
--> FOAM Warning :
    From function twoDPointCorrector::twoDPointCorrector(const polyMesh& mesh, const vector& n)
    in file twoDPointCorrector/twoDPointCorrector.C at line 164
    The number of points in the mesh is not equal to twice the number of edges normal to the plane - this may be OK only for wedge geometries.
    Please check the geometry or adjust the orthogonality tolerance.

and then strange message like this one

Code:

Correcting 2-D mesh motion ...done
3. I didn't have 2D case (i just wanted to have projected prisms on my symmPlane), so my mesh has a lot of bad elements and sHM gave up my mesh. At the end I had 'waved' mesh as i described at topic.

miro2000 August 20, 2013 02:18

oscillation on a surface probably means you overdid it with your smoothing operations.

If your surface is not smooth you should use a better (finer) stl, and not smooth so much. If I understand correctly (i didn't go trough the whole thread) you're meshing an airfoil in 3D? If so, you should check out the dictionary for sHM in incompressible/pimpleDyFoam/wingmotion.

cheers
- miro

skeptik August 20, 2013 02:25

sHM
 
Quote:

Originally Posted by miro2000 (Post 446799)
oscillation on a surface probably means you overdid it with your smoothing operations.

If your surface is not smooth you should use a better (finer) stl, and not smooth so much. If I understand correctly (i didn't go trough the whole thread) you're meshing an airfoil in 3D? If so, you should check out the dictionary for sHM in incompressible/pimpleDyFoam/wingmotion.

cheers
- miro

Thanks a lot for your advice and your answer.

But i think it's a vexed question. I mean that in case when one or two patches has 'empty' type sHM trying to 'syncronize' mesh. So points are aligned but in many cases point cloud is not regular, so it's produce additional iterations to find a good alignment. At the end user has waved mesh.


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