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snappyHexMesh ignoring skew limits from snappyhexmeshdict

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Old   April 2, 2013, 06:07
Default snappyHexMesh ignoring skew limits from snappyhexmeshdict
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Hey all,

I am seeing some interesting behavior from snappyHexMesh. Firstly, I am noticing that no matter what value I put for "maxBoundarySkewness" and "maxInternalSkewness," I get the same max skew (which is well over both limits.) This is a contrast from behavior with say maxOrthoLimit, where the mesh always has a maximum non orthogonality right under the limit I set in the snappyhexmeshdict.

Secondly, when the final mesh comes out, checkMesh reports a skew of 13. But at the same time it reports no skew over 5 & 6 when using the "read user-defined mesh quality criterions from system/meshQualityDict"

This is quite a contradiction! Perhaps there is a bug in the way skewness is calculated? Any ideas or suggestions?

Code:
Checking geometry...
    Overall domain bounding box (-15769.6 -10240 -50) (43622.4 0.117284 9166)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (-2.88268e-17 -3.10419e-15 1.05031e-15) OK.
    Max cell openness = 5.335e-16 OK.
    Max aspect ratio = 33.8837 OK.
    Minimum face area = 0.00472708. Maximum face area = 1.09071e+06.  Face area magnitudes OK.
    Min volume = 0.00616825. Max volume = 1.0742e+09.  Total volume = 5.60324e+12.  Cell volumes OK.
    Mesh non-orthogonality Max: 79.9759 average: 9.86647
   *Number of severely non-orthogonal faces: 2021.
    Non-orthogonality check OK.
  <<Writing 2021 non-orthogonal faces to set nonOrthoFaces
    Face pyramids OK.
 ***Max skewness = 13.1088, 1239 highly skew faces detected which may impair the quality of the results
  <<Writing 1239 skew faces to set skewFaces
    Coupled point location match (average 0) OK.
Checking faces in error :
    non-orthogonality >  80 degrees                        : 0
    faces with face pyramid volume < 1e-13                 : 0
    faces with concavity >  80 degrees                     : 4
    faces with skewness >   5 (internal) or   6 (boundary) : 0
    faces with interpolation weights (0..1)  <  0.05       : 102
    faces with volume ratio of neighbour cells <  0.01     : 0
    faces with face twist <  0.05                          : 197
    faces on cells with determinant < 0.001                : 0
  <<Writing 303 faces in error to set meshQualityFaces

Failed 2 mesh checks.
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Old   May 3, 2013, 10:24
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Ali
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I am facing the same problem. did anyone come up with a solution for that?
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Old   May 4, 2013, 05:56
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I think this might be related to a bug that is already reported: http://www.openfoam.org/mantisbt/view.php?id=825

Someone are probably working on it, and hopefully there will be a fix soon.
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Old   May 4, 2013, 09:17
Exclamation skewness problem with snappyHexMesh
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Isn't the bug report only for the checkMesh utility (severity=minor)? I didn't see reference to the problem in snappyHexMesh which should be severity=high. Is this correct?

Quote:
Originally Posted by haakon View Post
I think this might be related to a bug that is already reported: http://www.openfoam.org/mantisbt/view.php?id=825
Someone are probably working on it, and hopefully there will be a fix soon.
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Old   May 5, 2013, 04:12
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Sorry, my bad. When I saw this message, I thought "I remember something about a bug tagged with snappyHexMesh and skewness limits", and I didn't read properly before I posted.

Anyways, If you think this is a bug, report it. This might in the end be related to bug #825, since both checkMesh and snappyHexMesh does use some of the same classes when dealing with meshes.
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