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non-orthogonality errors, incorrectly oriented faces

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Old   July 26, 2010, 12:18
Default non-orthogonality errors, incorrectly oriented faces
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Markus Weinmann
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Hi all,

I am trying to load a fairly complex ccm mesh.
The mesh has been tested in StarCCM and seems to work fine.

When I load the mesh in OpenFOAM I get a bunch off errors and warnings (see below). The case does run for a few iterations before the simulation crashes.

I am particulary concerned about those 2 errors:

Error in face pyramids: 143 faces are incorrectly oriented
Number of non-orthogonality errors: 15.

How important are they and do they need fixing in StarCCM?

Any help is appreciated.

Markus






Checking topology...
Boundary definition OK.
Point usage OK.
<<Found 1101 neighbouring cells with multiple inbetween faces.
Upper triangular ordering OK.
<<Writing 2297 unordered faces to set upperTriangularFace
Topological cell zip-up check OK.
Face vertices OK.
***Number of duplicate (not baffle) faces found: 306
***Number of faces with non-consecutive shared points: 540
<<Writing 1405 faces with incorrect edges to set edgeFaces
Number of regions: 1 (OK).



Checking geometry...
Overall domain bounding box (-2.18829e-07 -7.47931 -0.277615) (2.86 12.042 4.66777)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-3.71575e-13 -8.51015e-14 -1.25127e-12) OK.
Max cell openness = 1.52626e-15 OK.
Max aspect ratio = 131.378 OK.
***Zero or negative face area detected. Minimum area: 0
<<Writing 1 zero area faces to set zeroAreaFaces
Min volume = 7.78059e-14. Max volume = 6.85685e-05. Total volume = 254.056. Cell volumes OK.
Mesh non-orthogonality Max: 121.889 average: 4.92652
*Number of severely non-orthogonal faces: 2880.
***Number of non-orthogonality errors: 15.
<<Writing 2895 non-orthogonal faces to set nonOrthoFaces
***Error in face pyramids: 143 faces are incorrectly oriented.
<<Writing 140 faces with incorrect orientation to set wrongOrientedFaces
***Max skewness = 88.8617, 233 highly skew faces detected which may impair the quality of the results
<<Writing 233 skew faces to set skewFaces
*Edges too small, min/max edge length = 0 0.0543461, number too small: 34
<<Writing 34 points on short edges to set shortEdges
*There are 5188 faces with concave angles between consecutive edges. Max concave angle = 89.9778 degrees.
<<Writing 5188 faces with concave angles to set concaveFaces
Face flatness (1 = flat, 0 = butterfly) : average = 0.999981 min = 0.0551237
*There are 447 faces with ratio between projected and actual area < 0.8
Minimum ratio (minimum flatness, maximum warpage) = 0.0551237
<<Writing 447 warped faces to set warpedFaces
Cell determinant (wellposedness) : minimum: 2.11744e-08 average: 8.24052
***Cells with small determinant found, number of cells: 189153
<<Writing 189153 under-determined cells to set underdeterminedCells

Failed 6 mesh checks.
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Old   July 27, 2010, 03:06
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Sebastian Gatzka
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Can you show the mesh how it is displayed in ParaView?
Anything strange on first glance?

Or can you even post the complete mesh?
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Old   July 27, 2010, 04:32
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Hi

the mesh has more than 30 mio. cells, so it is a bit hard to post the mesh here. Also, there is nothing very obvious wrong with the mesh when displayed in paraview.

The important question for me is which errors/warnings can be accepted/-ignored (skewed, non-orthogonal cells, multiple inbetween faces, unordered faces) and which need to be fixed in the grid generator (face orientation?, ...).

Thanks,
Markus
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Old   October 20, 2010, 06:58
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Mark Herskind
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No comments to this?

I have a similar problem with a mesh.. I'm trying to use snappyHexMesh on a terrain (large scale CFD for wind farm purposes), and when I have the sufficient cell size, I get errors:

Code:
 
Checking geometry...
    Overall domain bounding box (404868 4758933 490) (420868 4774933 7500)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (-4.989805e-18 -2.407661e-17 -3.776756e-14) OK.
 ***High aspect ratio cells found, Max aspect ratio: 3.113e+203, number of cells 19
  <<Writing 19 cells with high aspect ratio to set highAspectRatioCells
    Minumum face area = 1.61935. Maximum face area = 23599.98.  Face area magnitudes OK.
    Min volume = 2e-300. Max volume = 1737135.  Total volume = 1.317329e+12.  Cell volumes OK.
    Mesh non-orthogonality Max: 179.9979 average: 7.740474
   *Number of severely non-orthogonal faces: 141.
 ***Number of non-orthogonality errors: 151.
  <<Writing 292 non-orthogonal faces to set nonOrthoFaces
 ***Error in face pyramids: 280 faces are incorrectly oriented.
  <<Writing 164 faces with incorrect orientation to set wrongOrientedFaces
 ***Max skewness = 5.783191, 3 highly skew faces detected which may impair the quality of the results
  <<Writing 3 skew faces to set skewFaces
Failed 4 mesh checks.
Unfortunately, I can not share the mesh due to confidentiality reasons..

I'm wondering about the severity of these failed checks..
I my opinion the aspects ratio cells are not really of concern, as they are the remote cells in the very top of the domain..
The nonOrthogonality is neither of much concern I believe..
The skewness is only 3 cells, which I have located outside my area of interest

The one I'm wondering about is the incorrectly oriented faces.. How serious is this, and what would you recommend doing to avoid this error?
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Old   February 23, 2011, 12:32
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Hi.

I don't know if you still have the same problem since it is bit outdated however I would like to say that your computations will not be able to convergence as long as wrong oriented faces exist in your mesh. You may skip the others, like non-orthogonal faces and skewness etc.

If you could solve this issue, I would like to know your snappy settings for the boundary layer addition part in the snappyHexMeshDict. I have a similar trouble and now I'm trying to figure out what the optimal settings are.

Best,
Fatih.
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Old   February 8, 2012, 12:35
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Quote:
Originally Posted by fertinaz View Post
Hi.

I don't know if you still have the same problem since it is bit outdated however I would like to say that your computations will not be able to convergence as long as wrong oriented faces exist in your mesh. You may skip the others, like non-orthogonal faces and skewness etc.

If you could solve this issue, I would like to know your snappy settings for the boundary layer addition part in the snappyHexMeshDict. I have a similar trouble and now I'm trying to figure out what the optimal settings are.

Best,
Fatih.
Hey, Fatih,
I have the same problem now, after snappyHexMesh, some error like "incorrectly oriented faces" showed up.
Could you please tell me how to solve the problem?
Thank you so much!
Aqua
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Old   August 9, 2014, 06:21
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Ye Zhang
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Hi all,

Do you have any solutions now? I also have the same problem "incorrectly oriented faces" in my mesh. I do not know why. I generated the mesh by using Pointwise.

Any suggestions are appreciated!

Ye
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Old   November 17, 2014, 17:00
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Franjo Juretic
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Hello,

What is the format (ascii or binary) is used for storing the OpenFOAM mesh after conversion? In general, it is best to use binary because it preserves all information about the vertex coordinates.
This is especially critical in bnd layers, which may be of the same thickness as the truncated part of the vertex coordinates. Therefore, it may happen that a valid mesh becomes invalid after conversion.
Incorrectly oriented faces mean that the mesh is invalid because there exist face normals pointing into the owner cell instead of outside. This causes conservation problems because the fluxes through such face contribute to the cell with a wrong sign.
I hope this helps a bit.

Kind Regards,

Franjo

Quote:
Originally Posted by kiddmax View Post
Hi all,

Do you have any solutions now? I also have the same problem "incorrectly oriented faces" in my mesh. I do not know why. I generated the mesh by using Pointwise.

Any suggestions are appreciated!

Ye
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Old   June 8, 2015, 07:19
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Quote:
Originally Posted by cfdmarkus View Post
Hi all,

I am trying to load a fairly complex ccm mesh.
The mesh has been tested in StarCCM and seems to work fine.

When I load the mesh in OpenFOAM I get a bunch off errors and warnings (see below). The case does run for a few iterations before the simulation crashes.

I am particulary concerned about those 2 errors:

Error in face pyramids: 143 faces are incorrectly oriented
Number of non-orthogonality errors: 15.

How important are they and do they need fixing in StarCCM?

Any help is appreciated.

Markus






Checking topology...
Boundary definition OK.
Point usage OK.
<<Found 1101 neighbouring cells with multiple inbetween faces.
Upper triangular ordering OK.
<<Writing 2297 unordered faces to set upperTriangularFace
Topological cell zip-up check OK.
Face vertices OK.
***Number of duplicate (not baffle) faces found: 306
***Number of faces with non-consecutive shared points: 540
<<Writing 1405 faces with incorrect edges to set edgeFaces
Number of regions: 1 (OK).



Checking geometry...
Overall domain bounding box (-2.18829e-07 -7.47931 -0.277615) (2.86 12.042 4.66777)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (-3.71575e-13 -8.51015e-14 -1.25127e-12) OK.
Max cell openness = 1.52626e-15 OK.
Max aspect ratio = 131.378 OK.
***Zero or negative face area detected. Minimum area: 0
<<Writing 1 zero area faces to set zeroAreaFaces
Min volume = 7.78059e-14. Max volume = 6.85685e-05. Total volume = 254.056. Cell volumes OK.
Mesh non-orthogonality Max: 121.889 average: 4.92652
*Number of severely non-orthogonal faces: 2880.
***Number of non-orthogonality errors: 15.
<<Writing 2895 non-orthogonal faces to set nonOrthoFaces
***Error in face pyramids: 143 faces are incorrectly oriented.
<<Writing 140 faces with incorrect orientation to set wrongOrientedFaces
***Max skewness = 88.8617, 233 highly skew faces detected which may impair the quality of the results
<<Writing 233 skew faces to set skewFaces
*Edges too small, min/max edge length = 0 0.0543461, number too small: 34
<<Writing 34 points on short edges to set shortEdges
*There are 5188 faces with concave angles between consecutive edges. Max concave angle = 89.9778 degrees.
<<Writing 5188 faces with concave angles to set concaveFaces
Face flatness (1 = flat, 0 = butterfly) : average = 0.999981 min = 0.0551237
*There are 447 faces with ratio between projected and actual area < 0.8
Minimum ratio (minimum flatness, maximum warpage) = 0.0551237
<<Writing 447 warped faces to set warpedFaces
Cell determinant (wellposedness) : minimum: 2.11744e-08 average: 8.24052
***Cells with small determinant found, number of cells: 189153
<<Writing 189153 under-determined cells to set underdeterminedCells

Failed 6 mesh checks.
Hello all,

Does anyone know if the number of stars (*, ** or ***) before the error message indicates the severeness of the problem. Let's say if a complaint goes with ***, it should be fixed under any cirmumstances?

Best regards,

Kate
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Old   June 9, 2015, 10:50
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Franjo Juretic
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Hello,

Quote:
Originally Posted by KateEisenhower View Post
Hello all,

Does anyone know if the number of stars (*, ** or ***) before the error message indicates the severeness of the problem. Let's say if a complaint goes with ***, it should be fixed under any cirmumstances?
Your assumption is correct. The errors with three stars are the most important.
From my experience with OpenFOAM, the most important check is for face pyramids, and they must not be negative. If this check fails, it is almost impossible to get a meaningful solution because the discretisation is no longer conservative. Zero area faces make the mesh "disconnected" locally, and that can also cause problems with convergence.
Most other metrics like non-orthogonality, skewness, flatness can cause problems when they are located in regions of high gradient variation, like boundary layers, shear layers, etc.
Please bear in mind that it is extremely difficult to generate meshes satisfying all quality metrics, especially in complex geometries, and with small number of cells, so my suggestion is to focus on face pyramids, and zero are faces first.
I hope this helps a bit.

Regards,

Franjo
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