[Tobi]

Hi all,

i am trying to mesh a simple axis symmetric geometry.
For that I mesh a nonsymetric geometry (shown in pictures). Then I want to extrude the front with extrudeMesh to generate a 2d rotation symmetrc mesh.

This is working property but checkMesh give me a lot of errors.

Do anybody has a suggestion why this occure?

My steps:

1. generate backgroundmesh
2. snappyHexMesh (castellated + snap)
3. extrudeMesh


- I tryed flattenMesh befor extrude mesh but that is not working.

Here the output of checkMesh

Mesh stats
    points:           36991
    internal points:  0
    faces:            72242
    internal faces:   35524
    cells:            17919
    faces per cell:   6.0140633
    boundary patches: 7
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     17614
    prisms:        32
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     273
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            7   262
            8   11

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
                   Patch    Faces   Points                  Surface topology
                     top      244      490  ok (non-closed singly connected)
                    side       58      118  ok (non-closed singly connected)
                   front    17919    18506  ok (non-closed singly connected)
                    back    17919    18506  ok (non-closed singly connected)
           groundAndWall      492      985  ok (non-closed singly connected)
                   inlet        6       13  ok (non-closed singly connected)
                  nozzel       80      162  ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (0 -0.005 -0.0022343265) (0.11988579 0.02 0.0082343265)
    Mesh (non-empty, non-wedge) directions (1 1 0)
    Mesh (non-empty) directions (1 1 1)
    Wedge front with angle 2.4999999 degrees
    Wedge back with angle 2.4999999 degrees
    All edges aligned with or perpendicular to non-empty directions.
    Boundary openness (-1.5889318e-15 3.1319549e-16 -6.6387106e-15) OK.
    Max cell openness = 2.7260862e-16 OK.
    Max aspect ratio = 2.0340928 OK.
    Minimum face area = 2.7234933e-09. Maximum face area = 5.2528493e-06.  Face area magnitudes OK.
 ***Zero or negative cell volume detected.  Minimum negative volume: -2.6273155e-09, Number of negative volume cells: 17919
  <<Writing 17919 zero volume cells to set zeroVolumeCells
    Mesh non-orthogonality Max: 180 average: 177.62971
 ***Number of non-orthogonality errors: 35524.
  <<Writing 35524 non-orthogonal faces to set nonOrthoFaces
 ***Error in face pyramids: 107766 faces are incorrectly oriented.
  <<Writing 72242 faces with incorrect orientation to set wrongOrientedFaces
    Max skewness = 0.4904183 OK.
    Coupled point location match (average 0) OK.

Failed 3 mesh checks.

End

But befor I get a very big list of warnings:

At local face at (0.10928851 -0.0043930049 0.0077716393) the normal (0.043619418 -2.2166221e-07 -0.99904822) differs from the average normal (0.043619386 -4.2341179e-10 -0.99904822) by 4.9963981e-14
Either correct the patch or split it into planar parts
--> FOAM Warning : 
    From function wedgePolyPatch::calcGeometry(PstreamBuffers&)
    in file meshes/polyMesh/polyPatches/constraint/wedge/wedgePolyPatch.C at line 72
    Wedge patch 'back' is not planar.
At local face at (0.10929251 -0.0041364963 0.007771814) the normal (0.043618896 -4.4251257e-07 -0.99904824) differs from the average normal (0.043619386 -4.2341179e-10 -0.99904822) by 4.3602494e-13
Either correct the patch or split it into planar parts
--> FOAM Warning : 
    From function wedgePolyPatch::calcGeometry(PstreamBuffers&)
    in file meshes/polyMesh/polyPatches/constraint/wedge/wedgePolyPatch.C at line 72
    Wedge patch 'back' is not planar.
At local face at (0.11900384 -0.0044040385 0.00819582) the normal (0.043619617 4.8947379e-07 -0.99904821) differs from the average normal (0.043619386 -4.2341179e-10 -0.99904822) by 2.9339209e-13
Either correct the patch or split it into planar parts
--> FOAM Warning : 
    From function wedgePolyPatch::calcGeometry(PstreamBuffers&)
    in file meshes/polyMesh/polyPatches/constraint/wedge/wedgePolyPatch.C at line 72
    Wedge patch 'back' is not planar.
At local face at (0.11925451 -0.0044021974 0.0082067643) the normal (0.043619548 1.9122314e-07 -0.99904821) differs from the average normal (0.043619386 -4.2341179e-10 -0.99904822) by 6.2926615e-14
Either correct the patch or split it into planar parts
--> FOAM Warning : 
    From function wedgePolyPatch::calcGeometry(PstreamBuffers&)
    in file meshes/polyMesh/polyPatches/constraint/wedge/wedgePolyPatch.C at line 72
    Wedge patch 'back' is not planar.
At local face at (0.11925456 -0.0041549939 0.0082067666) the normal (0.043619468 -2.038851e-07 -0.99904822) differs from the average normal (0.043619386 -4.2341179e-10 -0.99904822) by 4.8028036e-14
Either correct the patch or split it into planar parts
--> FOAM Warning : 
    From function wedgePolyPatch::calcGeometry(PstreamBuffers&)
    in file meshes/polyMesh/polyPatches/constraint/wedge/wedgePolyPatch.C at line 72
    Wedge patch 'back' is not planar.
At local face at (0.11950626 -0.0043992163 0.008217756) the normal (0.043619139 7.7844624e-08 -0.99904823) differs from the average normal (0.043619386 -4.2341179e-10 -0.99904822) by 6.7515101e-14
Either correct the patch or split it into planar parts
--> FOAM Warning : 
    From function wedgePolyPatch::calcGeometry(PstreamBuffers&)
    in file meshes/polyMesh/polyPatches/constraint/wedge/wedgePolyPatch.C at line 72
    Wedge patch 'back' is not planar.
At local face at (0.11975968 -0.0043975095 0.0082288204) the normal (0.043619288 7.067434e-08 -0.99904823) differs from the average normal (0.043619386 -4.2341179e-10 -0.99904822) by 1.4659395e-14
Either correct the patch or split it into planar parts
--> FOAM Warning : 
    From function wedgePolyPatch::calcGeometry(PstreamBuffers&)
    in file meshes/polyMesh/polyPatches/constraint/wedge/wedgePolyPatch.C at line 72
    Wedge patch 'back' is not planar.
At local face at (0.11975944 -0.0041506596 0.0082288101) the normal (0.043619244 -2.5265662e-08 -0.99904823) differs from the average normal (0.043619386 -4.2341179e-10 -0.99904822) by 2.0892414e-14
Either correct the patch or split it into planar parts

Any hints are kindly appreciated
Regards Tobi

[Tobi]

Okay I managed a lot of things by changing the patches of extrusion from front to back. Now checkMesh is okay:

Mesh stats
    points:           36991
    internal points:  0
    faces:            72242
    internal faces:   35524
    cells:            17919
    faces per cell:   6.0140633
    boundary patches: 8
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     17614
    prisms:        32
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     273
    Breakdown of polyhedra by number of faces:
        faces   number of cells
            7   262
            8   11

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces...
                   Patch    Faces   Points                  Surface topology
                    axis        0        0                        ok (empty)
                     top      244      490  ok (non-closed singly connected)
                    side       58      118  ok (non-closed singly connected)
                   front    17919    18506  ok (non-closed singly connected)
                    back    17919    18506  ok (non-closed singly connected)
           groundAndWall      492      985  ok (non-closed singly connected)
                   inlet        6       13  ok (non-closed singly connected)
                  nozzel       80      162  ok (non-closed singly connected)

Checking geometry...
    Overall domain bounding box (0 -0.005 -0.0052343265) (0.11988579 0.02 0.0052343265)
    Mesh (non-empty, non-wedge) directions (1 1 0)
    Mesh (non-empty) directions (1 1 1)
    Wedge front with angle 2.5 degrees
    Wedge back with angle 2.5 degrees
    All edges aligned with or perpendicular to non-empty directions.
    Boundary openness (6.9999917e-16 -1.0560211e-15 -1.0271528e-14) OK.
    Max cell openness = 3.2088808e-16 OK.
    Max aspect ratio = 2.0340939 OK.
    Minimum face area = 2.7234931e-09. Maximum face area = 5.2528493e-06.  Face area magnitudes OK.
    Min volume = 6.1406691e-13. Max volume = 2.6273154e-09.  Total volume = 1.5537909e-05.  Cell volumes OK.
    Mesh non-orthogonality Max: 19.65403 average: 2.3702856
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.49041924 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

End

But I still got these extrem amount of warnings that the front and back are not planar ?

[Tobi]

Problem solved by changing writeFormat from ascii to binary.

http://www.cfd-online.com/Forums/ope...tml#post302438

[Antony_P]

Hi Tobi,

Thanks for the post. I am facing a similar problem. When i extrude mesh from patch as 'sector' it runs fine but checkMesh gives 2 errors.

but when i extrude as 'wedge', extrudeMesh is crashing.

Thanks & Regards,
Antony Ashley Raja

[Tobi]

Hi, Check out my tutorials at my Homepage. Maybe you an solve the problem with that.

[Antony_P]

Thank you very much !! The tutorial hydraulicJumpStream helped alot.

I have now solved the problem.

[zannatul]

Originally Posted by Tobi

Problem solved by changing writeFormat from ascii to binary.

http://www.cfd-online.com/Forums/ope...tml#post302438

Hi Tobi

I have followed your hydraulic jump stream tutorial and was able to create a wedge geometry. But I am getting exactly same warnings as you posted. It is saying the front and back wedge face is not planner. The checkMesh is giving me 3 errors. I have changed my write precision from ascii to binary but no improvement was achieved. I saw that at some places the mesh is not smooth may be which is making the wedge non planner. I am attaching my case here. Also I am attaching image showing non-smooth mesh. Please have a look at my case.Till now your suggestions helped me a lot to move forward. Help me one more time Please.

Thanks

Zannatul

[Tobi]

Hi,

I would like to ask you, if I can put your case as a demonstrating tutorial on my homepage?

Some hints to you case:

1. Why you place your BG mesh in such a bad way?
2. If you already had a regionSTL (join.stl), I would prefer to use this (your shm dict gets more clean)
3. Notice, you are using featureRefinement but you have problems refining the features. It is like what I did here: http://www.holzmann-cfd.de/index.php...n/feature-edge
4. nLayersBetweenCells is equal to 1. Bad choice...

My result is at least:

Checking geometry...
    Overall domain bounding box (5.381473299e-19 0 -0.006647594717) (0.1522549509 0.1400000006 0.006647594717)
    Mesh (non-empty, non-wedge) directions (1 1 0)
    Mesh (non-empty) directions (1 1 1)
    Wedge front with angle 2.499999999 degrees
    Wedge back with angle 2.499999999 degrees
    All edges aligned with or perpendicular to non-empty directions.
    Boundary openness (-1.57321546e-14 4.635052846e-19 1.398782485e-14) OK.
    Max cell openness = 3.237941764e-16 OK.
    Max aspect ratio = 2.360620704 OK.
    Minimum face area = 1.61861228e-08. Maximum face area = 1.452864706e-05.  Face area magnitudes OK.
    Min volume = 1.11902422e-11. Max volume = 1.127843696e-08.  Total volume = 0.0001021924827.  Cell volumes OK.
    Mesh non-orthogonality Max: 18.4156806 average: 0.4810143038
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.5287255358 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

End

Cheers,

[Tobi]

The case I made for your geometry is available on my homepage: http://holzmann-cfd.de/index.php/en/openfoam

Please tell me if I am not allowed to share it.

[zannatul]

Originally Posted by Tobi

The case I made for your geometry is available on my homepage: http://holzmann-cfd.de/index.php/en/openfoam

Please tell me if I am not allowed to share it.

Hi Tobi

Sorry for replying late. I am glad that you consider my case to be shareable in your homepage. You can do so. And thank you so much for looking in my case and your help to solve it. I am going to look over it. And I will follow the hints you have mentioned.

One thing I need to ask you is that what do you think can be a better way for my background mesh?

Thank you again.

Zannatul

[Tobi]

To you question: it is up to you ... The background mesh should be pure quadric. This is best for sHM.

Tobi

[zannatul]

Originally Posted by Tobi

To you question: it is up to you ... The background mesh should be pure quadric. This is best for sHM.

Tobi

Hi Tobi

Thank you for your reply. I really appreciate your help.

Zannatul

[zannatul]

Originally Posted by Tobi

Hi,

I would like to ask you, if I can put your case as a demonstrating tutorial on my homepage?

Some hints to you case:

1. Why you place your BG mesh in such a bad way?
2. If you already had a regionSTL (join.stl), I would prefer to use this (your shm dict gets more clean)
3. Notice, you are using featureRefinement but you have problems refining the features. It is like what I did here: http://www.holzmann-cfd.de/index.php...n/feature-edge
4. nLayersBetweenCells is equal to 1. Bad choice...

My result is at least:

Checking geometry...
    Overall domain bounding box (5.381473299e-19 0 -0.006647594717) (0.1522549509 0.1400000006 0.006647594717)
    Mesh (non-empty, non-wedge) directions (1 1 0)
    Mesh (non-empty) directions (1 1 1)
    Wedge front with angle 2.499999999 degrees
    Wedge back with angle 2.499999999 degrees
    All edges aligned with or perpendicular to non-empty directions.
    Boundary openness (-1.57321546e-14 4.635052846e-19 1.398782485e-14) OK.
    Max cell openness = 3.237941764e-16 OK.
    Max aspect ratio = 2.360620704 OK.
    Minimum face area = 1.61861228e-08. Maximum face area = 1.452864706e-05.  Face area magnitudes OK.
    Min volume = 1.11902422e-11. Max volume = 1.127843696e-08.  Total volume = 0.0001021924827.  Cell volumes OK.
    Mesh non-orthogonality Max: 18.4156806 average: 0.4810143038
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 0.5287255358 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

End

Cheers,

Hi Tobi

What I want now is finer mesh close to walls and coarse mesh inside. So I used Feature refinement level as 3. After extruding the mesh, nfaces of axis should be zero. But I am getting some value. So after I do create patch it is again saying wedge is not planar. My feature refinement is not good that is why I guess this error is occurring. I have seen that when you solved my case you got good feature edge refinement. What is the trick here?
I checked the tutorial you told me about it. I saw you used .obj file for feature refinement. In my case should I similarly use .obj file of the outline of my geometry? I have never used blender. Can solidworks do that?
Please let me know a solution for this problem. I have attached my case and two images for your understanding.

Thanks!

Zannatul

[Tobi]

Do Not use Features edge refinement it you Do Not Know how to use it.

[zannatul]

Originally Posted by Tobi

Do Not use Features edge refinement it you Do Not Know how to use it.

I am afraid for my work I need featureEdgeRefinement. But whether I use it or not, I am not getting nfaces of axis as zero after extruding (in boundary file) . I played with ncellsbetweenlevels and resolvefeatureangle, but with no improvement. May be I am not understanding what is a good way for what I want to achieve . Anyway, Thanks for your suggestion.

Zannatul

[Tobi]

You can use surfaceRefinement (because you will extrude at least and it does not matter in your case) or use featureEdge refinement and check out my tutorial on my homepage about featureEdge refinement.

Keep in mind that a surface refinement will lead to better curvature. If this will influence at last the 2d extrusion - i don't know.

[zannatul]

Originally Posted by Tobi

You can use surfaceRefinement (because you will extrude at least and it does not matter in your case) or use featureEdge refinement and check out my tutorial on my homepage about featureEdge refinement.

Keep in mind that a surface refinement will lead to better curvature. If this will influence at last the 2d extrusion - i don't know.

Hi Tobi

Thanks for the suggestion. If you do not mind can I ask you one thing? The case of mine you demonstrated in your page, in that case you have used 0 level surface refinement and 0 level feature refinement. But still the mesh along the curve was good and the wedge shape was perfect. Can you please briefly explain me this? Was it possible because the cells of the background mesh was very fine?

Zannatul

[wyldckat]

Quick answer: I took a brief look into the page and what's written on this current thread and:

Originally Posted by zannatul

The case of mine you demonstrated in your page, in that case you have used 0 level surface refinement and 0 level feature refinement. But still the mesh along the curve was good and the wedge shape was perfect. Can you please briefly explain me this? Was it possible because the cells of the background mesh was very fine?

The reason is very likely because the base mesh is uniform and has a good enough resolution.

If you use surface refinement, this means that snappyHexMesh might have certain regions that are more uniform than others, due to how the refinement transitions between levels and near the curves.

If you can provide detailed images with and without refinement, I can point out the reasons why this is happening.

[Tobi]

Thanks Bruno for the details. I want to add some more information. Using surfaceFeatureRefinement you have to be sure that sHM realize the feature edges. Some times it happens, that the feature edges have to be modified (position change). I demonstrated this in the "surfaceFeatureEdge" tutorial on my homepage.

In your case I would prefer the surfaceRefinement to get a smooth refinement at each of the wall faces. Also (as Bruno mentioned) I suggest you to use a uniform background mesh.

[zannatul]

Hi Bruno and Tobi
Extremely sorry for responding late. This is our spring break week and I am away from my work station. I will not be able to go through your suggestions and post my queries before next week. I will post next week. Thank you both for increasing my knowledge.

Zannatul