[Tobi]

Hi all,

i normally check my mesh with checkMesh.
In my present mesh there are no errors by using the standard version. But if i add some arguments like -allGeometry, -allTopologys I ll get errors.

So the question is. Are these errors critical?

- allGeometry

   *There are 350 faces with concave angles between consecutive edges. Max concave angle = 68.2256 degrees.
  <<Writing 350 faces with concave angles to set concaveFaces
    Face flatness (1 = flat, 0 = butterfly) : average = 0.997966  min = 0.458419
   *There are 19 faces with ratio between projected and actual area < 0.8
    Minimum ratio (minimum flatness, maximum warpage) = 0.458419
  <<Writing 19 warped faces to set warpedFaces
    Cell determinant (wellposedness) : minimum: 0.035225 average: 13.0762
    Cell determinant check OK.
 ***Concave cells (using face planes) found, number of cells: 8259
  <<Writing 8259 concave cells to set concaveCells

-allTopology

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Topological cell zip-up check OK.
  <<Number of duplicate (not baffle) faces found: 1. This might indicate a problem.
  <<Number of faces with non-consecutive shared points: 1. This might indicate a problem.
  <<Writing 3 faces with non-standard edge connectivity to set edgeFaces
    Number of regions: 1 (OK).

I know that *** errors are critical. I wrote out those cells and loaded the files into paraview.
the concave cells are good cells ?!? I am a bit confused with that output.

For answers and solutions I ll be very thankful couse in my solver one scalar is running away all the time :/
Tobi

[wyldckat]

Hi Tobi,

I personally always have trouble memorizing what concave means But that's what wikipedia is for: http://en.wikipedia.org/wiki/Concave

Therefore, concave cells are baaaaad.

If you converted the cellSet using foamToVTK, you should have used the option "-poly", so it will export using polyhedral meshes, instead of decomposing those cells into tetrahedral cells.

As for fixing these cells... refining only them might fix the problem... either that, or create the mesh again, with better quality parameters

Best regards,
Bruno

[Tobi]

Originally Posted by wyldckat

Hi Tobi,

I personally always have trouble memorizing what concave means But that's what wikipedia is for: http://en.wikipedia.org/wiki/Concave

Therefore, concave cells are baaaaad.

If you converted the cellSet using foamToVTK, you should have used the option "-poly", so it will export using polyhedral meshes, instead of decomposing those cells into tetrahedral cells.

As for fixing these cells... refining only them might fix the problem... either that, or create the mesh again, with better quality parameters

Best regards,
Bruno

Hi Bruno,

thanks for your replay.
With setSet I filtered the concave cells to a VTK format and had a look at those cells. These cells are on the curvature of my sphere and they seem like to be good. Hmmm ...

well I ll try your suggestions.
The quality parameters are the standard settings in snappyHexMesh and I think that these parameters standing for high resolution, arent they?

Thanks tobi

[Tobi]

Hi Bruno

I had a look to that cells again (screenshot).
There you can see my concave cells - but they are just normal hexaedral cells ? ? ?

Not like the one in your link.
I am confused?

Any suggestions?

[Tobi]

Hi Bruno,

Additionally I wrote that thread http://www.cfd-online.com/Forums/openfoam-meshing-utilities/61501-about-openfoam-concave-faces-cells.html#post191366

Eugene mentioned that concave cells are not a big problem

Tobi

[shipman]

Hi Tobi,

I have same error as same as you as follows. Could you tell me what is your observation about concave error? Can it to be corrected? or what i should do to solve this problem. bcs it gives also error during running of calculation.

Mesh stats
    points:           654382
    faces:            1596014
    internal faces:   1412748
    cells:            471322
    boundary patches: 3
    point zones:      0
    face zones:       0
    cell zones:       0

Overall number of cells of each type:
    hexahedra:     410213
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:     61109

Checking topology...
    Boundary definition OK.
    Cell to face addressing OK.
    Point usage OK.
    Upper triangular ordering OK.
    Face vertices OK.
    Topological cell zip-up check OK.
    Face-face connectivity OK.
    Number of regions: 1 (OK).

Checking patch topology for multiply connected surfaces ...
    Patch               Faces    Points   Surface topology                   Bounding box
    wall                182766   183793   ok (non-closed singly connected)   (-0.006 -0.008 -2.71051e-20) (0.00194 0.007 0.00194)
    outlet              100      121      ok (non-closed singly connected)   (0 -0.008 0) (0.00194 -0.008 0.00194)
    inlet               400      451      ok (non-closed singly connected)   (-0.006 0.007 0) (0.00194 0.007 0.00194)

Checking geometry...
    Overall domain bounding box (-0.006 -0.008 -2.71051e-20) (0.00194 0.007 0.00194)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (2.22526e-14 -1.42534e-17 -2.50737e-15) OK.
    Max cell openness = 2.06795e-16 OK.
    Max aspect ratio = 2.5 OK.
    Minumum face area = 3.75e-11. Maximum face area = 1.6e-07.  Face area magnitudes OK.
    Min volume = 7.03125e-16. Max volume = 6.4e-11.  Total volume = 1.37934e-07.  Cell volumes OK.
    Mesh non-orthogonality Max: 29.0546 average: 10.3431
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 1.6129 OK.
    Coupled point location match (average 0) OK.
    Face tets OK.
    Min/max edge length = 5e-06 0.0004 OK.
    All angles in faces OK.
    Face flatness (1 = flat, 0 = butterfly) : average = 1  min = 1
    All face flatness OK.
    Cell determinant (wellposedness) : minimum: 0.821136 average: 13.565
    Cell determinant check OK.
 ***Concave cells (using face planes) found, number of cells: 58628
  <<Writing 58628 concave cells to set concaveCells

Failed 1 mesh checks.

[wyldckat]

Greetings to all!

@George: I'll try to answer you on this topic at your other thread: http://www.cfd-online.com/Forums/ope...oam-error.html

Best regards,
Bruno

[mkhm]

Dear Tobias and Bruno,

I have similar errors for concave cells. The checkMesh runs fine but checkMesh -allGeometry indicates that it fails (Failed 1 mesh checks). The cases were running fine and I did not realize there was a problem. However, when I wanted to use refineMesh to create a new test case in order to check the sensitivity of my mesh, it failed due to the concave cells. In another test case, I wanted to mapFields the results of a coarser mesh to a refined one and it failed for the same reason. Is there any mean to circumvent this issue ? like merging or refining them ? Do you have any successful experience about these kind of meshes without redoing the mesh and simulations ?

Regards,
Mary

[petros]

Hi Mary,

Originally Posted by mkhm

However, when I wanted to use refineMesh to create a new test case in order to check the sensitivity of my mesh, it failed due to the concave cells.
Mary

Could you please post the code snippet of that error?

In general, if you have a relatively good mesh and the only warning from checkMesh is for concave cells, which you have visualised and confirmed that are proper hex cells, you shouldn't have any problem.