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-   -   Problem with "faces are incorrectly oriented" (http://www.cfd-online.com/Forums/openfoam-meshing/103013-problem-faces-incorrectly-oriented.html)

 The_Architect June 8, 2012 07:15

Problem with "faces are incorrectly oriented"

Hi,

I'm building a simple mesh with four rectangular blocks. The mesh is basically a basin for a ship simulation. After running the blockMesh command I get a mesh which looks as expected. My vertices and blocks are defined as following:

vertices
(
(-3 -1 -2) //0
(-3 0.2 -2)//1
(-3 0.2 2) //2
(-3 -1 2) //3
(6 -1 -2) //4
(6 0.2 -2) //5
(6 0.2 2) //6
(6 -1 2) //7
(-3 0 -2) //8
(-3 0 2) //9
(6 0 -2) //10
(6 0 2) //11
(-1 -1 -2) //12
(-1 -1 2) //13
(-1 0.2 -2) //14
(-1 0.2 2) //15
(-1 0 -2) //16
(-1 0 2) //17

);

blocks
(
hex (0 12 13 3 8 16 17 9) (20 40 10) simpleGrading (1 1 1) // lowInflow
hex (8 16 17 9 1 14 15 2) (20 40 3) simpleGrading (1 1 1) // highInflow
hex (12 4 7 13 16 10 11 17) (60 40 10) simpleGrading (1 1 1) // lowOutflow
hex (16 10 11 17 14 5 6 15) (60 40 3) simpleGrading (1 1 1) // highOutflow

);

Here is a picture of the mesh created:

http://i48.tinypic.com/3097v9k.png

However, if I run the checkMesh command i get the following report:

Checking geometry...
Overall domain bounding box (-3 -1 -2) (6 0.2 2)
Mesh (non-empty, non-wedge) directions (1 1 1)
Mesh (non-empty) directions (1 1 1)
Boundary openness (2.86187e-16 -2.61027e-15 6.96478e-16) OK.
***High aspect ratio cells found, Max aspect ratio: 6.99956e+197, number of cells 41600
<<Writing 41600 cells with high aspect ratio to set highAspectRatioCells
Minumum face area = 0.00666667. Maximum face area = 0.0116667. Face area magnitudes OK.
Min volume = 2e-300. Max volume = 2e-300. Total volume = 8.32e-296. Cell volumes OK.
Mesh non-orthogonality Max: 180 average: 180
***Number of non-orthogonality errors: 120040.
<<Writing 120040 non-orthogonal faces to set nonOrthoFaces
***Error in face pyramids: 249600 faces are incorrectly oriented.
<<Writing 129560 faces with incorrect orientation to set wrongOrientedFaces
Max skewness = 3.75088e-12 OK.
Coupled point location match (average 0) OK.

Failed 3 mesh checks.

End

If I try to run snappyHesMesh after this, I get a the following report:

--> FOAM Warning :
From function Foam::List<Foam::FixedList<Foam::label, 4> >Foam::Cloud<ParticleType>::faceTetIndices(label fI, label cI) const
in file meshes/polyMesh/polyMeshTetDecomposition/polyMeshTetDecomposition.C at line 561
No base point for face 119975, 4(43969 46429 46430 43970), produces a valid tet decomposition.

And finally, snappyHexMesh crashes with the following report:

--> FOAM FATAL ERROR:
Point (4.01251 -0.24185 0.215215) is not inside the mesh or on a face or edge.
Bounding box of the mesh (-3 -1 -2) (6 0.2 2)

which does not make sense as the point is clearly inside the mesh.

All of this seems really odd to be when considered the fact that the geometry is really simple and only hexahedrons are used, all of the same size.

Any help would be appreciated.

 anon_a June 8, 2012 08:28

You didn't mention the error messages of blockMesh, which are of this sort:

--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 128
zero or negative pyramid volume: -1.33333 for face 0

Your geometry is defined inside out. This is why it is black instead of white in paraFoam.
This is corrected by changing the order of vertex indices in the block section.
Please check the manual for blockMesh (and the forum! this is a very common mistake).

 vasava January 31, 2013 06:50

Thanks!!

I had the same problem and the tip worked perfectly.

Thank you anon_a.

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