CFD Online Discussion Forums - [Other] Single cubic cell (full case inc.) with det = 0. Why? :)

Hi everyone!

I'm running a case with many blockMeshDict hex blocks and was using

Code:

$ checkMesh -allTopology -allGeometry

results as a measure of mesh goodness. However, on one mesh my determinant values were all close to zero though the mesh looked good. I have managed to duplicate the effect with a very simple case using a single, cubic cell:

Code:

$ mkdir -p 0 system constant/polyMesh

Code:

system/controlDict: 

FoamFile {version 2.0; format ascii; class dictionary; location "system";

    object controlDict; }

deltaT 1; writeFrequency  1;

Code:

system/fvSchemes: 

FoamFile{version 2.0; format ascii; class dictionary; object fvSchemes;}

divSchemes { default none;}

gradSchemes { default none;}

laplacianSchemes {default none;}

Code:

system/fvSolution: 

FoamFile{ version 2.0; format ascii; class dictionary; object fvSolution;}

Code:

constant/polyMesh/blockMeshDict: 

FoamFile { version 2.0; format ascii; class dictionary; 

    object blockMeshDict; }



convertToMeters 1;



vertices (

   (0 0 0) (1 0 0) (1 1 0) (0 1 0)

   (0 0 1) (1 0 1) (1 1 1) (0 1 1)

) ;



blocks ( hex (0 1 2 3 4 5 6 7) air (1 1 1) simpleGrading (1 1 1) ) ;



// rhscrew looking in.

boundary (

   in { type patch; faces ( ( 3 7 4 0) ) ; }

  out { type patch; faces ( ( 6 2 1 5) ) ; }

front { type patch; faces ( ( 7 6 5 4) ) ; }

 back { type patch; faces ( ( 2 3 0 1) ) ; }

  top { type patch; faces ( ( 3 2 6 7) ) ; }

bottom{ type patch; faces ( ( 4 5 1 0) ) ; }

   )

Please create the mesh with

Code:

$blockMesh

and check the mesh with

Code:

$ checkMesh -allTopology -allGeometry

My OF 2.2.2-9240f8b967db running on up-to-date Ubuntu 12.04.4 LTS
shows,

Code:

Checking geometry...

    Overall domain bounding box (0 0 0) (1 1 1)

    Mesh (non-empty, non-wedge) directions (1 1 1)

    Mesh (non-empty) directions (1 1 1)

    Boundary openness (0 0 0) OK.

    Max cell openness = 0 OK.

    Max aspect ratio = 1 OK.

    Minimum face area = 1. Maximum face area = 1.  Face area magnitudes OK.

    Min volume = 1. Max volume = 1.  Total volume = 1.  Cell volumes OK.

    Non-orthogonality check OK.

    Face pyramids OK.

    Max skewness = 0 OK.

    Coupled point location match (average 0) OK.

    Face tets OK.

    Min/max edge length = 1 1 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 average: 0

 ***Cells with small determinant (< 0.001) found, number of cells: 1

  <<Writing 1 under-determined cells to set underdeterminedCells

    Concave cell check OK.



Failed 1 mesh checks.

but that cell looks lovely to me! Can anybody please explain why I'm getting a mesh failure for this case?

Thanks!

Best regards,

Mark.

P.S. I attended an OpenFOAM training course a few months ago in London and hoped there would be much post-training chat via a board put together by one of the guys on the course; but nothing came of it. Does anybody know if that group / board took off? :)