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Single cubic cell (full case inc.) with det = 0. Why? :)

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Old   February 19, 2014, 10:44
Default Single cubic cell (full case inc.) with det = 0. Why? :)
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ms
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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?

Last edited by anothr_acc; February 19, 2014 at 11:50.
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Old   February 21, 2014, 06:04
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ms
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I'm still interested, though ignoring the determinant results from checkMesh. Seems a pity...
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