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-   -   Meshing of A380 (http://www.cfd-online.com/Forums/openfoam-meshing-snappyhexmesh/122706-meshing-a380.html)

Mirage12 August 26, 2013 08:47

Meshing of A380
 
Hello Foamers :)

I am meshing an aircraft "A380" using snappyHexMesh :)

Here is my snappyHexMeshDict:


Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.2.0                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    object      snappyHexMeshDict;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Which of the steps to run
castellatedMesh true;
snap            true;
addLayers      false;


// Geometry. Definition of all surfaces. All surfaces are of class
// searchableSurface.
// Surfaces are used
// - to specify refinement for any mesh cell intersecting it
// - to specify refinement for any mesh cell inside/outside/near
// - to 'snap' the mesh boundary to the surface
geometry
{

  A380.stl
    {
        type triSurfaceMesh;
        name A380;
    }
box
{
type searchableBox;
min (-400 -400 -400);
max (400 400 400);
}


};




// Settings for the castellatedMesh generation.
castellatedMeshControls
{

    // Refinement parameters
    // ~~~~~~~~~~~~~~~~~~~~~

    // If local number of cells is >= maxLocalCells on any processor
    // switches from from refinement followed by balancing
    // (current method) to (weighted) balancing before refinement.
    maxLocalCells 50000000;

    // Overall cell limit (approximately). Refinement will stop immediately
    // upon reaching this number so a refinement level might not complete.
    // Note that this is the number of cells before removing the part which
    // is not 'visible' from the keepPoint. The final number of cells might
    // actually be a lot less.
    maxGlobalCells 50000000;

    // The surface refinement loop might spend lots of iterations
    // refining just a few cells. This setting will cause refinement
    // to stop if <= minimumRefine are selected for refinement. Note:
    // it will at least do one iteration (unless the number of cells
    // to refine is 0)
    minRefinementCells 1;

    // Allow a certain level of imbalance during refining
    // (since balancing is quite expensive)
    // Expressed as fraction of perfect balance (= overall number of cells /
    // nProcs). 0=balance always.
    maxLoadUnbalance 0.10;


    // Number of buffer layers between different levels.
    // 1 means normal 2:1 refinement restriction, larger means slower
    // refinement.
    nCellsBetweenLevels 3;



    // Explicit feature edge refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies a level for any cell intersected by its edges.
    // This is a featureEdgeMesh, read from constant/triSurface for now.
    features
    ({

file "A380.eMesh";

level 0;

}
     
    );



    // Surface based refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies two levels for every surface. The first is the minimum level,
    // every cell intersecting a surface gets refined up to the minimum level.
    // The second level is the maximum level. Cells that 'see' multiple
    // intersections where the intersections make an
    // angle > resolveFeatureAngle get refined up to the maximum level.

    refinementSurfaces
    {
        A380

        {
            // Surface-wise min and max refinement level
            level (5 6);
patchInfo 

{

type wall;

inGroups (A380);//aircraft is the first line of our ASCII-STL file,
                    //it is the patch name

}
        }
    }

    resolveFeatureAngle 30;


    // Region-wise refinement
    // ~~~~~~~~~~~~~~~~~~~~~~

    // Specifies refinement level for cells in relation to a surface. One of
    // three modes
    // - distance. 'levels' specifies per distance to the surface the
    //  wanted refinement level. The distances need to be specified in
    //  descending order.
    // - inside. 'levels' is only one entry and only the level is used. All
    //  cells inside the surface get refined up to the level. The surface
    //  needs to be closed for this to be possible.
    // - outside. Same but cells outside.

    refinementRegions
    {

        refinementBox
        {
            mode inside;
          levels ((5 5) (5 5) (5 5));
        }

       
       
    }


    // Mesh selection
    // ~~~~~~~~~~~~~~

    // After refinement patches get added for all refinementSurfaces and
    // all cells intersecting the surfaces get put into these patches. The
    // section reachable from the locationInMesh is kept.
    // NOTE: This point should never be on a face, always inside a cell, even
    // after refinement.
    locationInMesh (400 400 0);


    // Whether any faceZones (as specified in the refinementSurfaces)
    // are only on the boundary of corresponding cellZones or also allow
    // free-standing zone faces. Not used if there are no faceZones.
    allowFreeStandingZoneFaces true;
}



// Settings for the snapping.
snapControls
{
    //- Number of patch smoothing iterations before finding correspondence
    //  to surface
    nSmoothPatch 3;

    //- Relative distance for points to be attracted by surface feature point
    //  or edge. True distance is this factor times local
    //  maximum edge length.
    tolerance 4.0;

    //- Number of mesh displacement relaxation iterations.
    nSolveIter 0;

    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 5;
// Feature snapping

        //- Number of feature edge snapping iterations.
        //  Leave out altogether to disable.
        nFeatureSnapIter 0;

        //- Detect (geometric only) features by sampling the surface
        //  (default=false).
        implicitFeatureSnap false;

        //- Use castellatedMeshControls::features (default = true)
        explicitFeatureSnap true;

        //- Detect points on multiple surfaces (only for explicitFeatureSnap)
        multiRegionFeatureSnap false;
}



// Settings for the layer addition.
addLayersControls
{
    // Are the thickness parameters below relative to the undistorted
    // size of the refined cell outside layer (true) or absolute sizes (false).
    relativeSizes true;

    // Per final patch (so not geometry!) the layer information
    layers
    {
        A380
        {
            nSurfaceLayers 1;

        }
       
    }

    // Expansion factor for layer mesh
    expansionRatio 1.0;


    // Wanted thickness of final added cell layer. If multiple layers
    // is the thickness of the layer furthest away from the wall.
    // See relativeSizes parameter.
    finalLayerThickness 0.3;

    // Minimum thickness of cell layer. If for any reason layer
    // cannot be above minThickness do not add layer.
    // See relativeSizes parameter.
    minThickness 0.25;

    // If points get not extruded do nGrow layers of connected faces that are
    // also not grown. This helps convergence of the layer addition process
    // close to features.
    // Note: changed(corrected) w.r.t 17x! (didn't do anything in 17x)
    nGrow 0;


    // Advanced settings

    // When not to extrude surface. 0 is flat surface, 90 is when two faces
    // are perpendicular
    featureAngle 60;

    // Maximum number of snapping relaxation iterations. Should stop
    // before upon reaching a correct mesh.
    nRelaxIter 5;

    // Number of smoothing iterations of surface normals
    nSmoothSurfaceNormals 1;

    // Number of smoothing iterations of interior mesh movement direction
    nSmoothNormals 3;

    // Smooth layer thickness over surface patches
    nSmoothThickness 10;

    // Stop layer growth on highly warped cells
    maxFaceThicknessRatio 0.5;

    // Reduce layer growth where ratio thickness to medial
    // distance is large
    maxThicknessToMedialRatio 0.3;

    // Angle used to pick up medial axis points
    // Note: changed(corrected) w.r.t 16x! 90 degrees corresponds to 130 in 16x.
    minMedianAxisAngle 90;

    // Create buffer region for new layer terminations
    nBufferCellsNoExtrude 0;


    // Overall max number of layer addition iterations. The mesher will exit
    // if it reaches this number of iterations; possibly with an illegal
    // mesh.
    nLayerIter 50;

    // Max number of iterations after which relaxed meshQuality controls
    // get used. Up to nRelaxIter it uses the settings in meshQualityControls,
    // after nRelaxIter it uses the values in meshQualityControls::relaxed.
    nRelaxedIter 20;
}



// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
    //- Maximum non-orthogonality allowed. Set to 180 to disable.
    maxNonOrtho 65;

    //- Max skewness allowed. Set to <0 to disable.
    maxBoundarySkewness 20;
    maxInternalSkewness 4;

    //- Max concaveness allowed. Is angle (in degrees) below which concavity
    //  is allowed. 0 is straight face, <0 would be convex face.
    //  Set to 180 to disable.
    maxConcave 80;

    //- Minimum pyramid volume. Is absolute volume of cell pyramid.
    //  Set to a sensible fraction of the smallest cell volume expected.
    //  Set to very negative number (e.g. -1E30) to disable.
    minVol 1e-13;

    //- Minimum quality of the tet formed by the face-centre
    //  and variable base point minimum decomposition triangles and
    //  the cell centre.  Set to very negative number (e.g. -1E30) to
    //  disable.
    //    <0 = inside out tet,
    //      0 = flat tet
    //      1 = regular tet
    minTetQuality 1e-30;

    //- Minimum face area. Set to <0 to disable.
    minArea -1;

    //- Minimum face twist. Set to <-1 to disable. dot product of face normal
    //- and face centre triangles normal
    minTwist 0.05;

    //- minimum normalised cell determinant
    //- 1 = hex, <= 0 = folded or flattened illegal cell
    minDeterminant 0.001;

    //- minFaceWeight (0 -> 0.5)
    minFaceWeight 0.02;

    //- minVolRatio (0 -> 1)
    minVolRatio 0.01;

    //must be >0 for Fluent compatibility
    minTriangleTwist -1;

    //- if >0 : preserve single cells with all points on the surface if the
    //  resulting volume after snapping (by approximation) is larger than
    //  minVolCollapseRatio times old volume (i.e. not collapsed to flat cell).
    //  If <0 : delete always.
    //minVolCollapseRatio 0.5;


    // Advanced

    //- Number of error distribution iterations
    nSmoothScale 4;
    //- amount to scale back displacement at error points
    errorReduction 0.75;



    // Optional : some meshing phases allow usage of relaxed rules.
    // See e.g. addLayersControls::nRelaxedIter.
    relaxed
    {
        //- Maximum non-orthogonality allowed. Set to 180 to disable.
        maxNonOrtho 75;
    }
}


// Advanced

// Flags for optional output
// 0 : only write final meshes
// 1 : write intermediate meshes
// 2 : write volScalarField with cell
 for postprocessing
// 4 : write current intersections as .obj files
debug 0;


// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1e-6;


// ************************************************************************* //

Here is my checkMesh
Code:

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:          3442951
    faces:            10192500
    internal faces:  10057500
    cells:            3375000
    faces per cell:  6
    boundary patches: 3
    point zones:      0
    face zones:      0
    cell zones:      0

Overall number of cells of each type:
    hexahedra:    3375000
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:    0

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                 
    inlet              22500    22801    ok (non-closed singly connected) 
    outlet              22500    22801    ok (non-closed singly connected) 
    fixedWalls          90000    90600    ok (non-closed singly connected) 

Checking geometry...
    Overall domain bounding box (-400 -400 -400) (400 400 400)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (1.02233e-18 -1.9688e-18 -1.96972e-18) OK.
    Max cell openness = 1.31839e-16 OK.
    Max aspect ratio = 1 OK.
    Minimum face area = 28.4444. Maximum face area = 28.4444.  Face area magnitudes OK.
    Min volume = 151.704. Max volume = 151.704.  Total volume = 5.12e+08.  Cell volumes OK.
    Mesh non-orthogonality Max: 0 average: 0
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 8.52655e-14 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

--> FOAM Warning :
    From function polyMesh::readUpdateState polyMesh::readUpdate()
    in file meshes/polyMesh/polyMeshIO.C at line 204
    Number of patches has changed.  This may have unexpected consequences.  Proceed with care.
Time = 2

Mesh stats
    points:          9781151
    faces:            26102450
    internal faces:  24511827
    cells:            8169767
    faces per cell:  6.19531
    boundary patches: 4
    point zones:      0
    face zones:      0
    cell zones:      0

Overall number of cells of each type:
    hexahedra:    7656681
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:    513086
    Breakdown of polyhedra by number of faces:
        faces  number of cells
            6  152595
            8  2820
            9  231859
          10  517
          11  870
          12  80701
          13  93
          14  551
          15  39670
          16  6
          17  59
          18  3050
          20  7
          21  282
          24  6

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
                  inlet    22500    22801  ok (non-closed singly connected)
                  outlet    22500    22801  ok (non-closed singly connected)
              fixedWalls    90000    90600  ok (non-closed singly connected)
              A380_A380  1455623  1474663      ok (closed singly connected)

Checking geometry...
    Overall domain bounding box (-400 -400 -400) (400 400 400)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (3.75772e-18 -2.8035e-18 -2.16765e-18) OK.
    Max cell openness = 2.27306e-16 OK.
    Max aspect ratio = 1.0084 OK.
    Minimum face area = 0.0069139. Maximum face area = 28.4516.  Face area magnitudes OK.
    Min volume = 0.000576135. Max volume = 151.761.  Total volume = 5.11996e+08.  Cell volumes OK.
    Mesh non-orthogonality Max: 25.3367 average: 7.36434
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 1.01205 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

Time = 4

Mesh stats
    points:          9471318
    faces:            25692830
    internal faces:  24511827
    cells:            8169767
    faces per cell:  6.14518
    boundary patches: 4
    point zones:      0
    face zones:      0
    cell zones:      0

Overall number of cells of each type:
    hexahedra:    7351909
    prisms:        144354
    wedges:        0
    pyramids:      0
    tet wedges:    2480
    tetrahedra:    0
    polyhedra:    671024
    Breakdown of polyhedra by number of faces:
        faces  number of cells
            4  91439
            5  69428
            6  150359
            7  2362
            8  1607
            9  230819
          10  386
          11  767
          12  80313
          13  26
          14  491
          15  39627
          16  4
          17  56
          18  3045
          20  7
          21  282
          24  6

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
                  inlet    22500    22801  ok (non-closed singly connected)
                  outlet    22500    22801  ok (non-closed singly connected)
              fixedWalls    90000    90600  ok (non-closed singly connected)
              A380_A380  1046003  1164830      ok (closed singly connected)

Checking geometry...
    Overall domain bounding box (-400 -400 -400) (400 400 400)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (2.38306e-18 -2.72228e-18 5.44498e-18) OK.
    Max cell openness = 3.17729e-16 OK.
    Max aspect ratio = 5.66877 OK.
    Minimum face area = 0.00025335. Maximum face area = 28.4516.  Face area magnitudes OK.
    Min volume = 2.74107e-05. Max volume = 151.761.  Total volume = 5.11996e+08.  Cell volumes OK.
    Mesh non-orthogonality Max: 64.919 average: 7.95197
    Non-orthogonality check OK.
    Face pyramids OK.
 ***Max skewness = 6.52282, 71 highly skew faces detected which may impair the quality of the results
  <<Writing 71 skew faces to set skewFaces
    Coupled point location match (average 0) OK.

Failed 1 mesh checks.

End

As you see, the checkMesh mentioned that 1 mesh check failed.
I would like to ask you, if i can start the simulation despite this error ? and if yes how the error will affect my results .

Thank you for the support :)

zhengzh5 August 30, 2013 18:53

Quote:

Originally Posted by Mirage12 (Post 448089)
Hello Foamers :)

I am meshing an aircraft "A380" using snappyHexMesh :)

Here is my snappyHexMeshDict:


Code:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.2.0                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      dictionary;
    object      snappyHexMeshDict;
}

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Which of the steps to run
castellatedMesh true;
snap            true;
addLayers      false;


// Geometry. Definition of all surfaces. All surfaces are of class
// searchableSurface.
// Surfaces are used
// - to specify refinement for any mesh cell intersecting it
// - to specify refinement for any mesh cell inside/outside/near
// - to 'snap' the mesh boundary to the surface
geometry
{

  A380.stl
    {
        type triSurfaceMesh;
        name A380;
    }
box
{
type searchableBox;
min (-400 -400 -400);
max (400 400 400);
}


};




// Settings for the castellatedMesh generation.
castellatedMeshControls
{

    // Refinement parameters
    // ~~~~~~~~~~~~~~~~~~~~~

    // If local number of cells is >= maxLocalCells on any processor
    // switches from from refinement followed by balancing
    // (current method) to (weighted) balancing before refinement.
    maxLocalCells 50000000;

    // Overall cell limit (approximately). Refinement will stop immediately
    // upon reaching this number so a refinement level might not complete.
    // Note that this is the number of cells before removing the part which
    // is not 'visible' from the keepPoint. The final number of cells might
    // actually be a lot less.
    maxGlobalCells 50000000;

    // The surface refinement loop might spend lots of iterations
    // refining just a few cells. This setting will cause refinement
    // to stop if <= minimumRefine are selected for refinement. Note:
    // it will at least do one iteration (unless the number of cells
    // to refine is 0)
    minRefinementCells 1;

    // Allow a certain level of imbalance during refining
    // (since balancing is quite expensive)
    // Expressed as fraction of perfect balance (= overall number of cells /
    // nProcs). 0=balance always.
    maxLoadUnbalance 0.10;


    // Number of buffer layers between different levels.
    // 1 means normal 2:1 refinement restriction, larger means slower
    // refinement.
    nCellsBetweenLevels 3;



    // Explicit feature edge refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies a level for any cell intersected by its edges.
    // This is a featureEdgeMesh, read from constant/triSurface for now.
    features
    ({

file "A380.eMesh";

level 0;

}
     
    );



    // Surface based refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies two levels for every surface. The first is the minimum level,
    // every cell intersecting a surface gets refined up to the minimum level.
    // The second level is the maximum level. Cells that 'see' multiple
    // intersections where the intersections make an
    // angle > resolveFeatureAngle get refined up to the maximum level.

    refinementSurfaces
    {
        A380

        {
            // Surface-wise min and max refinement level
            level (5 6);
patchInfo 

{

type wall;

inGroups (A380);//aircraft is the first line of our ASCII-STL file,
                    //it is the patch name

}
        }
    }

    resolveFeatureAngle 30;


    // Region-wise refinement
    // ~~~~~~~~~~~~~~~~~~~~~~

    // Specifies refinement level for cells in relation to a surface. One of
    // three modes
    // - distance. 'levels' specifies per distance to the surface the
    //  wanted refinement level. The distances need to be specified in
    //  descending order.
    // - inside. 'levels' is only one entry and only the level is used. All
    //  cells inside the surface get refined up to the level. The surface
    //  needs to be closed for this to be possible.
    // - outside. Same but cells outside.

    refinementRegions
    {

        refinementBox
        {
            mode inside;
          levels ((5 5) (5 5) (5 5));
        }

       
       
    }


    // Mesh selection
    // ~~~~~~~~~~~~~~

    // After refinement patches get added for all refinementSurfaces and
    // all cells intersecting the surfaces get put into these patches. The
    // section reachable from the locationInMesh is kept.
    // NOTE: This point should never be on a face, always inside a cell, even
    // after refinement.
    locationInMesh (400 400 0);


    // Whether any faceZones (as specified in the refinementSurfaces)
    // are only on the boundary of corresponding cellZones or also allow
    // free-standing zone faces. Not used if there are no faceZones.
    allowFreeStandingZoneFaces true;
}



// Settings for the snapping.
snapControls
{
    //- Number of patch smoothing iterations before finding correspondence
    //  to surface
    nSmoothPatch 3;

    //- Relative distance for points to be attracted by surface feature point
    //  or edge. True distance is this factor times local
    //  maximum edge length.
    tolerance 4.0;

    //- Number of mesh displacement relaxation iterations.
    nSolveIter 0;

    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 5;
// Feature snapping

        //- Number of feature edge snapping iterations.
        //  Leave out altogether to disable.
        nFeatureSnapIter 0;

        //- Detect (geometric only) features by sampling the surface
        //  (default=false).
        implicitFeatureSnap false;

        //- Use castellatedMeshControls::features (default = true)
        explicitFeatureSnap true;

        //- Detect points on multiple surfaces (only for explicitFeatureSnap)
        multiRegionFeatureSnap false;
}



// Settings for the layer addition.
addLayersControls
{
    // Are the thickness parameters below relative to the undistorted
    // size of the refined cell outside layer (true) or absolute sizes (false).
    relativeSizes true;

    // Per final patch (so not geometry!) the layer information
    layers
    {
        A380
        {
            nSurfaceLayers 1;

        }
       
    }

    // Expansion factor for layer mesh
    expansionRatio 1.0;


    // Wanted thickness of final added cell layer. If multiple layers
    // is the thickness of the layer furthest away from the wall.
    // See relativeSizes parameter.
    finalLayerThickness 0.3;

    // Minimum thickness of cell layer. If for any reason layer
    // cannot be above minThickness do not add layer.
    // See relativeSizes parameter.
    minThickness 0.25;

    // If points get not extruded do nGrow layers of connected faces that are
    // also not grown. This helps convergence of the layer addition process
    // close to features.
    // Note: changed(corrected) w.r.t 17x! (didn't do anything in 17x)
    nGrow 0;


    // Advanced settings

    // When not to extrude surface. 0 is flat surface, 90 is when two faces
    // are perpendicular
    featureAngle 60;

    // Maximum number of snapping relaxation iterations. Should stop
    // before upon reaching a correct mesh.
    nRelaxIter 5;

    // Number of smoothing iterations of surface normals
    nSmoothSurfaceNormals 1;

    // Number of smoothing iterations of interior mesh movement direction
    nSmoothNormals 3;

    // Smooth layer thickness over surface patches
    nSmoothThickness 10;

    // Stop layer growth on highly warped cells
    maxFaceThicknessRatio 0.5;

    // Reduce layer growth where ratio thickness to medial
    // distance is large
    maxThicknessToMedialRatio 0.3;

    // Angle used to pick up medial axis points
    // Note: changed(corrected) w.r.t 16x! 90 degrees corresponds to 130 in 16x.
    minMedianAxisAngle 90;

    // Create buffer region for new layer terminations
    nBufferCellsNoExtrude 0;


    // Overall max number of layer addition iterations. The mesher will exit
    // if it reaches this number of iterations; possibly with an illegal
    // mesh.
    nLayerIter 50;

    // Max number of iterations after which relaxed meshQuality controls
    // get used. Up to nRelaxIter it uses the settings in meshQualityControls,
    // after nRelaxIter it uses the values in meshQualityControls::relaxed.
    nRelaxedIter 20;
}



// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
    //- Maximum non-orthogonality allowed. Set to 180 to disable.
    maxNonOrtho 65;

    //- Max skewness allowed. Set to <0 to disable.
    maxBoundarySkewness 20;
    maxInternalSkewness 4;

    //- Max concaveness allowed. Is angle (in degrees) below which concavity
    //  is allowed. 0 is straight face, <0 would be convex face.
    //  Set to 180 to disable.
    maxConcave 80;

    //- Minimum pyramid volume. Is absolute volume of cell pyramid.
    //  Set to a sensible fraction of the smallest cell volume expected.
    //  Set to very negative number (e.g. -1E30) to disable.
    minVol 1e-13;

    //- Minimum quality of the tet formed by the face-centre
    //  and variable base point minimum decomposition triangles and
    //  the cell centre.  Set to very negative number (e.g. -1E30) to
    //  disable.
    //    <0 = inside out tet,
    //      0 = flat tet
    //      1 = regular tet
    minTetQuality 1e-30;

    //- Minimum face area. Set to <0 to disable.
    minArea -1;

    //- Minimum face twist. Set to <-1 to disable. dot product of face normal
    //- and face centre triangles normal
    minTwist 0.05;

    //- minimum normalised cell determinant
    //- 1 = hex, <= 0 = folded or flattened illegal cell
    minDeterminant 0.001;

    //- minFaceWeight (0 -> 0.5)
    minFaceWeight 0.02;

    //- minVolRatio (0 -> 1)
    minVolRatio 0.01;

    //must be >0 for Fluent compatibility
    minTriangleTwist -1;

    //- if >0 : preserve single cells with all points on the surface if the
    //  resulting volume after snapping (by approximation) is larger than
    //  minVolCollapseRatio times old volume (i.e. not collapsed to flat cell).
    //  If <0 : delete always.
    //minVolCollapseRatio 0.5;


    // Advanced

    //- Number of error distribution iterations
    nSmoothScale 4;
    //- amount to scale back displacement at error points
    errorReduction 0.75;



    // Optional : some meshing phases allow usage of relaxed rules.
    // See e.g. addLayersControls::nRelaxedIter.
    relaxed
    {
        //- Maximum non-orthogonality allowed. Set to 180 to disable.
        maxNonOrtho 75;
    }
}


// Advanced

// Flags for optional output
// 0 : only write final meshes
// 1 : write intermediate meshes
// 2 : write volScalarField with cell
 for postprocessing
// 4 : write current intersections as .obj files
debug 0;


// Merge tolerance. Is fraction of overall bounding box of initial mesh.
// Note: the write tolerance needs to be higher than this.
mergeTolerance 1e-6;


// ************************************************************************* //

Here is my checkMesh
Code:

Create polyMesh for time = 0

Time = 0

Mesh stats
    points:          3442951
    faces:            10192500
    internal faces:  10057500
    cells:            3375000
    faces per cell:  6
    boundary patches: 3
    point zones:      0
    face zones:      0
    cell zones:      0

Overall number of cells of each type:
    hexahedra:    3375000
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:    0

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                 
    inlet              22500    22801    ok (non-closed singly connected) 
    outlet              22500    22801    ok (non-closed singly connected) 
    fixedWalls          90000    90600    ok (non-closed singly connected) 

Checking geometry...
    Overall domain bounding box (-400 -400 -400) (400 400 400)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (1.02233e-18 -1.9688e-18 -1.96972e-18) OK.
    Max cell openness = 1.31839e-16 OK.
    Max aspect ratio = 1 OK.
    Minimum face area = 28.4444. Maximum face area = 28.4444.  Face area magnitudes OK.
    Min volume = 151.704. Max volume = 151.704.  Total volume = 5.12e+08.  Cell volumes OK.
    Mesh non-orthogonality Max: 0 average: 0
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 8.52655e-14 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

--> FOAM Warning :
    From function polyMesh::readUpdateState polyMesh::readUpdate()
    in file meshes/polyMesh/polyMeshIO.C at line 204
    Number of patches has changed.  This may have unexpected consequences.  Proceed with care.
Time = 2

Mesh stats
    points:          9781151
    faces:            26102450
    internal faces:  24511827
    cells:            8169767
    faces per cell:  6.19531
    boundary patches: 4
    point zones:      0
    face zones:      0
    cell zones:      0

Overall number of cells of each type:
    hexahedra:    7656681
    prisms:        0
    wedges:        0
    pyramids:      0
    tet wedges:    0
    tetrahedra:    0
    polyhedra:    513086
    Breakdown of polyhedra by number of faces:
        faces  number of cells
            6  152595
            8  2820
            9  231859
          10  517
          11  870
          12  80701
          13  93
          14  551
          15  39670
          16  6
          17  59
          18  3050
          20  7
          21  282
          24  6

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
                  inlet    22500    22801  ok (non-closed singly connected)
                  outlet    22500    22801  ok (non-closed singly connected)
              fixedWalls    90000    90600  ok (non-closed singly connected)
              A380_A380  1455623  1474663      ok (closed singly connected)

Checking geometry...
    Overall domain bounding box (-400 -400 -400) (400 400 400)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (3.75772e-18 -2.8035e-18 -2.16765e-18) OK.
    Max cell openness = 2.27306e-16 OK.
    Max aspect ratio = 1.0084 OK.
    Minimum face area = 0.0069139. Maximum face area = 28.4516.  Face area magnitudes OK.
    Min volume = 0.000576135. Max volume = 151.761.  Total volume = 5.11996e+08.  Cell volumes OK.
    Mesh non-orthogonality Max: 25.3367 average: 7.36434
    Non-orthogonality check OK.
    Face pyramids OK.
    Max skewness = 1.01205 OK.
    Coupled point location match (average 0) OK.

Mesh OK.

Time = 4

Mesh stats
    points:          9471318
    faces:            25692830
    internal faces:  24511827
    cells:            8169767
    faces per cell:  6.14518
    boundary patches: 4
    point zones:      0
    face zones:      0
    cell zones:      0

Overall number of cells of each type:
    hexahedra:    7351909
    prisms:        144354
    wedges:        0
    pyramids:      0
    tet wedges:    2480
    tetrahedra:    0
    polyhedra:    671024
    Breakdown of polyhedra by number of faces:
        faces  number of cells
            4  91439
            5  69428
            6  150359
            7  2362
            8  1607
            9  230819
          10  386
          11  767
          12  80313
          13  26
          14  491
          15  39627
          16  4
          17  56
          18  3045
          20  7
          21  282
          24  6

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
                  inlet    22500    22801  ok (non-closed singly connected)
                  outlet    22500    22801  ok (non-closed singly connected)
              fixedWalls    90000    90600  ok (non-closed singly connected)
              A380_A380  1046003  1164830      ok (closed singly connected)

Checking geometry...
    Overall domain bounding box (-400 -400 -400) (400 400 400)
    Mesh (non-empty, non-wedge) directions (1 1 1)
    Mesh (non-empty) directions (1 1 1)
    Boundary openness (2.38306e-18 -2.72228e-18 5.44498e-18) OK.
    Max cell openness = 3.17729e-16 OK.
    Max aspect ratio = 5.66877 OK.
    Minimum face area = 0.00025335. Maximum face area = 28.4516.  Face area magnitudes OK.
    Min volume = 2.74107e-05. Max volume = 151.761.  Total volume = 5.11996e+08.  Cell volumes OK.
    Mesh non-orthogonality Max: 64.919 average: 7.95197
    Non-orthogonality check OK.
    Face pyramids OK.
 ***Max skewness = 6.52282, 71 highly skew faces detected which may impair the quality of the results
  <<Writing 71 skew faces to set skewFaces
    Coupled point location match (average 0) OK.

Failed 1 mesh checks.

End

As you see, the checkMesh mentioned that 1 mesh check failed.
I would like to ask you, if i can start the simulation despite this error ? and if yes how the error will affect my results .

Thank you for the support :)

I assume you're using dynamic mesh in some way? your best bet is to remesh and map the solution from the old mesh to the new mesh and continue with the simulation.

What i notice with the skewness error, depending on the direction of the skewness relative to the flow, sometimes it gives you very tiny steps, which essentially stalls the simulation. And i will imagine the skewness is probably going to effect the numerical diffusion in the direction its being stretched. Best to avoid them!

Mirage12 September 3, 2013 11:48

Thx for your answer :)


Actually i don't want to use a dynamic mesh... did i specify by mistake in the code that i require it ?

What do you mean with
Quote:

remesh and map the solution from the old mesh to the new mesh and continue with the simulation.
Could you please explain :)

Do you know how, can I correct the skewness error ?


Thanks !!:)

zhengzh5 September 3, 2013 14:28

Quote:

Originally Posted by Mirage12 (Post 449578)
Thx for your answer :)


Actually i don't want to use a dynamic mesh... did i specify by mistake in the code that i require it ?

What do you mean with
Could you please explain :)

Do you know how, can I correct the skewness error ?


Thanks !!:)

reading through your checkMesh log, it shows that the mesh is OK for time = 0 and 2, but failed the skewness check at time = 4. that means your mesh probably have changed inbetween time=2 and time=4. (is it supposed to?) do you have a dynamicMeshDict in ./constant directory? verify that first.

Mirage12 September 4, 2013 00:27

Hello Jace :)

I don't have a dynamicMeshDict in ./constant directory...
Do you know how to fix the failed check ?


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