[stefano.garbin]

Dear all,


I am trying to mesh a bike wheel with tyre using SHM.
STL file has a very good quality and is watertight (it's around 70Mb)
Here are the steps I am following:

-generate edge feature with surfaceFeatureExtract and verify them with paraview --> OK
-generate background mesh with blockMesh --> OK
-generate castellated mesh with SHM --> OK
-snap castellated mesh to STL surfaces and to explicit feature edges --> OK
-add 10 layers with 1st layer thickness of absolute size (relativeSizes false) -->???


In the last step I notices that inflated mesh looses snapping to some of the edge features, as in the attached pictures.
This is weird for me, and I don't understand what I am missing...
Any hint to get a good mesh (external aero)


Thanks


Stefano



I enclose snappyHexMeshDict and meshQualityDict

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2012                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

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


// 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
{
    rim.stl
    {
        type triSurfaceMesh;
        name rim;
    }

    hub.stl
    {
        type triSurfaceMesh;
        name hub;
    }

    //cil { type cylinder; point1 (0 0 -0.1); point2 (0 0 0.1); radius 0.5; }
    //cone {type searchableCone; point1 (0 0 -0.1); radius1 0.45; innerRadius1 0.2; point2 (0 0 0.1); radius2 0.45; innerRadius2 0.2; }

    refinementBox
     {
         type box;
         min  (-3.0 -0.35 -0.8);
         max  ( 0.5  0.8 0.2);
     }
}


// Settings for the castellatedMesh generation.
castellatedMeshControls
{

    maxLocalCells 1000000;
    maxGlobalCells 50000000;
    minRefinementCells 100; //10;
    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 "hub.eMesh";
            level 8;
        }

        {
            file "rim.eMesh";
            level 8;
        }


    );


    // 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
    {
        rim
        {
            // Surface-wise min and max refinement level
            //level (3 3);
            level (8 8);

            patchInfo
            {
                type wall;
            }
        }

        hub
        {
            // Surface-wise min and max refinement level
            //level (3 3);
            level (8 8);

            patchInfo
            {
                type wall;
            }
        }
    }

    // Resolve sharp angles
    resolveFeatureAngle 15;


    // 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 ((1E15 3));
                levels ((1E15 4));
                gapLevel    (3 0 8);
                gapMode     mixed;
            }

            //wheel_rim
            "rim.*"
            {
                mode distance;
                levels
                (
                    //(0.025 5)
                    //(0.1 4)
                    (0.05 5)
                );
            }
            "hub.*"
            {
                mode distance;
                levels
                (
                    //(0.025 5)
                    //(0.1 4)
                    (0.05 5)
                );
            }
    }


    // Mesh selection
    // ~~~~~~~~~~~~~~
    locationInMesh (-4.99 0.01 0.01);
    allowFreeStandingZoneFaces false; //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 2.0;

    //- Number of mesh displacement relaxation iterations.
    nSolveIter 30;

    //- 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 10;

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

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

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

        // Attract points only to the surface they originate from.
        // This can improve snapping of intersecting surfaces. Default is false.
        //strictRegionSnap true;
}



// 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; //false;
    relativeSizes false;
    thicknessModel firstAndRelativeFinal;
    //thicknessModel firstAndOverall;
    //thicknessModel firstAndExpansion;

    meshShrinker    displacementMotionSolver;
    solver          displacementLaplacian;

    displacementLaplacianCoeffs
    {
        diffusivity     quadratic inverseDistance 1(wall);
    }

    // Per final patch (so not geometry!) the layer information
    layers
    {

        //"wheel_rim.*"
        "rim.*"
        {
            nSurfaceLayers 10;
        }
        "hub.*"
        {
            nSurfaceLayers 10;
        }

    }

    // Expansion factor for layer mesh
    //expansionRatio 1.1; ////da usare con thicknessModel firstAndExpansion;

    // Wanted thickness of final added cell layer. If multiple layers
    // is the thickness of the layer furthest away from the wall.
    // Relative to undistorted size of cell outside layer.
    // See relativeSizes parameter.

    firstLayerThickness 0.01e-3;
    finalLayerThickness 0.3; //0.7;  //70% delle celle vicine //da usare con thicknessModel firstAndRelativeFinal;
    //thickness 0.2e-3; //da usare con thicknessModel firstAndOverall;

    // Minimum thickness of cell layer. If for any reason layer
    // cannot be above minThickness do not add layer.
    // Relative to undistorted size of cell outside layer.
    minThickness 0.002e-3; //0.1;

    // 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 1.7.x! (didn't do anything in 1.7.x)
    nGrow 0;

    // Advanced settings

    // When not to extrude surface. 0 is flat surface, 90 is when two faces
    // are perpendicular
    featureAngle 190; //330; //170; //30; //60;

    // At non-patched sides allow mesh to slip if extrusion direction makes
    // angle larger than slipFeatureAngle.
    slipFeatureAngle 30; //10;

    // Maximum number of snapping relaxation iterations. Should stop
    // before upon reaching a correct mesh.
    nRelaxIter 5; //3;

    // 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 1.7.x! 90 degrees corresponds to 130
    // in 1.7.x.
    minMedialAxisAngle 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 30;
}



// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
    #include "meshQualityDict"

}


// Advanced

// Write flags
writeFlags
(
    scalarLevels
    layerSets
    layerFields     // write volScalarField for layer coverage
);


// Debug flags
/*
debugFlags
(
    layerInfo
);
*/

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


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

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1912                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      meshQualityDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

//- 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 180;  //100;  //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
//mettere valore negativo e' l'unico modo di fare estrudere i layers
minTetQuality -1e30; //1e-15;

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

//- Minimum face twist. Set to <-1 to disable. dot product of face normal
//  (itself the average of the triangle normals)
//  and face centre triangles normal
minTwist 0.02;

//- Minimum normalised cell determinant. This is the determinant of all
//  the areas of internal faces. It is a measure of how much of the
//  outside area of the cell is to other cells. The idea is that if all
//  outside faces of the cell are 'floating' (zeroGradient) the
//  'fixedness' of the cell is determined by the area of the internal faces.
//  1 = hex, <= 0 = folded or flattened illegal cell
minDeterminant 0.001;

//- Relative position of face in relation to cell centres (0.5 for orthogonal
//  mesh) (0 -> 0.5)
minFaceWeight 0.05;

//- Volume ratio of neighbouring cells (0 -> 1)
minVolRatio 0.01;

//- Per triangle normal compared to that of preceding triangle. Must be >0
//  for Fluent compatibility
minTriangleTwist -1;


//- If >0 : preserve 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 0.1;



    // Advanced

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

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

[Yann]

Hi Stefano,

Which version are you using?
According to your files headers, you are using the OpenCFD version.

If I'm right, try adding this parameter into the addLayersControls section of your snappyHexMeshDict:

    mergePatchFacesAngle 45;

More information in the annotated snappyHexMeshDict.

Let us know if it solves your problem.

Cheers,
Yann