snappyHexMeshDict

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.4.0                                 |
|   \\  /    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;


//Optional: single region surfaces get patch names according to
//          surface only. Multi-region surfaces get patch name
//          surface "_ "region. Default is true
//singleRegionName 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
{
    box1x1x1
    {
        type searchableBox;
        min (1.5 1 -0.5);
        max (3.5 2 0.5);
    }

    sphere.stl
    {
        type triSurfaceMesh;

        //tolerance   1E-5;   // optional:non-default tolerance on intersections
        //maxTreeDepth 10;    // optional:depth of octree. Decrease only in case
                              // of memory limitations.

        // Per region the patchname. If not provided will be <surface>_<region>.
        // Note: this name cannot be used to identity this region in any
        //       other part of this dictionary; it is only a name
        //       for the combination of surface+region (which is only used
        //       when creating patches)
        regions
        {
            secondSolid
            {
                name mySecondPatch;
            }
        }
    }

    sphere2
    {
        type searchableSphere;
        centre  (1.5 1.5 1.5);
        radius  1.03;
    }
};

// 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 100000;

    // 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 2000000;

    // 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 0;

    // 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 1;


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

    // Specifies a level for any cell intersected by explicitly provided
    // edges.
    // This is a featureEdgeMesh, read from constant/triSurface for now.
    // Specify 'levels' in the same way as the 'distance' mode in the
    // refinementRegions (see below). The old specification
    //      level   2;
    // is equivalent to
    //      levels  ((0 2));

    features
    (
        //{
        //    file "someLine.eMesh";
        //    //level 2;
        //    levels ((0.0 2) (1.0 3));
        //}
    );


    // 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
    {
        sphere.stl
        {
            // Surface-wise min and max refinement level
            level (2 2);

            // Optional region-wise level specification
            regions
            {
                secondSolid
                {
                    level (3 3);
                }
            }

            // Optional specification of patch type (default is wall). No
            // constraint types (cyclic, symmetry) etc. are allowed.
            patchInfo
            {
                type patch;
                inGroups (meshedPatches);
            }


            //- Optional increment (on top of max level) in small gaps
            //gapLevelIncrement 2;

            //- Optional angle to detect small-large cell situation
            //  perpendicular to the surface. Is the angle of face w.r.t.
            //  the local surface normal. Use on flat(ish) surfaces only.
            //  Otherwise leave out or set to negative number.
            //perpendicularAngle 10;

            //- Optional faceZone and (for closed surface) cellZone with
            //  how to select the cells that are in the cellZone
            //  (inside / outside / specified insidePoint)
            //  The orientation of the faceZone is
            //  - if on cellZone(s) : point out of (maximum) cellZone
            //  - if freestanding   : oriented according to surface

            //faceZone sphere;
            //cellZone sphere;
            //cellZoneInside inside;  //outside/insidePoint

            //- Optional specification of what to do with faceZone faces:
            //      internal : keep them as internal faces (default)
            //      baffle   : create baffles from them. This gives more
            //                 freedom in mesh motion
            //      boundary : create free-standing boundary faces (baffles
            //                 but without the shared points)
            //faceType baffle;
        }
    }

    // Feature angle:
    // - used if min and max refinement level of a surface differ
    // - used if feature snapping (see snapControls below) is used
    resolveFeatureAngle 30;

    //- Optional increment (on top of max level) in small gaps
    //gapLevelIncrement 2;


    // Planar angle:
    // - used to determine if surface normals
    //   are roughly the same or opposite. Used
    //      - in proximity refinement
    //      - to decide when to merge free-standing baffles
    //        (if e.g. running in surfaceSimplify mode set this to 180 to
    //         merge all baffles)
    //      - in snapping to avoid snapping to nearest on 'wrong' side
    //        of thin gap
    //
    // If not specified same as resolveFeatureAngle
    planarAngle 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
    //   increasing 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
    {
        box1x1x1
        {
            mode inside;
            levels ((1.0 4));
        }
        //sphere.stl
        //{
        //    mode distance;
        //    levels ((1.0 5) (2.0 3));
        //}
    }

    // 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 (5 0.28 0.43);

    // 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;


    // Optional: do not remove cells likely to give snapping problems
    // handleSnapProblems false;

    // Optional: switch off topological test for cells to-be-squashed
    //           and use geometric test instead
    //useTopologicalSnapDetection false;
}

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

    // Maximum relative distance for points to be attracted by surface.
    // True distance is this factor times local maximum edge length.
    // Note: changed(corrected) w.r.t 17x! (17x used 2* tolerance)
    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;

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

        // Detect features between multiple surfaces
        // (only for explicitFeatureSnap, default = false)
        multiRegionFeatureSnap false;


    // wip: disable snapping to opposite near surfaces (revert to 22x behaviour)
    // detectNearSurfacesSnap 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;

    // Layer thickness specification. This can be specified in one of following
    // ways:
    // - expansionRatio and finalLayerThickness (cell nearest internal mesh)
    // - expansionRatio and firstLayerThickness (cell on surface)
    // - overall thickness and firstLayerThickness
    // - overall thickness and finalLayerThickness
    // - overall thickness and expansionRatio
    //
    // Note: the mode thus selected is global, i.e. one cannot override the
    //       mode on a per-patch basis (only the values can be overridden)

        // Expansion factor for layer mesh
        expansionRatio 1.0;

        // Wanted thickness of the layer furthest away from the wall.
        // If relativeSizes this is relative to undistorted size of cell
        // outside layer.
        finalLayerThickness 0.3;

        // Wanted thickness of the layer next to the wall.
        // If relativeSizes this is relative to undistorted size of cell
        // outside layer.
        //firstLayerThickness 0.3;

        // Wanted overall thickness of layers.
        // If relativeSizes this is relative to undistorted size of cell
        // outside layer.
        //thickness 0.5


    // Minimum overall thickness of total layers. If for any reason layer
    // cannot be above minThickness do not add layer.
    // If relativeSizes this is relative to undistorted size of cell
    // outside layer..
    minThickness 0.25;


    // Per final patch (so not geometry!) the layer information
    // Note: This behaviour changed after 21x. Any non-mentioned patches
    //       now slide unless:
    //          - nSurfaceLayers is explicitly mentioned to be 0.
    //          - angle to nearest surface < slipFeatureAngle (see below)
    layers
    {
        sphere.stl_firstSolid
        {
            nSurfaceLayers 1;

        }
        maxY
        {
            nSurfaceLayers 1;
            // Per patch layer data
            expansionRatio      1.3;
            finalLayerThickness 0.3;
            minThickness        0.1;
        }

        // Disable any mesh shrinking and layer addition on any point of
        // a patch by setting nSurfaceLayers to 0
        frozenPatches
        {
            nSurfaceLayers 0;
        }
    }

    // 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


    // Static analysis of starting mesh

        // When not to extrude surface. 0 is flat surface, 90 is when two faces
        // are perpendicular
        featureAngle 130;

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


    // Patch displacement

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

        // Smooth layer thickness over surface patches
        nSmoothThickness 10;



    // Medial axis analysis

        // Angle used to pick up medial axis points
        // Note: changed(corrected) w.r.t 17x! 90 degrees corresponds to 130
        // in 17x.
        minMedialAxisAngle 90;

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

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

        // Optional: limit the number of steps walking away from the surface.
        // Default is unlimited.
        //nMedialAxisIter 10;

        // Optional: smooth displacement after medial axis determination.
        // default is 0.
        //nSmoothDisplacement 90;

        // (wip)Optional: do not extrude a point if none of the surrounding points is
        // not extruded. Default is false.
        //detectExtrusionIsland true;


    // Mesh shrinking

        // Optional: at non-patched sides allow mesh to slip if extrusion
        // direction makes angle larger than slipFeatureAngle. Default is
        // 0.5*featureAngle.
        slipFeatureAngle 30;

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

        // 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 nRelaxedIter it uses the settings in
        // meshQualityControls,
        // after nRelaxedIter it uses the values in
        // meshQualityControls::relaxed.
        nRelaxedIter 20;

        // Additional reporting: if there are just a few faces where there
        // are mesh errors (after adding the layers) print their face centres.
        // This helps in tracking down problematic mesh areas.
        //additionalReporting true;
}

// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
    // Specify mesh quality constraints in separate dictionary so can
    // be reused (e.g. checkMesh -meshQuality)
    #include "meshQualityDict"


    // 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

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

// Advanced

//// Debug flags
//debugFlags
//(
//    mesh            // write intermediate meshes
//    intersections   // write current mesh intersections as .obj files
//    featureSeeds    // write information about explicit feature edge
//                    // refinement
//    attraction      // write attraction as .obj files
//    layerInfo       // write information about layers
//);
//
//// Write flags
//writeFlags
//(
//    scalarLevels    // write volScalarField with cellLevel for postprocessing
//    layerSets       // write cellSets, faceSets of faces in layer
//    layerFields     // write volScalarField for layer coverage
//);

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

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