[rietis]

Hello everybody.
I am fairly new to OpenFOAM.
I was thinking if there is a way how I can use snappyHexMesh for the walls in my geometry?
Just to the walls. I have zero expirience with snappyHexMesh, and I am trying to refine the mesh at the walls using this method.
I would be thankfull for any suggestions.

Have two boxes linked together with a path.

So I want to use snappyHexMesh at wall for a box, just one wall. Preatty much I copied the tuturiol and made few changes in the file, but still I am confused how to select to use snappyHexMesh at two or more certain walls



geometry
{

// Analytical shape; cylinder, sphere
plane {
type searchablePlane;
planeType pointAndNormal;
pointAndNormalDict {

basePoint (0 0 200);
normalVector (0 0 1);
}
}

....

};

refinementSurfaces
{
plane
{
level (2 3)
}
}



It did run, but did not made any changes to the grid.



Raitis.

[rietis]

This is the code for snappyHexMesh:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.3.0                                 |
|   \\  /    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
{
    
    // Analytical shape; cylinder, sphere
  planeA
    {
        type searchablePlane;

        planeType pointAndNormal;
        pointAndNormalDict
        {
            basePoint (0 0 200);
            normalVector (0 0 1);
        }
    }
};



// 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; //100 000

    // 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 3500000; //3 500 000

    // 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;


    // Number of buffer layers between different levels.
    // 1 means normal 2:1 refinement restriction, larger means slower
    // refinement.
    nCellsBetweenLevels 5;



    // 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 "someLine.eMesh";
        //    level 2;
        //}
    );



    // 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
    {
        planeA
        {
            // Surface-wise min and max refinement level
        level (2 3);
        //regions{"*.inlet|*.outlet"{level(3,4);}}    
        }
    }

    // Resolve sharp angles
    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
    {
     //  refinementPlane
        //{
          //  mode inside;
            //levels ((1E15 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 (0 0 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 false;
}



// 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 1.0;

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

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



// 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
    {
        
    }

    // 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.
    // Relative to undistorted size of cell outside layer.
    minThickness 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.
    nGrow 4;


    // Advanced settings

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

    // 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 2;

    // 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
    minMedianAxisAngle 90;

    // Create buffer region for new layer terminations
    nBufferCellsNoExtrude 4;

    // Overall max number of layer addition iterations
    nLayerIter 50;
}



// 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 projected area v.s. actual area. Set to -1 to disable.
    minFlatness 0.5;

    //- 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;
    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 0.02;

    //- 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;


    // Advanced

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


// Advanced

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


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

These ar the bondary names for my mesh

boundary
(
    fixedWalls
    {
        type wall;
        faces
        (         
       
    (41 44 31 27)
    (43 46 44 41)
    (37 39 46 43)
        );
    }

roof
    {
        type patch;
        faces
        (            
    (14 10 2 3)
    (15 11 10 14)
        );
    }
    
        inlet
    {
        type patch;
        faces
        (            
          (69 42 40 68)    
        );
    }

    outlet
    {
        type patch;
        faces
        (            
          (60 18 16 59)
    
        );
    }
    

);
mergePatchPairs
(
    

);

And I want to use snappyHexMesh at the bondaries for fixedWalls. I deleted some of the walls for convinience.
The coments in the snappyHexMEsh is not mine, but the file is taken from a tutorial.

Thank you in advance.

[rietis]

I Have been trying to get a finner mesh at the walls with the SHM, but somehow I never get what I need.

|   SO at this kind of wall I want to get finner mesh, in already existing 
|   geometry which I described previous. :)
|   
|   
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Using the blockMesh I am creating around 1 000 000 cells, but at the wall, I would like to get more. I understand that I could make another hex, but this would maka the length of the cell so much greater than the width and I do not want this.

As far I understood SHM gives the opportunity to create new surfaces inside the already existing mesh and/or export ect., but I would like just to get finner mesh at the walls.

I anyone is able to help I would realy appreciate.

Cheers

Raitis

[rietis]

I did not solved it, but I did go around the problem, which led to the imprresion that OpenFOAM can not solve certain types of problems well.

[alexB]

Hi Raitis,

although it could be a bit late.
Did you try to refine the mesh with the RefineMesh function like is it described for example in the tutorial cavitatingFoam/throttle. You can select the area where the mesh should be refined in topoSetDict files like in the tutorial.

Alex

[rietis]

Like at the defined wall? I did not try

[amuzeshi]

Originally Posted by alexB

Hi Raitis,

although it could be a bit late.
Did you try to refine the mesh with the RefineMesh function like is it described for example in the tutorial cavitatingFoam/throttle. You can select the area where the mesh should be refined in topoSetDict files like in the tutorial.

Alex

How about addLayers to a wall type patch which is not specified as an STL, but existing from the background mesh?
Thanks.

[amuzeshi]

Originally Posted by amuzeshi

How about addLayers to a wall type patch which is not specified as an STL, but existing from the background mesh?
Thanks.

I found the solution. It would be possible with searchablePlanes:

geometry
{
    plane
    {
        type            searchablePlane;
        planeType       pointAndNormal;
        pointAndNormalDict
        {
            basePoint       (0 -.2 0); // a point on the wall under question
            normalVector    (0 1 0); // normal to the wall under question (points inwards fluid domain)
        }
    }
...
}
...
addLayersControls
{
    plane
        {
            nSurfaceLayers 10;
        }
...
}
}