[boffin5]

As part of debugging a multiRegion convergence problem, I am trying to improve the mesh. There are two regions, one of which is a heat exchanger. Its region is made by placing the point in mesh such that the outer domain is subtracted, leaving only the heat exchanger.


I am trying to create layers on the mesh, but when I activate layers in SHMDict, all I get is per the attached image, with no layers created. In the image showing a cross-section, the dimensions of the heat exchanger are 0.04 X 0.14 meters. I have a mesh enhancement box called 'refbox' specified; this box fully encloses the HX.


Here is the text of SHMDict:

castellatedMesh   true;
snap              true;
addLayers         true;

geometry
{
        rad
    {
        type triSurfaceMesh;
        file "radiator.stl";        
    }

    refbox
    {
        type triSurfaceMesh;
        file    "refbox.stl";
    }
       
    refinementBox
    {
        type searchableBox;
        min ( 2.1 -0.5 -0.1);
        max ( 2.3  0.5  0.1);
    }
};

// Settings for the castellatedMesh generation.

castellatedMeshControls
{

    maxLocalCells 2000000;

    maxGlobalCells 4000000;

    minRefinementCells 0;

    maxLoadUnbalance 0.10;

    nCellsBetweenLevels 1;    //5

    // Explicit feature edge refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    
    features
    (
        {
            file "radiator.eMesh";
            level 5;
        }
    );



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

    refinementSurfaces
    {
        rad
        {
            // Surface-wise min and max refinement level
            
            level (4 4);
            
            /*cellZone           solid;
            faceZone           solid;
            cellZoneInside    inside;*/
            
            radinlet      {level (4 4); patchInfo {type patch;}}
            radoutlet     {level (1 1); patchInfo {type patch;}}
            radwalltop    {level (1 1); patchInfo {type wall; }}
            radwallbottom {level (1 1); patchInfo {type wall; }}
            radwall-lh    {level (1 1); patchInfo {type wall; }}
            radwall-rh    {level (1 1); patchInfo {type wall; }}
        }
    }


    // 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
    {
    
    refbox  
        {                
            mode inside;            //mode distance         
            levels ((1e15 5));      //levels ((0.02 4))
        }
        
    /*refinementBox
        {
            mode inside;
            levels ((1E15 5));
        }*/
    }

    locationInMesh (2.14 -0.20 0.11);

    allowFreeStandingZoneFaces no;
}

// 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 1.2;

    //- Number of mesh displacement relaxation iterations.
    nSolveIter 185;

    //- Maximum number of snapping relaxation iterations. Should stop
    //  before upon reaching a correct mesh.
    nRelaxIter 4;

    // Feature snapping

        //- Number of feature edge snapping iterations.
        //  Leave out altogether to disable.
        nFeatureSnapIter 5;

        //- 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
    {
        radinlet 
        {
            nSurfaceLayers  2;
        }        
        radoutlet
        {
            nSurfaceLayers  2;
         }
         radwalltop
        {
            nSurfaceLayers  2;
        }
         radwallbottom
        {
            nSurfaceLayers  2;
        }
         radwall-lh
        {
            nSurfaceLayers  2;
        }
         radwall-rh
        {
            nSurfaceLayers  2;
        }
     }

    // Expansion factor for layer mesh
    expansionRatio 1.1;

    // 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.
    // is the thickness of the layer furthest away from the wall.
    // See relativeSizes parameter.
    finalLayerThickness 0.7;

    // 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 0.0001;

    // 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 85;

    // At non-patched sides allow mesh to slip if extrusion direction makes
    // angle larger than slipFeatureAngle.
    slipFeatureAngle 25;

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

    // Number of smoothing iterations of surface normals
    nSmoothSurfaceNormals 4;

    // 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 0.2;

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

I thought the problem might have something to do with the mesh being inside, rather than outside the body. But I don't see a setting in SHMDict that pertains to that.


Might it be because I only have the radiator face patches in the layer settings, rather than a single volume? Although I don't specify a volume, the meshing proceeded okay, other than the inability create layers.



Any help resolving this problem will be greatly appreciated.

[Yann]

Hi Alan,

I think your patch names are not properly defined. radinlet, radoutlet, etc are subregions of your rad geometry, and layers you be defined like this:

rad_radinlet 
{
    nSurfaceLayers  2;
}        
rad_radoutlet
{
    nSurfaceLayers  2;
}
rad_radwalltop
{
    nSurfaceLayers  2;
}
rad_radwallbottom
{
    nSurfaceLayers  2;
}
rad_radwall-lh
{
    nSurfaceLayers  2;
}
rad_radwall-rh
{
    nSurfaceLayers  2;
}

You can verify it by checking your snappyHexMesh log. You will see the patch names listed at the beginning of snappyHexMesh. I guess on your current setting you should probably also see something when snappy start the layer addition step.

Cheer,
Yann