[Anamitra]

Hello everyone!!

I am trying to mesh two intersecting surfaces in snappyhexMesh.

Issue: I have two stl surfaces, stl1 and stl2. Both are close and sometimes intersecting. I would like to have both as separate patches and would also need a finer mesh around them. However, as I do understand that it might be bit difficult.

I tried with 'inside' - refinement box, 'distance' - from the surfaces ( which I didn't expect to work anyway).

Hence my question is,
-Are there other options which I might use?
-or is there any other meshing software which might help, and can also export the mesh to openfoam format later.

Please let me know if I should add some more info.

/*--------------------------------*- 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;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


castellatedMesh true;    // make basic mesh ?
snap            true;    // decide to snap back to surface ?
addLayers       false;   // decide to add viscous layers ?


geometry // Load in STL files here
{

	stl1.stl {type triSurfaceMesh; name stl1;}
	stl2.stl {type triSurfaceMesh; name stl2;}
	refinementBox 
        {
 	type searchableBox; 
        min (-3 -1 16.65); 
        max (15 4 18.95);
	}

//	refinementBox2 {type searchableBox; min ( -6 -85); max ( 10 3 -6);}

};

castellatedMeshControls
{
    maxLocalCells 2500000;  //max cells per CPU core
    maxGlobalCells 20000000; //max cells to use before mesh deletion step
    minRefinementCells 0;  //was 0 - zero means no bad cells are allowed during stages
    maxLoadUnbalance 0.10;
    nCellsBetweenLevels 4;  // expansion factor between each high & low refinement zone

// Explicit feature edge refinement


    features // taken from STL from each .eMesh file created by "SurfaceFeatureExtract" command
     (
//        {file "inlet.eMesh"; level 0;} // add STL files if needed
        {file "stl1.eMesh"; level 2;} 
	{file "stl2.eMesh"; level 2;} 
    );

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

    refinementSurfaces // Surface-wise min and max refinement level
    {
	stl1 {level (4 5);} 
	stl2 {level (3 4);} 
    }
  


    resolveFeatureAngle 60;  // Resolve sharp angles // Default 30
    refinementRegions        // In descending levels of fine-ness
    {


         stl2 { mode distance; levels ((0.008 5)); }
//       refinementBox2 { mode inside; levels ((1.0 5)); }
    }
    locationInMesh (5.235 6.235 17.235);  
//to decide which side of mesh to keep **
    allowFreeStandingZoneFaces true;
}


// Settings for the snapping.
snapControls
{
    nSmoothPatch 3;
    tolerance 2.0;
    nSolveIter 60;
    nRelaxIter 15;
    nFeatureSnapIter 15; // default is 10
    
// New settings from openfoam 2.2 onwards for SHMesh

    implicitFeatureSnap false; 
// default is false - detects without doing surfaceFeatureExtract

    explicitFeatureSnap true; 
// default is true

    multiRegionFeatureSnap false;
// deafault is false - detects features between multiple surfaces

}

// Settings for the layer addition.

addLayersControls 

//add the PATCH names from inside the STL file so STLpatchName_insideSTLName 

{
    relativeSizes true; // was true
    layers
    {
//	jetwall {nSurfaceLayers 4;} // was 3
    }

    expansionRatio 1.0;
    finalLayerThickness 0.03; //was 0.00016
    minThickness 0.00008; //was 0.0008
    nGrow 1; // was 1 


    // Advanced settings

    featureAngle 80; 
// was 70 //- When not to extrude surface. 0 is flat, 90 is right angle.
    nRelaxIter 3;  
//- Max# of snapping relaxation iter. Should stop before upon reaching a correct mesh.
    nSmoothSurfaceNormals 1;  
// Number of smoothing iterations of surface normals
    nSmoothNormals 3;
// Number of smoothing iterations of interior mesh movement direction
    nSmoothThickness 10;  
// Smooth layer thickness over surface patches
    maxFaceThicknessRatio 0.5; 
// Stop layer growth on highly warped cells
    maxThicknessToMedialRatio 0.3; 
// Reduce layer growth where ratio thickness to medial distance is large
    minMedianAxisAngle 130; 
// Angle used to pick up medial axis points
    nBufferCellsNoExtrude 0;   
// Create buffer region for new layer terminations
    nLayerIter 50; 
// Overall max number of layer addition iterations
}

// Generic mesh quality settings. At any undoable phase these determine
// where to undo.

meshQualityControls
{
    maxNonOrtho 65;
    maxBoundarySkewness 20;
    maxInternalSkewness 4;
    maxConcave 80;
    minFlatness 0.5;
    minVol 1e-14;
    minTetQuality 1e-9;
    minArea -1;
    minTwist 0.02;
    minDeterminant 0.001;
    minFaceWeight 0.02;
    minVolRatio 0.01;
    minTriangleTwist -1;

    // Advanced

    nSmoothScale 4;
    errorReduction 0.75;
}

// Advanced

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-4;