[Tobermory]

Dear Foamers

I have been battling with SHM to get a high quality, sharp mesh around a REALLY simple geometry - a surface mounted cube. I can generate a snapped mesh, no problem - the cube surfaces in the snapped mesh are all planar and the edges are located where expected. So far so good. Now I try and add the tiniest of layers at the base, and SHM seems to struggle with the edges at the top of the cube - these move, I guess as part of the mesh shrinkage to make room for the layer ... but there's nothing that I can do to encourage the edges to snap back to their proper place. See the attached plots for pictures of this. I know that the distortion is minor, but it bugs me and I want the corners/edges in the right place.

So here's my question - am I just inexperienced with SHM (that's true by the way) and have poor settings, or is SHM really this limited in what it can achieve? (I am not dishing SHM ... I just want to know the extent of its capabilities).

Re: my settings, I have the following in my surfaceFeaturesDict:

surfaces ("cube.stl");
includedAngle       150;
subsetFeatures
{
    nonManifoldEdges       no;
    openEdges       yes;
}

and my snappyHexMeshDict is:

castellatedMesh true;
snap            true;
addLayers       true;

geometry { 
    cube
    {
        type triSurfaceMesh;
        file "cube.stl";
    }


    refBox1
    {
        type            searchableBox;
        min             (-0.9 -0.9   0);
        max             ( 2.5  0.9 1.5);
    }

    refBox2
    {
        type            searchableBox;
        min             ( -2  -2    0);
        max             (  6   2  1.8);
    }

    refBox3
    {
        type            searchableBox;
        min             ( -3  -3    0);
        max             ( 10   3  2.4);
    }
};


castellatedMeshControls  {
	maxLocalCells 1000000;			//default 100000;
	maxGlobalCells 5000000;			//default 2000000;
	minRefinementCells 10;
	maxLoadUnbalance 0.10;
	nCellsBetweenLevels 5;

	//feature edge refinement - eMesh read from constant/triSurface
	features ( 		
		{ file "cube.eMesh"; level 4; }
	);

	//surface refinement
	refinementSurfaces {
	    cube { level (4 4);  patchInfo {type wall;} }
	}
	resolveFeatureAngle 30;

	//volume refinement
	refinementRegions { 
		refBox1 { mode inside; levels ((3 3)); } 
		refBox2 { mode inside; levels ((2 2)); } 
		refBox3 { mode inside; levels ((1 1)); } 
	}
	
	//other mesh parameters
	locationInMesh (1 0 1);
	allowFreeStandingZoneFaces true;
}


snapControls {
	nSmoothPatch 3;
	tolerance 2.0;
	nSolveIter 30;
	nRelaxIter 5;
	nFeatureSnapIter 10;
	implicitFeatureSnap false;
	explicitFeatureSnap true;
	multiRegionFeatureSnap false;
}

addLayersControls {
	relativeSizes false;
	expansionRatio 1.2;
	firstLayerThickness 0.004;
	//finalLayerThickness 0.136;
	//thickness 0.25;
	minThickness 0.001;
	layers { 
	    ground { nSurfaceLayers  1; }
	}
	nGrow 0;
	featureAngle 60;
	slipFeatureAngle 30;
	nRelaxIter 3;
	nSmoothSurfaceNormals 1;
	nSmoothNormals 3;
	nSmoothThickness 10;
	maxFaceThicknessRatio 0.5;
	maxThicknessToMedialRatio 0.3;
	minMedianAxisAngle 90;
	nBufferCellsNoExtrude 0;
	nLayerIter 50;
}

meshQualityControls { #include "meshQualityDict" }
writeFlags ( scalarLevels    layerSets     layerFields );
mergeTolerance 1e-6;

.

Any suggestions/comments on how to get SHM to preserve the geometry in the rest of the mesh during layer addition would be gratefully received.

Oh - and one more thing - and this is blowing my mind - when I plot the mesh in paraview, load in the cell coordinates (after running writeCellCentres) and pick off the coordinates of the upper edges, paraview reports these as having z<1 (cube top surface is at z=1), despite paraview clearly showing that these vertices are at z>1! What on earth is going on there?