[Chris123]

Hi There,
I have a Terrain-Area STL (Area.stl) file which I wanted to mesh with snappyHexMesh as the ground of my Box.
First I run blockMesh afterwards surfaceFeatureExtract and then snappy.
When snappy is finished, the patches of the Box defined in BlockMesh (minx,maxX,minX and maxY) disappears in the Boundary file inside the constant folder.
I am a bit desperate, because I did it already a view times with other terrain geometries, and I have not seen this kind of effect before. Can anyone tell me why this happened?
What I observe during snappyhexmesh is running,by an intermediate saving, the patches kept, but the nFaces entry are all set to 0, afterwards at the end, they are totally diapered.
Thank you.


Boundary File after snappyHexMesh:

1
(
    terrain
    {
        type            wall;
        inGroups        1(wall);
        nFaces          1269326;
        startFace       7528417;
    }
)

Boundary after BlockMesh

(
    minX
    {
        type            patch;
        nFaces          1000;
        startFace       288000;
    }
    maxX
    {
        type            patch;
        nFaces          1000;
        startFace       289000;
    }
    ground
    {
        type            wall;
        inGroups        1(wall);
        nFaces          10000;
        startFace       290000;
    }
    minY
    {
        type            patch;
        nFaces          1000;
        startFace       300000;
    }
    maxY
    {
        type            patch;
        nFaces          1000;
        startFace       301000;
    }
    topAtm
    {
        type            patch;
        nFaces          10000;
        startFace       302000;
    }
)

BlockMeshDict

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
backgroundMesh
{
    xMin   -24500;
    xMax   24500;
    yMin   -25500;
    yMax   25500;
    zMin     -100;
    zMax   1500;
    xCells  100;
    yCells  100;
    zCells  10;
}

convertToMeters 1;

vertices
(
    ($:backgroundMesh.xMin $:backgroundMesh.yMin $:backgroundMesh.zMin)
    ($:backgroundMesh.xMax $:backgroundMesh.yMin $:backgroundMesh.zMin)
    ($:backgroundMesh.xMax $:backgroundMesh.yMax $:backgroundMesh.zMin)
    ($:backgroundMesh.xMin $:backgroundMesh.yMax $:backgroundMesh.zMin)

    ($:backgroundMesh.xMin $:backgroundMesh.yMin $:backgroundMesh.zMax)
    ($:backgroundMesh.xMax $:backgroundMesh.yMin $:backgroundMesh.zMax)
    ($:backgroundMesh.xMax $:backgroundMesh.yMax $:backgroundMesh.zMax)
    ($:backgroundMesh.xMin $:backgroundMesh.yMax $:backgroundMesh.zMax)
);

blocks
(
    hex (0 1 2 3 4 5 6 7)
    (
        $:backgroundMesh.xCells
        $:backgroundMesh.yCells
        $:backgroundMesh.zCells
    )
    simpleGrading (1 1 1)
);

edges
(
);

boundary
(
    minX
    {
        type patch;
        faces
        (
            (0 3 7 4)
        );
    }

    maxX
    {
        type patch;
        faces
        (
            (1 5 6 2)
        );
    }
    ground
    {
        type wall;
        faces
       (
            (0 1 2 3)
        );
    }
    minY
    {
        type patch;
        faces
        (
            (0 4 5 1) 
        );
    }
	  maxY
    {
        type patch;
        faces
        (
 	 (3 2 6 7)
        );
    }
      topAtm
    {
        type patch;
        faces
        (    
            (4 7 6 5)
        );
    }
);
mergePatchPairs
(
);
// ************************************************************************* //

snappyHexMeshDict

FoamFile
{
        version	3.0;
        format      ascii;
        class       dictionary;
        object	snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


castellatedMesh  true;
snap             true;
addLayers        true;

geometry
{
        Area.stl
        {
                type triSurfaceMesh;
		name terrain
          patchinfo
          {
           type wall;
           }
         }  

          box
        {
        type searchableBox;
        min (-2000 -2000 0);
        max (2000 2000  2000);
        }
};

castellatedMeshControls
{
    maxLocalCells   200000000;
    maxGlobalCells  300000000;
    minRefinementCells 20;
    nCellsBetweenLevels 4;
    maxLoadUnbalance 0.1;
    allowFreeStandingZoneFaces true;
	resolveFeatureAngle	 30;
	features
	(
	{
		file "Area.eMesh" ;
		level 3 ;
	}
	);
	refinementSurfaces
	{
		terrain
         	{
			level (3 3); 
		 }
     

	    
        }

    
	refinementRegions
	{
           

    	}
	locationInMesh ( 0 0 10 ) ;
}

snapControls
{
    tolerance       2;
    implicitFeatureSnap false;
    explicitFeatureSnap true;
    multiRegionFeatureSnap true;
    detectNearSurfacesSnap true;
    nSmoothPatch    2;
    nSolveIter      50;
    nRelaxIter      5;
    nFeatureSnapIter 10;
}

addLayersControls
{

       layers
        {
           ground
           {
             nSurfaceLayers 7;
             firstLayerThickness 0.025;
             expansioRatio 1.22;
            }
       }
       firstLayerThickness 0.025;
       relativeSizes    true ;
       expansionRatio    1.2 ;

    featureAngle    85;
    slipFeatureAngle 30;
    nGrow           0;
    nBufferCellsNoExtrude 0;
    minMedianAxisAngle 90;
    maxFaceThicknessRatio 0.2;
    maxThicknessToMedialRatio 0.3;
    minThickness    0.001;
    nLayerIter      50;
    nRelaxIter      5;
    nSmoothSurfaceNormals 10;
    nSmoothNormals  3;
    nSmoothThickness 10;
    nRelaxedIter    30;
    nMedialAxisIter 10;

    displacementLaplacianCoeffs
    {
        diffusivity quadratic inverseDistance ("ground");
    }
}

meshQualityControls
{
    minVol          1e-20;
    minTetQuality   1e-20;
    minArea         1e-20;
    minTwist        0.005;
    minDeterminant  0.0001;
    minFaceWeight   0.002;
     minVolRatio     0.0001;
    minTriangleTwist -1;
    minFlatness     0.5;
    maxNonOrtho     65;
    maxBoundarySkewness 20;
    maxInternalSkewness 4;
    maxConcave      80;
    nSmoothScale    4;
    errorReduction  0.75;
    
    relaxed
    {
        maxNonOrtho     75;
        maxInternalSkewness 8;
    }
}
mergeTolerance  1e-08;
debug           0;

[RobertHB]

Difficult question to answer, especially since you have allready completed successful sHM runs. Here are a few ideas:
- Check your locationInMesh. Does it sit above the terrain and within your domain?
- sHM struggles with non-watertight stl-files. Does your Area.stl have any holes?
- How did you create your Area.stl? If it is constructed from multiple parts it becomes more likely that sHM will fail due to not being watertight.

[Chris123]

Dear Robert,
thank you for your help.
The problem was that I set the LocationInMesh inside the terrain STL file (Ground) and not inside the background mesh (generated by blockMesh) .

So I set it a bit higher and it works....
kind regards