[LucaFanchini]

Dear all I'm facing a problem... I'm trying to mesh a pipe inside a plate using snappyHexMesh.
I created my stl files using Inventor and I did the triangulation of the Stls using Salome.
I exported the stl files in Ascii code in order to rename the patches.
The problem is ... If I create a coarse mesh I obtain the patches I want: inlet, outlet, wall, wallOI and Pipe_to_Coolant (interface patch).
If I try to refine the mesh at level (2 2) SnappyHexMesh creates me an additional patch called pipe...
Also if I try to snap the patches are created.
I don't know if it will damage the results of the simulation.
Does anyone have a solution in order to cancel the additional patch?

I attach images.

This is the SnappyHexMeshDict:

// Which of the steps to run
castellatedMesh 1;
snap 0;
addLayers 0;


// 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
{
coolant
{
type triSurfaceMesh;
file "assieme.stl";
regions
{
inlet {name inlet;}
outlet {name outlet;}
wall {name wall;}
wallInletOutlet { name wallOI; }
}
}
pipe
{
type triSurfaceMesh;
file "interface.stl";
}
wall
{
type triSurfaceMesh;
file "wall.stl";
}
wallInletOutlet
{
type triSurfaceMesh;
file "wallInletOutlet.stl";
}
}


// 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 2000000;

// 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 10000000;

// 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 6;

// 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 0.0;


// Number of buffer layers between different levels.
// 1 means normal 2:1 refinement restriction, larger means slower
// refinement.
nCellsBetweenLevels 4;



// 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 "assieme.eMesh";
level 1;
}
{
file "interface.eMesh";
level 1;
}
{
file "wall.eMesh";
level 1;
}
{
file "wallInletOutlet.eMesh";
level 1;
}
);



// 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
{
coolant
{
level (1 1);
regions
{
wall {level (1 1); patchInfo { type wall; }}
wallInletOutlet {level (1 1); patchInfo { type wall; }}
}
}
pipe
{
level (1 1);

regions
{
inlet {level (1 1); patchInfo { type patch; }}
outlet {level (1 1); patchInfo { type patch; }}
}
}
}

// Resolve sharp angles
resolveFeatureAngle 60;


// 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
{

}


// 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.

locationsInMesh
(
(( -0.15 0 -0.015) Pipe)
(( 0 0.009 -0.015) Coolant)
);

// 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 thekqRWallFunction;re are no faceZones.
allowFreeStandingZoneFaces true;
}



// Settings for the snapping.
snapControls
{
//- Number of patch smoothing iterations before finding correspondence
// to surface
nSmoothPatch 4;

//- Relative distance for points to be attracted by surface feature point
// or edge. True distance is this factor times local
// maximum edge length.
tolerance 1.5;

//- Number of mesh displacement relaxation iterations.
nSolveIter 15;

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

// Feature snapping

//- Number of feature edge snapping iterations.
// Leave out altogether to disable.
nFeatureSnapIter 10;

//- 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
{
pipe
{
nSurfaceLayers 10;
}
coolant
{
nSurfaceLayers 6;
}
}

// Expansion factor for layer mesh
expansionRatio 1.05;

// 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.
// See relativeSizes parameter.
finalLayerThickness 0.6;

// 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 0.4;

// 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 1.7.x! (didn't do anything in 1.7.x)
nGrow 0;

// Advanced settings

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

// At non-patched sides allow mesh to slip if extrusion direction makes
// angle larger than slipFeatureAngle.
slipFeatureAngle 30;

// Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 6;

// Number of smoothing iterations of surface normals
nSmoothSurfaceNormals 2;

// Number of smoothing iterations of interior mesh movement direction
nSmoothNormals 6;

// Smooth layer thickness over surface patches
nSmoothThickness 20;

// 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
// Note: changed(corrected) w.r.t 1.7.x! 90 degrees corresponds to 130
// in 1.7.x.
minMedialAxisAngle 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 100;
}



// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
#include "meshQualityDict"


// Advanced

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


// Advanced

// Write flags
writeFlags
(
scalarLevels
layerSets
layerFields // write volScalarField for layer coverage
);


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


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

[Alczem]

Hey!


If snappy creates patches unexpectedly, it usually means that your input files are not great. I would take a look at the patch you don't want and check if the STL files are watertight there. If they are not, snappy might be trying to fill the gaps during the meshing process.

[arezayan87]

Dear Luca

it seems the stl file is not suite. please attach the stl file.
I guess it's better to repair the stl file with Blender or MeshLab.