[Bdew8556]

Hey everyone,

No idea why but my snappyhexmesh isn't deleting the cells inside my ellipse/airfoil. I've done a surface check and it's watertight.

Any thoughts??


/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: dev |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Which of the steps to run
castellatedMesh true;
snap true;
addLayers true;
mergeTolerance true;
geometry true;
castellatedMeshControls true;
snapControls true;
addLayersControls true;
meshQualityControls true;




// 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
{
ellipse_body
{
type triSurfaceMesh;
file "ellipse_body.stl";
regions
{
ascii
{
name ellipse_body;
}
}

ellipse_side1
{
type triSurfaceMesh;
file "ellipse_side1.stl";
regions
{
ascii
{
name ellipse_side1;
}
}


ellipse_side2
{
type triSurfaceMesh;
file "ellipse_side2.stl";
regions
{
ascii
{
name ellipse_side2;
}
}



};

// 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 100000;

// 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 2000000;

// 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 0;

// 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 0.10;


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


// 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 "ellipse_body.eMesh";
level 2;
}


{
file "ellipse_side1.eMesh";
level 2;
}


{
file "ellipse_side2.eMesh";
level 2;
}

);



// 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
{
// innerCylinderSmall
// {
// level (4 4);

// faceType boundary;
// cellZone innerCylinderSmall;
// faceZone innerCylinderSmall;
// cellZoneInside inside;
// }
ellipse_body
{
level (3 5);
}


ellipse_side1
{
level (3 5);
}

ellipse_side2
{
level (3 5);
}
}

// 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
// {
// innerCylinder
// {
// mode inside;
// levels ((1E15 3));
// }
// innerCylinderSmall
// {
// mode inside;
// levels ((1E15 4));
// }
// }


// 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.
locationInMesh (0.01 -0.5 0.01);


// 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 there are no faceZones.
allowFreeStandingZoneFaces false;
}



// 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 4.0; // 1.0;

//- Number of mesh displacement relaxation iterations.
nSolveIter 300;

//- 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 true;

// Use castellatedMeshControls::features (default = true)
explicitFeatureSnap false;

// Detect features between multiple surfaces
// (only for explicitFeatureSnap, default = false)
multiRegionFeatureSnap true;
}



// 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
{
}

// Expansion factor for layer mesh
expansionRatio 1.0;

// 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 0.3;

// 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 0.1;

// 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 30;

// Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 3;

// Number of smoothing iterations of surface normals
nSmoothSurfaceNormals 1;

// 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 0.3;

// 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;
}



// Generic mesh quality settings. At any undoable phase these determine
// where to undo.
meshQualityControls
{
//- Maximum non-orthogonality allowed. Set to 180 to disable.
maxNonOrtho 65;

//- Max skewness allowed. Set to <0 to disable.
maxBoundarySkewness 20;
maxInternalSkewness 4;

//- Max concaveness allowed. Is angle (in degrees) below which concavity
// is allowed. 0 is straight face, <0 would be convex face.
// Set to 180 to disable.
maxConcave 80;

//- Minimum pyramid volume. Is absolute volume of cell pyramid.
// Set to a sensible fraction of the smallest cell volume expected.
// Set to very negative number (e.g. -1E30) to disable.
minVol 1e-13;

//- Minimum quality of the tet formed by the face-centre
// and variable base point minimum decomposition triangles and
// the cell centre. This has to be a positive number for tracking
// to work. Set to very negative number (e.g. -1E30) to
// disable.
// <0 = inside out tet,
// 0 = flat tet
// 1 = regular tet
minTetQuality -1; // 1e-30;

//- Minimum face area. Set to <0 to disable.
minArea -1;

//- Minimum face twist. Set to <-1 to disable. dot product of face normal
// and face centre triangles normal
minTwist 0.01;

//- Minimum normalised cell determinant
// 1 = hex, <= 0 = folded or flattened illegal cell
minDeterminant 0.001;

//- minFaceWeight (0 -> 0.5)
minFaceWeight 0.05;

//- minVolRatio (0 -> 1)
minVolRatio 0.01;

// must be >0 for Fluent compatibility
minTriangleTwist -1;


// Advanced

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

// Optional : some meshing phases allow usage of relaxed rules.
// See e.g. addLayersControls::nRelaxedIter.
relaxed
{
//- Maximum non-orthogonality allowed. Set to 180 to disable.
maxNonOrtho 75;
}
}



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


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

[peterhess]

Hello Brett!

Well, it is no easy to find the reason just from the setups you uploaded.

Anyway, the first place to look is:

locationInMesh (0.01 -0.5 0.01);

The location should be inside the region you want to keep and not on a boundary.

How much cells do you have?

maxLocalCells 100000;

and

maxGlobalCells 2000000;

must be higher than than generated cells...

Upload the case please if those setups are right.

Regards

Peter

[Bdew8556]

Thanks Peter,

Do you mean run simpleFoam and then upload that case?

Basically it's an ellipse that I drew in fusion 360 then extruded and exported as an .stl file. I want to remove the inside of the object from the domain naturally.

My location in mesh is actually:

locationInMesh (3.5001 1.5001 1.9001);

So this is definitely outside the ellipse/airfoil.

Any thoughts?

Brett

[Bdew8556]

I uploaded the wrong file. Whoops!

/*--------------------------------*- C++ -*----------------------------------*\
| ========= | |
| \\ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \\ / O peration | Version: dev |
| \\ / A nd | Web: www.OpenFOAM.org |
| \\/ M anipulation | |
\*---------------------------------------------------------------------------*/
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Which of the steps to run
castellatedMesh true;
snap true;
addLayers true;
geometry true;
castellatedMeshControls true;
snapControls true;
addLayersControls true;
meshQualityControls true;

// 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
{
airfoil1
{
type triSurfaceMesh;
file "airfoil1.stl";
}

refinementBox
{
type searchableBox;
min (-1.5 -1 -1.5);
max ( 1.5 1 1.5);
}
};



// 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 100000;

// 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 200000;

// 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 5;

// 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 0.10;


// Number of buffer layers between different levels.
// 1 means normal 2:1 refinement restriction, larger means slower
// refinement.
nCellsBetweenLevels 3;



// 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 "airfoil1.eMesh";
level 2;
}
);



// 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
{
airfoil1
{
// Surface-wise min and max refinement level
level (2 4);

// Optional specification of patch type (default is wall). No
// constraint types (cyclic, symmetry) etc. are allowed.
patchInfo
{
type wall;
inGroups (airfoil1Group);
}
}
}

// Resolve sharp angles
resolveFeatureAngle 20;


// 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
{
refinementBox
{
mode inside;
levels ((1E15 4));
}
}


// 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.
locationInMesh (3.501 1.501 1.901);


// 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 there are no faceZones.
allowFreeStandingZoneFaces false;
}



// 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 0.5;

//- Number of mesh displacement relaxation iterations.
nSolveIter 5;

//- 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 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
{
"(airfoil1).*"
{
nSurfaceLayers 4;
}
}

// 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.
// See relativeSizes parameter.
finalLayerThickness 0.02;

// 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 0.005;

// 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 25;

// 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 3;

// Number of smoothing iterations of surface normals
nSmoothSurfaceNormals 3;

// Number of smoothing iterations of interior mesh movement direction
nSmoothNormals 3;

// Smooth layer thickness over surface patches
nSmoothThickness 5;

// 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 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 5;
}



// 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-2;


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

[peterhess]

Hello Brett!


I mean upload the case without generating anything!

no mesh and no results.

Just a clean case with the STL files , the blockMeshDict snappyHexMeshDict included...

Regards

Peter

[Bdew8556]

Hi Peter,

See attached. Hope this helps. Bit lost at the moment I must admit.

[peterhess]

Hello Brett,
I was not able to run the setups you uploaded...

I still work on it.

--------------------------------------------

Anyway, after running blockMesh, I ran checkMesh!

The blockMesh generats Mesh with 112 000 Cells.

As I mentioned before, This number must be smaller than:

maxLocalCells 100 000;

and

maxGlobalCells 200 000;

-----------------------------------------------

Increase those to:

maxLocalCells 1 000 000;

and

maxGlobalCells 2 000 000;

and see what happens...

I will continue testing.

Regards

Peter

PS: By the way, increasing the cells generated by blockMesh to such high number is not a good idea. It is better to start with coarse Mesh generated by blockMesh and refine it in snappy!

PS2: Your mesh has a bounding box of

Overall domain bounding box (-2 -2 -2) (5 2 2)

That means in X direction you have about 7 m! is that right?

[Bdew8556]

Thanks Peter,

That's very interesting. I see your point on mesh density.

I didn't know that about the max cells, so I'm learning already!

Be interesting to see what you find.

[peterhess]

Hello Brett,

After too many tests I decided myself to drop your snappyHexMeshDict and use my own one.

In the case uploaded here is a working Mesh generation with your geometry. You can use it as a layout.

The geometry has been simplified using Salome and the STL file inside is not identical with yours. The simplification was necessery cause the STL file was very complex and "bad".

Anyway, using the original STL file works also...

I reduced the Mesh size cause my PC ran out of memory. U can increase it by your needs...

Regards

Peter

ps: new case is uploaded!!!

[w.chaabouni]

Hello,
Actually I am also new in snappyHexMesh. I am trying to mesh a box with a cylindric whole. I starte with "castellatedMesh" only. the problem is that the result is only 1 part of the mesh (0.01x0.4x0.01 as dimensions). I join here thhe case directory. Please anyone can help me with it?