| pconen |
May 27, 2019 06:20 |
sHM - flat-/ double lined cells
Dear Foamers,
i'm face a Problem using sHM.
My mesh is for a mixing process with very large but also many small cells. I recognized that there are Cells that are really strange. They seem to be really flat or nearly double lined as you can see in the picture. I would like to know why these cells are generated and how I can improve this.
Here you can see my snappyHexMeshDict:
Code:
FoamFile
{
version 2.0;
format ascii;
class dictionary;
object snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
// Which of the steps to run
castellatedMesh true;
snap true;
addLayers false;
// 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
{
Mischstrecke.stl
{
type triSurfaceMesh;
name Mischstrecke;
regions
{
inlet_exhgas { name inlet_exhgas; }
inlet_air { name inlet_air; }
inlet_adblue { name inlet_adblue; }
outlet { name outlet; }
wall { name wall; }
injector { name injector; }
}
}
/*
refinementBox //USER DEFINED REGION NAME
{
type searchableBox; //REGION DEFINED BY BOUNDING BOX
min (-0.16 0.16 -1.00); //parameters
max ( 0.16 -0.16 -1.30);
}
*/
//- Refine a bit extra around the small centre hole
box
{
type searchableCylinder;
point1 (0 0.012 -1.105);
point2 (0 0.310 -1.105);
radius 0.022;
/*
type searchableBox; //Sphere
min (-0.160 -0.100 -1.150); //centre (0 0 -1.136);
max ( 0.160 0.310 -1.080); //radius 0.300;
*/
}
cyla //DynFaecher
{
type searchableCylinder;
point1 (0 0 -1.150);
point2 (0 0 -1.00);
radius 0.165;
}
cylb //StatFaecher; links
{
type searchableCylinder;
point1 (0 0 -2.300);
point2 (0 0 -2.000);
radius 0.165;
}
cylc //StatFaecher; rechts
{
type searchableCylinder;
point1 (0 0 -2.750);
point2 (0 0 -2.450);
radius 0.165;
}
cyld //Injektorkopf
{
type searchableCylinder;
point1 (0 0 -1.140);
point2 (0 0 -1.090);
radius 0.012;
}
};
// 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 3000000;
// 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 25;
// 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 "Mischstrecke.eMesh";
level 3;
}
);
// 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
{
Mischstrecke
{
// Surface-wise min and max refinement level
level (0 0);
regions
{
inlet_exhgas { level (0 0); patchInfo { type patch; }}
inlet_air { level (1 1); patchInfo { type patch; }}
inlet_adblue { level (2 2); patchInfo { type patch; }}
outlet { level (0 0); patchInfo { type patch; }}
wall { level (1 1); patchInfo { type wall; }}
injector { level (4 4); gapLevelIncrement 3; patchInfo { type wall; }}
//- Optional increment (on top of max level) in small gaps
}
}
}
// Resolve sharp angles
resolveFeatureAngle 45;
// 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
{
box
{
mode inside;
levels ((1 1)); //levels ((1E15 6));
}
cyla
{
mode inside;
levels ((2 2)); //levels ((1E15 6));
}
cylb
{
mode inside;
levels ((2 2)); //levels ((1E15 6));
}
cylc
{
mode inside;
levels ((2 2)); //levels ((1E15 6));
}
cyld
{
mode inside;
levels ((4 4)); //levels ((1E15 6));
}
}
// 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 0 -1.3);
// 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 15;
//- Relative distance for points to be attracted by surface feature point
// or edge. True distance is this factor times local
// maximum edge length.
tolerance 1.2;
//- Number of mesh displacement relaxation iterations.
nSolveIter 100; //30-300 (higher better, increasing time)
//- Maximum number of snapping relaxation iterations. Should stop
// before upon reaching a correct mesh.
nRelaxIter 10; //5 or higher
// Feature snapping
//- Number of feature edge snapping iterations.
// Leave out altogether to disable.
nFeatureSnapIter 20; //10 or higher
//- 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 false;
// Per final patch (so not geometry!) the layer information
layers
{
inlet_exhgas
{
nSurfaceLayers 0;
}
inlet_air
{
nSurfaceLayers 0;
}
inlet_adblue
{
nSurfaceLayers 0;
}
outlet
{
nSurfaceLayers 0;
}
wall
{
nSurfaceLayers 0;
}
injector
{
nSurfaceLayers 0;
}
}
// Expansion factor for layer mesh
expansionRatio 1;//1.2
// 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 0.0005;
// 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 0.00005;
// 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.
nGrow 0;
// Advanced settings
// When not to extrude surface. 0 is flat surface, 90 is when two faces
// are perpendicular
featureAngle 180;//75
// 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 8;// 3;
// Number of smoothing iterations of surface normals
nSmoothSurfaceNormals 6;// 1;
// Number of smoothing iterations of interior mesh movement direction
nSmoothNormals 8;// 3;
// Smooth layer thickness over surface patches
nSmoothThickness 10;
// Stop layer growth on highly warped cells
maxFaceThicknessRatio 0.8;// 0.5;
// Reduce layer growth where ratio thickness to medial
// distance is large
maxThicknessToMedialRatio 0.6;// 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;
nMedialAxisIter 4;
// 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;
nRelaxedIter 20;
}
// 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;
//
maxNonOrtho 75; //90;
minVol 1e-13;
minTetQuality 1e-15;
maxConcave 80;
minArea -1;
maxInternalSkewness 4; //4
maxBoundarySkewness 20; //20
minFaceWeight 0.02;
minVolRatio 0.01;
minTwist 0.02;
minTriangleTwist -1;
minDeterminant 0.001;
relaxed {}
}
// Advanced
// Write flags
writeFlags
(
// scalarLevels // write volScalarField with cellLevel for postprocessing
// layerSets // write cellSets, faceSets of faces in layer
// layerFields // write volScalarField for layer coverage
);
// Flags for optional output
// 0 : only write final meshes
// 1 : write intermediate meshes
// 2 : write volScalarField with cellLevel for postprocessing
// 4 : write current intersections as .obj files
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-7;
I hope I used tis forum in a correct way. If you need more information to help me, please let me know.
https://i.ibb.co/MDB0Qf3/sHM2.png
https://i.ibb.co/Kh4Kj6f/sHM1.png |
