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[snappyHexMesh] SnappyHexMesh stuck at "Introducing baffles..." |
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April 9, 2023, 16:49 |
SnappyHexMesh stuck at "Introducing baffles..."
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#1 |
Member
Ruggiero Guida
Join Date: Apr 2013
Location: World
Posts: 46
Rep Power: 13 |
I hope someone can provide some advice...
I am meshing a large city geometry with snappyHexMesh and it keeps getting stuck at Code:
Splitting mesh at surface intersections --------------------------------------- Introducing baffles for 18354934 faces that are intersected by the surface. Honestly, I am a bit lost and I am not sure what to check. I have been waiting for around an hour. The coarser version of the mesh for the same geometry goes through this part in a few minutes. If helpful, this is the snappyHexMeshDict Code:
// -*- C++ -*- // File generated by PyFoam - sorry for the ugliness FoamFile { version 2.0; format ascii; class dictionary; object snappyHexMeshDict; } castellatedMesh yes; snap yes; addLayers no; geometry { refinement_1H { type searchableCylinder; point1 (-10.712 413.668 -109.993); point2 (-10.712 413.668 42.916); radius 204.29628787216436; } refinement_3H { type searchableCylinder; point1 (-10.712 413.668 -109.993); point2 (-10.712 413.668 37.9068); radius 306.4444318082466; } refinement_5H { type searchableCylinder; point1 (-10.712 413.668 -109.993); point2 (-10.712 413.668 32.9068); radius 408.5925757443287; } refinement_regions { type triSurfaceMesh; file "refinement_regions.stl"; } mct-terrain.stl { name mct-terrain; type triSurfaceMesh; } fixed_surroundings.stl { name fixed_surroundings; type triSurfaceMesh; } far_buildings.stl { name far_buildings; type triSurfaceMesh; } boundary.stl { name boundary; regions { Bottom { name Bottom; } InletOutlet_0 { name InletOutlet_0; } InletOutlet_1 { name InletOutlet_1; } InletOutlet_2 { name InletOutlet_2; } InletOutlet_3 { name InletOutlet_3; } InletOutlet_4 { name InletOutlet_4; } InletOutlet_5 { name InletOutlet_5; } InletOutlet_6 { name InletOutlet_6; } InletOutlet_7 { name InletOutlet_7; } Top { name Top; } } type triSurfaceMesh; } } // Settings for the castellatedMesh generation. castellatedMeshControls { maxLocalCells 3859376; maxGlobalCells 247000000; // 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.// 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. // 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 4; // 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 0.1; // Number of buffer layers between different levels.// 1 means normal 2:1 refinement restriction, larger means slower// refinement. nCellsBetweenLevels 1; // Explicit feature edge refinement// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~// Specifies a level for any cell intersected by explicitly provided// edges.// This is a featureEdgeMesh, read from constant/triSurface for now.// Specify 'levels' in the same way as the 'distance' mode in the// refinementRegions (see below). The old specification// level 2;// is equivalent to// levels ((0 2)); features ( ); // 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.// Surface-wise min and max refinement level refinementSurfaces { mct-terrain { level ( 2 4 ); } boundary { level ( 2 4 ); } fixed_surroundings { level ( 2 3 ); } far_buildings { level ( 1 2 ); } //- Optional increment (on top of max level) in small gaps//gapLevelIncrement 2;//- Optional angle to detect small-large cell situation// perpendicular to the surface. Is the angle of face w.r.t.// the local surface normal. Use on flat(ish) surfaces only.// Otherwise leave out or set to negative number.//perpendicularAngle 10;//- Optional faceZone and (for closed surface) cellZone with// how to select the cells that are in the cellZone// (inside / outside / specified insidePoint)// The orientation of the faceZone is// - if on cellZone(s) : point out of (maximum) cellZone// - if freestanding : oriented according to surface//faceZone sphere;//cellZone sphere;//cellZoneInside inside; //outside/insidePoint//- Optional specification of what to do with faceZone faces:// internal : keep them as internal faces (default)// baffle : create baffles from them. This gives more// freedom in mesh motion// boundary : create free-standing boundary faces (baffles// but without the shared points)//faceType baffle; } // Feature angle:// - used if min and max refinement level of a surface differ// - used if feature snapping (see snapControls below) is used resolveFeatureAngle 30; //- Optional increment (on top of max level) in small gaps//gapLevelIncrement 2;// Planar angle:// - used to determine if surface normals// are roughly the same or opposite. Used// - in proximity refinement// - to decide when to merge free-standing baffles// (if e.g. running in surfaceSimplify mode set this to 180 to// merge all baffles)// - in snapping to avoid snapping to nearest on 'wrong' side// of thin gap//// If not specified same as resolveFeatureAngle planarAngle 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// increasing 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 { refinement_1H { mode inside; levels ( ( 1000000000000000.0 3 ) ); } refinement_3H { mode inside; levels ( ( 1000000000000000.0 2 ) ); } refinement_5H { mode inside; levels ( ( 1000000000000000.0 1 ) ); } mct-terrain { mode distance; levels ( ( 2.0 3 ) ); } fixed_surroundings { mode distance; levels ( ( 1.0 3 ) ( 4.0 2 ) ); } far_buildings { mode distance; levels ( ( 1.0 1 ) ( 4.0 1 ) ); } } // 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 (-10.712045025920519 413.66830664447565 929.9970092773438); // 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 no; } // Settings for the snapping. snapControls { nSmoothPatch 3; tolerance 2.0; // Number of patch smoothing iterations before finding correspondence// to surface// Maximum relative distance for points to be attracted by surface.// True distance is this factor times local maximum edge length.// Note: changed(corrected) w.r.t 17x! (17x used 2* tolerance) // Number of mesh displacement relaxation iterations. nSolveIter 300; // Maximum number of snapping relaxation iterations. Should stop// before upon reaching a correct mesh. nRelaxIter 10; // Feature snapping// Number of feature edge snapping iterations.// Leave out altogether to disable. nFeatureSnapIter 15; // Detect (geometric only) features by sampling the surface// (default=false). implicitFeatureSnap yes; explicitFeatureSnap no; multiRegionFeatureSnap no; } // Settings for the layer addition. addLayersControls { relativeSizes no; expansionRatio 1.05; // Are the thickness parameters below relative to the undistorted// size of the refined cell outside layer (true) or absolute sizes (false).// Layer thickness specification. This can be specified in one of following// ways:// - expansionRatio and finalLayerThickness (cell nearest internal mesh)// - expansionRatio and firstLayerThickness (cell on surface)// - overall thickness and firstLayerThickness// - overall thickness and finalLayerThickness// - overall thickness and expansionRatio//// Note: the mode thus selected is global, i.e. one cannot override the// mode on a per-patch basis (only the values can be overridden)// Expansion factor for layer mesh// Wanted thickness of the layer furthest away from the wall.// If relativeSizes this is relative to undistorted size of cell// outside layer. finalLayerThickness 0.25; // Wanted overall thickness of layers.// If relativeSizes this is relative to undistorted size of cell// outside layer.//thickness 0.5// Minimum overall thickness of total layers. If for any reason layer// cannot be above minThickness do not add layer.// If relativeSizes this is relative to undistorted size of cell// outside layer.. minThickness 0.1; // Per final patch (so not geometry!) the layer information// Note: This behaviour changed after 21x. Any non-mentioned patches// now slide unless:// - nSurfaceLayers is explicitly mentioned to be 0.// - angle to nearest surface < slipFeatureAngle (see below) layers { mct-terrain { nSurfaceLayers 4; } fixed_surroundings { nSurfaceLayers 0; } far_buildings { nSurfaceLayers 0; } } // 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// Static analysis of starting mesh// When not to extrude surface. 0 is flat surface, 90 is when two faces// are perpendicular featureAngle 310; // Stop layer growth on highly warped cells maxFaceThicknessRatio 1.0; // Patch displacement// Number of smoothing iterations of surface normals nSmoothSurfaceNormals 1; // Smooth layer thickness over surface patches nSmoothThickness 10; // Medial axis analysis// Angle used to pick up medial axis points// Note: changed(corrected) w.r.t 17x! 90 degrees corresponds to 130// in 17x. minMedianAxisAngle 5; // Reduce layer growth where ratio thickness to medial// distance is large maxThicknessToMedialRatio 0.3; // Number of smoothing iterations of interior mesh movement direction nSmoothNormals 3; // Optional: limit the number of steps walking away from the surface.// Default is unlimited.//nMedialAxisIter 10;// Optional: smooth displacement after medial axis determination.// default is 0.//nSmoothDisplacement 90;// (wip)Optional: do not extrude a point if none of the surrounding points is// not extruded. Default is false.//detectExtrusionIsland true; // Mesh shrinking // Optional: at non-patched sides allow mesh to slip if extrusion// direction makes angle larger than slipFeatureAngle. Default is// 0.5*featureAngle. slipFeatureAngle 80; // Maximum number of snapping relaxation iterations. Should stop// before upon reaching a correct mesh. nRelaxIter 3; // 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 10; // Max number of iterations after which relaxed meshQuality controls// get used. Up to nRelaxedIter it uses the settings in// meshQualityControls,// after nRelaxedIter it uses the values in// meshQualityControls::relaxed. nRelaxedIter 20; // Additional reporting: if there are just a few faces where there// are mesh errors (after adding the layers) print their face centres.// This helps in tracking down problematic mesh areas.//additionalReporting true; } // Generic mesh quality settings. At any undoable phase these determine// where to undo. meshQualityControls { #include "meshQualityDict" relaxed { maxNonOrtho 75; } // Specify mesh quality constraints in separate dictionary so can// be reused (e.g. checkMesh -meshQuality)// Optional : some meshing phases allow usage of relaxed rules.// See e.g. addLayersControls::nRelaxedIter.// Maximum non-orthogonality allowed. Set to 180 to disable.// Advanced// Number of error distribution iterations nSmoothScale 4; // amount to scale back displacement at error points errorReduction 0.75; } // Advanced//// Debug flags//debugFlags//(// mesh // write intermediate meshes// intersections // write current mesh intersections as .obj files// featureSeeds // write information about explicit feature edge// // refinement// attraction // write attraction as .obj files// layerInfo // write information about layers//);// writeFlags ( scalarLevels layerSets layerFields ); // write volScalarField with cellLevel for postprocessing// write cellSets, faceSets of faces in layer// 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-06; // ************************************************************************* // EDIT The "problem" seems to go away by setting the levels in the fixed_surrounding refinement surfaces to a value of (3 3) rather than (2 3). Code:
fixed_surroundings { level ( 3 (instead of 2) 3 ); } I made this change based on a suggestion of a colleague, but I do not really understand why it works. Last edited by Rojj; April 10, 2023 at 04:30. |
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June 30, 2023, 09:14 |
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#2 |
Member
Ruggiero Guida
Join Date: Apr 2013
Location: World
Posts: 46
Rep Power: 13 |
Just in case it helps. It seems that improving the quality of the STL triSurfaces also solves the problem.
I am using MeshLab to re-triangulate. The filter I use is called Remeshing: Isotropic Explicit Remeshing |
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