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July 5, 2017, 06:32 |
sHM too many cells
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#1 |
New Member
Thomas
Join Date: May 2017
Posts: 2
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Hi guys,
that's my first entry here! To my problem. In my SnappyHexMeshdict I've defined an amount of 15mio cells, but it seems to produce way more than that. CheckMesh tells me it's about 52~mio cells. Am I misunderstanding the definition of maxGlobalCells or what am I doing wrong here? snappyHexMeshDict: Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 4.1 | | \\ / 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. 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 { SHM_1.stl { type triSurfaceMesh; regions { tyre { name tyre; } } } SHM_2.stl { type triSurfaceMesh; regions { nozzle_body { name nozzle_body; } nozzle_inlet { name nozzle_inlet; } } } ground_nozzle_tyre { type searchableBox; min ( -1.8 -0.9 0 ); max ( 3.2 0.9 0.01 ); } ground_xmin { type searchableBox; min ( -6.4 -0.9 0 ); max ( -1.8 0.9 0.01 ); } ground_xmax { type searchableBox; min ( 3.2 -0.9 0 ); max ( 12.8 0.9 0.01 ); } ground_ymin { type searchableBox; min ( -6.4 -6.4 0 ); max ( 12.8 -0.9 0.01 ); } ground_ymax { type searchableBox; min ( -6.4 0.9 0 ); max ( 12.8 6.4 0.05 ); } }; // 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 1000000; // 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 15000000; // 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 "SHM_1.eMesh"; levels ((0.02 4)); } { file "SHM_2.eMesh"; levels ((0.02 4)); } ); // 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 { SHM_1.stl { level (3 4); regions { tyre { level (3 4); patchInfo { type wall;}} } } SHM_2.stl { level (3 4); regions { nozzle_body { level (3 4); patchInfo { type wall;}} nozzle_inlet { level (3 4); patchInfo { type patch;}} } } } // 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 { ground_nozzle_tyre { mode inside; levels (( 1e15 5 ) ); } ground_ymin { mode inside; levels (( 1e15 5 ) ); } ground_ymax { mode inside; levels (( 1e15 5 ) ); } ground_xmin { mode inside; levels (( 1e15 5 ) ); } ground_xmax { mode inside; levels (( 1e15 5 ) ); } } // 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 ( -2.55453 1.215 1.041564); // 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 1.2; //- Number of mesh displacement relaxation iterations. nSolveIter 30; //- 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 { SHM_1.stl_tyre { nSurfaceLayers 2; } SHM_2.stl_nozzle_body { nSurfaceLayers 2; } SHM_2.stl_nozzle_inlet { nSurfaceLayers 2; } ground_nozzle_tyre { nSurfaceLayers 1; } ground_xmin { nSurfaceLayers 1; } ground_xmax { nSurfaceLayers 1; } ground_ymin { nSurfaceLayers 1; } ground_ymax { nSurfaceLayers 1; } } // Expansion factor for layer mesh expansionRatio 1.3; // 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 60; // 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 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 { relaxed { } maxNonOrtho 65; maxBoundarySkewness 20; maxInternalSkewness 4; maxConcave 80; minFlatness 0.5; minVol 1e-13; minArea -1; minTwist 0.05; minDeterminant 0.001; minFaceWeight 0.05; minVolRatio 0.01; minTriangleTwist -1; minTetQuality -1; nSmoothScale 4; 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; // ************************************************************************* // Code:
/*---------------------------------------------------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 4.x | | \\ / A nd | Web: www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ Build : 4.x-422f1770e08a Exec : checkMesh Date : Jul 04 2017 Time : 20:52:07 Host : "zeus133" PID : 25384 Case : /home/kilotait/OF_Projects/02_try nProcs : 1 sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE). fileModificationChecking : Monitoring run-time modified files using timeStampMaster allowSystemOperations : Allowing user-supplied system call operations // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // Create time Create polyMesh for time = 0 Time = 0 Mesh stats points: 57407690 faces: 165491129 internal faces: 162103124 cells: 54045732 faces per cell: 6.06143 boundary patches: 9 point zones: 0 face zones: 0 cell zones: 0 Overall number of cells of each type: hexahedra: 52908466 prisms: 17711 wedges: 0 pyramids: 0 tet wedges: 19 tetrahedra: 0 polyhedra: 1119536 Breakdown of polyhedra by number of faces: faces number of cells 4 931 5 1119 6 16622 7 56 8 224 9 1089412 10 4 12 9634 15 1459 18 75 Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology wall-y-max 87075 91464 ok (non-closed singly connected) wall-x-min 17634 18505 ok (non-closed singly connected) wall-x-max 17631 18501 ok (non-closed singly connected) wall-y-min 6075 6256 ok (non-closed singly connected) wall-z-min-nearCar 3199872 3206681 ok (non-closed singly connected) wall-z-max 12150 12376 ok (non-closed singly connected) tyre 19341 20784 ok (non-closed singly connected) nozzle_body 27933 28395 ok (non-closed singly connected) nozzle_inlet 294 556 ok (non-closed singly connected) Checking geometry... Overall domain bounding box (-3.2 -1.8 -0.001) (6.4 1.8 3.199) Mesh has 3 geometric (non-empty/wedge) directions (1 1 1) Mesh has 3 solution (non-empty) directions (1 1 1) Boundary openness (5.87436e-15 -1.90617e-13 7.39134e-12) OK. Max cell openness = 3.43864e-16 OK. Max aspect ratio = 5.20353 OK. Minimum face area = 5.94441e-07. Maximum face area = 0.00511448. Face area magnitudes OK. Min volume = 7.46551e-10. Max volume = 0.00020505. Total volume = 110.53. Cell volumes OK. Mesh non-orthogonality Max: 64.3153 average: 3.59958 Non-orthogonality check OK. Face pyramids OK. Max skewness = 2.50984 OK. Coupled point location match (average 0) OK. Mesh OK. End Thanks in advance guys! Thomas Last edited by Knapsack; July 5, 2017 at 07:53. |
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July 6, 2017, 08:06 |
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#2 |
New Member
Join Date: Mar 2015
Posts: 16
Rep Power: 11 |
Hi,
I might be wrong, but I think that the maxGlobalCells parameter only applies to the first step of snappy (castellatedMesh). When you add the boundary layers, more cells are added, and that could be the cause of your high cells count. |
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July 8, 2017, 07:41 |
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#3 |
New Member
Thomas
Join Date: May 2017
Posts: 2
Rep Power: 0 |
It really differs in the outcome. If i set the maxGlobalCells to 15-20 mio cells, the outcome is nearly the same size.
If it set it to 30 mio cells it nearly "explodes" to ~60 mio cells in the end. But i will give it a try! Thanks Last edited by Knapsack; July 10, 2017 at 06:57. |
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