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[snappyHexMesh] Unable to generate the desired mesh |
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February 27, 2024, 00:53 |
Unable to generate the desired mesh
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#1 |
Member
Mohd Shaeq
Join Date: Aug 2023
Location: Leinfelden-Echterdingen
Posts: 30
Rep Power: 3 |
Hello,
I have been trying very hard to generate a hexahedral mesh for a relatively simple geometry with snappyHexMesh. Even though I have now gained a fair bit of experience in working with the utility, however, I have not been able to generate the desired mesh as not all the features/surfaces are correctly recognised. I have tried several values of level under the features and refinementSurfaces sub-dictionaries, unfortunately to no avail. Attached herewith are the images of the STL-surfaces and the generated mesh. The snappyHexMeshDict is as follows:- Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v1912 | | \\ / A nd | Website: www.openfoam.com | | \\/ 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 { Geometrie // STL filename { type triSurfaceMesh; file "Geometrie.stl"; regions { Brennkammer { name Brennkammer; } Einlass { name Einlass; } Kanal_aussen { name Kanal_aussen; } Kanal_innen { name Kanal_innen; } } } Verfeinerungszylinder1 { type searchableCylinder; point1 (0 0 -0.03); point2 (0 0 0.07); radius 0.001652; } Verfeinerungszylinder2 { type searchableCylinder; point1 (0 0 0); point2 (0 0 -0.02); radius 0.043; } }; // Settings for the castellatedMesh generation. castellatedMeshControls //sub-dictionary of controls for castellated mesh. { // 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 300000; //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 30000000; //1000000; // 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 10; //10; // 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 1; // 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 "Geometrie.eMesh"; level 5; //4; //5; //6 } ); // 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 { Geometrie { level (1 1); // default (min max) refinement for whole surface regions { Brennkammer { level (0 0); patchInfo { type wall; // Optional specification of patch type (default is wall). No constraint types (cyclic, symmetry) etc. are allowed. } } Einlass { level (6 6); patchInfo { type patch; // Optional specification of patch type (default is wall). No constraint types (cyclic, symmetry) etc. are allowed. } } Kanal_aussen { level (3 3); patchInfo { type wall; // Optional specification of patch type (default is wall). No constraint types (cyclic, symmetry) etc. are allowed. } } Kanal_innen { level (3 3); patchInfo { type wall; // Optional specification of patch type (default is wall). No constraint types (cyclic, symmetry) etc. are allowed. } } } } } // 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 { Geometrie { mode distance; levels ((0.005 3)); } Verfeinerungszylinder1 { mode inside; levels ((1E15 3)); } Verfeinerungszylinder2 { mode distance; levels ((0.02 2)); } }; // 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 -0.02); // 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 2.0; //- 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 true ; } 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 { Geometrie { nSurfaceLayers 2; } } // 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 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 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 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 50; } // Generic mesh quality settings. At any undoable phase these determine // where to undo. meshQualityControls { #include "meshQualityDict" maxNonOrtho 65; maxBoundarySkewness 20; maxInternalSkewness 4; maxConcave 80; minVol 1e-13; minTetQuality 1e-13; minArea -1; minTwist 0.05; minDeterminant 0.001; minFaceWeight 0.05; minVolRatio 0.01; minTriangleTwist -1; /* // 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; } // Advanced //- Number of error distribution iterations nSmoothScale 4; //- Amount to scale back displacement at error points errorReduction 0.75; */ // Advanced nSmoothScale 4; errorReduction 0.75; relaxed { maxNonOrtho 55; } //- Number of error distribution iterations nSmoothScale 4; //- Amount to scale back displacement at error points errorReduction 0.75; } // Write flags writeFlags ( scalarLevels // write volScalarField with cellLevel for postprocessing layerSets // write cellSets, faceSets of faces in layer 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; // ************************************************************************* // Kind regards, Mohd Shaeq |
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March 4, 2024, 03:18 |
Solved
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#2 |
Member
Mohd Shaeq
Join Date: Aug 2023
Location: Leinfelden-Echterdingen
Posts: 30
Rep Power: 3 |
I have been able to solve this problem. The trick lay in, as far as I can tell, employing inGroups under refinementSurfaces under the castellatedMeshControls sub-dictionary. The snappyHexMeshDict now reads as follows:-
Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v2112 | | \\ / A nd | Website: | | \\/ 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 { Geometrie { type triSurfaceMesh; file "Geometrie.stl"; regions { Brennkammer { name Brennkammer;} Einlass { name Einlass;} Kanal_aussen { name Kanal_aussen;} Kanal_innen { name Kanal_innen;} } } Verfeinerungszylinder1 { type searchableCylinder; point1 (0 0 -0.03); point2 (0 0 0.07); radius 0.0025; } Verfeinerungszylinder2 { type searchableCylinder; point1 (0 0 0); point2 (0 0 -0.02); radius 0.043; } }; // Settings for the castellatedMesh generation. castellatedMeshControls //sub-dictionary of controls for castellated mesh. { // 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 20000000; // 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 10; // 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 1; // 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 "Geometrie.eMesh"; level 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 { Geometrie { level (3 3); // Surface - wise min and max refinement level patchInfo { type wall; inGroups (GeometrieGroup); } regions { Einlass { level (1 1); patchInfo { type patch;} } Kanal_aussen { level (6 6); patchInfo { type wall;} } Kanal_innen { level (6 6); patchInfo { type wall;} } } } } // 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 { Verfeinerungszylinder1 { mode inside; levels ((1E15 1)); } Verfeinerungszylinder2 { mode distance; levels ((0.02 3)); } } // 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. // This is an outside point locationInMesh (-0.033 -0.033 0.0033); locationInMesh (0 0 -0.02); /*locationsInMesh ( (( 0 0 -0.02) Brennkammer) (( 0 0.00199 0.0068) Kanal_aussen) );*/ // 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 true; } // Settings for the snapping. snapControls { nSmoothPatch 3; tolerance 2.0; nSolveIter 30; nRelaxIter 5; // Feature snapping 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 true ; } 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 { Geometrie { nSurfaceLayers 3; } } // 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 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 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 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 50; } // 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; } // 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; // ************************************************************************* // Kind regards, Mohd Shaeq |
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