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[snappyHexMesh] snappyHexMesh & Mesh around a missile |
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March 17, 2014, 12:16 |
snappyHexMesh & Mesh around a missile
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#1 |
Senior Member
Sasan Ghomi
Join Date: Sep 2012
Location: Denmark
Posts: 292
Rep Power: 15 |
Hi Dear Foamers,
These days, I am trying to create a good mesh (C-type) around a missile by using snappyhexmesh. Actually, geometry of the missile is similar to picture3. After creating mesh, boundary of the missile got a bad shape (similar to picture1). I should say that whole the mesh is similar to picture2. Could anyone help me to create a good mesh around the missile? I appreciate your help. Thanks and best regards, Sasan. P.S. Honestly, I used solidworks for creating the geometry and afterwards I imported the geometry in salome for specifying names of the boundaries and after that I exported 3 .stl files and I converted them to 1 .stl file by using cat name.stl >> assemble.stl . I uploaded my case : https://mega.co.nz/#!NlYFXDhD!bYtW2A...WNgA02EeYERHrE snappyHexMeshDict : Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: 2.2.2 | | \\ / A nd | Web: www.OpenFOAM.org | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; object autoHexMeshDict; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // // 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 { projectile.stl { type triSurfaceMesh; name projectile; } //- Refine a bit extra around the small centre hole cylinder { type searchableCylinder; point1 (-9 0 0); point2 (4 0 0); radius 0.1; } }; // 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 10000; // 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 2500000; // 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; // Number of buffer layers between different levels. // 1 means normal 2:1 refinement restriction, larger means slower // refinement. nCellsBetweenLevels 10; // 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 "projectile.eMesh"; level 1; } ); // 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 { projectile { // Surface-wise min and max refinement level level (1 1); } patch3 { // Surface-wise min and max refinement level level (4 4); } } 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 { cylinder { mode inside; levels ((4 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. // This is an outside point locationInMesh (-0.033 -0.033 0.0033); locationInMesh (-30.06732 0.042216 0.0045678); // 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 { //- 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 1.0; //- 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) features by sampling the surface implicitFeatureSnap false; //- Use castellatedMeshControls::features explicitFeatureSnap true; //- 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 false; // Per final patch (so not geometry!) the layer information layers { "projectile_.*" { 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. // See relativeSizes parameter. finalLayerThickness 0.3; // Minimum thickness of cell layer. If for any reason layer // cannot be above minThickness do not add layer. // See relativeSizes parameter. minThickness 0.25; // 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 1; // 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 5; // 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 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; // Max number of iterations after which relaxed meshQuality controls // get used. Up to nRelaxIter it uses the settings in meshQualityControls, // after nRelaxIter it uses the values in meshQualityControls::relaxed. nRelaxedIter 20; } // Generic mesh quality settings. At any undoable phase these determine // where to undo. meshQualityControls { //- Maximum non-orthogonality allowed. Set to 180 to disable. maxNonOrtho 1; //- Max skewness allowed. Set to <0 to disable. maxBoundarySkewness 1; maxInternalSkewness 0.5; //- 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 90; //- 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. Set to very negative number (e.g. -1E30) to // disable. // <0 = inside out tet, // 0 = flat tet // 1 = regular tet minTetQuality 1e-9; //- 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 0.05; //- minimum normalised cell determinant //- 1 = hex, <= 0 = folded or flattened illegal cell minDeterminant 1; //- minFaceWeight (0 -> 0.5) minFaceWeight 0.05; //- minVolRatio (0 -> 1) minVolRatio 0.01; //must be >0 for Fluent compatibility minTriangleTwist 1; //- if >0 : preserve single cells with all points on the surface if the // resulting volume after snapping (by approximation) is larger than // minVolCollapseRatio times old volume (i.e. not collapsed to flat cell). // If <0 : delete always. //minVolCollapseRatio 0.5; // 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 10; } } // Advanced // 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-6; // ************************************************************************* // Last edited by sasanghomi; March 17, 2014 at 17:30. |
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March 18, 2014, 09:48 |
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#2 |
Senior Member
Kyle Mooney
Join Date: Jul 2009
Location: San Francisco, CA USA
Posts: 323
Rep Power: 18 |
I would give two recommendations:
1. Use OpenFOAM-2.3.x. OpenCFD is constantly patching snappyHexMesh. 2. Increase the min and max refinement level for the patch of interest like this or higher: Code:
projectile { // Surface-wise min and max refinement level level (4 4); } Cheers, Kyle |
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October 15, 2014, 19:54 |
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#3 | |
New Member
sd
Join Date: May 2014
Posts: 14
Rep Power: 12 |
Quote:
FoamFile { version 2.0; format ascii; class dictionary; object snappyHexMeshDict; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // // Which of the steps to run castellatedMesh true; // make basic mesh ? snap true; // decide to snap back to surface ? addLayers true;//false; // decide to add viscous layers ? geometry // Load in STL files here { inlet_1.stl {type triSurfaceMesh; name inlet_1;} outlet.stl {type triSurfaceMesh; name outlet;} inlet_2.stl {type triSurfaceMesh; name inlet_2;} inlet_3.stl {type triSurfaceMesh; name inlet_3;} wall.stl {type triSurfaceMesh; name wall;} //cylinder.stl {type triSurfaceMesh; name volume;} refineCylinder {type searchableCylinder; point1 (0 0 0); point2 (0 0 2); radius 0.13;} //refinementBox {type searchableBox; min (-0.5 -0.5 -0.5); max ( 0.5 0.5 0.5);} }; castellatedMeshControls { maxLocalCells 1000000; //max cells per CPU core maxGlobalCells 2000000; //max cells to use before mesh deletion step minRefinementCells 10; //was 0 - zero means no bad cells are allowed during refinement stages maxLoadUnbalance 0.10; nCellsBetweenLevels 1; // expansion factor between each high & low refinement zone // Explicit feature edge refinement // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ features // taken from STL from each .eMesh file created by "SurfaceFeatureExtract" command ( {file "inlet_1.eMesh"; level 2;} {file "outlet.eMesh"; level 2;} {file "wall.eMesh"; level 3;} {file "inlet_2.eMesh"; level 2;} {file "inlet_3.eMesh"; level 2;} ); // Surface based refinement // ~~~~~~~~~~~~~~~~~~~~~~~~ refinementSurfaces // Surface-wise min and max refinement level { inlet_1 {level (2 2);} outlet {level (2 2);} wall {level (5 5);} inlet_2 {level (2 2);} // was 4 4 inlet_3 {level (2 2);} // was 4 4 } resolveFeatureAngle 80; // Resolve sharp angles // Default 30 refinementRegions // In descending levels of fine-ness {refineCylinder {mode distance; levels ((1E15 2));}} // (0.002 3) (0.01 2));}} // was ((0.001 4) (0.003 3) (0.01 2)) locationInMesh (0.01 0.01 0.01); //to decide which side of mesh to keep ** allowFreeStandingZoneFaces true; } // Settings for the snapping. snapControls { nSmoothPatch 3; tolerance 4.0; nSolveIter 30; nRelaxIter 5; nFeatureSnapIter 15; // default is 10 // New settings from openfoam 2.2 onwards for SHMesh implicitFeatureSnap false; // default is false - detects without doing surfaceFeatureExtract explicitFeatureSnap true; // default is true multiRegionFeatureSnap false; // deafault is false - detects features between multiple surfaces } // Settings for the layer addition. addLayersControls //add the PATCH names from inside the STL file so STLpatchName_insideSTLName { relativeSizes false; // was true layers { wall {nSurfaceLayers 3;} // was 3 //visc_refine_1 // {nSurfaceLayers 3;} // was 3 //visc_refine_2 // {nSurfaceLayers 3;} // was 3 } expansionRatio 1.3; finalLayerThickness 0.00016; //was 0.00016 minThickness 0.00008; //was 0.00008 nGrow 0; // was 1 // Advanced settings featureAngle 80; // was 70 //- When not to extrude surface. 0 is flat, 90 is right angle. nRelaxIter 3; //- Max# of snapping relaxation iter. Should stop before upon reaching a correct mesh. nSmoothSurfaceNormals 1; // Number of smoothing iterations of surface normals nSmoothNormals 3; // Number of smoothing iterations of interior mesh movement direction nSmoothThickness 10; // Smooth layer thickness over surface patches maxFaceThicknessRatio 0.5; // Stop layer growth on highly warped cells maxThicknessToMedialRatio 0.3; // Reduce layer growth where ratio thickness to medial distance is large minMedianAxisAngle 130; // Angle used to pick up medial axis points nBufferCellsNoExtrude 0; // Create buffer region for new layer terminations nLayerIter 50; // Overall max number of layer addition iterations } // Generic mesh quality settings. At any undoable phase these determine // where to undo. meshQualityControls { maxNonOrtho 65; maxBoundarySkewness 20; maxInternalSkewness 4; maxConcave 80; minFlatness 0.5; minVol 1e-13; minTetQuality 1e-9; minArea -1; minTwist 0.02; minDeterminant 0.001; minFaceWeight 0.02; minVolRatio 0.01; minTriangleTwist -1; // Advanced nSmoothScale 4; errorReduction 0.75; } // Advanced 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-6; // ************************************************** *********************** // |
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