ICEM 原版培训教程(ANSYS 公司提供)7.pdf

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1、Chapter 4Chapter 4Volume MeshingICEM CFD IntroductoryCourse4-1ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663Volume MeshingTraining ManualIntroduction to volume meshing To automatically create 3D elements to fill volumetric domain Generally termed“unstructured”Main

2、ly tetraMainly tetra Full 3D analysis Where 2D approximations dont tell the full story Internal/External flow simulationInternal/External flow simulation Structural solid modeling Thermal stress Many more!Standard procedures Start from just geometry Octree tetra Robust Start from existing shell mesh

3、 Delauney/T-grid Quick Both geometry and shell mesh Portions of model obust Walk over features Cartesian Fastest Have to set sizes Quick Advancing Front Smoother gradients,size transition Hex Corealready meshed Inflation layers“Prism”4-2ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2

4、009Inventory#002663Have to set sizes Hex Core Hex DominantVolume MeshingTraining ManualGeneral Procedure First decide volume mesh parameters First decide volume mesh parameters Global Mesh Setup Volume Meshing Parameters Select Mesh TypeSelect Mesh Method for selected Type Load/create surface mesh A

5、s in Shell Meshing chapter Select Mesh Method for selected Type Set options for specific Methods Set mesh sizes Globally As in Shell Meshing For Delauney,Advancing Front,T-grid,Hex-Dominant Either of these types run from geometry will As in Shell Meshing Locally Part/Surface/Curve Mesh Setup As in S

6、hell Meshing For From geometry onlyfrom geometry will automatically create surface mesh using global and local Shell Mesh settings without any user input/editingOctreeCartesian Define volumetric region Typically for octree on complex modelsM lti ll If in doubt,run Shell Mesh first,then from existing

7、 mesh Compute MeshMh CtMh Compute Prism(optional)As separate process Multiple volumes Define density regions(optional)Applying mesh size within volume where geometry doesnt exist Mesh Compute Mesh Volume Mesh4-3ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663 Also o

8、ption to run automatically following tetra creationVolume MeshingTraining ManualBody/Material PointDefine Volumetric DomainOptionalOptional Recommended for complex geometries Multiple volumesGeometry-Create BodyMaterial Point Centroid of 2 points Select any two locations whose mid-point is within vo

9、lume Preferred At specified point Define volume region by“point”within volumeBy Topology Defines volume region by set of closed surfacesgy Must first Build Diagnostic Topology Entire model Automatically define all volumesSelected surfaces4-4ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Ju

10、ly 2009Inventory#002663 Selected surfaces User selects surfaces that form a closed volumeVolume MeshingTraining ManualMesh Types Tetra/mixed Most used TetraPure tetra With hex core Hexa(cartesian)filling majority volume Tetra(from delauney algorithm)used(yg)to fill between surface or top of inflatio

11、n layers and hex core Pyramids to make conformal between tetra tri and hex quad facesTetra/Prismq With inflation layers Prisms from tri surface mesh Hexas from quad surface mesh Tetra and/or hex core filling interior Pyramids to cap off any quad faces Of hex core or hex inflation layersMerged hybrid

12、 with structured hexTetra/Prism/Hexcore4-5ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663 Merged hybrid with structured hex meshVolume MeshingTraining ManualMesh Types Hexa-Dominant From existing quad meshGood quality hex near surface Good quality hex near surface

13、Somewhat poor in interior Typically good enough for static displacementstatic displacement Not covered in detail here Cartesian Automatic pure hexa Rectilinear mesh Staircase or Body fitted Fastest method for creating volume mesh4-6ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009In

14、ventory#002663 Not covered in detail hereVolume MeshingTraining ManualMesh Method Tetra/Mixed Robust(Octree)Same as Shell Meshing Patch IndependentSame as Shell Meshing Patch Independent Retains volumetric tetras If you have complex and/or dirty geometry Dont want to spend too much time with geometr

15、y cleanup Dont want to spend too much time with detailed shell meshing Dont want to spend time defeaturing geometryDon t want to spend time defeaturing geometry Just set appropriate mesh sizes on geometry Parts Surfaces Curves Review Shell Meshing chapter Part/Surface/Curve Mesh Setup4-7ANSYS,Inc.Pr

16、oprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663Volume MeshingTraining ManualOctree MethodICEM Tetra uses patch-independent Octree methodVolume first generated independent of surface modelNodes are projected to model surfaces,curves and pointsMesh detailSurface mesh is createdR

17、esulting mesh is independent of the underlying arrangement of surfacesNot all surface edges need to be captured!Not all surface edges need to be captured!Make curves/points dormantDeleteFilter points/curves under Build Diagnostic TopologyGeometryMeshSliver ignored4-8ANSYS,Inc.Proprietary 2009 ANSYS,

18、Inc.All rights reserved.July 2009Inventory#002663MeshVolume MeshingTraining ManualGeometry Requirements for Octree TetraTetra requires an enclosed surface model Run Build Diagnostic TopologyGeometry Repair tools quickly locateto find gaps/holes Octree can tolerate gaps smaller then the local element

19、 sizetools quickly locate and fix these problems.sizeRecommend points and curves at key featuresRecommend Material points toRecommend Material points to define volumes Will create a material point if none existsnone existsSet Global,Part,Surface,Curve Size ParametersAs in Shell MeshingMissing inlet

20、surface4-9ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663 As in Shell MeshingHole highlighted by yellow single edge curveVolume MeshingTraining ManualUsing Points and Curves Curves and points included Mesh size specified on curves and surfacesMesh captures detailCo

21、arse mesh walks over detail in surface model Curves and points affect which features are eatu es a ecaptured by the mesh!Build Topologyeasily creates the necessary points4-10ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663 Curves and points not included Mesh size sp

22、ecified only on surfacesnecessary points and curvesVolume MeshingTraining ManualOctree-Options Setup options:Global Mesh Setup Volume Meshing parameters Run as batch processp Runs as a separate process.GUI will stay interactive.Fast Transition Allows for a faster transition in element size from fine

23、r to coarser Reduce element count Edge Criteriong Split elements at a factor greater than set value to better capture geometry Define Thin cuts Tool for resolving thin gaps,sharp angles User selects pairs of opposing parts Resolve elements jumping from one side to another Smooth Automatically smooth

24、s after grid generation process Coarsen Fix Non-manifold Automatically tries to fix elements that jump from surface to another For a more detailed description go to Help Help Topics Help Manual Mesh Global Mesh Setup Volume Meshing Parameters Tetra/Mixed Robust(Octree)4-11ANSYS,Inc.Proprietary 2009

25、ANSYS,Inc.All rights reserved.July 2009Inventory#002663Volume MeshingTraining ManualOctree-Options Run options:Compute Mesh Volume Meshing Parameters Create Prism Layersy Will create prisms marked under Part Mesh Setup Immediately after tetra calculation Prism layers grown into existing tetra mesh C

26、reate Hexa-Core Will retain tri surface mesh(or tri-prism),throw away tetraWill retain tri surface mesh(or tri prism),throw away tetra mesh Fill volume interior with cartesian Cap off with pyramids Map tetra to tri or top prism face with delauney algorithm InputInput Select Geometry All,Visible Part

27、 by Part Meshes each part separately Mesh not conformal between partsp From file Select tetin file Use Existing Mesh Parts Select Parts that are already surface meshed Uses Make Consistent to match octree volume mesh to4-12ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#0

28、02663Uses Make Consistent to match octree volume mesh to existing surface meshVolume MeshingTraining ManualCurvature/Proximity Based RefinementCurvature/Proximity Based RefinementOctree onlyAutomatically subdivides to create elements that are smaller than the prescribed entity size in order to captu

29、re finer features Min size limit value entered is multiplied by the global Scale Factor and is a lower limit for the automatic subdivisionUsed primarily to avoid setting up meshing parameters specifically for individual entities thus allowing the geometry to determine the mesh sizePrescribed element

30、 size:Surface/Curve Max.Element Size times Scale FactorMin Size Limit:multiplied by Scale Factor=global minimumPrescribed size is adequate hereSize times Scale FactorAuto subdivision at tighter radius 4-13ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663at t g tead u

31、sof curvatureVolume MeshingTraining ManualCurve Based RefinementR fitRefinementNumber of elements along curvature if extrapolated to 360oPrescribed sizeMin size limitTo avoid subdivision always to global minimum which would otherwise result in too many elementselements Subdivision will stop once num

32、ber of elements along curve is reachedRefinement=12is reachedWont exceed global minimum set by natural size valueExampleExampleSpecified refinement achieved with larger elementsGlobal minimum(Size)not4-14ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663Global minimum

33、(Size)not realized,not necessary to capture curvatureVolume MeshingTraining ManualProximity Refinement,Elements in GapElements in GapNumber of cells desired in narrow gapsTo avoid subdivisionPrescribed sizeMin size limitTo avoid subdivision always to global minimum which would otherwise result in to

34、o many elementselements Subdivision will stop once number of cells in gap is reachedCells in Gap=5Will not override global minimum(Min size limit)ExampleOnly one element in gapPrescribed sizeMin size limit(1/5thsmaller)Only one element in gapCant go smaller than Min size limitHave to set smaller Min

35、 4-15ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663size limitCells in Gap=5Volume MeshingTraining ManualMesh Methods Tetra/Mixed Quick(Delauney)If already have Setup Options:Memory scaling factor To allocate more memory If already have good quality surface mesh Fr

36、om Shell Mh Usually does so automatically Expansion factor Growth ratio from surface Fill holes in volume meshMesh From Octree From imported surface mesh Use to fills holes/voids in existing volume mesh e.g.if bad quality region is deletedMesh all domains Uses initial point cloud;distributed so that

37、 the centroid of any Mesh all domains For multiple sets of closed volumes in one model Usually Flood fill after completecentroid of any tetra is outside circumsphere of any neighboring tetrap For multiple volumes Will assign tetras within closed volume to Part designated by Body or Material Point4-1

38、6ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663tetray Verbose output For troubleshootingVolume MeshingTraining ManualMesh Methods Tetra/Mixed Smooth(Advancing Front)Same as Quick(Delauney)butSame as Quick(Delauney)but Uses advancing front method that marches tetra

39、s from surface into interior Algorithm from GE/CFX Results in more gradual change in element size Results in more gradual change in element size“Better”but finer mesh Inut surface mesh has to be of fairly high quality Setup Options:Do Proximity CheckingCheck to properly fill small gaps Check to prop

40、erly fill small gaps Longer run time Tgrid Volume grid generation algorithm from Fluent Uses somewhat different delauney approach Gradual transition near surface Faster transition toward interior Setup Options:Use Background Mesh4-17ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009I

41、nventory#002663ppgVolume MeshingTraining ManualMesh Methods Run Options:Same for Delauney,Advancing Front,TGridCreate Prism Layers/Hexa-Core Create Prism Layers/Hexa-Core Same as for Octree Hexa-Core not available for Advancing Front,TGrid Input All Geometry Will run shell mesh first with no user in

42、put/editing Using parameters from Shell/Part/Surface/Curve Mesh Setup Review Shell Meshing chapter If doubtful as to shell mesh quality,run Shell Meshfirst,then use Existing Mesh Existing Mesh Part by Part/From File Same as for Octree Volume Part Name For newly created tetras4-18ANSYS,Inc.Proprietar

43、y 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663yVolume MeshingTraining ManualComparisonOctreeDelauneyAdv.front4-19ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663Volume MeshingTraining ManualSet Mesh SizesCtMh Dit Create Mesh DensityDefine volumetric

44、region with certain mesh size where no geometry exists,e.g.wake region behind a wingNot actual geometry!Mesh nodes not constrained to density object Can intersect geometryCan create densities within densitiesCan create densities within densities Always subdivides to smallest set sizeSet Size As for

45、surface/curve multiplied by global Scale FtFactor Ratio expansion ratio away from density object Width Number of layers from objectTypeType Points Select any number of points Size and Width(number of layers)will detemine“thickness”of volume if number of points selected is 1-3 4-8 creates polyhedral

46、volume4-20ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663 Entity bounds define region by bounding box of selected entitiesVolume MeshingTraining ManualPeriodicityDefine PeriodicityForces mesh alignment across periodic sidesFor meshing and solving only one section o

47、f ggysymmetrically repeatable geometryRotational PeriodicEnter Base,Axis,and AngleTranslational PeriodicTranslational PeriodicEnter dX,dY,dZ offsetTip:Place material point close to mid-plane4-21ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663Volume MeshingTraining M

48、anualWorkshops Workshop 1 Engine Block Model Build diagnostic topology Octree mesh Smooth mesh Curvature/proximity refinement Delaunay mesh Workshop 2 Valve Model Build diagnostic topology Create parts,Create body Set sizes Global,Surface,Curves,density Octree mesh4-22ANSYS,Inc.Proprietary 2009 ANSY

49、S,Inc.All rights reserved.July 2009Inventory#002663Volume MeshingTraining ManualWorkshops Workshop 3 Import Design Modeler file into ICEM Create Parts from Subsets Global,Part mesh set up Using ANSYS ICEM CFD Hexa to create a Cartesian initial grid with biasing Computing the mesh Viewing cut-planesgp4-23ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.July 2009Inventory#002663