1、Chapter 2Introduction to theANSYS Meshing ApplicationANSYS MeshingApplication IntroductionOverviewIntroduction to the ANSYS Meshing ApplicationMeshing Requirements for Different PhysicsANSYS Meshing WorkflowMeshing Methods for 3D and 2D geometriesWorkshop 2.1Automatic Meshing for a Multibody PartPro

2、gram Controlled InflationTransferring Mesh to CFX or FLUENTWorkbench Guiding PrinciplesParametric: Parameters drive systemPersistent: Model updates passed through systemHighly-automated: Baseline simulation w/limited inputFlexible: Able to add controls to influence resulting mesh (complete control o

3、ver model/simulation)Physics aware: Key off physics to automate modeling and simulation throughout systemAdaptive architecture: Open system that can be adapted to a customers processCAD neutral, meshing neutral, solver neutral, etc.What is the “ANSYS Meshing Application”?ANSYS has been working to in

4、tegrate “best in class” technologies from several sources:ICEM CFD TGridGAMBITCFXANSYS Prep/PostEtc.ANSYS Meshing Application OverviewThe objective of the ANSYS Meshing Application in Workbench is to provide access to common ANSYS Inc. meshing tools in a single location, for use by any analysis type

5、:FEA SimulationsMechanical Dynamics SimulationExplicit Dynamics SimulationAUTODYNANSYS LS DYNAElectromagnetic SimulationCFD SimulationANSYS CFXANSYS FLUENTMesh SpecificationPurposeFor both CFD (fluid) and FEA (solid) modelling, the software performs the computations at a range of discrete locations

6、within the domain. The purpose of meshing is to pose the solution domain into an appropriate number of locations for an accurate result.The basic building-blocks for a 3D mesh are:Manifold Example: Outer casting and internal flow region are meshed for coupled thermal/stress gas flow simulationTetrah

7、edrons(unstructured)Hexahedrons(usually structured)Prisms (formed when a tet mesh is extruded)Pyramids (where tet. and hex. cells meet)Mesh SpecificationConsiderationsDetail: How much geometric detail is relevant to the simulation physics.Including unnecessary detail can greatly increase the effort

8、required for the simulation.RefinementWhere in the domain are the most complex stress/flow gradients? These areas will require higher densities of mesh elements.Is it necessary to resolve this recess?Extra mesh applied across fluid boundary layerRefined mesh around bolt-holeMesh SpecificationEfficie

9、ncyGreater numbers of elements require more compute resource (memory / processing time). Balance the fidelity of the simulation with available resources.Mesh SpecificationQualityIn areas of high geometric complexity mesh elements can e distorted. Poor quality elements can lead to poor quality result

10、s or, in some cases, no results at all!There are a number of methods for measuring mesh element quality (mesh metrics*). For example, one important metric is the element Skewness. Skewness is a measure of the relative distortion of an element compared to its ideal shape and is scaled from 0 (Excelle

11、nt) to 1 (Unacceptable).*Further information on mesh metrics is available in the documentation and training lecture appendices Mesh SpecificationThis example illustrates an unconverged thermal field in a manifold solid casting. On closer inspection it is clear that the simulation is unable to resolv

12、e a sensible data field in the region of poor quality elements.The example with good quality elements demonstrates no problems in the solution field. The ANSYS Meshing Application provides many tools to help maximise mesh quality Example showing difference between good and poor meshes:FEA Meshing Is

13、suesStructural FEARefine mesh to capture gradients of concernE.g. temperature, strain energy, stress energy, displacement, etc.tet mesh dominated, but hex elements still preferredsome explicit FEA solvers require a hex mesh tet meshes for FEA are usually second order (include mid-side nodes on eleme

14、nt edges)CFD Meshing IssuesCFDRefine mesh to capture gradients of concernE.g. Velocity, pressure, temperature, etc.Mesh quality and smoothness critical for accurate results This leads to larger mesh sizes, often millions of elementstet mesh dominated, but hex elements still preferredtet meshes for C

15、FD are usually first order (no mid-side nodes on element edges)Mesh TypesTet Mesh and Tet/Prism hybridMesh TypesHex MeshMesh TypesTet Mesh1) Can be generated quickly, automatically, and for complicated geometryMesh can be generated in 2 steps:Step 1: Define element sizingStep 2: Generate MeshMesh Ty

16、pesTet Mesh2) Isotropic refinement in order to capture gradients in one direction, mesh is refined in all three directions cell counts rise rapidlyPerforated plate resulting in pressure drop in x directionxMesh TypesTet Mesh3) Inflation layer helps with refinement normal to the wall, but still isotr

17、opic in 2-D (surface mesh)Mesh TypesHex MeshFewer elements required to resolve physics for most CFD applications This hexahedral mesh, which provides the same resolution of flow physics, has LESS than half the amount of nodes as the tet-mesh)TETHEXMesh TypesHex MeshFewer elements required to resolve

18、 physics for most CFD applications. Anisotropic elements can be aligned with anisotropic physics (boundary layers, areas of tight curvature like wing leading and trailing edges) Mesh TypesHex MeshFor arbitrary geometries, hex meshing may require a multi-step process which can yield a high quality/hi

19、gh efficiency meshFor many simpler geometries, sweep techniques can be a simplerway to generate hex meshesSweepMultiZoneANSYS Meshing Application WorkflowThe ANSYS Meshing Application uses a divide & conquer approachA different Meshing Method can be applied to each part in the geometryMeshes between

20、 bodies in different parts will be non-matching or non-conformalMatched or conformal meshes will be generated for bodies in a single partAll meshes are written back to a common central databaseA number of different methods are available for 3D and2D geometryMeshing Methods for 3D GeometryThere are s

21、ix different meshing methods in the ANSYS Meshing Application for 3D Geometry:Automatic Tetrahedrons Patch ConformingPatch Independent(ICEM CFD Tetra algorithm) Swept Meshing MultiZone Hex Dominant CFX-MeshMeshing Methods for 2D GeometryThere are four different meshing methods in the ANSYS Meshing P

22、latform for 2D Geometry which can be applied to Surface Bodies or Shells: Automatic Method (Quadrilateral Dominant) All Triangles Uniform Quad/Tri Uniform QuadPatch Conforming TetrahedronsTetrahedrons Method with Patch Conforming AlgorithmFaces and their boundaries (edges and vertices) are respected

23、 Includes the Expansion Factor setting, which controls the internal growth rate of tetrahedrons with respect to boundary sizeIncludes inflation or boundary layer resolution for CFDCan be mixed with Sweep methods for bodies in a single part conformal meshes will be generatedTetrahedral MeshSwept Mesh

24、PrismTetPyramidElement ShapesPatch Independent TetrahedronsTetrahedrons Method with Patch Independent (ICEM CFD Tetra) AlgorithmFaces and their boundaries (edges and vertices) are not necessarily respected unless there is a load, boundary condition, or other object scoped to themUseful for gross def

25、eaturing or to produce a more uniformly sized mesh Simplified version of Tetra tightly integrated into the ANSYS Meshing ApplicationHonors standard ANSYS Meshing Application mesh sizing controlsTetra parts can also have inflation appliedCoarse mesh walks over detail in surface modelInflation layer a

26、pplied for CFDPrismTetPyramidElement ShapesSweep MethodProduces Hexes and/or PrismsBody must be SweepableSingle Source, Single TargetInflation can yield pure hex or prisms Extrusion removed to allow for swept meshingBody split into 2 parts to allow for swept meshingAllows for inflation layer (bounda

27、ry layer resolution) for CFDPrismHexElement ShapesThin Solid Sweep MeshingMultiple source/target faces Works at body level with other methodsMultiple elements through thickness possible for single body partsAutomatic MethodThe Automatic setting toggles between Tetrahedral (Patch Conforming) and Swep

28、t Meshing, depending upon whether the body is sweepable. Bodies in the same part will have a conformal mesh.No inflationProgrammed Controlled InflationTetrahedron (Patch Conforming)SweptTetrahedron (Patch Conforming)InflationInflation is plished by extruding faces normal to a boundary to increase th

29、e boundary mesh resolution, typically for CFDSmooth Transition from inflated layer to interior meshCollision avoidance: Stair-stepping Layer compressionPreview InflationPre vs. Post inflationAll methods can be inflated exceptfor Hex-Dominant and Thin SweepSweeping: Pure hex or wedgeMultiZone Sweep M

30、eshingNew feature for 12.0Automatic geometry positionWith the swept method, this part would have to be sliced into 3 bodies to get a pure hex meshWith MultiZone, it can be meshed directly!The hex-dominant meshing algorithm creates a quad-dominant surface mesh first, then hexahedral, pyramid and tetr

31、ahedral elements are filled in as needed. mended when a hex mesh is desired for a body that cannot be sweptUseful for bodies with large amounts of interior volumeNot useful for thin complicated bodies where the ratio of volume to surface area is lowNo boundary layer resolution for CFDMainly used for

32、 FEA analysisPrismHexTetPyramidElement ShapesHex-dominant mesh shown above:19,615 Hex (60%)5,108 Tet (16%)211 Prisms (1%)7,671 pyramids (24%)Hex-Dominant MethodCFX-Mesh MethodCFX-Mesh uses a loose integration.No Meshing Application sizings are respected or transferred to CFX-MeshSelecting Right Mous

33、e Edit on the Method launches the CFX-Mesh GUI.Define mesh settings/controls/inflationPreview & generate volume meshCommit the current mesh modelReturn to ANSYS Meshing Possible to Generate Mesh on a CFX-Mesh method without opening the applicationUses current or default settings Generate Volume Mesh

34、Inflation layer Pipe Tee MeshWorkshop 2.1GoalsThis workshop will illustrate the use of the Automatic Meshing Method for a single body part The transfer of the mesh toFLUENT and CFX is also demonstratedSpecifying GeometryCopy the pt.agdb file from the tutorial files folder to your working directorySt

35、art Workbench and double-click the Mesh entry in the Component Systems panel in the ToolboxRight-click on Geometry in the Mesh entry in the Project Schematic and select Import Geometry/BrowseBrowse to the pt.agdb file you copied and click OpenNote that the Geometry entry in the Project Schematic now

36、 has a green check mark indicating that geometry has been specifiedInitial MeshDouble-click the Mesh entry in theschematic or right-click and select Edit. This will open the Meshing ApplicationIn the Meshing Options panel set the Physics Preference to CFD, the Mesh Method to Automatic and press OKRi

37、ght click on Mesh and select Generate MeshUse the view manipulation tools and the axis triad to inspect the meshBased upon choice of physics (CFD), the Meshing Application has produced a mesh modating curvature, a reasonable sizing strategy and automatic selection of optimal mesh methods with minima

38、l user input. There are many ways in which the Meshing Application can control and improve the mesh. Some further mesh controls will now be demonstrated.Named SelectionsSet the Selection Filter to Faces and select one of the pipe end faces as shown. Right-click in the Model View and choose Create Na

39、med Selection. Enter velocity-inlet-1 for the Selection NameRepeat for the other two pipe end faces using the naming as shownThe Named Selections just created are listed in the Outline by expanding Named Selections. The names assigned here will be transferred to the CFD solver so the appropriate flo

40、w conditions can be applied on these surfaces. pressure-outletvelocity-inlet-1velocity-inlet-2InflationSelect Mesh in the Outline and expand Inflation in DetailsSet Use Automatic Tet Inflation to Program Controlled, leave other settingsRight click on Mesh and select Generate Mesh. Note the inflation

41、 layers are grown from all boundaries not assigned a Named Selection. The thickness of the inflation layers is calculated as a function of the surface mesh and applied fully automatically.Section PlanesOrient the model by clicking on the axis triad (+X Direction)Click on the New Section Plane icon i

42、n the menu bar. Left click, hold and drag the cursor in the direction of the arrow as illustrated to create the Section PlaneCreated Section Planes are listed (bottom left). Planes can be individually activated using the checkbox, deleted and toggled between 3D element view and 2D slice view. Try this now (you will need to rotate the model to see the cross-section)After the Section Plane has been created the Sectio