Mesh-Intro 14.0 L-07 Mesh Quality

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  • 2011ANSYS,Inc. December27,20111 Release14.0

    14.0Release

    IntroductiontoANSYSMeshing

    Lecture7MeshQuality

  • 2011ANSYS,Inc. December27,20112 Release14.0

    Whatyouwilllearnfromthispresentation

    ImpactoftheMeshQualityontheSolution Qualitycriteria Variousmethodsforcheckingthemeshquality ToolstoimprovequalityinMeshing Pinch Virtualtopology

    MeshQuality

  • 2011ANSYS,Inc. December27,20113 Release14.0

    CheckMeshQuality

    PreprocessingWorkflow

    Sketches and Planes

    Geometry Import Options

    3D Operations

    Direct CAD/Bi-Directional CAD

    Geometry Cleanup and

    Repair

    Automatic Cleanup

    Merge, Connect, Projection, Flow

    Volume Extraction, etc

    Extrude, Revolve, Sweep, etc

    3D Operations

    Boolean, Body Operations, Split,

    etc

    Meshing Methods

    Hybrid Mesh: Tet, Prisms, Pyramids

    Hexa Dominant, Sweep meshing

    Global Mesh Settings

    Local Mesh Settings

    Sizing, Body/Sphere of Influence, Match

    Control, etc

    GeometryCreationOR

    GeometryImport

    GeometryOperations Meshing Solver

    Assembly Meshing

  • 2011ANSYS,Inc. December27,20114 Release14.0

    MeshingProcessinANSYSMeshing

  • 2011ANSYS,Inc. December27,20115 Release14.0

    ImpactoftheMeshQualityGoodqualitymeshmeansthat Meshqualitycriteriaarewithincorrectrange Orthogonalquality

    Meshisvalidforstudiedphysic Boundarylayer

    Solutionisgridindependent Importantgeometrydetailsarewellcaptured

    Badqualitymeshcaninduce Convergencedifficulties Badphysicdescription DiffusesolutionUsermust Checkqualitycriteriaandimprovegridifneeded Thinkaboutmodelandsolversettingsbeforegeneratingthegrid Performmeshparametricstudy,meshadaption

  • 2011ANSYS,Inc. December27,20116 Release14.0

    Exampleshowingdifferencebetweenameshwithcellsfailingthequalitycriteriaandagoodmesh

    HotSpotsduetodeterioratedcells

    ImpactoftheMeshQualityontheSolution

  • 2011ANSYS,Inc. December27,20117 Release14.0

    (max,avg)CSKEW=(0.912,0.291) (max,avg)CAR=(62.731,7.402)

    (max,avg)CSKEW=(0.801,0.287) (max,avg)CAR=(8.153,1.298)

    VzMIN-100ft/min VzMAX400ft/min

    VzMIN-90ft/min VzMAX600ft/min

    ImpactoftheMeshQualityontheSolution

    Large cell size change

    M

    e

    s

    h

    2

    M

    e

    s

    h

    1

    Diffusionexample

  • 2011ANSYS,Inc. December27,20118 Release14.0

    Solutionrun with multiplemeshesNote:Forallruns thecomputed Y+is valid forwall function (firstcell notinlaminar zone)

    GridDependency

    DP0 DP1 DP2 DP3 DP4

    NbCells 500 3000 24000 190000 1.5M

    DP 0 DP 3

    2%

    x8

  • 2011ANSYS,Inc. December27,20119 Release14.0

    GridDependency Hexa cellscan bestretchedinstreamdirectiontoreducenumberofcells

    Biasdefined oninletandoutletwalls Biasdefined oninletedges

    16 000 cells (~DP2)Delta P = 310 Pa (~DP3)

  • 2011ANSYS,Inc. December27,201110 Release14.0

    Hexa:Concentrationinonedirection Anglesunchanged

    Tetra:Concentrationinonedirection Anglesdeteriorate

    Prism:Concentrationinonedirection Anglesunchanged

    Solutionforboundarylayerresolution:Hybridprism/tetrameshes Prisminnearwallregion,tetrainvolume Automated ReducedCPUtimeforgoodboundarylayerresolution

    Hexa vs.Tetra

  • 2011ANSYS,Inc. December27,201111 Release14.0

    DisplaysmeshinformationforNodesandElements

    ListofqualitycriteriafortheMeshMetric Selecttherequiredcriteriatogetdetailsforquality Itshowsminimum,maximum,averageandstandarddeviation

    Differentphysicsanddifferentsolvershavedifferentrequirementsformeshquality

    MeshmetricsavailableinANSYSMeshinginclude: ElementQuality AspectRatio JacobeanRation WarpingFactor ParallelDeviation MaximumCornerAngle Skewness OrthogonalQuality

    MeshStatisticsandMeshMetrics

    For Multi-Body Parts, go to corresponding body in Tree Outline to get its separate mesh statistics per part/body

  • 2011ANSYS,Inc. December27,201112 Release14.0

    OrthogonalQuality(OQ)

    Deriveddirectlyfrom

    Fluentsolverdiscretization

    Foracellitistheminimumof:

    computedforeachfacei

    Fortheface itiscomputedastheminimumofcomputedforeachedgeI

    WhereAi isthefacenormalvectorandfi isavectorfromthecentroid ofthecelltothecentroidofthatface,andci isavectorfromthecentroid ofthecelltothecentroid oftheadjacentcell,whereei isthevectorfromthecentroid ofthefacetothecentroid oftheedge

    Atboundariesandinternalwalls

    ci isignoredinthecomputationsofOQ

    MeshQualityMetrics

    A1

    A2

    A3

    f1f2f3

    c2c1

    c3

    A1

    A2

    A3

    e1e2e3

    Oncell

    |||| iiii

    fAfA

    |||| iiii

    cAcA

    |||| iiii

    eAeA

    Onface

    0 1Perfect Worst

  • 2011ANSYS,Inc. December27,201113 Release14.0

    Skewness

    Twomethodsfordeterminingskewness:1. EquilateralVolumedeviation:

    Skewness =

    Appliesonlyfortrianglesandtetrahedrons

    2. NormalizedAngledeviation:

    Skewness =

    Whereistheequiangularface/cell(60fortets andtris,and90forquadsandhexas) Appliestoallcellandfaceshapes Usedforhexa,prismsandpyramids

    e

    mine

    e

    emax ,180

    max

    minmax

    optimal cell size cell sizeoptimal cell size

    Optimal (equilateral) cell

    Actual cell

    Circumsphere

    MeshQualityMetrics

    e

    0 1Perfect Worst

  • 2011ANSYS,Inc. December27,201114 Release14.0

    MeshqualityMeshqualityrecommendations

    LowOrthogonalQualityorhighskewness valuesarenotrecommended

    Generallytrytokeepminimumorthogonalquality>0.1,ormaximumskewness

  • 2011ANSYS,Inc. December27,201115 Release14.0

    AspectRatio2D: Length/heightratio:x/y

    3D Arearatio Radiusratioofcircumscribed/inscribedcircle

    Limitationforsomeiterativesolvers A

  • 2011ANSYS,Inc. December27,201116 Release14.0

    SmoothnessChecked insolver VolumeChangeinFluent

    Available inAdapt/Volume 3D:i =Vi/Vnb

    ExpansionFactorinCFX Checkedduringmeshimport Ratiooflargesttosmallestelementvolumes

    surroundinganode

    Recommendation:Good: 1.0 < < 1.5Fair: 1.5 < < 2.5Poor: > 5 20

  • 2011ANSYS,Inc. December27,201117 Release14.0

    MeshMetricGraphDisplaysMeshMetricsgraphfortheelementqualitydistribution

    Differentelementtypesareplottedwithdifferentcolorbars

    Canbeaccessedthroughmenubarusingicon

    Clickonrequiredbartoseecorrespondingelementsinthegraphicsview

  • 2011ANSYS,Inc. December27,201118 Release14.0

    MeshMetricsControlsThehistogramdistributioncanbecontrolledusingbuttoninMeshMetrics

    ElementsonYAxiscanbeplottedwithtwomethods NumberofElements PercentofVolume/Area

    Optionstochangetherangeoneitheraxisaswellselectionforrequiredtypeofelementsformetricsdisplay

  • 2011ANSYS,Inc. December27,201119 Release14.0

    MeshMetricChartexample Interactivewaytoviewthecellsofdesiredqualityonly

    ClickonthehistogrambartodisplaycellsofthatqualityrangeintheGraphicsDisplay

  • 2011ANSYS,Inc. December27,201120 Release14.0

    Controlbuttonoptions VariousoptionstoexploreundertheControls

    MeshMetricChartexample

  • 2011ANSYS,Inc. December27,201121 Release14.0

    SectionPlanesDisplaysinternalelementsofthemesh

    Elementsoneithersideofplanecanbedisplayed Togglebetweencutorwholeelementsdisplay Elementsontheplane

    Multiplesectionplanesareallowed

    For large meshes, it is advisable to switch to geometry mode (click on geometry in the Tree Outline), create the section plane and then go back to mesh model

  • 2011ANSYS,Inc. December27,201122 Release14.0

    MeshQualityCheckforCFXTheCFXsolvercalculates3importantmeasuresofmesh

    qualityatthestartofarunandupdatesthemeachtimethemeshisdeformed

    MeshOrthogonality AspectRatio ExpansionFactor

    +--------------------------------------------------------------------+| Mesh Statistics |+--------------------------------------------------------------------+Domain Name: Air Duct

    Minimum Orthogonality Angle [degrees] = 20.4 okMaximum Aspect Ratio = 13.5 OKMaximum Mesh Expansion Factor = 700.4 !

    Domain Name: Water PipeMinimum Orthogonality Angle [degrees] = 32.8 okMaximum Aspect Ratio = 6.4 OKMaximum Mesh Expansion Factor = 73.5 !

    Global Mesh Quality Statistics :Minimum Orthogonality Angle [degrees] = 20.4 okMaximum Aspect Ratio = 13.5 OKMaximum Mesh Expansion Factor = 700.4 !

    Good(OK)

    Acceptable (ok)

    Questionable(!)

  • 2011ANSYS,Inc. December27,201123 Release14.0

    MeshQualityCheckforFLUENTGridchecktoolsavailable Check :Performvariousmeshconsistencychecks

    ReportQuality:listsworsevaluesoforthogonalqualityandaspectratio

    TUIcommandmesh/checkverbositysetsthelevelofdetailsinthereport

  • 2011ANSYS,Inc. December27,201124 Release14.0

    FactorsAffectingQualityGeometryproblems Smalledge Gaps SharpangleMeshingparameters SizingFunctionOn/Off Minsizetoolarge Inflationparameters Totalheight Maximumangle

    HardsizingMeshingmethods Patchconformalorpatchindependenttetra SweeporMultizone Cutcell

    Geometry cleanup in Design Modeler

    or

    Virtual topology & pinch in Meshing

    Mesh setting change

    Mesh setting change

    Direct meshing can be used to minimize remeshing time

  • 2011ANSYS,Inc. December27,201125 Release14.0

    VirtualTopology(VT) Whentouse?