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IntroductiontoANSYSMeshing

Lecture7MeshQuality

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Whatyouwilllearnfromthispresentation

ImpactoftheMeshQualityontheSolution Qualitycriteria Variousmethodsforcheckingthemeshquality ToolstoimprovequalityinMeshing Pinch Virtualtopology

MeshQuality

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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

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MeshingProcessinANSYSMeshing

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ImpactoftheMeshQualityGoodqualitymeshmeansthat Meshqualitycriteriaarewithincorrectrange Orthogonalquality

Meshisvalidforstudiedphysic Boundarylayer

Solutionisgridindependent Importantgeometrydetailsarewellcaptured

Badqualitymeshcaninduce Convergencedifficulties Badphysicdescription DiffusesolutionUsermust Checkqualitycriteriaandimprovegridifneeded Thinkaboutmodelandsolversettingsbeforegeneratingthegrid Performmeshparametricstudy,meshadaption

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Exampleshowingdifferencebetweenameshwithcellsfailingthequalitycriteriaandagoodmesh

HotSpotsduetodeterioratedcells

ImpactoftheMeshQualityontheSolution

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(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

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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

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GridDependency Hexa cellscan bestretchedinstreamdirectiontoreducenumberofcells

Biasdefined oninletandoutletwalls Biasdefined oninletedges

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

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Hexa:Concentrationinonedirection Anglesunchanged

Tetra:Concentrationinonedirection Anglesdeteriorate

Prism:Concentrationinonedirection Anglesunchanged

Solutionforboundarylayerresolution:Hybridprism/tetrameshes Prisminnearwallregion,tetrainvolume Automated ReducedCPUtimeforgoodboundarylayerresolution

Hexa vs.Tetra

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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

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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

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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

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MeshqualityMeshqualityrecommendations

LowOrthogonalQualityorhighskewness valuesarenotrecommended

Generallytrytokeepminimumorthogonalquality>0.1,ormaximumskewness

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AspectRatio2D: Length/heightratio:x/y

3D Arearatio Radiusratioofcircumscribed/inscribedcircle

Limitationforsomeiterativesolvers A

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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

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MeshMetricGraphDisplaysMeshMetricsgraphfortheelementqualitydistribution

Differentelementtypesareplottedwithdifferentcolorbars

Canbeaccessedthroughmenubarusingicon

Clickonrequiredbartoseecorrespondingelementsinthegraphicsview

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MeshMetricsControlsThehistogramdistributioncanbecontrolledusingbuttoninMeshMetrics

ElementsonYAxiscanbeplottedwithtwomethods NumberofElements PercentofVolume/Area

Optionstochangetherangeoneitheraxisaswellselectionforrequiredtypeofelementsformetricsdisplay

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MeshMetricChartexample Interactivewaytoviewthecellsofdesiredqualityonly

ClickonthehistogrambartodisplaycellsofthatqualityrangeintheGraphicsDisplay

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Controlbuttonoptions VariousoptionstoexploreundertheControls

MeshMetricChartexample

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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

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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(!)

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MeshQualityCheckforFLUENTGridchecktoolsavailable Check :Performvariousmeshconsistencychecks

ReportQuality:listsworsevaluesoforthogonalqualityandaspectratio

TUIcommandmesh/checkverbositysetsthelevelofdetailsinthereport

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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

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VirtualTopology(VT) Whentouse?