Building a Model in Ansys.docx
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Building a Model in Ansys.docx
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BuildingaModelinAnsys
BuildingaModel
Buildingafiniteelementmodelrequiresmoreofyourtimethananyotherpartoftheanalysis.First,youspecifyajobnameandanalysistitle.Then,youusethePREP7preprocessortodefinetheelementtypes,elementrealconstants,materialproperties,andthemodelgeometry.
SpecifyingaJobnameandAnalysisTitle
Thistaskisnotrequiredforananalysis,butisrecommended.
DefiningtheJobname
ThejobnameisanamethatidentifiestheANSYSjob.Whenyoudefineajobnameforananalysis,thejobnamebecomesthefirstpartofthenameofallfilestheanalysiscreates.(Theextensionorsuffixforthesefiles'namesisafileidentifiersuchas.DB.)Byusingajobnameforeachanalysis,youinsurethatnofilesareoverwritten.
Ifyoudonotspecifyajobname,allfilesreceivethenameFILEorfile,dependingontheoperatingsystem.Youcanchangethedefaultjobnameasfollows:
∙ByusingtheinitialjobnameentryoptionwhenyouentertheANSYSprogram,eitherviathelauncherorontheANSYSexecutioncommand.Fordetails,seetheANSYSOperationsGuide.
∙FromwithintheANSYSprogram,youcanuseeitherofthefollowing:
Command(s):
/FILNAME
GUI:
UtilityMenu>File>ChangeJobname
The/FILNAMEcommandisvalidonlyattheBeginlevel.ItletsyouchangethejobnameevenifyouspecifiedaninitialjobnameatANSYSentry.Thejobnameappliesonlytofilesyouopenafterusing/FILNAMEandnottofilesthatwerealreadyopen.Ifyouwanttostartnewfiles(suchasthelogfile,Jobname.LOG,anderrorfileJobname.ERR)whenyouissue/FILNAME,settheKeyargumenton/FILNAMEto1.Otherwise,thosefilesthatwerealreadyopenwillstillhavetheinitialjobname.
DefininganAnalysisTitle
The/TITLEcommand(UtilityMenu>File>ChangeTitle),definesatitlefortheanalysis.ANSYSincludesthetitleonallgraphicsdisplaysandonthesolutionoutput.Youcanissuethe/STITLEcommandtoaddsubtitles;thesewillappearintheoutput,butnotingraphicsdisplays.
DefiningUnits
TheANSYSprogramdoesnotassumeasystemofunitsforyouranalysis.Exceptinmagneticfieldanalyses,youcanuseanysystemofunitssolongasyoumakesurethatyouusethatsystemforallthedatayouenter.(Unitsmustbeconsistentforallinputdata.)
Formicro-electromechanicalsystems(MEMS),wheredimensionsareontheorderofmicrons,seetheconversionfactorsinSystemofUnitsintheANSYSCoupled-FieldAnalysisGuide.
Usingthe/UNITScommand,youcansetamarkerintheANSYSdatabaseindicatingthesystemofunitsthatyouareusing.Thiscommanddoesnotconvertdatafromonesystemofunitstoanother;itsimplyservesasarecordforsubsequentreviewsoftheanalysis.
DefiningElementTypes
TheANSYSelementlibrarycontainsmorethan150differentelementtypes.Eachelementtypehasauniquenumberandaprefixthatidentifiestheelementcategory:
BEAM4,PLANE77,SOLID96,etc.Thefollowingelementcategoriesareavailable:
BEAM
CIRCUit
COMBINation
CONTACt
FLUID
HF(HighFrequency)
HYPERelastic
INFINite
INTERface
LINK
MASS
MATRIX
MESH
PIPE
PLANE
PRETS(Pretension)
SHELL
SOLID
SOURCe
SURFace
TARGEt
TRANSducer
USER
VISCOelastic(orviscoplastic)
Theelementtypedetermines,amongotherthings:
∙Thedegree-of-freedomset(whichinturnimpliesthediscipline--structural,thermal,magnetic,electric,quadrilateral,brick,etc.)
∙Whethertheelementliesintwo-dimensionalorthree-dimensionalspace.
BEAM4,forexample,hassixstructuraldegreesoffreedom(UX,UY,UZ,ROTX,ROTY,ROTZ),isalineelement,andcanbemodeledin3-Dspace.PLANE77hasathermaldegreeoffreedom(TEMP),isaneight-nodequadrilateralelement,andcanbemodeledonlyin2-Dspace.
YoumustbeinPREP7,thegeneralpreprocessor,todefineelementtypes.Todoso,youusetheETfamilyofcommands(ET,ETCHG,etc.)ortheirGUIpathequivalents;seetheANSYSCommandsReferencefordetails.Youdefinetheelementtypebynameandgivetheelementatypereferencenumber.Forexample,thecommandsshownbelowdefinetwoelementtypes,BEAM4andSHELL63,andassignthemtypereferencenumbers1and2respectively.
ET,1,BEAM4
ET,2,SHELL63
Thistableoftypereferencenumberversuselementnameiscalledtheelementtypetable.Whiledefiningtheactualelements,youpointtotheappropriatetypereferencenumberusingtheTYPEcommand(MainMenu>Preprocessor>Create>Elements>ElemAttributes).
Manyelementtypeshaveadditionaloptions,knownasKEYOPTs,andarereferredtoasKEYOPT
(1),KEYOPT
(2),etc.Forexample,KEYOPT(9)forBEAM4allowsyoutochooseresultstobecalculatedatintermediatelocationsoneachelement,andKEYOPT(3)forSHELL63allowsyoutosuppressextradisplacementshapes.YoucanspecifyKEYOPTsusingtheETcommandortheKEYOPTcommand(MainMenu>Preprocessor>ElementType>Add/Edit/Delete).
DefiningElementRealConstants
Elementrealconstantsarepropertiesthatdependontheelementtype,suchascross-sectionalpropertiesofabeamelement.Forexample,realconstantsforBEAM3,the2-Dbeamelement,arearea(AREA),momentofinertia(IZZ),height(HEIGHT),sheardeflectionconstant(SHEARZ),initialstrain(ISTRN),andaddedmassperunitlength(ADDMAS).Notallelementtypesrequirerealconstants,anddifferentelementsofthesametypemayhavedifferentrealconstantvalues.
YoucanspecifyrealconstantsusingtheRfamilyofcommands(R,RMODIF,etc.)ortheirequivalentmenupaths;seetheANSYSCommandsReferenceforfurtherinformation.Aswithelementtypes,eachsetofrealconstantshasareferencenumber,andthetableofreferencenumberversusrealconstantsetiscalledtherealconstanttable.Whiledefiningtheelements,youpointtotheappropriaterealconstantreferencenumberusingtheREALcommand(MainMenu>Preprocessor>Create>Elements>ElemAttributes).
Whiledefiningrealconstants,keeptheserulesandguidelinesinmind:
∙WhenusingoneoftheRcommands,youmustenterrealconstantsintheordershowninTable4.n.1foreachelementtypeintheANSYSElementsReference.
∙Formodelsusingmultipleelementtypes,useaseparaterealconstantset(thatis,adifferentREALreferencenumber)foreachelementtype.TheANSYSprogramissuesawarningmessageifmultipleelementtypesreferencethesamerealconstantset.However,asingleelementtypemayreferenceseveralrealconstantsets.
∙Toverifyyourrealconstantinput,usetheRLISTandELISTcommands,withRKEY=1(shownbelow).RLISTlistsrealconstantvaluesforallsets.ThecommandELIST,,,,,1producesaneasier-to-readlistthatshows,foreachelement,therealconstantlabelsandtheirvalues.
Command(s):
ELIST
GUI:
UtilityMenu>List>Elements>Attributes+RealConst
UtilityMenu>List>Elements>AttributesOnly
UtilityMenu>List>Elements>Nodes+Attributes
UtilityMenu>List>Elements>Nodes+Attributes+RealConst
Command(s):
RLIST
GUI:
UtilityMenu>List>Properties>AllRealConstants
UtilityMenu>List>Properties>SpecifiedRealConst
∙Forlineandareaelementsthatrequiregeometrydata(cross-sectionalarea,thickness,diameter,etc.)tobespecifiedasrealconstants,youcanverifytheinputgraphicallybyusingthefollowingcommandsintheordershown:
Command(s):
/ESHAPEandEPLOT
GUI:
UtilityMenu>PlotCtrls>Style>SizeandShape
UtilityMenu>Plot>Elements
ANSYSdisplaystheelementsassolidelements,usingarectangularcross-sectionforlinkandshellelementsandacircularcross-sectionforpipeelements.Thecross-sectionproportionsaredeterminedfromtherealconstantvalues.
CreatingCrossSections
IfyouarebuildingamodelusingBEAM44,BEAM188,orBEAM189,youcanusethesectioncommands(SECTYPE,SECDATA,etc.)ortheirGUIpathequivalentstodefineandusecrosssectionsinyourmodels.SeeBeamAnalysisandCrossSectionsintheANSYSStructuralAnalysisGuideforinformationonhowtousetheBeamTooltocreatecrosssections.
DefiningMaterialProperties
Mostelementtypesrequirematerialproperties.Dependingontheapplication,materialpropertiescanbelinear(seeLinearMaterialProperties)ornonlinear(seeNonlinearMaterialProperties).
Aswithelementtypesandrealconstants,eachsetofmaterialpropertieshasamaterialreferencenumber.Thetableofmaterialreferencenumbersversusmaterialpropertysetsiscalledthematerialtable.Withinoneanalysis,youmayhavemultiplematerialpropertysets(tocorrespondwithmultiplematerialsusedinthemodel).ANSYSidentifieseachsetwithauniquereferencenumber.
Whiledefiningtheelements,youpointtotheappropriatematerialreferencenumberusingtheMATcommand.
LinearMaterialProperties
Linearmaterialpropertiescanbeconstantortemperature-dependent,andisotropicororthotropic.Todefineconstantmaterialproperties(eitherisotropicororthotropic),useoneofthefollowing:
Command(s):
MP
GUI:
MainMenu>Preprocessor>MaterialProps>MaterialModels
(SeeMaterialModelInterfacefordetailsontheGUI.)
Youalsomustspecifytheappropriatepropertylabel;forexampleEX,EY,EZforYoung'smodulus,KXX,KYY,KZZforthermalconductivity,andsoforth.ForisotropicmaterialyouneedtodefineonlytheX-directionproperty;theotherdirectionsdefaulttotheX-directionvalue.Forexample:
MP,EX,1,2E11!
Young'smodulusformaterialref.no.1is2E11
MP,DENS,1,7800!
Densityformaterialref.no.1is7800
MP,KXX,3,43!
Thermalconductivityformaterialref.no1is43
BesidesthedefaultsforY-andZ-directionproperties(whichdefaulttotheX-directionproperties),othermaterialpropertydefaultsarebuiltintoreducetheamountofinput.Forexample,Poisson'sratio(NUXY)defaultsto0.3,
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