CEL教程.docx

CEL教程.docx

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CEL教程

Chapter 13:

 CFXExpressionLanguage（CEL）

CFXExpressionLanguage（CEL）isaninterpreted,declarativelanguagethathasbeendevelopedtoenableCFXuserstoenhancetheirsimulationswithoutrecoursetowritingandlinkingseparateexternalFortranroutines.

YoucanuseCELexpressionsanywhereavalueisrequiredforinputinANSYSCFX.

CELcanbeusedto:

∙Definematerialpropertiesthatdependonothervariables.

∙Specifycomplexboundaryconditions.

∙Addtermstothesolvedequations.

Youcanalsomonitorthevalueofanexpressionduringthesolutionusingmonitorpoints.

Important:

ThereissomeCELthatworkselsewhereinANSYSCFX,butnotinCFD-Post.AnyexpressioncreatedinCFX-PreandusedasaDesignExplorationoutputparametercouldpotentiallycausefatalerrorsduringtheDesignExplorationrun,soyoushouldcreateallexpressionsforDesignExplorationoutputparametersinCFD-Post.

Thischapterdescribes:

∙CELFundamentals

∙CELOperators,Constants,andExpressions

∙CELExamples

∙CELTechnicalDetails

Release13.0-©2010SASIP,Inc.Allrightsreserved.

13.1. CELFundamentals

Thefollowingtopicswillbediscussed:

∙ValuesandExpressions

∙CFXExpressionLanguageStatements

Release13.0-©2010SASIP,Inc.Allrightsreserved.

13.1.1. ValuesandExpressions

CELcanbeusedtogeneratebothvaluesandexpressions.Valuesaredimensional（thatis,withunits）ordimensionlessconstants.Thesimplesttypeofdefinitionisthedimensionlessvalue,forexample:

b=3.743

Youcanalsospecifyavaluewithunits,forexample:

g=9.81[ms^-2]

ThedimensionsofthequantitiesofinterestforCFDcalculationscanbewrittenintermsofmass,length,time,temperatureandangle.Theconceptofunitsisfundamentaltothebehaviorofvaluesandexpressions.

Valuescanbeuseddirectly,ortheycanbeusedaspartofanexpression.Forexample,youcanuseanexpressiontoaddtwovaluestogether:

 =  + 

Inthisexample,youmaywanttopredefineand,butthisisnotrequired.However,inordertoaddtwoquantitiestogether,theymusthavethesamedimension;thatis,itismeaningfultoaddaquantityininchestooneexpressedinmeters,butitisnotmeaningfultoaddoneexpressedinkilogramstooneinsquarefeet.

Expressionscanalsobefunctionsofother（predefined）expressions:

 =  + 

UnitsfollowtheconventionsintherestofCFX,inthatacalculationhasasetofsolutionunits（bydefault,SIunits）,andthatanyquantitycanbedefinedeitherintermsofthesolutionunits,oranyothersetofunitswiththecorrectform.

Anexpressiondoesnothaveitsownunitsstring,butifitreferencesquantitiesthathavedimensions,thesewilldeterminetheresultingunitsfortheexpression.Forexample,ifanexpressiondependsinverselyonthesquareofthex coordinate,thenithasimplieddimensionsoflengthtothepower-2.

13.1.1.1. UsingLocatorsinExpressions

ACFXsimulationhasphysicsareasandmeshareas;physicsareasareboundarieswhilemeshareasareregions.Thesetwotypesofareacanoccupycompletelydifferentspacesinasimulation;however,thereisnorequirementthatareanamesbeuniquebetweenphysicsandmesh.Thiscanleadtoambiguitieswhenyouusethesenamesinexpressions.

Toavoidtheseambiguities,ANSYSCFXfirstcheckstoseeif"@"isaphysicsname;ifthisisnotfound,thenameischeckedinthelistofmeshnames.Thusif"in1"isboththenameofaphysicsareaandthenameofamesharea,"@"istakentoindicatethephysicsarea.

ANSYSCFXalsohas@REGIONCELsyntaxsothatyoucanidentifyanamedareaasbeingamesharea.Thustoidentifythemeshareain1,youwouldusethesyntax:

@REGION:

in1

Notethatifdoesnotappearasaphysicsnameorameshname,theexpressionfails.

Release13.0-©2010SASIP,Inc.Allrightsreserved.

13.1.2. CFXExpressionLanguageStatements

TheCFXExpressionLanguageisdeclarative.Youdeclarethenameanddefinitionoftheexpressionusingexpressionlanguagestatements.ThestatementsmustconformtoapredefinedsyntaxthatissimilartoFortranmathematicalstatementsandtoCstatementsforlogicalexpressions.

Thestatementmustconsistofthefollowing:

∙anumber,optionallywithassociatedunits.Thisdefinesaconstant.Constantswithoutunitsaretermeddimensionless.

∙formathematicalexpressions,oneormorereferencestomathematicalconstants,systemvariables,orexistinguservariables,separatedby+（addition）,-（subtraction）,* （multiplication）,/（division）and^（exponentiation）,withoptionalgroupingofthesebyparentheses.Thesyntaxrulesfortheseexpressionsarethesameasthoseforconventionalarithmetic.

∙forlogicalexpressionsinvolvingrelationaloperators,oneormorereferencestomathematicalconstantsorresultsfrommathematicalexpressions,separatedby<=（islessthanorequalto）,<（islessthan）,==（isequalto）,!

=（isnotequalto）,>（isgreaterthan）and>=（isgreaterthanorequalto）withoptionalgroupingofthesebyparentheses.

∙forlogicalexpressionsinvolvinglogicaloperators,oneormorereferencestologicalconstantsorresultsfromrelationaloperationsseparatedby!

（negation）,&&（logicalAND）and||（logicalOR）,withoptionalgroupingbyparentheses.

13.1.2.1. UseofConstants

Constantsdonotneedtobedefinedpriortobeingusedinanexpression.Forexample,youcouldchoosetoevaluatetheexpressionx+5[m].Or,youcoulddefineaconstant,b=5[m]andthencreateanexpressionx+b.

Thelogicalconstantsarefalseandtrue.Resultsoflogicalexpressionsareexpressedas0and1（correspondingtofalseandtrue,respectively）.

Theuseofconstantsmaybeofbenefitingeneratingcomplicatedexpressionsorifyouhaveseveralexpressionsthatusethesameconstants.

13.1.2.2. ExpressionSyntax

Allnumbersaretreatedasrealnumbers.

Theprecedenceofmathematicaloperatorsisasfollows（fromhighesttolowest）:

∙Thepoweroperator^asinx^y.

∙Theunaryminusornegationoperator-asin-x.

∙Multiplicationanddivisionasinx*y/z.

∙Additionandsubtractionasinx+y-z.

Pleasenotethat,asofANSYSCFX10.0,theprecedenceofmathematicaloperatorshasbeenmadeconsistentwithstandardprogramminglanguagessuchasFortranandC.Therefore,thepoweroperator,whichpreviouslyhadlowerprecedencethanunaryminus,nowhasthehighestprecedence.

Theprecedenceoflogicalandrelationaloperatorsisasfollows（fromhighesttolowest）:

∙Thenegationoperator!

asin!

x.

∙Therelationaloperatorsinvolvinglessthanorgreaterthan（<=,<,>and>=）asinx>=y.

∙Therelationaloperatorisequaltoandisnotequalto（==and!

=）asinx!

=y.

∙ThelogicalANDoperator（&&）asinx&&y.

∙ThelogicalORoperator（||）asinx||y.

13.1.2.3. Multiple-LineExpressions

Itisoftenuseful,particularlywithcomplexexpressions,tousemorethanonelinewhencreatingyourexpression.CFXallowsyoutousemultiplelinestogenerateanexpression,providedeachlineisseparatedbyanappropriateoperator.

Forexample,youmayhaveanequation,A+B/C,thatconsistsofthreecomplexterms,A,B,andC.Inthiscase,youcouldusethreelinestosimplifycreatingtheexpression:

A+

B

/C

Notethattheoperatormaybeusedattheendofaline（A+）oratthebeginningofaline（/C）.Youdonotneedtoentertheoperatortwice.

Oncetheexpressionhasbeencreated,itwillappearintheExistingDefinitionslistboxasifitweregeneratedonasingleline（A+B/C）.

Release13.0-©2010SASIP,Inc.Allrightsreserved.

13.2. CELOperators,Constants,andExpressions

Thefollowingtopicsarediscussed:

∙CELOperators

∙ConditionalifStatement

∙CELConstants

∙UsingExpressions

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13.2.1. CELOperators

CFXprovidesarangeofmathematical,logicalandoperationaloperatorsasbuilt-infunctionstohelpyoucreatecomplexexpressionsusingtheExpressiondetailsview.

Table 13.1  CELOperators

Operator

FirstOperand’sDimensions[x]

SecondOperand’sDimensions[y]

Operands’Values（Approx）

Result’sDimensions

-x

Any

Any

[x]

x+y

Any

[x]

Any

[x]

x-y

Any

[x]

Any

[x]

x*y

Any

Any

Any

[x]*[y]

x/y

Any

Any

 0

[x]/[y]

x^y（ifyisasimple,constant,integerexpression）

Any

Dimensionless

Any[a]

[x]^y

x^y（ifyisanysimple,constant,expression）

Any

Dimensionless

x>0

[x]^y

x^y（ifyisnotsimple&constant）

Dimensionless

Dimensionless

x>0

Dimensionless

!

x

Dimensionless

0or1

Dimensionless

x<=y

Any

[x]

0or1

Dimensionless

x

Any

[x]

0or1

Dimensionless

x>y

Any

[x]

0or1

Dimensionless

x>=y

Any

[x]

0or1

Dimensionless

x==y

Any

[x]

0or1

Dimensionless

x!

=y

Any

[x]

0or1

Dimensionless

x&&y

Dimensionless

Dimensionless

0or1

Dimensionless

x||y

Dimensionless

Dimensionless

0or1

Dimensionless

[a]Fory<0,xmustbenon-zero.

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13.2.2. ConditionalifStatement

CELsupportstheconditionalifstatementusingthefollowingsyntax:

if（cond_expr,true_expr,false_expr）

where:

∙cond_expr:

isthelogicalexpressionusedastheconditionaltest

∙true_expr:

isthemathematicalexpressionusedtodeterminetheresultiftheconditionaltestistrue.

∙false_expr:

isthemathematicalexpressionusedtodeterminetheresultiftheconditionaltestisfalse.

Note:

Theexpressionstrue_exprandfalse_exprarealwaysevaluatedindependentofwhethertheevaluationofcond_expristrueorfalse.Asaconsequence,aconditionalstate