ABAQUS声学分析-acoustics-lecture4

Copyright2005ABAQUS,Inc.Structural-AcousticAnalysiswithABAQUSCoupledStructural-AcousticAnalysisLecture4深圳ABAQUS培训深圳ANSYS深圳有限元培训培训•Introduction•Near-FieldandFar-FieldEffects•FullyCoupledAnalysis•SequentiallyCoupledAnalysis•Acoustic-to-StructuralSubmodeling•CoupledAcoustic-StructuralSubstructures•BoundaryImpedances•CreatingASIelementsongeometry•CreatingASIelementsonorphanmeshesCopyright2005ABAQUS,Inc.Structural-AcousticAnalysiswithABAQUSIntroductionCopyright2005ABAQUS,Inc.L4.4Structural-AcousticAnalysiswithABAQUSIntroduction•Structural-acousticcoupling–Iftheacousticmediumadjoinsastructure,structural-acousticcouplingoccursattheinterface.–Thepressurefieldintheacousticmediumcreatesanormalsurfacetractiononthestructure.–Theaccelerationfieldinthestructurecreatesthenaturalforcingtermatthefluidboundary.•Recallthatvolumetricaccelerationistheconjugateofacousticpressureinanacousticanalysis.Volumetricaccelerationiswhatyouapplyasaconcentratedloadinanacousticanalysis.–Generically,theacousticandstructuralfieldsmustbesolvedforsimultaneously.Copyright2005ABAQUS,Inc.L4.5Structural-AcousticAnalysiswithABAQUSIntroduction•Simplifications–Inairtheforcesonstructurescausedbytheairareusuallyweak.–Insuchacase,ratherthanperformingacoupledanalysis,youmightmodeltheeffectofthestructureontheacousticfluidusingboundaryconditionsorloadsontheacousticmodel.–Thevalueofacousticpressurecanbespecifieddirectly(*BOUNDARYinaninputfileorusetheABAQUS/CAELoadmodule).•Thisincludesthecaseofcomplicatedboundarypressurefieldscomputedinapreviousstructuralanalysis–see‘SequentiallyCoupledAnalysis’below.–Aconcentratedvolumetricaccelerationcanbespecified(*CLOADinaninputfileorusetheABAQUS/CAELoadmodule).–Adistributedvolumetricaccelerationcanbespecifiedusingthe*INCIDENTWAVEoptions.•RequirestheuseoftheKeywordsEditorinABAQUS/CAE.Copyright2005ABAQUS,Inc.L4.6Structural-AcousticAnalysiswithABAQUSIntroduction•Interfaceimpedances–Thestructural-acousticinterfacecanhaveanimpedance,Z,ofitsown.–Thismeansthattherelationshipbetweenthestructuralmotionandtheacousticpressureneednotbecontinuous:•Usedtoincludeeasilytheeffectsofthininterfacelayers,suchascarpetonthefloorofacar,ortheabsorptiveacousticcoatingofasubmarine.1()mfpZnuu.Copyright2005ABAQUS,Inc.Structural-AcousticAnalysiswithABAQUSNear-FieldandFar-FieldEffectsCopyright2005ABAQUS,Inc.L4.8Structural-AcousticAnalysiswithABAQUSNear-FieldandFar-FieldEffects•NearandfarfieldsVibratingmachineAirNearfieldFarfieldCopyright2005ABAQUS,Inc.L4.9Structural-AcousticAnalysiswithABAQUSNear-FieldandFar-FieldEffects•Nearfield–Theregionwithinonewavelengthoftheinterfaceisgenerallyconsideredthenearfield.•Near-fieldregionshrinkswithincreasingfrequency.–Thenear-fieldsolutiontendstobecomplicated.•Includes“evanescent”effects(effectsthatfadequickly).–Inthenearfieldthemeshhasastrongeffectonaccuracy.–Theelementsizeonbothsidesoftheinterfaceisgovernedbythemediumthatrequiresthefinermesh.Copyright2005ABAQUS,Inc.L4.10Structural-AcousticAnalysiswithABAQUSNear-FieldandFar-FieldEffects•Farfield–Beyondonewavelengththecomplexitiesofthenearfielddiminish.–Thenear-fieldmeshhaslimitedeffectonfar-fieldresults.•Whetherornotthenear-fieldmeshisrefinedoftendoesnotstronglyaffecttheresultsawayfromtheinterface.–Themeshinthefarfieldneedstobeappropriateonlyforthematerialandthesimulationrequirements,asdiscussedinLecture3.–Unlikeinstaticproblems,inacousticsimulationsthefarfieldisoscillatory,notconstant.•Thefar-fieldmeshstillneedstobefineenoughtocapturethesewaves.Copyright2005ABAQUS,Inc.L4.11Structural-AcousticAnalysiswithABAQUSNear-FieldandFar-FieldEffectsSpeakerwithfinelymeshedair(left)andcoarselymeshedair(right)Copyright2005ABAQUS,Inc.Structural-AcousticAnalysiswithABAQUSFullyCoupledAnalysisCopyright2005ABAQUS,Inc.L4.13Structural-AcousticAnalysiswithABAQUSFullyCoupledAnalysis•Whenisfullycoupledanalysisappropriate?–Fullycoupledanalysisisthemostgeneralapproachtostructural-acousticproblems.–Allproblemscanbesolvedappropriatelyusingthefullycoupledapproach.–Makesnoassumptionsaboutwhichdirectionhasthestrongestcouplingeffects.•StructuraldeformationAcousticpressure–Adrawbackofcoupledanalysisisthatitcanbeunnecessarilyexpensiveforlargeproblemswheretheacousticpressurehaslittleeffectonthestructure.•Inthesecasessequentiallycoupledanalysiscanbemoreefficient(discussedinthenextsection).Copyright2005ABAQUS,Inc.L4.14Structural-AcousticAnalysiswithABAQUSFullyCoupledAnalysis•CouplingwithASI(acoustic-structuralinterface)elements–Ifthestructuralmeshandtheacousticmeshsharenodesattheirinterface,liningtheinterfacewithASIelementsenforcestherequiredcoupling.–Whilethisapproachisavailable,butthesurface-basedapproachisgenerallyrecommended.ASIelementsliningmachinesurfaceVibratingmachineAirCopyright2005ABAQUS,Inc.L4.15Structural-AcousticAnalysiswithABAQUSFullyCoup