外文翻譯-應(yīng)用計(jì)算機(jī)輔助工程設(shè)計(jì)重型卡車車架

輔助工程設(shè)計(jì)重型貨車車架CarlosCosme,AmirGhasemiandJimmyGandevia摘要：近年來，重型貨車市場變得非常的注重重量和降低成本。這對設(shè)計(jì)工程師是重大挑戰(zhàn)，因?yàn)檫@些車輛被用在各種各樣的公路環(huán)境，從高速公路到嚴(yán)重的越野環(huán)境。目前的挑戰(zhàn)是在不犧牲耐用性和性能降低的前提下滿足質(zhì)量和成本。本文論述了運(yùn)用計(jì)算機(jī)集成、計(jì)算機(jī)輔助設(shè)計(jì)和工程軟件代碼（Pro/Engineer，ADAMS軟件和ANSYS）來輔助設(shè)計(jì)更改車架。特別是，本文集中論述了一個(gè)ADAMS多體動(dòng)力學(xué)模型，一個(gè)完整的卡車和拖車來模擬車輛的側(cè)翻穩(wěn)定性，平順性，和耐久性載荷。該模型包括一個(gè)采用靈活的框架模型模態(tài)綜合模式，探討了有限元分析程序。之間的多體仿真鏈接與有限元程序也可以用來傳輸、加載應(yīng)力分析有限元模型。所有代碼之間緊密連結(jié)，確保新的設(shè)計(jì)并行計(jì)算可快速用于設(shè)計(jì)和分析。一個(gè)說明這是如何已被使用的技術(shù)詳細(xì)的個(gè)案研究也包括在內(nèi)。簡介最近，重卡行業(yè)經(jīng)歷了汽車降低成本和重量的大發(fā)展。這一直是卡車制造商的主要挑戰(zhàn)，在不犧牲耐用性和性能的前提下，尋找好的方式來優(yōu)化他們的汽車設(shè)計(jì)。由于車架是車輛系統(tǒng)的重要組成部分，它經(jīng)常被用于完善。本文概述了電腦輔助工程（CAE）分析更改車架以及這些變化會如何影響車輛性能。重型卡車的車架是該車輛的骨干，上面集成了主要的卡車組成系統(tǒng)，如車軸，懸架，動(dòng)力總成，駕駛室。典型的結(jié)構(gòu)框架是梯形框架，中間交叉幾根橫梁。縱梁的斷面尺寸變化很大，根據(jù)在卡車上的受力而定。而且，需要考慮各種因素：重量，復(fù)雜性和成本。這些變化將取決于橫梁的作用和位置。請參考圖1插圖，一輛卡車的車架。然而，橫梁布置的變化帶來的影響還無法看出來。例如，如果橫梁的抗扭剛度降低，對汽車的側(cè)傾穩(wěn)定性和耐久性的影響是怎么的呢？設(shè)計(jì)工程師們需要對這些類型的問題給出答案以指導(dǎo)他們的工作。特別是，及時(shí)的設(shè)計(jì)和分析程序是必需的，這樣新的設(shè)計(jì)可以快速評估。圖1重型載貨汽車車架計(jì)算機(jī)輔助工程在過去的二十年中汽車自動(dòng)化設(shè)計(jì)工具CAE得到了巨大的發(fā)展。這項(xiàng)技術(shù)的已被很多汽車制造商采用以改善汽車設(shè)計(jì)來滿足快速增長的市場要求。當(dāng)今的結(jié)構(gòu)設(shè)計(jì)通常是使用兩個(gè)CAE工具：有限元分析（FEA）和多體系統(tǒng)（MSS），結(jié)合CAD提高設(shè)計(jì)和分析。在過去十五年里，CAD系統(tǒng)已取代繪圖板作為首選設(shè)計(jì)方法。它們使設(shè)計(jì)師和工程師能夠快速畫出卡車零部件，汽車真實(shí)模型和設(shè)計(jì)圖紙。先進(jìn)的CAD系統(tǒng)功能豐富，如參數(shù)化實(shí)體建模和大型裝配管理。他們已經(jīng)發(fā)展成為主要的數(shù)據(jù)庫，為工程信息尤其是CAD系統(tǒng)提供下游CAE應(yīng)用的重要數(shù)據(jù)。工程師通常使用有限元分析研究結(jié)構(gòu)構(gòu)件的強(qiáng)度。典型的有限元分析的重點(diǎn)是結(jié)構(gòu)應(yīng)力，撓度和自然頻率。首先對通常被稱為網(wǎng)格的離散結(jié)構(gòu)進(jìn)行分析。該網(wǎng)格是由節(jié)點(diǎn)和元素組成，而且經(jīng)常從CAD創(chuàng)建幾何系統(tǒng)。這些節(jié)點(diǎn)代表位移計(jì)算的結(jié)構(gòu)。他們定義的局部質(zhì)量，剛度和阻尼性能結(jié)構(gòu)。有關(guān)這些數(shù)量方程，可以自動(dòng)開發(fā)節(jié)點(diǎn)位移。其他投入，如邊界條件，載荷和材料特性，必須是由用戶定義。所有這些效果都需要小心的判斷和對有意義的結(jié)果進(jìn)行認(rèn)真的分析。結(jié)果后處理包括圖像變形負(fù)載結(jié)構(gòu)，彩色應(yīng)力輪廓，振型動(dòng)畫。MSS多體系統(tǒng)仿真方法研究了運(yùn)動(dòng)部件和組件，并經(jīng)常用來研究車輛暫?；蜍囕v的操作和動(dòng)態(tài)響應(yīng)。一個(gè)典型的完整的車型MSS將剛體組成（車輪，車軸，車架，發(fā)動(dòng)機(jī)，駕駛室）模擬成關(guān)節(jié)連接和理想化力元。MSS代碼自動(dòng)發(fā)展非線性微分方程和代數(shù)方程定義模型中的物體運(yùn)動(dòng)。該方程在數(shù)值上集成剛體位移，速度，加速度和受力。結(jié)果以圖形和動(dòng)畫顯示該系統(tǒng)的運(yùn)動(dòng)。至于有限元分析，CAD數(shù)據(jù)經(jīng)常使用MSS的發(fā)展模式。CAD幾何數(shù)據(jù)是用于建立MSS的布局模式，如接頭和力量元素的位置。CAD實(shí)體模型數(shù)據(jù)也可以用來估計(jì)每個(gè)剛體的位置，質(zhì)心和慣性特性。作用在剛體上的力可以用作MSS的輸入負(fù)載，有限元分析確定該剛體的結(jié)構(gòu)應(yīng)力。CAE技術(shù)在本文所討論的工具包括基與CAD的Pro/Engineer，ANSYS進(jìn)行有限元分析，以及基于ADAMS的MSS。下面的討論引用的是某型卡車的車架有限元分析。CAE重型汽車建模如上所述，在目前提供的CAD與CAE工具提供了大量的整合。盡管如此，這些工具是非常粗略的分析，仍然需要努力分析重型卡車和卡車車架。為了充分了解車架影響汽車操縱的變化，滾動(dòng)穩(wěn)定性，平順性和持久性，需要一個(gè)詳細(xì)的MSS模型，可以模擬所有這些影響。使用ADAMS軟件代碼，建立了WesterStar卡車的模型。圖二展示了在ADAMS環(huán)境下的模型。圖2ADAMS的MSS的模型該模型包括以下幾個(gè)特點(diǎn):?100剛體?180力元?45共同元素?415度-的自由度“MechanicsofHeavy-DutyTrucksandTruckCombinations",UMTRICourseNotes,July,1995.Stasa,FrankL.,“AppliedFiniteElementAnalysisforEngineers",CBSCollegePublishing,1985.Ottarsson,Gisli,“ModalFlexibilityMethodinADAMS/FLEX",MechanicalDynamics,Inc.,March,1998.“UsingADAMS/FLEX",MechanicalDynamics,Inc.,1997.“ADAMS/FiniteElementAnalysisReferenceManual",MechanicalDynamics,Inc.,November15,1994.“Pro/MESHandPro/FEMPost,User'sGuide",ParametricTechnologyCorporation,1997.“ANSYSStructuralAnalysisGuide",Analysis,Inc.,1994.Gillespie,ThomasD.,“FundamentalsofVehicleDynamics",SocietyofAutomotiveEngineers,Inc.,1992.Gobessi,MarkandArnold,Wes,“TheApplicationofBondedAluminumSandwichConstructionTechnologytoAchieveaLightweight,LowCostAutomotiveStructure",SAEpaper982279.1999-01-3760ApplicationofComputerAidedEngineeringintheDesignofHeavy-DutyTruckFramesCarlosCosme,AmirGhasemiandJimmyGandeviaWesternStarTrucks,Inc.Copyright?1999SocietyofAutomotiveEngineers,Inc.ABSTRACTsimulatevehiclehandling,rollstability,rideABSTRACTInrecentyearstheheavy-dutyClass8truckmarkethasbecomeveryfocusedonweightandcostreduction.Thisrepresentsamajorchallengefordesignengineerssincethesevehiclesareusedinawidevarietyofvocationsfromhighwaylinehaultologginginsevereoff-roadenvironments.Thechallengeistomeettheweightandcostreductiongoalswithoutsacrificingdurabilityandperformance.Thispaperdiscussestheintegrationofcomputeraideddesignandengineeringsoftwarecodes(Pro/Engineer,ADAMS,andANSYS)tosimulatetheeffectofdesignchangestothetruckframe.Inparticular,thispaperdiscusesthedevelopmentofanADAMSmulti-bodydynamicsmodelofafulltruckandtrailertoperformance,anddurabilityloading.Themodelincludesaflexibleframemodelusingacomponentmodesynthesisapproachwithmodesimportedfromafiniteelementanalysisprogram.Thelinkbetweenthemulti-bodysimulationandthefiniteelementcodeisalsousedtotransferloadsbacktothefiniteelementmodelforstressanalysis.Tightlinksbetweenallthecodesensuresthatnewdesigniterationscanbequicklyevaluatedforconcurrentdesignandanalysis.Adetailedcasestudyshowinghowthistechnologyhasbeenusedisalsoincluded.INTRODUCTIONRecentlytheheavytruckindustryhasexperiencedalargepushtodevelop

vehicleswithreducedcostandweight.Thishasbeenamajorchallengefortruckmanufacturersastheylookforwaystooptimizetheirvehicledesignswithoutsacrificingdurabilityorperformance.Sincethetruckframeisamajorcomponentinthevehiclesystem,itisoftenidentifiedforrefinement.Thispaperoutlinesacomputeraidedengineering(CAE)procedureforanalyzingchangestothetruckframeandhowthesechangesaffectvehicleperformance.Theframeofaheavytruckisthebackboneofthevehicleandintegratesthemaintruckcomponentsystemssuchastheaxles,suspension,powertrain,cab,andtrailer.ThetypicalframeisaladderstructureconsistingoftwoCchannelrailsconnectedbycross-members.Theframerailsvarygreatlyinlengthandcross-sectionaldimensionsdependingonthetruckapplication.Likewise,thecross-membersvaryindesign,weight,complexity,andcost.Thesevariationswilldependuponthecross-memberpurposeandlocation.RefertoFigure1foranillustrationofatruckframe.However,theeffectsofchangestotheframeandcross-membersarenotwellunderstood.Forexample,ifthetorsionalstiffnessofasuspensioncross-memberislowered,whatistheeffectonthevehicle'srollstability,handling,ride,anddurability?Designengineersrequireanswerstothesetypesofquestionstoguidethemintheirwork.Inparticular,aconcurrentdesignandanalysisprocedureisrequiredsothatnewdesignscanbequicklyevaluated.Figure1.Class8Heavy-DutyTruckFrameCOMPUTERAIDEDENGINEERINGInthelasttwentyyearstherehasbeenanenormousgrowthinthedevelopmentofCAEtoolsforautomotivedesign.Muchofthistechnologyhasbeenadoptedbythetruckindustryastruckmanufacturerslooktoimprovetheirdesignsinarapidlygrowingmarket.TodaystructuraldesignistypicallyperformedusingtwoCAEtools:finiteelementanalysis(FEA),andmulti-bodysystemsimulation(MSS).Thesearecombinedwithcomputeraideddesign(CAD)softwaretoimprovedesignandanalysiscommunication.CAD-InthelastfifteenyearsCADsystemshavereplaceddrawingboardsasthemethodofchoicefordesign.Theyenabledesignersandengineerstoquicklycreaterealisticmodelsoftruckcomponents,vehicleassemblies,anddesigndrawingsformanufacturing.AdvancedCADsystemsarerichinfeaturessuchasparametricsolidmodelandlargeassemblymanagement.Theyhaveevolvedtobecomemajordatabasesforengineeringinformation.Inparticular,CADsystemsprovideimportantdatafordownstreamCAEapplications.FEA-Finiteelementanalysisisusuallyusedbyengineerstostudythestrengthofstructuralcomponents.TypicalFEAactivityisfocusedonanalyzingstructuralstresses,deflections,andnaturalfrequencies.Theanalysisbeginswithadiscretizedrepresentationofastructureknownasamesh.ThemeshiscomposedofnodesandelementsandisoftencreatedwithgeometryfromaCADsystem.Thenodesrepresentpointsonthestructurewheredisplacementsarecalculated.Theelementsareboundedbysetsofnodesandencloseareasorvolumes.Theydefinethelocalmass,stiffness,anddampingpropertiesofthestructure.Equationsrelatingthesequantitiestothenodaldisplacementsareautomaticallydevelopedbythesoftwarecodes.Otherinputs,suchasboundaryconditions,appliedloads,andmaterialproperties,mustbedefinedbytheuser.Eachofthesequantitiesrequirescarefuljudgementformeaningfulresultstobeachieved.Resultspost-processingincludesimagesofdeformedstructuresunderload,colouredstresscontours,andmodeshapeanimations.MSS-Multi-bodysystemsimulationisusedtostudythemotionofcomponentsandassembliesandisoftenusedtostudyavehiclesuspensionoravehicle'shandlingandrideresponse.AtypicalMSSmodelofafullvehiclewillbecomposedofrigidbodies(wheels,axles,frame,engine,cab,andtrailer)connectedbyidealizedjointsandforceelements.TheMSScodeautomaticallydevelopsthenon-lineardifferentialandalgebraicequationsthatdefinethemotionofthebodiesinthemodel.Theequationsarenumericallyintegratedtoproducetimehistoriesofrigidbodydisplacements,velocities,accelerations,andforces.Resultsareviewedasgraphsandanimationsofthesystemmotion.AswithFEA,CADdataisoftenusedtodevelopaMSSmodel.GeometrydatafromaCADassemblyisusedtoestablishthelayoutoftheMSSmodelsuchasthelocationofjointsandforceelements.CADsolidmodeldataisalsousedtoestimatethelocationofthecenter-of-massandtheinertialpropertiesofeachrigidbody.ForcesactingonarigidbodyfromaMSScanbeusedasinputloadstoafiniteelementanalysistodeterminethestructuralstressesinthatrigidbody.TheCAEtoolsdiscussedinthispaperincludePro/EngineerforCAD,ANSYSforFEA,andADAMSforMSS.Thefollowingdiscussionreferencesthespecificcapabilitiesofthesecodesindevelopingacustomizedenvironmentfortheengineeringanalysisoftruckframes.CAECUSTOMIZATIONFORHEAVYTRUCKMODELLINGAsdescribedabove,thecurrentofferingofCADandCAEtoolsprovideagreatdealofintegration.Nonetheless,thesetoolsareverygeneralinscopeandasignificantcustomizationeffortisrequiredfortheanalysisofheavydutytrucksandtruckframes.Tofullyunderstandhowchangestothetruckframeimpactvehiclehandling,rollstability,ride,anddurabilityrequiresadetailedMSSmodelthatcansimulatealltheseeffects.UsingtheADAMSsoftwarecodesuchamodelwasdevelopedatWesternStarTrucks.RefertoFigure2foraviewofthemodelintheADAMSenvironment.Figure2.ADAMSMSSModelThemodelincludesthefollowingcharacteristics:100rigidbodies180forceelements45jointelements415degrees-of-freedomTherigidbodiesincludetheframe,cab,axles,wheels,engine,hood,radiator,leafsprings,suspensionarms,driveshafts,andthetrailer.MasspropertiesformanyofthesebodieswereestimatedusingsimplifiedsolidmodelsinPro/Engineer.Theforceelementsincludelinearandnon-linearbushielementsthatmodelrubberisolators,suchasthecabandenginemounts.Non-linearsinglecomponentforcesareusedtomodelairspringsandshockabsorbers.Propertydatafortheseelementsarederivedfromtestsperformedbycomponentsuppliers.Revolutejointsandsphericaljointsareusedtomodelconnectionpoints,suchaswheelbearingsandtorquerodpivots,respectively.Pro/Engineerassembliesareusedtodeterminethegeometriclocationoftheseelements.Sincetheheavytruckindustryoffersawidevarietyofvehiclelayouts,thelocationsofmanyofthetruck'ssubsystemsweremadeparametricforeasymodification.Forexample,thefrontaxlesubassembly(wheels,axles,leafsprings,andshockabsorbers)werelinkedtoavariabledefiningthelongitudinalpositionofthefrontaxle.Usingthistechnique,truckmodelswithdifferentfrontaxlepositionscanbequicklydevelopedbychangingthevalueofthisvariable.Thisprocedurewasduplicatedforthefollowingsubassemblies:rearsuspension,cab,engine,hood,andfifthwheelandtrailer.TiretoroadcontactishandledwiththeADAMSbuilt-intireroutinesandincludesmodelsfortirehandlinganddurabilityforces.InADAMSroadprofilesarerepresentedasameshoftrianglessimilartoafiniteelementmesh.ThegeometryandmeshfortheroadprofilesaregeneratedwithPro/Engineer.AcustomsoftwareprogramisthenusedtotranslatethemeshintotwofilesforADAMS:aroadfileformatforthesolvertodeterminethetire/roadinteractionforces,andagraphicsformattoviewtheroadduringpost-processinganimation.Thesefilesarestoredinacommondirectoryforeasyretrieval.Customcontrolalgorithmsweredevelopedtocontrolvehiclespeed,steering,anddrivetorque.Thesefunctionscanbequicklymodifiedtoexecutedifferentvehiclemaneuverssuchasrollstability,ahighspeedlanechange,ordurabilitybumpssimilartoaprovingground.Afterthesimulationsarerun,theforcesandtorquesactingontheframearewrittentodatafiles.AcustomsoftwareprogramisthenusedtoextracttheloadsatspecifictimestepsandwritethemtoanANSYSloadfile.TheloadfileisthenreadintoANSYSandappliedtoafiniteelementmodeloftheframe.Theframestressesarethencalculatedusinganinertialreliefsolution.Insummary,themodelusescustomsoftwareroutinesandtheexistinglinksbetweentheCADandCAEcodestocreateacustomenvironmentforevaluatingtheperformanceanddurabilityofaheavy-dutytruck.However,themodelassumesthatthetruckframeisarigid,underformablebody.Inreality,thetruckframecontainsagreatdealofflexibilitywhichcanimpactvehicleperformanceandstability.Asaresult,theseeffectsmustbecapturedinthemulti-bodysystemsimulation.CAESOLUTIONFORFRAMEFLEXIBILITYPREVIOUSTECHNIQUES-Inthepast,severaltechniqueshavebeenemployedtocaptureframeflexibilityinaMSSmodel.Threepopularmethodsare:bushings,massbeamelements,andFEAsuperelementreduction.Inthefirstmethodtheframeisdividedintotwoormorerigidbodiesconnectedtogetherwithforceelementshavingbushing-likeproperties:stiffnessanddampinginthreetranslationaldirectionsandthreerotationaldirections.Thebushingpropertiesareadjustedtogivetheoverallframebendingandtorsionalstiffness.Ascanbeexpected,thismethodiscumbersometouse,andifproperlytuned,itwillbecapableofcapturingonlythefundamentalbendingandtorsionalmodesoftheframe.Inthesecondmethodtheframeisdividedintoalargenumberofrigidbodiesinterconnectedbymasslessbeamelements.Thisissimilartothebushingmethodbutmanymorerigidbodiesareusuallyused,andtheyareconnectedwithmasslessbeamelementswhoseequations(Timoshenkobeamtheory)arebettersuitedtomodellingtruckframerailsandcross-members.Nonetheless,itistimeconsumingtobuildaframewiththismethodandcarefultuningofthebeamelementsisstillrequiredtocapturetheframe'sflexuralresponse.Thethirdmethodisthemostaccurateofthethreemethodsandisbasedonafiniteelementrepresentationoftheframe.Inthismethodthefiniteelementmodelisreducedtoasuperelementrepresentationwiththeoverallstiffnessandmasspropertiescondensedtoasetofmasternodes.Thereducedmodelischeckedagainsttheoriginalfiniteelementmodeltoensurethattheimportantframedynamicsarestillcaptured.ItisthenimportedintotheMSSenvironmentwherethesuperelementsandmasternodesareconvertedtoanequivalentrepresentationofrigidbodiesandforceelements.Althoughthismethodisbasedonafiniteelementsolution,itcanstillbedifficulttoachieveaccurateresults.Forexample,caremustbetakeninselectingthemasternodestoensurethatthemassandstiffnesscondensationprocessisaccurate.Allthemethodsdescribedabovearedifficulttouseforcreatinganaccurateflexiblemodelofatruckframe.Ingeneral,theyareonlycapableofcapturingthebasicframeresponse:thefirstfewbendingandtorsionalmodesandthegrossframestiffness.Ifeachmethodistowork,asignificanteffortisrequiredtotuneitspropertiestomatchsomereference,suchasstaticdeflectiontesting,modaltesting,orfiniteelementsimulationresults.Consequently,neithermethodissuitableforuseinaconcurrentdesignandanalysisenvironment-itwouldsimplytaketoolongtomakechangestothemodel,anditwouldnothaveadequatespatialresolutiontocapturesubtledesignchangestotheframe.COMPONENTMODESYNTHESISTECHNIQUE-RecentadvancesintheintegrationofFEAandMSShaveovercomethedifficultiesinthemethodsdescribedabove.Itisnowpossibletouseafiniteelementmodeldirectlyinamulti-bodysimulationusingamodalsuperpositiontechniqueknownascomponentmodesynthesis(CMS).Usingmodalsuperposition,thedeformationofastructurecanbedescribedbythecontributionofeachofitsmodes.Normally,averylargenumberofmodesarerequiredtoaccuratelycapturethedeformationsatpointswhereconstraintsareappliedtothestructure.CMSwasdevelopedtoalleviatethisproblem.Itcombinesnormalmodeswithconstraintmodes.Theseconstraintmodes,orstaticshapes,capturethedeformationofkeyareasofthestructurewithouthavingtomaintainanexcessivenumberofnormalmodes.Asaresult,theyarecomputationallymoreefficient.TheCMSprocedureadoptedintheADAMScodeisbasedonamodifiedversionoftheCraig-Bamptonapproach.Inthismethodthestructureisconsideredtohaveinterfacepointswhereconstraintsandforcesareapplied,andeachinterfacepointcanhaveuptosixdegrees-of-freedom:threetranslationsandthreerotations.Themotionofthestructureisthendescribedbyacombinationoftwosetsofmodes:constraintmodesfortheinterfacepoints,andfixedinterfacenormalmodes.Aconstraintmodeiscalculatedforeachdegree-of-freedomofaninterfacepoint,anditdescribesthestaticshapeofthestructurewhenthatdegree-of-freedomisgivenaunitdeflectionwhilekeepingthedegrees-of-freedomofalltheotherinterfacepointsfixed.Thisprocedureisrepeatedtodevelopafamilyofconstraintmodesforalltheinterfacepoints.Sincetheconstraintmodesarestaticshapes,theirfrequencyinformationisunknown.Thefixedinterfacenormalmodesrepresentthenormalmodesoftheentirestructurewhenallthedegrees-of-freedomofalltheinterfacepointsareheldfixed.Inthisform,theCraig-Bamptonmodesarenotideallysuitedforintegrationwiththemulti-bodyequationsofmotion.Forexample,theconstraintmodesaddrigidbodymodeswhichconflictwiththeADAMSnon-linearrigidbodymotions.Also,theconstraintmodesmaycontainhighfrequenciesthataredifficulttosolve.IntheADAMSimplementationtheseproblemsarehandledbyorthogonalizingtheCraig-Bamptonmodes.Thisidentifiestherigidbodymodesmakingthemeasytodisable.Italsoaddsfrequencyinformationtotheconstraintmodeswhichisvaluableforsettingintegrationparametersduringthemulti-bodysimulation.Afterorthogonalization,amodifiedsetofmodesexist:normalmodesfortheunconstrainedstructure(free-freelikemodessimilartothosecalculatedinatypicalFEAeigenvaluerun),andtheinterfacedegrees-of-freedom.SeeOttarsson[3]foracompletedescriptionofthismethod.AllthemodalcalculationsdescribedabovetakeplaceintheANSYSenvironmentandareperformedonafiniteelementmodeloftheframe.Tocomputethemodes,theuserselectsthenodesrepresentingtheinterfacepointswhereforcesandconstraintsentertheframe,andthenrunsamacrothatexecutestheappropriateANSYScommands.Thenumberofnormalmodestoincludeinthecalculationsarepassedasaparametertothemacro.ThefinalsetofmodesarewrittentoamodalneutralfileMNF)thatcanbereadbyADAMS.Theadvantageofthismodalsuperpositionmethodaremanyandinclude:Theframeisrepresentedbyasinglemodalneutralfile.Asaresult,itisveryeasytoreusetheframeinotherMSSmodels.Thefilescanbestoredincommondirectoryforarchivingandfutureuse.IntheMSSmodeltheframeisrepresentedasasingleflexiblebodyandnotalargenumberofrigidbodies.bodies.Thismakesitmucheasiertomanipulatetheframeinthemodel.Everyflexiblebodymodeaddsonlyonedegree-offreedomtothesimulation.Previousmethodsaddedmanymoredegreesoffreedomsincetheyusedalargenumberofrigidbodiesandeachoftheseaddedsixdegrees-of-freedom.Thelinear,flexiblecharacteristicsofframemodelaremoreaccuratesincetheyarebasedonafullfiniteelementmodelandnotacollectionofrigidbodiesandforceelements.Thismakesitmucheasiertotunethemodeltoagreewithmodaltestresults.Dampingisaddedonamodalbasis.Thus,dampingresultsfrommoda