Q/SZJ191001-2017模態(tài)分析與模型縮減NormalModesAnalysisandModelReduction20XX20XX-12-31實(shí)施20XX-11-27發(fā)布XXXX汽車工程技術(shù)有限公司發(fā)布Q/SZXX-X-2017模態(tài)分析與模型縮減范圍本標(biāo)準(zhǔn)規(guī)定了模態(tài)分析與模型縮減的方法。本標(biāo)準(zhǔn)適用于CAE部門模態(tài)分析與模型縮減。規(guī)范性引用文件無。術(shù)語和定義無。摘要Abstract由于耐久分析共享模型需求日益增長、更高頻率段內(nèi)更加準(zhǔn)確分析、原來是簡化模型建模（如座椅和動力總成）現(xiàn)在要詳細(xì)建模、自動網(wǎng)格劃分軟件應(yīng)用等因素，整個系統(tǒng)的自由度規(guī)模增長速度已快于計算機(jī)存儲和內(nèi)存的增長。一個典型的SUV模型自由度規(guī)模很容易就超過了一百萬。如此大規(guī)模NASTRAN格式模型，如果不進(jìn)行模型縮減的話，甚至在超級計算機(jī)上也難以運(yùn)行。因此超單元和模態(tài)綜合法在NASTRAN計算中廣泛使用。相對于常規(guī)的超單元技術(shù)，有的NASTRAN分析模塊需要更小的數(shù)據(jù)規(guī)模。模態(tài)縮減法就比較適合這種情況。將設(shè)計變更比較頻繁的部分放在一個超單元，也非常有效率?，F(xiàn)在超單元法和模態(tài)綜合法在每個超單元建立過程中，分為兩個步驟：第一步是先提取部件模態(tài)；第二步是創(chuàng)建相應(yīng)數(shù)據(jù)文件。這些將隨后討論。而在這兩步前，整個模型要先劃分為很多超單元。Withtheincreaseinsharingcomponentmodelswiththedurability,pushingforbetteraccuracyinhigherfrequency,moredetailedshellmodelingforsomecomponenttraditionallymodeledaslumpedmasssuchasseatsandpowertrain,andavailabilityofauto-meshingsoftware,thetotalnumberofDOFsinafullsystemmodelhasoutgrowntheavailablecomputerdiskstorageormemory.AtypicalSUVsystemmodelcaneasilytoponemillionDOFs.ItisimpossibletoprocesssuchlargemodelsinNASTRANevenonasupercomputerwithoutsometypeofmodelreduction.ThewidelyusedmodelreductionmethodisNASTRANsuper-elementtechnique.Theresidualflexibilityeffectsduetomodaltruncationareproperlyaccountedforinthismethod.Itisalsoaveryefficientmethodwhenmanydesigniterationsremaininonesuper-element.Currentlythesuper-element/CMSmethodconsistsoftwostepsforeachsuper-element:thefirststepistoextractcomponentmodesandthesecondstepistocreatethedatabasefile.Theyarediscussedinthefollowingparagraphs.Beforestartingtorunthetwosteps,thesystemmodelshouldbedividedintomanysuper-elements.流程圖無。工具描述ToolDescription仿真分析過程中需要用到的如下軟件:Thefollowingsoftwarefacilitatestheanalyticalsimulationprocess:前處理(Preprocessors):Hypermesh求解器(AnalysisCode):Nastran后處理(Postprocessors):HyperView建模和分析過程Modeling/AnalysisProcedure單位Units分析中所用單位制如下所示:Theunitsusedintheanalysisareasfollows:力(Force) 牛頓(N)質(zhì)量(Mass) 噸(Ton)長度(Length) 毫米(mm)時間(Time) 秒(Second)內(nèi)容Contents無。坐標(biāo)系CoordinateSystems無。建模技巧ModelingTechniques超單元劃分Super-elementPartition整車模型要基于如下因素進(jìn)行超單元的劃分：不同子系統(tǒng)、零部件模型規(guī)模、設(shè)計變更需求、計算機(jī)資源和運(yùn)行時間。按照子系統(tǒng)劃分超單元，通常只需要很少的連接點(diǎn)，而且也便于分部門管理。零部件模型規(guī)模也是超單元劃分的一個因素，例如內(nèi)飾車身（包括座椅、儀表板、前端模塊）可以當(dāng)作一個超單元，如果儀表板和座椅模型規(guī)模較大，也可以分成四個（白車身、前端模塊、儀表板和座椅等）。默認(rèn)一個超單元對應(yīng)的模型節(jié)點(diǎn)數(shù)不超過十萬。設(shè)計變更頻繁的也要考慮建立超單元，例如車架后端改變頻繁，就要考慮將車架后端分開建超單元，甚至整個車架要建個超單元。在分析中劃分和使用超單元的壞處是需要額外的時間與精力來做這個事情。同時，使用超單元將使模型結(jié)構(gòu)變得更加復(fù)雜，從而導(dǎo)致與之相關(guān)的錯誤。例如，如果一個剛體單元跨過兩個超單元會產(chǎn)生依賴錯誤。Avehiclesystemmodelistypicallydividedintoseveralsuper-elementsbasedonthefollowingfactors:naturalboundaryofdifferentsubsystems;modelingsizeofacomponent;intendedanalysisiterations;andcomputerresources,andruntime.Dividingsuper-elementsalongsubsystemboundariesusuallyyieldsasmallnumberofinterfacepoints.Itiseasytomanagewhenthereisateamofengineersworkingondifferentsubsystemmodels.Componentmodelsizeisanotherfactorinsuper-elementpartition.Forexample,atrimmedbody(includingseats,IP,FESM)maybetreatedasonesinglesuper-elementorasfourseparatedsuper-elements(oneeachforbody,FESM,IP,andseat)ifalargedetailedIPandseatmodelareused.Asaruleofthumbnoonesuper-elementshouldcontainmorethan100,000grids.Theintendedanalysisiterationsofthemodelshouldalsobeconsideredwhendividingsuper-elements.Forexample,ifmanydesignchangeiterationsareanticipatedontherearsectionoftheframealone,itmaybeworthconsideringputtingtherearsectionoftheframeintooneseparatedsuper-elementfromtherestoftheframe.Eventhewholeframecanbeeasilyhandledbyusingonesuper-element.Thedisadvantageofdividingandrunningasystemmodelusingsuper-elementsistheextratimeandeffortneededtocreateandtoprocessthesuper-elements.Also,byusingsuper-elementsthemodelstructurebecomesmorecomplicatedandpotentiallyintroducesmoremodelingerrorsrelatedtosuper-elements.Forexample,arigidelementcrossingtwosuper-elementsmayhavedependencyproblemsthatneedtobecorrected.超單元模型縮減Super-elementModelReduction第一步超單元/模態(tài)綜合法第一步是為每個超單元提取合適的模態(tài)數(shù)（實(shí)模態(tài)、邊界模態(tài)、殘余模態(tài)等）。涉及到如下NASTRAN卡片：SESET：定義超單元節(jié)點(diǎn)。注意如果節(jié)點(diǎn)不包含在SESET中，則默認(rèn)在殘余的超單元中；SPOINT和SEQSET：定義部件模態(tài)縮減中保留模態(tài)的數(shù)目，必須等于或大于計算的模態(tài)數(shù)目；EIGRL：特征值提取。當(dāng)進(jìn)行自由模態(tài)計算時，要設(shè)定一個小的起始頻率值，以排除剛體模態(tài)。提取的模態(tài)頻率應(yīng)兩倍或三倍于掃頻范圍；SECSET：設(shè)置連接節(jié)點(diǎn)以獲取自由邊界條件。NASTRAN默認(rèn)在進(jìn)行特征值和特征向量提取時，固定所有的連接節(jié)點(diǎn)；SET和SEUSET1：所有連接節(jié)點(diǎn)、顯示節(jié)點(diǎn)（PLOTEL單元節(jié)點(diǎn)）、激勵節(jié)點(diǎn)和響應(yīng)節(jié)點(diǎn)；在15.1的例子中包含了第一步的分析卡片。貨車車箱被定義為超單元500，連接節(jié)點(diǎn)是螺栓。固定邊界用于提取特征值，所以沒有SECSET卡片。部件模態(tài)縮減的保留模態(tài)頻率至100Hz。第二步超單元/模態(tài)綜合法第二步是基于第一步生成的OUTPUT2文件來創(chuàng)建一個縮減超單元。需要準(zhǔn)備如下卡片：SESET：同第一步SPOINT和SEQSET：同第一步GRID：所有連接節(jié)點(diǎn)、顯示節(jié)點(diǎn)（PLOTEL單元節(jié)點(diǎn)）、激勵節(jié)點(diǎn)和響應(yīng)節(jié)點(diǎn)；PLOTEL：上述所有節(jié)點(diǎn)。每個連接節(jié)點(diǎn)用PLOTEL單元連起來；CSUPEXT：定義超單元與外部連接節(jié)點(diǎn)；見15.2中例子Step1Super-element/CMSThefirststepofthesuper-element/CMSanalysisistoextracttheappropriatemodes(normalmodes,boundarymodes,residualmodes,etc.)foreachsuper-element.TheuserneedstopreparethefollowingNASTRANinputcards:SESET:definesthesuper-elementgrids.NotethatifagridisnotincludedinSESETcard,itisintheresidualsuper-elementbydefault.SPOINTandSEQSET:definesthenumberofmodesretainedforcomponentmodereduction.Itshouldbeequaltoorlargerthanthemodescalculated.EIGRL:foreigenvalueextraction.Asmallstartingfrequencyshouldbeusedtoexcluderigidbodymodeswhenfreeboundaryconditionisused.Asaruleofthumballmodesshouldbeextracteduptotwotothreehigherinfrequencythantheintendedanalysisfrequency.SECSET:specifiesinterfacegrid(s)tohaveafreeboundarycondition.ThedefaultinNASTRANistousefixedboundaryconditionforallinterfacegridswhenperformingeigenvalue-eigenvectorextraction.SETandSEUSET1:forallinterfacegrids,displaygrids(PLOTELgrids),gridsforexcitationsandresponses.Example15.1containsasampledecktorunstepone.Thesuper-element/CMSrelatedcardsareinitalicfont.Itisapickupboxmodeldefinedassuper-element500.Theinterfacegridsaretheboltconnectiontotheframe.ThefixedboundaryconditionisusedforeigenvaluesextractionsoSECSETcardispresent.Modesupto100Hzareretainedforcomponentreduction.Step2Super-element/CMSThesecondstepofthesuper-element/CMSanalysisistocreateareducedsuper-elementdatabasefromtheoutput2filegeneratedbystep1.Theuserneedstopreparethefollowingcards:SESET:itasinstep1SPOINTandSEQSET:sameasinstep1GRID:forallinterfacegrids,displaygrids(PLOTELgrids),gridsforexcitationsandresponse.PLOTEL:forabovegrids.EachinterfacegridshouldconnecttooneinteriorgridbyaPLOTEL.CSUPEXT:definesinterfacegridsexteriortothesuper-element.Asampledecktorunstep2forthesamepickupboxmodelisincludedinExample15.2.模態(tài)分析NormalModesAnalysis完成第一步和第二步后，直接對模型進(jìn)行模態(tài)分析。首先在NASTRAN文件的執(zhí)行部分用DBLOCATE/ASSIGN來添加每個超單元的數(shù)據(jù)；其次在SUBCASE中增加對每個超單元的控制；最后所有在第二步生成的超單元卡片要包含在NASTRAN文件的數(shù)據(jù)部分。見15.3中例子，該例子省略了部分內(nèi)容。Afterthecompletionofbothsteponeandsteptwoforeachsuper-elementcomponent,normalmodeanalysisforthesystemmodelisstraightforward.First,DBLOCATE/ASSIGNstatementsneedtobeaddedtotheexecutivefilesectiontoincludethedatabaseforeachsuper-element.Second,aSUBCASEisaddedtothecasecontrolsectionforeachsuper-element.Finally,allsuper-elementcardsusedinthesteptwoshouldbeincludedinthebulk-datafilesectionforeachsuper-element.Asampledecktorunthesystemmodelcontainingsuper-element/CMScomponentsisincludedinExample13.3.Tosavespacemostofthecardsnotspecificallyrelatedtosuper-elementareomitted.假設(shè)和限制Assumptions/Limitations無。載荷和邊界條件Loads/BoundaryConditions無。結(jié)果Results無。性能要求PerformanceRequirements無。分析要求ANALYSISREQUIREMENTS無。參考文件DOCUMENTATION無。聯(lián)系人CONTACTS無。例子EXAMPLESSampleInputDeckforStep1ASSIGNOUTPUT2='/home/nvhcae/BOX/box.out2',UNIT=99,DELETEIDNVHCAESOL103TIME999INCLUDESSSALTERDIR:'alter1ga.v705'CENDTITLE=step1SUBTITLE=SUPERMENET100ECHO=NONE$SET501=5010000,5010001,5010002,5010003,5010004,5010005,5010006,5010007,5010008,5010009,5010010,5010011,5010012,5010013,5000123,5000124,5000129,5000130,5000131,5000132,5000125,5000126DISPLACEMENT(PUNCH)=501$SUBCASE50SEALL=500SUPER=500METHOD=500PARTN=501PARAM,MAKEMAT,500PARAM,MATFILE,99BEGINBULK$1234567890EIGRL5001.0100.0$$paramcardshere$INCLUDE'/home/nvhcae/BOX/box.nast'$SESET,500,5010000,THRU,5500000$DEFUSETU2U2SEUSET1500U212350100005010001501000250100035010004SEUSET1500U2123502319150001255000126$SPOINT500001THRU500100SEQSEHRU500100$ENDDATASampleInputDeckforStep2ASSIGNINPUTT2='/home/nvhcae/BOX/box.out2',UNIT=99ASSIGNMASTER='/home/nvhcae/BOX/box.MASTER',DELETE$IDNVHCAETIME9999DIAG8SOL103INCLUDESSSALTERDIR:'alter2ga.v705'CENDTITLE=CMSofBoxSUBTITLE=CREATEEXTERNALDATABASE.$SUBCASE50SEALL=500SUPER=500METHOD=500$PARAM,INFILE,99$BEGINBULK$PARAM,DBALL,MASTERPARAM,IFP,MASTER$PARAM,EPPRT,1.0E-5$GRID50100005560.948-631.250837.9995GRID50100015114.520-622.999827.9995GRID50231903624.793-822.005828.0000GRID50231914196.479-821.999827.8600$PLOTEL540000150231925400000PLOTEL540000250231925400001PLOTEL502395050100805010089PLOTEL502395150100895010095$SESET,500,5010000,THRU,5500000$CSUPEXT,500,5000121,5000122,5000123,5000124CSUPEXT,500,5000129,5000130,5000131,5000132CSUPEXT,500,5000125,5000126$SPOINT500001THRU500100SEQSEHRU500100$ENDDATASampleDeckforSystemNormalModeAnalysisContainingSuperelement/CMSComponentsNASTRANSPARSE=25AUTOASGN=3$$CabSuperElementDBLOCATEDATABLK=(*)WHERE(SEID=100ORPEID=100)LOGICAL=SE100ASSIGNSE100='/home/nvhcae/MASTER/cab.MASTER'$$FrameSuperElementDBLOCATEDATABLK=(*)WHERE(SEID=200ORPEID=200)LOGICAL=SE200ASSIGNSE200='/home/nvhcae/MASTER/frame.MASTER'$$BoxSuperElementDBLOCATEDATABLK=(*)WHERE(SEID=500ORPEID=500)LOGICAL=SE500ASSIGNSE500='/home/nvhcae/MASTER/box.