模态分析与模型缩减

Q/SZJ191001-2017模态分析与模型缩减NormalModesAnalysisandModelReduction20XX20XX-12-31实施20XX-11-27发布XXXX汽车工程技术有限公司发布Q/SZXX-X-2017模态分析与模型缩减范围本标准规定了模态分析与模型缩减的方法。本标准适用于CAE部门模态分析与模型缩减。规范性引用文件无。术语和定义无。摘要Abstract由于耐久分析共享模型需求日益增长、更高频率段内更加准确分析、原来是简化模型建模（如座椅和动力总成）现在要详细建模、自动网格划分软件应用等因素，整个系统的自由度规模增长速度已快于计算机存储和内存的增长。一个典型的SUV模型自由度规模很容易就超过了一百万。如此大规模NASTRAN格式模型，如果不进行模型缩减的话，甚至在超级计算机上也难以运行。因此超单元和模态综合法在NASTRAN计算中广泛使用。相对于常规的超单元技术，有的NASTRAN分析模块需要更小的数据规模。模态缩减法就比较适合这种情况。将设计变更比较频繁的部分放在一个超单元，也非常有效率。现在超单元法和模态综合法在每个超单元建立过程中，分为两个步骤：第一步是先提取部件模态；第二步是创建相应数据文件。这些将随后讨论。而在这两步前，整个模型要先划分为很多超单元。Withtheincreaseinsharingcomponentmodelswiththedurability,pushingforbetteraccuracyinhigherfrequency,moredetailedshellmodelingforsomecomponenttraditionallymodeledaslumpedmasssuchasseatsandpowertrain,andavailabilityofauto-meshingsoftware,thetotalnumberofDOFsinafullsystemmodelhasoutgrowntheavailablecomputerdiskstorageormemory.AtypicalSUVsystemmodelcaneasilytoponemillionDOFs.ItisimpossibletoprocesssuchlargemodelsinNASTRANevenonasupercomputerwithoutsometypeofmodelreduction.ThewidelyusedmodelreductionmethodisNASTRANsuper-elementtechnique.Theresidualflexibilityeffectsduetomodaltruncationareproperlyaccountedforinthismethod.Itisalsoaveryefficientmethodwhenmanydesigniterationsremaininonesuper-element.Currentlythesuper-element/CMSmethodconsistsoftwostepsforeachsuper-element:thefirststepistoextractcomponentmodesandthesecondstepistocreatethedatabasefile.Theyarediscussedinthefollowingparagraphs.Beforestartingtorunthetwosteps,thesystemmodelshouldbedividedintomanysuper-elements.流程图无。工具描述ToolDescription仿真分析过程中需要用到的如下软件:Thefollowingsoftwarefacilitatestheanalyticalsimulationprocess:前处理(Preprocessors):Hypermesh求解器(AnalysisCode):Nastran后处理(Postprocessors):HyperView建模和分析过程Modeling/AnalysisProcedure单位Units分析中所用单位制如下所示:Theunitsusedintheanalysisareasfollows:力(Force) 牛顿(N)质量(Mass) 吨(Ton)长度(Length) 毫米(mm)时间(Time) 秒(Second)内容Contents无。坐标系CoordinateSystems无。建模技巧ModelingTechniques超单元划分Super-elementPartition整车模型要基于如下因素进行超单元的划分：不同子系统、零部件模型规模、设计变更需求、计算机资源和运行时间。按照子系统划分超单元，通常只需要很少的连接点，而且也便于分部门管理。零部件模型规模也是超单元划分的一个因素，例如内饰车身（包括座椅、仪表板、前端模块）可以当作一个超单元，如果仪表板和座椅模型规模较大，也可以分成四个（白车身、前端模块、仪表板和座椅等）。默认一个超单元对应的模型节点数不超过十万。设计变更频繁的也要考虑建立超单元，例如车架后端改变频繁，就要考虑将车架后端分开建超单元，甚至整个车架要建个超单元。在分析中划分和使用超单元的坏处是需要额外的时间与精力来做这个事情。同时，使用超单元将使模型结构变得更加复杂，从而导致与之相关的错误。例如，如果一个刚体单元跨过两个超单元会产生依赖错误。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.超单元模型缩减Super-elementModelReduction第一步超单元/模态综合法第一步是为每个超单元提取合适的模态数（实模态、边界模态、残余模态等）。涉及到如下NASTRAN卡片：SESET：定义超单元节点。注意如果节点不包含在SESET中，则默认在残余的超单元中；SPOINT和SEQSET：定义部件模态缩减中保留模态的数目，必须等于或大于计算的模态数目；EIGRL：特征值提取。当进行自由模态计算时，要设定一个小的起始频率值，以排除刚体模态。提取的模态频率应两倍或三倍于扫频范围；SECSET：设置连接节点以获取自由边界条件。NASTRAN默认在进行特征值和特征向量提取时，固定所有的连接节点；SET和SEUSET1：所有连接节点、显示节点（PLOTEL单元节点）、激励节点和响应节点；在15.1的例子中包含了第一步的分析卡片。货车车箱被定义为超单元500，连接节点是螺栓。固定边界用于提取特征值，所以没有SECSET卡片。部件模态缩减的保留模态频率至100Hz。第二步超单元/模态综合法第二步是基于第一步生成的OUTPUT2文件来创建一个缩减超单元。需要准备如下卡片：SESET：同第一步SPOINT和SEQSET：同第一步GRID：所有连接节点、显示节点（PLOTEL单元节点）、激励节点和响应节点；PLOTEL：上述所有节点。每个连接节点用PLOTEL单元连起来；CSUPEXT：定义超单元与外部连接节点；见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.模态分析NormalModesAnalysis完成第一步和第二步后，直接对模型进行模态分析。首先在NASTRAN文件的执行部分用DBLOCATE/ASSIGN来添加每个超单元的数据；其次在SUBCASE中增加对每个超单元的控制；最后所有在第二步生成的超单元卡片要包含在NASTRAN文件的数据部分。见15.3中例子，该例子省略了部分内容。Afterthecompletionofbothsteponeandsteptwoforeachsuper-elementcomponent,normalmodeanalysisforthesystemmodelisstraightforward.First,DBLOCATE/ASSIGNstatementsneedtobeaddedtotheexecutivefilesectiontoincludethedatabaseforeachsuper-element.Second,aSUBCASEisaddedtothecasecontrolsectionforeachsuper-element.Finally,allsuper-elementcardsusedinthesteptwoshouldbeincludedinthebulk-datafilesectionforeachsuper-element.Asampledecktorunthesystemmodelcontainingsuper-element/CMScomponentsisincludedinExample13.3.Tosavespacemostofthecardsnotspecificallyrelatedtosuper-elementareomitted.假设和限制Assumptions/Limitations无。载荷和边界条件Loads/BoundaryConditions无。结果Results无。性能要求PerformanceRequirements无。分析要求ANALYSISREQUIREMENTS无。参考文件DOCUMENTATION无。联系人CONTACTS无。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.