Ansys培训_随机振动分析课件.ppt

欢迎进入ANSYS技培训第五天,随机振动(PSD)分析,主要内容,定义和目的Workbench随机振动分析功能分析流程,随机振动分析定义和目的,什么是随机振动分析基于概率的谱分析.典型应用如火箭发射时结构承受的载荷谱，每次发射的谱不同，但统计规律相同.,Reference:RandomvibrationsinmechanicalsystemsbyCrandall&Mark,和确定性谱分析不同，随机振动不能用瞬态动力学分析代替.应用基于概率的功率谱密度分析，分析载荷作用过程中的统计规律,Imagefrom“RandomVibrationsTheoryandPractice”byWirsching,PaezandOrtiz.,随机振动分析定义和目的,什么是PSD?PSD是激励和响应的方差随频率的变化。PSD曲线围成的面积是响应的方差.PSD的单位是方差/Hz(如加速度功率谱的单位是G2/Hz).PSD可以是位移、速度、加速度、力或压力.,随机振动分析定义和目的,输入:结构的自然频率和阵型功率谱密度曲线输出:1s位移和应力（用于疲劳分析）.,随机振动分析定义和目的,载荷:单点激励得到结果:相对或绝对的1s输出整体结构的结果，可以进行云图显示.1s位移,速度或加速度后处理:1s可以进行云图显示.,随机振动分析Workbench随机振动功能,Model:输电铁架Analysis:地面激励PSD分析.Steps:进行模态和随机振动分析，并显示结果.,随机振动分析随机振动分析流程,打开,Tower.dsdb.,Browsetofileifnotinlist,随机振动分析随机振动分析流程,打开分析向导,随机振动分析随机振动分析流程,利用分析向导可以简单地建立分析流程.可以看到运行随机振动分析之前需要进行模态分析.,随机振动分析随机振动分析流程,点击OK可以看到如图所示信息当提示“SpecifyNumberofModes”，输入12,随机振动分析随机振动分析流程,下一步是插入约束，插入fixedsupport.,随机振动分析随机振动分析流程,模态分析结束.可以查看模态结果，如右图所示.可以查看动画.,随机振动分析随机振动分析流程,可以看到在谱分析中的初始条件已经自动设置成模态分析的结果.设置阻尼（恒定阻尼比）0.05,随机振动分析随机振动分析流程,插入一个PSDBaseExcitation.在弹出的PSDBaseExcitation详情串口，选择新的PSD载荷.选择带G的加速度PSD，单位G2/Hz.设置PSD曲线,随机振动分析随机振动分析流程,选择激励方向为Y.选择Solve.求解结束后可以查看结果，可以选择1sigma到3sigma结果.,随机振动分析随机振动分析流程,2019/12/14,19,可编辑,如果列出了结果更改阻尼比为0.05，查看结果.,随机振动分析随机振动分析流程,按阻尼比0.05重新计算.,随机振动分析随机振动分析流程,练习,查看如图所示桁架结构在加速度PSD激励下的响应,Workshop目标,目标是研究桁架结构的振动特性.这个练习将检查钢结构桁架由于加速度谱产生的位移和应力.PSD谱可分为加速度、速度和位移.Thespectrumwilltypicallybemeasuredduringphysicaltestsordocumentedinawrittenspecificationrelatingtothesystemorcomponent.ThedatapointscanbeenteredforeachFreq&Amplitude,orafunctioncanbeentered.,Workshop假定,TheGirderhasfixedconstraintsalongallloweredges.Theboundaryconditionswillbeappliedtoedges.,Workshop起始页,FromtheWorkBenchProjectLauncherstartSimulation.ifalreadyinSimulationuseFileNewFortrainingpurposes,choose“No:donotsaveanyitems”OnceinSimulationclickonGeometryFromFiletobrowseforandopengirder.agdb,Workshop设置,WhentheGeometryhasloaded,choose“RandomVibration”fromtheMapofAnalysisTypesNote,themapwillautomaticallyhighlight“Modal”toosincemodalisaprecursortoRandomVibrationsimulation.ClickOK,thusacceptingthedefaultnumberofmodesChoosetheU.S.inchpoundunitsystem.“UnitsU.S.Customary(in,lbm,lbf,)”,1,2,3,Workshop前处理-壳体厚度,TheGirdergeometryconsistsofsurfacebodies(forshellmeshing)Thefirstpreprocessingtaskistospecifythethicknessofallthesurfaces.ClicktofullyexpandtheGirder“Geometry”branch.IntheDetailspane,noticethatthe“Thickness”fieldaredisplayedinyellowtoindicatetheyareundefined.SelectallthebodiestoassignauniformthicknessLMBtoselectthetopBodyinthePartlist.HoldandLMBonthelastSurfaceBody.Note:Byhighlighting“all”,wecansetthethicknessonthefirstone,andthesamethicknessgetsassignedtoallofthem.Ofcourseoneormoreindividualbodiescanberedefinedtodifferentthicknesseslaterifnecessary.Leftclickinthethicknessfieldandsetthethickness=0.5”,5,4,Workshop前处理-接触,Theassemblytobeshellmeshedconsistsofmultiplesurfacebodiesseparatedbysmalloffsetsthataccountforthephysicalspacingbetweentheneutral(axis)planesofeachpieceofsteel.Weneedtouse“Bonded”Contactinordertosimulatetheeffectofweldedand/orboltedassemblyconnectivity.ClickonConnectionsCreateAutomaticContactTheDefaultdefinitionis“Bonded”,6,Workshop前处理-网格尺寸,TheassemblyconsistsofmultipleslenderbodiesplusalargeflatRoofplate.Wewanttospecifyarelativelyfinemeshsizeontheslendermembersbutalargerelementuptop.Byassigninglargerelementsonthelargeroof,wepreserveCPUtimeandareabletousefiner(usuallymoreaccurate)elementselsewhere.ChangetoBodySelect.OntheOutlineTree,RMBontheMeshobjectInsertSizing(forslenderbodies)InDetails,Replace“Default”sizewith2(inches)RMBinGraphicsWindow,SelectAllButthenholdandLMBsingleselectonthe“roofbody”tounselectthatpartfromthisSizeobject.ApplyInsertSizing(forthelarge“roof”body)Enter“4”forsizeinDetails(forthelargetopplate).UseSingleSelectandLMBonthelargeBody.ApplyPreviewthemesh,MeshGenerateMeshIfdesired,repeatthestepsabovetoincreaseordecreaseelementsizesasdesiredtoenhancethemodelorreduceCPUtime.,LargerElementsonroof,7,8,9,10,Workshop环境,Fortheloweredgesofthetruss,highlightthe“Modal”branchintheOutlineandInsertFixedSupports.SwitchtoedgeselectionmodeasnecessaryReorientmodelasnecessarythroughout.anendviewmightbemostconvenient.SwitchtoBoxSelectDragtheLMBtoselecttheedgesatthebottomofthelowergirders.Click“Apply”intheDetailswindow,11,12,13,Workshop环境,ForthePSDBaseExcitationloads,attheRandomVibrationBranch,InsertPSDBaseExcitationIntheDetailsofthePSDLoad,change“Direction”to“YAxis”forthisparticularXYZorientation.ForLoadDatachoseNewPSDLoad,14,15,16,WorkshopPSD载荷,PDSdatainthiscaseis“Acceleration”Tabledatapoints,soinsurethat“PSDAcceleration”and“Table”isselected.ClickonOKThenenterthetabledataforFREQvs.Acceleration.Thegraphautomaticallyupdateswitheachdatapoint.Eventually,clickontheSimulationtab(attheverytop)toexit“EngineeringData”andreturnSimulationmode.,17,18,Workshop求解,InsurethattheDetails“InitialCondition”fortheRandomVibrationobjectis“Modal”WiththebranchesforModal(aswellasRandomVibration)prepared,wearereadytosolvethissimulation.Asafinalcheckverifythestatussymbolsnexttothebranches.Allbranchesshouldhaveeither:Lighteningbolt(ready)Greencheckmark(complete)Solve.ToolBarButtonSolveNote:solvingfromtheToolbar“thunderbolt”causesallunsolvedbranchestobesolved.Hadwewishedtosolveonlyonebranch(suchas“Modal”inthiscase)wecouldhavehighlightedonlythebranchorobjecttobesolvedanduseRMBSolve.,19,Workshop模态分析结果,Afterthesolutioniscompletedyoucanreviewthe(precursor)modalshapesforeachfrequency.IntheOutlineTreepertainingtoModal,clickonSolution(withintheModalbranch)ClickontheModalSolutionBranchintheTree.ThenLMBonthetopoftheFrequencyColumninthe“TabularData”region,andRMBCreateModeShapeResultsThiswillinsert“TotalDeformation”objectsintheTreeforallmodessolved.ClickonClickon“Solve”toolbarbuttonsothenew“result”objectscanbeevaluated,20,Workshop随机振动分析结果,NowreviewRandomVibrationresults.Duetotheappliedspectrum,youcanInsertDeformationsStrainsStressesInsertDeformationDirectionalSpecifytheZ“Orientation”directionintheDetailsPaneInsertStrainNormalForinstance,specifyY“Orientation”intheDetailsPaneInsertStressEquivalent(vonMises)Cli