Ansys培训-随机振动分析

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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G^2/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AccelerationFrequencyF1F2F3F4A2A3A4A1Workshop–假定TheGirderhasfixedconstraintsalongallloweredges.Theboundaryconditionswillbeappliedtoedges.Workshop–起始页FromtheWorkBenchProjectLauncherstartSimulation.ifalreadyinSimulationuse>File>NewFortrainingpurposes,choose“No:donotsaveanyitems”OnceinSimulationclickon>Geometry>FromFile…tobrowseforandopengirder.agdbWorkshop–设置WhentheGeometryhasloaded,choose“RandomVibration”fromtheMapofAnalysisTypesNote,themapwillautomaticallyhighlight“Modal”toosincemodalisaprecursortoRandomVibrationsimulation.ClickOK,thusacceptingthedefaultnumberofmodesChoosetheU.S.inchpoundunitsystem.“Units>U.S.Customary(in,lbm,lbf,…)”123Workshop–前处理-壳体厚度TheGirdergeometryconsistsofsurfacebodies(forshellmeshing)Thefirstpreprocessingtaskistospecifythethicknessofallthesurfaces.ClicktofullyexpandtheGirder“Geometry”branch.IntheDetailspane,noticethatthe“Thickness”fieldaredisplayedinyellowtoindicatetheyareundefined.SelectallthebodiestoassignauniformthicknessLMBtoselectthetopBodyinthePartlist.Hold<shift>andLMBonthelastSurfaceBody.Note:Byhighlighting“all”,wecansetthethicknessonthefirstone,andthesamethicknessgetsassignedtoallofthem.Ofcourseoneormoreindividualbodiescanberedefinedtodifferentthicknesseslaterifnecessary.Leftclickinthethicknessfieldandsetthethickness=0.5”54Workshop–前处理-接触Theassemblytobeshellmeshedconsistsofmultiplesurfacebodiesseparatedbysmalloffsetsthataccountforthephysicalspacingbetweentheneutral(axis)planesofeachpieceofsteel.Weneedtouse“Bonded”Contactinordertosimulatetheeffectofweldedand/orboltedassemblyconnectivity.Clickon>Connections>CreateAutomaticContactTheDefaultdefinitionis“Bonded”6Workshop–前处理-网格尺寸TheassemblyconsistsofmultipleslenderbodiesplusalargeflatRoofplate.Wewanttospecifyarelativelyfinemeshsizeontheslendermembersbutalargerelementuptop.Byassigninglargerelementsonthelargeroof,wepreserveCPUtimeandareabletousefiner(usuallymoreaccurate)elementselsewhere.ChangetoBodySelect.OntheOutlineTree,RMBontheMeshobject>Insert>Sizing(forslenderbodies)InDetails,Replace“Default”sizewith2(inches)RMBinGraphicsWindow,>SelectAllButthenhold<CTRL>andLMBsingleselectonthe“roofbody”tounselectthatpartfromthisSizeobject.>Apply>Insert>Sizing(forthelarge“roof”body)Enter“4”forsizeinDetails(forthelargetopplate).UseSingleSelectandLMBonthelargeBody.>ApplyPreviewthemesh,>Mesh>GenerateMeshIfdesired,repeatthestepsabovetoincreaseordecreaseelementsizesasdesiredtoenhancethemodelorreduceCPUtime.LargerElementsonroof78,910Workshop–环境Fortheloweredgesofthetruss,highlightthe“Modal”branchintheOutlineand >Insert>FixedSupports.SwitchtoedgeselectionmodeasnecessaryReorientmodelasnecessarythroughout.anendviewmightbemostconvenient.SwitchtoBoxSelectDragtheLMBtoselecttheedgesatthebottomofthelowergirders.Click“Apply”intheDetailswindow111213Workshop–环境ForthePSDBaseExcitationloads,attheRandomVibrationBranch,>Insert>PSDBaseExcitationIntheDetailsofthePSDLoad,change“Direction”to“YAxis”forthisparticularXYZorientation.For>LoadDatachose>NewPSDLoad141516AccelerationFrequencyF1F2F3F4A2A3A4A1Workshop–PSD载荷PDSdatainthiscaseis“Acceleration”Tabledatapoints,soinsurethat“PSDAcceleration”and“Table”isselected.Clickon>OKThenenterthetabledatafor FREQvs.Acceleration.Thegraphautomaticallyupdateswitheachdatapoint.Eventually,clickonthe>Simulationtab(attheverytop)toexit“EngineeringData”andreturnSimulationmode.1718Workshop–求解InsurethattheDetails“InitialCondition”fortheRandomVibrationobjectis“Modal”WiththebranchesforModal(aswellasRandomVibration)prepared,wearereadytosolvethissimulation.Asafinalcheckverifythestatussymbolsnexttothebranches.Allbranchesshouldhaveeither:Lighteningbolt(ready)Greencheckmark(complete)Solve.ToolBarButton>SolveNote:solvingfromtheToolbar“thunderbolt”causesallunsolvedbranchestobesolved.Hadwewishedtosolveonlyonebranch(suchas“Modal”inthiscase)wecouldhavehighlightedonlythebranchorobjecttobesolvedanduseRMB>Solve.19Workshop–模态分析结果Afterthesolutioniscompletedyoucanreviewthe(precursor)modalshapesforeachfrequency.IntheOutlineTreepertainingtoModal,clickonSolution(withintheModalbranch)ClickontheModalSolutionBranchintheTree.ThenLMBonthetopoftheFrequencyColumninthe“TabularData”region,and>RMB>CreateModeShapeResultsThiswill