Ansys培训_随机振动分析.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 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 ifalreadyinSimulationuse File NewFortrainingpurposes choose No donotsaveanyitems OnceinSimulationclickon Geometry FromFile tobrowseforandopengirder agdb Workshop 设置 WhentheGeometryhasloaded choose RandomVibration fromtheMapofAnalysisTypesNote themapwillautomaticallyhighlight Modal toosincemodalisaprecursortoRandomVibrationsimulation ClickOK thusacceptingthedefaultnumberofmodesChoosetheU S inchpoundunitsystem Units U 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 Clickon Connections CreateAutomaticContactTheDefaultdefinitionis Bonded 6 Workshop 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 SelectAllButthenholdandLMBsingleselectonthe roofbody tounselectthatpartfromthisSizeobject Apply Insert Sizing forthelarge roof body Enter 4 forsizeinDetails forthelargetopplate UseSingleSelectandLMBonthelargeBody ApplyPreviewthemesh Mesh GenerateMeshIfdesired repeatthestepsabovetoincreaseordecreaseelementsizesasdesiredtoenhancethemodelorreduceCPUtime LargerElementsonroof 7 8 9 10 Workshop 环境 Fortheloweredgesofthetruss highlightthe Modal branchintheOutlineand Insert FixedSupports SwitchtoedgeselectionmodeasnecessaryReorientmodelasnecessarythroughout anendviewmightbemostconvenient SwitchtoBoxSelectDragtheLMBtoselecttheedgesatthebottomofthelowergirders Click Apply intheDetailswindow 11 12 13 Workshop 环境 ForthePSDBaseExcitationloads attheRandomVibrationBranch Insert PSDBaseExcitationIntheDetailsofthePSDLoad change Direction to YAxis forthisparticularXYZorientation For LoadDatachose NewPSDLoad 14 15 16 Workshop PSD载荷 PDSdatainthiscaseis Acceleration Tabledatapoints soinsurethat PSDAcceleration and Table isselected Clickon OKThenenterthetabledataforFREQvs Acceleration Thegraphautomaticallyupdateswitheachdatapoint Eventually clickonthe Simulationtab attheverytop toexit EngineeringData andreturnSimulationmode 17 18 Workshop 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 19 Workshop 模态分析结果 Afterthesolutioniscompletedyoucanreviewthe precursor modalshapesforeachfrequency IntheOutlineTreepertainingtoModal clickonSolution withintheModalbranch ClickontheModalSolutionBranchintheTree ThenLMBonthetopoftheFrequencyColumninthe TabularData region and RMB CreateModeShapeResultsThiswillinsert TotalDeformation objectsintheTreeforallmodessolved ClickonClickon Solve toolbarbuttonsothenew result objectscanbeevaluated 20 Workshop 随机振动分析结果 NowreviewRandomVibrationresults Duetotheappliedspectrum youcan InsertDeformationsStrainsStresses Insert Deformation DirectionalSpecifytheZ Orientation directionintheDetailsPane Insert Strain NormalForinstance specifyY Orientation intheDetailsPane Insert Stress Equival