弹性力学基础及有限元法-12.ppt

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1、内蒙古科技大学机械工程学院刘学杰2015-05动力学问题的有限元法，动态分析FEM&ANSYS-12有限元法及实践-12FiniteElementMethod(FEM)&thePracticeOutline概要1.Review回顾2.有限元法:动力学问题3.动态分析实例—模态分析Review回顾：1学习报告：13组-王炎2静态分析小结1）平面问题：三节点单元、四节点单元……2)空间问题3)案例动力学方程：与静态有什么不同？Elementalvolume位移/displacementsu,v,w应变/strains应力/stressNot-steadyl

2、oadsanymore动力学方程：与静态有什么不同？1.质量矩阵及阻尼矩阵动力学方程质量矩阵及阻尼矩阵特征值问题纽马克法动力响应和逐步积分法纽马克法综合纽马克法计算步骤1）初始计算（1）形成刚度矩阵K、质量矩阵M、组逆矩阵C（2）获得初始值（3）选择步长参数和，并计算下列有关常数（4）形成“刚度”矩阵（5）分解矩阵2）对于每个时间步长进行下列计算（1）计算时刻的“载荷”矢量（2）解矩阵方程求时刻的位移（3）计算时刻的加速度、速度综合纽马克法计算步骤Whatisamodalanalysis?Amodalanalysisisusedtodeterminethe

3、naturalfrequenciesandmodeshapesofastructure.Thenaturalfrequenciesandmodeshapesareimportantparametersinthedesignofastructurefordynamicloadingconditions.ThenaturalfrequenciesandmodeshapesarealsorequiredifyouwanttodoaspectrumanalysisoraHarmonicResponseAnalysisortransientanalysis.What

4、isamodalanalysis?Theequationforastaticanalysis:Theequationforadynamicanalysis:Theequationforamodalanalysis:TheprocedureforamodalanalysisTheprocedureforamodalanalysisconsistsoffourmainsteps:Buildthemodel.Applyloadsandobtainthesolution.Expandthemodes.Reviewtheresults.BuildtheModelWh

5、enbuildingyourmodel,rememberthesepoints:1.Onlylinearbehaviorisvalidinamodalanalysis.Ifyouspecifynonlinearelements,theyaretreatedaslinear.Forexample,ifyouincludeacontactelement,itsstiffnessarecalculatedbasedonitsinitialstatusandneverchange.2.Materialpropertiescanbelinear,isotropico

6、rorthotropic,andconstantortemperature-dependent.YoumustdefinebothYoung'smodulus(EX)(orstiffnessinsomeform)anddensity(DENS)(ormassinsomeform)foramodalanalysis.Nonlinearpropertiesareignored.Ifapplyingelementdamping,youmustdefinetherequiredrealconstantsforthespecificelementtype(COMBI

7、N7,COMBIN14,COMBIN37,andsoon).ApplyingLoadsandObtaintheSolutionDefineAnalysisTypeandOptionsOption1:NewAnalysisOption2:AnalysisType:ModalOption3:Mode-ExtractionMethod(Chooseoneoftheextractionmethodslistedbelow).1.BlockLanczosmethod(default)2.Subspacemethod3.PowerDynamicsmethod4.Red

8、uced(Householder)method5.Unsymmet