CAD_CAM技术_第八章.CAE分析.ppt

LS-DYNA Overview,计算机辅助工程分析,C A E,1,前言,有限单元法又称有限元素法,(Finite Element Method FEM),，是计算力学中的一种重要的方法，它是,20,世纪,50,年代末,60,年代初兴起的,应用数学、现代力学及计算机科学,相互渗透、综合利用的边缘科学，是现代科学和工程计算方面最令人鼓舞的重大成就之一。,有限元法最初应用在工程科学技术中，它是一种数学物理方法，用于模拟并且解决工程力学、热学、电磁学等物理问题。它作为一个具有理论基础和广泛应用效力的数值分析方法，,可以求解过去用解析方法无法求解的问题，对于边界条件和结构形状都不规则的复杂问题，,有限元方法是一种有效的现代分析方法。,1,前言,1.1,有限元法的产生,有限元思想并非现代社会的产物，早在公元,3,世纪，我国古代数学家,刘徽,就提出,用割圆术求圆周长,的方法，即用有限个正多边形逼近圆周，边数越多，周长与直径的比值就越接近一个常数。这就是有限元思想的萌芽。,1.2,有限元法的基本理论,有限元法的基本思想是：,先将研究对象的连续求解区域离散为一组有限个、且按一定方式相互联结在一起的单元组合体。,然后对单元（小区域）进行力学分析。,最后再整体分析。,这种化整为零，集零为整的方法就是有限元的基本思路。,真实系统,有限元模型,有限元模型,是真实系统理想化的数学抽象,1.3,有限元法的应用实例,有限元模型由一些简单形状的单元组成，单元间通过节点连接，并承受一定载荷,节点,:,空间中的坐标位置，具有一定自由度和存在相互物理作用,单元,:,一组节点自由度间相互作用的数值矩阵描述（称,刚度或系数矩阵,),单元有,线,、,面,或,实体,以及二维或三维的单元等种类,载荷,约束：,就是消灭自由度！？,机械,CAD/CAM,技术,1.3,有限元法的应用实例,1.3,有限元法的应用实例,静态分析,实例,1,板的静力分析,.,avi,实例,2,角架的静力分析,.,avi,实例,33D,基本范例,.,avi,实例,4,梁的自然振动分析,.,avi,实例,5,板的屈曲分析,.,avi,1.3,有限元法的应用实例,手机跌落分析,商务通、移动电话跌落分析,1.3,有限元法的应用实例,机床振动有限元分析,1.3,有限元法的应用实例,金属板料成形数值模拟,注塑成形数值模拟,1.3,有限元法的应用实例,制造过程的模拟,深拉,液压成形,超弹成形,轧制,挤压,冲压,加工,钻,所有的这些成形过程可以利用,LS-DYNA,程序的质量缩放和变化工具速度功能来模拟,1.3,有限元法的应用实例,所有汽车工业的碰撞,轿车,卡车,公共汽车,火车,轮船,航行器,1.3,有限元法的应用实例,接触/碰撞,跌落试验,摆锤碰撞试验,喷气发动机扇片的包容性分析,1.3,有限元法的应用实例,金属挤压成型：温度分布和变化,齿轮滚动接触应力分析,轧制,注塑成形,1.3,有限元法的应用实例,超音速导弹飞行,轿车后悬架弹簧支座冲压过程,反潜鱼雷入水,潜射导弹,穿甲碎片,水下爆炸对舰船冲击,1.3,有限元法的应用实例,LIVERMORE,SOFTWARE,TECHNOLOGY,CORPORATION,ENGINEERING TECHNOLOGY ASSOCIATES,LS-DYNA,Overview,Ls-,dyna,求解器,得出,d3plot,文件,模型建立,网格划分,属性定义,接触设置,边界条件,结果分析,模拟动画,前处理,计算,后处理,有限元分析流程,有限元分析流程,前处理,有限元法的前处理,有限元前处理包括,：,模型建立、网格划分、单元属性定义、材料属性定义、确定载荷类型、设置接触条件和边界条件、,网格划分单元非常重要，有限元分析的精度取决于网格划分的密度,太密会大大增加计算时间，计算精度却不会成比例地提高，通常采取将网格在高应力区局部加密的办法,有限元法分析计算时，依据分析对象不同，采用的,单元类型,也不同。分析对象划分成什么样的单元，要根据结构本身的,形状特点,，,综合载荷,、,约束,等情况全面考虑而定，所选单元类型应能逼近实际受力状态，单元形状应能接近实际边界轮廓,有限元分析流程,单元类型,经常采用的单元,：,线单元,壳单元,二维实体单元,三维实体单元,线单元,:,梁单元,：用于螺栓，薄壁管件，,C,型截面构件，角钢或细长薄膜构件（只需膜应力和弯应力的情况）等模型,杆单元：,用于弹簧、螺杆、预应力螺杆和薄膜桁架等模型,弹簧单元：,用于弹簧螺杆、或细长构件，或通过刚度等效替代复杂结构等模型,有限元分析流程,经常采用的单元,：,线单元,壳单元,二维实体单元,三维实体单元,壳单元用于薄板或曲面模型,壳单元分析应用基本原则：每块面板的主尺寸不低于其厚度的十倍,有限元分析流程,单元类型,经常采用的单元,：,线单元,壳单元,二维实体单元,三维实体单元,二维实体单元用于模拟实体截面,需在整体笛卡尔,X-Y,平面内建立模型,所有的荷载均作用在,X-Y,平面内，并且其响应（位移）也在,X-Y,平面内,Y,X,Z,有限元分析流程,单元类型,经常采用的单元,：,线单元,壳单元,二维实体单元,三维实体单元,由于几何、材料、荷载或分析要求考虑细节等原因造成无法采用更简单单元进行建模的结构分析,或从三维,CAD,系统转化过来的几何模型转成二维或壳体需要花费大量的时间和精力的情况,有限元分析流程,单元类型,Beam Element Formulation,-Hughes-Liu with cross section integration(default),-,Belytschko-Schwer,Resultant Beam,-Truss and Spotweld Beam,-Belytschko-Schwer full cross section integration,-Belytschko-Schwer Tubular Beam with cross section integration,-Discrete Beam/Cable,-2D plane Strain Shell Beam,-2D Axisymmetric Shell Element,Shell Element Formulation,-Hughes-Liu,-,Belytschko-Tsay,(default),-BCIZ Triangular Shell,-,Belytschko-Tsay,Membrane,-S/R Hughes-Liu,-S/R Co-rotational Hughes-Liu,-,Belytschko,-Leviathan Shell,-Fully Integrated,Belytschko-Tsay,Membrane,-,Belytschko,-Wong-Chiang,Solid Element Formulation,-,Constant Stress Solid(default),-Fully Integrated S/R Solid,-Fully Integrated 8 Nodes Solid with Nodal Rotations,Thick Shell Element Formulation,Discrete(spring/damper),Seatbelt&Mass Element Formulations,Element Formulations,-,在立体单元中存在,24,种变形模式,（,In a solid elements there are 24 deformation modes including:,）,6 rigid body modes,12 hourglass modes,6 non-zero energy modes,-,控制零能模式有多种方法：增加材料刚度或增加粘性以增加抵抗变形的力,（,The control of the zero energy modes is accomplished by adding either viscous or stiffness based forces to resist the formation of these modes in order to keep them from corrupting the solution.,）,-,控制沙漏系数为,0.050.12(,默认为,0.1),更大的值又会产生不稳定,（,Use hourglass parameters between.05 and.12 since higher values can cause instabilities(default=0.10).,）,Element Formulations/Solid,-,在立体单元中存在,24,种变形模式,（,In a solid elements there are 24 deformation modes including:,）,6 rigid body modes,12 hourglass modes,6 non-zero energy modes,-,控制零能模式有多种方法：增加材料刚度或增加粘性以增加抵抗变形的力,（,The control of the zero energy modes is accomplished by adding either viscous or stiffness based forces to resist the formation of these modes in order to keep them from corrupting the solution.,）,-,控制沙漏系数为,0.050.12(,默认为,0.1),更大的值又会产生不稳定,（,Use hourglass parameters between.05 and.12 since higher values can cause instabilities(default=0.10).,）,Element Formulations/Solid,LS-DYNA,包括有大量的材料模型，几乎对所有应用都有对应的材料,相对于隐式分析,LS-DYNA,提供了相当大的材料库,LS-DYNA,提供了,implicit,中不具备的特性,:,应变率相关塑性模型,温度敏感塑性材料,应力和应变失效准则模型,空材料,状态方程模型,有限元分析流程,材料类型,Linear Elastic,Isotropic(with Fluid Option),Orthotropic,Anisotropic,Plasticity,Rate Independent(2),Rate Sensitive(8),Composite Damage,Concrete,Other,Rigid bodies,Cables,Fluid,Nonlinear Elastic,Blatz-Ko,Rubber,Mooney-,Rivlin,Rubber,Viscoelastic,Foam,Isotropic(4),Orthotropic,Equation of State,Temp.&strain rate dependent plasticity,Null materials,有限元分析流程,材料类型,LS-DYNA vs.970,包括有,140,多种材料模型,（,comprehend 140+Material Models,）,涉及的材料类型有,（,material models implemented are:,）,弹性,（,Elastic(orthotropic elastic,elastic with viscosity,),）,弹塑性,（,Elastoplastic,(isotropic or anisotropic plasticity,piecewise linear isotropic plasticity,temperature and rate dependent plasticity,),）,刚性,（,Rigid,）,橡胶,(Rubber),泡沫,（,Foam(viscous,crushable,),）,蜂窝铝,（,Honeycomb,）,纤维,（,Fabric,）,其他,（,Others(,polymeer,composite,concrete,soil,ceramic,),）,Material Models,*,MAT,LS-DYNA has historically referenced materials by type identifiers.Below these,identifiers are given with the corresponding keyword name.The numbers in brackets identify the,element formulations for which the material model is implemented:,TYPE 1:*MAT_ELASTIC 0,1H,1B,1I,1T,2,3,TYPE 2:*MAT_ORTHOTROPIC_ELASTIC 0,2,3,TYPE 3:*MAT_PLASTIC_KINEMATIC 0,1H,1I,1T,2,3,TYPE 4:*MAT_ELASTIC_PLASTIC_THERMAL 0,2,3,TYPE 5:*MAT_SOIL_AND_FOAM 0,TYPE 6:*MAT_VISCOELASTIC 0,1H,TYPE 7:*MAT_BLATZ-KO_RUBBER 0,2,TYPE 8:*MAT_HIGH_EXPLOSIVE_BURN 0,TYPE 9:*MAT_NULL 0,1,2,TYPE 10:*MAT_ELASTIC_PLASTIC_HYDRO 0,TYPE.,0-Solids,1H-Hughes-Liu beam,1B-,Belytschko,resultant beam,1I-,Belytschko,integrated solid and tubular beams,1T-Truss,1D-Discrete beam,1SW-,Spotweld,beam,2-Shells,3-Thick shells.,4-Special airbag element.,Material Models,Material Models/Plastic Behavior,Under,uniaxial,tensile loading,the following phases can be observed,Elastic,Yield,Plastic Hardening,Necking,Rupture,hardening,rupture,onset of necking,Material Models/Plastic Behavior,Conveniently neglects work hardening,Material Models/Plastic Behavior,Stress-strain curve is approximated using two straight lines,Youngs Modulus and Tangent Modulus,AIRBAG_SINGLE_SURFACE,AUTOMATIC_GENERAL,AUTOMATIC_NODES_TO_SURFACE,AUTOMATIC_ONE_WAY_SURFACE_TO_SURFACE,AUTOMATIC_SINGLE_SURFACE,AUTOMATIC_SURFACE_TO_SURFACE,CONSTRAINT_NODES_TO_SURFACE,CONSTRAINT_SURFACE_TO_SURFACE,DRAWBEAD,ERODING_NODES_TO_SURFACE,ERODING_SINGLE_SURFACE,ERODING_SURFACE_TO_SURFACE,FORCE_TRANSDUCER_CONSTRAINT,FORCE_TRANSDUCER_PENALTY,FORMING_NODES_TO_SURFACE,FORMING_ONE_WAY_SURFACE_TO_SURFACE,FORMING_SURFACE_TO_SURFACE,NODES_TO_SURFACE,ONE_WAY_SURFACE_TO_SURFACE,RIGID_NODES_TO_RIGID_BODY,RIGID_BODY_ONE_WA,Y_,TO_RIGID_BODY,RIGID_BODY_TWO_WA,Y_,TO_RIGID_BODY,SINGLE_EDGE,SINGLE_SURFACE,SLIDING_ONLY,SLIDING_ONLY_PENALTY,SURFACE_TO_SURFACE,TIEBREAK_NODES_TO_SURFACE,TIEBREAK_SURFACE_TO_SURFACE,TIED_NODES_TO_SURFACE,TIED_SHELL_EDGE_TO_SURFACE,TIED_SURFACE_TO_SURFACE,TIED_SURFACE_TO_SURFACE_FAILURE,*,CONTACT_,有限元分析流程,接触设置,Surface-to-Surface(S2S):,SURFACE_TO_SURFACE Type 3,AUTOMATIC _SURFACE_TO_SURFACE Type a3,FORMING_SURFACE_TO_SURFACE Type m3,CONSTRAINT_SURFACE_TO_SURFACEType 17,ERODING_SURFACE_TO_SURFACEType 14,接触力只是在压缩的时候，而拉伸的时候没有,（,Compression only-tension is not carried,）,滑移通过摩擦在反映,（,Sliding can be resisted by friction,）,完全对称，主从面的选择是任意的,（,Fully symmetric,choice of slave and master surface arbitrary,）,除了,AUTOMATIC,类型，需要考虑接触面的方向,（,Orientation is necessary except for AUTOMATIC_ type,）,Contact/Surface-to-Surface(S2S),Nodes-to-Surface(N2S):,NODES_TO_SURFACE Type 5,AUTOMATIC _NODES_TO_SURFACE Type a5,FORMING_NODES_TO_SURFACE Type m5,CONSTRAINT_NODES_TO_SURFACEType 18,ERODING_NODES_TO_SURFACEType 16,从面是用节点（集）来定义的,（,Slave side is defined by individual nodes instead of segments,）,不是对称的，主从面的选择不是任意的,（,Not-symmetric,choice of slave and master surface not arbitrary,）,通常，网格粗糙的一边应该定义成主面,（,Generally,the coarser side should be the master surface,）,点对面的接触是效率非常快,（,Nodes-to-surface contact is computationally efficient,）,特别适合于点对刚性体的接触,（,Especially suited to nodes contacting rigid bodies,）,Contact/Nodes-to-Surface(N2S),Single Surface:,AIRBAG_SINGLE_SURFACE Type a13,AUTOMATIC_GENERALType 26,AUTOMATIC_SINGLE_SURFACEType 13,ERODING_SINGLE_SURFACEType 15,SINGLE_SURFACEType 4,与面对面接触相同，除了,（,Same as surface-to-surface except that,：）,总是考虑厚度偏置,（,Thickness offsets are always used,）,除了,Type 4,：,SINGLE_SURFACE,，不需考虑接触面的方向,(Segment orientation is not needed except for SINGLE_SURFACE),只有通过定义力的传感器才能得到接触力,（,Reaction forces can be obtained only by using force transducer definitions,）,Contact/Single Surface,Initial Contact Interpenetrations(Interference),Cause major difficulties,通常很快就会导致不稳定,（,Calculation may go unstable with 250 time steps-often sooner.,）,LS-DYNA tries to correct geometry,在第一步,DYNA,会将穿透的节点移动到接触面上来,（,Moves interpenetrating nodes to contact surface on first cycle.,）,但是这样又会导致与其他面穿透,（,Movement may cause interpenetrations in another contact surface.,）,Some geometries cannot be easily modified,Contact/Interpenetrations(Interference),初始穿透,Initial Interference,Modeling errors,detected,undetected,Input errors,Coarse meshes,Shell edges closer to brick elements than 1/2 shell thickness,Interpenetrations can lead to incorrect results,Contact/Interpenetrations(Interference),Edge-to-edge contact is not detected!,Contact/Edge-to-Edge Interference,建议,（,Recommendations,）,划分网格时要保证面与面之间有足够的间隙,（,Adequately offset adjacent surfaces to account for part thickness during the mesh generation phase,）,保证高质量的网格,（,Uniform meshes or consistently refined meshes can improve results,）,小心定义壳单元和梁单元的尺寸，特别对于刚性体,（,Be very careful when defining thickness on shell and beam section definitions-especially for rigid bodies,）,使用厚度偏置,（,Use thickness offsets always,）,避免尖角,（,Avoid sharp corners,）,对于柔性体之间单向接触，网格粗糙的面应该定义成主面,（,For a one way treatment between deformable bodies make the master side the one with the coarser mesh,）,对于柔性体与刚体之间的单向接触，刚性体应该定义成主面,（,For a one way treatment between a rigid and deformable body make the master side the rigid body,）,默认值即可,（,Default values are good reference values,）,尽量定义带有,AUTOMATIC,选项的接触算法,（,Automatic contact input simplifies the problem definition and is generally more reliable,）,不要重复定义接触,（,Do not doubly define contact,）,如果有必要，可以缩放,part,的厚度,（,Scale back part thickness if necessary(scaling a 1.5mm thickness to.75mm should not cause problems;scaling to.075mm might),）,警告：如果厚度很薄，有可能会使接触失效,（,Warning:if a part is too thin contact failure will probably occur,）,Contact/Recommendations,Overall:,高质量网格,（,good mesh quality,）,避免初始穿透,（,avoid initial penetration,）,在,LS-DYNA,的每步迭代算法中，都要通过所有的单元来确定最小的时间步长,（,During the solution LS-Dyna loop through the elements and determine a new,timestep,size by taking the minimum value over all elements.,）,where,N,is the number of elements.,为了计算的稳定性，取一个缩放系数为,0.9,（默认值）或更小的值。所以如果想减少计算时间，那就要让时间步长尽可能的大,（,For stability reasons the scale factor is typically set to a value of.90(default)or some smaller value.To decrease solution time we desire to use the large possible stable,timestep,size.,）,Timestep,Timestep,临界时间步长,Critical(or minimum)time step size,:,where C is the sound wave propagation speed in 3D-continuum:,Timestep,Timestep,Examples of Sound Speeds,In Different Materials,AIR 331 m/s,WATER1478 m/s,STEEL5240 m/s,ALUMINUM5328 m/s,TITANIUM5220 m/s,PLEXIGLASS2598 m/s,在普通的汽车用金属铝和钢中声波的传播速度为,5000,毫米,/,秒左右,（,The acoustic,wavespeed,for the 2 most common automotive metals,steel and aluminum,are in the range of 5000.m/s.,）,在两种材料中，单元的特征长度为,5,毫米则它的时间步长为,1,微秒，通常作为工业标准,（,In both materials,an element characteristic length of about 5.mm will lead to a,timestep,of 1.,s,frequently set as a standard in the industry.,）,由于时间步长的原因，我们控制单元的最小长度为,5,毫米，因此车模型的几何模型通常在有限元中不能完全反映出来。这样在如今的车模型中就会有很大的局限性：要求的最小单元尺寸经常与详细几何模型会有冲突,。（,Since a reasonable,timestep,leads to a minimum,sidelength,of 5.mm,car body geometries can usually not be respected completely by FE.This is the most serious limitation of vehicle models today:the required minimum element size often prevents geometrically detailed and/or sufficiently dense mesh.,）,Timestep,*,DATABASE_,OPTION,Options for ASCII files include(if the file is not specified it will not be created):,SECFORC,Cross section forces,RWFORC,Wall forces,NODOUT,Nodal point data,ELOUT,Element data,GLSTAT,Global data,SSSTAT,Subsystem data,DEFORC,Discrete elements,MATSUM,Material energies,NCFORC,Nodal interface forces,RCFORC,Resultant interface forces,DEFGEO,Deformed geometry file,SPCFORC,SPC reaction forces,SWFORC,Nodal constraint reaction forces(,spotwelds,and rivets),ABSTAT,Airbag statistics,NODFOR,Nodal force groups,BNDOUT,Boundary condition forces and energy,RBDOUT,Rigid body data,GCEOUT,Geometric contact entities,SLEOUT,Sliding interface energy,JNTFORC,Joint force file,SBTOUT,Seat belt output file,AVSFLT,AVS database,MOVIE,MOVIE,MPGS,MPGS,TRHIST,Tracer particle history information,TPRINT,Thermal output,Output Database ASCII,*,DATABASE_BINARY_,OPTION,Options for binary output files with the default names given include:,D3PLOT,Dt,for complete output states,D3THDT,Dt,for time history data of element subsets,D3DRLF,Dynamic relaxation database,D3DUMP,Binary output restart files,RUNRSF,Binary output restart file,INTFOR,Dt,for output of contact interface data,XTFILE,Flag to specify output of extra time history data,Output Database Binary,创建模型要确保单位的统一,（,The units in LS-DYNA must be consistent.,）,One way of testing whether a set of units is consistent is to check that:,1(force unit)=1(mass unit)x 1(acceleration unit),and that 1(acceleration unit)=1(length unit)/1(time unit,),2,Examples of sets of consistent units are:,Units,Units,创建模型要确保单位的统一,（,The units in LS-DYNA must be consistent.,）,Units,Units,前处理设置不当通常导致的错误,Most common sudden termination input errors:,输入格式不正确,（,incorrect input format,）,单位,（,units,）,材料属性,（,material properties,）,载荷，边界条件和初始条件,（,loads,boundary conditions and initial conditions,）,初始穿透,（,initial contact interference,）,Even after a successful run,the model can still contain problems:,单位,（,units,）,小尺寸,/,角度单元,（,small size/angle elements,）,单元的长宽比，翘曲问题,（,element aspect ratios,angles and,warpage,）,重复的节点和单元,（,duplicate nodes and elements,）,计算,有限元分析流程,隐式算法,（,Implicit,Solver,）,LS-DYNA,显式非线性动态算法,（,Explicit,Nonlinear,Dynamics,）,多种单元积分形式,（,Comprehensive,Element,Formulation,）,丰富的材料模型,（,Extensive,Material,Models,）,自动的接触算法,（,Automated,Contact,Algorithms,）,有限元法的求解器,有限元分析流程,后处理,有限元分析流程,变形图,有限元分析结束后，由于节点数目多，输出数据量非常庞大，如静态受力分析后节点的位移量、固有频率计算后的振型,如果靠人工分析这些数据，不仅工作量巨大，容易出错，而且也很不直观,通常使用后置处理器自动处理分析结果，并根据操作者的要求形象化为：,变形图,、,应力等值线图,、,应力应变彩色浓淡图,、,矢量图,及,振型图,，,，直观显示载荷作用下零件的变形，零件各部分的应力、应变或温度场的分布,应力应变彩色浓淡图,矢量图,一阶振型叠加网格图,二阶振型叠加网格,有限元分析流程,有限元法的后处理,LIVERMORE,SOFTWARE,TECHNOLOGY,CORPORATION,ENGINEERING TECHNOLOGY ASSOCIATES,K,文件,$,$DEFINE TWO NODES,$,*NODE,10101 x y z,10201 x y z,$,$DEFIN