大范围运动柔性机械臂斜碰撞动力学分析

对作大范围运动柔性机械臂系统,进行斜碰撞动力学分析.基于柔性多体系统刚柔耦合动力学理论,计入耦合变形项,全面考虑大范围刚体运动与弹性小变形运动的耦合,建立系统连续动力学方程.引入斜碰撞力学模型,将法向和切向碰撞力以广义力的形式加入动力学方程中,对系统进行斜碰撞动力学建模分析.法向碰撞模型选取基于连续接触力法的非线性弹簧阻尼模型,切向碰撞模型选取一种修正Coulomb摩擦模型,对切向摩擦力进行统一描述.给出接触、分离判据,实现不同状态的动力学模型转换与求解.对斜碰撞全局动力学进行了仿真验证,分析了柔性机械臂全局过程的动力学特性变化以及碰撞对大范围运动和小变形运动的作用,并对比了不同碰撞方向对大范围运动、变形、机械能、碰撞力等动力学参数的影响.     

基于碰撞响应的三维空间多刚体实时运动仿真

该文将计算机科学与理论力学相结合，以刚性球体为例介绍了多刚体物理运动仿真的步骤和方法。首先论述了单个及多个刚体的运动仿真步骤以及应用叠加原理计算合力及合力矩的方法。然后，针对刚体运动中的不同碰撞响应类型：碰撞接触与临时接触，提出分别建立不同的碰撞响应力学模型，前者采用动量及动量矩定理建立响应模型，后者通过分析刚体的受力和运动状态建立相应的动力学模型。最后，详细讨论了刚性球体的碰撞仿真，包括它的碰撞测定、碰撞响应模型的建立及求解等，实现了三维空间中刚性球体实时、精确、快速的运动仿真，为以后多刚体大规模仿真奠定基础。     

多体系统动力学仿真中的接触碰撞模型分析

为了明确多体系统动力学仿真时接触碰撞模型的选择依据,对恢复系数模型,IMPACT函数模型,迟滞阻尼模型三种模型进行了分析讨论,并指出了模型中各参数的物理意义.最后以小球与平面碰撞问题为例,通过理论推导与试验相结合的方法确定了模型的参数,在ADAMS软件中进行了仿真计算,得到了三种模型的计算结果.计算结果表明,恢复系数方法只能得到碰撞后的速度;IMPACT函数模型可以得到较好的仿真结果,但是参数确定困难;修正的迟滞阻尼模型可以解决恢复系数接近1的接触问题.     

基于接触碰撞理论的锭子动力学仿真研究及实践

为减小锭杆顶端振幅对纺纱质量的影响，分析了基于接触碰撞理论的锭子动力学仿真中的分离－接触－碰撞三状态，建立了非变形经典碰撞模型和接触变形模型。建立切换点判定方程计算状态切换点，求解动力学微分方程以获得接触力和碰撞冲量作为失空输入求得模态振型和不平衡响应。比较两类多体动力学仿真结果，提出用碰撞耗能来研究锭子振动控制问题的方法。     

参数化列车碰撞平台的动力学建模与仿真

轨道车辆的设计过程中,有限元碰撞仿真方法建模复杂、修改周期长.为快速计算准确的列车碰撞响应,基于车辆-轨道耦合动力学理论,使用Matlab程序语言,建立参数化列车碰撞平台.根据实际参数,将车辆实体模型转化为数学模型,将连续轨道模型离散为弹性点支承模型;基于Hertz接触理论,使用向量法建立轮轨相互作用模型;将车钩缓冲装置、吸能防爬装置和悬挂装置的力学特性转化为非线性迟滞特性数学模型;采用修正双步长显式积分算法对参数化模型进行时域求解.将有限元仿真结果与参数化仿真结果在速度、加速度以及最大轮对抬升量方面进行对比,结果表明,两种模型的速度变化趋势相同,加速度绝对误差小于1m/s2,轮对抬升量峰值相对误差1.67％,各项指标的相对误差保持在10％以内,对参数化列车碰撞平台的准确性进行了验证.研究结果为揭示列车碰撞后的响应机理建立了仿真基础,为轨道车辆的耐撞性设计中参数的选定提供了一定的理论支撑.     

汽车转向机构间隙运动副的碰撞接触分析

应用多体动力学分析方法及仿真技术研究了某汽车转向机构间隙运动副在转向过程中的碰撞接触特性.首先应用ADAMS软件创建了该车的仿真模型.由悬架系统、转向系统、行驶系统等系统纰成.其次研究了『H]隙运动副的碰撞接触特性,包括转向横拉杆与转向梯形臂之间的运动副及转向梯形臂与悬架之间的运动副.根据实际工作特征,前者运动副采用空间圆柱铰模型,后者运动副采用平面圆柱铰模型.最后对模型进行了仿真分析.仿真结果表明,转向过程中,两问隙运动副的碰撞接触力与间隙大小成非线性关系,多个运动副间隙共存状念下各间隙运动副的碰撞接触力发生变化.这些研究结果为转向机构零部件设计、动力学特性分析提供了更为准确的实验依据.     

多体系统多点碰撞接触问题的数值求解方法

多体系统多点接触碰撞问题可以归结为一个将系统的动力学方程与并协性约束方程相结合的问题.针对这样一个含并协性条件的混合方程组,建立了基于 LCP 格式的包含碰撞/接触问题的多刚体系统动力学分析框架,提出了一种基于步长评价准则的变时间步长的数值求解策略,实现了无摩擦情况下多刚体系统多点接触碰撞问题的数值算法.最后给出了数值算例,验证了算法的有效性.     

薄壁管抗撞性能的多目标结构优化

以交通工具中部分锥形薄壁方管的安全装置作为研究对象,建立以薄壁管在碰撞过程中吸收能量最大化,比吸能最大化和初始碰撞力峰值最小化为多目标的优化问题.用锥形部分的几何参数作为设计变量,在保证不降低薄壁管吸能能力的情况下,通过对其结构的优化达到初始碰撞力峰值最小化的目的.论文采用有限元软件LS-DYNA得到不同几何参数模型的碰撞信息,用响应面法构造近似函数,同时引入权系数以表征各个目标在优化问题中的重要程度,并采用理想点法求解多目标优化问题,分析了锥形薄壁方管各几何参数对结构的能量吸收、比吸能和初始碰撞力峰值的影响,最终得到了给定权系数下的最优模型.     

太阳电池阵展开与锁定过程的多体动力学分析

柔性太阳电池阵展开动力学分析一般将板间的铰链视为理想铰,展开到位时施加与角度相关的撞击力矩模拟锁定过程.本文采用多体动力学方法,在动力学建模时将板间铰链视为物体,考虑太阳电池阵的刚柔耦合效应,基于Hertz接触理论,建立锁销和锁槽的碰撞模型.然后实现了太阳电池阵展开锁定全过程的动力学数值仿真,并研究了碰撞模型中参数的选取对仿真结果的影响.研究结果表明,碰撞参数的选取不仅影响铰间碰撞力的大小,还会影响整个系统锁定后的频率响应.最后给出了如何选取碰撞参数进行太阳电池阵展开与锁定动力学仿真的策略.     

基于游戏中区域检测碰撞的改进措施

该文改进了传统的区域检测碰撞算法不能检测处于不同高度的运动小球是否发生碰撞的状况,通过比较两球圆心距与其半径和的大小,分析并设计实验来检测两球在不同高度上是否发生碰撞,但由于采集图片的问题以及球的半径不够精确,会出现两球并未真正发生碰撞却检测出碰撞的结果。实验最终可以检测两运动小球在不同高度上是否发生碰撞。     

Chain Vibration and Dynamic Stress in Three-Dimensional Multibody Tracked Vehicles

A three-dimensional computational finite element procedure for the vibration and dynamic stress analysis of the track link chains of off-road vehicles is presented in this paper. The numerical procedure developed in this investigation integrates classical constrained multibody dynamics methods with finite element capabilities. The nonlinear equations of motion of the three-dimensional tracked vehicle model in which the track link s are considered flexible bodies, are obtained using the floating frame of reference formulation. Three-dimensional contact force models are used to describe the interaction of the track chain links with the vehicle components and the ground. The dynamic equations of motion are first presented in terms of a coupled set of reference and elastic coordinates of the track links. Assuming that the structural flexibility of the track links does not have a significant effect on their overall rigid body motion as well as the vehicle dynamics, a partially linearized set of differential equations of motion of the track links is obtained. The equations associated with the rigid body motion are used to predict the generalized contact, inertia, and constraint forces associated with the deformation degrees of freedom of the track links. These forces are introduced to the track link flexibility equations which are used to calculate the deformations of the links resulting from the vehicle motion. A detailed three-dimensional finite element model of the track link is developed and utilized to predict the natural frequencies and mode shapes. The terms that represent the rigid body inertia, centrifugal and Coriolis forces in the equations of motion associated with the elastic coordinates of the track link are described in detail. A computational procedure for determining the generalized constraint forces associated with the elastic coordinates of the deformable chain links is presented. The finite element model is then used to determine the deformations of the track links resulting from the contact, inertia, and constraint forces. The results of the dynamic stress analysis of the track links are presented and the differences between these results and the results obtained by using the static stress analysis are demonstrated.     

Finite Element Analysis of 6300 Deep Groove Ball Bearing

Rolling bearing is widely used in mechanical support, its general components are the inner ring, outer ring, the ball, retainer etc.. Now many companies in developed countries and university in the rolling bearing as the research object, and has made great progress in design theory, the experiment method and production technology etc. We will use the finite element ANSYS to establish the model of deep groove ball bearing. Through the contact analysis, we can get the contact stress between the rings and balls, strain, contact state, penetration, sliding distance and the friction stress distribution. These values are compared to the theoretical values with Hertz theory, and they have better consistency, provide the good theoretical basis for the optimization design of rolling bearings.     

Cable installation simulation by using a multibody dynamic model

A major concern when installing the cables into the underground conduit is minimizing the tensile forces exerted on the cables as they are pulled. This knowledge makes it possible to avoid over conservative design practices and to achieve substantial saving during construction. A general computing algorithm of predicting the tensile force of the cable pulled through the underground conduit with an arbitrary configuration is presented in this paper, which is based on multibody system dynamic formulation. The presented multibody dynamic model for this problem consists of the cable, the underground conduit, and the interaction between the cable and the conduit. In this paper, the cable is modeled by the finite cable element based on an absolute nodal coordinate formulation. The interaction between the cable and the underground conduit is described by the Hertz contact theory. Numerical examples are presented to illustrate the effectiveness and efficiency of the proposed method for estimating the cable tension.     

Analysis of dynamic characteristics of a HDD spindle system supported by ball bearing due to temperature variation

 This paper presents a method to investigate the characteristics of a ball bearing and the dynamics of a HDD spindle system due to temperature variation. Finite element model is developed for the rotating and stationary parts of a HDD spindle system separately to determine their thermal deformations by using ANSYS, a finite element program. Then, the relative position of the rotating part with respect to the stationary part is determined by solving the equilibrium equation of the contact force between upper and lower ball bearings. The validity of the proposed method is verified by comparing the theoretical natural frequencies of a HDD spindle system with the experimental ones before and after temperature variation. The proposed method makes it possible to predict the characteristics of a ball bearing and the dynamics of a HDD spindle system due to temperature variation. It shows that the elevated temperature results in the increase of contact angle and the decrease of bearing deformation, contact force and bearing stiffness, which result in the decrease of the natural frequencies of a HDD spindle system. Received: 20 June 2002 / Accepted: 28 August 2002     

Influences of denucleation on contact force of facet joints under whole body vibration

To investigate the influence of the injured disc, frequency, load and damping on the facet contact forces of the low lumbar spine on the condition of whole body vibration, a detailed 3-D nonlinear finite element model was created based on the actual geometrical data of embalmed vertebrae of lumbar spine. The denucleation and facetectomy, together with removal of the capsular ligaments was employed to mimic the injury conditions of lumbar spine after surgery. The compression cyclic force was assumed to mimic the dynamic loads of transport vehicles. The results show that the high frequency vibration might increase both of the value and the vibration amplitude of facet contact forces of the lumbar spine under whole body vibration. The nucleus removal may increase significantly the facet contact forces. Although damping can decrease the vibration amplitude of facet contact forces for intact models, it has less effect on the vibration amplitude of facet contact force for the denucleated models. The denucleation of intervertebral discs is more harmful to the facet articulation on the condition of whole body vibration.     

Influences of denucleation on contact force of facet joints under whole body vibration

To investigate the influence of the injured disc, frequency, load and damping on the facet contact forces of the low lumbar spine on the condition of whole body vibration, a detailed 3-D nonlinear finite element model was created based on the actual geometrical data of embalmed vertebrae of lumbar spine. The denucleation and facetectomy, together with removal of the capsular ligaments was employed to mimic the injury conditions of lumbar spine after surgery. The compression cyclic force was assumed to mimic the dynamic loads of transport vehicles. The results show that the high frequency vibration might increase both of the value and the vibration amplitude of facet contact forces of the lumbar spine under whole body vibration. The nucleus removal may increase significantly the facet contact forces. Although damping can decrease the vibration amplitude of facet contact forces for intact models, it has less effect on the vibration amplitude of facet contact force for the denucleated models. The denucleation of intervertebral discs is more harmful to the facet articulation on the condition of whole body vibration.     

Metamodelling of wheel–rail normal contact in railway crossings with elasto-plastic material behaviour

A metamodel considering material plasticity is presented for computationally efficient prediction of wheel–rail normal contact in railway switches and crossings (S&C). The metamodel is inspired by the contact theory of Hertz, and for a given material, it computes the size of the contact patch and the maximum contact pressure as a function of the normal force and the local curvatures of the bodies in contact. The model is calibrated based on finite element (FE) simulations with an elasto-plastic material model and is demonstrated for rail steel grade R350HT. The error of simplifying the contact geometry is discussed and quantified. For a moderate difference in contact curvature between wheel and rail, the metamodel is able to accurately predict the size of the contact patch and the maximum contact pressure. The accuracy is worse when there is a small difference in contact curvature, where the influence of variation in curvature within the contact patch becomes more significant. However, it is shown that such conditions lead to contact stresses that contribute less to accumulated plastic deformation. The metamodel allows for a vast reduction of computational effort compared to the original FE model as it is given in analytical form.

     

桥梁复合材料防撞护舷的结构设计

采用有限元法对某3 000 t船舶与桥梁防撞护舷碰撞的动力学特性进行分析.通过将护舷试样的碰撞试验与有限元计算结果进行对比,完善该防撞护舷的有限元模型,使其更可靠.用ANSYS/LS DYNA模拟3 000 t船舶撞击3种不同护舷（D型、圆环型和板型）的过程.不同护舷吸能结果表明：对于D型护舷,船舶会碰到桥墩,失去作用;对于板型护舷,船舶变形严重;圆环型护舷的效果最好.     

Analysis of contact through finite element gaps

A numerical technique is described for analyzing contact of disconnected structures through the use of finite element gaps. A special gap element is used, together with a stress invariance principle, to model the contact process. The solution is achieved through an iterative procedure which adjusts the modulus of the gap elements. The numerical procedure is described and results are given for two problems of differing complexity. The first is a classical Hertz problem involving contact between a sphere and a rigid plane. The second problem is concerned with the thermostructural analysis of the beat shield for a Radioisotope Thermoelectric Generator design.     

The effect of contact interface on dynamic characteristics of composite structures

In this project, nonlinear characteristics on the rolling interface of a linear guide were studied by the finite element analysis and experimental verification. Contact of the ball/surface rolling interface in the rolling guides was simulated as a three-dimensional membrane element without thickness. By introducing Hertzian contact theory and applying proper normal/shear stiffness to such contact elements in the overall finite element model, dynamic behaviors of linear guides affected by preload were thus investigated. In the finite element procedure, three contact models, 1D point-to-point, 2D point-to-point and 3D surface-to-surface, were sequentially introduced for purpose of verification with experiments. As a validation in this project, vibrational experiments on linear guides with different preloads were conducted and related frequency spectrums were derived. Both the finite element and the experimental results reveal that the natural frequency of a linear guide increases with the increment of the preload. In addition, the dynamic characteristics predicted by finite element analysis agree well with those measured from instrumental experiments. The proposal of current study may provide an alternate and reliable way for understanding of the dynamic characteristic of the rolling contact components in machine design field.