基于深度学习方法的含间隙铰链多刚体系统的动力学建模与分析

机械系统中,铰接处接触力受铰间间隙量大小、运动副各部件的材料属性、运动过程中的接触状态等因素的影响,表现出很强的非线性。传统的间隙铰摩擦理论模型主要关注对摩擦现象描述的普适性,而难以精确地描述摩擦过程中摩擦力的非线性特征。基于物理样机试验获得的数据,使用深度学习方法建立了间隙铰非线性接触力神经网络模型,通过摩擦试验生成接触摩擦力数据集,结合旋转铰间隙接触碰撞力混合模型生成接触碰撞力数据集,对模型进行训练和测试,得到了旋转间隙铰的神经网络动力学模型。在此基础上,结合拉格朗日方程对含间隙铰的曲柄滑块机构进行建模,建立了“多刚体系统-间隙铰-多刚体系统”的动力学模型,通过仿真分析得到系统关键参数的动力学响应,并与物理试验结果进行了对比,验证了基于深度学习方法获得的间隙铰模型的正确性,为深度学习方法在非线性系统动力学建模方向上的应用提供了一个可行的思路。     

基于多刚体离散元模型的柔顺机构动力分析新方法

柔顺机构是部分或者全部由其构件的预期弹性变形来传递运动和力,这使得构件的弹性变形一般都较大。它的分析一般属于几何非线性问题。基于弹性体的多刚体离散元模型,研究了柔顺段和柔顺机构的多刚体离散元建模方法,推导了柔顺机构系统的一般控制方程,该方程可以解决柔顺机构的特征频率和几何非线性变形问题。并给出了算例,计算结果表明多刚体离散元方法能较好解决柔顺机构的几何非线性静力学和动力学分析。     

多新息模型辨识PMSM双曲正切滑模定位控制

永磁同步电机伺服系统是一个复杂的非线性系统,模型参数、摩擦等因素使其难以用准确的数学模型表示.针对永磁同步电机伺服系统存在不确定参数、摩擦及外部扰动现象,提出一种基于多新息模型辨识的双曲正切滑模定位策略.首先,将永磁同步电机的模型进行状态离散化,并用多新息模型辨识方法对系统的模型参数进行辨识;然后根据离散化的辨识系统状...     

4自由度并联机构刚体动力学模型

以一种具有空间SCARA运动(三维平动和一维转动)的四自由度并联机构为研究对象,系统研究其简化刚体动力学模型的创建方法,提高了力矩求解精度。在运动学分析的基础上,利用虚功原理,建立机构的完备刚体动力学模型,并利用ADAMS校验该模型的正确性。考虑机构各活动构件的结构和运动状态,建立机构的单变量简化刚体动力学模型,奠定了变量优化的模型基础。以机构沿标准轨迹运动时,将完备模型和简化模型计算所得的单轴驱动力矩差值的最大值的绝对值的平均值作为优化目标,分析各尺度参数对优化目标的影响规律,为简化模型的最优变量确定提供指导。以一组给定参数为例,利用单目标优化方法,求解出变量最优值,通过与现有简化方法对比,验证了所述方法的有效性。     

基于RecurDyn软件的采煤机牵引部传动系统动力学仿真

基于非线性理论和多体接触动力学理论,建立了采煤机牵引部齿轮传动系统的全刚体模型和刚-柔耦合模型,运用Ansys软件将刚性齿轮柔性化,将建好的模型分别导入到RecurDyn多体动力学软件中进行仿真分析,在仿真动画环境下直观、动态的描述了轮齿啮合接触过程,并根据仿真结果对传动系统进行了优化改进。对比全刚体模型和刚-柔耦合模型的仿真结果,研究表明牵引部传动系统采用刚-柔耦合多体动力学模型的动态性能更符合实际,同时也解决了大型机械传动系统进行多体接触仿真的难题,为齿轮多体动力学模型在工程中的应用奠定了基础。     

关于梁与刚体接触问题的讨论

讨论了梁与刚体接触的问题,推导出了悬臂梁与刚体接触的压力公式。研究结果表明,梁与刚体接触问题本质上是非线性问题。计算梁自由端的挠度时,可以对非线性项进行线性简化;计算梁与刚体接触处之间梁段接触压力时,对非线性项进行线性简化是不合适的。     

摩擦提升机摩擦传动特性建模

以非线性有限元法和多体动力学理论为理论基础,通过采用考虑剪切变形的二维梁单元的绝对节点坐标方程来描述钢丝绳的柔性变形,借助于单元节点相对于摩擦轮的线-线接触方法,建立了摩擦提升机摩擦传动系统的多点动态接触动力学模型。研究表明,构建的摩擦提升机多点接触动力学计算模型由于综合考虑了钢丝绳的柔性体效应、钢丝绳与摩擦轮之间的动态接触、摩擦轮转速、摩擦系数等因素的影响,为分析摩擦提升机提升过程中,摩擦接触处钢丝绳的接触力、张力、滑动、接触等摩擦传动特征提供了一个有效的研究工具。     

设计参数优化对弧齿锥齿轮动力学特性影响的对比研究

以弧齿锥齿轮的压力角、刀尖圆角半径、大小轮齿厚比等设计参数为优化对象,基于多体多自由度动力学方程以及混合润滑摩擦模型,对齿轮系统动态特性进行对比研究。综合考虑了系统的时变摩擦力、动态啮合力、传递误差以及齿侧间隙等非线性因素的影响,同时考虑到实际工作中齿轮啮合处于既有润滑油膜接触又有粗糙峰接触的混合弹流润滑状态。对系统动态响应进行求解,结果表明,相较于优化设计参数前,优化后的弧齿锥齿轮在动态啮合力及动态传递误差方面都具有更优的表现。最后,通过试验台架进行试验验证了研究结果的准确性。     

基于拉格朗日乘子法的Delta并联机器人简化刚体动力学建模方法

针对广泛应用于高速抓放操作的Delta并联机器人,提出了一种基于拉格朗日乘子法的刚体动力学建模方法,并利用约束方程的全微分求解出了动力学模型的显示表达式。建立了机器人的逆运动学以及刚体动力学模型,考虑机器人从动臂臂杆为轻质碳纤维杆,两端为较重的金属附件的特点,建立了简化刚体动力学模型。并针对机器人常用的高速抓放轨迹进行仿真,将简化前后的2种动力学模型与ADAMS仿真结果进行对比。     

考虑摩擦作用的多柔体系统点--面碰撞模型

提出了考虑摩擦作用的多柔性体系统的点－面碰撞模型,基于Ｈｅｒｔｚ接触理论和非线性阻尼项描述法向碰撞接触过程的动力学特性,利用线性届接触刚度考虑碰撞过程中的摩擦作用。针对作大范围回转运动的柔性梁与一固定斜面发生碰撞的情况,在考虑刚柔耦合效应的多柔性系统动力学建模理论的基础上,精细研究了系统斜碰撞过程中的动力学行为。     

滚动轴承刚柔多体接触动力学分析

以柔性多体动力学理论为基础,提出了以相对坐标描述刚柔多体接触滚动轴承的递推数值分析方法。以球轴承为例,研究了滚动轴承刚柔多体接触输出响应的动态特性。综合考虑滚动体与轴承内外圈滚道的时变接触刚度、柔性接触、摩擦、离心力等非线性因素,分析出转速、摩擦力和预紧力对滚动轴承的时变接触力和时变振动位移的影响。结果表明,以相对坐标描述刚柔多体接触滚动轴承的动力学模型,可以有效地解决滚动体与滚道间的时变接触振动响应和柔性接触等非线性接触动力学问题。     

Analysis of the nonlinear behavior of gear pairs considering hydrodynamic lubrication and sliding friction

This paper describes an analysis of the nonlinear behavior of gear pairs according to the direct contact elastic deformation model over a wide range of speeds, considering the hydrodynamic effects and friction force. The inclusion of the hydrodynamic effect facilitates nonlinearity by increasing the overlap range (i.e., multiple solution regimes) and damping, as well as decreasing elastic deformation and tooth reaction forces. The effects of various lubrication parameters, such as viscosity and film width, on the nonlinear dynamic behavior were analyzed. While the viscosity has a strong effect on the behavior of gear pair systems, friction has very little effect on torsional behavior. Although the model of direct contact without friction has overall nonlinear behavior similar to the model including hydrodynamic effects with friction, the time data of these models are different due to the squeeze effect. This paper was recommended for publication in revised form by Associate Editor Eung-Soo Shin Cheon Gill-Jeong received his B.S. in Mechanical Engineering from Seoul National University (SNU), Korea, in 1981. He then received his M.S. and Ph.D. degrees from SNU in 1983 and 1988, respectively. He served as a senior research engineer at Seoul National University Hospital and Daewoo Heavy Industry for several years. Dr. Cheon is currently a Professor at the Division of Mechanical Engineering at Wonkwang University in Iksan, Korea. His research interests include dynamics, tribology, and design engineering.     

Dynamic analysis of planar mechanical systems with clearance joints using a new nonlinear contact force model

We investigated the dynamic behavior of planar mechanical systems with clearance joints. First, the contact effect in clearance joint was studied using a new nonlinear contact force model, and the rationality of this model was verified by the results of numerical simulations, which are based on a journal and bearing contact model. Then, the dynamic characteristics of a planar slider-crank mechanism with clearance were analyzed based on the new nonlinear contact force model, and the friction effect of clearance joint was also considered using modified Coulomb friction model. Finally, the numerical results of the influence of clearance size on the acceleration of slider are presented, and compared with the published experimental results. The numerical and experimental results show that the new nonlinear contact force model presented in this paper is an effective method to predict the dynamic behavior of planar mechanical system with clearance joints, and appears to be suitable for a wide range of impact situations, especially with low coefficient of restitution.     

Enhanced friction model for high-speed right-angle gear dynamics

The modeling of elastohydrodynamic lubrication friction and the analysis of its dynamic effect on right-angle gears, such as hypoid and spiral bevel types are performed in the present study. Unlike the classically applied empirical constant coefficient of friction at the contacting tooth surfaces, the enhanced physics-based gear mesh friction model is both spatial and time-varying. The underlying formulation assumes mixed elastohydrodynamic lubrication (EHL) condition in which the division and load distribution between the full film and asperity contact zones are determined by the film thickness ratio and load sharing coefficient. In the proposed time-varying friction model, the calculation of friction coefficient is performed at each contact grid inside the instantaneous contact area that is being subjected to mineral oil lubrication. The effective friction coefficient and directional parameters synthesized from the net frictional and normal contact forces are then incorporated into a nonlinear time-varying right-angle gear dynamic model. Using this model, the effect of friction on the gear dynamic response due to the transmission error and mesh excitations is analyzed. Also, parametric studies are performed by varying torque, surface roughness and lubrication properties to understand the salient role of tooth sliding friction in gear dynamics. The simulation results are included. But experimental verification is needed.     

MODELING COMPLIANT NONPENETRATION CONSTRAINT FOR VP MOTION SIMULATION

A unilateral non-penetration constraint dynamical simulation model with friction is constructed based on compliant model for mechanical system VP (virtual prototyping) simulation. This model combines computer graphics with multi-body system dynamics. It avoids handling multiplicity of solution, such as cases of no solution, multi-solution brought about by friction during traditional construction of non-penetration constraint based on rigid model. At the same time, the realism of VE (virtual environment) is improved in process of simulation. Furthermore, the valid condition of rolling and sliding unilateral contact is constituted based on singular perturbation and linear complementary theory. Finally, the compliant method is verified by an interaction between a multi-legged robot and VE.     

混合润滑条件下的斯特封高速摩擦与密封特性

为准确研究斯特封高速摩擦与密封特性,基于混合润滑理论,综合流体空化效应、密封接触变形和微观粗糙峰接触等因素影响,建立了斯特封摩擦与密封的数值计算模型。研究了往复运动速度和密封压力对油膜厚度、摩擦力和泄漏量的影响,搭建了往复密封试验台来验证模型的准确性。结果表明：计算摩擦力与实验摩擦力相近。混合润滑模型能更好地模拟高速柱塞副斯特封的摩擦与密封特性,油膜压力与粗糙度接触压力共同影响密封性能,但粗糙度接触摩擦起主导作用。     

盘式制动器的结构场有限元分析

首先探讨盘式制动器在制动过程中的摩擦接触和非线性动力学问题.具体的分析方法包括:摩擦接触算法,非线性有限元方法.按照制动盘与摩擦片的实际几何尺寸,建立了具有速度可变效应的三维瞬态结构应力有限元模型,利用非线性有限元方法,较真实地模拟了制动器的制动过程.通过以上分析得出制动过程的一些结构上的性能变化.将同相同制动条件下的实心盘式制动器和通风盘式制动器对比,得出通风盘式制动器在制动过程中的接触应力,各向位移等.     

Brake squeal: Linear and nonlinear numerical approaches

“Brake squeal” groups a large set of high-frequency sound emissions from brake systems. They are generated during the braking phase and are characterized by a harmonic spectrum. The onset of squeal is due to an unstable behaviour occurring in linear conditions during the braking phase, and a general approach used by several authors to determine the system instabilities is the complex eigenvalues analysis. When the brake begins to squeal, the response of the system reaches a new limit cycle where the linear models cannot be used anymore. This paper presents the integration of two different numerical procedures to identify the mechanism bringing to squeal instability and to analyse its dynamics. The first approach is a finite element modal analysis of the brake system and is used to identify its eigenvalues and to relate them to the squeal occurrence. The second one is a specific finite element programme, Plast3, appropriate for nonlinear dynamic analyses in the time domain and is particularly addressed to study contact problems with friction between deformable bodies. This programme computes the contact stresses and permits to determine the dynamics of the system along the contact surface, both in the linear and nonlinear fields. The two models are compared and the onset of squeal is predicted both in the frequency domain by the linear model and in the time domain by the nonlinear one. The instability predictions, obtained by the two models, are discussed. To simplify the dynamics of its components, the study is carried out on a simple model, made of a disc, a small friction pad and a beam supporting the pad. The geometry of the model is related to an experimental set-up used to validate the models and to compare the numerical results with the experiments.     

Friction behavior of quenched and tempered steel in partial and gross slip conditions in fretting point contact

Tangential traction caused by friction in contacting surfaces is a major factor in fretting fatigue that increases stress levels and leads to a reduction in fatigue life. Friction in fretting contact was studied in partial, mixed and gross slip conditions on quenched and tempered steel. Measurements were made with sphere-on-plane contact geometry for polished and ground surfaces. Friction was evaluated from on-line energy ratio and, after the tests, from wear marks. A maximum friction coefficient of over 1.0 was measured at mixed slip zone with polished surfaces, whereas ground surfaces promote lower values in similar operating conditions. The friction coefficient dependence on load cycles and loading frequency is also presented and briefly discussed. The friction data and understanding thus gained is to be used for evaluation of crack initiation with the numerical fretting fatigue model.     

A numerical model for mixed lubrication taking into account surface topography,tangential adhesion effects and plastic deformations

The present paper focuses on numerical investigations of mixed lubrication phenomena. Generally minimized for sliding systems, this type of lubricated contact is essential to ensure the original basic function of a lubricated friction system. As analyses of such a contact are hardly possible with experimental facilities, the finite element method was chosen to model the occurring friction phenomena at the micro-scale. A three-dimensional model is implemented considering two lubricated real rough bodies, Bowden and Tabor adhesion model and heat generation occurring in the solid–solid contact. Present analysis gives an overview on how surface roughness and machining direction influence the friction behavior as well as the contact and fluid pressure fields in mixed lubricated systems. First results are in accordance with the literature but therefore require the use of a statistical approach to deliver quantitative results in adequation with real systems.