Chaotic rocking vibration of a rigid block with sliding motion under two-dimensional harmonic excitation

This research deals with the influence of nonlinearities associated with impact and sliding upon the rocking behavior of a rigid block, which is subjected to two-dimensional horizontal and vertical excitation. Nonlinearities in the vibration were found to depend strongly on the effect of the impact between the block and the base, which involves an abrupt reduction in the system’s kinetic energy. In particular, when sliding occurs, the rocking behavior is substantially changed. Response analysis using a non-dimensional rocking equation was carried out for a variety of excitation levels and excitation frequencies. The chaos responses were observed over a wide response region, particularly, in the cases of high vertical displacement and violent sliding motion, and the chaos characteristics appear in the time histories, Poincare maps, power spectra and Lyapunov exponents of the rocking responses. The complex behavior of chaotic response, in phase space, is illustrated by the Poincare map. The distribution of the rocking response is described by bifurcation diagrams and the effects of sliding motion are examined through the several rocking response examples.     

Effect of thermal deformation on machine tool slide guide motion

This paper describes the effects on machine slide-guide contact conditions caused by thermal deformation. Since a slide guide has a large friction surface, the motion is greatly influenced by thermal distortion caused by heat generation in the ball nut and the bearing support, during machining processes. This study investigated the typical behavior of the friction coefficient in response to both the external load and the linear speed. This then led to investigating the thermal effects on the slide motion. The thermal deformation of the slide table was measured with respect to the running time and the linear motion and the frictional power were monitored and compared directly with the thermal distortion.     

Chaotic behavior on rocking vibration of rigid body block structure under two-dimensional sinusoidal excitation (in the case of no sliding)

This present work focuses on the influence of nonlinearities associated with impact on the rocking behavior of a rigid body block subjected to a two-dimensional excitation in the horizontal and vertical directions. The nonlinearities in rocking system are found to be strongly dependent on the impact between the block and the base that abruptly reduces the kinetic energy. In this study, the rocking systems of the two types are considered : The first is an undamped rocking system model that disregards the energy dissipation during the impact and the second is a damped rocking system, which incorporates energy dissipation during the impact. The response analysis is carried out by a numerical method using a non-dimensional rocking equation in which the variations in the excitation levels are considered. Chaos responses are observed over a wide range of parameter values, and particularly in the case of large vertical displacements, the chaotic characteristics are observed in the time histories, Poincare sections, the power spectral density and the largest Lyapunov exponents of the rocking responses. Complex behavior characteristics of rocking responses are illustrated by the Poincare sections.     

Numerical analysis of TEHL line contact problem under reciprocating motion

This paper presents a full numerical analysis to simulate the thermal elastohydrodynamic lubrication (TEHL) of steel–steel line contact problem under reciprocating motion. The equation system is solved using multigrid techniques. General tribological behaviors of TEHL under reciprocating motion are explained. Comparison between thermal and isothermal results reveals the importance of thermal effect in prediction of the traction coefficient and film thickness. The influences of frequency, stroke length, and applied load on the variations of film thickness, pressure and traction coefficient during one working cycle are discussed. Furthermore, the influence of slide–roll ratio on tribo-characteristics of oil film under same entraining velocity is revealed.     

On the planar motion of rigid bodies with point contact

We study the so called roll-slide motions between curves with point contact under planar motion. We consider instantaneous time based kinematics, and assume the presence of a tactile sensor to measure the relative motion at the point of contact. It is indicated how the derived kinematic relationships can be applied to sensor-based robotic path planning.     

Limit analysis of frames involving unilateral supports with frictional contact

We consider the classical limit analysis problem of frame structures made up of rigid perfectly plastic members and involving some supports in unilateral frictional contact with the ground. A direct formulation as a mixed complementarity problem (MCP) is used. For the Coulomb case, which forms the focus of this paper, the corresponding MCP may admit multiple upper bound collapse load solutions. In order to identify the least upper bound solution, we propose two algorithms. The first one attempts to enumerate the possible multiple solutions, or at least map the solution space if the solutions are connected. The second scheme tries to find the least upper bound by directly formulating and solving a single nonconvex optimization problem, known in the literature as a mathematical program with equilibrium constraints (MPEC). Two simple examples are provided to illustrate application of these approaches. They also serve to highlight some key features of such structures.     

基于虚拟样机的拉延压力机外滑块机构运动性能研究

针对双动拉延机外滑块工作机构的特点,分析了外滑块传动系统的的运动特性.利用仿真软件建立了双动拉延机的串联四杆外滑块工作机构的多体动力学模型,进行了运动学仿真分析,同时,建立了相应的曲柄滑块机构,对两种机构的滑块位移、速度与加速度曲线进行了比较.结果表明:与曲柄滑块机构相比,该串联四杆机构在下死点附近的速度低、加速度小、具有急回特性的特点.研究结果可对拉延压力机的开发提供参考.     

滑履磨机应力分析

利用有限元分析方法对φ4.6×14 m滑履磨机进行了应力计算,得到了滑履磨机筒体的变形及应力分布,以及滑环和托瓦的接触应力情况.     

四元数在刚体姿态运动可视化仿真中的应用

近年来, 随着高性能计算机的广泛应用及飞行器姿态控制研究的迅速发展, 四元数理论得以广泛应用. 四元数不仅计算简单, 而且避免了欧拉角存在的奇异性问题, 因此在航天飞行器姿态控制当中被广泛应用. 本文利用Simulink仿真技术, 用四元数法建立了刚体姿态仿真模型, 并利用VRML虚拟现实场景实现了姿态运动的可视化. 仿真结果显示该Simulink仿真模型能够准确反映出刚体的姿态运动情况, 对于飞行器姿态控制的研究具有一定的参考价值.     

Numerical study of droplet motion in a microchannel with different contact angles

The droplet motion in a microchannel with different contact angles, which is applicable to a typical proton exchange membrane fuel cell (PEMFC), was studied numerically by solving the equations governing the conservation of mass and momentum. The gas-liquid interface or droplet shape was determined by a level set method which was modified to treat the static and dynamic contact angles. The matching conditions at the interface were accurately imposed by incorporating the ghost fluid approach based on a sharp-interface representation. Based on the numerical results, the droplet dynamics including the sliding and detachment of droplets was found to depend significantly on the contact angle. Also, the effects of inlet flow velocity, droplet size and side wall on the droplet motion were investigated. This paper was recommended for publication in revised form by Associate Editor Haecheon Choi Gihun Son received a B.S. and M.S. degree in Mechanical Engineering from Seoul National University in 1986 and 1988, respectively. He then went on to receive his Ph.D. degrees from UCLA in 1996. Dr. Son is currently a Professor of Mechanical Engineering at Sogang University in Seoul, Korea. Dr. Son’s research interests are in the area of multiphase dynamics, heat transfer, and power system simulation. Jiyoung Choi received a B.S. degree in Mechanical Engineering from Sogang University in 2005. He is a graduate student of Mechanical Engineering at Sogang University in Seoul, Korea. Choi’s research interests are in the area of PEM fuel cell and microfluidics.     

基于ANSYS Workbench的DVG850滑座的拓扑优化

以DVG850高速立式加工中心的基础件滑座为研究对象,使用SolidWorks进行了三维建模,通过SolidWorks与ANSYS Workbench的嵌套,将三维模型导入有限元软件ANSYS Workbench,对滑座模型进行了静刚度分析,并运用ANSYS DesignXplorer对其进行了优化设计,保证了滑座的静刚度要求,减少了滑座10%的质量,加强了相关移动部件的运动性能。     

On the instantaneous acceleration of points in a rigid body

This work re-examines some classical results in the kinematics of points in space using modern vector-matrix methods. In particular, some very simple Lie theory allows the velocities and accelerations of points to be found in terms of the instantaneous twist of the motion and its derivative. From these results many of the classical results follow rather simply.Although most of the results are well known, some new material is presented. In particular, the discriminant curve that separates cases with one or three real acceleration axes is found and plotted. Another new result concerns the chords to the cubic of inflexion points. It is shown that for points on such a chord the osculating planes of the point's trajectories are parallel. Also a new result is found which distinguishes between cases where the Bresse hyperboloid of points whose velocities and accelerations are perpendicular, has one or two sheets.     

Stick-slip conditions in the general motion of a planar rigid body

In this paper we study combined translational and rotational (general) motion of planar rigid bodies in the presence of dry coulomb friction contact. Despite the cases where the body has pure translational/ rotational motion or can be assumed as a point mass, during the general motion, distinct points of the rigid body move in different directions which cause the friction force vector at each point to be different. Therefore, the direction and the magnitude of the overall friction force cannot be intuitively defined. Here the concept of instantaneous center of rotation is used as an effective method to determine the resultant friction force and moment. The main contribution of this paper is to propose novel stick-slip switching conditions for the general in-plane motion of rigid bodies. Simulation results for some combination of external forces are provided and some experimental tests are designed and conducted for practical verification of the proposed stick-slip conditions.     

AutoCAD脚本文件及幻灯片文件的定制与使用

介绍在AutoCAD环境下，如何定制包含一系列AutoCAD命令的脚本文件和可以形象展示教学内容及产品信息的幻灯片文件，如何用幻灯片文件循环播放幻灯片，提高绘图效率，实现Auto—CAD的高级应用。     

形态分析法在拉链头装配方案设计中的应用

介绍应用形态分析法设计拉链头自动装配机的步骤、过程和具体方法。在拉链头自动装配机的设计过程中,将装配要素分解为若干可相互独立的基本元素,经过系统搜索和程式化求解,得到经过优化的零件装配形态,为拉链头自动装配机设计创造了良好的条件。     

浅谈动态轨道衡与秤体结构

本文从一个侧面介绍了我国动态轨道衡秤体结构的演变过程,通过几十年的工业实验与应用,使设计更为合理科学且简洁明快。     

Note on the complete contact between a flat rigid punch and an elastic layer attached to a dissimilar substrate

The contact pressure distribution is found for a square ended rigid punch, pressing normally onto an elastic layer, itself attached to an elastically dissimilar half-plane, under plane deformation. Each interface may be either frictionless or adhesive, and it is shown that the shear traction assumption has only a very small influence on the contact pressure, which is found as a perturbation on the classical Flamant half-plane solution. For thin layers the contact pressure distribution is only weakly dependent on the pad aspect ratio.     

人体运动实时捕捉仪器设计与应用

将人体运动实时捕捉下来 ,实现数字化处理与同步图像显示 ,将在影视广告制作、体育运动分析、康复效果跟踪等许多方面具有潜在的应用前景。本文系统介绍人体运动实时捕捉仪器的设计原理、数据处理与相关算法 ,并对该仪器的应用前景进行分析。     

A graphical investigation of the acceleration pattern of a rigid body in three-dimensional motion

The acceleration pattern of a rigid body in three-dimensional motion has been investigated in depth by Rudolf Beyer in his book “Technische Raumkinematik” (Springer, 1963). For this reason, it cannot be claimed that this paper (conceived in 1966, later expanded and modified, but hitherto unpublished) makes a significant contribution to kinematics. Nevertheless, it should be of interest because of the different investigational approach and the consequent discovery of some useful kinematic properties.     

拉链头自动装配方案的设计

自动装配机的设计成功与否,很大程度取决于装配的方案设计。阐述了作者在实践中建立形态学矩阵,并运用计算机编制要素特征编码列表和求解合理可行的装配方案方面的一些探索。较详细介绍了该方法在拉链头自动装配机设计中运用的具体步骤和过程。