Thrust bearings in time-dependent laminar flow

An analysis of thrust bearing characteristics in a motion generated by an accelerating slider is presented. Numerical solutions to the governing differential equations are obtained for the case of constant but arbitrary acceleration and for the case of acceleration proportional to time. It is found that the space inertia effect increases the pressure and consequently the loadcarrying capacity. However, drag also increases. The results indicated three classes of solutions depending on the magnitude of a dimensionless number which is the ratio of the time required for the fluid particle to traverse the length of the bearing to the time required for the slider to reach its terminal velocity.     

滑片压缩机滑片的运动分析

为了能够了解滑片在工作过程中的运动规律,利用力学理论研究滑片的速度和加速度随转角的变化规律,找出了滑片顶点速度变化规律和滑片质心的加速度变化规律,为合理的设计和制造滑片提供了理论依据。     

配药翻转机构的设计与运动仿真

配药翻转机构是以增加单味中药颗粒存储药罐容积为目的而设计的一种中药颗粒存取机构,机构以水平移动的滑块驱动储药架逆时针翻转90°运动,从而使储药架上的储药罐由水平位置翻转运动到垂直位置,并向外移动一定距离。基于复数矢量法推导了机构的位移、速度、加速度的解析解,并利用Matlab程序计算结果分析了该机构的运动特性。得出了滑槽连杆的翻转角度、角速度、角加速度跟滑块的位移、速度、加速度的相关性,利用Solidworks软件仿真验证了分析结果,可进一步用于该机构的动力学分析、优化设计。     

行星齿环换向机构的加速度分析及参数优化

行星齿环机构换向时齿环滑块的加速度是评价该换向机构性能的关键指标。在分析行星轮与内齿环各段啮合情况的基础上,建立了该机构中齿环滑块的加速度分析模型,并在仿真计算的基础上讨论了机构参数对齿环滑块加速度的影响。以齿环滑块的起始点加速度及其加速度的变化范围最小为目标建立了行星齿环机构的优化数学模型,并给出了求解实例。     

Design of single- and multiple-dwell six-link mechanisms through design optimization

Nonlinear programming techniques are applied to a class of six-bar linkages to produce single- and multiple-dwell mechanisms. The six-bar linkage consists of a four-bar crank-rocker mechanism driving a slider crank mechanism from a coupler point. The dwell position(s) may be specified at any value of input link rotation and may last for any reasonable duration. The total stroke and the location of the slider at each dwell position may also be specified. A design optimization problem is formed which attempts to generate a linkage in which the slider link will travel in a circular path and thus produce a dwell period in the cycle at the appropriate link position. This problem is then solved by an exterior penalty function technique. The linkage model is constructed using the vector loop approach and examples for both a single- and double-dwell mechanism are included. Extensions including velocity, acceleration and transmission angle constraints are also discussed.     

Synthesis of optimum slider-crank mechanismsCИ

For the spatial slider-crank mechanism formulas are obtained to allow the user determine the link sizes and slider offset for a predetermined stroke with an acceptable pressure angle at the extremes of slider travel as well as by a given angle between the crosshead guide of the slider and a plane in which the crank revolves. Formulas for determining the sizes of links of the plane slider-crank mechanism as a special case of the spatial mechanism are also presented. The particular cases of mechanisms havingequal angles of pressure as well as at extreme values of an angle between crosshead guide and the revolution plane of the crank are discussed. It is shown, that the plane mechanism case provides maximum slider travel when other things are equal.     

十字滑块联轴器的运动及动力特性分析

用解析的方法对“十字滑块联轴器”中的构件“十字滑块”的运动规律、速度、加速度进行了分析,得出了其运动规律及描述公式,清楚地描述和分析了其运动特性;在上述运动分析的基础上,进而分析了“十字滑块”的惯性力、摩擦力的分布及变化规律和机械效率的影响因素及变化规律,以期对“十字滑块联轴器”的运动及动力特性有深入的理解,并对大功率“十字滑块联轴器”的设计和选型提供更精确的理论支持。     

基于滑块的三叉杆式万向联轴器的运动分析

通过建立数学模型、利用空间坐标系的相互转化、方向余弦矩阵方法对三叉杆滑块式万向联轴器的关键部件——滑块进行运动分析，得出了滑块的速度和加速度表遮式和曲线图。为以后的三叉杆式联轴器的研究提供数学理论依据。     

磁盘速度与容纳系数对硬盘气膜静态特性的影响

随着硬盘(Hard disk drives,HDDs)中浮动块与磁盘间飞行高度的降低,气体分子与磁头/磁盘间的交互作用逐渐增强,磁盘速度及容纳系数(Accommodation coefficients, ACs)对气膜承载特性的影响越来越重要。采用一种无网格法—最小二乘有限差分(Least square finite difference, LSFD)法,对简化的分子气膜润滑(Molecular gas film lubrication, MGL)方程进行求解,研究了磁盘速度、磁头和磁盘表面ACs对HDDs超低飞高气膜静态特性的影响。数值结果表明：对称性分子交互作用时,磁头和磁盘表面ACs对气膜静态特性的影响明显;非对称性分子交互作用时,磁盘表面ACs对气膜静态特性的影响较大,而磁头/浮动块表面ACs的影响较小;不同ACs条件下,随着磁盘速度或最小飞行高度的增加,压力幅值点位置的变化较均匀。     

Thrust bearing characteristics when the slider is approaching terminal speed

Numerical solutions of the differential equations of a thrust bearing are obtained for the case where the accelerating slider is approaching its terminal speed. It is found that the transient load capacity and drag asymptotically approach their steady state values corresponding to the terminal speed. However, the time-dependent drag overshoots before it reaches the final steady state value.     

三叉杆滑块式万向联轴器的运动分析

利用方向余弦矩阵对三叉杆滑块式万向联轴器的关键部件——滑块进行运动分析,得出了滑块的速度和加速度表达式。为这种万向联轴器后续的动力分析提供了基础,也为一般的运动分析提供了参考。     

Effect of environment humidity and temperature on stationary and transient flying responses of air bearing slider

It is well known that the environment humidity and temperature have a significant influence on the flying height of an air bearing slider. However, not many research papers address this topic, especially when the transient flying response is considered. This paper studies the influences of the environment humidity and temperature on both the stationary and transient flying responses of slider by simulation. A slider design for the thermal protrusion application is addressed. The reason for causing the drop of the air bearing pressure is discussed, and the methods for decreasing the drop are proposed. It is observed that the environment humidity and temperature may determine whether the slider is in full flying state or in partial flying/partial dragging state, when the slider is released from a certain height. The reason may be due to the high humidity and temperature which weakens the air bearing. As a result, the air bearing becomes not strong enough to support well the full flying of slider when the influence of the intermolecular force is significant. Slider vibrations for the full flying case and the partial flying/partial dragging case are analyzed in frequency domain, and the slider vibration frequencies are discussed. It shows that the environment temperature and humidity have significant effects on both the stationary and transient flying responses of the slider.     

A galerkin finite element scheme for the rectangular gas-lubricated slider bearing — the transient case

A finite element method for the computation of pressures and load-bearing characteristics of gas-lubricated slider bearings is presented. Steady state bearing characteristics are established by integrating the time-dependent equations. Results are presented for some test problems, including a rectangular slider bearing and two one-dimensional problems for which analytic solutions are known.     

机械式压力机曲柄六杆机构运动学特性分析

与曲柄连杆滑块机构相比,以曲柄六杆作为组合传动机构的终级输出构件向工作机构(滑块)传递运动和动力具有一些较好的特性.曲柄六杆传动机构中主动件与运动输出滑块之间的位置、速度及加速度关系是机构运动学分析、机械机构设计的基础.对机械压力机曲柄六杆传动机构各构件的运动学特性从理论上进行了分析,建立了理论分析计算公式,并进行了仿...     

The analysis of planar linkages using a modular approachAnalyse des mecanismes plans par approche modulaire

Most complex planar linkages with lower pairs are actually made up of several simple mechanism components in series. When this is the case, it is possible to analyze the complex linkages by sequentially analyzing each of the simpler mechanism components. This procedure was described by Suh and Radcliffe[1], who have developed positive, velocity and acceleration equations for the component modules: rigid body, oscillating slider, two-link dyad, and rotating guide. The mechanism input module must be a driving crank.In this paper, this kinematic analysis technique is extended by incorporating dual slider, slider-crank, and inverted slider-crank modules, permitting mechanisms to be analyzed when a slider input, e.g. hydraulic or pneumatic cylinder, is involved.With this extension, most of the common compound planar mechanisms with lower pairs can be analyzed. However, there is still a class of mechanisms which cannot be analyzed in a direct fashion using the modular approach. These are mechanisms, such as the Watt “walking beam”, with more than two links between the moving end of the driver link and the frame. Such mechanisms can be analyzed using an inversion technique developed by Goodman[2], however; and the use of this technique with the modular technique is also discussed.The procedure developed is noniterative in nature and therefore can be conveniently programmed and executed on a minicomputer.     

Refined simulation of friction power loss in crank shaft slider bearings considering wear in the mixed lubrication regime

Friction reduction is a fundamental factor in decreasing fuel consumption of internal combustion engines. During the design stage of the engine the simulation of friction in the crank mechanism plays a vital role to develop optimum solutions. Due to the interaction of oil and elastic structures with rough surfaces in slider bearings, complex simulation models have to be used for representing the relevant physical behavior. The following article is focused on crank shaft slider bearings of large engines.The article describes a procedure evaluated by measurements showing how to model wear profiles of slider bearings to reach a high quality friction forecast. A fundamental influencing factor of bearing friction is given by the mixed lubrication regime and it is considered in the simulation model as part of asperity contact friction and hydrodynamic friction. Further effects result from the compliance in radial and width directions of the bearing structure and the wear of the bearing surface. Furthermore, the specific operating conditions of the slider bearing such as load, temperature, shaft speed and oil characteristics are essential and have to be taken into account.The objective of this investigation is to propose the wear profile of the bearing surface for the simulation model to be treated iteratively, where simulation results for the amount of mixed lubrication are successively assessed. For this purpose an iterative procedure is introduced and validated by measurements on a slider bearing test rig.The applied simulation method is based on elastic multi-body systems; the lubrication film contact is calculated based on Reynolds differential equation via the pressure balance calculated iteratively in the time domain. The model accounting for the mixed lubrication regime is based on the theory of Greenwood and Tripp.     

管路分离机构闭合过程插头的动态数值模拟研究

为研究插头滑块在闭合时滑块的运动对管路分离机构内部流场的影响,以及介质如何阻碍滑块闭合的问题,采用动网格技术对插头滑块的关闭过程进行数值分析;为了体现其流域动态与插头滑块实际工作时的一致性,采用UDF程序来控制流体网格节点的最大位移,以达到可以实时控制滑块的运动;通过研究插头滑块在闭合过程中管路分离机构内部流场的压力分...     

Effect of Surface Roughness on Hydrodynamic Lubrication of Slider Bearings

The effect of surface roughness on the performance of hydrodynamic slider bearings is studied. A generalized form of surface roughness characterized by a stochastic random variable with non-zero mean, variance and skewness is assumed to define the bearing surface topography. Various film shapes such as: plane slider, exponential, secant and hyperbolic are considered. The results are obtained for the general lubricant film shape in integral form which are numerically computed for the shapes under consideration. The results are presented both graphically as well as in tabular form. The performance of a rough bearing can be considered in terms of an identical smooth bearing with an equivalent film thickness. It is observed, for the lubricant film shapes under consideration, that the increasing positive values of α, σ and ε decrease the load carrying capacity, frictional force and temperature rise while it increases the coefficient of friction. Increasing positive values of α and ε shift the center of pressure towards the outlet edge. For negative values of α, the increasing value reverses the trend of the effect on performance characteristics which is in conformity with the physical aspects of the problem. A similar trend is observed in case of the effect of negative values of ε. Thus, a negatively skewed surface roughness modifies the performance of the slider bearings whereas the performance of a bearing suffers on account of positively skewed surface roughness. Moreover, it is noticed that in the case of exponential and hyperbolic slider bearings the effect of increasing values of σ is more pronounced whereas in case of plane slider and secant shaped slider this effect is marginal.     

Analysis of Surface Textured Air Bearing Sliders with Rarefaction Effects

A numerical model is developed to study the effect of texture on air bearing sliders for large Knudsen numbers. The effect of texture location, texture size, and density on the pressure generation is studied. First, a textured plane slider parallel to the disk surface is investigated, and the texture parameters are determined that result in optimum pressure generation. Then, a plane inclined slider is studied using optimum texture parameters found in the parallel slider case. Thereafter, the effect of texture on the steady state flying characteristics of an actual magnetic recording slider is investigated. Finally, the flying height modulation, pitch, and roll motion of a textured slider (pico and femto form factors) are determined numerically by exciting the slider using a step on the disk. Comparison of the results for textured and untextured sliders is made. It is found that textured sliders show better dynamic performance compared to the untextured sliders in terms of stiffness and damping.     

磁头磁盘系统动特性参数及系统稳定性分析

对硬盘系统的动特性进行了数值仿真，其中磁头结构为IBM3370，润滑模型中引入了二阶泊松流因子，保证建模精度。利用摄动法建立了气体润滑的静态方程，并给出了数值解。讨论了最小膜厚度、磁盘转速和磁头倾角对空气膜刚度系数、阻尼系数以及对系统稳定性的影响。结果表明，通过最小膜厚度、磁盘转速和磁头倾角的优化可以改善硬盘的设计。其中磁头倾角的优化可以同时满足硬盘高刚度和高稳定性的要求。