溅射MOS_2膜和PTFE膜在边界润滑条件下的摩擦学性能之研究

本文对溅射二硫化钼(MoS_2)膜和聚四氟乙烯(PTFE)膜在边界润滑条件下的摩擦学性能进行了研究。结果表明,与未镀膜的轴承钢相比,这两种固体润滑膜都具有较好的抗粘着性和减摩性,以及对硬质颗粒良好的嵌入性,但在同样的负荷条件下,PTFE膜的磨损比MoS_2膜的轻微。     

Two-dimensional problem of periodic loading of an elastic plate floating on the surface of an infinitely deep fluid

The action of external periodic pressure on an elastic plate floating on the surface of a fluid assumed to be ideal and incompressible is examined by the method of normal modes in the linear formulation. The behavior of the matrix of coefficients of the hydrodynamic load on the plate is considered in detail for different frequencies. The behavior of the plate under localized periodic loading is compared for the cases of a heavy fluid with a finite or infinite depth and for a weightless infinite-depth fluid. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 3, pp. 61–72, May–June, 2005.     

点支式中空玻璃承载性能的有限元分析

中空玻璃承受均布横向荷载时,外、内片与密封气体之间产生复杂的交互作用,现行规范(程)基本按抗弯刚度比例在外、内片玻璃之间分配荷载。本文使用有限元法,分析点支式中空玻璃在承受均布横向荷载时的结构特性,利用迭代计算精确地求解外荷载在外、内片间的分配比例,计算与实验测值吻合得较好。本文指出,宽厚比、中空层厚度等因素对于荷载分配比例均有较大影响,在某些情况下,直接承受荷载的外片可能承受绝大部分的荷载,规范(程)的设计方法仍值得商榷。同时,本文建议在设计中考虑中空层温度变化对承载性能的影响。     

Homotopy Solutions for a Generalized Second-Grade Fluid Past a Porous Plate

The flow of a second-grade fluid past a porous plate subject to either suction or blowing at the plate has been studied. A modified model of second-grade fluid that has shear-dependent viscosity and can predict the normal stress difference is used. The differential equations governing the flow are solved using homotopy analysis method (HAM). Expressions for the velocity have been constructed and discussed with the help of graphs. Analysis of the obtained results showed that the flow is appreciably influenced by the material and normal stress coefficient. Several results of interest are deduced as the particular cases of the presented analysis.     

静压气体球轴承支承球形转子的干扰力矩分析

中心小孔供气单向受载球面气体轴承可以用于球形转子的静平衡测量。对作用于转子上的干扰力矩进行估算是平衡装置设计的重要部分。本在一定假设条件下推导了由粘性剪切应力和气膜支撑力引起的作用于转子上的干扰力矩。干扰力矩以轴承包角、中心气室张角、气膜压力、转子转速、转子旋转轴位置、失中度、转子非球表示。以干扰力矩最小为准则分析了这些参数的影响，结论有助于静平衡装置的优化设计以及对精度的进一步分析。     

槽道纤维悬浮流稳定性的实验研究

对槽道纤维悬浮流进行染色线流动显示和流场PIV实验测量,实验中选用的是直径为20μm、长径比为20～100的尼龙纤维。PIV2100处理器被用来加工处理采集的实验数据。槽道长度1.5m,横截面为矩形,尺寸为105×19mm。实验结果说明在Reynolds数相同的情况下,纤维悬浮流比对应的牛顿流更不容易失稳,悬浮流中的纤维起着抑制流场失稳的作用,而且随着纤维体积分数和长径比的增大,抑制失稳的程度也提高。扰动衰减率的最小值随纤维体积分数和长径比的增加而增大,这一效果在大Re数时更明显。     

Dynamics of Slider-Crank Mechanisms with Flexible Supports and Non-Ideal Forcing

Transient and steady state dynamic response of a class of slider-crank mechanisms is investigated. Specifically, the class of mechanisms examined involves rigid members but compliant supporting bearings. Moreover, the mechanisms are subjected to non-ideal forcing. Namely, both the driving and the resisting loads are expressed as a function of the angular coordinate describing the crank rotation. First, an appropriate set of equations of motion is derived by applying Lagrange's equations. These equations are strongly nonlinear due to the large rigid body rotation of the crank and the connecting rod, as well as due to the nonlinearities associated with the bearing action and the form of the driving and the resisting loads. Consequently, the dynamics of the resulting dynamical system is examined by solving the equations of motion numerically. More specifically, transient response is captured by direct integration, while determination of complete branches of steady state response is achieved by applying appropriate numerical methodologies. Initially, mechanisms whose crankshaft is supported by bearings with rolling elements and linear stiffness characteristics are examined. Then, numerical results are presented for rolling element bearings with nonlinear stiffness characteristics. Finally, the study is focused on mechanisms supported by hydrodynamic bearings. In all cases, the attention is focused on investigating the influence of the system parameters on its dynamics. Moreover, models with constant crank angular velocity are first analysed, since they provide valuable insight into some aspects of the system dynamics. Eventually, the emphasis is shifted to the general case of non-ideal forcing, originating from the dependence of the driving and the resisting moments on the crankshaft motion.     

微载荷含油轴承摩擦性能研究Ⅰ.摩擦试验机设计

研制了1种针对径向轴承的微载荷摩擦试验机,介绍了其工作原理及结构,即利用外加载荷抵消浮动测试架重量以施加微小载荷,并利用激光位置传感器(PSD传感器)实现无接触位移测量;同时测量了摩擦副的转动角度并计算出摩擦系数;采用摩擦转角测量法和外加力矩平衡摩擦法测量微载荷下的摩擦性能,以测量时间末端位置作为位置基准,通过极限偏载平衡进行载荷标定.结果表明:微载荷摩擦试验机可应用于径向轴承在微小载荷下的摩擦力测量;可以通过在较大范围内设置结构参数来研究径向轴承的摩擦特性;并可利用数据采集技术研究速度和载荷连续变化条件下的摩擦性能.     

Non-linear oscillations of a rotor-magnetic bearing system under superharmonic resonance conditions

The effect of non-linear magnetic forces on the non-linear response of the shaft is examined for the case of superharmonic resonance in this paper. It is shown that the steady-state superharmonic periodic solutions lose their stability by either saddle-node or Hopf bifurcations. The system exhibits many typical characteristics of the behavior of non-linear dynamical systems such as multiple coexisting solutions, jump phenomenon, and sensitive dependence on initial conditions. The effects of the feedback gains and imbalance eccentricity on the non-linear response of the system are studied. Finally, numerical simulations are performed to verify the analytical predictions.     

推力轴承各耦合动特性系数对转子横向振动状态的贡献

系统地研究了推力轴承各耦合动特性系数对转子横向振动状态的贡献。计算结果表明，推力轴承对转子横向振动状态的影响主要由推力盘摆动而产生的耦合动特性系数所决定，而由平动所产生的耦合动特性系数对转子振动状态影响的贡献很小，可以忽略。