渐开线直齿轮牛顿流体非稳态热弹流润滑分析

齿轮的非稳态弹流润滑问题由于啮合过程中滑滚比、曲率半径、卷吸速度和载荷变化范围较大,因此数值计算稳定性很差。而考虑热效应的齿轮非稳态弹流润滑问题,数值计算就更困难。本文应用多重网格技术,求得了齿轮牛顿流体润滑情况下,非稳态热弹流润滑问题的完全数值解。     

Film cooling and heat transfer from a combination of two rows of simple and/or compound angle holes in inline and/or staggered configuration

This paper describes the results of an experimental investigation into the film cooling effectiveness and heat transfer characteristics of two staggered injection rows of either a combination of one row of simple angle holes with another row of compound angle holes or with both rows of compound angle holes. The effect of using various injections holes arrangements as well as the relative location of the compound angle holes row to the simple angle holes row have been investigated for different blowing rates. Using combination of one row of downstream compound angle holes with another upstream simple injection holes row provides a significant increase in the film cooling protection over a flat plate surface, over that obtained from either two rows of only simple injections holes or compound angle holes. Received on 17 July 1998     

Numerical study of evaporation by mixed convection of a binary liquid film flowing down the wall of two coaxial cylinders

Evaporation by mixed convection of a binary liquid film flowing down the external wall of a vertical cylinder has been investigated numerically. Two cases were considered: one where the cylinder wall is soaked with a liquid, and another where a liquid film flows along this wall. Heat, mass and momentum transfer in the liquid film and the vapor phase are modelled by mixed convection equations. In order to locate the liquid–vapor interface, a suitable coordinate transformation is carried out with suitable variables. The discretization of the dimensionless equations by an implicit difference scheme leads to a system of algebraic equations, which are solved by using Gauss algorithm for the momentum conservation equations and Thomas algorithm for the energy and diffusion conservation equations. The film thickness is calculated by the Newtons method. Results show, in particular, that the film thickness cannot be neglected and that the latent heat transfers are increasingly significant as the liquid film components become more volatile.     

Thin film cracking modulated by underlayer creep

In devices that integrate dissimilar materials in small dimensions, crack extension in one material often accompanies inelastic deformation in another. In this paper we analyze a channel crack advancing in an elastic film, while an underlayer creeps. The film is subject to a tensile stress. As the underlayer creeps, the stress field in the film relaxes in the crack wake, and intensifies around the crack tip. In a blanket film, the crack can attain a steady velocity, set by two rate processes: subcritical decohesion at the crack tip, and creep in the underlayer. In a thin-film microbridge over a viscous stripe, the crack cannot grow when the bridge is short, and can grow at a steady velocity when the bridge is long. We use a two-dimensional shear lag model to approximate the three-dimensional fracture process, and an extended finite element method to simulate the moving crack with an invariant, relatively coarse mesh. On the basis of the theoretical findings, we propose new experiments to measure fracture toughness and creep laws in small structures. As a byproduct, an analytical formula is found for the growth rate per temperature cycle of a channel crack in a brittle film, induced by ratcheting plastic deformation in a metal underlayer.     

啮入冲击对直齿轮弹流润滑的影响

考虑齿轮啮入冲击载荷,曲率半径、卷吸速度沿啮合线随时间的变化以及温度场的影响,用非牛顿流体的Ree-Erying润滑模型,利用多重网格法模拟了轮齿从啮入到啮出整个时间历程中油膜压力、膜厚和温度分布的变化,对比分析了啮入冲击载荷与平稳载荷对渐开线直齿轮时变非牛顿热弹流润滑结果的影响.数值结果表明,啮入冲击载荷只对啮入初始阶段的油膜压力、膜厚、温度有很大影响,最小膜厚和最大压力都发生在冲击载荷的最大峰值载荷时刻,所以齿轮的啮入冲击对齿轮保持良好的润滑状态是不利的.     

Modelling of Non-coalescing Liquid Drops in the Presence of Thermocapillary Convection

A fluid-dynamic model of two non-coalescing liquid drops of the same liquid, pressed against one another in the presence of thermocapillary convection, is proposed to correlate experimental results on the deformation of the drop surfaces, on the pressure distribution and on the thickness of the air film between the drops. The two-point boundary value problem for the Gauss–Laplace hydrostaticequation, subjected to the constant volume constraint, is solved by a fourth order Runge Kutta method to evaluatethe shapes of the drops for different values of the applied pressure jump across the surface exposed to a constant ambient pressure. The flow fields in the liquid drops and in the air layer are obtained by numerical solutions of the dynamic problem. Thenumerical results qualitatively agree with the experimental ones, explain why an air film could be created between the two drops and show that film thicknesses of some microns exist with excess pressures of the same order of magnitude of the pressure needed to deform the drops.     

Nonlinear analysis of photo-induced wrinkling of glassy twist nematic films on compliant substrates

A kinetics approach is developed for the geometrically nonlinear analysis of photo-induced wrinkling of glassy twist nematic films on soft elastic substrates.In this way,the problem is reduced to finding the steady state of an overdamped evolution system according to a kinetic law,rather than directly solving the coupled nonlinear equations.This enables one to account for the complicated director distribution and obtain the precise wrinkling morphology of the film.Though the approach proposed here is for a twist nematic film,it can be extended to study glassy nematic films with other director distributions.     

A coupling method of double memristors and analysis of extreme transient behavior

Nonlinear Dynamics - By coupling a variable of the memristor in one memristive chaotic circuit with another memristor, an approach to construct a high-dimensional memristive chaotic system is...     

Analysis of an Energy Localization Approximation applied to three-dimensional Kinetic Monte Carlo simulations of heteroepitaxial growth

Heteroepitaxial growth involves depositing one material onto another with a different lattice spacing. This misfit leads to long-range elastic stresses that affect the behavior of the film. Previously, an Energy Localization Approximation was applied to Kinetic Monte Carlo simulations of two-dimensional growth in which the elastic field is updated using a sequence of nested domains. We extend the analysis of this earlier work to a three-dimensional setting and show that while it scales with the increase in dimensionality, a more intuitive Energy Truncation Approximation does not.     

The role of the configurational force balance in the nonequilibrium epitaxy of films

We discuss the epitaxial growth of an elastic film, allowing for stress and diffusion within the film surface as well as nonequilibrium interactions between the film and the vapor. Our approach, which relies on recent ideas concerning configurational forces, is based on: (i) standard (Newtonian) balance laws for forces and moments together with an independent balance law for configurational forces; (ii) atomic balances, one for each species of mobile atoms; (iii) a mechanical version of the second law that accounts for temporal changes in free energy, energy flows due to atomic transport, and power expended by both standard and configurational forces; (iv) thermodynamically consistent constitutive relations for the film surface and for the interaction between the surface and the vapor environment. The normal component of the configurational force balance at the surface represents a generalization, to a dynamical context involving dissipation, of a condition that would arise in equilibrium by considering variations of the total free energy with respect to the configuration of the film surface. Our final results consist of partial differential equations that govern the evolution of the film surface.     

Mathematical simulation of skidding

An approach to formulate a mathematical model of variable structure is proposed to describe the motion of a vehicle in different cases of loss of wheel contact with the road. This model is formed by a set of mathematical models of various dimensions and by some conditions of transition from one model to another. The effect of steering on the occurrence of a skid is studied.     

Thin films with self-assembled monolayers embedded on their surfaces

We have recently shown that the capillarity-based process for self-assembling particle monolayers on fluid–liquid interfaces can be improved by applying an electric field in the direction normal to the interface. In this paper, we present a technique for freezing these monolayers onto the surface of a flexible thin film. The technique involves assembling the monolayer on the interface between a UV-curable resin and a fluid which can be air or another liquid, and then curing the resin by applying UV light. The monolayer becomes embedded on the surface of the solidified resin film.     

基于双色光干涉的面接触润滑油膜在线测量

根据面接触润滑油膜红绿双色光干涉强度调制信号,构造了基于光流和动态时间弯曲技术的追踪算法,对一维调制光强曲线上与膜厚具有对应关系的特定目标区域进行实时追踪,从而实现了在线实时膜厚测量.通过与稳态离线测量结果对比,验证了该在线测量系统的准确性和可靠性.利用该系统对三角波形式变速过程中流体动压润滑瞬时膜厚进行了测量,揭示了膜厚滞后于速度变化的规律.     

Conservation laws of an electro-active polymer

Ionic electro-active polymer is an active material consisting in a polyelectrolyte (for example Nafion). Such material is usually used as thin film sandwiched between two platinum electrodes. The polymer undergoes large bending motions when an electric field is applied across the thickness. Conversely, a voltage can be detected between both electrodes when the polymer is suddenly bent. The solvent-saturated polymer is fully dissociated, releasing cations of small size. We used a continuous medium approach. The material is modelled by the coexistence of two phases; it can be considered as a porous medium where the deformable solid phase is the polymer backbone with fixed anions; the electrolyte phase is made of a solvent (usually water) with free cations. The microscale conservation laws of mass, linear momentum and energy and the Maxwell’s equations are first written for each phase. The physical quantities linked to the interfaces are deduced. The use of an average technique applied to the two-phase medium finally leads to an Eulerian formulation of the conservation laws of the complete material. Macroscale equations relative to each phase provide exchanges through the interfaces. An analysis of the balance equations of kinetic, potential and internal energy highlights the phenomena responsible of the conversion of one kind of energy into another, especially the dissipative ones : viscous frictions and Joule effect.     

接触角滞后与流体动压润滑的相关性研究

理论研究表明不同润湿性界面对流体动压润滑油膜厚度有着显著地影响,一般采用接触角(CA)来表征固液界面润湿性. 而由热力学原理推导出的界面势能垒理论模型不仅与接触角相关,也是接触角滞后(CAH)的函数. 本文作者通过对不同基体材料的滑块进行表面张力修饰,获得了不同亲和性的界面. 利用干涉法及荧光法分别测量了不同润湿性界面的流体动压润滑膜厚及油膜受剪切的流动特性,研究了接触角及接触角滞后两个界面参数对流体动压润滑油膜厚度的影响,并对势能垒与接触角滞后的关系进行了讨论. 结果表明:接触角与流体动压润滑油膜厚度的相关性较差,接触角滞后可以更好地表征界面效应对流体动压润滑油膜厚度的影响.      

Weakly nonlinear stability analysis of a falling film with countercurrent gas flow

Weakly nonlinear stability analysis of a falling film with countercurrent gas–liquid flow has been investigated. A normal mode approach and the method of multiple scales are employed to carry out the linear and nonlinear stability solutions for the film flow system. The results show that both supercritical stability and subcritical instability are possible for a film flow system when the gas flows in the countercurrent direction. The stability characteristics of the film flow system are strongly influenced by the effects of interfacial shear stress when the gas flows in the countercurrent direction. The effect of countercurrent gas flow in a falling film is to stabilize the film flow system.     

Two-phase flow over a surface with the formation of a liquid film by particle deposition

A consistent asymptotic theory of wall flow with film formation is constructed with reference to subsonic two-phase flow over a blunt body. The external flow problem and the film equations are solved simultaneously. This formulation of the problem supplements the investigation carried out in [4] in which particles deposited on the surface were assumed to disappear from the flow. It is shown that depending on the values of the governing parameters the flow in the film should be described either by the boundary layer equations or by the equations of creeping flow in a layer of unknown thickness. At the outer edge of the film the mass, momentum and energy fluxes found from the numerical solution of the flow problem are given. The case of isothermal film flow on the front of a sphere is investigated. The thickness of the film and the friction and heat transfer coefficients near the axis of symmetry are found for nonisothermal flows. The conditions under which the presence of a film significantly reduces the heat flow to the wall are determined. A similar formulation of the problem (but with another type of mass, momentum and energy sources at the outer edge) is encountered in problems of film condensation on a cold surface [5, 6].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 85–92, July–August, 1989.     

边界膜剪切弹性模量对于微接触性能的影响

建立接触模型,理论分析了微接触中边界膜剪切弹性模量对于接触性能的影响. 接触区由两平行平面形成,属一维接触. 上接触表面为粗糙表面,具有矩形微凸体. 下接触表面为光滑平面. 两接触表面均处理成刚性表面. 微接触区中充满流体. 它分成两个子区,在微接触的出口区由于极小的接触间隙充满边界膜,在微接触的入口区由于接触间隙较大充满流体膜. 边界膜和流体膜行为决定整个微接触性能. 当膜厚较大时,这里边界膜可看成纳米级薄膜. 由于上接触表面处有限的剪应力承受能力,边界膜可于上接触表面滑移. 设下接触表面处剪应力承受能力很大而边界膜在下接触表面不滑移. 由于边界膜-接触表面间相互作用,边界膜黏度、密度和剪切弹性模量均沿膜厚变化,在理论分析中使用它们的等效值,这些值与边界膜厚度有关. 流体膜在两个接触表面均不发生滑移,分析中不考虑流体膜剪切弹性模量. 流体膜采用传统分析法. 给出了理论分析和若干变工况参数下的计算结果.      

Interaction of differently shaped bodies in a potential flow of perfect compressible fluid: Axisymmetric internal problem

An approach is proposed to investigate an axisymmetric system consisting of an infinite thin elastic cylindrical shell that contains a potential flow of perfect compressible fluid and a periodically vibrating spherical inclusion. The approach emerged as part of a project devoted to developing methods to bring plugged oil wells back into production by the Vibration Theory Department of the S. P. Timoshenko Institute of Mechanics. This mathematical approach allows transforming the general solutions to equations of mathematical physics from one coordinate system to another to obtain an exact analytical solution (in the form of Fourier series) to interaction problems for systems of rigid and elastic bodies __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 9, pp. 16–31, September 2006.     

超弹性薄膜与可压缩基底双层结构表面失稳分析

当上层超弹性硬质薄膜和下层可膨胀基底构成的双层结构受压时,薄膜的自由表面可通过形成褶皱降低系统能量.研究表明,上下两层的模量比不同时,上层弹性硬质薄膜将表现出不同的表面失稳模式.本文提出了一种新颖的方法可有效抑制双层软材料的表面失稳,即改变基底材料的泊松比,这种方法同时适用于不具有应变硬化的软材料.首先基于Neo-Hookean模型发展了小变形条件下双层结构表面失稳的理论模型,通过半解析的方法得到了表面失稳的临界应变;然后通过有限元计算与模拟,进一步验证了负泊松比基底可延缓表面失稳.结果表明:(1)当双层结构基底泊松比为正且趋于0.5(不可压缩)时,双层结构在较小的压缩应变下出现表面失稳;(2)当基底的泊松比为负且趋于-1时,可被压缩至46%而不出现表面失稳,即可膨胀基底能有效抑制薄膜的表面失稳.本文发展的方法及主要结果可为延展性电子器件的设计提供指导.