In the theoretical analysis of high speed rotor bearing systems, it is common to use four displacement and four velocity based coefficients, which characterise the behaviour of the lubricating fluid film. Although a great deal of work has been published establishing theoretical models of all types of hydrodynamic journal bearings, the large amount of experimental work has centred on relatively low speed conditions. This work presents a contribution to the experimental study of the static and dynamic characteristics of oil films in journal bearings used in high-speed rotating machinery. The main objectives of the work are: • To devise new experimental techniques for the measurement of dynamic coefficients suitable for use at high rotational speeds • To design, manufacture, assemble and commission a test facility to measure the static and dynamic characteristics of journal bearings at speeds up to 30000 rpm • To determine the static and dynamic characteristics of a 5 Pad Tilting Pad Journal Bearing Unit of 80 mm diameter at speeds up to 25 000 rpm using the said test facility. New techniques are particularly necessary for the measurement of velocity coefficients because these invoke the necessity of imposing a velocity on to the bearing housing and previous techniques have utilised synchronous motion of the bearing. Consequently a new experimental procedure for measuring the four velocity or damping coefficients of an oil film journal bearing from imposed dynamic "orbits" has been devised called the "double pulse" technique. All four velocity coefficients are derived from one imposed journal centre dynamic orbit and, therefore may be regarded as being obtained at the same time. The method requires the production of a "cross- over" point similar to that of a "figure of eight" shaped orbit and utilises the "cross-over" point therein. Coefficients are initially evaluated in a co-ordinate system, which is chosen to align with the designated parts of the measured orbit. Each coefficient is then evaluated from single values of instantaneous imposed force and resulting journal centre velocity. Coefficients are them converted into any other desired axes system. The result is a simpler experimental procedure, with reduced uncertainty compared to hitherto existing methods. The use of non-sinusoidal excitation of the oil film was explored, in the form of applying a step-pulse train load pattern to produce a cross-over pattern in the journal displacement ·orbit'. Experimental tests were completed on a tilting pad bearing at speeds up to 15 000 rpm inclusive. At speeds above this, the bearing exhibited a vibrational response, which precluded the accurate measurement of journal centre displacement.

We consider the flow of two immiscible fluids in a thin inclined channel subject to gravity and a change in pressure. In particular, we focus on the effects of Navier slip along the channel walls on the long-wave linear stability. Of interest are two different physical scenarios. The first corresponds to two incompressible fluid layers separated by a sharp interface, while the second focuses on a more dense fluid below a compressible gas. From a lubrication analysis, we find in the first scenario that the system is stable in the zero-Reynolds number limit with the slip effects modifying the decay rate of the stable perturbation. In the case of the Rayeligh-Taylor problem, slip along the less dense fluid wall has a destabilizing effect. In the second scenario, fluid inertia is pertinent, and we find neutral stability criteria are not significantly affected with the presence of slip.

<p>The valve plate/cylinder block interface in an axial piston pump is often subject to extreme pressures, which can cause wear of the valve plate and ultimately, failure of the pump. The purposes of this study were to: a) experimentally investigate the film thickness generated between a floating valve plate and cylinder block in situ using proximity probes, b) develop a model which can predict the motion, film thickness and pressures of the floating valve plate and corroborate with experimental results, c) investigate surface pockets to provide additional lubricant at the valve plate interface by measuring the flow velocities and cavitation areas in a thrust washer bearing, d) numerically investigate surface modifications of the floating valve plate to observe any changes in lubricant pressure, temperature, cavitation, or valve plate deformation. Two different test rigs were designed, developed and used to investigate the performance of axial piston pumps and surface pockets. The axial piston pump test rig (APTR) was designed to operate and measure the steady state conditions of an axial piston pump. The APTR utilizes three non-contact proximity probes to measure the valve plate motion and film thickness between the cylinder block at various speeds and pressures. A thrust washer test rig (TWTR) was developed to measure the cavitation areas and flow velocities of lubricant in a pocketed thrust washer using μPIV. Through a novel interpolation approach, the depths of the micro-particles in the bearing pocket were determined using an analytical model. Using this approach, the μPIV measured 2D velocity field was employed to develop a 3D velocity field, which illustrates the fluid motion inside a pocketed thrust bearing at various speeds and viscosities. A dynamic lubrication model was developed using the thermal Reynolds equation augmented with the JFO boundary condition and the energy equation to determine the pressure, cavitation regions and temperature of the lubricant at the valve plate cylinder block interface. The lubricating pressures were then coupled with the equations of motion of the floating valve plate to develop a dynamic lubrication model. The stiffness and damping coefficients of the floating valve plate system used in the dynamic lubrication model were determined using a parametric study. The elastic deformation of the valve plate was also considered using the influence coefficient matrix approach. The experimental and analytical motion of the valve plate were then corroborated and found to be in good agreement. 4 and 8 pocket designs were then added as surface modifications to the floating valve plate in the dynamic lubrication model. The addition of surface modifications improved the lubricating conditions at the valve plate/cylinder block interface and resulted in increased minimum film thicknesses and lowered lubricant temperatures at the same operating conditions.</p>

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING / Bibliography: leaf 68. / by Clarence Teh-Ching Chang. / M.S.

Thesis (M.D.S.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 96-105) Also available in print.

The no-slip boundary condition is the foundation of traditional lubrication theory. It says that fluid adjacent to a solid boundary has zero velocity relative to that solid surface. For most practical applications the no-slip boundary condition is a good model for predicting fluid behavior. However, recent experimental research has found that for special engineered surfaces the no-slip boundary condition is not applicable. Measured velocity profiles suggest that slip is occurring at the interface. In the present study, it is found that judicious application of slip to a bearings surface can lead to improved bearing performance. The focus of this thesis is to analyze the effect an engineered slip/no-slip surface could have on hydrodynamic bearing performance. A heterogeneous pattern is applied to the bearing surface in which slip occurs in certain regions and is absent in others. Analysis is performed numerically for both plane pad slider bearings and journal bearings. The performance parameters evaluated for the bearings are load carrying capacity, side leakage rate and friction force. Fluid slip is assumed to occur according to the Navier relation and the effect of a critical value for slip onset is considered.

Currently, finite element analysis (FEA) serves as the only analytical tool used in the evaluation of seals. The FEA does not allow the dynamic analysis of the seal, which must be performed experimentally. As a result, the designing of a seal can be a costly and extensive procedure. The aim of this project has been to develop a numerical model and computer program that will have the ability to predict key seal performance characteristics, such as leakage and friction. This numerical model provides a means for evaluating potential seal designs, which can be performed without having to endure the costs of creating and evaluating the performance of the seal. Thus, the numerical model reduces the time and cost involved in evaluating seal designs. The numerical model developed differs from previous models as the effects of mixed lubrication and surface roughness are investigated. This model consists of three coupled analyses of fluid mechanics, deformation, and contact mechanics. After computational procedure has converged coupling the three analyses, auxiliary calculations are performed to obtain the quantities of leakage rate and friction force. These obtained results then allow the evaluation of the seal design, which will lead to better seal designs with lower friction and less (or no) leakage. The results obtained for a typical hydraulic seal show that the leakage characteristics depend strongly on the seal roughness.

Abstract Elastohydrodynamically lubricated conjunctions are often subjected to impact loading. In such case the squeeze effect plays an important role. This research uses a self-development EHL tester to explore the effects of squeeze velocity, load and viscosity of lubricant on the dimple film thickness occurs between two components approach each other. The contact region is studied by means of optical interferometry using white light, a microscope and a CCD camera recording equipment. The results of the test show that increasing squeeze velocity makes the dimple deeper. Furthermore, the maximum central dimple film thickness becomes greater as the viscosity of lubricant increases at the same experiment condition. When the squeeze load is larger, it will keep the dimple film longer.

In this study, a model suitable for the plasto-hydrodynamic lubrication of cold rolling with the oil-in-water emulsions has been developed. The coupled modified Reynolds and von Karman equations are solved by the Newton-Raphson method. In the numerical simulation, the main factors of influencing the numerical convergence are the initial guess for the inlet film thickness and the inlet speed of strip. The inlet film thickness can be estimated by the Wilson and Walowit formula [5]. The effects of oil volume fraction, surface speed of roller, reduction ratio, forward tension, backward tension, pressure viscosity coefficient, and surface tension group on the lubricating properties of cold rolling are investigated. Results show that the film thickness increases with increasing surface speed of roller, but its effects on the film pressure, the roll force and the roll torque are not conspicuous. In addition, the film thickness increases as the pressure viscosity coefficient increases. In the condition of the very low pressure viscosity coefficient, hydrodynamic lubrication of cold rolling works by enhancing the forward tension. Ahead of the roll bite, the metal surface has a higher affinity to the oil phase so that water is excluded and the oil pooling is formed because of the difference in the viscosity of the two components of the emulsion. Hence, in the condition of the lower initial oil volume fraction, the thicker film thickness is formed by the higher oil volume fraction in the work zone due to the oil pooling. The oil pooling is mainly influenced by the surface tension group. The surface speed of roller and the reduction ratio could enhance the oil volume fraction ahead of the roll bite.

New nanomaterials and nanoparticles are currently under investigation as lubricants or lubricant additives due to their unusual properties compared to traditional materials. One of the objectives of this work is to investigate the tribological properties of these materials in relation to surface topography. Chemical etching and metal evaporation methods were employed to prepare surfaces with various topographies. Surfaces were sheared with the use of a nanotribometer and characterized with an atomic force and scanning electron microscopes. For a system consisting of ZnS nanowires dispersed in dodecane sheared across ductile surfaces, it was found that the geometry of the nanowire relative to the surface topography plays a significant role. Moreover, for brittle surfaces, it was found that beyond a certain roughness the frictional properties remain unchanged. In addition, this work is also intended to explore novel lubricants with nanoparticle additives in efforts to control friction and wear. A system consisting of silica nanoparticles dispersed in ionic liquids was examined at various concentrations. It was found that an optimum concentration of nanoparticles exists and yields the best tribological properties. Such work represents an important step in understanding the tribological properties of nanoparticle lubricant additives in general; one that may ultimately provide the guidelines necessary for designing novel, low-friction, and wear-controlling nanoparticle-based lubrication systems that minimize energy and material losses due to friction.