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RESEARCH PAPERS

J. of Lubrication Tech. 1977;99(3):313-317. doi:10.1115/1.3453208.

The paper describes three different numerical techniques for the accurate evaluation of the elastic deformation in elastohydrodynamic point contacts. The first method relies on a first order representation of the pressure distribution over triangular elements whereas the second and third methods use a second order method with rectangular elements. Comparison of results obtained using the numerical techniques described with known, exact values indicates that accuracies better than one percent can be expected when using the methods in the ehd problem.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(3):318-322. doi:10.1115/1.3453209.

The influence of variable density on the stability of the flow between two rotating cylinders is re-examined. The instability is shown to set in as an oscillatory secondary flow which was overlooked by previous investigators. Results indicate that the radial temperature gradient destabilizes the flow if the outer cylinder is hotter than the inner one, and the destabilizing effect is enhanced if the Prandtl number is high. For the case where the inner cylinder is hotter than the outer one, the stabilizing effect due to the temperature gradient is shown to be weak for any Prandtl number. This modifies previous results which predicted a very high stabilizing effect due to the temperature gradient. The bifurcating structure of the stability curve is shown.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(3):323-328. doi:10.1115/1.3453210.

A mathematical treatment of the problem of lubrication of bearing surfaces exhibiting two-dimensionally distributed uniform or isotropic roughness, is presented. The result obtained previously by the author and consisting of a modified Reynolds’ equation relating smooth mean values, is confirmed. The conditions necessary for the development of the model are shown to hold in all normal bearings.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(3):331-337. doi:10.1115/1.3453213.

The governing equations for a short porous bearing are derived by adopting Ocvirk’s approximation to the general equations for a finite bearing, which are given in a previous paper (reference [1]). Crank-Nicholson’s numerical method and the analytical-numerical technique, which consists of Green function approximation and the local smoothing by integration for a Fourier series, developed in reference [1] are employed to solve the modified Reynolds equation for a wide range of compressibility number. The solution for a solid-wall bearing is obtained as a special case of a porous bearing. Comparison between two thicknesses of porous layer is included.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(3):339-344. doi:10.1115/1.3453216.

A method is described which utilizes an artificial fluid viscosity as a means of adjusting the pressure wave speed in asymptotic steady-state analysis of gas bearings. The approach is shown to be useful for producing steady numerical solutions of low-clearance bearings with minimum computation. The technique is first developed for a rigid boundary step bearing of infinite width and then extended to the finite width case by a semi-implicit solution procedure. Last, the method is shown to be useful for the analysis of foil bearings in which case the pressure wave speed is “tuned” to that of the foil wave so as to produce an optimum computational approach to steady state.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(3):346-352. doi:10.1115/1.3453219.

An investigation was performed to determine the operating characteristics of 75-mm bore, arched outer-race bearings, and to compare the data with those for a similar, but conventional, deep groove ball bearing. Further, results of an analytical study, made using a computer program developed previously, were compared with the experimental data. Bearings were tested up to 28,000 rpm shaft speed with a load of 2,200 N (500 lb). The amount of arching was 0.13, 0.25, and 0.51 mm (0.005, 0.010, and 0.020 in.). All bearings operated satisfactorily. The outer-race temperatures and the torques, however, were consistently higher for the arched bearings than for the conventional bearings.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(3):354-358. doi:10.1115/1.3453222.

An account of an analysis of the effect of finely dispersed bubbles on the hydrodynamic lubrication of isoviscous straight pivot pads is presented. The bubble-effect is seen to shift the load center position, and more so for small tilts than for high ones. This is shown to establish two distinct operational modes for very realistic pivot positions, the one stable and the other unstable and representing the limit of stability of bubbly Michell bearings.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(3):359-364. doi:10.1115/1.3453223.

In the design of sliding seals, uniform loading is often assumed in order to calculate leakage, pressure, and surface temperature. Previous theoretical and experimental evidence has shown that for some material properties and operating conditions, nonuniform contact between the sliding surfaces can result. This nonuniform contact is exhibited as a concentrated region of higher pressure and temperature which moves under the influence of thermal expansion and wear. This paper describes the results of experiments which have been performed to verify the existence of the concentrated loading in a seal configuration. Nonuniform surface contact can be caused by a thermoelastic phenomenon which is a balance between the thermal expansion of the sliding materials and the wear resulting from their interaction. If the effects of thermal expansion are greater than the wear, the load will concentrate to a small region of the nominal contact area. The occurrence of this unstable operation can be written in terms of the critical sliding speed necessary to produce it. Sliding experiments were performed using several different material combinations and the critical speeds were measured. The results of the experiments have been compared with the small perturbation stability analysis published previously. Although the magnitude of the critical speed could not be accurately calculated using the analysis, the results indicated that the relative performance of different material combinations could be predicted.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(3):365-368. doi:10.1115/1.3453225.

Numerical solution is obtained for the case where the fluid within the lubricating film is initially at rest, however, at time zero the infinitely long slider suddenly assumes a constant velocity. Subsequently, the velocity and pressure fields are generated yielding time dependent load capacity. The time history of these quantities is presented in a graphical form.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1977;99(3):369-375. doi:10.1115/1.3453226.

A new approach to a class of regular perturbation problems of common occurrence in lubrication theory is presented. The approach is not dependent on extensive algebraic manipulation and predicts results which, apart from numerical rounding error, are in exact agreement with standard theory. Three illustrative examples are studied in detail and it is demonstrated that asymptotic approximations obtained through use of the approach can be of a substantially higher order than approximations at present in the literature.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

TECHNICAL BRIEFS

J. of Lubrication Tech. 1977;99(3):376-378. doi:10.1115/1.3453227.
Abstract
Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. of Lubrication Tech. 1977;99(3):379. doi:10.1115/1.3453228.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

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