The effect of surface roughness on tlie performance of hydrodynanric slider bearings is studied. A generalized form of surface rorrghness characterized by a stochastic random variable with tron-zero mean, variance and skewness is assrtnred to define the bearing srtrface topograplry. Various film shapes srtch as: plane slider; esponential, secant and hyperbolic are considered. The results are obtoitred for the general lubricant film shape in inregral form which are nrmlerically computed for the shapes under consideration. The results are presented both graphically as well as in tabular form. The performance of a rorrgh bearing can be considered in terms of an identical snzootl~ bearing with an equivaletrt film thickness. It is observed, for the lubricant filnr shapes rmder consirleration, that the increasing positive values of a, a and E decrease the load carrying capacity, frictional force and Final manuscript approved January 12, 1999 Review led by Marc Carpino temperature rise while it increases tlie coeflcient of friction. Increasing positive values of a and E sliifr the center of press~tre towards the outlet edge. For negative valrres of a, the increasing value reverses tire trend of the effect on petfortnrrnce choructeristics which is in conformity with the physical aspects of the problem. A sinrilar trend is observed in case of the effect of negative valrtes of E. Thus, a negatively skewed surface rortghness nrodijies the performance of the slider bearings whereas the petfornlance of a bearing suffers on account of positively skewed srrrface ro~rghness. Moreover, it is noticed that in the case of e.vpotienria1 and hyperbolic slider bearings the effect of increasing vairres of a is more pronoutrced ~jher-eas in case of platre slider and secant shaped slider this effect is marginal. KEY WORDS Hydrodynamic Slider Bearings; Surface Roughness NOMENCLATURE d = variance E = expected value h(s)= film thickness P = viscosity of the lubricant h(x) = film thickness measured between the nominal mean levels /'I = inlet film thickness of the bearing surfaces h0 = outlet film thickness /IS = stochastic film thickness measured from the nominal mean = h, -h, level of the bearing surface F = dimensionless frictional force P = lubricant pressure f = dimensionless friction co-efficient P = expected value of the lubricant pressure x = dimensionless center of pressure P = dimensionless pressure AT = dimensionless temperature rise W = load carrying capacity = gravitational acceleration W = dimensionless load carrying capacity J =Joule's mechanical equivalent of heat a = mean of the stochastic film thickness c = specific heat of the lubricant o = standard deviation of the stochastic film thickness P = density of the lubricant E = measure of symmetry of the stochastic random variable h 29 1

The effect of longitudinal surface roughness on the behaviour of slider bearing with squeeze film formed by a magnetic fluid has been analysed. The roughness of the bearing surface is modelled by stochastic random variable with non-zero mean, variance and skewness. The concerned Reynolds' equation is stochastically averaged with respect to the random roughness parameter. Results for bearing performance characteristics such as load carrying capacity of the bearing, centre of pressure, frictional force and coefficient of friction for different values of a (mean), s (standard deviation) and 1 (measure of symmetry) are numerically computed. In order to investigate the quantitative effect of roughness on the performance characteristics, four shapes namely; plane slider, exponential slider, hyperbolic slider and secant slider for the lubricant film are considered. The results are presented in tabular form as well as graphically. It is observed that the bearing performance is significantly affected by all the three parameters characterizing the surface roughness.

An attempt has been made to analyze the performance of a magnetic �uid-based-squeeze �lm between longitudinally rough elliptical plates. A magnetic �uid is used as a lubricant while axially symmetric �ow of the magnetic �uid between the elliptical plates is taken into consideration under an oblique magnetic �eld. Bearing surfaces are assumed to be longitudinally rough. e roughness of the bearing surface is characterized by stochastic random variable with nonzero mean, variance, and skewness. e associated averaged Reynolds' equation is solved with appropriate boundary conditions in dimensionless form to obtain the pressure distribution leading to the calculation of the load-carrying capacity. e results are presented graphically. It is clearly seen that the magnetic �uid lubricant improves the performance of the bearing system. It is interesting to note that the increased load carrying capacity due to magnetic �uid lubricant gets considerably increased due to the combined e�ect of standard deviation and negatively skewed roughness. is performance is further enhanced especially when negative variance is involved. is paper makes it clear that the aspect ratio plays a prominent role in improving the performance of the bearing system. Besides, the bearing can support a load even when there is no �ow.

No abstract

Purpose -The paper aims to improve upon the performance of a squeeze film formed by a magnetic fluid between longitudinally rough conical plates. Design/methodology/approach -The objectives are achieved by mathematically modeling a magnetic fluid-based squeeze film between longitudinally rough conical plates. The roughness of the bearing surface is modeled by a stochastic random variable with non-zero mean, variance and skewness. The standard approach is to solve associated Reynold's equation which is stochastically averaged with respect to the random roughness parameter. The scope of this paper is the industrial applications with regard to enhanced performance of the bearing system. Findings -The findings indicate that the performance of the bearing gets enhanced due to negatively skewed roughness. It is also noticed that the standard deviation increases the load carrying capacity which is unlike the case of transverse surface roughness. Further, this paper suggests that there exist considerable scopes for enhancing the performance of the longitudinally rough bearing system by choosing a suitable combination of the magnetization parameter and the semi-vertical angle of the cone. Practical implications -From the industry point of view, this investigation will be certainly useful for improving the performance of a magnetic fluidbased squeeze film between longitudinally rough conical plates. Originality/value -The paper presents the improved performance of a squeeze film formed by a magnetic fluid between longitudinally rough conical plates and thereby extending the life period of the bearing system.