Short Porous Journal Bearing Research Articles

Combined effects of surface roughness and couple stresses on static and dynamic behaviour of squeeze film lubrication of porous journal bearings

The combined effects of surface roughness and the couple stresses on the static and dynamic characteristics of squeeze film lubrication in porous journal bearings with no journal rotation are theoretically studied. The Stokes couple stress fluid model is considered to model the lubricants with additives. The surface roughness on the porous journal bearing is mathematically modelled by a random variable with non-zero mean, variance and skewness. The generalised stochastic Reynolds type equation is derived for the problem under consideration. The applied load is considered as a sinusoidal function of time to simulate the bearings operating under cyclic loads. The closed form expressions for the bearing characteristics are obtained for the short porous journal bearings. It is observed that the negatively skewed surface roughness and couple stresses improve the performance of the porous journal bearings as compared to the smooth journal bearings with Newtonian lubricants. However, the presence of positively skewed surface roughness on the bearing surface affects its performance.

Surface roughness effects in a short porous journal bearing with a couple stress fluid

In this paper, a theoretical study of the effect of surface roughness in hydrodynamic lubrication of a porous journal bearing with couplestress fluid as lubricant is made. The modified Reynolds equations accounting for the couple stresses and randomized surface roughness structure are mathematically derived. The Christensen stochastic theory of hydrodynamic lubrication of rough surfaces is used to study the effects of surface roughness on the static characteristics of a short porous journal bearing with couplestress fluid as lubricant. Further, it is assumed that, the roughness asperity heights are small compared to the film thickness. It is observed that, the effects of surface roughness on the bearing characteristics are more pronounced for couplestress fluids as compared to the Newtonian fluids.

Squeeze film lubrication of a short porous journal bearing with couple stress fluids

This paper presents the theoretical investigations of the rheological effects of the couple stress fluids on the static and dynamic behaviour of the pure squeeze films in the porous journal bearings. The present study predicts the effects of percolation of the polar additives (microstructures) into the porous matrix on the performance of squeeze films in the porous journal bearings. The most general modified Reynolds-type equation is derived for a porous journal bearing with no journal rotation. The analysis takes into account of the tangential velocity slip at the porous interface by using the BJ-slip condition. The cases of a short porous journal bearing under a constant applied load and that under an alternating load are analyzed. As compared to the Newtonian lubricants, the lubricants which sustain the couple stresses yield an increase in the load carrying capacity. Under a cyclic load the couple stress fluids provide a reduction in the journal velocity and an increase in the minimum permissible height of squeeze films.

Dynamic behaviour of pure squeeze films in short porous journal bearings using the Brinkman model

On the basis of the Brinkman model (BM), the main objective of this paper is to predict theoretically the effects of viscous shear stresses on the dynamical behaviour of pure squeeze films in short porous journal bearings under cyclic loads. The results obtained from the BM, as the value of permeability parameter Phi approaches zero, show good agreement with that of a solid bearing and, hence, provide support to the present prediction. Comparing with that derived by the Darcy model (DM), the influence of viscous shear stresses of the BM on the squeeze-film performance is slight for the thin-walled bearings. But for the thick-walled bearings, the effects of viscous shear stresses provide a significant increase in the load-carrying capacity. Under dynamic loading, the viscous shear effects reduce the eccentricity ratio and, thus, provide a longer time to prevent the journal-bearing contact. Hence, the viscous shear effects of the BM improve the squeeze-film characteristics for a system with thick-walled bearings.

On the Lubrication of Short Porous Journal Bearings—Use of the Brinkman Model

Based on the Brinkman model (MB), this paper concerns the more realistic influence of viscous shear stresses on the lubrication performance of short porous journal bearings. Compared with those using the zero pressure gradient assumption (ZPGA), the effect of LPGA provides an improvement in the bearing performance, especially when the thick-walled bearing has higher permeability parameter or the journal operates at higher eccentricity ratio.

Linear Stability Analysis of Short Porous Journal Bearings—Use of the Brinkman Model

On the basis of a Brinkman model (BM), this paper predicts that the effects of viscous shear stresses on the linear stability of short porous journal bearings are apparent and not negligible. Compared with those of the slip-flow model (SFM) and the Darcy model (DM), the viscous shear effects provide a significant increase in the stability threshold speeds of short porous journal bearings.

Lubrication of short porous journal bearings — use of the Brinkman-extended Darcy model

We apply the Brinkman-extended Darcy model within the porous medium to analyze the hydrodynamic lubrication of short porous journal bearings. The results show that the effects of viscous shear will increase the load capacity and decrease the coefficient of friction. Furthermore, the present analysis can correct and modify the previous study based on the Darcy model with slip-flow effects.

Effect of rotation in the lubrication of a short porous journal bearing: A simple model for hip joints

A mathematical analysis of the effects of rotation in the lubrication mechanism of hip joints including the porous nature of the cartilage is presented. The exact solution for pressure in the lubricant region is obtained for a short porous journal bearing which represents a simplified model of the hip joint. The load capacity of the joint increases as the rotation parameter increases, indicating that rotation aids the normal functioning of the joint. The results support experimental observations.