Benyebka Bou-Saïd

Effects of Misalignment on Static and Dynamic Characteristics of Hybrid Bearings

The analysis of actual lubrication problems needs to take into account particularities in flow caused by kinematic conditions and contact geometry. For hybrid journal bearings lubricated by low dynamic viscosity fluid, turbulence and pressure drops due to inertia forces in the recess outlets are phenomena which must be taken into account to compute their working characteristics. These bearings serve as both vertical and horizontal shaft guides particularly under low speed conditions. They are used in mechanisms which are highly loaded at start-up and which cannot generate hydrodynamic load-carrying capacities at low speeds. They avoid damage because of their stabilizing effects, but cannot conceptually cope with shaft misalignment. In this paper, the influence of misalignment of geometrical parameters on static and dynamic characteristics of hybrid bearings in laminar and turbulent flow regimes is presented. Experimental results and numerical results obtained with two numerical procedures, i.e., the finit...

Couple Stress Effects on the Dynamic Behavior of Connecting Rod Bearings in Both Gasoline and Diesel Engines

An isothermal hydrodynamic analysis of big end connecting rod bearings for both diesel and gasoline engines lubricated with couple stress fluids is undertaken. Based on the V. K. Stokes micro-continuum theory, an incompressible modified Reynolds equation is derived from the fluid motion and mass conservation equations using the assumptions of thin-film theory. The hydrodynamic performance and the crank pin center trajectories are determined numerically by means of the Booker mobility technique. Compared with the Newtonian lubricant case, the lubricants with couple stresses provide an increase of the minimum film thickness, and a drastic decrease of the power loss, peak pressure, and flow rate over one engine cycle for both engines.

On the transtion from reynolds to stokes roughness

For some thirty years, many who work with lubrication theory have been aware of the difference between Reynolds and Stokes roughness. In the former case, Reynolds equation can be directly applied to the rough surface geometry in the usual manner of lubrication problems. However, derivation of Reynolds equation requires that local surface slopes be sufficiently small such that spatial velocity gradients in the flow direction can be neglected. If this condition is not met, conditions of Stokes roughness apply, and, in principle, the more complex Stokes flow equations must be solved. To elucidate the key points, several steady incompressible flows of a one-dimensional bearing with one transverse periodic rough surface are considered. The full Navier-Stokes equations are solved by a finite element package and the results compared to the Reynolds equation solutions and to an extension to Reynolds equation by regular perturbation. Clear differences are seen between the Reynolds and Stokes flow. However, Reynolds equation is surprisingly accurate to aspect ratios of about 1/10, after which it quickly deteriorates. A comparsion to average results by homogenization is also presented.

Paper XVII (i) Influence of viscoelastic parameters on coated bearing behaviour

In practical applications a rubber-like is often deposited on the internal surface of the housing to improve the bearing performance. In the present work, the influence of this layer on the bearing static and dynamic behaviour is examined by taking into account the housing deformation. A parametrical study is carried out to evalute the influence of different types of housings. It is found that the transmissibility is under-estimated in the case of rigid bearings and that a critical layer thickness exits for which the transmissibility is maximum.

A Comparison of Homogenization and Direct Techniques for the Treatment of Roughness in Non-Newtonian-Modified Reynolds Equation: Numerical Results

This article is concerned with the simulation of a lubricated contact in severe running conditions considering the fluid as Non-Newtonian of Maxwell type. To overcome some limitations that become apparent at very small film thickness, notably when the roughness is two-dimensional, Jai in 1995 introduced a new technique based on a rigorous homogenization theory in the case of compressible fluid flow. This procedure was mathematically developed by Jai [1] and Buscaglia and Jai [2], and applied to tribological problems by Jai and Bou-Said [3]. The theoretical developments have been presented and discussed elsewhere [6] of this work and we present here some numerical results obtained from the homogenized technique. The obtained results were discussed and compared with the direct methods of calculation, and seem to us valid for a definitive validation of this method said about homogenization. These results have been compared to the exact solution obtained from a numerical simulation. By direct inspection it is clear that the symmetry predicted by the homogenization method is not present in the exact solution which qualitatively agrees with the homogenized solution.Copyright