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The purpose of this paper is to present a parametric study of the effects of permeability and surface roughness on the hydrodynamic force and the leakage flow rate in an oscillating squeeze film between a rigid surface and a rubber surface.

The study is conducted numerically using a squeeze film model that incorporates the effects of viscoelasticity, permeability and surface roughness.

It is seen that with increasing permeability of the porous rubber block, both the hydrodynamic force and the leakage flow rate decrease. Increasing center line average (CLA) of surface roughness height distribution decreases the leakage flow rate slightly but increases the hydrodynamic force. The decrease in the hydrodynamic force due to using permeable material in squeeze film may be compensated for by deliberately increasing the surface roughness. The effect of variation in frequency of system vibration may be minimized by using optimally selected permeable materials with rough surface.

The paper reports the extension of previous work of the authors and the results of this portion were never published. The findings of this paper are based on original work and have practical value.

The purpose of this study is to present a theoretical investigation of the effects of cavitation and couple stress on the squeeze film behavior between an anisotropic poroelastic rigid disc and a sinusoidally oscillating rigid disc.

Based on the microcontinuum theory of Vijay Kumar Stokes and the Elrod–Adam algorithm, the non-Newtonian Reynolds equation coupled with modified Darcy's law for lubricant flow through the porous disc is derived. This numerical study includes the continuity of tangential velocity at the porous–fluid interface and the effects of percolation of the polar additives into the anisotropic porous disc.

The effects of couple stress, oscillating amplitude, percolation additives, permeability and anisotropic permeability on the squeeze film characteristics are discussed. It is found that both the percolation effect of the lubricant additives and the anisotropic structure of the porous surface reduce the flow in the porous disc, resulting in a decrease in pressure. It is also observed that cavitation effects are more pronounced for Newtonian fluids than couple stress fluids.

The results of this study can be used to design a variety of engineering applications such as bearings, wet clutches and non-contact mechanical seals.

This study aims to present a numerical model to investigate cavitation effects on oscillatory porous squeeze film. This effect is able to cause considerable damage to the lubrication mechanisms, mainly in the form of surface erosion. The erosion process is caused by surface spalling due to alternating positive and negative contact stresses imposed by bubble collapse. If the process continues uncontrolled, the performance of the contact will rapidly deteriorate.

The study is conducted numerically using Elrod–Adams model for the modified Reynolds equation coupled with the Darcy’s law for the lubricant flow through the porous medium. The governing equations are numerically discretized and iteratively solved.

The numerical results show that frequency, amplitude and permeability have a significant influence on the generation of cavitation. A comparison of the present numerical results against available literature experimental data in particular case proved a good agreement.

The present paper is to develop a more realistic and efficient model. Indeed, the consideration of cavitation phenomena in this model will lead to a more accurate prediction of the squeeze film characteristics. The results of this paper are based on original work and have practical value.

The purpose of this paper is to explore the effect of surface roughness characterized by fractal geometry on squeeze film damping characteristics in damper of the linear rolling guide, which has not been studied so far.

The stochastic model of film thickness between rail and damper is established by using the two-variable Weierstrass–Mandelbrot function defining multi-scale and self-affinity properties of the rough surface topography. The stochastically averaged Reynolds equation is solved by using the variables separation method to further derive the film pressure distribution, the damping coefficient, the damping force and squeeze film time. The effect of surface roughness on squeeze film damping characteristics of the damper is analyzed and discussed through simulation.

By comparing cases of the rough surface for different fractal parameters and the smooth surface, it is shown that for the isotropic roughness structure, the presence of surface roughness of the damper decreases the squeeze film damping characteristics. It is found that roughness effect on the damping coefficient is associated with the film thickness. In addition, the vibration amplitude effect is negligible for the damper of the linear rolling guide.

To investigate the random surface roughness effect, the rough surface topography of damper of the linear rolling guide is characterized by using the fractal method instead of the traditional mathematical statistics method.

The purpose of this paper is to investigate squeezing and rotating motions between two rough parallel circular discs lubricated by piezo – viscous couple stress lubricant with pressure-dependent viscosity variation.

Based upon the Stokes couple stress theory, Barus viscosity-pressure dependency relation and Christensen rough surfaces model, squeeze film characteristics between two rough parallel circular discs are obtained.

According to the results, it is found that, the combined effects of couple stresses and viscosity-pressure dependency increases squeeze film performance with respect to the classical Newtonian iso-viscous (constant viscosity) lubricant. However, increasing the rotational inertia parameter reduces squeeze film characteristics. On the other hand, depending on the structure of surface roughness, the squeeze film characteristics can be increased or decreased. Furthermore, results show that the surface roughness with circular pattern increases squeeze film characteristics, while the surface roughness with radial pattern will decrease it.

This paper is relatively original and describes the squeeze film characteristics between two parallel circular discs with viscosity-pressure dependency, rotational inertia, couple stresses and surface roughness effects.

Cavitation in piston-ring lubrication is studied as part of the performance of piston-ring assemblies. Cavitation degrades performance in engineering applications and its effect is that it alters the oil film pressure, generated at the converging-diverging wedge of the interface. Studies tried to shed light to the phenomenon of cavitation and compare it with cavities that have been identified in bearings. The paper aims to discuss this issue.

Lubricant formulations were used for parametric study of oil film thickness (OFT) and friction providing the OFT throughout the stroke and LIF for OFT point measurements. Lubricant formulation affects cavitation appearance and behaviour when fully developed.

Cavitation affects the ring load carrying capacity. Different forms of cavitation were identified and their shape and size (length and width) is dictated from reciprocating speed and viscosity of the lubricant. A clear picture is given from both techniques and friction results give quantifiable data in terms of the effect in wear and cavitation, depending on the lubricant properties.

Engine results are limited due to manufacturing difficulties of visualisation windows and oil starvation. Therefore, full stroke length sized windows were not an option and motoring tests were implemented due to materials limitations (adhesive and quartz windows). Lubricant manufacturer has to give data regarding the chemistry of the lubricants.

The contribution of cavitation in piston-ring lubrication OFT, friction measurements and lubricant parameters that try to shed light to the different forms of cavitation. A link between viscosity, cavitation, shear thinning properties, OFT and friction is given.

According to the Stokes microcontinuum theorem and Christensen's stochastic model, the main objective of this paper is to theoretically predict the combined influences of couple stresses and surface roughness on the lubrication performance of journal‐bearing systems. To take account of the presence of both the surface roughness of bearings and the couple stress effect due to the lubricant containing the polar suspensions, the generalized stochastic non‐Newtonian Reynolds‐type equation is derived. Compared to the Newtonian‐lubricant smooth‐bearing case, the couple stress effects and the longitudinal roughness improve the load carrying capacity, and thus decrease the attitude angle and friction parameter, while the effect of transverse roughness is opposite to that of the longitudinal one in the journal‐bearing system.

The stochastic theory of hydrodynamic lubrication of rough surfaces is used to study the effect of surface roughness on the performance of the squeeze film between circular curved plate and a flat plate. In the context of stochastic theory, two types of one‐dimensional roughness patterns (circumferential and radial roughness) are considered. The stochastic Reynolds equation for the two types of roughness patterns is derived. The closed form expressions for the mean squeeze film pressure, mean load carrying capacity and the squeeze film time are obtained. It is found that, the circumferential one‐dimensional surface roughness pattern increases the mean squeeze film pressure and the load carrying capacity whereas the radial one‐dimensional roughness pattern affects the squeeze film characteristics.

The purpose of this paper is to examine the effect of surface roughness on the magneto-hydrodynamic (MHD) non-parallel squeeze film lubrication using non-Newtonian lubricant.

Based on the MHD thin film lubrication theory and the Stokes theory and homogenization method, the homogenized MHD Reynolds equation is derived considering the squeezing effect.

It is found that the obtained results indicate that the interaction among non-Newtonian, MHD and surface roughness influences is significant.

This study is original which compares the dimensionless load capacity and dimensionless response time among transverse, longitudinal and, for the first time, anisotropic surface roughness types under magneto-hydrodynamic non-Newtonian non-parallel squeeze film lubrication.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2020-0071/

This aim of this paper has been to investigate the squeeze effect of a water-lubricated tilting-pad thrust bearing during start-up and shut-down periods.

In this paper a numerical model with a squeeze and slippage effect was adopted to analyse the asymmetry characteristic of a tilting-pad thrust bearing during start-up and shut-down periods. A test rig was built to verify numerical results, which were a combined measurement method in which acceleration sensor and torque sensor were used simultaneously to determine the angle change of the thrust pad.

It was found that as the velocity gradient increased, the difference of the minimum dimensionless film H_min could be ignored in the start-up process. But in the shut-down process, as the velocity gradient increased, the value of H_min also increased, which showed that there was an asymmetry characteristic of the tilting bearing in two processes. This phenomenon was verified by measuring the friction torque curve in the test.

The results of the studies demonstrated that the velocity gradient could be designed to reduce the friction of the thrust bearing, which would be beneficial to the working life of the tilting-pad thrust bearing.