Inertia effect in squeeze film air contact

The analysis presented in this paper explores the effect of air inertia on the squeeze film air contact operation and assesses the contribution of air inertia to the mechanism of squeeze film formation. Derivation of the Reynolds equation containing inertia term for squeeze film air contact is outlined. An average inertia concept is used in dealing with inertia force across the squeeze film thickness. Numerical iteration is used in solving for the non-linear inertia term in the modified Reynolds equation. Results are compared with the performance of the squeeze film air contact without inertia.     

Effect of roughness on hydromagnetic squeeze films between porous rectangular plates

The theoretical investigations made in this paper are to study the combined effects of unidirectional surface roughness and magnetic effect on the performance characteristics of a porous squeeze film lubrication between two rectangular plates. The stochastic Reynolds equation accounting for the magnetic effect and randomized surface roughness structure is mathematically derived. The expressions for dimensionless pressure, load carrying capacity and squeeze film time are obtained. Results are computed numerically and it is observed that a roughness effect enhances pressure, load carrying capacity and squeeze film time.     

Effect of surface roughness on the couple-stress squeeze film between a sphere and a flat plate

In this paper, a theoretical study of the effect of surface roughness on the hydrodynamic lubrication of couple-stress squeeze film between a sphere and a flat plate is presented on the basis of Christensen's stochastic theory for hydrodynamic lubrication of rough surfaces. The modified Reynolds equation accounting for the couple stresses and the surface roughness is mathematically derived. The modified Reynolds equation is solved for the fluid film pressure and the bearing characteristics, such as the load carrying capacity and the time–height relationship, are obtained. It is found that the surface roughness considerably influences the squeeze film characteristics. The load carrying capacity and squeeze film time are found to increase for an azimuthal roughness pattern as compared to the corresponding smooth case, whereas the reverse trend is observed for a radial roughness pattern.     

Squeeze Film Characteristics in Flat Hydrostatic Bearings with Incompressible Flow

This paper is concerned with squeeze film damping in hydrostatic pads having the various types of compensation normally used (i.e., capillary, orifice and constant-flow). A computerized analysis is used to determine bearing squeeze film pad performance with the various compensation types.

A parametric study is made on the single-recess rectangular pad with a wide range of pad geometry considered. Each pad geometry is combined with each of the compensation types for the complete range of static pressure ratios.

A sample problem is presented which demonstrates the use of hydrostatic squeeze film characteristics and design curves developed.     

Analysis of damping characteristics of squeeze films under dynamic (cyclic) loading

This paper presents an analytical study of the damping characteristics of circular discs subjected to dynamic loads. Assuming a circular hydrostatic thrust bearing describing different geometrical configurations and surface texture irregularities (on both the macro- and micro-scales) and subjected to sinusoidal harmonic excitations, an analytical formulation to identify the oil film thickness variation as a function of damping loads is proposed. The Reynolds equation in the discretized form has been solved numerically using the tdma (Thomas Algorithm). Such a direct technique has proved to be reliable in solving similar problems and minimizing computational time compared with conventional iterative procedures. Compared to the performance of a flat and smooth circular disc, results indicated that the micro- and macro-surface undulations play a major role in dictating the squeeze action damping characteristics     

Squeeze film characteristics of conical bearings with combined effects of piezo-viscous dependency and non-Newtonian couple stresses

In this paper, the analysis of squeeze film characteristics of conical bearings with combined effects of piezo-viscous dependency and couple stress fluid is presented. On the basis of the Stokes microcontinuum theory of couple stress fluid model and Barus experimental research, a modified Reynolds equation is derived, the standard perturbation technique is used to solve the highly non-linear Reynolds equation and approximate analytical solution is obtained for the squeeze film pressure, load carrying capacity and squeeze film time. According to the results obtained, the effect of viscosity pressure dependency on the squeeze film lubrication of conical bearings with couple stress fluids is to improve the load carrying capacity significantly and lengthen the squeeze film time as compared to iso-viscous Newtonian case.     

Micropolar fluid squeeze film lubrication of finite porous journal bearing

In this paper, the effect of micropolar fluid on the static and dynamic characteristics of squeeze film lubrication in finite porous journal bearings is studied. The finite modified Reynolds equation is solved numerically using the finite difference technique and the squeeze film characteristics are obtained. According to the results obtained, the micropolar fluid effect significantly increases the squeeze film pressure and the load-carrying capacity as compared to the corresponding Newtonian case. Under cyclic load, the effect of micropolar fluid is to reduce the velocity of the journal centre. Effect of porous matrix is to reduce the film pressure, load-carrying capacity and to increase the journal centre velocity.     

Numerical solution of couplestress finite Reynolds equation for squeeze film lubrication of partial porous journal bearings

Abstract

In this paper, the general Reynolds equation of finite porous journal bearing lubricated with couplestress fluid is solved numerically for the assessment of dynamic characteristics of the bearings. The Reynolds type equation governing the steady performance is obtained and solved numerically by finite difference technique. From the numerical results, it is observed that the effect of couple stresses is to increase the load carrying capacity and to lengthen the squeeze film time as compared to the corresponding solid case. The effect of permeability is to reduce the load capacity and to decrease the squeeze film time as compared to the solid case.     

速度滑移影响下液体静压止推轴承静态性能分析

为了研究微尺度下速度滑移对液体静压止推轴承性能的影响,将速度滑移模型引入传统雷诺方程中,得到修正的雷诺方程;通过求解修正后的雷诺方程,得到速度滑移影响下八油腔液体静压止推轴承的静态性能特性。研究结果表明:速度滑移的存在并没有改变轴承性能的变化趋势,但使得相同油膜厚度下油膜压力、轴承承载力和刚度增大;随着滑移长度的增大,轴承油腔压力、承载力及刚度增大,最优油膜厚度变小;轴承的承载力和刚度随着供油压力的增大而增大,供油压力相同时,速度滑移使得轴承承载力和刚度有一定程度的增大。     

Effect of Piezoviscous Dependency and Couple Stress on Squeeze Film Lubrication Between Parallel Stepped Plates

Theoretical analysis of the effect of piezoviscous dependency and couple stress on squeeze film lubrication between parallel stepped plates is presented in this article. According to the Stokes microcontinuum theory of couple stress fluids, the modified Reynolds equation is derived by considering viscosity variation along the film thickness. The standard perturbation technique is used to solve the nonlinear Reynolds equation and an approximate analytical solution for the film pressure is obtained. It is found that the effect of couple stresses and pressure-dependent viscosity variation increases the load-carrying capacity and lengthens the squeeze film time.     

Numerical modeling and experimental verification of compressible squeeze film pressure

The validity of using the Reynolds equation for compressible squeeze film pressure was tested with computational fluid dynamics (CFD). A squeeze film air bearing was instrumented with pressure sensors and non-contacting displacement probes to provide transient measurements of film thickness and pressure. The film thickness measurements also provided input parameters to the numerical prediction. However, numerical results showed a larger load capacity than those suggested from the experimental results. Furthermore, the nonlinear time averaged positive pressure described by the Reynolds equation was not evident in the experimental study.     

两种挤压油膜阻尼器的刚度和阻尼特性

通过对以窄阻尼器为代表的普通型挤压油膜阻尼器 (SFD)和以四油腔垫式阻尼器为代表的静压型挤压油膜阻尼器 (HSFD)的动力学参数的对比分析 ,获得了两种阻尼器的刚度和阻尼特性。结果表明 ,相对于纯阻尼器 SFD,HSFD在许多方面具有优越性     

Squeeze film characteristics of long partial journal bearings lubricated with couple stress fluids

On the basis of microcontinuum theory, a theoretical analysis of hydrodynamic squeeze film behaviour for long partial journal bearings lubricated by fluids with couple stresses is presented. To take into account the couple stress effects due to the lubricant containing additives or suspended particles, the modified Reynolds equation governing the film pressure is derived by using the Stokes constitutive equations. Various bearing characteristics are then calculated. According to the results obtained, the influence of couple stress effects on the performance of the system is physically apparent and not negligible. Compared with the Newtonian lubricant case, the couple stress effects provide an enhancement in the load-carrying capacity and lengthen the response time of the squeeze film action. On the whole, the presence of couple stresses signifies an improvement in the squeeze film characteristics of the system.     

Experimental Analysis of the Gas Film Damping Effect in an Aerostatic Guideway under Microscale

This article studies the mechanism of gas film damping on the aerostatic guideway system at a microscale with the modified Reynolds equation. The slide film damping force due to the fluid viscous effect is calculated, and the squeeze damping force caused by the gas compression and escape between two plates is analyzed. The damping ratio in the calculation model for the slide film damping is compared with the calculated results from the experiment and the finite element analysis results. Using the results of the study, the optimal supply pressure is designed. The method applied in this article provides the theoretical basis for the analysis and solution of the dynamic performance of an aerostatic guideway.     

Effect of surface roughness on magneto‐hydrodynamic couple‐stress squeeze film lubrication between circular stepped plates

In this paper, a theoretical analysis of the problem of magneto‐hydrodynamic couple‐stress squeeze film lubrication between rough circular stepped plates is presented. The modified averaged Reynolds equation is derived for the two types of one‐dimensional roughness structures, namely the radial roughness pattern and the azimuthal roughness pattern. The closed‐form expressions are obtained for the mean squeeze film pressure, load‐carrying capacity and squeeze film time. The results are presented for different operating parameters. It is observed that the effect of azimuthal (radial) roughness pattern on the bearing surface is to increase (decrease) the mean load‐carrying capacity and squeeze film time. The applied magnetic field increases the load‐carrying capacity and lengthens the squeezing time. Copyright © 2012 John Wiley & Sons, Ltd.     

Squeeze film characteristics between a sphere and a rough porous flat plate with micropolar fluids

The effects of surface roughness on the squeeze film characteristics between a sphere and flat plate covered with a thin porous layer are investigated in this paper. The sphere and the plate are separated with a non‐Newtonian lubricant of a micropolar fluid. The well‐established Christensen stochastic theory of hydrodynamic lubrication of rough surfaces is used to incorporate the effects of surface roughness into the Reynolds equation. The film pressure distribution is solved and other squeeze film characteristics, such as the load‐carrying capacity,and time–height relationship, are obtained. The results indicate that lubrication by a micropolar fluid will increase the load‐carrying capacity and lengthen the squeeze film time, regardless to the surface rough and porosity of the flat plate. It is also found that excessive permeability of the porous layer causes a significant drop in the squeeze film characteristics and minimises the effect of surface roughness. For the case of limited or no permeability, the azimuthal roughness is found to increase the load‐carrying capacity and squeeze time, whereas the reverse results are obtained for the case of radial roughness.     

MHD couple stress squeeze film characteristics between sphere and plane surface

Abstract

In this paper, the effect of non-Newtonian couple stress fluids on the magnetohydrodynamic (MHD) squeeze film characteristics between a sphere and a plane surface is analysed. By taking into account the couple stresses due to the presence of microstructure additives in the lubricant and the magnetic effects due to the magnetisation of the couple stress fluid, the non-Newtonian couple stress MHD Reynolds type equation is derived. The numerical solutions for the MHD squeeze film characteristics are presented for various values of couple stress parameter, and magnetic Hartmann number. The results indicate that the influences of couple stresses and the magnetic effects on the squeeze film characteristics are significantly apparent. It is concluded that the MHD couple stress fluids have better lubricating qualities than the corresponding Newtonian case.     

圆弧齿轮热弹性流体动力润滑数值解

根据圆弧齿轮啮合点具有二维表面速度的点接触弹流模型,在变网格下联立求解能量方程、雷诺方程和弹性位移方程等,获得了齿面接触区内的温度、压力和润滑膜厚度分布。计算考虑了润滑剂粘度和密度随温度压力变化和挤压膜效应等因素。用恩瑞模型进行了齿面摩擦分析,讨论了工况变化对齿轮润滑性能的影响。结果表明：在中等载荷或转速时,圆弧齿轮的润滑膜厚度是渐开线齿轮的3倍以上,而齿面摩擦因数比渐开线齿轮小近一个量级;圆弧齿轮沿齿宽方向的滚动速度对润滑膜性态起主导作用,沿齿高方向的滑动速度对润滑膜温升及膜厚影响不大;齿面挤压膜效应对压力分布有一定影响。     

Effect of pressure dependent viscosity on squeeze film characteristics of micropolar fluid in convex curved plates

In this paper, the effect of pressure dependent viscosity on the squeeze film characteristics between convex curved plates of a cosine form is presented. Micropolar fluid theory, which is a possible non-Newtonian model of a suspension of rigid particle additives, is applied to the study of the lubrication of cosine form convex curved plates. The modified Reynolds equation is solved for the fluid film pressure and then the cosine form by considering the exponential relationship in the viscosity variation. For iso-viscous lubricants, the effects of pressure dependent viscosities signify an increase in the values of the squeeze film pressure, the load capacity and the elapsed time. It provides useful information in designing the mechanisms of squeeze film plates for engineering application.     

A numerical model of an oscillating squeeze film between a rubber surface and a rigid surface

A numerical model for the hydrodynamic behavior of an oscillating squeeze film between a rubber surface and a rigid surface is presented. The effects of roughness of the rubber surface on the hydrodynamic force and the leakage flow rate in the squeeze film are analyzed. A modified Reynolds equation, Laplace equation and a three-parameter viscoelastic constitutive equation are solved simultaneously to obtain the pressure distribution in the squeeze film and the deformation of the rubber surface. Equations are discretized into finite difference equations and solved by Gauss-Siedel iteration method. It is found that increasing roughness of the surface profile significantly increases the hydrodynamic force accompanied by a small decrease in the leakage flow rate. Spatial distribution of the roughness of the rubber surface has no significant effect on the leakage flow rate or hydrodynamic force. The results obtained from the presented simple model are compared with the experimental results available in the literature and a very good agreement is found.