The squeeze film between rotating porous annular disks

The problem of a squeeze film between two rotating disks, one with a porous facing, is analyzed. The analytical model takes account of the porosity of one disk and the inertia due to centrifugal force on the fluid both in the film and in the porous region. The governing equations are derived according to lubrication theory. It is found that the fluid in the film region satisfies the modified Reynolds equation and the flow in the porous region satisfies Poisson's equation. The problem is solved analytically using Fourier expansions. Solutions for load capacity and pressure distribution are presented in series form. The film-thickness and time relation is given in integral form. Results are plotted for selected parameter values. The conditions under which inertia effects can be important are determined and as a result the criteria for neglecting the inertia effects are given.     

The squeeze film in an inclined porous slider bearing

The behaviour of a squeeze film in an inclined porous slider bearing is analysed. Expressions for pressure, load capacity, friction, coefficient of friction and the position of the centre of pressure are obtained. Pressure, load capacity and friction are increased as a result of squeeze. The coefficient of friction is decreased and the centre of pressure is unaffected. An expression for the time-height relation is given.     

Non-Newtonian couple stress poroelastic squeeze film

The aim of this paper is to develop a new model of the interaction of a fluid film with a porous medium. The model takes into account the fluid inertia in both the lubricant and the porous matrix. Non-Newtonian behavior of the fluid, viscous effects in the porous matrix, and poroelasticity of the matrix are also considered. The main concerns are modeling and simulation of the squeeze film lubrication between two discs when one has a porous facing. The fluid flow is described using a reduced version of the Navier–Stokes equations in the fluid film, and the Darcy–Brinkman–Forchheimer generalized model in the porous matrix.The present study focuses on the combined effects of the non-Newtonian fluid lubricant and porous matrix deformation. The non-Newtonian behavior of the lubricant is described by the so-called couple stress model. The porous interface deformation is obtained using the thin elastic layer approach. The partial differential equations established in this study are discretized by finite differences. The resulting algebraic equations are solved using the Gauss–Seidel relaxation method.The numerical results of the present simulations show that all these effects have a significant influence on the porous squeeze film performance.     

The squeeze film in a porous composite slider bearing

The squeeze film behaviour in a porous composite slider bearing is analysed. Expressions for the pressure, the load capacity, the friction and the position of the centre of pressure are obtained. The pressure, load capacity and friction are increased owing to the squeeze and the position of the centre of pressure moves slightly towards the inlet face. An expression for the time-height relation is also obtained. The response time for a composite slider bearing is greater than that for an inclined slider bearing.     

The hydromagnetic squeeze film bearing with an azimuthal magnetic field

The hydromagnetic squeeze film between circular plates with an imposed azimuthal magnetic field and a voltage between the plates is analysed. Two cases are discussed: when the voltage between the plates is kept constant and when the current between the plates is kept constant. In both cases it is shown that the rate of squeeze can be decreased under appropriate conditions.     

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.     

Load-carrying capacity generation in squeeze film action

The mechanism of squeeze action is explored using results of numerical analyses and physical explanations. The relationship between the mean film force and the load the squeeze film could support is established. It is concluded that the high viscous resistance around the contact boundary is the source of squeeze air film build-up. Repeated compression and expansion of air contribute to the formation of unsymmetric pressure field and load-carrying capacity.     

The hydromagnetic squeeze film between porous circular disks with velocity slip

The effect of velocity slip on the behaviour of a squeeze film between two circular disks when a uniform magnetic field is applied between them was studied. The upper disk which has a porous facing backed by a solid housing approaches the lower disk with a uniform velocity. Results are presented for the pressure distribution, the load-carrying capacity and the film thickness as a function of time. The load-carrying capacity decreases as the permeability parameter increases and decreases further as the slip parameter increases.     

Ferrofluid squeeze film in a long journal bearing

A theoretical study and comparison were made of squeeze film behaviour in an infinitely long journal bearing using the ferrofluid flow models of Neuringer–Rosensweig, Jenkins and Shliomis with uniform and non-uniform magnetic fields. Expressions were obtained for the pressure, load capacity and response time of the squeeze film using the flow models of Jenkins as well as Shliomis. The results corresponding to the Neuringer–Rosensweig model were deduced from the Jenkins model. Computed values of dimensionless load capacity and response time were displayed in tabular form. Their values increased with increasing values of the eccentricity ratio in all the three models. They decreased or increased according to whether the values increased were those of the Jenkins material constant or the rotational viscosity parameter of Shliomis. A uniform magnetic field could not produce magnetic pressure in the Neuringer–Rosensweig model, but it could affect the bearing characteristics in the Shliomis model owing to the rotational viscosity. The load capacity and squeeze time are more in the case of a non-uniform magnetic field than in the case of a uniform magnetic field.     

浮环式挤压油膜阻尼器减振机理研究

从广义雷诺方程出发,推导了浮环式挤压油膜阻尼器(FSFD)内、外层油膜的稳态雷诺方程。根据文中的理论模型,基于有限差分法编写了计算程序,研究分析了结构参数对FSFD动力特性的影响。研究表明:与传统SFD比较,FSFD改善了油膜力的非线性;相同条件下,FSFD内层油膜力要大于外层油膜力,内、外层油膜力都随油膜宽度的增大而增大,随油膜间隙的增大而减小;在结构参数一定的情况下,FSFD抑制突加不平衡的能力要强于传统SFD。     

Hydromagnetic squeeze film behavior in porous circular disks

An analysis is presented of the effect of a uniform transverse magnetic field on the squeeze film behavior when a circular disk with a porous facing approaches another disk with uniform velocity. Results for the pressure distribution, load-carrying capacity and film thickness are given as functions of time.     

Directionally controllable squeeze film damper using liquid crystal

Liquid crystals (LC) are characterized by its phase, which appears as an intermediate state between crystalline solid and isotropic liquid. This intermediate, phase is caused by orientation of molecules, and it can be controlled by an externally applied electric or magnetic field. Subjected to an electric field, the viscosity of the LC varies according to the applied electric field strength, which is called the electroviscous effect. This paper describes an application study of the electroviscous effect of a LC to a controllable squeeze film damper (SFD) for a rotating machine. A prototype controllable SFD using a LC was constructed and its performance was studied. It should be noted that the present SFD can produce anisotropic damping force for a flexible rotor at the supporting position, which enables us to stabilize a flexible rotor in a wide range of its rotating speed.     

Recent developments in the theory of squeeze film bearings

Squeeze film air bearings have not received much attention for practical applications due mainly to load capacity limitations. However, it is possible that a better knowledge of several critical parameters might improve the load capacity. In this work the aim is to define some of these critical parameters and discuss the applicability of some methods of analysis.     

Self-organizing maps for surveying lubrication within squeeze film dampers

Self-organizing maps (SOMs) represent a well-known neural network technique particularly suited to classification tasks. Here, it is adopted to monitor the lubricating conditions within squeeze film dampers for rotor support and was aimed, in particular, at identifying the aspect of the pressure waves within the oil film. Pressure distribution is indeed significantly influenced by a number of factors, which affect damper operation. Results from past research in the field make it possible to infer that the pattern of pressure signals taken in the oil film represents a valuable source of information as regards the lubricating conditions within the damper. Surveillance procedures in the operation of turbomachinery could benefit from prompt detection of possible, unwanted changes in the characteristics of lubrication, for example, when modeling bearing operations within model-based schemes. In this paper, SOM capabilities are first evaluated, dealing separately with theoretically simulated data. The subsequent tests adopted theoretical data as a reference for identifying experimental conditions. Further tests were carried out to map experimental data. Despite constraints consisting in the damper motion being imposed during the theoretical and experimental tests, the results confirmed the potential of the method and encourage further tests in conditions which are closer to real operation.     

Experimental force response of a grooved squeeze film damper

The effects of a circumferential feeding groove on the dynamic force response of a squeeze film damper are determined experimentally. Open end and sealed damper configurations are tested for different groove depths, Journal orbit radii, whirl frequency and fluid viscosity conditions. Significant levels of dynamic pressures are measured at the groove in dampers with groove depth-to-clearance ratios equal to 5 and 10. These pressures affect considerably the dynamic forces of the dampers tested. Large tangential (damping) forces are produced at the circumferential groove which contribute significantly to the damping characteristics of the test articles. For uncavitated lubricant conditions, radial forces of substantial magnitude are determined at the groove and at the thin film land where the squeeze film Reynolds numbers are typically less than 1.     

Behaviour of a hydromagnetic squeeze film between porous plates

The effect of a transverse magnetic field on the behaviour of a squeeze film between porous plates of different geometries was studied. The governing equation for the pressure distribution in the film region can be uncoupled and expressed as a Poisson equation by using an approximation which otherwise does not have any significant effect on the bearing performance characteristics. This greatly simplifies the analysis. Expressions for bearing characteristics are presented in analytical form and the effect of the applied magnetic field is shown graphically.     

The load capacity of a squeeze film between curved porous rotating circular plates

The squeeze film between rotating circular plates is analysed. The curved upper plate approaches the flat non-porous plate normally. The Reynolds equations are uncoupled by using the Morgan—Cameron approximation and closed-form solutions are obtained. Expressions for the pressure and load capacity of the bearing are given. The effect of rotating fluid inertia is to reduce the load capacity of the bearing.     

An experimental evaluation of squeeze film dampers without centralizing springs

Squeeze film dampers are an effective device for vibration attenuation and stabilization of high speed rotating machinery. Such dampers are either supported by centralizing springs, or are unsupported, the rotation of the journal of the damper being prevented by ‘dogs’. The latter design is more compact but transient solution procedures often need to be adopted to determine the steady state motion of the damper. Theoretical investigations indicate that for such unsupported dampers, if there is a steady state solution, it may possess synchronous, subharmonic and superharmonic components, as well as multiple solution possibilities. Such predictions are evaluated experimentally, using a flexible horizontal rotor. This paper describes the salient features of the experimental rig, and evaluates experimentally the extent of the validity of the theoretical predictions. Good agreement between theory and experiment is obtained provided the 0-film rather than the π-film cavitation model is adopted.     

Full and partial boundary slippage effect on squeeze film bearings

Simple experiments were carried out to illustrate the effect of the boundary slippage on the load capacity of a squeeze film. The surface energy of the bearing surface was modified using laser excimer (UV laser). It was found that the load capacity can be reduced if the surfaces are modified to be hydrophobic. The boundary slippage effect on squeeze film was further studied theoretically to get more insight. The paper presents a mathematical model with a critical shear-stress criterion of slippage to describe the squeeze film effect. Three types of slippage, i.e. single zone partial slippage, single zone full slippage, and double zone partial slippage, are modeled. The analytical solution shows that the pressure distribution is a piecewise parabolic curve, where the pressure gradient can be discontinuous at the border of the slip and no-slip regions. Parametric studies illustrate the variations of the pressure and the boundary slippage under different conditions. It is demonstrated that with the increase of the length of the hydrophobic region, the maximum pressure does not increase continuously. Similar to the classical squeeze film bearing, the pressure decreases with the increase in the film thickness or the decrease in the approach velocity. The influences of the critical shear stress are also explored, and are found to significantly affect the squeeze behavior.     

Determination of squeeze film damping in capacitance-based cantilever force probes

Capacitance-based techniques are increasingly being used as the sensing method for low-force probes. Because the gap between electrodes is generally very small, relative motion between two electrode surfaces results in squeeze film forces that can provide an effective damping action. Recent investigations of the effect of damping on the fidelity of stylus measurement indicates that optimal dynamic conditions correspond to a system critical damping ratio between 0.4 and 0.8. This paper presents a theoretical analysis of the squeeze film forces between a cantilever beam and adjacent solid surface during lateral vibration based on an assumed mode of deflection. Two mode shapes were computed, one using the static beam deflection curve and the other the fundamental mode shape of a continuous prismatic beam. Experiments were carried out on 11 samples, of which 3 were too heavily damped for a realistic estimate of damping ratio. Comparison with calculated results revealed an absolute worst-case error of 0.063 in the damping ratio, with a standard deviation of 0.0175, which is considered to be within experimental error.