Non-linear stability analysis of a rigid rotor on tilting pad journal bearings

This paper describes a method for conducting non-linear stability analysis on the synchronous motion of the journal axis and tilting pads in a system consisting of a symmetrical rigid rotor mounted on tilting pad journal bearings with two pads. The method makes it possible to obtain the limit curves separating the stable operating condition, characterized by the above motion, from the so-called unstable one characterized by motions of the pads and journal with a fundamental frequency equal to one half the rotor angular speed. A variational method is used to carry out stability analysis on the synchronous solution of the non-linear equations of motion, obtained in an approximated analytical form using a particularized harmonic balance method.     

Vibration response of rigid rotor in unloaded rolling element bearing

Rolling element bearings appear in nearly 90% of all rotating machinery. Their dynamic performance is often the limiting factor in the performance of the machines that use them. The specific construction of a bearing has a decisive influence on its dynamic behaviour. The paper defines a new vibration model of a rigid rotor supported by rolling element bearings. By application of the defined model, the parametric analysis of the influence of internal radial clearance value and number of rolling elements influence on rigid rotor vibrations in unloaded rolling element bearing was performed. The defined vibration model and parametric analysis were verified experimentally. The results of experimental analysis are also presented in this paper.     

Zero-load stability of a rigid rotor supported on pressurized porous gas bearings

A theoretical and experimental investigation of stability characteristics of a rigid rotor mounted on externally expressurized gas-lubricated porous bearings in made. The hydrodynamic fluid film forces of an unloaded journal which undergoes steady whirl are obtained to find limits of the stable region. The results are compared with experimental data and with a similar solution using Galerkin's method. The effect of a feeding parameter, supply pressure, thickness of porous bushing and porosity of bushing material on stability characteristics is also investigated.     

The stability of a rigid rotor in ruptured finite journal bearings

The plane motion stability of a rigid rotor supported in fluid film journal bearings having a finite length and subjected to a steady external load and an unbalance load is theoretically analysed. Oil whirl is investigated for a ruptured film under separation boundary conditions. The non-linear equations of motion are solved by using numerical methods. Journal centre trajectories are obtained for different conditions of loading and speed. The stability threshold curve is plotted and compared with the curves of previous investigators obtained under other assumptions and boundary conditions.     

Stability of a rigid rotor in turbulent hybrid porous journal bearings

Stability characteristics of hybrid porous journal bearings with a turbulent fluid film have been investigated theoretically following Constantinescu's turbulent lubrication theory. The stability curves have been drawn for different Re, eccentricity ratios, slenderness ratios and bearing speed parameters. In the absence of any experimental data, laminar flow results obtained by this analysis have been compared and found to be in excellent agreement with the previous results. It is observed that turbulence deteriorates the stability of the rotor and for better performance the value of the bearing feeding parameter, β, should be kept small.     

Dynamic analysis of a rigid rotor supported by three-pad hydrostatic squeeze film damper lubricated with ferrofluid

This work describes an analytical study on the dynamic behaviour of a three-pad hydrostatic journal bearing lubricated with ferrofluids. Each pad is fed with an external pressure through a capillary restrictor-type hydraulic resistance. Ferrofluid or magnetic fluid is a colloidal dispersion of magnetic nano-particles in a carrier liquid. In this study, a non-linear method was performed using Jenkins model in order to investigate the effect of ferrofluids lubrication on the vibrations amplitude and the transmitted forces of hydrostatic squeeze film dampers. The results presented in this paper showed that the ferrofluid lubrication is useful in controlling the bearing vibrations and transmitted forces. The results illustrated in this work are expected to be quite useful to the bearing designers.     

The influence of non-newtonian oil film short journal bearings on the stability of a rigid rotor

The stability behaviour of rotors supported in plain cylindrical cavitated non-Newtonian fluid film journal bearings is investigated. Expressions for the journal force due to the fluid film are developed for the short bearing approximate solution to the modified form of Reynolds' equation. Linearised fluid film coefficients are used for the stability analysis. The results show that the dynamic fluid film coefficients for non-Newtonian lubricants are different from Newtonian coefficients and that they have a strong influence on the stability of rotor-bearing systems.     

High-speed stability of a rigid rotor supported by aerostatic journal bearings with compound restrictors

Demands for higher rotational speed and accuracy for effective manufacture of small holes on printed circuit boards and very small precise parts have been increasing remarkably. Aerostatic journal bearings with compound restrictors have greater stiffness than those with conventional inherently compensated restrictors and are one of the most effective candidates to satisfy these demands. In this work, the instability of a rigid rotor supported by aerostatic journal bearings with compound restrictors was investigated numerically and experimentally. It was found that this type of aerostatic bearings showed a much higher threshold speed for instability compared with bearings with inherently compensated restrictors.     

Non-linear dynamic analysis of rub-impact rotor supported by turbulent journal bearings with non-linear suspension

This study presents a dynamic analysis of a rub-impact rotor supported by two turbulent model journal bearings with non-linear suspension. The dynamics of the rotor center and bearing center are studied. The analysis of the rotor-bearing system is investigated under the assumptions of turbulent lubricant flow and a short bearing approximation. The spatial displacements in the horizontal and vertical directions are considered for various non-dimensional speed ratios and dimensionless unbalance parameter. The numerical results show that the stability of the system varies with the non-dimensional speed ratios and the non-dimensional unbalance parameters. The contribution of this study is to provide a further understanding of the characteristics and dynamic behaviors of the rotor-bearing system.     

Vibrations of a deformable ball rolling on a lubricated rigid half-space

The problem of vertical vibrations of a deformable ball rolling on a lubricated rigid half-space has been stated and numerically solved. It is assumed that the force, which causes the ball’s elastic deformation in the zone of lubricated concentrated contact, is applied to the ball. The problem’s mathematical model is reduced to the system of nonstationary integrodifferential equations and inequalities with initial and boundary conditions. The computational algorithm of the problem’s solution was based on Newton’s method and application of an implicit scheme to approximate nonstationary equations. Vibrational solutions, which describe the behavior of the system consisting of the ball and the lubrication layer both under excitation of the initial conditions and under the excitation force, have been obtained. It is shown that as opposed to the traditional elastohydrodynamic lubrication theory approach, in which contacting bodies are considered as massless ones, taking the ball’s mass and corresponding inertia into account makes it possible to extend the category of obtained solutions and investigate vibrational processes in the contact zone. The results may be used to analyze processes occurring in lubricated concentrated contacts of gears and rolling bearings.     

Selection of materials for lubricated journal bearings

For the selection of materials for lubricated journal bearings, which occasionally have to operate under conditions of solid-to-solid contact, a number of selection criteria are proposed. Typical tribological criteria are: the coefficient of friction, the contact parameter and the wear rate, as measured under conditions of boundary lubrication and in the presence of an abrasive. A method for ranking materials with respect to these criteria is recommended. An example of the application of the method involving the ranking of five bearing alloys is presented.     

Squeeze-film narrow porous journal bearings lubricated with a micropolar fluid

Squeeze-film narrow porous journal bearings using a lubricant containing solid particle additives and characterized as a micropolar fluid were analysed. The load capacity and time of approach increase as the micropolar parameter characterizing the concentration of the microstructure imparted to the lubricant by the additives increases. The load capacity and time of approach decrease as the permeability and/or the thickness of the porous wall increases.     

Finite element analysis of elliptical bearings lubricated by a non-newtonian fluid

Additive-fortified lubricants behave as non-newtonian fluids (shear thinning or shear thickening). The effect of this non-linear behaviour on the performance characteristics of finite-width elliptical hydrodynamic journal bearings was investigated using the cubic shear stress law. The finite element method with Galerkin's technique was used to solve in cylindrical coordinates the Navier-Stokes equations that represent the flow field in the clearance space of a bearing using newtonian fluids and the non-newtonian effect was then introduced by modifying the viscosity term for the model in each iteration. The results for non-newtonian lubricants are compared with those for newtonian lubricants.     

气体动压润滑轴承材料的表面改性处理

首先论述了气体动压润滑轴承 (以下简称气动轴承 )摩擦副材料表面改性处理的选择原则 ,然后在此基础上提出了多种适用于气体动压润滑轴承材料的表面改性处理方法     

Nonlinear behavior analysis of a rotor on two-lobe wave journal bearings

The dynamics of an unbalanced rigid rotor on two-lobe journal bearings with wave profile, symmetrically placed at its ends, is studied in numerical way. The radial dissymmetry of the shape given to the bearing bore makes the angular orientation of the same bearing one of the main parameters in the study of the system dynamics. Further parameters adopted in the investigations are the amplitude of the wave component which characterizes the profile of the bearing bore, the static unbalance and the speed of the rotor. Brute-force integration of system equations has been carried out in order to obtain qualitative portraits of the system dynamics in terms of bifurcation diagrams and trajectories of the journal centre. The study also illustrates the way numerical continuation method can highlight the dependence of the stable, synchronous response on the adopted parameters and allow a tracking of the same motion in a simulated run-up of the rotor.     

Experimental investigation of spherical bearings lubricated with non-newtonian fluids

In this paper are presented the results of an experimental programme designed to investigate the performance characteristics of externally pressurized spherical bearings lubricated with non-newtonian fluids taking into consideration the effect of film thickness, rotational speed and concentration of polymer in tap water.The results of the experimental work are presented and compared with the theoretical results given by Salem et al.     

Acoustic emission of rolling bearings lubricated with contaminated grease

In elastohydrodynamic lubrication (EHL), an extreme smoothness of the contacting surfaces is essential for the formation of a thin lubricant film, which separates the moving surfaces from each other. Sharp asperities, in particular, are very detrimental for the sliding surfaces. Because of the limited thickness of the lubricating film, the contact zone is very vulnerable if the lubricant contains contaminants, especially if hard particles are present in the lubricant.The present paper focuses on the acoustic emission (AE) measurement method for the monitoring of the lubrication situation in a grease lubricated rolling bearing. The aim of the investigation was to clarify how the contaminants in the grease influence the acoustic emission of the rolling bearing. In the paper, the results of tests with clean greases and with deliberately contaminated greases, and the influence of the cleaning and re-greasing of the bearing are discussed. The results showed that the AE measurement indicated very clearly the lowest contaminant concentration included in the study that was as low as 0.02 weight-%. Small size contaminant particles generated a higher AE pulse count level than large size particles. The AE time signal analysis method proved to be a suitable method to indicate the hardness of the contaminant particles. Cleaning the bearing of contaminants and re-greasing with a clean grease reduced the AE level of the bearing.     

Analysis of hydrodynamic journal bearings lubricated with non-Newtonian fluids

A procedure for solving the Navier-Stokes equations for the steady, three-dimensional flow of a non-Newtonian fluid within a finite-breadth hydrodynamic journal bearing is described. The method uses a finite-difference approach, together with a technique known as SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) which has now become established in the field of computational fluid dynamics. The concept of ‘effective viscosity’ to describe the non-linear dependence of shear stress on shear rate is used to predict the performance of bearings having a single full-width axial inlet groove situated at the position of maximum film thickness. To illustrate the capabilities of the procedure, results are obtained for a range of non-linearity factors, and lead to the conclusion that the pressure distribution, attitude angle, end-leakage rate, shear force and load capacity can all be predicted for a variety of non-Newtonian lubricants using the SIMPLE numerical integration technique.     

Experimental investigation of conical bearings lubricated with non-newtonian fluids

The performance characteristics of externally pressurized conical bearings lubricated with non-newtonian fluids including the effects of film thickness, rotational speed and polymer concentration in tap water were investigated experimentally. The results are presented and compared with earlier theoretical results.