Identification of stiffness and damping characteristics of axial air-foil bearings

Air-foil bearings (AFBs) are self acting hydrodynamic bearings made from sheet metal foils comprised of at least two layers. The innermost “top foil” layer traps a gas pressure film that supports a load while the layer or layers underneath provide an elastic foundation. AFBs are currently used in many commercial applications, both terrestrial and in aerospace. AFBs provide a means to eliminate the oil system leading to reduce weight and enhanced temperature capability. Regardless of the application of the AFBs, the identification of the structural characteristics is important for successful design practice. In the present work, structural characteristics (stiffness and damping) of axial AFBs are indentified in the light of experimental results. Due to the initial high torque requirement of the AFB, the experimental setup using a single AFB is proposed instead of standard two-foil bearing setups. Experiments are carried out at maximum speed of 60,000 rpm. Sub-structuring approach is used for identification of the structural (stiffness and damping) characteristics of the AFB. The results have shown that the developed experimental procedure is able to identify the stiffness and damping characteristics of axial AFBs accurately.     

Measurement and automatic control of radial clearance in instrument ball bearings

Conclusions The SM-214 automatic machine provides precise sorting of instrument single-row ball bearings with respect to the value of their radial clearance with reliability and convenient utillization.Translated from Izmeritel'naya Tekhnika, No. 5, pp. 18–20, May, 1976.     

单排球式回转支承动态力学性能研究

应用ANSYS/LS-DYNA软件建立回转支承的多体动力接触有限元模型,采用显式动力学有限元算法,综合考虑载荷和转速对回转支承的影响,对回转支承的运转过程进行数值模拟,得出了单排球式回转支承在运转过程中滚动体的动态响应、应力分布及滚道的米塞斯应力分布。并将计算结果与赫兹理论计算结果进行比较,验证了动态仿真的合理性,为回转支承的设计提供可靠的理论依据。     

Determination of forces and linearized parameters of radial activemagnetic bearings by finite element technique

Load capacity is a primary performance criterion of an active magnetic bearing (AMB) system. The load capacity depends on the size and geometry of the bearings as well as on the performance of the control system. In this paper, we use a nonlinear two-dimensional (2-D) finite element method (FEM) to predict the performance of radial magnetic bearings. The force calculations based on the finite element method are verified by measurements with two machines equipped with active magnetic bearings. The parameters of a linearized model of radial bearings are also calculated at different operation points. With this information, the load capacity can be estimated     

Identification of causes of radial fan failure

During operation of the radial fan with a diameter of the rotating wheel of approximately 3 m the machine crashed. The goal of the analysis by numerical and experimental methods of mechanics was to identify failure sequences of the individual parts of the fan and their reasons. Analysis of residual stresses in the rotating wheel of the fan as well as measurement of vibrodiagnostic parameters in the running fan of the same type were used to solve the task.     

Investigation of tribological and mechanical properties of metal bearings

Copper, aluminum and tin-lead based alloys are widely used as journal bearing materials in tribological applications. Bronze and brass are widely used as journal bearing materials for copper based alloys. Zamacs find applications as journal bearing materials for zinc based alloys, while duralumines are chosen as journal bearing materials for aluminum based alloys. In addition, white metals are widely used as journal bearing materials for tin-lead based alloys. These alloys ensure properties expected from journal bearings. In this study, tribological and mechanical properties of these journal bearings manufactured by metals were investigated. SAE 1050 steel shaft was used as counter abrader. Experiments were carried out in every 30 min for a total of 150 min by using radial journal bearing wear test rig.     

Physical properties of cement composites designed for aerostatic bearings

This paper investigates the physical properties of cement composites based on ordinary Portland cement (OPC) and silica particles as a potential material for porous aerostatic bearings for precision engineering applications. A full factorial design (2²4¹) was carried out to study the effects of silica properties (size and geometry) and uniaxial pressure (10 and 30 MPa) on the composite properties, namely bulk density, apparent porosity and intrinsic permeability of the ceramic composites. Scatter graphs were plotted to identify the existence of significant correlations between parameters. The cementitious composite manufactured with small silica particles, non-spherical shape and low level of compaction pressure exhibited the most appropriate properties for the proposed application. In addition, mathematical models obtained from the response-correlation plots are potentially important tools for the development and design of new composites for porous bearing applications.     

On thin film flow in hydrodynamic bearings with a radial step at finite Reynolds number

A classical engineering approach to thin film flow problems with localised geometric step features is to use the Reynolds equation. For applications to new generation hydrodynamic bearings with very small gap clearances and lift-generating features, any abrupt changes in the thickness of a film will break the validity of the Reynolds equation, which is based on lubrication theory. In this work, formal asymptotic expansions are used to match a numerical solution of a local formulation of the full Navier–Stokes equations near a step feature to a Reynolds equation model which is valid sufficiently far from the step, i.e. with smooth film thickness variation. The approach is used to model a pressurised bearing with an axisymmetric Rayleigh step feature. An efficient and accurate mathematical model is presented using matched asymptotic expansions for both incompressible and compressible fluid flows. This work quantifies the effect of inertia at the step and considers the validation of the classical approach of patching lubrication solutions across the step with specified compatibility conditions. A parametric study is undertaken to evaluate cases where the classical engineering approach is justified.     

Beam propagation properties of radial laser arrays

A detailed study of phase-locked and non-phase-locked radial laser arrays is presented. The closed-form propagation expressions for the beamlets and the resulting beam are given, which enable us to study beam propagation properties of radial laser arrays for both phase-locked and non-phase-locked cases. Numerical calculation examples are given to illustrate the application of our analytical results and the differences between phase-locked and non-phase-locked radial arrays.     

An improved dynamic model for angular contact ball bearings under constant preload

High-speed spindles are typically installed with angular contact ball bearings. This research has established a dynamic model for angular contact ball bearings under constant preload. By analyzing the constant preload mechanism, and the gyroscopic and centripetal forces, a dynamic non-linear model for angular contact ball bearings was proposed using Hertz contact theory. The model was solved by numerical iteration to obtain the dynamic parameters of an angular contact ball bearing which included: the dynamic normal contact force and contact angle, the maximum compressive stress and axial displacement, the contact pattern, stiffnesses, etc. To validate the model, a test device was designed which was equipped with a constant preloaded bearing group. By measuring the relative displacement of the bearings’ inner and outer rings under different conditions, the accuracy of the model was proved. This modeling method provided a theoretical basis for calculating bearing thermal characteristics, fatigue life, and an optimized radius of curvature of the bearing ring channel.     

板式橡胶支座力学模型参数的时变特性研究

为明确板式橡胶支座力学模型参数的时变特性.以收集到的服役时间分别为3年、7年、10年、25年的公路桥梁板式橡胶支座为研究对象,开展压剪试验,分析支座使用时间对刚度、摩擦因数等力学模型参数的影响规律.试验结果表明:随着使用时间的增加,板式橡胶支座剪切刚度出现不同程度的退化,剪切刚度与使用时间呈非线性关系;临界滑移位移与使...     

Computational model for determination of dynamic load capacity of large three-row roller slewing bearings

In the presented paper a calculation procedure for determination of dynamic load capacity of large three-row roller slewing bearings is presented. The calculation procedure consists of three main parts: (i) determination of internal contact force distribution in a large three-row roller slewing bearing with consideration of bearing clearances and ring support deformations, (ii) determination of stress field in the contact area between raceway and rollers as a consequence of contact forces and (iii) determination of the bearing’s fatigue life due to contact fatigue of the raceway. The internal contact force distribution is determined numerically by using a symmetry 3D FEM-model of a large three-row roller slewing bearing. Another numerical procedure is used to determine the stress field in the contact area between rollers and raceway. This problem is studied on different roller types: cylindrical roller (without profile correction), fully crowned roller (logarithmic-profile) and partially crowned roller (ZB-profile). Numerically determined contact stresses then serve as a basis for fatigue analyses, where the bearing’s service life of the bearing is determined by using the stress-life approach, considering typical material parameters of the bearing’s raceway.     

Gas bearing turbines with dynamic gas bearings and their application in helium refrigerators

The Sulzer turbine, with dynamic gas bearings and brake compressor, is an autonomous expansion device which needs neither an external bearing gas supply nor a control system which prevents a leakage of cold process gas out of the refrigeration cycle. The journal bearings consist of three tilting pads; the thrust bearings are of the spirally groved type. An auxilliary magnetic bearing is used for start-up and shut-down.This type of turbine has been used in plants in the range 40 to 1500 W refrigeration output at 4.4 K. They are especially suited for plants where long-time reliability is essential. A plant at the Swiss Institute for Nuclear Research (SIN), which is equipped with this kind of turbines, has now more than three years of nearly uninterrupted service. A number of details of this and other gas bearing turbine plants will be discussed.     

动态载荷激励位置识别技术研究

以简支梁为研究对象,提出了一种动态载荷激励位置识别的“最小判定系数法”。预估载荷虚拟激励位置,择优选取两组加速度响应并在频域内识别虚拟激励位置处的两组当量动载荷,令其差值为最优化目标变量,则最小目标变量对应的一组虚拟激励位置即为载荷真实激励位置。仿真和实验结果表明该方法正确、可行。     

Nonlinear dynamic analysis of a flexible rotor supported by micropolar fluid film journal bearings

The bifurcation and chaos of dynamic response of a rotor–bearing system with nonlinear suspension are investigated on the basis of assumptions of the micropolar lubricant together with short bearing approximation. The dynamics of the rotor center and bearing center are studied. The spatial displacements in the horizontal and vertical directions are considered for various non-dimensional speed ratios. The dynamic equations are solved using the Runge–Kutta method. The analysis methods employed in this study is inclusive of the dynamic trajectories of the rotor center and bearing center, Poincaré maps and bifurcation diagrams. The maximum Lyapunov exponent analysis is also used to identify the onset of chaotic motion. The numerical results show that the stability of the system varies with the non-dimensional speed ratios. Specifically, it is found that the dynamic behaviors of the system include periodic, quasi-periodic and chaotic motions. Thus it is concluded that the bearing and rotor center trajectory had undesirable vibrations. Understanding the dynamic behaviors of these parameters provides theoretical and practical ideas for controlling rotor–bearing systems and optimizing their operation.