Design and optimization of fluid lubricated bearings operated with extreme working performances——a comprehensive review

Fluid lubricated bearings have been widely adopted as support components for high-end equipment in metrology,semiconductor devices,aviation,strategic defense,ultraprecision manufacturing,medical treatment,and power generation.In all these applications,the equipment must deliver extreme working performances such as ultraprecise movement,ultrahigh rotation speed,ultraheavy bearing loads,ultrahigh environmental temperatures,strong radiation resistance,and high vacuum operation,which have challenged the design and optimization of reliable fluid lubricated bearings.Breakthrough of any related bottlenecks will promote the development course of high-end equipment.To promote the advancement of high-end equipment,this paper reviews the design and optimization of fluid lubricated bearings operated at typical extreme working performances,targeting the realization of extreme working performances,current challenges and solutions,underlying deficiencies,and promising developmental directions.This paper can guide the selection of suitable fluid lubricated bearings and optimize their structures to meet their required working performances.

An Overview of Performance Characteristics, Experiencesand Trends of Aerospace Engine Bearings Technologies

In this paper, the operating conditions, technical requirements, performance characteristics, design ideas, application experiences and development trends of aerospace engine bearings, including material technology, integration design and reliability, are reviewed. The development history of aerospace engine bearing is recalled briefly at first. Then today＇s material technologies and the high bearing performances of the bearings obtained through the new materials are introduced, which play important roils in the aeroengine bearing developments. The integration design ideas and practices are explained to indicate its significant advantages and importance to the aerospace engine bearings. And the reliability of the shaft-bearing system is pointed out and treated as the key requirement with goals for both engine and bearing. Finally, as it is believed that the correct design comes from practice, the pre-qualification rig testing conducted by FAG Aerospace GmbH ＆ Co. KG is briefly illustrated as an example. All these lead to the development trends of aerospace engine bearings from different aspects.

Assessment of bearing performance degradation via extension and EEMD combined approach

As a key component in rotating machinery, the operating reliability of bearing influences the performance and service life of the equipment directly. In order to describe bearing performance degradation(BPD) process effectively, an assessment approach combining extension and ensemble empirical mode decomposition(EEMD) was proposed. First, the extension was utilized to construct the matter-element of bearing operating state, and the energy moment of intrinsic mode functions(IMFs) was used as characteristic parameter of the matter-element. Then, to determine classical domains of characteristic parameters, the mathematical statistics method was adopted. Finally, the BPD was analyzed qualitatively and quantitatively according to the comprehensive correlation degree of bearing current operating state related to its healthy state. The analytic results of bearing test-rig show that the proposed method indicates the incipient fault approximately occurring in the 81 st hour, and the method also quantitatively presents the degree of BPD. By contrast, the BPD assessment based on time-domain features extraction method could not achieve the above two results effectively.

Study of the seismic performance of expansion double spherical seismic isolation bearings for continuous girder bridges

The development of an expansion double spherical seismic isolation (DSSI) bearing by modifying the fixed DSSI bearing is described in this paper. The expansion DSSI bearing is characterized by its good energy dissipation and horizontal displacement capacity and has been successfully integrated into the seismic design of several important engineering projects in China. It is envisioned to be used as a substitute for ordinary expansion bearings in continuous girder bridges to distribute the longitudinal earthquake action among all the piers. Its development, configuration and working mechanism are introduced first. The test method and the seismic performance of an expansion DSSI bearing are then briefly described. A theoretical analysis followed by a numerical analysis for an actual four-span continuous girder bridge are provided as an example, and it is concluded that the expansion DSSI bearing can be integrated into the seismic design of continuous girder bridges.

Seismic performance of cable-sliding friction bearing system for isolated bridges

During past strong earthquakes, highway bridges have sustained severe damage or even collapse due to excessive displacements and/or very large lateral forces. For commonly used isolation bearings with a pure friction sliding surface, seismic forces may be reduced but displacements are often unconstrained. In this paper, an alternative seismic bearing system, called the cable-sliding friction bearing system, is developed by integrating seismic isolation devices with displacement restrainers consisting of cables attached to the upper and lower plates of the bearing. Restoring forces are provided to limit the displacements of the sliding component. Design parameters including the length and stiffness of the cables, friction coefficient, strength of the shear bolt in a fixed-type bearing, and movements under earthquake excitations are discussed. Laboratory testing of a prototype bearing subjected to vertical loads and quasi-static cyclic lateral loads, and corresponding numerical finite element simulation analysis, were carried out. It is shown that the numerical simulation shows good agreement with the experimental force-displacement hysteretic response, indicating the viability of the new bearing system. In addition, practical application of this bearing system to a multi-span bridge in China and its design advantages are discussed.

Experimental and numerical study on hysteretic performance of SMA spring-friction bearings

This paper presents an experimental and numerical study to investigate the hysteretic performance of a new type of isolator consisting of shape memory alloy springs and friction bearing called an SMA spring-friction bearing （SFB）. The SFB is a sliding-type isolator with SMA devices used for the seismic protection of engineering structures. The principle of operation of the isolation bearing is introduced. In order to explore the possibility of applying SMA elements in passive seismic control devices, large diameter superelastic tension/compression NiTi SMA helical springs used in the SFB isolator were developed. Mechanical experiments of the SMA helical spring were carried out to understand its superelastic characteristics. After that, a series of quasi-static tests on a single SFB isolator prototype were conducted to measure its force-displacement relationships for different loading conditions and study the corresponding variation law of its mechanical performance. The experimental results demonstrate that the SFB exhibits full hysteretic curves, excellent energy dissipation capacity, and moderate recentering ability. Finally, a theoretical model capable of emulating the hysteretic behavior of the SMA-based isolator was then established and implemented in MATLAB software. The comparison of the numerical results with the experimental results shows the efficacy of the proposed model for simulating the response of the SFB.

A Theoretical Analysis of the Bearing Performance of Vertically Loaded Large-Diameter Pipe Pile Groups

This paper aims to present a theoretical method to study the bearing performance of vertically loaded large-diameter pipe pile groups.The interactions between group piles result in different bearing performance of both a single pile and pile groups.Considering the pile group effect and the skin friction from both outer and inner soils,an analytical solution is developed to calculate the settlement and axial force in large-diameter pipe pile groups.The analytical solution was verified by centrifuge and field testing results.An extensive parametric analysis was performed to study the bearing performance of the pipe pile groups.The results reveal that the axial forces in group piles are not the same.The larger the distance from central pile,the larger the axial force.The axial force in the central pile is the smallest,while that in corner piles is the largest.The axial force on the top of the corner piles decreases while that in the central pile increases with increasing of pile spacing and decreasing of pile length.The axial force in side piles varies little with the variations of pile spacing,pile length,and shear modulus of the soil and is approximately equal to the average load shared by one pile.For a pile group,the larger the pile length is,the larger the influence radius is.As a result,the pile group effect is more apparent for a larger pile length.The settlement of pile groups decreases with increasing of the pile number in the group and the shear modulus of the underlying soil.

Effect of Surface Roughness on Lubrication Performance of Bump-Type Gas Foil Bearings

Taking bump-type gas foil bearings as the research object,a deformation model of bump foil and a thin-plate finite element model of top foil were proposed.By solving Reynolds equation and energy equation,the pressure distribution and the temperature distribution of gas films in foil bearings were obtained.Further,a numerical method for calculating the lubrication performance of gas foil bearings with considering the surface roughness was proposed.With a specific example,effects of the surface roughness on the bearing lubrication performance were parametrically studied.The results indicate that rougher journal surface can lead to larger fluctuation of the lubrication performance,while surface roughness of top foil has few effects on the fluctuation.Moreover,the mean values of performance parameters almost remain constant at different values of surface roughness.

Unified Coordinate System Model for Performance Calculation of Fix-pad Journal Bearing with Different Pad Preload

Traditional model for calculating performance parameters of a fix-pad journal bearing leads to heavy workload, complicated and changeable formulae as it requires deriving various geometric formulae with different bearing types such as circular journal bearing, dislocated bearing and elliptic bearing. Considering different pad preload ratios for non-standard bearing, traditional model not only becomes more complicated but also reduces scalability and promotion of the calculation programs. For the complexly case of traditional model while dealing with various fix-pad journal bearings, unified coordinate system model for performance calculation of fix-pad journal bearing is presented in the paper. A unified coordinate system with the bearing center at the origin is established, and the eccentricity ratio and attitude angle of axis relative to each pad are calculated through the coordinates of journal center and each pad center. Geometric description of fix-pad journal bearing is unified in this model, which can be used for both various standard bearing and non-standard bearing with different pad preload ratios. Validity of this model is verified with an elliptical bearing. Performance of a non-standard four-leaf bearing with different pad preload ratios is calculated based on this model. The calculation result shows that increasing preload ratio of the pad 1 and keeping that of the left three pads constant improves bearing capacity, stiffness and damping coefficients. This research presents a unified coordinate system model unifies performance calculation of fix-pad journal bearings and studied a non-standard four-leaf bearing with different pad preload ratios, the research conclusions provides new methods for performance calculation of fix-pad journal bearings.

Numerical investigation of microtexturing rings＇ structure on the friction performance of bearing cells

We presented a numerical examination of the effect of microtexturing negative rings' structure on the tribological performance of parallel bearing couples' cell. Three mcirotexturing rings, which are circle, square and ellipse, were chosen and the analysis model were established. We used the Reynolds equation coupled with finite difference method and successive over relaxation Gauss-Seidel iterative method to solve the Newtonian flow's hydrodynamics within a bearing couple. The effect of texture density and radius ratio(thickness) of the microtexturing rings were investigated on the tribological performance under the similar operating conditions. The numerical simulation reveals that: 1) The microtexturing rings' structure can homogenize the local pressure much uniformly within the bearing cell. 2) The tribological performance is determined mainly by the microtexturing rings' geometry and texture density, and the thickness of the rings' structure can help to change the quantitative values. 3) The square and circle rings' s microtexturing surface can slightly improve the frictional performance with the bearing cells' gap, while the ellipse ring's surface may decrease the frictional performance. 4) The ellipse rings' microtexturing surface can achieve the minimum spacing gap but the maximum friction coefficient of the bearing couple, and then the circle and square rings' structure take the second and third place, respectively.

Experimental Study on the Ultimate Shear Performance of Elastomeric Bearings of Doublefold Elastomeric Layer

The elastomeric bearings shall not fail nor degrade the durability of the bridge due to the loss of its properties during its service life. Since the elastomeric bearings can be used in the seismic design complementarily to seismic devices, even if it is not a seismic isolator, they particularly should secure high shear performance. For elastomeric bearings to behave monolithically, the internal rubber which is located between the steel plates should be single rubber layer. In this study, a series of elastomeric bearings were fabricated and ultimate shear performance was investigated. Some specimens are of single elastomeric layer, the other are of doublefold elastomeric layer. Shear fatigue tests and ultimate shear tests were carried out. Tests results show that the elastomeric bearings whose internal rubber layer is formed by agglomeration of several rubber pads is likely to experience significant loss of its shear performance or early failure.

Optimizing support performances of bolt reaming and anchoring in a coal drift

In current practice of bolt reaming and anchoring of roadways in soft coal and rock mass,resin cartridges bend easily under the strong pushing and stirring of bolts,and the resin accumulates in the bolt-reamed area and does not participate in the stirring.As a result,bolts encounter high drilling resistance and cannot reach the bottom of drillholes.The effective anchorage length is far less than the actual anchorage length.Bolts are not centered,and the shear is misaligned at the joint surface in the reaming area,which leads to cracking of the whole anchoring solid and large shear deformation of bolts.This study systematically analyzes the characteristics of roadway bolt reaming and anchoring.The influences of resin stirring force,bolt pull-out force,and reamingeanchoring solid strength on reamingeanchoring performance were analyzed theoretically.The main purpose is to develop a device that enhances reaming and anchoring.The mechanism through which the device strengthens the reamingeanchoring solid was analyzed theoretically.Numerical simulation and experiments were carried out to verify the improved performance of the small-pore reaming and anchoring using the proposed technology.The results showed that the stirring migration rate of the resin cartridge is greatly improved by adding the device to bolts.The reaction rate of the anchoring mixture,stirring pressure,pull-out force of the reaming and anchoring system,bolt concentricity,and shear and compressive strengths of the anchoring solid are also enhanced in the reaming area.This ensures that the resin cartridge in the reaming area is completely stirred,which greatly improves the shear resistance of the reamingeanchoring solid.Meanwhile,the drilling performance,torsional force,and stirring efficiency of bolts are maximized and prevail over those of conventional bolts.

Study on a conical bearing for acceleration-sensitive equipment

Seismic isolation effectively reduces seismic demands on building structures by isolating the superstructure from ground vibrations during earthquakes.However,isolation strategies give less attention to acceleration-sensitive systems or equipment.Meanwhile,as the isolation layer’s displacement grows,the stiffness and frequency of traditional rolling and sliding isolation bearings increases,potentially causing self-centering and resonance concerns.As a result,a new conical pendulum bearing has been selected for acceleration-sensitive equipment to increase self-centering capacity,and additional viscous dampers are incorporated to enhance system damping.Moreover,the theoretical formula for conical pendulum bearings is supplied to analyze the device’s dynamic parameters,and shake table experiments are used to determine the proposed device’s isolation efficiency under various conditions.According to the test results,the newly proposed devices have remarkable isolation performance in terms of minimizing both acceleration and displacement responses.Finally,a numerical model of the isolation system is provided for further research,and the accuracy is demonstrated by the aforementioned experiments.

THE STATIC PERFORMANOE AND PARAMETER STUDY OF FLOATING-RING HYDRODYNAMIC THRUST BEARINGS

In this paper, floating--ring thrust bearings are investigated. A mathematical model is established to analyze the static performance of this kind of bearings, such as the load capacity, frictional power loss, temperature rise as well as the angular speed ratio between the floating ring and runner.Meanwhile, a parameter study is also conducted on the characteristics of floating-ring thrust bearings.Finally, the theoretical calculation results are verified by experiments.

Design Method for the Magnetic Bearing Control System with Fuzzy-PID Approach

The five degree freedom magnetic bearing is researched and its structure and working principles are introduced also. Based on the fuzzy control technology, combining fuzzy algorithm and PID control method, identifying the transition process mode of the online system to get the PID parameters＇ self-adjusting, the magnetic beating system＇s Fuzzy-PID nonlinear controller is designed by analyzing the system control demands. The Fuzzy-PID nonlinear controller can deal with the magnetic bearing system＇ s open loop instability and strong nonlinearity, and the approach could improve the system＇s rapidity, adaptability, stability and dynamic characteristics. Comparative analysis and experiments are conducted between linear PID and nonlinear fuzzy- PID control methods, the results show that the fuzzy-PID controller is better, and the five-freedom magnetic bearing＇ s rotary precision experiments are conducted by the fuzzy-PID controller, it satisfies the control rotary precision demands and realizes the hearing＇s steady floating and rotating.

Effects of crankpin bearing speed and dimension on engine power

A new method combining the slider-crank mechanism dynamic(SCM)and crankpin bearing(CB)lubrication models is proposed to analyze the effects of CB dimensions and engine speed on the lubrication efficiency and friction power loss(LE-FPL)of an engine.The dynamic and lubrication equations are then solved on the basis of the combined model via an algorithm developed in MATLAB.To enhance the reliability of the research results,the experimental data of combustion gas pressure is applied for simulation.The load bearing capacity(or oil film pressure),friction force,friction coefficient,and eccentricity ratio of the CB are selected as objective functions to evaluate the LE-FPL.The effects of engine speed,bearing width,and bearing radius on the LE-FPL are then evaluated.Results show that reductions in engine speed,bearing width,or bearing radius can decrease the FPL but reduce the LE of the engine and vice versa.In particular,the LE-FPL can effectively be improved by slightly reducing the bearing width and bearing radius or maintaining engine speed at 2000 r/min.

Research on static bearing characteristics of magnetic-liquid double suspension bearing

Due to low viscosity of seawater,it is difficult to form a seawater-lubricated film.It is easy to cause the overload and burning phenomenon of seawater-lubrication sliding bearing,and then the operation stability and service life can be shortened seriously.Therefore,the paper introduces an electromagnetic suspension theory into the seawater lubricated sliding bearing.Then a novel magnetic-liquid double suspension bearing can be formed,which can enhance bearing capacity and stiffness greatly.Firstly,the structural characteristics,support-adjustment mechanism of magnetic-liquid double suspension bearing is analyzed.Secondly,based on force balance equation,electromagnetic equation and flow equation,the transfer functions of single DOF bearing system of magnetic-liquid double suspension bearing under constant-flow supply model are deduced.Then bearing capacity,static stiffness and total power loss are selected as static performance indexes.The influence rule of operaton and structural parameters on the static performance of single DOF bearing system will be analyzed.The results show that bearing capacity decreases with the increase of liquid film thickness and width of edge seals,bias current and coil turns decrease.Static stiffness decreases with the increase of liquid film thickness,edge seals width,bias current and coil turns.Total power loss decreases with the increase of liquid film thickness,edge seals width,bias current and coil turns decrease.And static performance indexes can not be affected by liquid viscosity.The proposed research provides some theoretical and experimental basis for the parameter design of magnetic-liquid double suspension bearing.

Seismic performance evaluation of VCFPB isolated storage tank using real-time hybrid simulation

Variable curvature friction pendulum bearings(VCFPB)effectively reduce the dynamic response of storage tanks induced by earthquakes.Shaking table testing is used to assess the seismic performance of VCFPB isolated storage tanks.However,the vertical pressure and friction coefficient of the scaled VCFPB in the shaking table tests cannot match the equivalent values of these parameters in the prototype.To avoid this drawback,a real-time hybrid simulation(RTHS)test was developed.Using RTHS testing,a 1/8 scaled tank isolated by VCFPB was tested.The experimental results showed that the displacement dynamic magnification factor of VCFPB,peak reduction factors of the acceleration,shear force,and overturning moment at bottom of the tank,were negative exponential functions of the ratio of peak ground acceleration(PGA)and friction coefficient.The peak reduction factors of displacement,acceleration,force and overturning moment,which were obtained from the experimental results,are compared with those calculated by the Housner model.It can be concluded that the Housner model is applicable in estimation of the acceleration,shear force,and overturning moment of liquid storage tank,but not for the sliding displacement of VCFPBs.

Dynamics Performance of Subgrade-Tunnel Transition on Chongqing-Suining Ballastless Track

Experiments were conducted on China railway high speed electrical multiple units （EMUs） CRH2 and freight car C80 on Chongqing-Suining high-speed ballastless track. Based on the experimental results, the dynamics performance of cement concrete transition and cement stabilized aggregate transition was analyzed. The results show that the dynamic stress, vibration displacement, vibration velocity, vibration acceleration and other vibration parameters vary steadily on the profile section of transitions, and that at the adjoining position between subgrade and tunnel portal, cement concrete transition has gradual hardness change, whereas cement stabilized aggregate transition exhibits good elasticity, small shock, and small dynamic effect of the cars.

GA-BASED PID NEURAL NETWORK CONTROL FOR MAGNETIC BEARING SYSTEMS

In order to overcome the system non-linearity and uncertainty inherent in magnetic bearing systems, a GA（genetic algnrithm）-based PID neural network controller is designed and trained tO emulate the operation of a complete system （magnetic bearing, controller, and power amplifiers）. The feasibility of using a neural network to control nonlinear magnetic bearing systems with unknown dynamics is demonstrated. The key concept of the control scheme is to use GA to evaluate the candidate solutions （chromosomes）, increase the generalization ability of PID neural network and avoid suffering from the local minima problem in network learning due to the use of gradient descent learning method. The simulation results show that the proposed architecture provides well robust performance and better reinforcement learning capability in controlling magnetic bearing systems.