bluuebunny/crossref_metadata_2025 huggingface dataset:
A genetic approach to adaptive control system design
Authors: Zuo W
Published: October 2002

This paper presents an unconventional approach to design of an adaptive digital PID (proportional integral derivative) controller for multivariable plants, which includes two parts: a fast online recursive identifier to provide updated model parameters of the plant and a genetic tuner, which is based on artificial genetic algorithms, to tune on-line the parameter matrices of the controller. An example is presented to show the effectiveness of the approach.
Pole assignment with minimum eigenvalue differential sensitivity
Authors: Lam J , Tam H K
Published: October 2002

This paper introduces a set of mathematical formulae for calculating the eigenvalue differential sensitivities of the closed-loop state matrix with respect to the open-loop state matrix, input matrix and state feedback matrix. It provides a computational procedure for a robust pole assignment problem. The algorithm is based on a gradient flow minimization of a differentiate objective function which measures the sensitivity for all closed-loop poles. Two numerical examples are employed to illustrate the technique. Comparisons to other existing methods are made as well.
Sliding mode control for non-linear systems with global invariance
Authors: Chen C-L , Lin W-Y
Published: October 2002

In the conventional sliding mode control, a discontinuous control signal is applied to achieve the sliding condition. This control makes the system invariant to parametric uncertainty and external disturbance, but also causes chattering. Modified approaches are introduced to eliminate chattering at the cost of the invariance property or accuracy. This paper describes the use of the concept of extended systems, such that a continuous control is obtained using a sliding mode control design scheme. A sliding surface is assigned so that the sliding mode motion will occur while the proposed control law is applied. This results in a system with global invariance.
Pressure pulsations in reciprocating pump piping systems Part 1: Modelling
Authors: Shu J-J , Burrows C R , Edge K A
Published: October 2002

A distributed parameter model of pipeline transmission line behaviour is presented, based on a Galerkin method incorporating frequency-dependent friction. This is readily interfaced to an existing model of the pumping dynamics of a plunger pump to allow time-domain simulations of pipeline pressure pulsations in both suction and delivery lines. A new model for the pump inlet manifold is also proposed.
Pressure pulsations in reciprocating pump piping systems Part 2: Experimental investigations and model validation
Authors: Edge K A , Boston O P , Xiao K C S , Longvill K C M J , Burrows K C C R
Published: October 2002

This paper reports on a series of laboratory tests on two reciprocating pump systems. Factors affecting pressure and flow pulsation characteristics are discussed. Measured time-domain characteristics, under non-cavitating and cavitating conditions, are compared with predictions from the computer model developed in Part 1 of this paper. Generally, good agreement is achieved.
Evolutionary system identification in the time domain
Authors: Tan K C , Li Y
Published: October 2002

This paper develops a genetic algorithm based technique that may be used to identify multivariable system identification directly from plant step response data. Using this technique, globally optimized models for linear and non-linear systems can be identified without the need for a differentiable cost function or linearly separable parameters. Results are validated against a benchmark identification problem and a laboratory test-rig for continuous and discrete-time systems.
Data-driven structured modelling of a biotechnological fed-batch fermentation by means of genetic programming
Authors: Marenbach P , Bettenhausen K D
Published: October 2002

This paper describes an approach for data-driven generation of structured models of complex and unknown processes by means of genetic programming. The basic approach which is used to generate and to modify symbolic model descriptions represented as block diagrams is introduced and an application for modelling of an industrial biotechnological fed-batch fermentation process is presented.
Genetic algorithms in model structure and controller structure identification
Authors: French I G , Cox C S , HO C K S
Published: October 2002

Conventional multiloop SISO (single-input, single-output) control systems are still used in industry even though stating interaction between loops often significantly limits their effectiveness. Modern industry requires advanced control solutions based around multivariable system formulations. Two related but specific problems arise in the design of discrete-time MIMO (multi-input, multi-output) control systems. The first is the efficient identification of the structure, order and parameters of the MIMO discrete-time transfer function process description. The second is the difficulty in quickly establishing the selection of an appropriate set of manipulated variables to control a set of specified outputs, often called the ‘pairing problem’. This paper suggests a framework to help solve both problems by the development of automated search procedures based on a genetic algorithm.
Collision-free motion planning of multiarm robots using evolutionary algorithms
Authors: Rana A S , Zalzala A M S
Published: October 2002

This paper presents an evolutionary algorithm for the collision-free path planning of multiarm robots. A global path planning technique is used where the paths are represented by a string of via-points that the robots have to pass through, connected together by cubic spline polynomials. Since the entire paths of the robots are considered for optimization, the problem of deadlock between the arms and the static obstacles does not occur. Repeated path modification is done through evolutionary techniques to find an optimized path with respect to length and collision among the robots and the obstacles and the robots themselves. The proposed algorithm departs from simple genetic algorithms in that floating point vector strings represent the chromosomes and customized operators are used to improve upon the performance of the search. Moreover, a local search is carried out on each individual in addition to the global population based search. The result is a highly efficient path-planning algorithm that can deal with complex problems easily. Simulation results are presented for collision-free paths planned for two planar arms and then for two 3 degree-of-freedom (DOF) PUMA®-like arms moving in three-dimensional operational space.
Model reference adaptive control of an electrohydraulic motor drive using an artificial neural network compensator
Authors: Nishiumi T , Watton J
Published: October 2002

An artificial neural network is used as the feedback compensation element of a servovalve/ motor speed control system. The network is established on a variable gain/acceleration feedback principle and trained using computer simulation techniques. The network is then emulated as a real-time controller to significantly improve the speed characteristic of the motor. It is then shown how a feedforward network utilizing the motor pressure differential and speed may be readily adapted, in response to changes in motor speed, supply pressure and load torque, to track the prescribed input/output dynamic model.
Fault diagnosis of a hydraulic actuator circuit using neural networks—an output vector space classification approach
Authors: Crowther W J , Edge K A , Burrows C R , Atkinson R M , Woollons D J
Published: October 2002

This paper presents a neural network approach to fault diagnosis of dynamic engineering systems based on the classification of surfaces in system output vector space. A simple second-order system is used to illustrate graphically the nature of the diagnosis problem and to develop theory. The approach is then applied to the diagnosis of a laboratory-based hydraulic actuator circuit. Results are presented for networks trained on both simulation and experimental data. An important achievement is the diagnosis of experimental faults using a network trained only on simulation data.
Analogue solution to the modelling and simulation of distributed-lumped parameter systems
Authors: Bartlett H , Whalley R
Published: October 2002

This paper presents an analogue solution to the modelling and simulation of distributed-lumped parameter systems. The solution is simple and is computationally attractive when compared with equivalent analytical approaches. To illustrate versatility two worked examples, taken from widely employed industrial applications, are presented. In the first the air flow in a long road tunnel is investigated while the second application shows the dynamical performance of a wide-faced rotor for a paper manufacturing process. The generality of the method and the industrial relevance of the proposal are demonstrated thereby.
Gain bounds in the minimal controller synthesis algorithm
Authors: Stoten D P , Sebusang S E M
Published: October 2002

Owing to its high responsiveness to noise disturbances, the minimal controller synthesis (MCS) algorithm can occasionally suffer from the long-term effect of measurement errors, resulting in gain wind-up, closed-loop signal aliasing and hence instability. To counteract this effect, an algorithm is proposed that extends MCS in such a way as to confine the adaptive gain evolutions by using automatically adjusting bounding ‘corridors’. The proof of stability is based upon the original version for MCS, and an implementation study supports the theoretical assertions that the modified algorithm prevents gain wind-up without significantly compromising adaptive effort.
Optimization of feedback gains for a hydraulic servo system by genetic algorithms
Authors: Hyun J H , Lee C O
Published: October 2002

The optimal values of the five feedback gains of a double-loop controller for the speed control of an overcentred variable-displacement hydraulic motor are experimentally determined by using genetic algorithms. The reciprocal of the criterion of integration of time multiplied by absolute error is proposed as the fitness function that evaluates the performance of the control. The appropriate specification of the genetic algorithms and the search range of each control gain for the speed control system are presented. It is found that the near-optimal values of the feedback gains can be obtained within ten generations, which corresponds to about 100 experiments. The optimal gains are also obtained when the inertia or the supply pressure is varied. Optimized feedback gains are confirmed by plotting the fitness function in a given gain space. The fitness distribution indicates that finding the optimal feedback gains by manual tuning is an extremely time-consuming task, and that the genetic algorithm is an efficient scheme economizing time and labour, in optimizing feedback gains for hydraulic servo systems.
Sliding mode control of an electrohydraulic servo motor using a gain scheduling type observer and controller
Authors: Yanada H , Shimahara M
Published: October 2002

The present paper is concerned with the enhancement of robustness of an electrohydraulic servo motor operated using a sliding mode control scheme. A sliding mode control scheme combined with an asymptotic observer is useful as a means to depress chattering, but the mismatch of the parameters between the actual system and its observer model makes the transient estimation errors of states great, and the robustness is lowered. In this investigation, paying attention to the fact that the most dominant parameter of an electrohydraulic servo system is the inertia, an on-line inertia estimation method utilizing pressure sensors is developed. A new, gain scheduling type of observer, which is constructed using two linear observers and an estimate of the inertia, is presented. It is demonstrated that the robustness of an electrohydraulic servo motor is improved by using the proposed observer and that the robustness is more enhanced by varying the controller parameters according to the value of the estimate of the inertia.
Modelling and identification of a wire-cable vibration isolator via a cyclic loading test
Authors: Ni Y Q , Ko J M , Wong C W , Zhan S
Published: October 2002

A cyclic loading test was carried out on a wire-cable vibration isolator to obtain experimentally its hysteretic behaviour in shear, roll and tension-compression respectively. In shear and roll modes, the isolator exhibits symmetric soft-hardening hysteresis loops under cyclic loading, namely the hysteresis loops display a softening stiffness in relatively small deformations and diverge to exhibiting a hardening stiffness at large deformation levels. In the tension-compression mode, the isolator exhibits asymmetric hysteresis loops, which constitute a segment of a hardening overlapping envelope in the loading curves. In recognizing the inapplicability of existing hysteretic models, two improved Bouc-Wen models are proposed within the framework of the mathematical Duhem hysteresis operator, to represent the symmetric soft-hardening hysteresis loops and the asymmetric hysteresis loops with a hardening overlapping envelope respectively.
Diagnostics of a coolant system via neural networks
Authors: Martin K F , Marzi M H
Published: October 2002

The application of a neural network (NN) to diagnose faults in a machine tool coolant system is described. The measured variable in the system is the pump outlet pressure; the transient response of this as the flow valve is closed is used as a pattern for fault recognition.

A two-stage diagnostic system using a back propagation NN at each stage is described and this is trained by using data from the coolant system under healthy (i. e. unfaulty) and faulty conditions. The faults are simulated on the real coolant system. Novel (i. e. previously unmet) faults are defined by maximum values of a ‘deviation’ which is used to allocate faults.

The diagnostic system is shown to be capable of first deciding whether the system is healthy or faulty; if faulty, it then decides whether one of the three common faults or a novel fault is occurring. Having made the decision that one of the common faults is occurring, it is then capable of deciding, from four different levels, the approximate severity level of the fault. Of 345 tests on the coolant system the diagnostic system allocated the fault 99 per cent correctly and the severity level 96 per cent correctly.
Sensor fault detection in flight control systems based on the Kalman filter innovation sequence
Authors: Caliskan F , Hajiyev C M
Published: October 2002

In this paper, a real-time approach to detect the faults affecting the mean and the covariance matrix of the Kalman filter innovation sequence is presented. The ratio of two quadratic forms for which the matrices are theoretical and selected covariance matrices, as monitoring statistics, is used. The arguments of the optimal quadratic form that maximize the above statistics are determined to detect the faults in sensors rapidly. The longitudinal dynamics of an aircraft control system, as an example, is considered, and detection of the faults in pitch gyroscope affecting the mean and the covariance matrix is examined.
Design and testing of a robust linear controller for secondary controlled hydraulic drive
Authors: Berg H , Ivantysynova M
Published: October 2002

Variable-displacement hydraulic motors supplied from a constant pressure source, also called ‘secondary controlled hydraulic drives’ (SCHDs), are modern hydrostatic rotary drives that combine the advantages of excellent dynamic behaviour and low energy consumption. Mainly because of problems with the control system they can only be found in a few industrial applications. This paper presents a novel approach to the position and speed control of SCHDs. To improve the state of the art in terms of static and dynamic performance and to facilitate the implementation procedure, a robust high-bandwidth control system with a new structure is developed. Although highly nonlinear phenomena such as saturation and static friction occur, linear frequency domain methods are used successfully in order to meet demanding specifications.
A time-encoded signal-processing approach to fault classification of an electrohydraulic pressure control system and its application to a hot steel strip rolling mill
Authors: Freebody N , Watton J
Published: October 2002

A technique is presented whereby time domain signals may be classified in terms of four shape parameters. These parameters are processed to create a condition indicator, its variation being used to identify system faults. In this study, the leakage flowrate and a faulty servo-valve are identified on a pressure control system and a comparison is made with a conventional fast Fourier transform approach and a commercial software package, time-encoded signal processing and recognition. A new code, CARCODE, is then applied to 28 servo-valve-controlled work roll bending circuits on a seven-stand hot steel strip rolling mill and a simple graphics presentation is developed to aid real-time condition monitoring.
Frequency-shaped sliding mode control of an electrohydraulic servo-motor
Authors: Yanada H , Ohnishi H
Published: October 2002

A frequency-shaped sliding mode control (SMC) scheme that utilizes a classical filtering theory is applied to a positioning system of an electrohydraulic servo-motor with long transmission lines. It is shown that the chattering phenomenon can be fully suppressed by the scheme used regardless of the existence of a number of unmodelled dynamics. However, it is also shown that, in the case of the frequency-shaped SMC scheme used, the disturbance does not satisfy the matching condition regarding the augmented system consisting of the plant and filter and that the frequency-shaped SMC scheme does not have enough robustness to steady disturbances. A revision is made to the frequency-shaped SMC scheme used in order to enhance the robustness to steady disturbances. A high robustness of the revised frequency-shaped SMC scheme is demonstrated by experiment.
Robust control for uncertain discrete-time jump linear systems with time delay
Authors: Cao Yong-Yan , Frank P M
Published: October 2002

This paper is concerned with the robust stochastic stabilization and H∞ disturbance attenuation for uncertain discrete-time Markovian jump linear time-delay systems subject to norm-bounded parameter uncertainties. The transition of the jumping parameters is governed by a finite-state Markov process. First a sufficient condition on stochastic stability is proposed using the stochastic Lyapunov functional approach. Then sufficient conditions on robust stochastic stabilizing and γ-suboptimal H∞ memoryless state feedback controllers are presented. It is shown that a stochastic stabilizing H∞ state feedback controller can be constructed through numerical solution of a set of coupled linear matrix inequalities.
Hybrid modelling, simulation and torque control of a marine propulsion system
Authors: Bartlett H , Whalley R , Rizvi S S I
Published: October 2002

A propulsion dynamics investigation of a single-screw powered ship, driven by two gas turbines in a combined gas and gas (COGAG) arrangement is presented. Distributed-lumped (hybrid) modelling techniques are applied to the propulsion drive-train consisting of two prime movers, a primary drive shaft, a reduction gearbox, a secondary drive shaft and a propeller. The study in this paper, unlike earlier studies, does not lump the drive-train components as discussed by Rubis [1] into analytically simple but unrepresentative pointwise models. By way of contrast, modelling and simulation techniques for distributed-lumped systems are presented herein, enabling the torsional vibration and stress analysis of the long drive shafts to be investigated with accuracy. As a result of this a torque control scheme can be derived for fuel flow regulation purposes, enabling superior speed and shaft torque control to be achieved. The results presented show the simulated dynamic responses associated with the propulsion unit, shaft and propeller following fuel flow changes.
Low-order dynamic model for flexible hydraulic cranes
Authors: Linjama M , Virvalo T
Published: October 2002

A method to obtain a low-order but accurate dynamic model for multilink flexible hydraulic cranes is presented. An efficient model is achieved by using the assumed modes method with consistent kinematics and by a careful selection of assumed modes. A special type of assumed modes, namely force modes, is presented. These modes consider pointwise forces and moments caused by hydraulic cylinders. The finite element method is used in the calculation of assumed modes, which allows non-uniform links to be modelled with the same accuracy as uniform links. The guidelines for the selection of the number and type of assumed modes are also given. A commercial log loader is used as an example. Three flexible links and two cylinders are modelled. Compared with a high-order finite element model, it is found that, altogether, five force modes are sufficient to achieve a high degree of agreement in the three lowest natural frequencies of the crane. Simulated open-loop responses also show good agreement with measured responses. The structural flexibility has a strong effect on the response of the crane and neglecting flexibility yields incorrect values of the natural frequency, amplitude and damping of force responses of cylinders.
Performance improvement of robot manipulator control using an on-line neural network compensator
Authors: Tso S K , Fung Y H , Lin N L
Published: October 2002

This paper is concerned with the application of neural networks for adaptive compensation of the structured and unstructured uncertainties of the robot manipulator. The controller consists of a model-based term and a neural network on-line adaptive compensation term. It is shown that the neural network adaptive compensation is a universal scheme which is able to cope with totally different classes of system uncertainties. Novel adaptive learning algorithms for tuning the weights of the neural network are proposed. A suitable error filtered signal for training the neural network can be easily obtained from the controller design without using any model knowledge of the robot manipulator itself. The closed-loop system with neural network adaptation on line is guaranteed to be stable in the Lyapunov sense.
The operation of radial lip seals in contaminated environments and the significance of the test rig design
Authors: Shore K. W. , Hall F. R. , Hampshire J. M. , Carnell G. D.
Published: October 2002

The performance and basic rating life of rotating contact ball bearings have increased substantially over recent years, but the performance of radial lip seals, designed to protect these bearings against the ingress of contaminants, has not. In particular, the failure of the lip seals used to protect self-lubricating ball bearings has been identified as a major cause of bearing failure. To understand in detail the mechanisms of failure, these bearings and seals have to be assessed by performing carefully controlled experimental tests. As elastomeric lip seals are intrinsically sensitive to test conditions, their performance is often subject to statistical scatter. Therefore, the design of test rigs to carry out this research is vital so as to eliminate as many unwanted variables as possible. Typical test rigs and the usual tests previously carried out by the major bearing manufacturers are detailed, and the performance of both the test rigs and the seals are discussed. A new radial lip seal test rig, designed specifically for assessing seal performance is shown, and improved test methods and data logging are detailed. Typical lip seal test results are presented and analysed. The aim of this work is to characterize empirically lip seal behaviour under both contaminated and uncontaminated conditions, enabling a deeper understanding of lip seal performance to aid future improved lip seal designs to be formulated.
Studies of failure mechanisms for head-disc interface using in situ instrumentation
Authors: Xu J , Bhushan B
Published: October 2002

The failure mechanism for a head-disc interface has been studied using in situ multi-instrumentation. Combined with ex situ atomic force microscopy observations, the sequence of events for the failure of a head-disc interface is proposed as depletion of the lubricant on laser bumps, uniform wear of the carbon coating on laser bumps, failure of the carbon coating on laser bumps and abrasive wear of the underlying substrate.
On the influence of kinematics in the performance of the pin-disc machine
Authors: Meozzi M
Published: October 2002

The kinematics of the pin-disc and of the disc-disc friction and wear test machines is considered, taking into account the main geometrical errors produced by construction tolerances; some observations are then proposed on the efficiency of various constraint solutions in controlling the experimental conditions minimizing the effect of such errors.
The behaviour of low-amplitude surface roughness under line contacts: Non-Newtonian fluids
Authors: Hooke C. J.
Published: October 2002

As a rough surface passes under an elastohydrodynamically lubricated (EHL) contact the surface profile is modified, with long-wavelength components being reduced in amplitude. The behaviour of the shorter wavelengths is complex. Where both surfaces have the same velocity-pure rolling-the roughness passes through the contact unaltered. Where there is relative slip and the fluid is assumed to be piezoviscous and Newtonian, analysis predicts that the roughness will be flattened. It is replaced by a surface profile with a different wavelength travelling through the contact at the entrainment velocity. The amplitude of this complementary wave may be smaller or larger than the roughness it replaces.

This behaviour has not been found experimentally and does not occur in soft contacts where piezoviscous effects are absent. This paper extends a previous analysis for Newtonian fluids to include shear rate effects. It shows that while these effects are relatively unimportant for pure rolling they have a major influence where there is relative sliding of the surfaces. The formation of the complementary wave is largely eliminated and, at short wavelengths, instead of being modified the original roughness passes unchanged through the contact.
Grease passing through an elastohydrodynamic contact under pure rolling conditions
Authors: Eriksson P , Wikström V , Larsson R
Published: October 2002

Using optical interferometry in a standard ball-and-disc apparatus and a high-speed video camera with light enhancer, thickener particles entering a grease-lubricated elastohydrodynamic (EHD) contact were traced as they passed through the contact in pure rolling. In previous studies, it has not been possible to track specific particles but, due to the short exposure time and high recording rates used here, sharp images of a passing particle could be captured. Two greases, based on the same synthetic poly(α-olefin) but thickened with Li-12-OH and lithium complex respectively were studied and for a freshly lubricated track it could be documented that the lithium complex thickener causes fewer, but larger, particles to pass the contact. The influence of the base oil bleeding on film formation is also discussed in the paper.
Development of polytetrafluoroethylene composite lining for a hydrogenerator thrust pad application
Authors: Choudhary T. R. , Sethuramiah A , Prakash O , Rao G. V.
Published: October 2002

Babbitt is the usual lining material in the pads of hydrogenerator thrust bearings. During the start and stop of a hydroturbine, boundary lubrication dominates in the bearing and significant heating can occur in the contact. To avoid this problem, the rotor is normally jacked up. Another solution to the problem is polymer thrust pads with low friction. Such pads are extensively used in Russia and China. With these pads, jacking of the rotor is not necessary. Higher load-carrying capacity for these pads is also claimed. The present work describes the development of polytetrafluoroethylene (PTFE) composite pads for thrust pad application. In this approach, the composite is directly adhered to the steel backing unlike the present pad design where the pure PTFE is attached to the steel backing with bronze wire interface. The work involved material selection with a pin-on-disc machine followed by adhesive selection on the basis of bond strength tests under static and cyclic shear stresses. Finally the pads were evaluated in a scaled-down thrust bearing test rig for friction and wear behaviour. The results obtained show that bronze-filled PTFE lining directly adhering to steel backing is a successful replacement to babbitt.
Durability and failure mechanisms of digital tapes in a rotary tape drive
Authors: Luk A , Bhushan B
Published: October 2002

The durability and failure mechanism of digital metal-evaporated (ME) and digital metal particulate (MP) tapes were investigated. Shuttle and pause mode tests were performed at ambient and different environmental conditions using a modified digital camcorder as a wear tester. Physical and chemical analyses of worn surfaces were conducted to study failure mechanisms. Digital ME tape exhibited higher overall durability than digital MP tape and Hi-8 ME tape without a diamond-like carbon (DLC) overcoat in the study. The performance of digital ME tape was sensitive to temperature and relative humidity. In the pause test, digital ME tape demonstrated highest durability under hot and moderate humidity conditions and lowest durability under cold and dry conditions. The reasons for high durability for digital ME tape compared with digital MP tape and Hi-8 ME tape without a DLC overcoat lie in lubricant selection, controlled surface topography and DLC coating. With the correct combinations of these three parameters, the durability of ME tape is vastly improved.
Studies on degradation mechanisms of lubricants for magnetic thin-film rigid disks
Authors: Zhao X , Bhushan B
Published: October 2002

The decomposition mechanisms of the perfluoropolyether (PFPE) lubricants have been studied through calculation of chemical reaction kinetics and several experimental approaches. Four degradation mechanisms were considered: thermal and catalytic decomposition, triboelectrical decomposition and mechanical scission. The results show that the effect of catalytic reaction on the degradation of the PFPE lubricants is negligible in sliding conditions because of the short contact time, small contact area and low interface temperature. Illumination with ultraviolet light is found to accelerate the decomposition of the lubricant, reducing the head-disk interface durability and causing more gaseous fragments because low-energy electrons created by the illumination interact with the lubricant molecules, activating and breaking up the molecules. A decomposition mechanism of the lubricant from the effect of low-energy electrons is proposed. Mechanical shear is also found to have an important effect on the decomposition of the lubricant. The partial pressures of the gaseous fragments of the lubricant increase rapidly with increase in the sliding velocity. The temperature from ambient up to 70 °C has no obvious effect on the decomposition of the PFPE lubricant, although higher temperatures are expected to be detrimental. Dominant degradation mechanisms in the sliding conditions are triboelectrical reaction and mechanical scission.
Transient elastohydrodynamic analysis of rough surfaces using a novel coupled differential deflection method
Authors: Elcoate C. D. , Evans H. P. , Hughes T. G. , Snidle R. W.
Published: October 2002

The paper presents a transient analysis technique for line contact elastohydrodynamic lubrication problems using coupled elastic and hydrodynamic equations. Full coupling is made possible by use of a novel differential deflection formulation. The lubricant is treated as non-Newtonian with a non-linear Eyring-type relationship between shear stress and shear strain rate. Results are presented for moving rough surfaces where the roughness data are taken from profilometer traces of run-in ground surfaces. A complete range of slide-roll ratios has been considered and results are shown for one rough surface in rolling/sliding motion against a smooth surface with extremely low lambda ratios (ratio of minimum film clearance to r. m.s. roughness). Results are also shown for two rough surfaces in contact under severe thin-film high-roughness conditions.
Thermal elastohydrodynamic analysis of circular contacts Part 1: Newtonian model
Authors: Kim H. J. , Ehret P , Dowson D , Taylor C. M.
Published: October 2002

Solutions of the thermal elastohydrodynamically lubricated point contact problems are presented for both low and high Peclet number conditions. The surface temperatures are calculated using the full expression of the moving heat source equation given by Carslaw and Jaeger. Of interest is the potential of the method to predict solutions for pure sliding conditions in which one surface velocity is zero. The energy equation is treated as a two-dimensional problem by approximating the variation in temperature across the film with a quadratic profile. To solve the strongly non-linear set of equations which govern the problem a relaxation scheme is proposed which takes advantage of the weak coupling between the Reynolds equation and energy equation in the high-pressure region of the contact. The iterative process corresponds to a two-stage process in which pressure and temperature are relaxed independently. The numerical scheme provides a stable and fast convergence and has the added advantage of allowing the isothermal relaxation schemes for pressure previously developed to be reused.
A computational study of hydrodynamically lubricated convex and concave journal bearings
Authors: Pandazaras C. N. , Petropoulos G. P.
Published: October 2002

In the present study, computational data are presented regarding the tribological behaviour of convex and concave journal bearing configurations under hydrodynamic lubrication. In specific cases these results may improve journal bearing tribological properties especially by decreasing the specific tribosystem friction losses. In this direction, a journal bearing anti-friction optimization procedure is enabled.
Effect of a circumferential feeding groove in a short squeeze-film damper
Authors: Tan Q , Li W , Xia X
Published: October 2002

The present work investigates the effects of a circumferential feeding groove in a short squeeze-film damper (SFD) on fluid force and dynamic responses of a rotor in SFDs. The groove is taken as a special damper to analyse the effects. The dynamic performance of the SFD with the groove is attributed to two film lands, the special damper and their interactions. From this viewpoint, the fluid force in the groove is analysed on the basis of the linearized Navier-Stokes equations. Analysis of the fluid force in film lands is carried out using a simplified Navier-Stokes equation to include fluid inertia. Then, from the continuity condition and the Navier-Stokes equation, fluid interactions between the groove and the film lands are investigated. The two analyses are combined together by investigation of the interactions, resulting in new models for fluid force predictions. The new models are compared with published work. The comparisons show that the new models give better predictions and correction with experimental data than traditional theory. The new models provide a significant improvement on the results obtained by traditional theory, especially for tangential force. Based on the new models, the present work also analyses effects of the groove on the unbalance response and stability of a rigid rotor in SFDs. Comparisons with published work show that the groove affects the unbalance response of a rotor system. The effects of the groove on dynamic coefficients of SFD cause the response of the rotor system to be stable for some range of system parameters, being different from the results of traditional theory. This is important for designing a rotor system.
The lubrication of metal-on-metal total hip joints: A slide down the Stribeck curve
Authors: Smith S. L. , Dowson D , Goldsmith A. A. J.
Published: October 2002

Metal-on-metal joints can exhibit profoundly different modes of lubrication when tested in a hip simulator. A range of metal-on-metal joints of similar diameters differing only in diametral clearance can demonstrate differences in lubrication conditions during simulator testing, as can joints differing principally in diameter. Simulated walking cycles can similarly cause differences in lubricating conditions through the application of different motion and loading cycles.

In this study, and work conducted previously by the authors, metal-on-metal joints were tested in 25 per cent bovine serum in a hip simulator. A simple resistivity technique was used to detect surface contact, or separation, in a lubrication study, while a wear study used a gravimetric protocol extending over at least 2000000 cycles duration. Simulated physiological and simplified walking cycles were used during the studies to investigate the effect of motion and load on lubrication and wear. Joints of 16, 22.225, 28 and 36 mm nominal diameter were tested to investigate the effect of diameter, while the effect of diametral clearance was studied using joints of 36 mm diameter with a range of diametral clearances from 97 to 170μm.

The trend of an idealized Stribeck curve, plotted as coefficient of friction versus the dimensionless Sommerfeld parameter (viscosity × sliding velocity × radius of the femoral head/load), indicates the lubrication regime prevalent in a joint. Boundary, mixed and fluid-film lubrication, shown by the three classic regions on an idealized Stribeck curve, were all demonstrated using metal-on-metal joints in a hip simulator. The different modes of lubrication prevalent in the joints resulted in wear rates spanning two orders of magnitude between joints differing principally in diameter. Similarly, a reduction in diametral clearance caused a general increase in the proportion of surface separation per simulated walking cycle. Likewise, a simplified walking cycle generated more surface separation per walking cycle for the same joint subjected to a simulated physiological cycle. However, the two walking cycles generated no significant difference in simulator wear rates.
Life ratings for ball and roller bearings
Authors: Harris T. A. , Barnsby R. M.
Published: October 2002

Since the beginning of the twentieth century, bearing manufacturers and users have sought to predict the fatigue endurance of ball and roller bearings. The first generally accepted method to predict bearing life and rate bearings accordingly was published in 1947 by Lundberg and Palmgren (LP). This method was adopted in the United States as the basis for a Standard in 1956, and it remains the basis for the current ISO Standard. The LP theory, however, pertains only to bearings manufactured from AISI 52100 through-hardened steel, and it permits ratings for bearings loaded solely by the Hertz stresses associated with simple applied loading. To accommodate the various steels from which bearings are manufactured and the effect of lubrication on fatigue life, the life calculated according to the LP method was adjusted by life modification factors; this multiplicative life factor concept was inserted into the ISO Standard during the 1970s. Even with these life factors, fatigue lives experienced in many bearing applications substantially exceeded the predictions. In 1985, Ioannides and Harris (IH) proposed a method based on the LP theory, but including a fatigue limit stress. Life predicted according to their method could ideally be infinite if the fatigue limit stress is not exceeded. Moreover, as opposed to the LP theory, which relies on Hertz stresses alone, the IH method permitted consideration of the totality of stresses acting on the rolling contact members. The IH method has now been further developed into an even more generalized Stress-Life method. This method, which is still based on the LP formulation, employs a single stress-life factor to modify the LP predicted fatigue life. In the fatigue life prediction for a bearing application, the stress-life factor integrates the effect on life of all applied, induced and material residual stresses together with empirically determined fatigue limit stresses. This paper details the historical development of bearing life ratings culminating in the detailed methods of application of the stress-life method.
Elastohydrodynamic properties and boundary lubrication performance of polyolester in a hydrofluoroether refrigerant environment
Authors: Muraki M , Sano T , Dong D
Published: October 2002

The electrohydrodynamic (EHD) properties of polyolester (POE) in refrigerant environments were determined with a ball-on-sapphire disc-type EHD tester. The film thickness and the traction were both lower for hydrofluoroether HFE-245mc than for hydrofluorocarbon (HFC) at an identical gas pressure. This is because of the higher refrigerant concentration (RC) for HFE-245mc than for HFC, which resulted in a lower atmospheric viscosity and a lower viscosity-pressure coefficient of the refrigerant/POE mixture for HFE-245mc. The boundary lubrication performance was studied with a block-on-ring type tribometer. The coefficient of friction in HFE-245mc was lower than that in HFC, and HFE-245mc was superior to HFC in terms of antiwear performance. X-ray photoelectron spectroscopy (XPS) of the surface film showed the presence of FeF2 and iron oxide whose concentration was much higher, and the boundary film thickness was much thicker for HFE-245mc than for HFC. Thus, it was inferred that HFE-245mc adsorbed on to the rubbing surface was decomposed to form an effective antiwear film having a low shear resistance which resulted in reduction in the friction and wear.
Study on the cavitation mechanism in hydraulic oil flow using a needle projection
Authors: Washio S , Takahashi S , Kawahara S , Kishitani M
Published: October 2002

Cavitation occurring at a sharp projection in a hydraulic oil flow was observed in as much detail as possible, using, variously, a microscope, a high-speed video camera, laser beams, an electric charge detector and a photomultiplier. At the tip of the needle employed as a projection, a tiny cavity as small as several tens of micrometres in length suddenly emerged and would not go away. As cavitation became more vigorous, flashes occurred intermittently around the needle and positive electrical charges were generated which synchronized with the flashing. The electrode inserted downstream from the needle detected negative charge from the oil, which was also synchronous with the flashing. Observing the needle tip with the microscope made it possible to determine exactly the moment of cavitation inception, which turned out to depend on the oil temperature as well as the downstream pressure. All these findings tend to reinforce the ‘rip-off’ hypothesis previously proposed by the present authors for the cavitation mechanism.
Extended expansion of the Reynolds equation
Authors: Martin J. K.
Published: October 2002

Principles of a continuously adjustable hydrodynamic bearing concept are outlined and the governing Reynolds equation is given. The equation is non-dimensionalized and expanded taking into account non-uniform variations in the fluid-film thickness. Also given are observations of predicted operating characteristics of one form of the bearing.
The efficiency and friction of plastic cylindrical gears Part 1: Influence of materials
Authors: Walton D , Cropper A. B. , Weale D. J. , Meuleman P Klein
Published: October 2002

Little has been published on the efficiency of plastic gears despite the fact that plastic gears are used in large quantities in a variety of machines. Among the many applications where plastic gears are used, one is where any form of lubrication must be avoided, such as in office printing and food-processing equipment, but dry running can lead to high friction and associated high temperatures. As more is understood about plastic gears, the trend is towards high-power applications where inefficiencies become even more important. As high temperatures must be avoided with plastics, knowledge of efficiencies and friction is essential in the rating of plastic gears. This paper looks at the efficiencies of plastic spur gears made from a range of polymers and polymer composites used in plastic gear manufacture. Tests were conducted in like-like and dissimilar material configurations for plastic gears as well as plastic-steel combinations. Tests were also carried out to assess the effect of grease lubrication. A test rig was developed to measure gear tooth meshing losses accurately and this facility is reported in the paper. Efficiencies were shown to be both load and speed dependent. Using equations developed for calculating efficiencies, average coefficients of friction for tooth meshing were determined for particular materials and operating conditions from measured efficiencies. These coefficients were compared with values obtained from classical tribological tests such as thrust washer and roll/slide apparatus.
Study of externally-pressurized gas-lubricated two-layered porous journal bearings: A steady state analysis
Authors: Saha N , Majumdar B. C.
Published: October 2002

The steady state performance of gas-lubricated two-layered porous journal bearings is analysed theoretically by an iterative method considering three-dimensional flow through the porous matrix and two-dimensional flow in the bearing clearance. In the absence of any available data for two layers, the results obtained for a single layer have been compared with previous results and have been found to be in excellent agreement. The effect of supply pressure, bearing number, feeding parameter and length-diameter ratio on the static characteristics is investigated and presented in the form of design charts. It has been observed that two-layered porous bearings give higher load-carrying capacity than single-layered bearings.
Effect of operating environment on failure mechanism of a head-tape interface in a linear tape drive with a belt-driven cartridge
Authors: Goldade A. V. , Bhushan B
Published: October 2002

The effect of the operating environment on the failure mechanism of a head-tape interface in a linear tape drive with a belt-driven cartridge was studied. A modified commercial drive with magnetoresistive head and metal particle tape were used. Durability tests for the full tape length were performed at ambient and extreme environmental conditions. Head output, coefficient of friction and number of dropouts per minute were measured during the test. Optical and atomic force microscopy and Auger electron spectroscopy were used to evaluate changes at the head-tape interface at the end of the tests. Magnetic and tribological performance of head-tape interface is the best at low temperatures and low relative humidities. Increases in both temperature and relative humidity result in performance degradation, with the worst performance at the highest temperature. At ambient conditions, sporadic variations in the coefficient of friction and the number of dropouts per minute are observed, associated with a cycle of stain formation and removal. Possible mechanisms responsible for the observed tribological behaviour of the interface at various environmental conditions are discussed.