bluuebunny/crossref_metadata_2025 huggingface dataset:
New design methods of actuator saturation compensators for proportional, integral and derivative controllers
Authors: Hui K , Chan C W
Published: October 2002

This paper proposes five new schemes of saturation compensator designs for PID (proportional, integral and derivative) controllers. Unlike previous works, these are derived using frequency domain techniques. Based on stability analysis of the compensated systems, comparisons of stabilities of the compensation schemes relative to each other are established, with the result that their relative orders depend only on the PI/PID parameters. A new class of variable-structure compensators is also proposed. These variable-structure compensators combine the advantages of their individual constituents to achieve better results. Design procedures, for both fixed- and variable-structure compensators, are then presented as the main theme of this paper. Results for the relative stabilities and design procedures are illustrated with examples, showing the validity and superiority of the proposed methods.
A non-linear model of a rotary pneumatic servo system
Authors: Tillett N D , Vaughan N D , Bowyer A
Published: October 2002

A simulation model of a rotary pneumatic servo system has been developed and verified against an experimental system. The double-acting rotary actuator is a novel device utilizing flexible inflatable bladders. The device differs from conventional pneumatic cylinders in that it exhibits low levels of friction, as it has no sliding seals, but it does suffer from hysteresis caused by bladder distortion. The objective of this study was to develop a tool with which to investigate the effect of various forms of hysteresis and other parameters on system performance. The dynamic model utilizes a linearized analysis of pneumatic components based on earlier studies. The principal advance described in this paper relates to the inclusion of non-linear elements. These are hysteresis caused by friction or the distortion of flexible components, and a digital controller implementation. The simulation successfully predicted all major modes of behaviour. Simplified models of rubber and coulomb friction-induced hysteresis modified simulation performance in line with experimental results. An investigation in simulation showed that coulomb friction-induced hysteresis had a greater damping effect than that caused by distorting the bladders. This result applies only to position control, as hysteresis has been shown not to provide damping in trajectory control applications.
Condition monitoring in composite materials: An integrated systems approach
Authors: Culshaw B , Pierce S G , Staszekski W J
Published: October 2002

This paper presents the results of a collaborative project, the objective of which was to investigate the potential offered by combining ultrasonic Lamb wave interrogation of composite material structures, insonifying the whole structure, with a single wavefront integrating optical fibre detector. The system, which was designed primarily for condition monitoring rather than defect imaging, proved to be capable of detecting small (centimetre square) delaminations, millimetre-sized holes and impact damages of a few joules, all with insonification wavelengths of the order of 2 cm. Data extraction proved to be extremely important since the damage-detection process relies essentially on analysing scattering signatures rather than attempting to image defects and damage. The system—dubbed SISCO (Structurally Integrated Systems for comprehensive evaluation of COmposites)—indicates that self-monitoring structures can be efficiently designed using controlled insonification and a relatively sparse sensor array, presenting a contrast to the more conventional imaging approach involving far more complex sensing arrays and detection and signal processing algorithms.
A method to reduce noise in hydraulic systems by optimizing pipe clamp locations
Authors: Kwong A H M , Edge K A
Published: October 2002

This paper describes a novel technique to reduce noise and vibration in hydraulic systems. The approach involves finding the best hydraulic circuit mounting locations to avoid excessive coupling between the hydraulic pipes and the supporting structures. Using a well-developed transfer matrix method, the dynamic response to disturbance by fluid flow ripples can be predicted at all pipe locations. By making appropriate assumptions concerning the mounting impedance, the force and displacement parameters involved in clamping the pipes can be estimated. These results can be used to quantify the fitness of the hydraulic circuit in an optimization program using genetic algorithms. An example is included using a simple hydraulic rig. The predicted results for the best and worst clamping locations are compared. Experimental studies have confirmed that, with the optimal clamping locations, significant reductions in both noise and vibration were obtained.
Trajectory tracking control of robot manipulators using a neural-network-based torque compensator
Authors: Li Q , Tso S K , Zhang W J
Published: October 2002

In this paper, an adaptive neural-network-based torque compensator is developed for the trajectory-tracking control of robot manipulators. The overall control structure employs a classical non-linear decoupling controller for actuating torque computation based on an approximated robot dynamic model. To suppress the effects of uncertainties associated with the estimated model, a supplementary neural network algorithm is developed to generate compensation torques. The weight adaptation rule for this neuro-compensator is derived on the basis of the Lyapunov stability theory. Both global system stability and the error convergence can then be guaranteed. Simulation studies on a two-link robot manipulator demonstrate that high performance of the proposed control algorithm could be achieved under severe modelling uncertainties.
Genetic design of dynamically optimal robotic manipulators
Authors: Papakostas K D , Mouroutsos S G , Porter B
Published: October 2002

This paper presents a procedure for the genetic design of dynamically optimal robotic manipulators. This design procedure is task oriented and minimizes the reaction forces and moments induced by the manipulator during the execution of specific trajectories. These forces and moments are included in an objective function and their reduction is achieved by using genetic algorithms to calculate the balance weight and the associated eccentricity for each link for which the base reaction is minimized. This genetic design technique is illustrated by application to a planar RR manipulator.
Thermal modelling using mixed energy and pseudo bond graphs
Authors: Gawthrop P J
Published: October 2002

Pseudo and true bond graphs have been seen as competing approaches to modelling thermodynamic systems. This paper provides a simple mechanism for mixing the two approaches to obtain the best features of each. In so doing, an alternative and more accessible approach to thermodynamic modelling than that provided by classical texts is given.
Robust control of a 1.5 MW free turbine engine
Authors: Gomma H W , Owens D H , Rossiter D
Published: October 2002

This paper describes the robust control design of a 1.5 MW free turbine with complex load. A non-linear model of the engine with load has been developed within Simulink from details previously presented. State space H∞ control designs are performed using a linearized model to represent the key components in the multiloop control configuration. The performance criteria are specified in terms of stability margins, bandwidth and desired response of the engine to a severe load disturbance. The engine is subject to constraints on its manipulated variable (i. e. the throttle valve angle). The H∞ design is simplified to a classical proportional-plus-integral (PI) controller. The results show that the PI control produces results similar to H∞ at low speeds but that H∞, gives better robustness and performance at higher speeds. Non-linear simulations with parameter changes support the conclusion that the design is robust.
Adaptive general regression neural network for modelling of dynamic plants
Authors: Seng T L , Khalid M , Yusof R
Published: October 2002

This paper proposes an integrated general regression neural network (GRNN) adaptation scheme for dynamic plant modelling. The scheme can be used in a noisy and dynamic environment for on-line process control. It possesses several distinguished features compared with the original GRNN proposed by Specht, such as a flexible pattern nodes add-in and delete-off mechanism, a dynamic initial sigma assignment using a non-statistical method, automatic target adjustment and sigma tuning. These adaptation strategies are formulated on the basis of the inherent advantageous features found in GRNN, such as highly localized pattern nodes, good interpolation capability and instantaneous learning. Good modelling performance was obtained when the GRNN is tested on a linear plant in a noisy environment. It performs better than the well-known extended recursive least-squares identification algorithm. In this paper, analysis of the effects of some of the adaptation parameters involving a non-linear plant is also investigated. The results show that the proposed methodology is computationally efficient and exhibits several attractive features such as fast learning, flexible network sizing and good robustness, which are suitable for the construction of estimators or predictors for many model-based adaptive control strategies.
Substructural control design for serial flexible structures using the linear quadratic Gaussian method
Authors: Sunar M
Published: October 2002

A substructural control technique is developed for serial flexible structures using the linear quadratic Gaussian control method. A flexible structure is suitably decomposed into substructures, and subcontrollers and subobservers are designed for the substructures. The subcontroller forces generated within the substructures are taken into account when designing the subcontrollers and subobservers, which are assembled to obtain the global controller and observer for the entire structure. The technique is illustrated with the aid of a numerical example, which demonstrates the accuracy of the proposed substructural control technique compared with the complete structural control technique. The substructural control technique is expected to yield great computational savings in the control design of large serial flexible structures with accuracy.
Mechanical drive control
Authors: Whalley R , Mitchell D , Ebrahimi M
Published: October 2002

Mechanical drives, for weapon platforms, comprising relatively long shafts with inertia discs, representing the motor armature, gearing, platform and load inertias, etc., are considered. Analysis procedures are employed to model a system which has driving and braking torque inputs. Two outputs arising from the motor armature angular changes and the load inertia position, which is to be regulated, are available. Procedures enabling the dominant oscillatory modes of the system to be influenced by proportional control are outlined. Performance enhancement using passive networks is employed, providing thereby further design flexibility. The responses of the system under open- and closed-loop conditions are computed. The simplicity of the approach which can also be applied to systems having an unequal number of inputs and outputs is commented upon.
A methodology to reduce large overshoot in a direct neural control system
Authors: Yuan M , Hong G S , Poo A N
Published: October 2002

Direct neural control presented a good relearning performance in tracking a desired trajectory. However, random distribution of the initial weights of the neural network controller results in large initial overshoots. In this paper, a closed-loop training method for a direct neural controller is proposed, aiming to generate ‘good’ initial weights for direct control. The training data are generated on the on-line trajectory tracking using a conventional control guide. Pre-training of the neural network concentrates on a subset that system states mainly fall in. The simulation studies for a single-link manipulator have verified that the trained direct neural control system exhibits a better system response than an untrained neural control system does in trajectory tracking and set-point regulation with significantly reduced initial overshoots.
Robust strategies for active vibration control of plate-like structures: Theory and experiment
Authors: Sadri A M , Wynne R J , Wright J R
Published: October 2002

The theoretical modelling of the vibration of a plate-like active structure incorporating piezoelectric actuators is presented using the Rayleigh-Ritz method. The model was used to design multi-variable controllers (linear quadratic Gaussian and H∞) for a cantilever plate with two piezoelectric actuators providing the controlled strain input to the plate with two non-collocated sensors providing the feedback signals. A technique for the optimal placement of piezoelectric actuators is developed using modal controllability and a genetic algorithm as the search engine. The proposed controllers were then implemented experimentally and the measured results compared favourably with those predicted from simulation studies. The results show that considerable disturbance attenuation can be achieved in lightly damped modes of the structure using optimal placement of piezoelectric actuators and multi-variable controllers.
Intelligent product manuals
Authors: Pham T D , Dimov S S , Setchi R M
Published: October 2002

This paper presents a new approach to integrating advanced information technologies for intelligent product support. The paper promotes the concept of intelligent product manuals and outlines their main characteristics. Based on this concept, an integrated technology solution called ProManual is developed. The characteristics of ProManual are integration of three-dimensional product data, expert knowledge, virtual reality and hypermedia, interactivity, platform independence and distribution through the World Wide Web. The proposed integrated solution provides active assistance to the user by conveying product information and knowledge in a way that improves user performance.
Lubricant properties for input to hydrodynamic and elastohydrodynamic lubrication analyses
Authors: Larsson R , Larsson P. O. , Eriksson E , Sjöberg M , Höglund E
Published: October 2002

The properties of a number of common lubricants have been measured, namely the viscosity, elastohydrodynamic lubrication (EHL) friction coefficient, density, thermal conductivity and heat capacity per unit volume. These properties have been measured within relatively broad pressure and temperature ranges. The lubricants tested were naphthenic and paraffinic mineral oils, blends of these, polyalphaolefins and a polyglycol.

Physical-empirical expressions have been developed upon the basis of the measurement results and a number of lubricant constants, or lubricant parameters, have been determined for each lubricant. These expressions can be used in engineering computational tools for lubrication analysis. The use of such analyses is expected to increase into the new millennium and it is thus important to provide reliable and relevant input data.
The mixed phase of gearbox synchromesh operation
Authors: Paffoni B , Progri R , Gras R
Published: October 2002

Earlier studies allowed the present authors to divide the period of synchronization into three stages of operation: viscous, mixed and dry. Expressions for estimating the pressure, axial, force, torque and friction coefficent were obtained. This investigation allows the determination of the initial values necessary for the study of the second stage presented here. The second stage occurs in the presence of a variable friction coefficient for which a model is proposed. The influence of the variable friction coefficient on the velocity and duration of synchronization is presented. The theoretical model is compared with experimental results.
Experimental measurement of big-end bearing journal orbits
Authors: Goodwin M. J. , Groves C , Nikolajsen J , Ogrodnik P. J.
Published: October 2002

This paper describes a novel experimental approach to the measurement of big-end bearing journal motion in reciprocating machinery. The procedure is based upon measurements recorded from inductive displacement transducers mounted in the crankshaft, which measure the instantaneous clearance between crankshaft journal and the big-end bearing surface of the connecting rod. The results of the work demonstrate that the procedure is a feasible way of collecting experimental data for comparison with the output from theoretical models. Experimental data are presented for a single-cylinder four-stroke compression ignition engine operating under various load conditions.
Elastohydrodynamic lubrication of a circular point contact for a compliant layered surface bonded to a rigid substrate Part 2: Numerical results
Authors: Jin Z. M.
Published: October 2002

Both the theoretical formulation and the numerical analysis of the elastohydrodynamic lubrication problem of a circular point contact of a compliant layered surface firmly bonded to a rigid substrate have been present in the earlier paper, Part 1. The numerical method is applied, in this paper, to a compliant layered surface firmly bonded to a rigid substrate. The results of the film thickness and pressure distribution are presented for a wide range of ratios of the contact radius to the layer thickness and Poisson's ratio. It has been shown that the film thickness for a layered surface can be predicted from the semi-infinite solid assumption when the ratio of the contact radius to the layer thickness is less than or equal to 0.25. Furthermore, it has been demonstrated that, for a layered surface with Poisson's ratio equal to 0.4, the elastohydrodynamic solutions based on the simple constrained column model are reasonably accurate when the contact radius is larger than or equal to the layer thickness. General non-dimensional solutions of the minimum and central film thicknesses have been presented using the Moes load and film thickness parameters as a function of the ratio of the contact radius to the layer thickness and Poisson's ratio. All the numerical solutions of both the central and the minimum (along the centre of contact in the entraining direction) film thicknesses have been curve fitted using a least-squares technique. A normal human hip joint has been chosen as an example to illustrate the application of the present study.
Effects of a thickener structure on grease elastohydrodynamic lubrication films
Authors: Kaneta M , Ogata T , Takubo Y , Naka M
Published: October 2002

The effects of the thickener structure and base oil viscosity on the grease film formation in rolling point elastohydrodynamic contacts have been discussed on the basis of direct observation using the optical interferometry technique. Three different types of diurea greases without additives have been used as test greases. As the base oils three kinds of ether-type synthetic oils having similar molecular structures but different viscosities were used. The film behaviour of fresh greases has also been compared with that of the degraded greases. It has been found that the behaviour of grease elastohydrodynamic lubrication films is basically influenced by the thickener structure and base oil viscosity. The adhesion or deposition of the thickener on the contacting surfaces and oil starvation which affect film formation depend on the thickener structure, base oil viscosity and rolling speed. Furthermore, it has been suggested that there is an optimum temperature which gives a maximum film thickness according to the consistency of the grease.
Chaotic response of a short journal bearing
Authors: Brown R. D. , Drummond G , Addison P. S.
Published: October 2002

The non-linear response of fluid-film bearings has been studied for nearly 40 years. Apart from a paper on aperiodic behaviour by Holmes et al. in 1978, much of the work has concentrated on limit cycle behaviour and the practical bounds of linear models. Brindley et al. in 1990 examined the free vibration of a rigid rotor supported by a short bearing oil film. Numerical integration of the equations of motion demonstrated the existence of both large and small limit cycles at operating conditions close to the stability boundary. Hopf bifurcations were shown to exist using a theoretical method. Brindley et al. clearly recognized that the inclusion of unbalance in the model would produce a wider range of behaviour but no results were presented.

In recent years the chaotic response of many non-linear systems has received much attention. The main requirements for chaos in a dynamic system are sufficient non-linearity and a minimum of three first-order differential equations. These conditions are satisfied by a rigid journal supported on a hydrodynamic bearing film operating at a high eccentricity. At moderate levels of unbalance the bearing is stable and the behaviour is approximated by a linear treatment. Nevertheless, when the rotating unbalance force exceeds the static load, the bearing is intermittently unloaded and chaos can result.

In this paper the region of interest is bounded by three parameters, the dynamic-static force ratio, the operating eccentricity and the non-dimensional frequency ω √ C/g, the latter an established measure of stability. For values of ω √ C/g above 2.5, and eccentricity ratios greater than 0.65 a region of chaos is established for a moderate range of dynamic-static force ratio values. If the unbalance is increased further, the response again becomes periodic, as might be expected. There is a possibility that turbomachinery with heavily loaded bearings may experience chaotic behaviour.
Transient elastohydrodynamic analysis of an overhead cam/tappet contact
Authors: Messé S , Lubrecht A. A.
Published: October 2002

The friction in automotive engines is mainly caused by three components: the engine bearings, the piston-ring assembly and the valve train. In order to improve reliability and performance and to reduce fuel consumption, manufacturers have to reduce engine friction. To do this a better understanding of these components is necessary. In this paper, the valve train is studied for a direct-acting system. A transient elastohydrodynamic lubrication analysis is developed. The model includes the variation in the radius of curvature of the cam, the variation in the hydrodynamic velocity and the variation in the load. The film thickness is calculated as a function of time and space. In order to reduce the computing time, multi-grid and multi-level multi-integration techniques are used. Results show squeeze-film effects and ejection of lubricant on hydrodynamic speed reversion.
Influence of geometric parameters and operating conditions on the thermohydrodynamic behaviour of plain journal bearings
Authors: Pierre I , Fillon M
Published: October 2002

Hydrodynamic journal bearings are essential components of high-speed machinery. In severe operating conditions, the thermal dissipation is not a negligible phenomenon. Therefore, a three-dimensional thermohydrodynamic (THD) analysis has been developed that includes lubricant rupture and re-formation phenomena by conserving the mass flowrate. Then, the predictions obtained with the proposed numerical model are validated by comparison with the measurements reported in the literature. The effects of various geometric factors (length, diameter and radial clearance) and operating conditions (rotational speed, applied load and lubricant) on the journal bearing behaviour are analysed and discussed in order to inform bearing designers. Thus, it can be predicted that the bearing performance obtained highly depends on operating conditions and geometric configuration.
Modelling of surfaces with a bimodal roughness distribution
Authors: Peng W , Bhushan B
Published: October 2002

Most contact analyses assume that the surface heights and peak (summit) height distributions follow a single modal distribution, Gaussian or non-Gaussian. However, height distributions of many surfaces follow multi-modal distributions. In this study, for the first time, algorithms are developed to generate various bimodal surfaces on the computer. Statistical analyses and contact analyses of these surfaces have been carried out. The present algorithms are applied to particulate tapes and head-finishing processes to illustrate the effect of the bimodal distribution on the contact performance. From these analyses, an optimum bimodal roughness distribution is predicted for minimum friction and wear.
Effect of particulate contamination on the friction and wear of a magnetic head-rigid disk interface
Authors: Chandra S , Bhushan B
Published: October 2002

Particulate contamination studies were carried out with laser-textured and mechanically textured magnetic rigid disks and nanosliders. The effects of particle concentration and its size, particle material, duration of exposure to contamination, interface speed and disk textures were studied. The head-disk interface (HDI) durability increased as particle concentration decreased. The effect of different hard-particle materials was attributed to how easily it can form agglomerates. Data indicate that limited-time exposure to a class 10 000 environment will not deter tribological performance of the HDI. In a contaminated environment, head flying in the data zone exhibited higher durability than that in the-lase textured zone. However, the mechanically textured disk and the data zone of laser-textured disks showed comparable durability in the presence of contamination. The HDI damage mechanism and pattern changed as the disk speed changed. A failure mechanism to show how the airborne particles interact with the interface is presented. The effects of the HDI geometry, flying height, pitch angle which controls the air flow pattern govern the failure mechanism in the flying mode.
Tribology on the macroscale to nanoscale of microelectromechanical system materials: A review
Authors: Bhushan B
Published: October 2002

Silicon-based microelectromechanical system (MEMS) devices are made from single-crystal silicon, polycrystalline silicon (polysilicon) films obtained by low-pressure chemical vapour deposition and certain ceramic films. For high-temperature applications, SiC films are being developed to replace polysilicon films. Tribology in the MEMS devices requiring relative motion is of importance. Atomic force microscopy/friction force microscopy (AFM/FFM) and nanoindentation techniques have been used for tribological studies on a microscale to nanoscale on materials of interest. These techniques have been used to study surface roughness, friction, scratching and wear, indentation and boundary lubrication of bulk and treated silicon, polysilicon films and SiC films, Macroscale friction and wear tests have also been conducted using the ball-on-flat tribometer. Measurements of microscale and macroscale frictional forces show that friction values on both scales of all the silicon samples are about the same for different silicon materials and higher than that of SiC. The microscale values are lower than the macroscale values as there is less ploughing contribution in the microscale measurements. Surface roughness has an effect on friction. In microscale and macroscale tests, C+-implanted, oxidized and plasma-enhanced chemically vapour-deposited oxide-coated single-crystal silicon samples exhibit much larger scratching and wear resistance than untreated samples. Polysilicon films and undoped single-crystal silicon show similar friction and wear characteristics. The doping of polysilicon film does not significantly affect its tribological properties. Microscratching, microwear and nanoindentation, and macroscale friction and wear studies indicate that SiC films are superior to the other materials currently used in MEMS devices. Higher hardness and fracture toughness of the SiC film is believed to be responsible for its superior mechanical integrity and lower friction. Chemically grafted self-assembled monolayers and chemically bonded liquid lubricants show promising performance for boundary lubrication in MEMS devices.
On the effects of the temperature profile approximation in thermal Newtonian solutions of elastohydrodynamic lubrication line contacts
Authors: Kazama T , Ehret P , Taylor C. M.
Published: October 2002

The assumptions of a quadratic temperature profile and mean viscosity across the film, which are frequently used in the analysis of thermal elastohydrodynamic lubrication (EHL), are examined and discussed. Two different approaches for solving the thermal EHL problem are compared for line contact conditions, namely (a) a one-dimensional model based upon both the assumption of a quadratic temperature profile and the adoption of the mean physical properties across the film and (b) a two-dimensional model which includes changes in temperature and physical properties of a lubricant across the film and which takes into account the conditions of reverse flow and heat convection across the film occurring at the inlet region. A multi-grid algorithm is implemented to solve these two conditions. The temperature profile and the general solutions in the conjunction obtained in both approaches are compared. For the one-dimensional model, results reveal that temperature peaks just prior to the inlet of the conjunction. This feature is not apparent in the two-dimensional model and results in lower values in film thickness and larger frictional coefficients than in the two-dimensional model. In the high-pressure region, both equations yield almost the same mean temperature.
Static and dynamic behaviour of squeeze-film lubrication of narrow porous journal bearings with coupled stress fluid
Authors: Naduvinamani N. B. , Hiremath P. S. , Gurubasavaraj G
Published: October 2002

In this paper an attempt has been made to study the rheological effects of coupled stress fluids on the static and dynamic behaviour of squeeze-film lubrication in porous journal bearings. A generalized modified form of the Reynolds equation is derived for the squeeze-film lubrication of porous journal bearings with a coupled stress fluid as the lubricant. The analysis takes into account the velocity slip at the surface of the porous medium by using the Beavers-Joseph criterion. A closed-form expression for the squeeze-film pressure is obtained for the narrow porous journal bearing. The cases of a constant applied load and an alternating applied load are analysed. It is observed that the effect of coupled stress is to increase significantly the squeeze-film pressure and the load-carrying capacity compared with the Newtonian case. Under cyclic loading, the coupled stresses developed in the fluid cause a reduction in the velocity of the journal centre and an increase in the minimum permissible squeeze-film thickness.
Elastohydrodynamic film formation at the start-up of the motion
Authors: Glovnea R. P. , Spikes H. A.
Published: October 2002

This paper describes an experimental study of elastohydrodynamic (EHD) lubricating film formation during the start-up of motion of a point contact from rest. EHD film thickness was measured using ultra-thin optical interferometry. It was found that film thickness behaviour depends strongly upon acceleration. When motion starts, most lubricants form a front that travels across the contact with its initial thickness unchanged. At some point, depending upon the acceleration, a second front often forms, so that the lubricant film has a characteristic stepped profile. This behaviour occurs in both pure sliding and pure rolling conditions. The development of film profile over time can be used to chart the speed of motion of the fluid film in the contact. In pure rolling conditions, the first film front travels through the conjunction at a speed lower than the entrainment speed in the first half of the contact and higher in the second half. In pure sliding it travels at a velocity higher than the entrainment speed across the whole width of the contact. The leading edge moves as a core of lubricant with a velocity constant through 60 per cent of its thickness.

At very high accelerations, the central film thickness shows damped oscillations about the steady state final entrainment speed value. These oscillations are similar to those found theoretically by other workers for an accelerated slider bearing using a Navier-Stokes analysis. It is believed that some of the non-classical EHD behaviour observed on start-up may result from the finite rate of momentum transfer across the fluid film.
Friction-reducing contact area expansion in upsetting
Authors: Tan X
Published: October 2002

The most obvious problem in static and dynamic upsetting is dealing with the effects of friction. In upsetting with friction, the final contact area can be divided into two parts: the expanded original contact area and the immigrated contact area. In this paper, upsetting of aluminium alloy AA 6082, low-carbon steel W. No. 1.0303 and stainless steel W. No. 1.4301 with three kinds of machined end surface lubricated by five different lubricants is carried out. Finite element analyses applying five different friction models are performed to estimate the contact areas and metal flows. Contact area configurations and two parameters, namely the friction area ratio and immigrated contact area ratio, are suggested. The influences of reduction, lubrication and temperature on the contact areas are experimentally and theoretically investigated. It is found that reducing the contact area expansion is a basic characteristic of friction in upsetting by both experiments and finite element method simulations.
Determination of film thickness, pressure and temperature in elastohydrodynamic lubrication in the past 20 years in Germany
Authors: Höhn B-R , Michaelis K , Kopatsch F
Published: October 2002

Highly loaded lubricated rolling and sliding contacts, such as gear contacts or roller bearing contacts, are extremely important for the durability of most gear applications. It has always been the objective of tribologists to determine the film thickness, pressure and temperature distributions in elastohydrodynamic lubrication contacts. This paper gives a survey of the research work that has been carried out in this field in Germany in the past 20 years.
Effects of transversely oriented defects and thickener lumps on grease elastohydrodynamic lubrication films
Authors: Kaneta M , Nishikawa H , Naka M
Published: October 2002

Using the optical interferometry technique, transient behaviour of grease films at an elastrohydrodynamic lubrication (EHL) point contact caused by a transversely oriented groove and long bump passing through the contact area is directly observed with three different types of diurea grease without additives. The effects of the thickener content on the grease film formation are also examined. It has been found that the behaviour of EHL films depends strongly on the thickener structure, and the effects of surface defects on EHL films become pronounced as the film thickness decreases. It has also been found that the thickener lumps move through the EHL conjunction while repeating attachment to the surfaces and detachment from them, and the thickener lumps deposited on the surfaces affect the film behaviour as a kind of solid bump.
Stability and bifurcation of a rigid rotor-magnetic bearing system equipped with a thrust magnetic bearing
Authors: Ho Y. S. , Liu H , Yu L
Published: October 2002

This paper is concerned with the stability and bifurcation of a rigid rotor support by journal and thrust active magnetic bearing (TAMB). The system is modelled as a five-axis controlled active magnetic bearing-rotor system (AMBRS), and the system equations are formulated by combining the equations of motion of the rotor and the equations of the decentralized proportional-integral-derivative controllers. For this AMBRS, the magnetic forces of the journal and TAMB are strongly non-linear with respect to control current and shaft displacement. This study focuses on the influence of non-linearities on the stability and bifurcation of T periodic motion of the AMBRS subjected to the influence of TAMB and mass eccentricity. In the stability analysis, only periodic motion is investigated. The periodic motions and their stability margin are obtained by shooting method and path-following technique. The local stability and bifurcation behaviours of periodic motions are obtained by the Floquet theory. The results indicate that TAMB and mass eccentricity have great influence on non-linear stability and bifurcation of the T periodic motion of the system and cause the spill-over of system non-linear dynamics and degradation of stability and bifurcation of T periodic motion. Therefore, sufficient attention should be paid to these factors in the analysis and design of rigid rotor systems equipped with TAMBs in order to ensure system reliability.
Diamond-like carbon coatings in rolling contacts
Authors: Sjöström H , Wikström V
Published: October 2002

The use of diamond-like carbon (DLC) coatings to improve the performance of more complex mechanical components or systems is currently increasing rapidly. Higher demands on robustness and reliability and less maintenance imply that incremental improvements in steel or lubricants is no longer sufficient and therefore DLC coatings, belonging to the family of hard wear-resistant coatings, have become a realistic option also for components such as bearings, gears, joints or cams. This paper describes the development of DLC coatings for highly loaded components with complex geometry made from low-temperature stabilized steel, exemplifies their performance with test results and discusses relevant test and quality control methods for component coatings. Finally, an outlook on the future of surface engineering of components is given.
Three-dimensional thermohydrodynamic analysis of axially grooved journal bearings
Authors: Nassab S A Gandjalikhan , Moayeri M. S.
Published: October 2002

A thermohydrodynamic analysis of an axially grooved fluid film journal bearing, based on computational fluid dynamics (CFD) techniques is presented. The bearing has a finite length and operates under incompressible laminar flow and steady conditions. This analysis is based on the numerical solution of the full three-dimensional Navier-Stokes equation, coupled with the energy equation in the lubricant flow and the heat conduction equations in the bearing and the shaft. Considering the complexity of the physical geometry, conformal mapping is used to generate an orthogonal grid and the governing equations are transformed in the computational domain. Discretized forms of the transformed equations are obtained by the control volume method and solved by the semi-implicit method for pressure-linked equations (SIMPLE algorithm). In this study, cavitation effects are also considered by introducing an appropriate three-dimensional cavitation model. The liquid fraction in the cavitated region is computed on the basis of continuity requirements and, rather than the flow of gas and liquid in this region, a homogeneous mixture with equivalent properties is assumed and the governing equations still apply. From this method, the lubricant velocity, pressure and temperature distributions in the circumferential, cross-film and axial directions are obtained without any approximation. Also, a comparison is made between two-dimensional and three-dimensional analyses and the effect of bearing length on performance is studied. The numerical results are compared with several experimental data sets and good agreement is found.
Abrasion processes in wear and manufacturing
Authors: Hutchings I. M.
Published: October 2002

Abrasion by hard particles is responsible for wear in many practical situations, but can also be used constructively in grinding and polishing processes. A brief overview of abrasion is presented, followed by an historical survey of polishing and a discussion of laboratory abrasion test methods.
Laboratory research facility for testing hydrodynamic thrust bearings
Authors: Glavatskih S. B.
Published: October 2002

A research facility has been designed and manufactured to study performance characteristics of industrial hydrodynamic thrust bearings. The facility includes a test rig containing two identical tilting pad thrust bearings operating against separate collars. A shaft supported by two journal bearings is driven by a 143kW variable-speed d.c. motor. The bearings are tested in a balanced pair to accommodate the substantial axial force generated by hydraulic cylinders. Bearing instrumentation encompasses a distribution of thermocouples, pressure transducers and oil-film thickness sensors of eddy current type. Two piezoelectric transducers for pressure profile measurements and three thermistors are mounted in one of the shaft collars. Additional instrumentation includes thermocouples, pressure sensors, flowmeters, a load cell and inductive sensors. Signals from all sensors are logged by a personal computer-based high-speed data acquisition system that acquires the measured data, conditions them and presents the results on line. Power losses are obtained by monitoring bearing friction torque and by the calorimetric technique. A detailed description of the research facility is provided together with some representative results of equalizing tilting pad thrust bearing performance obtained for the steady state and transient operating conditions.
Design and development of an elastomer-based pneumatic seal using finite element analysis
Authors: Calvert C , Tirovic M , Stolarski T
Published: October 2002

To create a dynamic seal where sealing action takes place between surfaces in sliding contact, a variety of different shaped seals can be used. One such example is the lobed ‘O’ ring. This paper presents details of the experimental and analytical procedures used in order to develop a lobed seal design. To develop adequate and productive procedures, finite element models were created and non-linear analysis of an existing seal design was conducted in order to build further knowledge and understanding of the seal's performance characteristics. Experimental procedures have been developed to confirm these findings. Results obtained from the finite element analyses (FEAs) provided a very favourable comparison with empirical data and procedures developed were used to devise a new higher-performance seal. Key areas of improvement were reduced frictional forces, increased seal stability and higher operating pressures and temperatures. An irradiated polymer was used for the existing and new seal designs. This meant that manufacturing methods, valve body and spool dimensions were unchanged (making both seal designs interchangeable), but the potential of extending the temperature range was limited. The new seal design achieved all design objectives and procedures developed demonstrated that FEA is a very powerful tool in designing high-performance seals in a short time and at low cost.
Comparison between experimental film thickness measurements and elastohydrodynamic analysis in a connecting-rod bearing
Authors: Moreau H , Maspeyrot P , Bonneau D , Frène J
Published: October 2002

This paper describes the experimental measurements and the theoretical calculations of oil-film thickness in a dynamically loaded connecting-rod big-end bearing. Four eddy current gap sensors for each bearing are used to measure the oil-film thickness and to deduce the bearing trajectories. Experimental data for crankshaft main bearings are easy to obtain but connecting-rod bearings are more difficult to control due to the difficulty of installing instrumentation on connecting-rods that are rotating and reciprocating. The solution uses a mechanical linkage fixed under the piston axis. The elastohydrodynamic model considers connecting-rod elastic deformations. The calculation process uses finite element and Newton-Raphson methods for the numerical analysis. Comparisons of both the load and crankshaft speed effects are made between experiment and the theory.
Dynamic behaviours of piston rings and their practical impact. Part 1: Ring flutter and ring collapse and their effects on gas flow and oil transport
Authors: Tian T
Published: October 2002

This paper describes the physics of two major dynamic behaviours of the piston rings, namely ring flutter and ring collapse, and their effects on gas flow and oil transport. The analysis was conducted by applying a theoretical model in a spark ignition engine and a heavy-duty diesel engine. Parameters that have great influence on these dynamic behaviours are discussed for these two different types of engine and different rings. Specifically, the importance of ring twist, torsional stiffness and ring-groove clearance to ring flutter are discussed in detail. For ring radial collapse, the paper presents a simple formula that determines value of the critical parameters to eliminate ring radial collapse. Emphases are placed on the importance of mechanical designs in changing the performance of the piston ring pack in blowby and oil consumption.
On the friction-position control relationship
Authors: Capone G , della Valle S , Guida D , d'Agostino V
Published: October 2002

A theoretical analysis of the dynamic behaviour of mechanical systems characterized by coupled elements subjected to friction force from the sliding surface is proposed. With reference to systems with one degree of freedom and approximating the friction force as a piecewise linear function, i.e. straight line segments with a suitable slope, the positioning errors in the stop phase are studied. Dimensionless analytical relations used to predict the size of positioning errors and dimensionless diagrams are provided.
The influence of piston ring tribology on the diffusion of fuel through oil films
Authors: Thomson A , Radcliffe C. D. , Taylor C. M.
Published: October 2002

The absorption and desorption of fuel into oil films is considered to be responsible for a significant proportion of the unburnt hydrocarbon emissions from spark ignition engines. A model has been developed which allows the prediction of the effect of engine parameters on this source. Results show that engine speed, operating temperature and oil-film thickness are controlling parameters. The work highlights the link with ring pack tribology and makes some estimates on the overall effect of temperature and engine speed.
In situ instrumentation for localized wear studies of magnetic thin-film disks
Authors: Bhushan B , Forehand S M
Published: October 2002

An experimental set-up and a procedure to make in situ localized measurements of various wear processes on magnetic thin-film disks are developed. The coefficient of friction, acoustic emission and optical reflectance are monitored simultaneously. Results are analysed to determine ‘precursors to failure’ and to compare the effects of lubricant, surface roughness, overcoat and normal load on disk wear. Disk wear is observed to follow a pattern of lubricant depletion followed by head slider-overcoat asperity contact. Wear tracks are formed after asperity contact. Lubricant extends disk wear life, as does a polished surface texture, and an SiO2 overcoat wears more slowly than a diamond-like carbon overcoat. The experimental methodology developed in this study should be of interest in studying precursors to failure of any moving interface.