bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical studies of an impingement-conditioned small direct-injection diesel engine
Authors: Bai C , Gildein H , Breitling T
Published: October 2002

Numerical studies are performed to identify an optimal range of geometric parameters in connection with the design of an impingement-conditioned small direct-injection diesel engine. The parametric studies were made in a pressure chamber with a circular protrusion on to which sprays are directed to impinge. Computational runs were made for 24 cases carefully chosen to allow examination of the effects on post-impingement spray characteristics of the following parameters: (a) the nozzle-plate distance and (b) the size and geometry pattern of the protrusion. An optimal range of these parameters has been identified through an analysis of the calculated results in terms of vapour concentration, the Sauter mean diameter of the wall spray and the dispersed wall spray volume. The results obtained also reveal that, by just changing the size of the impingement surface and the impingement distance, local fuel vaporization efficiency can be increased as high as 40 per cent under the same injection and ambient conditions. This raises the possibility that spray impingement may be conditioned in a manner ensuring good fuel distribution and a sufficient fuel-air mixing rate without even resorting to swirling air, thus improving substantially the engine efficiency.
A study of the adaptive control of spark timing using cylinder pressure in a spark ignition engine
Authors: Cho H , Lee J , Yoo J
Published: October 2002

Spark timing is one of the major parameters influencing engine performance and emissions. In most of today's automotive spark ignition (SI) engines an electronic control unit controls spark timing based on preset values that are functions of load and speed. In this system, the preset spark timing can be different from the optimum value owing to deviations from mass production, ageing effects and a number of other factors.

In the present study, a control logic is investigated for the real-time adaptation of spark timing to the optimal value. The simulation program, including an engineering model for cycle-by-cycle combustion variation, is developed for investigating the spark timing control logic. It has been found that the location of the peak pressure in the cylinder is one of the appropriate parameters used to estimate the optimum spark timing. It is also shown that experimental results reflect the simulation outputs and reasonableness of the spark timing control logic for location of the peak pressure.
Statistical uncertainty in automotive emissions testing
Authors: Kandylas I. P. , Stamatelos A. M. , Dimitriadis S. G.
Published: October 2002

Automotive exhaust emission testing according to legislated procedures and driving cycles is a routine process today in the United States, Europe and SE Asia. In practice, the selection of catalytic converters and the general design of exhaust aftertreatment systems are mainly aimed at the attainment of the legislated emissions limits with a reasonable safety margin. However, during the system optimization process, the catalyst and/or exhaust system manufacturer screens a large number of catalysts with a significant number of system design variations. In this process, certain levels of statistical uncertainty are present and must be seriously taken into account as stricter emissions standards are addressed and the safety margins become leaner. A methodology is developed and presented in this paper that is able to determine confidence levels in the attainment of specific emissions limits. This methodology combines results from experimental assessment of the distributions of engine-out emissions and catalyst activity by employing a previously developed and extensively validated model of a diesel oxidation catalyst. In this way, the emissions control system optimization is substantially aided and the required experimental effort is considerably reduced.
A simple analytical model for estimating air leakage through rotary valves
Authors: Rogers J , Bradley M S A , Pittman A N , Farnish R J , Reed A R
Published: October 2002

This paper presents an analytical model from which to estimate the air leakage through rotary valves feeding positive-pressure pneumatic conveying systems. Estimating air leakage through rotary valves is an important part of the design of certain pneumatic conveying systems. Accounting for leakage assists in estimating blower and bin vent requirements and reduces maintenance costs and downtime. An overestimate of the leakage can contribute to inefficiencies, excessive pipeline wear and particle attrition, while an underestimate can lead to blocked pipelines and severely reduced solid flowrates through the valve.

The formulation of the analytical model presented in this paper is based on the principle of air flow through multiple orifice plates in series. The leakage rate across a pressure differential is determined by treating each constriction between rotor blade and casing as an orifice plate. The validity of the model is confirmed by comparing its results to previously recorded empirical data.

Note that, while this paper addresses rotary valves feeding positive-pressure pneumatic conveying systems, the same principles can be used for the design of vacuum pneumatic conveying systems. For vacuum systems the air density and differential pressure must be accounted for in order to estimate the air leakage rate in the opposite direction through the valve. Accounting for this type of leakage is especially important for vacuum systems with (a) multiple feed points, in order to ensure that adequate upstream transport velocities are reached, and (b) inert gas as the transport medium, where air leakage into the system can dilute the conveying gas.
Segregation of binary mixtures of particles during the filling of a two-dimensional representation of a hopper
Authors: Salter G F , Farnish R J , Bradley M S A , Burnett A J
Published: October 2002

This paper contains a summary of results obtained from experiments carried out at The Wolfson Centre for Bulk Solids Handling Technology at the University of Greenwich on the segregation of dry binary particle mixtures of the same material when they fill a hopper. A test facility has been built which represents a two-dimensional segment of a hopper. Binary mixtures were fed into this container using amplitude feedback-controlled vibratory feeders via a static in-line mixer and one of two different feed chute designs; one curved and the other straight. ‘Thieving’ probes were used to sample the segregated heap of material from the hopper. The contents of each probe then underwent size analysis to ascertain the change in the size distribution from that of the original mixture. It is shown that a mechanism, termed embedment, caused by the vertical component of the feed velocity on impact with the forming heap, has a dramatic effect on the segregation process. A detailed discussion of the relationship between the possible mechanisms occurring in the heap formation process in the light of the segregation patterns observed is given.
Performance and flow characterization studies of a vortex slurry transportation unit
Authors: Faram M G , O'Doherty T , Syred N
Published: October 2002

Conventional equipment for the transportation of solid-liquid mixtures is often subject to wear-related problems. A recent innovation, which is a fully fluidic non-moving part device, utilizes vortex flows for the mixing and transportation of slurries. Its novelty lies in the fact that it is driven by an external fluid supply and thus contains no moving parts in direct contact with the slurry material. Slurry mixing is an integral part of the process, and thus the need for pre-treatment of slurries is eliminated. An extensive series of studies has been carried out to investigate both the performance aspects of the device and the underlying phenomena involved in its operation. This paper presents experimental results of both performance and operational studies of this novel slurry transportation system.
Diagnosis of process faults with neural networks and principal component analysis
Authors: Gomm J B , Weerasinghe M , Williams D
Published: October 2002

Industrial plants often have many process variable measurements available, which can be monitored for fault detection and diagnosis. Using all these variables as inputs to an artificial neural network for fault diagnosis can result in an impractically large network, with consequent long training times and high computational requirement during use. Principal component analysis (PCA) is investigated in this paper for generating a reduced number of variables to be used as neural network inputs for fault diagnosis. The main application described is to a real industrial nuclear fuel processing plant. A simulated chemical process was also used to assist the development of the techniques. Results in both applications demonstrate satisfactory fault diagnosis performance with a reduction in the number of neural network parameters of approximately 50 per cent using PCA. The paper also includes some introductory material on PCA and neural networks, and their application to process fault diagnosis.
Outdoor testing of evacuated-tube heat-pipe solar collectors
Authors: Ng K C , Yap C , Khor T H
Published: October 2002

The paper presents the steady state performance of two types of commercially available evacuated-tube heat-pipe solar collector that were tested under the meteorological conditions of Singapore. The tests were made in arrays of collectors in contrast with the normal tests performed under controlled laboratory conditions. A theoretical model is also presented to predict the collector efficiency as well as the collectable energy during a steady state test. Within the range of expected coolant temperatures, the efficiency and the heat loss coefficient of collectors are measured and a linear expression can adequately depict their characteristics.
Experimental and analytical study of thermal stresses during pipe freezing
Authors: Keary A C , Syngellakis S , Bowen R J
Published: October 2002

A review of experimental investigations on stress development during the blockage of a water-filled pipe by freezing was undertaken with the parallel development of an effective finite element thermal stress model. A wide spread of measured stress values was noted as well as a degree of uncertainty in the cases when the gauge output did not return to zero at the end of the freezing cycle. A methodical examination of stress—and temperature—time histories showed that it is possible to divide a freeze into three stages: filling, constant wall temperature and thawing. Since each stage produces quantitatively and qualitatively different stress states, it needs to be examined separately. The filling stage causes stresses through the pipe wall, which vary from tensile on the outside surface to compressive on the inside. These stresses can be significant but are also short lived and their magnitude may be greatly affected in practice by the way that the coolant is applied. During the constant-temperature phase, when the pipe wall temperature is maintained at the coolant temperature, the stresses are mainly compressive, their variation is small within the freezing jacket and they appear to depend on the diameter—thickness ratio. A significant difference between the behaviour within the jacket and at the end of the jacket is sometimes observed. Finally, tensile stresses arise during the reverse process of thawing. Comparison of experimental data with numerical predictions confirmed the above observations regarding the magnitude, distribution and nature of the developing stresses. There are important quantitative and qualitative differences between measured and predicted values, which can be explained by the uncertainty and scarcity of data as well as the simplicity of the adopted material model for ice behaviour.
A model to predict the life of pneumatic conveyor bends
Authors: Hanson R , Allsopp D , Deng T , Smith D , Bradley M S A , Hutchings I M , Patel M K
Published: October 2002

A new approach to the prediction of bend lifetime in pneumatic conveyors, subject to erosive wear is described. Mathematical modelling is exploited.

Commercial Computational Fluid Dynamics (CFD) software is used for the prediction of air flow and particle tracks, and custom code for the modelling of bend erosion and lifetime prediction. The custom code uses a toroidal geometry, and employs a range of empirical data rather than trying to fit classical erosion models to a particular circumstance. The data used was obtained relatively quickly and easily from a gas-blast erosion tester.

A full-scale pneumatic conveying rig was used to validate a sample of the bend lifetime predictions, and the results suggest accuracy of within ±65%, using calibration methods.

Finally, the work is distilled into user-friendly interactive software that will make erosion lifetime predictions for a wide range of bends under varying conveying conditions. This could be a valuable tool for the pneumatic conveyor design or maintenance engineer.
Numerical analysis of multiple jets discharging into a confined cylindrical crossflow
Authors: Tao Y , Adler W , Specht E
Published: October 2002

A row of jets discharging normally into a confined cylindrical crossflow is numerically investigated using the control-volume-based finite difference method. Interest is focused on determining the relationship between the temperature trajectory and the upstream flow and geometric variables. Parameter variations studied include nozzle diameter, number of nozzles, duct radius, jet and mainstream volume-flow, temperature ratio, and dynamic pressure ratio. The dynamic pressure ratio, the number of nozzles, and nozzle spacing are found to be significant variables. A logarithmic function describing the relationship between penetration depth and dynamic pressure divided by the square of the number of nozzles is derived by fitting the data of the computation results. The values for penetration depth and nozzle spacing are described for optimum mixing. A suggested design procedure is presented, which can be used as a first approach in configuration design.
The distribution of a viscous liquid through a perforated tube
Authors: Gilbertson M A
Published: October 2002

One of the methods by which a slab of material can be made is by laying down a mixture of liquids that react and form a solid. This can be done by passing them through a moving perforated tube. A problem often experienced in such equipment is that liquid can spend too long somewhere within the tube so that solidification takes place prematurely and the tube becomes blocked. An experimental study of the flow of a viscous liquid through a perforated tube has been undertaken to identify where and why this may occur and how it might be eliminated. Most of the liquid flows straight through the tube and the perforations and has a short residence time; however, an air pocket forms at the end of the tube near which there is a region of slowly moving or stagnant fluid. This pattern does not seem to be affected by the presence of holes upstream nor to be very sensitive to fluid viscosity, and cannot be wholly prevented by changing the position of the final hole. However, the amount of slow-moving liquid can be much reduced by altering the geometry of the end of the tube so that it tapers towards the end.
Solid/liquid separation by sedimentation
Authors: Holdich R G , Butt G
Published: October 2002

The analysis of batch sedimentation tests performed for the purpose of continuous sedimentation vessel design is described. Conventional design techniques employ the concept of settling flux with, under certain conditions, a constitutive equation linking solid concentration and pressure in a unique and time-independent manner.

Experimental studies employing measurement of local concentration and the liquid pressure gradient during sedimentation were used to determine the limits of the conventional design techniques. A 'maximum fluidized concentration' is defined which is the value above which it is difficult to maintain stable flux conditions and is the limit of applicability of conventional design methods based on settling flux. It is shown that the suspended solids contribute towards the liquid pressure gradient and, therefore, to the buoyancy experienced by the settling solids. However, during settlement the liquid pressure gradient reverts to the hydrostatic gradient alone; hence the buoyancy effect is a function of sedimentation time. Additional considerations also suggest that a unique relation between concentration and pressure should only be used as a constituent term in a time-dependent consolidation model. Current research effort includes a suitable method of linking time-dependent consolidation theory, under conditions of extremely low applied pressure, and sedimentation flux analysis.
Development of a high-temperature ceramic to metal seal
Authors: Beck S B M , Langston P R , Ewan B C R , Messer P E , Smyth R , Swithenbank J , Taylor D A W
Published: October 2002

Research is currently being conducted into the construction of high-temperature (>1000°C) tubular heat exchangers that are to operate with a large pressure differential between low-pressure combustion gas and a process fluid. High operating temperatures preclude the use of metals. Therefore it is necessary to use ceramic heat transfer components and to insulate other components to counteract the direct heat. As the high-temperature ceramic heat transfer tubes exhibit a variable thermal expansion relative to the outer metallic casing and tube sheet, it is necessary for the seals to slide. This prevents excessive axial stress being set up in the ceramic tubes, thus prolonging their life.
Sliding mesh computational fluid dynamics—a predictive tool in stirred tank design
Authors: Jaworski Z , Wyszynski M L , Moore I P T , Nienow A W
Published: October 2002

The use of a fully predictive numerical model of flow in a stirred, baffled tank is presented and validated for the laminar flow regime. This approach employs a commercial computational fluid dynamics (CFD) package with sliding mesh facility. The comparison of computed and experimental values for various flow characteristics shows a very good agreement without the need to input any experimental values for the boundary or initial conditions. It is proposed that the model/experiment error ratio (involving relative errors) may be generally adopted as a criterion for the quality of CFD modelling. This ratio should not be much larger, and does not need to be smaller, than unity. The ratio obtained in this work was just over unity. The state of the art CFD packages are now believed to be able to form a suitable basis for the process engineering aspects of an integrated design of stirred tanks, including mechanical engineering and other related issues.
Disc refiner analysis
Authors: Whalley R , Mitchell D
Published: October 2002

A general non-linear model of a disc refiner for the preparation of the raw material used in paper and board manufacture, from processed mechanical and chemical pulp, is derived. Thereafter, a linear description is constructed for analysis and process design purposes. The time domain responses of the models are presented for purposes of comparison and simulation is employed to confirm the predicted condition of torsional resonance. The effect of this excitation on the reciprocal shredding and shearing action of the machine is commented upon.
Remaining life of a vessel containing an internal corner crack under repeated thermal shock
Authors: Ng H W , Lee C K
Published: October 2002

The remaining life for a hypothetical pressure vessel containing a defect which is subject to thermal shock has been calculated. Twelve cases of thermal shock loads of different severity characterized by the dimensionless parameters, Biot (B) and Fourier (F) numbers, were analysed by finite element modelling (FEM). The estimation of remaining life for each case was carried out based on the PD6493 defect assessment procedure (1). The effect of thermal shock on the crack growth rate was quantified showing that more severe shocks accelerate crack growth while less severe shocks may lead to slow growth or eventual crack arrest.
An appreciation of common cause failures in reliability
Authors: Hanks B J
Published: October 2002

Equipment reliability may fall short of expectation due to the simultaneous failure of similar items arising from a common weakness. This paper discusses various aspects of common cause failures and how allowances can be made for them in reliability studies.
Non-linear dynamic analysis of cantilever whipping pipes
Authors: Reid S R , Yang J L
Published: October 2002

This paper presents the results of numerical dynamic analyses of a number of pipe whip problems based on non-linear shell theory using the DYNA3D (version 6.0) finite element code. The calculations are mainly concerned with the transient deformation of the pipes during the whipping process. The main purpose of the study is to check the efficacy of a recently published theoretical elastic-plastic, hardening-softening (e-p-h-s) model for pipe whip developed by Reid et al. [1, 2]. This model is based upon beam theory but allows for the effects of ovalization of the pipe cross-section on the moment-curvature constitutive behaviour of the pipe. It is shown that the results using DYNA3D are in good agreement with both experimental data and the e-p-h-s model predictions and confirms the accuracy of the latter. While the DYNA3D study is not exhaustive, the localized shell bending deformation of whipping pipes in which ‘kinks’ are formed is reproduced with reasonable accuracy and it has permitted the effect of the strain-rate sensitivity of the yield stress of the pipe material to be examined in a preliminary manner.
Creep of welded pipes
Authors: Hyde T H , Sun W
Published: October 2002

Creep continuum damage mechanics analyses and peak stationary state stresses in the base, heat-affected zone and weld materials of a welded joint in a pipe were used to obtain failure times. The properties related to a1/2Cr1/2Mo1/4V:21/4Cr1Mo welded joint were used in the analyses. Similar analyses were performed on cross-weld specimens. The predictions indicate that, for moderate systems loading, using the mean diameter hoop stress in conjunction with cross-weld creep test data would result in safe failure predictions for the welded pipes. The results also indicate that reasonably accurate predictions of safety factors would be obtained using peak stationary state stresses, thus eliminating the need for the more complex and time-consuming creep continuum damage mechanics analyses.
An experimental study of the collapse of horizontal saddle-supported storage vessels
Authors: Chan G C M , Tooth A S , Spence J
Published: October 2002

The use of plastic analysis in the design of horizontal vessels, used for liquid or gas storage, and supported on twin saddles, allows better utilization of the vessel's material and avoids the problems of categorizing the elastic stresses when designing the component. To understand how the vessel collapses onto the saddle, experiments were conducted on a range of model vessels (40 in all) with different radius-thickness ratios ( R/t) and supported on saddles which were either loosely fitted or welded to the vessel. The experimental results show that different collapse mechanisms occurred for loose and welded saddles and also that the modes of failure were dependent upon the value of R/t for the vessel. In general, progressive plastic collapse occurred in those vessels with low values of R/t and elastic-plastic buckling for vessels when higher R/t ratios were employed. This paper presents the detailed experimental results, which are used as the basis of a theoretical design approach; the latter will appear in future papers considering both plastic collapse and buckling failure.
A review of design for safety methodology for large marine and offshore engineering systems
Authors: Wang J
Published: October 2002

This paper deals with problems involving the incorporation of safety into the design process of large marine and offshore engineering products from the initial stages. In this paper, the characteristics of large marine and offshore products are described and their design process is studied together with a proposed design framework. After investigating the current design for safety status of large marine and offshore products, a design for safety methodology is proposed in a generic sense and discussed in the context of the design process. The phases in the proposed design for safety methodology are studied together with their objectives and requirements. Finally, concluding remarks are given.
Load cell for dynamic measurement of cutting forces generated during ultrasonic drilling and milling of hard materials
Authors: Wiercigroch M , Neilson R D , Player M A
Published: October 2002

In this work, a novel design of load cell for the measurement of the dynamic forces generated during ultrasonic drilling and milling of hard materials is presented. The transducer, which allows for simultaneous sensing of three components of force, has been designed to minimize the influence of cross-coupling between the components acting in the three perpendicular directions and to measure low levels of force (typically a few tens of Newtons in magnitude) while retaining high mechanical stiffness. This is achieved by utilizing a membrane element for vertical measurement coupled with a multi-beam arrangement for the horizontal axes. The results from static and dynamic analyses of the proposed design conducted using analytical expressions for the membrane and finite element methods for the beam structures are presented. The paper also describes the associated instrumentation set-up, calibration and some example experimental results.
Effects of imperfections on fatigue initiation in railway wheels
Authors: Ekberg A , Marais J
Published: October 2002

The paper begins with a description of three observed types of fatigue failure. It continues with a discussion on fatigue mechanisms and numerical modelling of rolling contact fatigue, especially in the presence of material defects. Based on this discussion, the main mechanisms behind the three types of failure are analysed from a mechanical point of view. Finally, practical implications of the results in this paper are discussed and some suggestions of means of preventing fatigue failure of railway wheels are put forward. Future research areas are indicated.
An investigation into the attenuation of wind speed by the use of windbreaks in the vicinity of overhead wires
Authors: Scanlon T. J. , Oldroyd A. B.
Published: October 2002

An experimental and computational analysis of the efficacy of windbreaks for the attenuation of wind speed in the vicinity of overhead wires is presented. This work has been specifically applied to the case of oscillation of overhead catenary contact wires in a cross-wind. A wind tunnel subscale model of a windbreak/overhead wire configuration is presented and discussed with regard to the feasibility of reducing the aerodynamically induced oscillations encountered in such situations. This porous blockage placed upstream of the simulated overhead wire attempts to represent the influence of a windbreak/shelterbelt on the reduction of the vibration phenomenon known as galloping. In conjunction with this experimental study, a computational fluid dynamics (CFD) analysis has been carried out in order to assess the influence of the shelterbelt on the catenary wires in a typical full-scale scenario. The results indicate that a dense shelterbelt of height H positioned between 2-8 tree heights, H, upstream of the suspended cables provides a sufficient reduction in wind speed to reduce significantly the amplitude of wire vibration.
The slipstream and wake of a high-speed train
Authors: Baker C. J. , Dalley S. J. , Johnson T , Quinn A , Wright N. G.
Published: October 2002

This paper describes the results of experimental work to determine the structure of the slipstream and wake of a high speed train. The experiments were carried out using a 1/25th scale model of a four-coach train on a moving model rig (MMR). Flow velocities were measured using a rake of single hot films positioned close to the model side or roof. Tests were carried out at different model speeds, with and without the simulation of a crosswind. Velocity time histories for each configuration were obtained from ensemble averages of the results of a number of runs. A small number of particle imaging velocimetry (PIV) experiments were also carried out, and a wavelet analysis revealed details of the unsteady flow structure around the vehicle. It was shown that the flowfield around the vehicle could be divided into a number of different regions of distinct flow characteristics: an upstream region, a nose region, a boundary layer region, a near wake region and a far wake region. If the results were suitably normalized, the effect of model speed was small. The effect of crosswinds was to add an increment to the slipstream and wake velocities, and this resulted in very high slipstream velocities in the nose region.
Design synthesis of non-symmetrically loaded high-performance disc brakes Part 1
Authors: Tirovic M , Ali G
Published: October 2002

Wheel-mounted disc brakes are exposed to severe non-symmetrical mechanical and thermal loads. The paper describes the design process for two high-performance, hub-mounted discs of different size and duty. The development has resulted in two very successful but fundamentally different hub designs and manufacturing methods. Initially, finite element analyses used in the design optimization were mainly concentrated on bulk thermal effects. Recently, in order further to improve the design process, analyses have included macro thermal effects, providing valuable results, particularly related to the prediction of disc permanent coning, one of the most critical design requirements.
Effect of cracks on the dynamic response of a simple beam subject to a moving load
Authors: Mahmoud M. A.
Published: October 2002

The effect of transverse cracks on the dynamic behaviour of simply supported undamped Bernoulli-Euler beams was determined. Crack presence in the beam results in higher deflection and alters the beam response patterns. In particular, for a given speed, the largest deflection in the beam takes longer to build up, and a discontinuity appears in the slope of the deflected shape of the beam at the crack location. In addition, for certain speeds the beam changes its pattern of deflection from downwards to upwards as the load leaves the beam. Crack effects become more noticeable as crack depth increases.
Some railroad settlement models—A critical review
Authors: Dahlberg T
Published: October 2002

Mathematical models to simulate railroad track settlements are reviewed and commented upon. There do not seem to be any generally accepted damage and settlement equations describing the long-term behaviour of the track. This also seems to be the case for the ballast material. Most descriptions of the settlement found in the literature are empirical; only different suggestions to describe the track settlement from a phenomenological point of view are available. The track settlement is mostly considered to be a function of number of loading cycles and/or a function of the magnitude of the loading. The settlement should also be a function of the properties of the ballast and subground materials, but very little has been found on this in the literature.

By use of the finite element program LS-DYNA, a computer model (very simple) has been created to simulate the long-term behaviour of the track. The model consists of a rail, rigid sleepers, non-linear ballast springs (stiffnesses) and ballast damping. In a solid element beneath each ballast spring, track settlement can be accumulated. Settlement will occur if the stresses in that element exceed a yield limit of the element material. Also ‘hanging sleepers’ may be modelled and obtained as a result of the track settlement.
Freight car curving performance in braked conditions
Authors: Berghuvud A
Published: October 2002

Railway freight vehicles that are run with full payload on long downhill slopes with many tight curves must be braked more or less continuously. The influence of braking on the curving performance of iron ore freight cars equipped with different types of three-piece bogie designs and pneumatically actuated single-block tread brakes run on curved track in a downhill slope is investigated. The focus is put on the change in performance in terms of self-steering ability, track forces and expected wear in contacts between wheels and rails. Modelling and simulation of the strongly non-linear dynamic interaction between vehicle and track in braked conditions are performed. The large influence of wheel/rail profile matching and the quite different responses to braking for the studied vehicles are shown.
Railway Safety's Safety Risk Model
Authors: Muttram R. I.
Published: October 2002

Railway Safety is an organization that coordinates the activities of the fragmented railway industry in the United Kingdom with respect to safety. It was formed from the Safety and Standards Directorate (S & SD) of Railtrack plc, the owner and operator of the UK railway infrastructure, with the objective of giving it increased independence. When the author, who is currently CEO of Railway Safety, was appointed Director of S & SD in late 1997, one of the projects he launched was the Safety Risk Model. This paper describes that model, which is one of a suite of tools developed in recent years to improve the targeting of the industry's efforts in safety improvement in an impartial and scientifically supportable manner. The model uses fault tree analysis and cause/consequence techniques to predict residual levels of safety risk, after the industry's current safety control measures are applied, using observed safety performance data. The output of the model is used to produce a regularly updated ‘Risk Profile Bulletin’, which is used by Railtrack and UK train operators in the production of their statutory Safety Cases. The model can also be used to test the effect of proposed new controls on risk levels.
Active vibration control of a railway pantograph
Authors: Wu T. X. , Brennan M. J.
Published: October 2002

Current collection for electrical trains can be improved by the use of an active pantograph. To design such a system the behaviour of both the active pantograph and the overhead catenary system must be considered together. In this paper a two degrees-of-freedom model of an active pantograph, combined with a time-varying spring representing the catenary's influence, is employed and its dynamic performance is studied. Based on this model, three types of control strategies for an active pantograph are proposed and investigated, and all these models consider the interaction of the pantograph with the overhead wire. Two possible positions for mounting an actuator on the pantograph are considered and compared. From these active pantograph models the magnitude of the control force required can be estimated, and the advantages and disadvantages are discussed. The optimal control strategy shows the best performance, but introduces measurement difficulties because it needs full-state feedback. Classical feedback control is the least difficult to implement, but a compromise between the stability and the performance should be reached.
The effect of strain hardening on shakedown limits of a pearlitic rail steel
Authors: Jones C. P. , Tyfour W. R. , Beynon J. H. , Kapoor A
Published: October 2002

The load limit below which a material remains elastic for the first application of load is known as the elastic limit. However, material in a railway rail is loaded not once but many times and the load limit below which the material remains elastic in the steady state is known as the elastic shakedown limit. This limit is higher than the elastic limit, and is the basis of tribological design. Such limits are known for solids which have hardness unvarying with depth. However, techniques of heat treatment or coating lead to a variation in hardness with depth for which the effect on the shakedown limit has only recently been established. In the present work the influence of strain hardening on the shakedown limit of a pearlitic rail steel has been analysed. The data used were taken from an experimental study by Tyfour et al. (1) in which wheel-rail contact was simulated by rolling-sliding line contact. The results indicate that the load bearing capacity increases to about four times that without strain hardening in line contact, and even more in point contact.
Control and operation of tilting train services
Authors: Schmid F
Published: October 2002

Discussions on the best way forward to achieve reductions in journey time without the investment normally associated with the construction of new high-speed railways tend to concentrate on the technical issues to be resolved rather than on the very significant operational, legal and human issues that affect the economies of any high-speed railway operation. Many engineers and operators associated with long-established railway systems (1-4) view the introduction of tilting trains as the best way forward in situations where speed limits are imposed by track built with the objective of minimizing expenditure on civil works. Although there are instances where the introduction of tilting trains has yielded the benefits sought, there are many situations where the environment of the railway business effectively excludes this option. The author of the present paper has attempted to review the tilt debate from an operations angle, stimulated by some comments by Meyer (5), and focuses on developments in Great Britain.
The dynamics of railway vehicles—from Stephenson to Carter
Authors: Wickens A. H.
Published: October 2002

The special feature of the dynamics of railway vehicles, i.e. the propensity to oscillation in the lateral plane, arises from the use of the wheelset with its solid axle and coned wheels. This paper traces the early history of the wheelset and how it was incorporated in the design of locomotives and rolling stock and discusses the ensuing dynamic problems. The development of ideas about stability and steering in curves is then considered up to the time of Carter, who in 1916 can be said to have been the first to formulate essentially correct equations of motion and solve them.
The long road to solution of the railway hunting and curving problems
Authors: Gilchrist A. O.
Published: October 2002

Two theoretical problems in railway vehicle mechanics required an exceptionally long time-scale for their solution: the ‘hunting’ problem and the prediction of curving behaviour. Here the history of each is recounted from the point of first recognition (in theoretical terms) to effective solution. Also briefly described is the parallel development of rolling contact theory, which is needed in both applications.
Renaissance of trams in Germany—five case studies
Authors: Topp H. H.
Published: October 2002

Until the end of the 1950s the tram was the most important mode of urban transport in Germany. In the following 30 years drastic cuts were made in the tram network. This trend has now been reversed: new tramways are being built and old ones upgraded. Five case studies represent different developments of tram and light rail systems in German cities: (a) Hannover, which is typical of the stepwise development of a tram system into a partly underground light rail system; (b) Karlsruhe, where the most intensive utilization of railroad tracks is taking place, including the world's first dual-current tram; (c) Oberhausen, where for the first time in Germany a tram was reintroduced in 1996; (d) Saabrücken, which represents the second case of tram reintroduction according to the Karlsruhe model in 1997; and finally (e) Munich, where dense U-Bahn and S-Bahn networks are going to be complemented by new or reopened tram lines.
Performance of a rail car equipped with independently rotating wheelsets having yaw control
Authors: Dukkipati R. V. , Narayanaswamy S
Published: October 2002

Rail vehicles experience problems of hunting and severe wheel/rail wear which result in lower critical speeds. The design of the conventional railway wheelset, consisting of two wheels mounted rigidly on an axle, is one of the main factors inhibiting high-speed operation of rail vehicles. In this paper the potential for good dynamic stability at high speeds and improved ride comfort in a rail vehicle equipped with an independently rotating wheelset (IRW) having yaw control are examined. The control for the yaw rotation is provided by a state-variable feedback controller.
Class 323 electric multiple units
Authors: Webber B
Published: October 2002

The Class 323 electric multiple unit came into being essentially as a 25 kV regional equivalent of the BRB Class 465 Networker units. Principal features include 23 m aluminium bodyshells and three-phase traction equipment without an interference current monitor. In addition it is the first 25 kV rolling stock in the United Kingdom to incorporate regenerative braking. The paper describes the design and build of Class 323, making reference to both its intended use and the newly formed company awarded the contract. Some of the more significant service experiences are referred to, together with reliability and availability issues.
Estimation of train resistance coefficients in tunnels from measurements during routine operation
Authors: Vardy A. E. , Reinke P
Published: October 2002

The measurement of train resistance characteristics in railway tunnels can be a difficult and costly task. This is especially likely when the operator has to provide special trains and large numbers of staff. It would be a considerable advantage if the resistance characteristics could be measured during routine operation with scheduled trains. In May 1996, night-time tests were planned for aerodynamic measurements in the Grauholz Tunnel in Switzerland. They required the installation of pressure, velocity and temperature sensors in the tunnel. The opportunity was taken to record conditions during scheduled operation and this paper reports the use of the data to infer resistance coefficients of trains. It is shown that consistent interpretations are possible, but only when the gaps between successive trains are sufficiently large. Accurate measurements of air velocity are necessary to clarify conditions in the tunnel before train entry. The most important resistance parameter for a long train is its skin friction coefficient. It is found that this can be as low as 0.003 for a modern, streamlined passenger train, but as high as 0.010 for a non-uniform freight train.
Railway passengers and noise
Authors: Hardy A. E. J.
Published: October 2002

Noise has long been established as having a major influence on the overall passenger environment. Unfortunately, the processes involved are often misunderstood and consequently the acoustic environment inside many vehicles is more a result of chance than any design process. By considering the user of the vehicles this paper shows how appropriate noise control measures can be devised so that the maximum improvement in the passenger noise environment is achieved for minimum cost.
On the velocity profile of inclined jets in a boundary layer for vorticity production
Authors: Bray T P , Garry K P
Published: October 2002

The velocity profiles of air-jet vortex generators have been investigated, and the effect of varying velocity profiles on vortex production has been assessed. In the simplest case of a jet generated by fluid effusing through a cylindrical hole drilled into a solid surface, the internal flow in the nozzle is critical to the development of jets to be used for vortex production. A series of Pitot traverses through a range of jet diameters and pitch angles has been made in order to characterize the jet development. In order to produce an axisymmetric jet profile, modifications were made to the jet nozzles, thereby overcoming the critical flow features within the jet nozzle.

In order to assess the jets for vortex production, a range of air-jet vortex generator configurations have been used to produce discrete vortices in a turbulent flat plate boundary layer. Velocity vectors were measured over a cross-stream plane through the vortices, from which the vorticity could be derived across the plane. The vorticity at the centre of the vortex (or the peak vorticity) was then used as an indication of the strength of the vortices. It has been shown that the nature of the jet velocity profile is not significant to the strength of the vortex, so long as the average jet velocity is held constant.
Dynamic instability of laminated composite rectangular plates subjected to non-uniform harmonic in-plane edge loading
Authors: Sahu S K , Datta P K
Published: October 2002

The dynamic instability behaviour of isotropic, cross-ply and angle-ply laminated composite plates under combined uniaxial and harmonically varying in-plane point or patch loads is investigated using finite element analysis. The first-order shear deformation theory is used to model the composite laminates, considering the effects of transverse shear deformation and rotary inertia. The effects of various geometrical parameters, boundary conditions, lamination and load parameters on the principal dynamic instability regions of composite plates are studied in detail. The preferential orientations depending on the instability regions for simply supported patch and point loaded plates have been suggested for angle-ply plates. The dynamic instability region has been influenced by the restraint provided at the edges.
Study of the aerodynamics of in-plane motion
Authors: Shaw S T , Qin N
Published: October 2002

A computational analysis is performed of the unsteady aerodynamics associated with the blade sections of helicopter rotors in forward flight. The unsteady flow is studied through solutions of the two- dimensional Reynolds averaged Navier-Stokes equations together with a strongly coupled two-equation model of turbulence. Two motions are studied.

The first motion is that of an aerofoil subjected to harmonic in-plane oscillations. The influence of advance ratio and reduced frequency is investigated. It is shown that, in the absence of shock waves, the flow is periodic with a reduced frequency equal to that of the forcing motion. However, the flow development lags behind the forcing motion. Furthermore, for constant reduced frequency the phase lag is independent of advance ratio.

In addition to harmonic motion, the aerodynamic response to a step change in Mach number is investigated. Using an assumed form of the response of lift coefficient to a step change in Mach number, a lift transfer operator for step changes in Mach number is obtained in the Laplace domain. An analytical expression for the response to harmonic Mach number oscillations is then obtained from the transfer operator. The resulting formulation for the aerodynamic response confirms that the lag between the forcing motion and the aerodynamic response is independent of advance ratio.
Numerical predictions of turbulent underexpanded sonic jets using a pressure-based methodology
Authors: Birkby P , Page G J
Published: October 2002

The objective of this work is to model underexpanded turbulent sonic jets. A pressure-based computational fluid dynamics methodology has been employed, incorporating extensions to handle high speed flows. A standard two-equation turbulence model is used, with an optional compressibility correction. Comparison with experimental jet centre-line Mach number showed the correct shock cell wavelength but a too rapid decay. The compressibility correction had no effect on the shock cell decay but increased the potential core length to give better agreement with experiment. Calculations for nozzle pressure ratios up to 30 showed the variation of Mach disc location in good agreement with experiment. For nozzle pressure ratios above 6, unsteady solutions were observed, emanating from the intersection of the Mach disc with the shear layer. Experimental work has identified similar large-scale instabilities; the peak mode of the prediction had a Strouhal number of 0.16, close to experimental values.