bluuebunny/crossref_metadata_2025 huggingface dataset:
Measured dependence of the attenuation of audio-frequency sound on concentration in flowing particulate suspensions
Authors: Moss S H O , Attenborough K , Woodhead S R
Published: October 2002

The relationship between the attenuation of sound at frequencies between 500 and 3500 Hz and the concentration of flowing suspensions of various powdered solids has been explored. The suspensions were conveyed in a pipeline of 53 mm diameter and the particle concentration was varied up to a maximum of 2.8 kg/kg. Three materials were tested: flour (mean radius, 27 μm), olivine sand (mean radius, 278 μm) and barytes. The feasibility of measuring the acoustic attenuation of particulate suspensions at audio-frequencies and relating the measured attenuation to concentration has been demonstrated. Although the audio-frequency attenuation is smaller at a given concentration than at ultrasonic frequencies, audio-frequency measurements are less susceptible to inhomogeneity of flow and to in-pipe turbulence than ultrasonic measurements.
The capacitive method as an industrial experimental technique of analysis of the cavitation and two-phase flows
Authors: Lucia U
Published: October 2002

The capacitive method is analysed and developed. It is proposed as an experimental technique for the industrial analysis of hydrodynamic cavitation and for the experimental study of two-phase flows.
Finite element simulation of arc welding distortion and correction in thin sidepanel sheets of a railway coach
Authors: Kumaran M Senthil , Kumar R Krishna , Sriraman S
Published: October 2002

Manual metal arc welding of the thin sheet sidepanel subassemblies of a railway coach shell causes deformation on the exterior surface. Welding creates residual stresses and distortions because of the elastoplastic response of the sheet to the transient, localized thermal expansion and contraction. Various strategies minimize the distortion, but a basic understanding of the mechanism is required. The welding process has been mathematically modelled using a general-purpose finite element code ABAQUS. The transient temperature fields and the associated stress, strain and strain fields have been calculated by a coupled thermomechanical analysis. To improve the exterior appearance of the coach shell, a technique called the magnetic forming process has been proposed. This process is designed to restore the original geometry of the deformed sidepanel sheet. The effectiveness of this process has been studied in detail. The magnetic forming process, simulated to flatten and straighten the thin sheet, is calculated to yield good results.
Development of new commuter trains in Tokyo
Authors: Sato Y
Published: October 2002

The East Japan Railway (EJR) operates a 7500 km railway network that covers Tokyo and the northern and eastern areas of Japan. Its transportation is concentrated in the Tokyo area. It has about 8000 electric multiple units (EMUs) for this transportation, and is constructing 300-400 EMUs per year to improve trains or to replace old ones and to improve passenger services. After the division of the Japanese National Railways (JNR) in 1987, EJR replaced about half of the EMUs in Tokyo with newly developed trains that had a lightweight stainless body and a regenerating brake. EJR is developing the new Series E231 train to succeed them from the year 2000. It has adopted information technology for control, passenger information and self-diagnosis. The new train uses 50 per cent less energy than the old ones, replaces checking and inspection with a diagnosis system and reduces construction costs by about 10 per cent by comparison with Series 209 developed in 1992. EJR is constructing the EMUs itself and designed E231 with the collaboration of a car constructor using a CALS (computer aided logistics system). A prototype was completed in October 1998. After bench and running tests, it was put into service in March 1999. The trains, in series production, will be completed from March 2000 by EJR and the car constructor. EJR will construct 950 Series E231 trains before March 2003.
Stability of RYNSORD, a decentralized algorithm for railway networks, under perturbations
Authors: Lee T S , Ghosh S
Published: October 2002

RYNSORD, a novel, decentralized algorithm with soft reservation for efficient scheduling and congestion mitigation in railway networks, has been recently introduced in the literature. It is a specific instance of the asynchronous distributed decision-making (ADDM) class of systems, a fundamental property of which is stability. Stability refers to the behaviour of systems under representative perturbations to their environments, given that ADDM systems are intended to be real, complex and, to some extent, mission-critical systems, and are subject to unexpected changes in their operating conditions. This paper introduces an intuitive definition of stability for RYNSORD that reflects those used in control systems and physics, and presents an in-depth stability analysis of RYNSORD. The analysis utilizes three types of stability: strongly stable, marginally stable and unstable. The perturbations are classified as either changes in the input pattern or changes in one or more characteristics of the system, such as hardware failures. The study utilizes a large-scale simulation of a subset of the Eastern United States railroad network. Trains are initiated at stochastically generated times at each of the stations and are bound for randomly selected destinations. In the study, firstly, a steady-state operating point is identified. Secondly, the system is perturbed by increasing the rate of trains inserted into the system temporarily, i.e. for a finite interval. Thirdly, an examination of whether and when the system returns to the previous steady state yields the results of stability analysis. Performance results indicate that, while RYNSORD is strongly stable with respect to input traffic rate perturbations of finite durations, it is marginally stable to unstable under permanent track segment and communication link failures, reflecting a balanced assessment of the strengths and weaknesses of RYNSORD.
Ultrasonic measurements of nominal contact area and contact pressure in a wheel-rail system
Authors: Pau M , Aymerich F , Ginesu F
Published: October 2002

For more than a century, the contact between wheel and rail has been the subject of careful investigation by scientists and railway technicians. Many efforts have been made to understand a series of phenomena (wear, pitting, fatigue, failures, etc.) that are closely related to processes occurring in such a small contact patch. A huge amount of numerical and theoretical research work (starting from Hertz's theory) has been carried out, but there is a noteworthy lack of experimental tests, which is probably due mainly to difficulties in accessing the contact area with conventional techniques. In the present paper, an experimental investigation dealing with the evaluation of the contact area and stresses transmitted across it is proposed: the technique employed is based on a non-invasive ultrasonic method that analyses the reflection of ultrasonic waves by the contact interface. By using a set-up commonly employed in many non-destructive testing (NDT) analyses it was possible to obtain graphic maps of static contact conditions, and several tests were carried out to evaluate changes with increases in external load. Results show reasonable agreement with Hertz's theoretical predictions and suggest a possible future use of the ultrasonic method to investigate contact during motion.
Equilibrium of crack growth and wear rates during unlubricated rolling-sliding contact of pearlitic rail steel
Authors: Fletcher D. I. , Beynon J. H.
Published: October 2002

It is generally accepted that large rolling contact fatigue cracks in rails do not develop during unlubricated rolling-sliding contact, and damage under these conditions is restricted to wear of the rail steel. However, close examination of a worn rail steel surface reveals the presence of a multitude of wear flakes, the roots of which closely resemble shallow rolling contact fatigue cracks.

Experiments have been conducted under unlubricated rolling-sliding conditions to examine the early development of flakes, or cracks, using a laboratory-based, twin-disc test machine to simulate the contact pressure and slip characteristic of the contact between a rail and a locomotive driving wheel. Small defects were found after as few as 125 unlubricated contact cycles. It was found that an equilibrium between crack growth rate and surface wear rate was established after approximately 10 000 cycles, leading to a shallow steady state crack depth. Initial crack growth by ratchetting (accumulation of unidirectional plastic strain until the critical failure strain of the material is reached), followed by shear stress-driven crack growth described by fracture mechanics, was found to be a sequence of mechanisms in qualitative agreement with the observed crack growth and steady state crack depth.
Rail movement and ground waves caused by high-speed trains approaching track-soil critical velocities
Authors: Krylov V. V. , Dawson A. R. , Heelis M. E. , Collop A. C.
Published: October 2002

The increased speeds of modern trains are normally accompanied with increased transient movements of the rail and ground, which are especially high when train speeds approach some critical wave velocities in the track-ground system. These transient movements may cause large rail deflections, as well as structural vibrations and associated noise in nearby buildings. There are two main critical wave velocities in the track-ground system: the velocity of the Rayleigh surface wave in the ground and the minimum phase velocity of bending waves propagating in the track supported by ballast, the latter velocity being referred to as the track critical velocity. Both these velocities can be exceeded by modern high-speed trains, especially in the case of very soft soil where both critical velocities become very low. The discussion in this paper focuses on the effects of transient rail deflections on associated ground vibrations in the cases of train speeds approaching and exceeding Rayleigh wave and track critical velocities. The obtained theoretical results are illustrated by numerical calculations for TGV and Eurostar high-speed trains travelling along typical tracks built on soft soil.
Network 21: Impact on rail freight traffic
Authors: Fricke E , Pohl M
Published: October 2002

Following the rail reform in Germany, Deutsche Bahn remained in the ownership of the German State but the company was divided into a number of subsidiaries, including long-distance and regional operators and DB Netz AG, the infrastructure manager. This market-driven organization is obliged to recover completely the costs of infrastructure provision by levying utilization charges (principle of full cost coverage). Hence, the market conditions of railway undertakings, such as those providing rail freight services, are at least partially determined by the level of costs of providing the infrastructure.

The current high level of costs at DB Netz AG must be significantly reduced if the railways are to hold their own against intense competitive pressure from road and waterways. It will not be possible to achieve this goal purely by continuing with on-going rationalization measures and additional investment in the track infrastructure (new and upgraded lines). Both the rail reform goal of switching more traffic to rail and the purely commercial interests of DB Netz AG necessitate a comprehensive increase in productivity and enhancement of product at realistic market prices.

In order to achieve these objectives, DB Netz AG chose a novel form of network management which relies strongly on the separation of traffic flows of different types. This was defined as the Network 21 strategy. The Network 21 strategy will also enhance the ability of operators to deliver both passenger and freight services in a more timely manner.
Problems caused by the motorway/railway freight traffic share in the Tyrol
Authors: Knoflacher H
Published: October 2002

Managing transit freight traffic across the Alps was an important source of income for the regional population for several hundred years. The introduction of technical transport systems, first railway followed by car and truck, changed the situation radically. No more stops were necessary and therefore the positive economic effects from transit traffic for the local alpine population were lost. The benefits moved to big economic structures outside the alpine regions. Noise and air pollution from uncontrolled growth of truck traffic in narrow alpine valleys had negative effects on quality of life as well as on tourism. Resistance against transit freight traffic through the Alps therefore has an economic background too.

To shift goods from road to rail, a toll on haulage charge over the Brenner route was introduced. Harmonization with European rules removed this financial barrier by about 90 per cent. Improvements of rail infrastructure, like the bypass of Innsbruck, have no effect on the modal split. Also, the eco-point system is not an effective instrument as it is not obeyed by the relevant neighbours in the European Union (EU). Road transport is therefore not only faster and simpler but also much cheaper than rail. Effective measures must be introduced to reach the desired goals, especially as these are also officially declared goals of the EU commission. A night-time ban for trucks, a better management on the rail network (not only in the Alps, but in the whole of Europe) and a substantial increase in costs for road freight transport will be necessary. If the alpine freight transit problem is not reduced by politicians, it is very likely that the local population will increasingly block the north-south traffic on the road.
On the fatigue design method for high-speed railway axles
Authors: Hirakawa K , Kubota M
Published: October 2002

Fatigue failure of the railway axle, which has been a source of difficulty for engineers since railroad service started in the early part of the nineteenth century, was the beginning of the study of metal fatigue. In order to maintain the safety of a high-speed railway system, a large number of investigations and experiments have been carried out by outstanding researchers ever since, and many improvements have been made in the material, manufacturing, heat treatment and design methods. In comparing Japan and Europe on the fatigue design philosophy of the high-speed railway axle, it is recognized that there is a difference between the Japanese Shinkansen and the European TGV and ICE. The critical parts for fatigue strength are the press-fitted parts which suffer from fretting fatigue damage, such as the wheel seat, gear seat and brake disc seat. In Europe, the larger diameter of the press-fitted part makes the fillet the critical part. In Japan, however, the fatigue strength of the press-fitted part is increased by an induction hardening method. Also, a stress-relief groove is made at the closely press-fitted part of the axle. For several years, no fretting fatigue cracks in Shinkansen axles have been detected by magnetic particle inspection. It is noted that improvements over many years have been successful in achieving the safety of high-speed railway axles. These problems will be studied in this paper.
On the optimal design of railway passenger vehicles
Authors: Mastinu G. R. M. , Gobbi M
Published: October 2002

A method is presented for the concept design of railway passenger vehicles. The method requires adequate mathematical modelling for describing quantitatively the many relationships between vehicle parameters and vehicle performance indexes. The main purpose of the method is defining the layout of vehicles (i.e. length, number of wheelsets, etc.) in order to obtain the lowest possible life cycle cost (LCC). The method is based on multiobjective programming (MOP), a branch of operations research. By the proposed method, the optimal design of railway passenger vehicles can be performed in a theoretically correct and rigorous way. Genetic algorithms (GAs) are used to find the numerical solution to the problem. The optimal design of urban, suburban and intercity (IC) passenger vehicles is performed in order to obtain the best compromise between conflicting requirements such as maximum payload, minimum tare weight and axle load, minimum track deterioration, maximum ride comfort, etc. It is shown that, with respect to modern vehicles, a major improvement in LCC would be gained if shorter vehicles and newly designed wheelsets and/or bogies could be adopted. Should this happen, new families of passenger vehicles with two or three axles would be the optimal solutions to be built.
Analysis and design of a low-noise railway wheel
Authors: Cervello S , Donzella G , Pola A , Scepi M
Published: October 2002

The design and construction of a new ‘constrained layer’ damping treatment for railway wheels is presented. A numerical procedure was used for the loss factor calculation. This procedure, first verified on a plate by means of experimental modal analyses, allowed the best treatment thickness and arrangement to be chosen among those commercially available and technologically feasible. The work ended with the construction of a prototype and subsequent tests in the laboratory and in the field. The success of these tests justified the start of production of low-noise wheels treated in this way.
Energy absorption requirement for crashworthy vehicles
Authors: Lu G
Published: October 2002

A study of the design energy requirements for crashworthy vehicles has been carried out. Linear model analysis has proved very useful in understanding the collision behaviour of two trains, particular ly the interaction between the vehicles. It was found that the coupler elements provide isolation to the vehicles and reduce the inuence of subsequent vehicles on the impact of preceding vehicles. Calculation formulae for the energy absorption requirement for both leading and intermediate ends are presented. These have been derived from simulation results of ve projects and would be applicable to all rail vehicles in collisions. It is recommended that a collision between two rakes of three or four vehicles would be sufcient to represent the behaviour of longer rakes. It is believed that this study contributes towards a better understanding of energy absorption in a rail collision.
A model for rubber springs in the dynamic analysis of rail vehicles
Authors: Berg M
Published: October 2002

A non-linear dynamic rubber spring model is proposed. The model mainly aims at representing the mechanical behaviour of rubber suspension components in rail vehicles for the frequency range of 0-20 Hz. The model is one-dimensional with a relationship between force and motion based on a superposition of elastic, friction and viscous forces. Inclusion of a friction force means that increased stiffness at small displacement amplitudes as well as rate-independent damping (hysteresis) can be considered. The present model has five parameters. Comparisons between model and measurement results are carried out for harmonic excitations, emphasizing the stiffness and damping dependence on displacement amplitude and frequency. But a case with a harmonic excitation superposed on a ramp function is also illustrated. The model results show good agreement with the measurement results. The present model should therefore be a suitable tool in the field of rail vehicle dynamics analysis and simulation.
The effect of block braking on the residual stress state of a solid railway wheel
Authors: Donzella G , Scepi M , Solazzi L , Trombini F
Published: October 2002

A finite element, numerical model of a solid railway wheel was perfected permitting the simulation of a block braking operation. The analyses performed, backed by experimental tests, permitted the degree of variation in the residual stress state (induced by differential quenching heat treatment and successive tempering) caused by particularly heavy braking to be evaluated. The results highlight the influence of the main braking parameters (force and time) and the thermal history previously suffered by the wheel. Finally, the thermal fatigue strength of the component, although in an approximate way, was checked on the basis of the calculated stress state and through the introduction of the data of a real and particularly significant route into the model. This demonstrated the broad safety margin with which the wheel operates and also brought to light the dangerous nature of particularly severe braking which can drastically modify the residual stresses induced by the heat treatment, moving them towards tensile stresses.
Full-scale railway wheel flat experiments
Authors: Jergéus J , Odenmarck C , Lundén R , Sotkovszki P , Karlsson B , Gullers P
Published: October 2002

Extensive field experiments (the ‘Silinge wheel flat experiments’) with a moving train have been designed, performed (at Silinge) and evaluated. More than 200 wheel flats were formed under controlled conditions involving different wheel loads, train speeds and sliding durations, and the friction coefficient between the wheel and the rail was also varied (and indirectly measured). Samples extracted from flats of the tested wheels have been metallographically examined with respect to phase transformations and cracks. A numerical model for wheel flat prediction has been qualitatively verified and quantitatively calibrated. In the experiments, martensite was found beneath all flats and cracks were observed in most cases. It is concluded that the risk for future spalling should be considered for all wheelsets with flats. A damaged wheelset should be taken out of service as quickly as possible. When reprofiling the wheels, all martensite and an additional layer of several millimetres should be machined off.
Review of the theory of the compression wave generated when a high-speed train enters a tunnel
Authors: Howe M. S.
Published: October 2002

A review is given of the analytical theory of the compression wave generated when a high-speed train enters a tunnel. The waveform can be calculated exactly at subsonic train Mach numbers for a tunnel consisting of an unflanged cylinder of semicircular cross-section, which has been the subject of extensive experimental study. An analysis of this case reveals how an approximate theory can be developed for arbitrary tunnel portals and train Mach numbers as large as 0.4. Details are given for flanged portals of both semicircular and rectangular cross-sections. Non-linear steepening in a very long tunnel is responsible for an intense, environmentally harmful Micropressure wave, which propagates as a pulse from the distant tunnel exit when the compression wave arrives, with amplitude proportional to the maximum gradient in the compression wavefront. The theory permits the design of tunnel portals that greatly increase the initial wave thickness (thereby tending to inhibit wave steepening), either by flaring the portal or by installing a tunnel entrance ‘hood’, which allows high-pressure air produced by the train to be vented away through windows in the sidewalls. A formula is given for the ‘optimum’ flared portal, which produces a pressure gradient across the wavefront that is constant and an overall minimum, so that the pressure in the wavefront increases linearly and provides the maximal protection against shock formation.
A model for predicting the effect of temperature force of continuous welded rail track
Authors: Luo Y
Published: October 2002

This paper presents a method for investigating the dynamic characteristic of railway continuous welded rail (CWR) track subjected to the longitudinal force in the rail owing to fluctuation in temperature. The influences of the temperature force on the vibration modes and resonant frequencies are analysed with a harmonically varying, transverse, concentrated force at the centre of one span of the rail. The effects of track parameters such as rail mass, support stiffness and support length are also considered. Some conclusions of practical interest are drawn from the study to enhance the understanding of the physical problems of CWR track.
Fundamental issues in intelligent transportation systems
Authors: Ghosh S
Published: October 2002

The notion of transportation refers to the movement of people and goods across non-trivial geographical distances. Its history is as old as our civilization and its importance and scope are enormous, ranging from people walking on the earth's surface to carts and chariots driven by animals, automobiles, trains, airplanes and ships. To date, the discipline of transportation has experienced two major revolutions. Prior to the discovery of electromagnetic communication, information on the transport of goods and people was propagated along with the transported material and, in essence, their transit speeds were identical. The use of electromagnetic communication, the first major revolution in the discipline of transportation, made the propagation of information about the movement of goods and people significantly faster than the actual transport of the material at limited speeds. This resulted in superior planning as well as tracking of the movement of material through the transportation network. The availability of computing engines fuelled the second major revolution in transportation systems wherein fast and precise computers were exploited efficiently to control and coordinate the transport of goods and people across the system. For a number of reasons, including simplicity and the desire to maintain consistent control, the information and guidance providers of the transportation systems evolved as centralized units. A central control collected information about every entity within a specific transportation system and provided guidance and information to them as necessary. Today, the transportation discipline is on the brink of experiencing the third major revolution and possibly the most complex-the transformation from the centralized paradigm to the asynchronous, distributed paradigm which will integrate fast computers and high-performance computer networks through novel computer algorithms. This paper presents fundamental issues and principles underlying today's and tomorrow's intelligent transportation systems, including railways, highways, air travel, cargo networks and personalized rapid transportation systems. These principles have been utilized successfully in developing systems for railways and vehicles that have been reported in the literature. The paper also presents motivations for further research into the key areas of modelling and simulation and visualization of intelligent transportation systems.
Collision behaviour of crashworthy vehicles in rakes
Authors: Lu G
Published: October 2002

An analytical investigation of the collision behaviour of crashworthy vehicles in rakes has been carried out. A dynamic simulation program for analysing large plastic deformation has been developed. A collision model comprising two identical JUNIPER trains, Alstom's new developed modular train, is presented, and a detailed dynamic simulation study is made to determine the energy absorption over the two collapsing trains. Calculation results confirm that the crashworthiness design of the JUNIPER vehicles is adequate. A comparison between the British Railway Group standard structure design and the JUNIPER structure design was carried out to justify the design difference. Further improvement of the crashworthiness design is also discussed and is being applied to the new vehicle design.
Coupled effect between damage and elastoviscoplasticity of type 28CrMoV5-08 steel under complex loading
Authors: El Abdi R. J.
Published: October 2002

This paper is devoted to the study of the coupled effect between damage and elastoviscoplasticity of the 28CrMoV5-08 steel used in railway brake discs under thermomechanical loading. Isothermal and anisothermal experimental uniaxial cyclical traction-compression tests on cylindrical samples are carried out to identify the fatigue damage law and the number of cycles to fracture versus temperature. An application of the coupled constitutive equations to the stress analysis of real railway brake discs under two types of stop braking is given. The obtained cycled curves are compared with others deduced from a simple model without damage.
Development of analysis tools for spline couplings
Authors: Adey R A , Baynham J , Taylor J W
Published: October 2002

Improved shaft spline design methods are required to meet the needs of new civil aero engine designs that have higher bypass ratios and reduced core sizes. The paper describes the development of new analytical techniques to predict the contact stresses and load transfer mechanisms in spline couplings. Applications are presented and comparisons made with experimental data. The availability of prediction from the computational models for proposed transmission joint designs will allow the exploitation of fretting and wear experimental data to predict durability.
Investigation of the separation bubble formed behind the sharp leading edge of a flat plate at incidence
Authors: Crompton M J , Barrett R V
Published: October 2002

Detailed measurements of the separation bubble formed behind the sharp leading edge of a flat plate at low speeds and incidence are reported. The Reynolds number based on chord length ranged from 0.1 × 105 to 5.5 × 105.

Extensive use of laser Doppler anemometry allowed detailed velocity measurements throughout the bubble. The particular advantages of laser Doppler anemometry in this application were its ability to define flow direction without ambiguity and its non-intrusiveness. It allowed the mean reattachment point to be accurately determined. The static pressure distribution along the plate was also measured.

The length of the separation bubble was primarily determined by the plate incidence, although small variations occurred with Reynolds number because of its influence on the rate of entrainment and growth of the shear layer. Above about 105, the Reynolds number effect was no longer evident.

The reverse flow boundary layer in the bubble exhibited signs of periodic stabilization before separating close to the leading edge, forming a small secondary bubble rotating in the opposite sense to the main bubble.
The modelling of direct chemical kinetic effects in turbulent flames
Authors: Lindstedt R P
Published: October 2002

Combustion chemistry-related effects have traditionally been of secondary importance in the design of gas turbine combustors. However, the need to deal with issues such as flame stability, relight and pollutant emissions has served to bring chemical kinetics and the coupling of finite rate chemistry with turbulent flow fields to the centre of combustor design. Indeed, improved cycle efficiency and more stringent environmental legislation, as defined by the ICAO, are current key motivators in combustor design. Furthermore, lean premixed prevaporized (LPP) combustion systems, increasingly used for power generation, often operate close to the lean blow-off limit and are prone to extinction/reignition type phenomena. Thus, current key design issues require that direct chemical kinetic effects be accounted for accurately in any simulation procedure. The transported probability density function (PDF) approach uniquely offers the potential of facilitating the accurate modelling of such effects. The present paper thus assesses the ability of this technique to model kinetically controlled phenomena, such as carbon monoxide emissions and flame blow-off, through the application of a transported PDF method closed at the joint scalar level. The closure for the velocity field is at the second moment level, and a key feature of the present work is the use of comprehensive chemical kinetic mechanisms. The latter are derived from recent work by Lindstedt and co-workers that has resulted in a compact 141 reactions and 28 species mechanism for LNG combustion. The systematically reduced form used here features 14 independent C/H/O scalars, with the remaining species incorporated via steady state approximations. Computations have been performed for hydrogen/carbon dioxide and methane flames. The former (high Reynolds number) flames permit an assessment of the modelling of flame blow-off, and the methane flame has been selected to obtain an indication of the influence of differential diffusion effects among gaseous species. The agreement with experimental data is excellent. The predicted blow-off, velocity is within 10 per cent of the experimental value and it is further shown that experimental levels of major and minor species are well reproduced. Interestingly, comparisons of experimental data with prediction indicate only a modest influence of differential diffusion effects on gaseous species. A comparison with previous modelling efforts, featuring smaller scalar spaces, permits the conclusion that accurate chemistry is a prerequisite for quantitative predications of finite rate chemical kinetic effects.
Sensitivity of the dynamic behaviour of random rotating Timoshenko beams to system parameter changes
Authors: Lin S-C
Published: October 2002

A computational procedure has been developed to evaluate the influence of the random parameter changes to the dynamic behaviour of rotating Timoshenko beams. Based on the mean-centred second-order perturbation technique and non-linear eigenvalue analysis, the stochastic modal analysis is developed for stochastic sensitivity measures of rotating beams with uncertain material and sectional properties, uncertain geometric parameters and a random rotating velocity. A consistent linearization of the fully geometrically non-linear beam theory and the virtual work principle are used to derive the governing equations of a rotating Timoshenko beam, and a power series method is employed for the non-linear eigenvalue analysis to obtain the natural frequencies and vibration modes. A sensitivity analysis is performed to identify the important factors influencing the variation in frequency responses. To establish the validity of the present probabilistic approach, numerical examples with results obtained by using the Monte Carlo method are given for comparison.
Ascending node alteration of polar orbiting spacecraft using low-thrust propulsion
Authors: Welch C S
Published: October 2002

This paper describes the controlled alteration of a spacecraft's orbital elements using low-thrust propulsion. It starts with a general consideration of the problem based upon Lagrange's equations and then examines its reduction to address the quasi-circular orbits appropriate to satellite emplacement. Following this, the paper describes the optimization of low-thrust manoeuvers and extends this to show that constant thrust angle techniques may be used to obtain near-optimum wedge angle and radius alterations. The alteration of ascending node is then addressed, in particular showing how the node may be altered by combined changes to inclination and altitude. This is illustrated by considering an optimum transfer between polar orbits.
A flight control design of a re-entry vehicle using a double-loop control system with fuzzy gain-scheduling
Authors: Fujimori A , Nikiforuk P N , Gupta M M
Published: October 2002

This paper presents a flight control design of an Automatic Landing FLight EXperiment (ALFLEX) vehicle using a double-loop control system (DLCS) with the fuzzy gain-scheduling (FGS) state feedback. The DLCS consists of an inner and an outer loop. The inner-loop control law is designed by the FGS state feedback to guarantee the stability over the entire operating range of the ALFLEX vehicle, while the outer loop control law is designed by a static gain to improve the tracking property. Futhermore, guidance laws for the longitudinal and the lateral directions are included in the control system to navigate the ALFLEX vehicle to a reference trajectory even if the initial condition is deviated from the nominal. The designed DLCS showed satisfactory performance in the numerical simulation of the ALFLEX vehicle.
Optimal and near-optimal take-off manoeuvres in the presence of windshear
Authors: Elferink K , Visser H G
Published: October 2002

This paper is concerned with the development of short-range forward-look guidance strategies for take-off manoeuvres in the presence of windshear, with reference to flight in the vertical and horizontal planes. In addition to the horizontal shear, the presence of a downdraught is assumed. First, two open-loop optimal escape strategies are considered, i.e. a performance maintaining strategy and a survival strategy, where it is assumed that the windshear is detected in an early stage of the encounter. Next, two closed-loop guidance strategies featuring short-range forward-look detection, which closely approximate the open-loop optimal solutions, are developed. Numerical results show that lateral manoeuvring, in which an aircraft is turned away from the microburst, improves the flight performance significantly in both optimal escape strategies. The simulation results demonstrate that the employed closed-loop guidance strategies are able to approximate closely the open-loop optimal trajectories, in both longitudinal and lateral escape manoeuvres.
Sensitivity study of the effects of manufacturing defects on the performance of a redundant hydraulic secondary flight control
Authors: Borello L , Villero G
Published: October 2002

Redundant flight control systems, designed in order to ensure the necessary safety level even in failure conditions, may behave improperly during normal operations, if the system architecture is unsuitable, when manufacturing defects are present. This work analyses the response of a secondary flight control hydraulic servo-mechanism, designed according to different redundancy architectures, when manufacturing defects are present. These defects may consist of non-symmetrical overlap of the passageways or incorrect null position with no input current (caused by an asymmetric geometry of the feedback spring or of the first-stage spring, resulting from an undesired magnetic field in the first-stage torque motor, etc.). These defects come into the usual quality standards of the components and must be accepted because they are not removable owing to the accuracy of the manufacturing processes. In the opinion of the authors this paper concerns a topic quite neglected, but important in the technical literature. To the best of their knowledge, no specific scientific work in this field is available, except for some industrial technical reports. Since the above-mentioned problems adversely effect the proper operation of the servo-mechanism, it is necessary to introduce some equalization devices able to improve substantially the improper behaviours. By means of an appropriate physical-mathematical model of a typical electro-hydraulic servo-mechanism, the work evaluates the effects of manufacturing defects in different cases and the effectiveness of the eventual compensation devices in limiting the improper behaviours.
Finite element torsional buckling analysis of shafts with non-concentric bores
Authors: Robotham W S , Hyde T H , Williams E J
Published: October 2002

The demand for more powerful and efficient aeroengines results in the need to design improved main driveshafts. The design requirement may be to increase the torque capacity of the shafts, to reduce the outer diameter or to reduce the weight. Meeting these requirements tends to increase the likelihood of the shaft buckling and research was carried out to investigate the factors influencing the torsional buckling of shaft sections in order to provide an improved analysis method applicable to typical gas turbine aeroengine shafts. This paper uses finite element analysis to examine the effect of bore concentricity on the elastic-plastic buckling of shafts subjected to pure torsional loading. Equations were developed to predict the buckling torque for a range of shaft geometries and levels of bore eccentricity.
Materials for military helicopters
Authors: Edwards M R
Published: October 2002

The materials essential to the modern military helicopter are reviewed. In addition to materials of high specific strength and stiffness, such as aluminium alloys and fibre-reinforced composites, more specialized materials are also considered. These include materials for armour protection and signature reduction. As helicopters are used closer to the battle zone and in more important military roles, these requirements of protection and low observability become more important.
Fuel-related issues concerning the future of aviation
Authors: Armstrong F W , Allen J E , Denning R M
Published: October 2002

The paper discusses some major fuel-related issues which will influence the development of aviation over the next 50 years. Provided that global economic development is not halted by world- scale war or crisis, the demand for civil air transport is likely to continue to expand. The consequent rising requirement for aviation fuel is considered in relation to the projection that the total oil extraction rate from relatively accessible fields will reach a peak and then decline. The fuel options for aviation, against such a scenario, are explored. It is concluded that if the aviation demand cannot be met economically from conventional oilfield sources, supplementation by kerosene-like fuel synthesized from other feedstocks is much more likely, in the timeframe considered, than the radical step of a move to liquid hydrogen. The latter could be delayed until much later unless necessitated by constraints on carbon emissions. Other issues relating to aero-engine emissions are discussed, including the present uncertainties regarding the environmental significance of injection into the atmosphere at aircraft operating altitudes. The implications of restricting operations to the troposphere, to avoid the lower mixing rates of the stratosphere, are considered briefly.
Riveted single lap joints. Part 1: A numerical parametric study
Authors: Fung C-P , Smart J
Published: October 2002

Snap and countersunk riveted single lap joints with either one or two-rows of rivets have been analysed using finite elements and fatigue tests have been performed.

In this first paper, a numerical parametric study, the joints are subjected to an alternating cyclic load and plasticity and non-linear geometry are considered. The stresses around the rivet hole and the deformed shapes of the joints are presented together with the effects of varying the clamping force, the interference fit of the rivet, the coefficient of friction and the geometry of the joints when the joints are subjected to various loading histories. The effect of changing the variables is shown to be in agreement with other published data
Visualization of non-equilibrium dissociating flows
Authors: Han J H , Kennaugh A , Poll D I A
Published: October 2002

A Mach-Zehnder interferometer has been used for both flow-field visualization and quantitative assessment of aerodynamic parameters in a shock tube environment. Of special interest are the high- temperature effects in the post-shock region of bodies travelling at hypervelocity. Infinite-fringe interferograms give the density contours of the flow field and, in combination with an equilibrium real gas code, they can be used to provide information on the non-equilibrium state of the dissociating flow.
Simulation of a prototype electrically powered integrated actuator for civil aircraft
Authors: Crowder R , Maxwell C
Published: October 2002

Developments in the design and proposed operation of large civil aircraft have resulted in aircraft manufacturers and equipment suppliers developing new system concepts, one of which is the all or more electric aircraft. In the all or more electric aircraft the distribution of power for flight actuation will be through the electrical system, as opposed to the currently used bulk hydraulic system. In order to implement power-by-wire, high-performance electrically powered actuators will be required. The paper discusses the design details, and the simulation of an electrohydrostatic actuator suitable for use in primary flight control systems of a civil aircraft. The paper presents experimental and simulation results, and identifies the parameters that will critically affect the performance of an actuator.
Missile captive firing, modelling and control
Authors: Whalley R , Ebrahimi M
Published: October 2002

The pitch plane manoeuvring characteristics of a solid propellant missile under captive firing conditions are considered. Analysis techniques are used to establish the dynamic model of the suspended, lumped parameter representation of the vehicle, which is regulated directionally by thrust vectoring. Three-term feedback control is employed to confine the response of the system to both demanded input changes and external load disturbances from airstream turbulence and defensive projectile debris strikes. Simulated manoeuvring characteristics are computed for demonstration purposes.
Practical issues relating to statistical failure analysis of aero gas turbines
Authors: Cole G K
Published: October 2002

Statistical failure analysis of aero gas turbines presents many special problems. Various difficulties must be overcome, including the paucity and form of available data with its heavily censored nature, selecting the right analysis method, the validity of the underlying modelling assumptions and the correct interpretation of the results.

This paper outlines the formal Rolls-Royce approach to quantifying numerical risk for safety and reliability, and the pivotal role played by the Weibull distribution. It reviews the generic forms of the censored failure data obtained from test and service environments. The limitations of the current analysis techniques are reviewed.
Two parallel plane jets: Comparison of the performance of three turbulence models
Authors: Lai J C S , Nasr A
Published: October 2002

There have been many investigations in the literature to examine the performance of different turbulence models in predicting flow over backward-facing steps where the flow is bounded by solid boundaries. However, the evaluation of different turbulence models in predicting free shear layers with no solid boundaries, such as two parallel plane jets, is limited. In this paper, the velocity field of two parallel plane jets with a small nozzle separation ratio of s/ w = 4:25 determined by laser Doppler anemometry (LDA) is first presented. These experimental results are used to examine the performance of three turbulence models (i.e. k - ɛ, RNG k - ɛ and Reynolds stress) in predicting this flow field. The effects of computational domain size, grid resolution and different discretization schemes on the predictions are discussed. The existence of a recirculation flow region, a merging region and a combined region in the two parallel plane jet configuration has been predicted qualitatively by all three turbulence models. On the other hand, quantitative agreement between predictions and measurements varied by as much as 18 per cent for the merging length while the jet spread in the outer shear layer has been substantially under- predicted by all three models.
Improving diffusion-controlled microgravity experiments by facility orientation
Authors: Savino R , Monti R
Published: October 2002

Residual-g (gravity) and g-jitter will be unavoidable sources of undesirable convection during diffusion-dominated fluid science or materials science experiments on the International Space Station. In this paper the facility orientation is proposed as an alternative to passive or active isolation devices, which would be not efficient against any residual-g, to minimize g-disturbances during microgravity experiments. A numerical study for a typical fluid physics experiment shows that both residual-g and g-jitter may be detrimental but also beneficial to achieve purely diffusive conditions, according to the orientation of the residual-g vector and of the vibration direction, relative to the direction of the density gradient. The results of the computations indicate that for the different configurations investigated, corresponding to different relative orientations between residual-g and g-jitter, the experimental facility can be properly oriented to minimize the convection disturbances.