bluuebunny/crossref_metadata_2025 huggingface dataset:
An introduction to China's rail transport Part 1: History, present and future of China's railways
Authors: Xue X , Schmid F , Smith R. A.
Published: October 2002

In this paper an introduction is given to the history, current situation and future plans of China's railway industry. The history of China's railway is divided into four development phases: the phase in Imperial China, the phase in the Republic of China and the phases before and after the economic rejuvenation of the People's Republic of China. An introduction to the current situation and future plans includes the major projects under construction and development trends of China's railways. The environment of China's railways is also presented. This is the first of two papers on the railway scene in China.
Coupled single-axle running gears—a new radial steering design
Authors: Polach O
Published: October 2002

New railway vehicle concepts with broader and shorter carbodies necessitate new running gear concepts. One of the possibilities, the single-axle running gear, offers several advantages. The disadvantage of the conventional single-axle running gear during curving can be counteracted with a simple coupling between the single-axle running gears of the neighbouring carbodies.

This paper presents parameter analysis and design principle of the coupled single-axle running gears. They can be constructed for an almost ideal curve negotiation in a great range of curve radii. The coupling of the running gears not only improves the running characteristics in a curve but also increases the stability limit. Bombardier Transportation Winterthur has developed the coupled single-axle running gears called FEBA. The test runs with prototype as well as with serial running gears in the Norwegian commuter train Class 72 have fully confirmed the anticipated running characteristics.
Train position and speed estimation using wheel velocity measurements
Authors: Allotta B , Colla V , Malvezzi M
Published: October 2002

In order to improve safety and efficiency in the management of modern railways, several systems for monitoring and control of traffic are being developed. Automatic train protection (ATP) systems command an emergency braking procedure if dangerous situations occur, such as insufficient braking distance to one of the next target positions and target velocities. A novel ATP system named SCMT, to be installed on trains running on Italian railways, is currently being designed. One of the components of SCMT is a module for estimating train speed and positions between fixed balises, which communicate to the on-board system the distance to next targets and the velocity requirements at targets.

In this paper algorithms are described for distance to target and velocity estimation, capable of compensating for poor wheel-rail adhesion conditions where conventional odometry algorithms may fail. The algorithms were derived using a variety of methods including neural networks, fuzzy logic and crisp logic. The system was designed and trained using a wide set of experimental data, obtained from test runs carried out with different types of vehicles and conditions (in particular, degraded adhesion conditions were investigated).
Wheel-rail dynamics with closely conformal contact Part 1: Dynamic modelling and stability analysis
Authors: Bhaskar A , Johnson K. L. , Wood G. D. , Woodhouse J
Published: October 2002

Observations on the Vancouver mass transit system suggest that noise, vibration and corrugation of the rail appear to be associated with close conformity between the transverse profiles of the wheel and rail. To investigate this, a dynamic model of the wheel and rail under conditions of close conformity has been developed. Previous work has suggested that motion of the wheel could be neglected, so the model comprises two subsystems: (a) the rail and its supports, and (b) the contact between wheel and rail. A dynamic model of a continuously supported rail is presented, which is consistent with similar models in the literature. Conformal contact has been represented in two ways: (a) as a single highly eccentric elliptical contact, and (b) as a two-point contact. Novel ‘rolling contact mechanics’ have been incorporated in both these models. The complete system is closed: oscillations of the rail give rise to fluctuating contact forces, which in turn excite the rail. A linear stability analysis of the system shows it to be stable under all conditions examined, thus precluding the possibility of self-excited oscillations occurring on a perfectly smooth rail. The model can then be used to investigate the forced response to existing roughness on the railhead, which is the subject of a companion paper (1).
Frequency dependent stiffness and damping of railpads
Authors: Fenander Å
Published: October 2002

The vertical stiffness and damping of studded rubber railpads have been measured, both in a complete track and in a test rig, as functions of frequency under different static preloads. Also, for more compact polymer-based railpads, track measurements were performed. The stiffness of the studded railpads was found to increase strongly with preload, but only weakly with frequency. The loss factor of the studded railpads was found to be nearly independent of preload and to increase only slightly with frequency. A fractional derivative model of the dynamic behaviour of the railpad is proposed.
Detection of corrugation and wheelflats of railway wheels using energy and cepstrum analysis of rail acceleration
Authors: Bracciali A , Cascini G
Published: October 2002

Rolling stock and track damage due to localized (wheelflats) and global (corrugation) railway wheel tread defects is extremely serious, and several devices have been developed to detect these defects. An original experimental and numerical procedure for detection of wheel corrugation and wheelflats has been developed and validated; it processes rail acceleration signals collected by using combined energy and cepstrum analysis criteria. The use of cepstrum analysis proved to be particularly useful as it allows the discrimination of wheelflats independently from the presence of other defects, even when their effects are hidden in globally high acceleration levels due to heavy corrugation. A short survey of damage induced by wheelflats is presented; optimal measurement conditions and extensive examples are then detailed. The results are discussed with particular reference to the applicability of the technique developed to automated detection devices.
The development of an integrated suspension control technology for passenger trains
Authors: Stribersky A , Müller H , Rath B
Published: October 2002

In recent years there has been a growing demand for electronically controlled suspensions in rail vehicles. Active car body tilting as well as active or semi-active suspension control have been implemented successfully by industry. This paper describes the development of a suspension control technology which integrates active tilting, active lateral positioning and semi-active damping of a rail vehicle's car body. The focus is on computer simulation as well as on hardware development.
The experience of the SJ X2000 tilting train and its effect on the market
Authors: Nelldal B-L
Published: October 2002

X2000 is a tilting train that was introduced as a new product by the Swedish State Railways (SJ) on the 450 km line between Stockholm and Gothenburg in 1991. Travelling times have been reduced from 4 to 3 h or 25 per cent by the tilting device and increased top speed up to 200 km/h. Now rail can really compete with air. The rail market share of the rail-air market between the Stockholm and Gothenburg regions increased from 42 to 57 per cent between 1990 and 1996. The success of X2000 can, in addition to the travelling times, also be explained by higher comfort, service and quality as well as by the image of X2000 as a new product.
The new European electromagnetic compatibility standards for railways
Authors: Allan J , Armstrong D. S.
Published: October 2002

The EC directive on electromagnetic compatibility (EMC) was first agreed in 1989. Generic EMC standards appeared in the early 1990s. However, a transition period was implemented throughout the community from 1992 until December 1995, largely in order for product-specific standards to appear and also to allow time for industry to adapt to the change in legislation. At radio frequencies, the railway industry in the United Kingdom had made use of a standard produced by the Railway Industry Association (RIA) Committee 18 prior to the European Commission (EC) directive. This committee has made a substantial contribution to the Cenelec (European Committee for Electrotechnical Standardization) working groups which have produced five railway EMC pre-standards (ENV50121-1 to ENV50121-5) which were agreed in December 1995. There is a need in the period of two to three years from this date to develop the pre-standards and trial them with a view to turning them into full standards. Compliance with the EMC directive must be via the technical construction file route until the ENVs are converted to ENs and published in the official journal. This paper explains the standards used in the United Kingdom for EMC on railways prior to the EC directive and it describes the progress made towards developing the European pre-standards covering ‘A description of railway EMC’(ENV50121-1), ‘A method of measurement and cartography’ (ENV50121-2), ‘Railway vehicles’ (ENV50121-3), ‘Railway signalling’ (ENV50121-4) and ‘Fixed power installations’ (ENV50121-5). The paper shows the derivation of the major parts of the standards, including details of railway test data used to determine limits. The paper concludes by showing the implications for the railway industry in implementation and the expected progress in the next five years.
Safe passage to Europe—Eurostar's in-cab signalling systems
Authors: Pincock A. J. L.
Published: October 2002

This paper describes the in-cab signalling systems used on Eurostar trains. It categorizes them in terms of their function as basic signal repetition systems (AWS, BRS and TBL1), beacon-based speed supervision systems (KVB and TBL2) and continuous in-cab signalling systems (TVM) and reviews their relative merits. The aim of the paper is to enable the reader to recognize the three generic groups of in-cab signalling systems and understand the philosopy behind the systems within each group.
Structural strength analysis of the bogie frame in Taipei rapid transit systems
Authors: Oyan C
Published: October 2002

The importance of bogie fatigue in railway rolling stock has been recognized as a contributing factor in structural failure. A bogie frame designed for Taipei rapid transit systems is analysed in order to confirm the technical strength requirements for static and dynamic loadings. A numerical finite element analysis is utilized in view of the complex geometry, and detailed plots are also presented in this report to give a complete understanding of the behaviour of the bogie frame. The von Mises stresses are adopted as equivalent stresses in the static strength calculation while the principal stresses are adopted in fatigue strength evaluation. Material yield stress and modified Goodman diagrams showing the permissible stress ranges are used as failure criteria respectively for static and dynamic loadings. It is demonstrated that the static strength and fatigue strength of the bogie frame satisfy the strength requirements specified by Taipei rapid transit systems.
Innovations in tram and light rail systems
Authors: Topp H. H.
Published: October 2002

Some 350 tram or light rail transit (LRT) systems are operated worldwide. After a period of little interest in trams during the 1960s and heavy cutbacks or total abandonment of tram networks, a renaissance combined with sociological and technical innovations is now taking place, especially in North America and Western Europe. More than 100 cities worldwide are considering the introduction of a tram/ LRT system.

After defining tram and LRT and dealing with nine different types of tram/LRT, this article focuses on current innovations mainly in German and European cities like Hannover, Karlsruhe, Kassel, Oberhausen, Saarbrücken, Sheffield and Vienna. Sociological innovations encompass a changed perception of urban transport, changed traffic policies, the image of modern trams in the view of the citizens, tram or LRT in pedestrian malls, and the high appeal of well-designed vehicles and stops. On the technical side, innovations include low-floor vehicles, modular vehicle systems, lighter and less expensive vehicles, raised platforms at stops, the use of telematics in public transport for central control of vehicles, traffic lights actuated by vehicles, dynamic information of passengers, and track sharing by railway and LRT vehicles. Finally, tram and LRT systems are appropriate to fill the gap in capacity between bus and metro at construction expenses of about a tenth of a metro system.
The importance of imaginary forces and kinematic-type non-linearities for the description of railway vehicle dynamics
Authors: Zboiński K
Published: October 2002

This article presents the results of investigations into the practical significance of taking into account all inertial forces in the dynamic equations of motion of a railway vehicle. The results apply to traditional and numerical ways of building the equations. Two types of inertial forces have been investigated: the so-called imaginary forces and equation terms called kinematic-type non-linearities. The first arise from the description of vehicle vibrations, for motion on a curved track, relative to the moving coordinate systems associated with the track. Both types of inertial forces are frequently disregarded in the equations. The main emphasis is put on recent results utilizing numerical simulation, although some reference to earlier work is made. The results show that omission of the imaginary forces can have important practical significance in describing railway vehicle dynamics in certain cases. This paper suggests that some research habits existing for years should be changed.
Thermodynamic studies of a novel aeroengine concept
Authors: Panting J R , Pullen K R
Published: October 2002

The purpose of the work described is to indicate the potential of a high-speed, spark ignition compound-turbocharged engine as an alternative to the gas turbine powered turboprop. Using relatively simple thermal cycle models, it is possible to show that such a compound-turbocharged engine should be capable of achieving very high thermal efficiency levels. A more sophisticated model of this engine type confirms these findings. It proves more difficult to estimate the power-weight ratio, but the specific power output of such an engine, measured in units of kW/1, is shown to be very high. In addition, such a thermally efficient engine type will permit a much reduced take-off fuel payload. As well as modelling the compound-turbocharged engine itself, comparisons are also made with the conventional gas turbine. The study focuses on propeller shaft input powers in the region of 1 MW.

A suitable design strategy for the new engine type is discussed, including the requirement for a lightweight, continuously variable transmission system. At present, it is intended to employ a high-speed electrical transmission system for this purpose, and this relatively new technology is briefly highlighted.
The double-fuselage layout: A preliminary case study of a possible way of reducing the development costs for new high-capacity aircraft
Authors: Chiesa S , Di Sciuva M , Maggiore P
Published: October 2002

The double-fuselage layout, sometimes proposed in the past, is considered to be an alternative (by utilizing a great number of components of an existing aircraft) to a new aircraft (with the traditional layout) of about twice the size of the existing aircraft. The development cost reduction is attractive if the technical performance of the double-fuselage is comparable with that of the hypothetical new aircraft.

The first aim of the present work is to sketch a double-fuselage layout with similar values of wing loading, thrust-weight ratio and aspect ratio to the reference new aircraft of increased size. On the basis of this sketch, some other topics are discussed, such as the landing gear and tail surface configurations, ground operations, etc. Particular attention has to be paid to structural problems related to the double-fuselage layout, especially the different modes of stress in structural elements of the original aircraft.
Modelling and identification of non-linear aerodynamic functions using B-splines
Authors: Bruce P D , Kellett M G
Published: October 2002

A method of using B-splines to represent non-linear aerodynamic functions in flight dynamic modelling is presented. This method offers potential advantages over traditional look-up table and polynomial representations for the problem of parameter identification from flight test data. The method offers a natural fit to an underlying smooth function with guaranteed continuity properties. In addition, the B-spline coefficients offer improved conditioning to the identification process, encouraging improved convergence properties of identification algorithms. A reduction in the number of flight tests required is possible, since large portions of non-linear functions can be identified from large-amplitude manoeuvres. In addition, when used with the maximum likelihood estimation method, the Cramer-Rao estimates of parameter confidence are preserved and can be expressed in a B-spline format.
Life enhancement of fatigue-aged fastener holes using the cold expansion process
Authors: Gaerke J , Zhang X , Wang Z
Published: October 2002

This paper examines the benefits of cold expanding fastener holes at various stages of the fatigue life in a 2024-T351 low-load transfer joint. The specimens were pre-cycled to 25, 50 and 75 per cent of the baseline fatigue life of a non-expanded specimen and then cold expanded prior to cycling to final failure. The experimental test was designed to provide a close comparison with standard maintenance practices for aircraft structures and used the FALSTAFF spectrum which was derived from actual flight loading. The test results have indicated that part-life cold expansion can provide substantial improvements in fatigue life, but the actual benefit is dependent upon the degree of precycling and he length of existing cracks when the specimen is cold expanded. Additionally, tests on open hole specimens of the same material and thickness were also carried out, with attempts being made to predict the crack growth lives of these specimes.
Evaluation of navigation errors based on ergodic processes
Authors: Jin H , Zhang H Y
Published: October 2002

The problems of estimation and test of navigation errors are discussed in this paper. Based on Poor's estimation algorithm, the error model of a navigation system is studied from the stochastic process point of view, and the ergodicity of a stochastic process is extended to the ergodicity of a multivariate stochastic process. It is pointed out that Poor's estimation algorithm should be based on the ergodicity of a multivariate stochastic process for practical use and a sufficient condition is given for its application. In addition, Poor's estimation algorithm is extended to the case of any n navigation systems.

The hypothesis test problem of a navigation system accuracy is also discussed in this paper. By using the multivariate statistical analysis theory, the hypothesis test problem of the error covariance matrix of every navigation system can be solved by testing the hypothesis of the relative error covariance matrix between two different navigation systems.
Hysteresis and bifurcation of flow in fuel injection nozzles
Authors: Ramamurthi K , Nandakumar K , Shankar S , Patnaik R
Published: October 2002

Separated flows due to cavitation and attached flows with and without cavitation are investigated for sharp-edged nozzles. The influence of the nozzle diameter, length—diameter ratio and Reynolds number on the bifurcation between the two states of flow is determined. A zone of hysteresis is seen to be present in small sharp-edged nozzles having length—diameter ratios of about 1.5—5 owing to a delayed bifurcation from cavitated flow to attached flow. The role of nozzle diameters and imperfections in the sharp-edged entry is determined. The onset of separated flows arising from cavitation and subsequent reattachment due to cessation of cavitation occur at threshold values of the cavitation number which vary with the nozzle diameter and the length—diameter ratio. The time for transition from cavitated flow to attached flow is discussed.
Parametric modelling and dynamic characterization of a two-degree-of-freedom twin-rotor multi-input multi-output system
Authors: Ahmad S M , Chipperfield A J , Tokhi M O
Published: October 2002

A mathematical model for the dynamic characterization of a two-degree-of-freedom (2 DOF) twin-rotor multi-input multi-output (MIMO) system (TRMS) in hover is extracted using a black box system identification technique. The behaviour of the TRMS, in certain aspects, resembles that of a helicopter, with a significant cross-coupling between longitudinal and lateral directional motions. Hence, it is an interesting identification and control problem. Identification for a 2 DOF, rigid-body, discrete-time linear model is presented in detail. The extracted model has a good degree of prediction capability. The modelling approach presented is suitable for complex new-generation air vehicles.
Identification of chemical and vibrational relaxation regimes in rocket nozzle flow via a quasi-linear formulation
Authors: Lentini D
Published: October 2002

A quasi-linear formulation is proposed for high-speed finite-rate chemically reacting mixtures of imperfect gases, i.e. thermally perfect gases with specific heat varying with temperature, as an extension of a previously developed formulation for perfect gases. The form is suitable for application of accurate and fast algorithms. In particular, the resulting equations keep the same formalism already derived for reacting mixtures of perfect gases, thus indicating the potential for a straightforward extension of existing computational algorithms. In order to assess the applicability of the approach, the assumption of vibrational equilibrium needs to be verified. Accordingly, vibrational, as well as chemical, relaxation regimes are checked in a high expansion ratio rocket nozzle, indicating that the assumption under consideration is fully warranted. The effect of nozzle size on engine performance is also predicted.
A combined testing and modelling approach to the prediction of the fretting fatigue performance of splined shafts
Authors: Limmer L , Nowell D , Hills D A
Published: October 2002

Splined shafts used in gas turbines are being subjected to an ever more arduous set of loads, but the strength of this class of joints has hitherto not been probed. This paper describes preliminary contributions to determining this by first performing a finite element analysis of the spline overall in order to determine the contact conditions, including surface slip displacement. These conditions are then reproduced in a simplified fretting fatigue apparatus in order to reduce the number of prototypical tests required.
Comparison of numerical and experimental analyses for contact problems under normal and tangential loads
Authors: Burguete R L , Patterson E A
Published: October 2002

The methods of finite element (FE) analysis and stress frozen photoelasticity were used to investigate the stresses resulting from the contact of an infinite cylinder with an elastic half-space for comparison with the well-known theoretical solution. Two load cases were studied, that of a load normal to the plane and another where a normal and tangential load are applied to the cylinder. The coefficient of friction was controlled in the photoelastic experiment and the same value used in the finite element analysis. Plots of the Cartesian stresses in the plane of symmetry, the Cartesian shear stress along a line below the surface and the full field of the Cartesian shear stress were obtained and compared. As a result of these analyses, more complex tests were performed which involved using finite element methods and photoelasticity to investigate the stress distributions in the roots of two types of dovetail joint from the compressor of a gas turbine engine. It was found that the two methods yielded results that correlated very closely. The correlation between the experimental, numerical and theoretical results is very close and suggests that combining the experimental and numerical techniques provides a reliable method of stress determination in complex components and structures.
Aerodynamic, dynamic and conceptual design of a fire-fighting aircraft
Authors: Goraj Z , Frydrychewicz A , Ransom E C P , Self A , Wagstaff P
Published: October 2002

This paper presents an evaluation of available aircraft types and demonstrates the lack of a low cost aircraft optimized for fighting forest fires, spreading viscous liquids for land reclamation and spraying pesticides over forest areas. It shows that among critical areas demanding special consideration are (a) the development of mathematical models for the water bomb-aircraft separation and the aircraft transient dynamics following separation, (b) the identification of parameters influencing the coherence of the water column and effectiveness of water delivery for fire fighting, (c) choice of aircraft configuration and (d) hopper configuration. Design and numerical analysis have led to the selection of the biplane as the best aircraft. The main aerodynamic characteristics for the selected aircraft have been computed by means of panel methods, the so-called modified Hess method for thick wings and bodies and/or the vortex lattice method for thin lifting surfaces. Different gaps and staggers and their influence on aerodynamic characteristics have been analysed. It has been found that shifting the lower wing rearwards (positive stagger) while keeping the angle of attack constant results in a small increase of induced drag and an almost constant value of the lift curve slope as well as an increase in the pitching moment curve slope. The increase of drag is disadvantageous, whereas the increase of the pitching moment curve slope means that the neutral point of stability is moved forward (a disadvantage from the stability point of view). The influence of the biplane configuration on downwash in the vicinity of the horizontal plane and aircraft dynamic stability is also discussed. Another important concept—developed at PZL-Okecie and presented in this paper—consists in using parts from existing aircraft. The pilot's cabin, the rear part of the fuselage with control surfaces and wings originate from the PZL-106 ‘Kruk’. This diminishes the cost of design and prototype construction as well as of the cost of aircraft production. It has been shown that an important cost factor in the operation of such a fire-fighting aircraft is the weight of the agent which may be carried for the same fuel consumption. This cost factor, representing the economical efficiency of a fire-fighting aircraft, has been computed and compared for a number of fire-fighting aircraft. The design under consideration (called the PZL-240 ‘Pelikan’) has the above-mentioned factor equal to 14, whereas the average value for other aircraft is about 8.
Blowdown and fluid hammer studies for a satellite reaction control subsystem
Authors: Yang A-S , Kuo T-C
Published: October 2002

Blowdown and fluid hammer characteristics are studied for a satellite reaction control subsystem. A flow channel network numerical scheme is used to determine the blowdown pressure profile and the steady state pressure drops in the propellant lines. For the transient fluid analysis, a theoretical model based on the method of characteristics (MOC) is solved to simulate the time-dependent transport behaviour of the propellant flow. Predicted results show that the blowdown pressure profile in continuous mode operation ranges from 24.5 to 5.5 bar throughout the lifetime of propellant usage. Under a tank pressure of 24.5 bar, the predicted peak values of the pressure fluctuations caused by the fluid hammer waves are nearly the same and equal to 25.4 bar at the locations of the latching isolation valve inlet and the thruster valve inlet. The Fourier spectral analysis also indicates that the induced excitation from the fluid hammer pressure oscillations will not resonantly couple with the thruster assembly and fuel lines. In considering the fluid hammer effect due to the abrupt closure of valves, the pressure spikes will not lead to any damage to the propulsion components or lines during normal operation.
A comparison of blade tip timing data analysis methods
Authors: Carrington I B , Wright J R , Cooper J E , Dimitriadis G
Published: October 2002

The experimental determination of the vibration characteristics of rotating engine blades is very important for fatigue failure considerations. One of the most promising techniques for measuring the frequency of blade vibrations is blade tip timing. In this paper, three vibration analysis methods were specifically formulated and applied to the tip timing problem for the first time, using data obtained from a simple mathematical blade tip timing simulation. The results from the methods were compared statistically in order to determine which of the techniques is more suitable. One of the methods, the global autoregressive instrumental variables approach, produced satisfactory results at realistic noise levels. However, all of the techniques produced biased results under certain circumstances.
Active vibration control of a space truss using a lead zirconate titanate stack actuator
Authors: Song G , Vlattas J , Johnson S E , Agrawal B N
Published: October 2002

This paper presents design, implementation and experimental results of active vibration control of Naval Postgraduate School (NPS) space truss using a piezoelectric ceramic stack actuator. The NPS space truss represents a flexible spacecraft structure that may support interferometer, antenna and other vibration-sensitive instrumentation. To simulate the effects of a spacecraft disturbance on the truss, a proof mass actuator is incorporated on the structure to excite the truss. To reduce the vibrations caused by the proof mass actuator, an active strut member is installed along a diagonal of the base bay of the truss. The active strut element consists of a piezoelectric ceramic actuator stack, a force transducer and mechanical interfaces. An integral plus double-integral force controller is designed to suppress vibration of the truss. Experimental results demonstrate that the active piezoceramic strut actuator can effectively reduce truss vibration.
Analysis of piecewise linear aeroelastic systems using numerical continuation
Authors: Roberts I , Jones D P , Lieven N A J , di Bernado M , Champneys A R
Published: October 2002

This paper demonstrates the application of a numerical continuation method to dynamic piecewise aeroelastic systems. The aeroelastic system is initially converted into a state space form and then into a set of equations which solve the system as the motion moves between different linear zones in a free-play motion. Once an initial condition is found that satisfies these sets of equations, a continuation method is used to find all other possible solutions of the same period for a variation in any parameter. This process can then be repeated for different order systems, allowing the limit cycle behaviour of the whole system to be built up. The solutions found using this method have been shown to be the same as those found using a more traditional Runge-Kutta type of approach with a considerable time saving and added flexibility through multiple parameter variation.
The dynamic analysis of mechanical systems and structures with large parameter variations
Authors: Whalley R , Ebrahimi M
Published: October 2002

A general approach to the analysis of mechanical systems and structures where large parameter variations occur is outlined. Aircraft and missile problems where there are acknowledged changes in the system model coefficients are identified. Performance variations associated with operational conditions are investigated. Simple solutions to the determinantal equation are proposed.
A design of active flutter suppression control systems using μ synthesis and controller reduction
Authors: Fujimori A , Nikiforuk P N
Published: October 2002

This paper presents a control synthesis of a two-dimensional aerofoil active flutter suppression (2D-AFS) using μ synthesis and the extended coprime factorization (weighted) (ECFW) controller reduction method in numerical simulation. A multiplicative uncertainty representation is chosen as a structured uncertainty model of the 2D-AFS system because H∞ norm of the uncertainty due to changes in the flight velocity is calculated small by using the multiplicative uncertainty representation. Controllers are designed by μ synthesis in the frame of the robust stability and the robust control performance problems. Furthermore, using the ECFW controller reduction method, a seventh-order controller whose performances are almost the same as those of the original controller is obtained.
A method for the production of carpet plots for notched compression strength of carbon fibre reinforced plastic multidirectional laminates
Authors: Soutis C , Edge E C
Published: October 2002

This paper outlines a newly developed method for the calculation of the notched compression strength of carbon fibre reinforced plastic (CFRP) laminates. The BAe-Warton laminate strength prediction method (1) is used to predict the unnotched strength of the laminate and the Soutis et al. model (2) to predict the notch effect. Notched and unnotched strengths are reported for a wide range of T800/924C and T800/5245C carbon fibre—epoxy multidirectional laminates with 0°, ±45° and/or 90° lay-ups; results are compared with theoretical predictions and in most cases the error is less than 10 per cent. Carpet plots of open hole compression strength for different T800/5245C lay-ups tested at room temperature (RT)/dry and 100°C/wet are produced. Finally, the open hole strengths generated by the Soutis et al. (2) model are factored by using appropriate experimental data to allow for plain and countersunk filled holes.
Studies on twin non-parallel unventilated high-speed jets
Authors: Elangovan S , Solaiappan A , Rathakrishnan E
Published: October 2002

The interaction of twin high-speed jets is an important problem which is most relevant to aircraft engine exhaust systems. Many studies have been carried out on twin parallel high-speed jets, but similar studies for non-parallel configurations are almost absent. Such an investigation would be useful in understanding jet flow fields associated with V/STOL aircraft. The present work is an attempt to investigate experimentally the interaction of two high-speed axisymmetric jets obliquely oriented towards each other. Twin nozzles of exit diameter ( D) 10 mm are set on a common end wall with their axes intersecting each other at half-angles ( α) of 0, 5, 10 and 15°. The centre-to-centre spacings ( S) of the nozzles, non-dimensionalized as S/D, are varied as 3.1, 4 and 5. The nozzles are operated at fully expanded sonic and underexpanded exit conditions to yield fully expanded Mach numbers Mj of 1, 1.19, 1.41 and 1.52. Some of the conclusions arrived at were based on the experimental results and are given below.

In the case of sonic jets, the variation of mean velocity along the nozzle block centre-line can be correlated with empirical equations based on the geometric intersection distance and the maximum centre- line velocity. In general, at a particular nozzle spacing and angle of interception, the merging distance decreases with increasing fully expanded Mach numbers. In most of the cases, the complete combining of the twin jets into a single jet occurs downstream of the geometric intersection point, the location of the combining point being strongly influenced by the fully expanded Mach number.
Avionics cooling-rate trade-off modelling for ultra-high capacity aircraft
Authors: Fielding J P , Vaziry-Z M A F
Published: October 2002

A computer aided conceptual aircraft design methodology (CACAD) has been developed to size ultra-high capacity jet transport aircraft. Modules were also developed for predicting maintenance costs of each airframe and avionics system and these were incorporated into CACAD. A methodology was developed to enhance the reliability of avionics systems, based on experimentally-proven engineering design solutions. A number of avionics cooling techniques were investigated, and reliability and maintainability models of thermal management were developed and linked to an avionics maintenance cost module. Further models were produced to investigate the impact of proposed changes on the environmental control systems, engine-provided bleeds and power off-takes. It was found that increased flowrates above the normally recommended values for the avionics bay, and to the flight deck instruments, may increase the reliability of the avionics systems, and also increase aircraft dispatch reliability. They may not, however, greatly improve direct operating costs (DOC), due to significant fuel penalties. A separate refrigeration unit was investigated and found to be a feasible cost-effective measure, even allowing for increased engine fuel consumption caused by the effect of the engine power off-take required to drive the refrigeration unit.
Advances in electro-optic systems for targeting
Authors: Thomson G
Published: October 2002

Throughout history, ‘optics’ have been used as the primary sense for weapon aiming. Military aircraft have now been using electro-optic avionic systems for more than 50 years to provide aiming precision in a variety of targeting applications. Recent conflicts have made significant use of the precision of electro-optic (E-O) systems such as the thermal imaging and airborne laser designator (TIALD) to strike specific targets, by day and night, while minimizing the risk of unintentional collateral damage. Many of these E-O systems provide a convenient ‘CNN news compatible’ video and the use and effectiveness of the TIALD have been witnessed by many people on television. Perhaps not so obvious are the underlying advances in E-O technology and the extensive enhancements that have made this all possible. The United Kingdom is a world leader in E-O technology and continues to research and develop new systems to meet anticipated future needs. The author examines the basis for use of electro-optic avionics in targeting applications and describes the depth of the technology employed to meet the precision requirements. A few examples of E-O systems are examined, together with a discussion of future directions.
Non-destructive testing of aerospace composite materials using digital shearography
Authors: Steinchen W , Yang L , Kupfer G , Mäckel P
Published: October 2002

Digital shearography, a laser interferometry technique in conjunction with the digital imaging processing, has the potential for identifying defects both in small- and large-scale structures. This paper will focus on the recent development of digital shearography for non-destructive testing (NDT). With the improvement of the measuring methods and the development of a small and mobile measuring device in conjunction with a user-guided program, Shearwin, this laser inspection technique can be used easily in the environment of fieldwork. A few examples show its application in the aerospace industry for NDT of composites, e.g. GLARE panel, honeycomb structure and glass (or carbon)-fibre-reinforced plastics, etc.
Measurement of autogyro control forces
Authors: Shippen J M
Published: October 2002

An attempt is made to construct a data-acquisition system to measure the in-flight loads of an autogyro. These results give an indication of the scale of pilot forces and of those acting in the control linkage of the rotor.
The flow characteristics of a confined square jet with mixing tabs
Authors: Yu S C M , Hou Y X , Low S C
Published: October 2002

The flow characteristics of a confined square jet with mixing tabs have been determined by measurements obtained using a two-component laser Doppler anemometer at a Reynolds number of 1.026 × 105 (based on the exit hydraulic diameter, DH = 60 mm, and bulk mean velocity, Ur, of the stream at 1.71 m/s). Both tabs of rectangular and triangular shapes are considered with the same height-breadth ratio ( h/b = 1.35) and with their apex leaning downstream. Altogether four tabs have been used, with one tab each located at the centre of each side wall at the exit plane. Each tab is found to produce a dominant pair of counter-rotating streamwise vortices. The combined effects of the four tabs bifurcate the jet into four ‘fingers’, resulting in a significant increase in entrainment at the downstream locations. The strength of the streamwise vorticity generated by the rectangular tabs is some 30 per cent higher than the triangular ones and decays faster with downstream distance. This appears due to a larger tab surface area which creates a larger pressure differential across the rectangular tab than the triangular tab. The region of high turbulent kinetic energy is found firstly at the locations where the streamwise vortices stretch the normal vortices and subsequently at locations where the streamwise vortices break down, resulting in significant mixing enhancement. Finally, the effects of the so-called secondary tabs have also been examined and are found to enhance the mixing further. The orientation of the secondary tabs is, however, crucial for the mixing enhancement to occur.
Design study of a split-torque helicopter transmission
Authors: White G
Published: October 2002

A helicopter transmission with split-torque drive trains to the main rotor and tail rotor drive shaft is described. A design based on two 1200 kW engines supplying torque to a 350 r/min main shaft demonstrates a weight reduction of 40 per cent, extreme low height and reduced losses.

Four double-helical pinions drive a combining gear and provide a 10:1 reduction ratio to the main shaft; flexible torque tubes, set by fine-difference splines, control the division of torque between pairs of pinions. Rotor loads bypass the transmission housings and pass to the fuselage through a large-diameter mast that encloses an integral sump and cooler.
Non-linear dynamics, loss of synchronization and symmetry breaking
Authors: Ashwin P
Published: October 2002

Some aspects of the dynamics of systems of coupled non-linear oscillators are discussed. By examining statistical properties of the dynamics, there can be synchronized states that are dynamically stable but nevertheless unstable on addition of noise. Some indication is given of how ergodic theory can help understand such bifurcations in general.
Statistical aspects of failure of fibre-reinforced composites
Authors: Wisnom M R
Published: October 2002

Composite materials show significant variability in strength, which means that statistical effects need to be considered when predicting failure. Experimental results are presented which show decreasing strength with increasing stressed volume of material. Approaches accounting for this in predicting strength using Weibull statistics are discussed.
Turbulent rotating flow calculations: An assessment of two-equation anisotropic and Reynolds stress models
Authors: Yuan S P , So R M C
Published: October 2002

The stress field in a rotating turbulent internal flow is highly anisotropic. This is true irrespective of whether the axis of rotation is aligned with or normal to the mean flow plane. Consequently, turbulent rotating flow is very difficult to model. This paper attempts to assess the relative merits of three different ways to account for stress anisotropies in a rotating flow. One is to assume an anisotropic stress tensor, another is to model the anisotropy of the dissipation rate tensor, while a third is to solve the stress transport equations directly. Two different near-wall two-equation models and one Reynolds stress closure are considered. All the models tested are asymptotically consistent near the wall. The predictions are compared with measurements and direct numerical simulation data. Calculations of turbulent flows with inlet swirl numbers up to 1.3, with and without a central recirculation, reveal that none of the anisotropic two-equation models tested is capable of replicating the mean velocity field at these swirl numbers. This investigation, therefore, indicates that neither the assumption of anisotropic stress tensor nor that of an anisotropic dissipation rate tensor is sufficient to model flows with medium to high rotation correctly. It is further found that, at very high rotation rates, even the Reynolds stress closure fails to predict accurately the extent of the central recirculation zone.
Kinetic modelling of the ignition delays in monomethylhydrazine/hydrogen/oxygen/argon gaseous mixtures
Authors: Catoire L , Ludwig T , Dupré G , Paillard C
Published: October 2002

The objective of this study is to estimate the efficiency of ignition promotion or inhibition for H2=O2=Ar mixtures by monomethylhydrazine (CH3NHNH2, noted MMH), a propellant widely used in rocket propulsion systems. This is accomplished by computations performed with a detailed kinetic model. The model is validated with experimental ignition delays obtained behind a reflected shock wave in mixtures of MMH=O2=Ar, MMH=O2=H2=Ar and H2=O2=Ar. Good agreement (to about 25 per cent) is obtained between experimental and computed ignition delays with the mixtures of MMH=H2=O2=Ar at high temperatures (900–1170 K), in the pressure range 225–414 kPa. For the mixtures of H2=O2=Ar the agreement is also good over a very large range of temperatures (960±2300 K), pressures (up 5 MPa) and compositions (from highly diluted mixtures to undiluted). This model shows that, for the mixtures under consideration, MMH added in relatively small amounts (up to 10 per cent with respect to hydrogen) is an inhibitor or a promoter, depending on the amount added, under 1000 K and an inhibitor above 1000 K.
Merlin to 2000
Authors: Barker J C
Published: October 2002

This paper traces the history and development of the EH101 helicopter from its inception to its imminent delivery. It is the product of a joint venture between the industries and governments of Britain and Italy and is due to be in service in 1998 in Britain and 2000 in Italy. With five operators beginning operations in the next four years there are exciting prospects for the use and development of the helicopter.
The modelling and validation of the vertical dynamics of a hot air balloon
Authors: Ellenrieder T J
Published: October 2002

The contemporary interest in automatic altitude control systems for balloons has precipitated the need for dynamic models of the vertical balloon motion. This paper develops the vertical dynamics equations of a hot air balloon from first principles and successfully validates the results against three sets of flight test data from a typical balloon. It is concluded that the developed model is of sufficient fidelity for the proposed dynamic modelling needed in the development of flight control systems. However, further areas of model improvement are highlighted, which would extend the applicability of the balloon model.