C.J. Goodman

Monitoring Lateral Track Irregularity from In-Service Railway Vehicles

Abstract Maintaining the alignment of railway track is vitally important for the smooth and safe passage of railway vehicles. Poor track alignment can result in poor ride quality, flange contact, or even flange climb. Accurate horizontal track geometry can be measured using a dedicated track recording vehicle or from a full track geometry recording system mounted on an in-service vehicle. This paper describes the use of sensors mounted on the bogie of an in-service vehicle to estimate the mean track alignment without the use of optical or contact sensors. In principle, either bogie lateral acceleration or yaw rate can be processed to give an estimate of mean lateral track irregularity, but a yaw rate gyro provides consistent estimates down to lower vehicle speeds than does an accelerometer and does not require compensation for the effects of bogie roll. An improved estimate can be obtained by inverting the dynamic relationship between the mean track alignment and the bogie yaw motion. This is demonstrated with results from a Class 175 vehicle. Continually monitoring the lateral response of a bogie on an in-service vehicle, using only a yaw rate gyro, can provide data enabling the prioritization of maintenance operations.

Distributed quantitative and qualitative fault diagnosis: railway junction case study

Abstract The paper develops a novel, comprehensive, reasoned approach to fault diagnosis in a class of reciprocating, electro-mechanical equipment referred to as single throw mechanical equipment (STME). STMEs are widely used in many industrial applications—examples of which include automatic doors, mechanical presses and barrier systems. A formal definition of the STME is initially presented. In this paper, an electro-pneumatic railway point machine within a railway junction is taken as a case study. The proposed approach distributes the fault diagnosis process across a geographical area interconnected using fieldbus data communication networks. This allows for the fault detection and isolation of multiple assets within close proximity to one another at a minimal cost. A robust, straightforward, quantitative method based on abstract static models and structured residuals is used for fault detection and preliminary diagnosis is suggested. This is capable of being implemented at an asset level on an embedded processor. Fault isolation is carried out at one central point in the distributed architecture; thus allowing full fault diagnosis of multiple assets to be carried out economically. Details of a hybrid quantitative and qualitative, neuro-fuzzy network suitable for carrying out fault isolation is discussed and results collected from a laboratory based test-rig are presented.

Metro traffic regulation from the passenger perspective

Abstract Maintaining metro ridership in the future will require an increasing focus on customer perceptions of the service quality. This work outlines a process whereby passenger expectations may be encapsulated into a mathematical evaluation function that can then be used in an on-line optimization procedure. The function proposed penalizes excess waiting time, travelling time and congestion following a disturbance such as a platform delay. With the function defined, the problem resolves into finding a set of optimum arrival and departure times (the decision variables) that minimizes this penalty function. Ultimately, the concept is intended to form part of an on-line, real-time traffic controller residing on the despatching computer in a control centre. An embedded simulation is used to perform the optimization calculations, and several techniques are described that reduce the computing time needed to a level feasible for on-line use. Comparisons are made with some previous control algorithms. Using data based on the Hong Kong Island Line, it is shown that the new controller performs well, albeit when using the newly proposed evaluation function as the test criterion.

Industrial fault diagnosis: Pneumatic train door case study

Abstract A practical, robust method of fault detection and diagnosis of a class of pneumatic train door commonly found in rapid transit systems is presented. The methodology followed is intended to be applied within a practical system where computation is distributed across a local data network for economic reasons. The health of the system is ascertained by extracting features from the trajectory profiles of the train door. This is incorporated into a low-level fault detection scheme, which relies upon using simple parity equations. Detailed diagnostics are carried out once a fault has been detected; for this purpose neural network models are utilized. This method of detection and diagnosis is implemented in a distributed architecture resulting in a practical, low-cost industrial solution. It is feasible to integrate the results of the diagnosis process directly into an operators maintenance information system (MIS), thus producing a proactive maintenance regime.

Modelling passenger flows at a transport interchange using Petri nets

Abstract Modelling passenger flows within a transport interchange is a compromise between computational speed and accuracy, especially if the model is to be embedded within an optimization procedure for managing the effects of disrupted traffic. Petri nets offer the possibility of the standardized representation of a concurrent dynamic system. Such a representation consists of a network formed by places that are linked together by arcs and transitions, and tokens that move around in this network. Using coloured Petri nets (CPNs) allows information to be associated with each token, such as the number of passengers represented by the token, the destinations of subgroups of those passengers and data related to measures such as accumulated passenger transit times. Practicalities such as the variation of walking speeds between passengers and the restricted capacity of features of the interchange infrastructure, such as escalators, can also be incorporated. Furthermore, the model is capable of being extended to represent the transport services themselves, at least within a reasonable area outside the interchange.

Optimal Train Control at a Junction in the Main Line Rail Network using a New Object-Oriented Signalling System Model

On a main line railway network with many junctions, this paper describes how the delay of a train is likely to cause delays to many other trains, especially because of conflicts at junctions. Optimizing one junction, however, may have an adverse effect on other parts of the rail network because of the mixed-traffic situation of most main line railways. To approach the complicated problem of optimal re-scheduling in response to the delay of a train, an efficient algorithm must be sought. The authors have taken a junction as an example, and have performed numerical optimization on a case when the services through this junction are disrupted. The objective criterion is the weighted sum of train times. The optimization program uses the Object-Oriented Multi-Train Simulator (OOMTS) developed by Birmingham University, as an embedded simulator. In the optimization routine, a Genetic Algorithm (GA) was used to optimize the order of route setting. In this paper, the authors give details of a model junction, and a brief explanation of the OOMTS. The authors then explain how a GA can be applied to solve this problem, especially the chromosomal expression of the problem. The results of numerical optimizations for different weighting parameters are shown based on which the authors discuss the feasibility of the proposed method.

Dynamic re-scheduling of trains after disruption

This paper reviewed the general concepts and procedures being applied to the control of train services following disruption. Systems vary from simply encapsulating known rules for recovery to using full scale simulation and optimization embedded in an on-line real-time controller. The computer-generated control inputs can be applied directly to the railway or used to advise the human line controllers. Systems employing stored algorithms are already in operation, often taking direct control from small disturbances but handing back to the line controllers when the disturbances exceed a set level. Railways require enormous investment in infrastructure and it is therefore imperative that means are sought to maximize the utilization of that infrastructure. This paper reviews some of the applications of computers to the particular problem of recovering from traffic disturbances in way that seek to minimize the consequent loss of capacity. To some extent, the processes of re-scheduling after disruption are similar to scheduling in the first place, and thus some reference will be made to methods being used for automatic time-tabling. The management of recovery can vary between entirely manual and entirely automatic, with full predictive modeling and rigorous mathematical optimization procedures. In practice, such systems already exist, and those under research and development, are generally something of a comprise between these two extremes. Even so, a key issue for system designers is whether to allow the computers to control the traffic directly without reference to the line controllers, or whether they should only operate in the decision support role. Again, practical experience is leading towards systems incorporating both concepts and using one or the other depending on the severity of the disruption.

An architecture for system-wide fault detection and isolation

Abstract A novel approach to distributed fault detection and isolation (FDI) is presented. Consideration is given to an appropriate architecture and communication method for a truly distributed FDI system. As part of the discussion on system architecture, regard is given to the correct level at which fault detection, diagnosis and isolation should be carried out. The case study of an automatic door as part of a building automation system is presented. Recognized faults are induced on the asset and detection methods formulated. It is demonstrated that, by implementing the fault detection algorithms at a lower level, it is possible to carry out FDI over a system consisting of many assets. This allows maintenance staff more precise information regarding the health of the whole system and allows system-wide isolation and in-depth diagnostics to be applied in the event of a fault being detected. The architecture discussed allows the implementation of system-wide FDI at a fraction of the cost of stand-alone systems.

Investigation into the Computational Techniques of Power System Modelling for a DC Railway

This paper describes how the use of computer simulation techniques is now a fundamental part of the design process for electrified railways and at the feasibility stage clients will often request detailed calculations to be performed for the basic design. This will establish a level of confidence in both the project and basic design parameters that will justify the capital expenditure further on in the project life-cycle. This paper addresses how the total impedance of a railway network may be represented, where the impedances of the traction return circuit and traction power system are either combined together to form one impedance or studied independent of one another. The accuracy of the modeling in this manner, particularly how it affects the accuracy of rail voltage results shall be assessed. It will also examine how much impedance is typically in the rails and what proportion this needs to be before it has an unacceptable effect on the numerical results. To assess this, a range of proportions will be studied, for example 70% of the total impedance to be modeled in the conductor with 30% modeled in the rails, 60%/40%, etc. In this way, a proper scientific assessment of the combined or split calculation methods can be made via simplified case studies.

An Optimal Traffic Regulation Method For MetroType Railways Based On Passenger OrientedTraffic Evaluation

An optimal traffic regulation method based on passenger oriented traffic evaluation was developed. To formulate the passenger oriented traffic evaluation function, concepts of passenger expectation and passenger inconvenience were introduced. Using the function, a traffic regulation problem is described as an optimisation problem to find an optimum set of departure times and arrival times that gives the minimum passenger inconvenience. This problem is large scale because decision variables are departure times and arrival times of all trains at each station. At the same time, this problem is a constrained problem because there are constraints that restricts interval between departure time and arrival time. A online optimisation method to solve the problem was developed. To cope with the constraints, an idea of gradient projection is utilised in the developed method. To reduce computing time to practical level, three techniques, decomposition of partial derivatives, fixed length receding horizon and recursive optimisation are used. Simulation results show that the proposed method can reduce passenger inconvenience up to 57 % compared with two previously proposed methods with realistic computing time required in optimisation. Transactions on the Built Environment vol 34,