Proceedings of the Institution of Mechanical Engineers,Part F: Journal of Rail and Rapid Transit

This study investigates the dynamic response of a locomotive drive system experiencing wheel/rail saturation adhesion. A dynamic locomotive model is created and then integrated with electromechanical and control systems to simulate the vibration in the component parts of the drive system. The model is used to investigate the drive system’s sensitivity to resonance effects. The obtained results show that the wheel/rail stick-slip state can experience both longitudinal vibrations and self-excited vibrations in the drive system. Different parts of the drive system are excited by the two types of vibrations; however, in both cases the main frequencies are multiples of the natural frequency vibration of the drive system. It is necessary to select an appropriate value for the motor suspension rubber stiffness if structural resonances of the drive system under wheel/rail saturated adhesion are to be avoided.

The combination of low-frequency lateral and roll motions experienced in tilting trains can provoke motion sickness. The incidence of sickness depends on vehicle design and subject demographics. Vehicle design affects the location of the centre-of-roll, which influences passenger perception of motion. Age and gender have large influences on susceptibility to sickness, but little is known about the effects of ethnicity and body size. This study investigated the influence of both the vertical position of the centre-of-roll and subject characteristics (ethnicity, weight, stature and sickness susceptibility) on sickness caused by fully roll-compensated lateral oscillation. It was hypothesised that sickness would be greater when full compensation occurred at the head than when full compensation occurred at the seat. Sixty subjects experienced a 0.2-Hz lateral oscillation combined with ±7.3° of roll, so that the lateral acceleration was fully compensated at either the seat surface or 800 mm above the seat (i.e. average head height). Illness ratings and symptom scores were recorded every minute for 50 min (i.e. during a 5-min acclimatisation period, a 30-min exposure period and a 15-min recovery period). Although the mean illness ratings were greater when full compensation occurred at the head than at the seat, the difference was not statistically significant. Weight and stature were not associated with motion sickness, but illness ratings were much greater in Asian subjects than in European subjects. It is concluded that differences in susceptibility between Asians and Europeans have a greater effect on motion sickness than the height of the centre-of-rotation during roll-compensated lateral acceleration.

High-speed trains push air to the front, sides and over the top to form a train slipstream. The extension of the slipstream to the side, top and wake flow depends on train speed, train shape, ambient conditions and the environment in which the train operates. In this paper, the slipstream and wake flow of a 1/20th scale model of a simplified five-coach ICE2-shape train running in two different environments; in open air and when passing a platform, were obtained using large-eddy simulation (LES). The flow Reynolds number was taken to be 300,000; based on the speed and height of the train. The effect of the platform height on the train slipstream was investigated by performing simulations on a platform of different heights: 20, 60, 90 cm. To investigate the effect of mesh resolution on the results, two different computations were performed for the case of the flow around the train running in the open air using a different number of mesh nodes; a fine mesh consisting of 18,000,000 nodes and a coarse mesh consisting of 12,000,000 nodes. The results of the coarse mesh simulation were deemed to be comparable to those from the fine mesh simulation. The LES results were also compared with full-scale data and a good agreement obtained. A number of different flow regions were observed in the train slipstream: upstream region, nose region, boundary layer region, inter-carriage gap region, tail region and wake region. Localized velocity peaks were obtained near the nose of the train and in the near wake region. Coherent structures were formed at the nose, roof and inter-carriage gaps of the train. These structures spread in the slipstream and extend a long distance behind the train in the far wake flow. The maximum slipstream turbulent intensity was found in the near wake flow. The results showed that there is a significant effect of the platform height on the slipstream velocity and nose and tail pressure pulses. However, there is only a minor effect of the platform height on the static pressure along the body of the train compared with that on the nose and tail pressure pulses. In general, the slipstream velocity in the lower region of a train running in the open air was found to be larger than that around a train passing a platform. This has been related to the effect of the underbody complexities of the train.

This is the first part of a two-part paper that describes the results of an experimental investigation to measure the aerodynamic pressure forces on structures in the vicinity of railway tracks. The investigations were carried out in order to obtain a fundamental understanding of the nature of the phenomenon and to obtain data for a variety of railway infrastructure geometries of particular relevance to the UK situation, in order to provide material for a National Annex to the relevant Eurocode. The experiments were carried out on the moving model TRAIN Rig, with models of three different sorts of trains with different nose types, and a variety of infrastructures types: vertical hoardings, overbridges, station canopies and trestle platforms. The transient loads that were measured had a characteristic form: a positive pressure peak followed by a negative pressure peak. In general the magnitudes of the two peaks were different, and varied with infrastructure type and position, as well as with train type. As would be expected, the more streamlined the train, the lower were the magnitudes of the pressure transients. A comparison of the experimental results was made with a variety of existing model- scale and full-scale data and a broad consistency was demonstrated, within the limits that the rather different experimental conditions in the various cases would allow. An analysis of the scaling of these pressure transients was carried out, and it was shown that whilst there was a reasonable coalescence around a theoretical formulation, the complexity of the flows involved meant that a general scaling formulation could not be achieved. Part 2 of this paper will consider the application of the results to the development of revised standards formulations.

Leaves on railway tracks affect the level of adhesion between the wheel and rail, especially in autumn. When crushed by wheels, leaves form a tarnished, low level of adhesion layer that sticks to the railhead and often requires mechanical removal. A Stockholm local traffic track with a long history of adhesion problems was subjected to field tests on railhead contamination. On five occasions under different conditions, spaced over a year, the friction coefficient was measured using a tribometer and samples of the rail were taken. The techniques of electron spectroscopy for chemical analysis and glow discharge optical emission spectrometry were conducted to determine the composition of the top layer of rail contaminants and hardness was measured using the nano-indentation technique. The tarnished layer contains much higher contents of calcium, carbon and nitrogen than do leaf residue layers and uncontaminated samples. These high element contents are generated from the leaf material, which chemically reacts with the bulk material. The hardness of the tarnished layer is one-fifth that of the non-tarnished layer of the same running band. A chemical reaction occurs from the surface to a depth of several microns. The thickness of the friction-reducing oxide layer can be used to predict the friction coefficient and extent of leaf contamination.

Models that can predict the correct logistics actions that need to be taken to ensure the availability of spare parts during maintenance of railway vehicles are of considerable interest. Since the occurrence of defects is a random phenomenon it is not possible to know in advance what spare parts will be required at any point in time. This situation requires the creation of a stochastic model that can incorporate uncertainty. Deterministic and stochastic models of maintenance logistics are based on the assumption of a non-zero stock level of spare parts. Carrying an extensive inventory of parts requires a large financial outlay and it is still often the case that a required spare part is not immediately available and has to be obtained. This paper shows, provided certain conditions are met, that it is possible to create cost-effective maintenance procedures even if the required spare part is not immediately available. Thus, the amount of money locked up in stock can be effectively regulated, thus reducing operating costs.

The temperature rise of wheels and blocks due to frictional heating during railway tread braking along with the transfer of heat through the wheel–rail contact is studied in this paper. In particular, heat partitioning between block, wheel and rail for stop braking cycles is considered. The wheels are of interest because they are a limiting factor for railway tread braking systems. Two types of thermal models are employed to investigate the maximum temperatures over the wheel tread. In a circumferential (plane) model of wheel, block and rail, the heat transfer problem is studied by use of a finite element formulation of the two-dimensional time-dependent convection–diffusion equation. The hot spot phenomenon is simulated by introducing a prescribed wheel-fixed contact pressure distribution between wheel and block. In an axisymmetric (axial) model of wheel, block and rail, the lateral movements of the wheel–rail contact are studied. A general result is that the cooling effect provided by the rail is important when local temperatures on the tread are considered, but not when studying bulk temperatures created in a single stop braking event. Furthermore, it is found from the lateral movements of the wheel–rail contact that slow oscillations result in maximum temperatures over the wheel tread that are somewhat lower than for travelling on straight track (rolling at the rolling circle).