Evert Andersson

Assessment of train-overturning risk due to strong cross-winds

Abstract This paper describes the methodology for safety assessment related to the risk of a train overturning in strong cross-winds. As an example, this methodology is applied on the high-speed line Botniabanan being built for a maximum speed of 250 km/h in the northeast coastal region of Sweden. The process starts with a systematic identification of locations along the line having a potential high risk of overturning due to cross-winds. This is followed by a cross-disciplinary study. The first step is to estimate the probabilities of wind velocity and wind directions. The next step is aerodynamic computation of overturning forces and moments acting on relevant types of train. Further, the critical overturning wind velocity is determined by a multi-body simulation technique. Finally, the overturning accident frequency is calculated. The calculated risk is compared with generally accepted risk levels in modern train operation.

Influence of different conditions for tilt compensation on symptoms of motion sickness in tilting trains

Increased speeds of trains can be achieved by using tilting trains that decrease the lateral acceleration experienced by passengers on curves, thereby allowing trains to run typically 25-30% faster on existing curved track and maintaining good ride comfort. Unfortunately, motion sickness in tilting trains is a major problem for some passengers. To investigate the incidence of motion sickness and the extent to which different tilt compensation strategies influence its occurrence, tests were conducted with a tilting train on a track with a large number of curves. Eighty healthy volunteers were studied, selected partly for their susceptibility. Three different cars were evaluated during 3 test days, with each test ride lasting about 3 h. On four occasions per test ride, the subjects answered a questionnaire concerning activities during the ride, ride comfort, ability to work and read, vegetative symptoms, fatigue, sleepiness, nausea and well-being. Subjects estimation of average ride comfort and ability to work and read was good in all conditions. However, 10% of the test subjects reported various symptoms of motion sickness (SMS). A 55% degree of tilt compensation of the lateral acceleration instead of the normal 70% reduced the symptoms of motion sickness incidence (SMSI) by 25-40%. SMSI correlated poorly with motion doses, which integrates vertical or lateral acceleration but correlated well with roll acceleration motion dose (r2 = 0.43, p < 0.001). For women, riding backward (p < 0.001) minimized SMSI, but men were insensitive to direction. Future railway design will have to optimize tilt systems by both minimizing motion sickness and avoiding excessive lateral acceleration or jerk.

Determining the deterioration cost for railway tracks

Abstract The cost of maintaining and renewing railway tracks affected by traffic-dependent deterioration is considerable. It is important not only to have proper maintenance regimes, but also to have knowledge of the interaction between vehicles and track in order to reduce the deterioration of both. In a joint project between Banverket (Swedish Rail Administration) and KTH (Royal Institute of Technology, Stockholm), a model for track deterioration is developed, considering track settlement, component fatigue, abrasive wear, and rolling contact fatigue of rails. The basis of the model is taken from what is considered as state-of-the-art knowledge. The model is used as a basis for a proposed new track access charging regime for Banverket, able to differ between vehicle types based on their characteristics and tendency to deteriorate the tracks. The model is implemented in an Excel® environment and applied to Swedish mainline traffic and vehicles. Using representative vehicle characteristics in determining track deterioration, it is predicted that there are large differences between different vehicles regarding their deterioration of the tracks. The model predicts axle load, unsprung mass, and wheelset steering capability as decisive for track deterioration. The model is believed to predict realistic results also for heavy-haul rail operations.

Dynamic simulation of derailments and its consequences

This article describes the necessary prerequisites and methodology in progress for studying train vehicle derailments and means of minimising the risk of catastrophic consequences. A comprehensive model has been developed and used in the multi-body system (MBS) simulation software for studying pre- and post-derailment vehicle behaviour. An axle-mounted brake disc and vertically extended bogie frames have shown empirically, as well as by MBS simulations, a potential to favourably influence the sequence of events in case of wheel flange climbing derailments. The MBS simulation methodology has been presented. Examples of how critical geometrical parameters affect the ability of these mechanisms to act as substitute guidance are presented. Further, a finite element (FE) model is developed for studying the impact phenomenon between a rail vehicle wheel and concrete sleepers. In particular, the proposed FE model will be used for obtaining hysteresis data for the wheel–sleeper force as functions of concrete indentation, for further development of the MBS simulations technique.

Experimental and theoretical analysis of freight wagon link suspension

Abstract Link suspension is the most prevailing suspension system for two-axle freight wagons and still frequently used for four-axle freight wagons in central and western Europe. The system design is simple and has existed for more than 100 years. However, still, the characteristics are not fully understood. This article focuses on the lateral characteristics of the link suspension. First, results from stationary measurements on freight wagons and laboratory tests on single links are presented. Then, a simulation mathematical model is proposed. Finally, the influence of various parameters on the link characteristics is investigated. With the developed simulation model, many of the stability problems of link suspension running gears can be explained, but further research is needed to fully understand the characteristics and to be able to recommend improvements. From the tests, it also becomes obvious that the characteristics of different links can vary significantly from each other depending on age and maintenance status.

Post-derailment dynamic simulation of rail vehicles : Methodology and applications

An earlier developed multi-body system post-derailment module, that predicts the wheelsets’ behaviour after impact with concrete sleepers, is upgraded to account for possible wheel–rail fastener impact situations, after train derailments at high speed. The vertical stiffness describing the wheel–fastener impact behaviour is calibrated and validated based on two authentic derailment cases. Geometrical specifications that permit a brake disc and a bogie frame to act as substitute guidance mechanisms after flange climbing derailments on curved track are presented for an X 2000 trailer car. Further, an introductory analysis on the post-derailment vehicle behaviour on tangent track after a ‘flange on rail head’ derailment condition is also presented as a function of bogie yaw resistance. The risk of carbody overturning after derailments on tangent track is assessed as a function of coupler height and carbody centre of gravity as well as bogie transversal beam position.

An Overview of Some High-speed Train Derailments: Means of Minimizing Consequences Based on Empirical Observations

Abstract Studies published on rail vehicles— post-derailment behaviour as a means of minimizing consequences are surprisingly scarce. This paper sets a first step to reduce this lack of knowledge by analysing a collection of incident/accident case studies, with the main focus on the course of events immediately after derailments. This is mainly with respect to whether the train stays upright and close to the track centre-line and is ‘safe’ or deviates laterally with a probable serious consequence. Accordingly, an empirical database is established containing as much relevant information as possible of past incidents and accidents occurring at speeds over 70 km/h due to mechanical failure close to the running gear/track interface, as well as other causes that ultimately brought the train into a derailed situation. Although two derailments are never the same, certain patterns appeared to emerge based on the descriptions available in each incident or accident report. Mechanical restrictions between axles and bogie frames appear to minimize the risk of derailments after an axle failure on the outside of the wheel. Once derailed, evidence suggests that certain low-reaching parts on the wheelset or the bogie frame may act as substitute guidance mechanisms, thereby minimizing large lateral train deviations. However, for a large number of events, the available information does not allow conclusions based on observations only. This paper is the first in a forthcoming series dealing with the possibilities of minimizing devastating consequences of high-speed derailments by appropriate measures and features in the train design including the running gear.

Influence of link suspension characteristics variation on two-axle freight wagon dynamics

The link suspension is the most prevailing suspension system for freight wagons in central and western Europe. Link suspension systems have strong non-linear characteristics including a hysteresis loop. The loop exhibits usually three characteristic sections with different tangential stiffnesses. The actual contact geometry of the links and end bearings has a significant influence on the characteristics. By wear in ordinary service, the contact geometry changes considerably, thus causing the characteristics to change. In summary, it appears that the link suspension characteristics are very sensitive to several factors, being hard to control in the real world of freight wagon operations. The various stiffnesses and hysteresis loops are found to have a strong influence on the ride qualities of vehicles. This paper presents non-linear multibody simulations investigating these matters. As long as the characteristics cannot be controlled within closer limits than found in this study, there is a strong need for the sensitivity analysis to be made, both in predictive multibody simulations of vehicle dynamics as well as for verification and acceptance tests.

On Minimizing Derailment Risks and Consequences for Passenger Trains at Higher Speeds

The first part of this article deals with the possibility of preventing wheel climbing derailments after an axle journal failure by implementing mechanical restrictions between the wheelsets and the bogie. A multi-body system (MBS) computer model is developed to account for such an axle failure condition, which is successfully validated by comparing the pre-derailment sequence of events with two authentic cases. An extensive parameter analysis on the maximum vertical and longitudinal play between the wheelset and the bogie, required to prevent a high-speed power or trailer car to derail, is performed for various combinations of running conditions in curves. Once an actual derailment has occurred on conventional passenger trains at 200 km/h, extensive MBS simulations are performed on the feasibility of utilizing alternative substitute guidance mechanisms, such as low-reaching parts of bogie frame, axle box, or brake disc, as means of minimizing the lateral deviation. Results are presented in terms of geometrical parameters that lead to a successful engagement with the rail for a total of 12 different derailment scenarios. These are caused by an axle journal failure, an impact with a small object on the track, or a high rail failure. Minimizing the lateral deviation is also investigated by means of restraining the maximum coupler yaw angle and altering the bogie yaw stiffness. Time-domain simulations are also performed in terms of lateral track forces and derailment ratio when negotiating a tight horizontal ‘S-curve’. Further, the articulated train concept is investigated in terms of the post-derailment vehicle behaviour after derailments on tangent and curved track at a speed of 200 km/h. In this respect, a trainset consisting of one power car and four articulated passenger trailer cars is modelled in the MBS software. Results in terms of lateral deviation and maximum carbody roll angle are presented as a function of different inter-carbody damper characteristics and running gear features. The feasibility of these damper characteristics is also tested in terms of lateral track forces and derailment ratio when negotiating a tight horizontal S-curve.

Lateral Track Forces at High Speed Curving Comparisons of Practical and Theoretical Results of Swedish High Speed Train X2000

SUMMARY This paper initially describes the main features of the radial selfsteering bogies, which have been developed for the high speed train X2000, suburban trains and other applications. One of the main goals with these bogies is to reduce lateral track forces at high speed curving. This development has been supported by extensive theoretical investigations parallel to practical tests and verifications. Since around 1973 the main tool for theoretical analysis has been time domain simulations of non-linear vehicle-track models under influence of perfect and irregular track geometry. There are models for vertical/longitudinal and for lateral dynamics. The models are assembled and utilised in a specialised computer program, SIMFO, and in a more general computer code, GENSYS, the latter having full 3-dimensional capability. A frequently used model for lateral dynamics of a four-axle bogie vehicle with 37 degrees of freedom (DOF) is shown as an example. In order to avoid an unrealistically stiff lateral cou...