John A. Elkins

RAIL CORRUGATION ON NORTH AMERICAN TRANSIT SYSTEMS

Abstract This paper describes work which has greatly improved our understanding of the processes by which rail corrugation typically develops on North American Transit systems. Several types of corrugation were identified from observations and measurements in the field. A new mechanism for corrugation formation is proposed for the most common type of corrugation observed, and a mathematical model has accordingly been developed which combines both low frequency and high frequency behaviour of the vehicle/track system. The mathematical model itself, plus results from it and from measurements are discussed here. Novel recommendations for corrugation mitigation are made.

TESTING AND ANALYSIS TECHNIQUES FOR SAFETY ASSESSMENT OF RAIL VEHICLES: THE STATE-OF-THE-ART.

Abstract The methods currently being used in North America, Britain and Europe for the safety assessment of rail vehicles are discussed. There is considerable disparity between the methods that have been developed in the different countries. These differences, and the possible reasons for them, are discussed in the paper. Finally, conclusions are drawn and some recommendations are made for the future direction of safety assessment methods.

PREDICTION OF WHEEL/RAIL INTERACTION: THE STATE-OF-THE-ART

SUMMARY This paper presents a survey of the state-of-the-art in predicting wheel/rail interaction. Current methods are presented for calculating contact geometry, defining the wheel/rail kinematic expressions, and obtaining contact plane forces due to creep. The paper concludes by examining where future research should be focused. While techniques for predicting wheel/rail interaction have developed considerably over the last twenty years, there is room for still further improvement.

Traction and curving behaviour of a railway bogie

In conventional railway systems, vehicles exert traction and must also negotiate curves. The creep forces between a bogie and the track are shown here for a wide range of curve radii (300–1800 m), a wide range of applied traction (traction ratios of 0, 0.14 and 0.28) and for bogies of widely different yaw stiffness, which is the factor that most affects a bogie’s curving performance. Traction destroys the steering performance of any bogie, increasing the lateral displacement of the critical leading wheelset and also its angle of attack, thereby increasing the tendency for ‘squeal’ noise. The resultant wheel/rail creep forces also typically increase and change orientation significantly. There is a significant difference in creep force across both wheelsets, with slip occurring first at the leading wheel on the high rail. For modest levels of applied traction, low yaw stiffness improves curving performance. However, low yaw stiffness becomes ever less beneficial as traction increases. Indeed, at levels of applied traction typical of modern locomotives, a bogie and the wheelsets within it behave essentially as a rigid bogie, regardless of the yaw stiffness.

Track structure modeling with NUCARS and its validatation

SUMMARY This paper presents the development of a methodology for simulating flexible track structures in the *NUCARS™ vehicle/track interaction multi-body simulation program. Several different track modeling methods were evaluated and example results arc compared. The implementation of the chosen track model in NUCARS is described. Simulations and comparisons with test data from three research and test programs are presented. This paper discusses the limitations of the methodology and the ongoing development of the NUCARS software to improve the simulation of track structure interaction with vehicle dynamics.

Rail Vehicle Dynamics for the 21st Century

Although railway vehicles were first used in the 18th century, it was only in the 20th century that engineers began to understand their dynamics and were able to write down, and solve, their equations of motion. The single most fundamental property of a railway vehicle is the use of a steel wheel running on a steel rail with all the traction, braking and guidance forces being transmitted through a small contact area between the wheel and the rail. While the inherent guidance provided by a conical wheelset running on rails was known even to George Stephenson in 1821, who described its kinematic oscillation, it is only in the last 40 years that an adequate theory has been available for vehicle suspension designers to use. It is well known that a mechanical system that is subject to non-conservative forces may become dynamically unstable under certain conditions. In a railway vehicle the non-conservative forces arise at the contact point between the wheel and rail due to creepage, and the sustained lateral and yawing oscillation that results in some vehicles is known as hunting. This paper traces the developments in railway dynamics up to the end of the 20th century and discusses the latest developments, with predictions as to what the future might hold.

TRAIN RESISTANCE MEASUREMENTS USING A ROLLER RIG

SUMMARY This paper describes the results of a test program performed on a conventional three-piece freight car truck, utilizing the Roll Dynamics Unit (RDU) at the Transportation Test Center (TTC) in Pueblo, Colorado. The purpose of the test program was to determine the steady state behavior, in particular the train resistance or drag, that resulted from axle misalignments and simulated curves. The drag of each axle and the angles of attack with respect to the rollers were measured during the experiment. These results were compared with predictions from a mathematical model that had been developed specifically for the purpose of predicting the steady state behavior of a vehicle running on rollers. The predictions from this “roller model” were also compared with the results from a “curving model”, which is able to predict the steady state behavior of a vehicle running on track.

Prediction of Rail Roll Deflections due to Adjacent Trucks

SUMMARY This paper describes a static track model that has been developed to predict rail roll deflections resulting from the wheel/rail forces exerted by a number of adjacent trucks. A particular problem of rail rollover derailments with articulated cars is discussed in order to provide a background to the reason for the model development. Details of the model are described followed by predictions of rail head lateral deflections and fastener vertical loads.