A method of predicting variable speed rail corrugation growth using standard statistical moments

Wear-type rail corrugation is a significant problem in the railway transport industry. Some recent work has suggested that speed control can be used as an effective tool to minimize the rate of corrugation growth. This has brought about the need to model corrugation growth under variable passing speed. Variable speed rail corrugation growth modelling normally consists of either numerical simulation of a sequence of varied speed wheel passes or direct integration of a probabilistic passing speed distribution function; both of which are computationally expensive. This paper investigates the use of the statistical moments of the speed probability density function to greatly improve the computational speed of variable speed corrugation growth models and compares results of changing standard deviation and skewness to numerical integration models. It also identifies the effects of individual statistical moments on corrugation growth to provide better insight into control methods. The new modelling method correlated well with the numerical integration models for small standard deviations in speed (less than 10%) and highlighted a need to consider kurtosis in predicting the performance of speed control based corrugation mitigation schemes. For larger standard deviations in speed, higher than 4th order effects need to be considered

Probabilistic Prediction of Wheel Squeal under Field Humidity Variation

This research examines the effect of changes in coefficient of friction due to humidity on the likelihood of wheel squeal events occurring in practice. Theoretical mechanics based modeling is developed and compared to a database of field measurements of wheel squeal occurrences at a field site in Australia. In particular, a relatively simplified model of wheel squeal is developed based on existing literature but notably incorporates probabilistic mechanics to account for field parameter variations and hence allows direct comparisons with field data. The model is then tuned to field site conditions at which over 2 million wheel passes have been monitored for a period of 3 years. The comparison indicates that field measured trends for the effect of relative humidity on coefficient of friction and hence the occurrences of wheel squeal have been able to be predicted using the very efficient model

The effects of passing speed distribution on rail corrugation growth rate

The transportation phenomenon known as wear-type rail corrugation is a significant problem in railway engineering, which manifests as a periodic wear pattern developing on the surface of the wheel and rail with use. Some field studies and recent theoretical results by the current authors have suggested that uniformity in pass speed causes an increase in corrugation growth rate. This paper presents the predicted change in corrugation growth rate and dominant wavelengths with change in passing speed distribution, based on state of the art cornering growth modelling techniques

The effect of non-uniform train speed distribution on rail corrugation growth in curves/corners

Rail corrugation is a significant problem in railway engineering, manifesting as an oscillatory wear pattern on the rail head. These profile variations induce unwanted vibrations, excessive noise and other associated problems. Constant train speed for consecutive train passes has been shown to accelerate corrugation growth while widening the probabilistic speed distribution can be shown to mitigate the phenomena. This paper extends this research by investigating the effect of non-uniformity (or asymmetry) in speed distribution on corrugation growth on curved track/corners. To this end, an efficient corrugation growth prediction model is further developed to include quasistatic bogie cornering dynamics and investigated under non-uniform speed distribution conditions. The results indicate that under typical cornering conditions, the rate of corrugation growth is increased (or decreased) when the mean or skewness of the distributed set of passing speeds is biased to higher (or lower) speeds. In particular, for the conditions investigated, controlling (or not controlling) skewness could achieve a further 12% (or −20%) in corrugation growth rate reduction from a nominal 41% reduction due to symmetric speed variation. Hence, non-uniform speed distribution could cause up to a 50% reduction in predicted effectiveness of widened speed distribution control to reduce corrugation growth rate

Effects of variable pass speed on wear-type corrugation growth

A feedback model for wear-type rail corrugation has been modified to account for vehicle speed variations over successive passages, so that the effect on corrugation amplitude growth can be investigated. The feedback model encapsulates the most critical interactions occurring between the wheel/rail structural dynamics, rolling contact mechanics and rail wear. Using this model, numerical and analytical investigations are performed to quantitatively identify the effect of deliberately changing the speed of successive vehicle passages in a statistically controlled manner. The effect of different initial track profiles on the results is also investigated. The results provide insight into a possible alternative means of retarding wear-type corrugation growth. (C) 2008 Elsevier Ltd. All rights reserved

Investigation of the effect of relative humidity on lateral force in rolling contact and curve squeal

Curve squeal is the result of the lateral force in rolling contact of rail and wheels along curves. Recently, field measurements of wheel squeal occurrences at a site in Australia showed an increasing possibility for a squeal event to occur as the relative humidity increases. To verify these results, a new method is developed on a testrig to measure the lateral and vertical force simultaneously, so as to determine the friction-creep curve and lateral contact damping. The friction-creep curves at different speeds are also modelled analytically and compared with experimental measurements. To investigate the effect of relative humidity on squeal and effective contact damping, the relative humidity inside the acoustic enclosure of testrig was adjusted under controlled conditions of 50%, 70% and 90%, and the results show that squeal is more likely in high relative humidity

A model of the wear due to the rolling contact of a wheel over a general rail profile

Recent research has suggested that the contact mechanics between the wheel and rail in railway systems may act as a geometric filter for wear-type rail corrugation. This filter is hypothesized to work alongside the dynamics to create the wear pattern, attenuating some wavelengths (and associated frequencies) while promoting others, and hence influencing the spectra of noise produced. It has been proposed that this effect may give rise to the field observation of the speed insensitivity of the dominant wavelength of short pitch corrugation. This type of corrugation is responsible for an annoying tonal noise in the range of 500-800 Hz. In this paper a simplified model of the wear due to the rolling contact of a wheel over a general rail profile is presented. This model is simple to implement and allows for an investigation into the non-linear behaviour of the dynamic wear, not discussed in previous research. The relevance of these results to the transportation noise phenomenon of wear-type rail corrugation is discussed

A method of predicting variable speed rail corrugation growth using standard statistical moments

Wear-type rail corrugation is a significant problem in the railway transport industry. Some recent work has suggested that speed control can be used as an effective tool to minimize the rate of corrugation growth. This has brought about the need to model corrugation growth under variable passing speed. Variable speed rail corrugation growth modelling normally consists of either numerical simulation of a sequence of varied speed wheel passes or direct integration of a probabilistic passing speed distribution function; both of which are computationally expensive. This paper investigates the use of the statistical moments of the speed probability density function to greatly improve the computational speed of variable speed corrugation growth models and compares results of changing standard deviation and skewness to numerical integration models. It also identifies the effects of individual statistical moments on corrugation growth to provide better insight into control methods. The new modelling method correlated well with the numerical integration models for small standard deviations in speed (less than 10%) and highlighted a need to consider kurtosis in predicting the performance of speed control based corrugation mitigation schemes. For larger standard deviations in speed, higher than 4th order effects need to be considered