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

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

Railway corrugation noise growth prediction

Rail corrugation is a frequent rail wear pattern along tangents and curves that result in distinct undesirable noise. Rail corrugation is a common aspect in all transit systems and much research has been pursued to predict and mitigate its growth on track but prediction of resultant noise growth has not been a focus. This paper provides the experimental validation of Railway Rolling Noise Prediction Software (RRNPS) model for the prediction of railway corrugation noise growth with tangent track. The model is based on the mechanics of vehicle and track interactions. It is validated by means of several experiments that have been performed along a straight railway line. Through comparisons of predictions with measurements, it is shown that the RRNPS model gives reliable predictions on rail corrugation growth and corresponding noise growth. Subsequently this model is used to predict how speed, normal force, wheelset traffic and ballast vertical stiffness affect corrugation growth and its corresponding noise growth

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

Validation of a tangent track corrugation model with a two disk test rig

Test rig validation of theoretical predictions of the effect of various parameters on rail corrugation development is investigated. Particular focus is given to the effects of mean speed on wavelength of formation, increased traction ratio on growth rate and speed variation and friction control for corrugation mitigation. The test rig results concur with theoretically predicted trends under the conditions investigated and provide more detailed insight into the mechanism by which friction modifiers may reduce corrugation growth in tangent track conditions. Results also highlight the significance of contact patch widening during the initial stages of corrugation growth. The results also show that reductions in growth rate from nominal conditions of up to approximately 6 times are possible with speed variation and friction modifier application

Investigation about the effect of angle of attack and relative humidity on wheel squeal

In order to validate prediction models of wheel sqeal, a two-disk rolling contact test rig has ben developed to investigate fundamental behaviour. This test rig has been modified to allow for a range of angles of attack to be set and measured accurately, with a relative error about 1%. On the other hand, in order to perfom a controlled investigation of the effects of humidity on wheel squeal, a humidity control system was set up in the enclosure of the test rig. Squel noise was recorded at the different angle of attack, rolling speed and relative humidity, and the analysed results not only indicate the effect of these parameters initially, but also correlate well with results from modal test and FEA. Furtermore, the test rig was retrofitted to measure the lateral force at the rolling contact patch with strain gauges on leaf springs