Simulation of rail roughness growth on small radius curves using a non-Hertzian and non-steady wheel–rail contact model

A time-domain model for the prediction of long-term growth of rail roughness (corrugation) on small radius curves is presented. Both low-frequency vehicle dynamics due to curving and high-frequency vehicle–track dynamics excited by short-wavelength rail irregularities are accounted for. The influence of non-Hertzian and non-steady effects in the wheel–rail contact model on rail wear is studied. The model features a contact detection method that accounts for wheelset yaw angle as well as surface irregularities and structural flexibilities of wheelset and rail. The development of corrugation on a small radius curve is found to be highly influenced by the wheel–rail friction coefficient. For vehicle speed 25 km/h and friction coefficient 0.3, predictions of long-term roughness growth on the low rail show decreasing magnitudes in the entire studied wavelength interval. For friction coefficient 0.6, roughness growth is found at several wavelengths. The corresponding calculation for the high rail contact of the trailing wheelset indicates no roughness growth independent of friction coefficient. The importance of accounting for the phase between the calculated wear and the present rail irregularity is demonstrated

Mechanical track deterioration due to lateral geometry irregularities

This thesis deals with how a degraded track geometry influences further degradation of the geometry and the formation of rolling contact fatigue (RCF) and wear of rails. The overall objective is optimisation of railway maintenance. For this, further understanding and quantification of the deterioration of track components are needed. Dynamic multibody simulations have been performed featuring different wagons, and a track with different curve radii and different levels of track geometry degradation. With the resulting wheel/rail interaction degradation indicators are evaluated. Increased track shift forces are considered as an indicator of further track geometry degradation. Two different RCF indices (one shakedown map based and one wear number based) are used to quantify surface degradation of rails. Measured lateral track irregularities were found to follow a normal distribution reasonably well. Furthermore, the standard deviation of track shift forces was shown to have a linear relationship with the standard deviation of the lateral irregularities. For large curve radii an increase of the level of lateral irregularities increases the length of rail affected by RCF. The opposite is predicted for small curve radii where the length of rail affected by RCF decreases with increasing levels of lateral irregularities. For very small curve radii it was shown that the degradation mechanism shifts from pure wear for low levels of lateral irregularities to a mixed wear/RCF degradation for higher levels of lateral irregularities. Amplification of lateral irregularities in different wavelength spans revealed that an amplification of longer wavelengths (between 10--50 metres) had the largest influence on the length of rail affected by RCF in shallow curves. A correlation study between predicted tangential wheel/rail contact forces and lateral irregularities (amplitudes of the irregularities, first order derivatives and second order derivatives) was carried out. No significant correlation was found

Measurement methods and analysis tools for rail irregularities. A case study for urban tram track

Rail irregularities, in particular for urban railway infrastructures, are one of the main causes for the generation of noise and vibrations. In addition, repetitive loading may also lead to decay of the structural elements of the rolling stock. This further causes an increase in maintenance costs and reduction of service life. Monitoring these defects on a periodic basis enables the network rail managers to apply proactive measures to limit further damage. This paper discusses the measurement methods for rail corrugation with particular regard to the analysis tools for evaluating the thresholds of acceptability in relation to the tramway Italian transport system. Furthermore, a method of analysis has been proposed: an application of the methodology used for treating road profiles has been also utilized for the data processing of rail profilometric data

A direct method for analyzing the vertical vehicle-structure interaction

A new method for the dynamic analysis of the vertical vehicle-structure interaction is presented. The vehicle and structure systems can be discretized with various types of finite elements and may have any degree of complexity. The equations of both systems are complemented with additional compatibility equations to ensure contact between the vehicles and the structure. The equations of motion and the compatibility equations form a single system that is solved directly, thus avoiding the iterative procedure used by other authors to satisfy the compatibility between the vehicle and structure. For large structural systems the proposed method is usually more efficient than those that frequently update and factorize the system matrix. Some numerical examples have shown that the proposed formulation is accurate and efficient

Robust control for independently rotating wheelsets on a railway vehicle using practical sensors

This paper presents the development of H-infinity control strategy for the active steering of railway vehicles with independently rotating wheelsets. The primary objective of the active steering is to stabilize the wheelset and to provide a guidance control. Some fundamental problems for active steering are addressed in the study. The developed controller is able to maintain stability and good performance when parameter variations occur, in particular at the wheel-rail interface. The control is also robust against structured uncertainties that are not included in the model such as actuator dynamics. Furthermore the control design is formulated to use only practical sensors of inertial and speed measurements, as some basic measurements required for active steering such as wheel-rail lateral displacement cannot be easily and economically measured in practice

Rail roughness and rolling noise in tramways

Companies which manage railway networks have to cope continually with the problem of operating safety and maintenance intervention issues related to rail surface irregularities. A lot of experience has been gained in recent years in railway applications but the case of tramways is quite different; in this field there are no specific criteria to define any intervention on rail surface restoration. This paper shows measurements carried out on some stretches of a tram network with the CAT equipment (Corrugation Analysis Trolley) for the principal purpose of detecting different states of degradation of the rails and identifying a level of deterioration to be associated with the need for maintenance through rail grinding. The measured roughness is used as an input parameter into prediction models for both rolling noise and ground vibration to show the potential effect that high levels of roughness can have in urban environment. Rolling noise predictions are also compared with noise measurements to illustrate the applicability of the modelling approach. Particular attention is given to the way the contact filter needs to be modelled in the specific case of trams that generally operate at low speed. Finally an empirical approach to assess vibration levels in buildings is presented

Probabilistic simulation for the certification of railway vehicles

The present dynamic certification process that is based on experiments has been essentially built on the basis of experience. The introduction of simulation techniques into this process would be of great interest. However, an accurate simulation of complex, nonlinear systems is a difficult task, in particular when rare events (for example, unstable behaviour) are considered. After analysing the system and the currently utilized procedure, this paper proposes a method to achieve, in some particular cases, a simulation-based certification. It focuses on the need for precise and representative excitations (running conditions) and on their variable nature. A probabilistic approach is therefore proposed and illustrated using an example. First, this paper presents a short description of the vehicle / track system and of the experimental procedure. The proposed simulation process is then described. The requirement to analyse a set of running conditions that is at least as large as the one tested experimentally is explained. In the third section, a sensitivity analysis to determine the most influential parameters of the system is reported. Finally, the proposed method is summarized and an application is presented

Design of an autonomous teleoperated cargo transporting vehicle for lunar base operations

At the turn of the century NASA plans to begin construction of a lunar base. The base will likely consist of developed areas (i.e., habitation, laboratory, landing and launching sites, power plant) separated from each other due to safety considerations. The Self-Repositioning Track Vehicle (SRTV) was designed to transport cargo between these base facilities. The SRTV operates by using two robotic arms to raise and position segments of track upon which the vehicle travels. The SRTV utilizes the semiautonomous mobility (SAM) method of teleoperation; actuator-controlled interlocking track sections; two robotic arms each with five degrees of freedom; and these materials: titanium for structural members and aluminum for shell members, with the possible use of light-weight, high-strength composites

Integration of crosswind forces into train dynamic modelling

In this paper a new method is used to calculate unsteady wind loadings acting on a railway vehicle. The method takes input data from wind tunnel testing or from computational fluid dynamics simulations (one example of each is presented in this article), for aerodynamic force and moment coefficients and combines these with fluctuating wind velocity time histories and train speed to produce wind force time histories on the train. This method is fast and efficient and this has allowed the wind forces to be applied to a vehicle dynamics simulation for a long length of track. Two typical vehicles (one passenger, one freight) have been modelled using the vehicle dynamics simulation package ‘VAMPIRE®’, which allows detailed modelling of the vehicle suspension and wheel—rail contact. The aerodynamic coefficients of the passenger train have been obtained from wind tunnel tests while those of the freight train have been obtained through fluid dynamic computations using large-eddy simulation. Wind loadings were calculated for the same vehicles for a range of average wind speeds and applied to the vehicle models using a user routine within the VAMPIRE package. Track irregularities measured by a track recording coach for a 40 km section of the main line route from London to King's Lynn were used as input to the vehicle simulations. The simulated vehicle behaviour was assessed against two key indicators for derailment; the Y/Q ratio, which is an indicator of wheel climb derailment, and the Δ Q/Q value, which indicates wheel unloading and therefore potential roll over. The results show that vehicle derailment by either indicator is not predicted for either vehicle for any mean wind speed up to 20 m/s (with consequent gusts up to around 30 m/s). At a higher mean wind speed of 25 m/s derailment is predicted for the passenger vehicle and the unladen freight vehicle (but not for the laden freight vehicle)