System Identification I

Dynamics of structures

This paper is a review of the effect of vehicle characteristics on ground- and track borne-vibrations from railways. It combines traditional theory with modern thinking and uses a range of numerical analysis and experimental results to provide a broad analysis of the subject area. First, the effect of different train types on vibration propagation is investigated. Then, despite not being the focus of this work, numerical approaches to vibration propagation modelling within the track and soil are briefly touched upon. Next an in-depth discussion is presented related to the evolution of numerical models, with analysis of the suitability of various modelling approaches for analysing vehicle effects. The differences between quasi-static and dynamic characteristics are also discussed with insights into defects such as wheel/rail irregularities. Additionally, as an appendix, a modest database of train types are presented along with detailed information related to their physical attributes. It is hoped that this information may provide assistance to future researchers attempting to simulate railway vehicle vibrations. It is concluded that train type and the contact conditions at the wheel/rail interface can be influential in the generation of vibration. Therefore, where possible, when using numerical approach, the vehicle should be modelled in detail. Additionally, it was found that there are a wide variety of modelling approaches capable of simulating train types effects. If non-linear behaviour needs to be included in the model, then time domain simulations are preferable, however if the system can be assumed linear then frequency domain simulations are suitable due to their reduced computational demand.

https://www.tandfonline.com/doi/pdf/10.1080/23248378.2014.897791

Railway-induced ground vibrations – a review of vehicle effects

Suspension components play key roles in the running behaviour of rail vehicles, and therefore, mathematical models of suspension components are essential ingredients of railway vehicle multi-body models. The aims of this paper are to review existing models for railway vehicle suspension components and their use for railway vehicle dynamics multi-body simulations, to describe how model parameters can be defined and to discuss the required level of detail of component models in view of the accuracy expected from the overall simulation model. This paper also addresses track models in use for railway vehicle dynamics simulations, recognising their relevance as an indispensable component of the system simulation model. Finally, this paper reviews methods presently in use for the checking and validation of the simulation model.

Modelling of suspension components in a rail vehicle dynamics context

This paper presents a view of the current state of monitoring track geometry condition from in-service vehicles. It considers technology used to provide condition monitoring; some issues of processing and the determination of location; how things have evolved over the past decade; and what is being, or could/should be done in future research. Monitoring railway track geometry from an in-service vehicle is an attractive proposition that has become a reality in the past decade. However, this is only the beginning. Seeing the same track over and over again provides an opportunity for observing track geometry degradation that can potentially be used to inform maintenance decisions. Furthermore, it is possible to extend the use of track condition information to identify if maintenance is effective, and to monitor the degradation of individual faults such as dipped joints. There are full unattended track geometry measurement systems running on in-service vehicles in the UK and elsewhere around the world, feedin...

/pdf/perspectives-on-railway-track-geometry-condition-monitoring-24z7xbb52q.pdf

Perspectives on railway track geometry condition monitoring from in-service railway vehicles

The paper proposes a mathematical model of train–turnout interaction in the mid-frequency range (0–500 Hz). The model accounts for the effects of rail profile variation along the track and of local variation of track flexibility. The proposed approach is able to represent the condition of one wheel being simultaneously in contact with more than one rail, allowing the accurate prediction of the effect of wheels being transferred from one rail to another when passing over the switch toe and the crossing nose. Comprehensive results of train–turnout interaction during the negotiation of the main and the branch lines are presented, including the effect of wear of wheel/rail profiles and presence of track misalignment. In the final part of the paper, comparisons are performed between the results of numerical simulations and line measurements performed on two different turnouts for urban railway lines, showing a good agreement between experimental and numerical results.

Mathematical Modelling of Train-turnout Interaction

The mathematical model of suspension components in a railway vehicle may have an important effect on the results of vehicle dynamics simulations and their accuracy in reproducing the actual vehicle behaviour. This paper aims to define and compare alternative mathematical modelling approaches for the secondary airspring suspension and to assess their effect on the accuracy of rail vehicle dynamics multibody simulation. To derive reliable models of the suspension, a quasi-static and dynamic characterisation of the suspension was performed by means of a full-scale laboratory experiment. Based on this, two different modelling approaches were developed for the airspring suspension: a quasi-static one, in which the frequency-dependent behaviour of the suspension is neglected, but the coupling between shear and roll stiffness is included, and a dynamic one in which additionally the frequency-dependent behaviour of the suspension in vertical direction is represented using a thermodynamic model, and additionally the dependency of lateral/roll stiffness parameters on the load is incorporated. The results of vehicle dynamics simulations in curved track and/or in the presence of crosswinds and the results of ride comfort calculations are presented, to assess the effect of the models developed, in comparison with a simpler model only reproducing the vertical and lateral stiffness of the suspension. It is demonstrated that the quasi-static coupling effect between shear and roll deformation in the airsprings can have a large effect on the simulation of load transfer effects in curved track and in the presence of crosswinds, and hence remarkably affect the assessment of ride safety and track loading, whereas the dynamic model of the airspring suspension appears to be required when wheel unloading under the action of crosswind is evaluated. Finally, it is shown that a dynamic model of the airspring is required to assess ride comfort correctly, especially when the pneumatic layout of the suspension includes a long pipe between the airspring and the reservoir.

Mathematical modelling of the secondary airspring suspension in railway vehicles and its effect on safety and ride comfort

Estimation of lateral and cross alignment in a railway track based on vehicle dynamics measurements

http://ssi.civil.ntua.gr/downloads/journals/2009-JSV_Effects%20of%20train%20impacts%20on%20urban%20turnouts%20Modelling%20and%20validation%20through%20measurements.pdf

Effects of train impacts on urban turnouts: Modelling and validation through measurements

In the paper, a method for the estimation of track irregularities having wavelength above 20 m is presented. The method is based on measurements performed on-board a vehicle negotiating the line at service speed and on model-based techniques for the post processing of measurements. The accuracy of the method with respect to measuring noise and parameter uncertainty is investigated by numerical experiments and finally the method is applied to line measurements.

Stefano Alfi

Papers

Mathematical Modelling of Train-turnout Interaction

Mathematical modelling of the secondary airspring suspension in railway vehicles and its effect on safety and ride comfort

Estimation of lateral and cross alignment in a railway track based on vehicle dynamics measurements

Effects of train impacts on urban turnouts: Modelling and validation through measurements

Estimation of long wavelength track irregularities from on board measurement