Stefano Bruni

Control and monitoring for railway vehicle dynamics

Over the last twenty to thirty years, railway vehicle dynamics has changed from being an essentially mechanical engineering discipline to one that is increasingly starting to include sensors, electronics and computer processing. This paper surveys the application of these technologies to suspensions and running gear, focused upon the complementary issues of control (which has been reviewed within Vehicle System Dynamics previously) and monitoring (which has not previously been reviewed). The theory, concepts and implementation status are assessed in each case, from which the paper identifies the key trends and concludes with a forward look at what is likely to develop over the next years.

Numerical Simulation of Pantograph-Overhead Equipment Interaction

Summary The main features of a mathematical model for the simulation of pantograph-catenary dynamic interaction are presented and, in particular, some aspects related to the catenary and pantograph schematisation are outlined. The model enables to investigate the behaviour of the system in a relatively large frequency range (up to 100 Hz), due to the inclusion of the bending modes of the collector head. In order to simulate the contact between wire and collector, a procedure based on the penalty method is adopted, and it is shown by means of a numerical test case that the method reproduces the constraint acting at the pantograph-catenary interface over a wide frequency range with high accuracy, provided that suitable values are given to the contact parameters. The problem of minimising the numerical disturbances due to the discretisation of the contact wire is also discussed, showing that the entity of these disturbances can be reduced to acceptable values by adopting a proper discretisation of the contact wire, so that no post-filtering of simulation results is required. Applications to some specific aspects of current collection are presented, and comparisons with available experimental data from line tests are shown.

Modelling of suspension components in a rail vehicle dynamics context

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.

The results of the pantograph–catenary interaction benchmark

This paper describes the results of a voluntary benchmark initiative concerning the simulation of pantograph–catenary interaction, which was proposed and coordinated by Politecnico di Milano and participated by 10 research institutions established in 9 different countries across Europe and Asia. The aims of the benchmark are to assess the dispersion of results on the same simulation study cases, to demonstrate the accuracy of numerical methodologies and simulation models and to identify the best suited modelling approaches to study pantograph–catenary interaction. One static and three dynamic simulation cases were defined for a non-existing but realistic high-speed pantograph–catenary couple. These cases were run using 10 of the major simulation codes presently in use for the study of pantograph–catenary interaction, and the results are presented and critically discussed here. All input data required to run the study cases are also provided, allowing the use of this benchmark as a term of comparison for other simulation codes.

Experimental and numerical investigation on the derailment of a railway wheelset with solid axle

This paper presents the results of an experimental and numerical investigation on the derailment of a railway wheelset with solid axle. Tests were carried out under quasi-steady-state conditions, on a full-scale roller rig, and allowed to point out the effect of different parameters like the wheelsets angle of attack and the ratio between the vertical loads acting on the flanging and non-flanging wheels. On the basis of the test results, some existing derailment criteria are analysed in this paper and two new criteria are proposed. A model of wheel–rail contact is proposed for the mathematical modelling of the flange climb process, and numerical vs. experimental comparisons are used to obtain model validation.

Comparisons between wind tunnel tests on a full aeroelastic model of the proposed bridge over Stretto di Messina and numerical results

Abstract The final draft of the proposed bridge over Stretto di Messina was concluded by a 1:250 scale full bridge aeroelastic model study, that was constructed and tested at DMI in the “Martin Jensen” wind tunnel. The tests aimed at verifying the aerodynamic behaviour of the bridge in smooth and turbulent flow, for flow perpendicular to the bridge axis and at yaw angles, and to verify the threshold of the flutter instability. The analytical approach in the time domain, developed by Politecnico di Milano in order to simulate the bridge response to turbulent wind is described here. The experimental results are presented and compared to the numerical results.

Wear of railway wheel profiles: a comparison between experimental results and a mathematical model

SUMMARY The paper presents the results of experimental and numerical investigations on regular wear of wheel profiles. Experimental tests were performed on a full-scale roller rig and allowed to measure the evolution of wheel profiles as well as contact forces and several quantities describing the motion of the wheelset. As to the numerical investigations, a wear prediction model was developed, based on the interfacing of a multi-body simulation code for rail vehicle dynamics, of a local contact analysis model and of a material wear model that assumes a proportionality relationship between wear and frictional power. The validation of this model by comparisons with the measurement performed on the roller rig is still in progress. Some preliminary results are shown in this paper.

Mathematical modelling of train–turnout interaction

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.

Modelling the Viscoelastic Behaviour of Elastomeric Components: An Application to the Simulation of Train-Track Interaction

The paper deals with the experimental characterisation of the frequency dependent behaviour of elastomeric track components and with the definition of appropriate models in time domain for these elements. It is shown in particular that the dynamic stiffness of elastomeric components depends on both amplitude and frequency of deformation. Moreover, the dissipative behaviour is closer to the hysteretic hypothesis than to the viscous one. Some simple models allowing to reproduce the measured behaviour of these elements are defined and a procedure for the identification of their parameters is set-up. It is shown that rather simple models can provide better results than the classical ones composed by a spring in parallel to a viscous damper. It is also shown that the introduction of these models into a finite element description of the track provides a significant improvement in the calculation of track inertance and on the results of the simulation of train-track interaction.

Turbulence effect on flutter velocity in long span suspended bridges

Abstract The study deals with the problem of turbulence effect on the instability of a long span suspended bridge subjected to wind action. In particular it is shown how, with reference to the quasi static corrected theory, it is possible to explain the results obtained in a wind tunnel on “taut strip” and complete 3D models.