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Railway track dynamic modelling
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The railway vehicles are an increasing mean of transportation due to, its reduced impact on environment and high level of comfort provided. These reasons have contributed to settle a positive perception of railway traffic into the European society. In this upward context, the railway industrial sector tackles some important challenges; maintaining low operational costs and controlling the nuisance by-products of trains operation, the most important being railway noise. Track dynamic plays a main role for both issues, since a significant part of the operational costs are associated with the track maintenance tasks and, the noise generated by the track can be dominant in many operational situations. This explains why prediction tools are highly valued by railway companies. The work presented in this licentiate thesis proposes methodologies for accurate and efficient modelling of railway track dynamics. Two core axes have led the development of this task, on one hand, the rail modelling and, on the other hand, the characterisation of the finite length nature of track supports. Firstly, concerning the rail modelling technique, it has evolved under two major premises. On one hand, regarding the frequency domain, it should describe high frequency behaviour of the rail. In order to accomplish with this first premise, a model based on Timoshenko beam theory is used, which can accurately account for the vertical rail behaviour up to 2500 Hz. On the other hand, with respect to the time domain, the response should be smooth and free of discontinuities. This last condition is fulfilled by implementation of the Timoshenko local deformation. Secondly, a model of support that considers its finite length nature is sought. For this purpose, a Timoshenko element over elastic foundation is formulated. Thus, the common model of support, which is based on a concentrated connection, is substituted by a distributed model of support. In this way, several enhancements are achieved; the temporal contact force response is smoothed and a more realistic shape is obtained, the amplitude of the displacement due to the parametric excitation is reduced and the magnitude associated to the ‘pin-pin’ frequency is not overestimated.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. , p. 45
Series
TRITA-AVE, ISSN 1651-7660 ; 34
Keywords [en]
Track modelling, Timoshenko element, local deformation, response discontinuity, distributed supports
National Category
Vehicle Engineering
Research subject
Engineering Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-207180ISBN: 978-91-7729-440-5 (print)OAI: oai:DiVA.org:kth-207180DiVA, id: diva2:1096621
Presentation
2017-06-09, Munin, Teknikringen 8, Flyget, våningsplan E, KTH Campus, Stockholm, 10:15 (Swedish)
Opponent
Supervisors
Note

QC 20170522

Available from: 2017-05-22 Created: 2017-05-18 Last updated: 2017-05-22Bibliographically approved
List of papers
1. Implementation of Timoshenko element local deflection for vertical track modelling
Open this publication in new window or tab >>Implementation of Timoshenko element local deflection for vertical track modelling
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(English)Article in journal (Refereed) Submitted
Abstract [en]

A vertical track model suitable for the study of the dynamic response and the interaction between wheel and rail in the time domain is developed by using Timoshenko beam elements, and its performance is optimized by accounting for the local deflection of these type of elements. Implementation of the local system enables to obtain an accurate description of the contact force in a more computational efficient way than other numerical methods, and it leads to an almost total elimination of the discontinuities caused by the moving nature of the load and the shear incompatibilities introduced by the conventional formulation with Timoshenko beam elements. The work presented here describes both static and dynamic approaches of the local system directly obtained through the resolution of the beam governing equations. Two resolution strategies for the timedomain response are proposed, along with the local system formulation. The first is based on numerical integration of the whole system by introducing a Newmark scheme followed by a Newton–Raphson iterative process. The second resolution strategy is based on a numerical convolution integration, which is able to reduce significantly the computational cost of the simulation. This last resolution methodology together with implementation of the local system approach, join a computationally efficient routine and an accurate description of the track dynamic, which are valuable features for dynamics simulations. The results are validated by comparison with those from previous works.

Keywords
Timoshenko element, Local deformation, Discontinuity in slope deflection, Newmark integrator, Convolution product
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-207582 (URN)
Note

QC 20170522

Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2017-05-23Bibliographically approved
2. Distributed support modelling for vertical track dynamic analysis
Open this publication in new window or tab >>Distributed support modelling for vertical track dynamic analysis
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(English)Article in journal (Refereed) Submitted
Abstract [en]

The finite length nature of rail-pad supports is characterised by a Timoshenko beam element formulation over an elastic foundation, giving rise to the distributed support element (TEEF). The new element is integrated into a vertical track model, which is solved in frequency and time domain. The developed formulation is obtained by solving the governing equations of a Timoshenko beam for this particular case. The interaction between sleeper and rail via the elastic connection is considered in an analytical, compact and efficient way. The modelling technique results in realistic amplitudes of the ‘pin-pin’ vibration mode and, additionally, it leads to a smooth evolution of the contact force temporal response and to reduced amplitudes of the rail vertical oscillation, as compared to the results from concentrated connection support models. Simulations are performed for both parametric and sinusoidal roughness excitation. The model of support proposed here is compared with a previous finite length model developed by other authors, coming to the conclusion that the proposed model gives accurate results at a reduced computational cost.

Keywords
Rail-pads; track models; distributed support; sleeper; corrugation; parametric excitation
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-207585 (URN)
Note

QC 20170522

Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2017-05-23Bibliographically approved

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