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Development of new techniques for the numerical modelling of railway track dynamics. Application to rolling noise assessment
KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The numerical modelling is widely employed for the prediction of the railway track dynamic behaviour, which is of utmost importance for the characterisation of the undesired medium-high frequency phenomena, such as corrugation, wheel-out-of-roundness and noise emission. This study is devoted to the improvement of railway track numerical modelling, the efficient resolution of the problem in the time domain and the assessment of rolling noise for different approaches of the track modelling.

Regarding the enhancement of the railway track numerical modelling, two main core ideas have led the development of this task. On the one hand, the rail modelling, and on the other hand, the characterisation of the finite length nature of track supports. The proposals of this work include two basic premises, accuracy and computational efficiency.

Firstly, the study makes use of Timoshenko beam theory for the numerical description of the rail. However, the conventional Timoshenko finite element involves drawbacks for the description of the rail dynamic behaviour and the calculation of the wheel-rail interaction in the time domain. These problems are addressed by improving the finite element formulation, which is based on the description of its local displacements.

Secondly, the versatility of numerical methods is exploited to develop a distributed model of support. It substitutes the usual concentrated model, which entails overestimation of the periodicity effects and disruption of the wheel-rail interaction in the time domain.

Thirdly, the advantages of the formulation of numerical models in the frequency domain are explored focusing on the ability to fairly describe the sleeper dynamics, the enhancement of the model boundaries and the realistic modelling of the track components dissipative behaviour. Moreover, the frequency domain response can be used to obtain the wheel-rail interaction in the time domain efficiently, by means of the moving Green's function.

Lastly, this work deals with the assessment of rolling noise, in which particular emphasis is made on the influence of track dynamics in the noise prediction. At this regard, a methodology is proposed to account for the track periodicity, load speed and finite length of supports.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. , p. 158
Series
TRITA-SCI-FOU ; 2019:07
Keywords [en]
Track modelling, Timoshenko element, local deformation, distributed supports, moving Green's functions, rolling noise
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-244379ISBN: 978-91-7873-102-2 (print)OAI: oai:DiVA.org:kth-244379DiVA, id: diva2:1290334
Public defence
2019-03-15, Salón de Grados, Paseo Manuel Lardizábal, 13, San Sebastián, Spain, 11:00 (English)
Opponent
Supervisors
Note

QC 20190220

Available from: 2019-02-21 Created: 2019-02-20 Last updated: 2019-02-21Bibliographically 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)In: 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: 2019-08-07Bibliographically 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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2018 (English)In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 56, no 4, p. 529-552Article in journal (Refereed) Published
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. 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 pinned-pinned' 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 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.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
Keywords
Rail-pads, track models, distributed support, sleeper, corrugation, parametric excitation
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-223525 (URN)10.1080/00423114.2017.1394473 (DOI)000424429600003 ()2-s2.0-85032814670 (Scopus ID)
Note

QC 20180222

Available from: 2018-02-22 Created: 2018-02-22 Last updated: 2019-02-20Bibliographically approved
3. Modelling of the track supports with elements over elastic foundation together with dynamic internal degrees of freedom
Open this publication in new window or tab >>Modelling of the track supports with elements over elastic foundation together with dynamic internal degrees of freedom
2018 (English)In: Proceedings of ISMA 2018 - International Conference on Noise and Vibration Engineering and USD 2018 - International Conference on Uncertainty in Structural Dynamics2018, Pages 3255-326828th International Conference on Noise and Vibration Engineering, ISMA 2018 and 7th International Conference on Uncertainty in Structural Dynamics, USD 2018; Leuven; Belgium; 17 September 2018 through 19 September 2018 / [ed] W. Desmet, B. Pluymers, D. Moens, W. Rottiers, KU Leuven - Departement Werktuigkunde , 2018, p. 3255-3268Conference paper, Published paper (Refereed)
Abstract [en]

Formulation of the Timoshenko elements is improved with the use of internal degrees of freedom (iDOF) representing the local displacements, leading to a new finite element approach specially devoted to the numeric analysis of the track dynamics. The dynamic formulation of the local displacement is proved to correct the frequency content of the track model. Regarding time domain studies, this approach avoids the displacement underestimation and shear discontinuity between elements, which are sources of inaccuracies and irregular behaviour.  Those rail sections located above the supports are modelled with Timoshenko element over elastic foundation (TEEF), and the rest with conventional Timoshenko elements (TIM4). By using TEEF prompt disruption of the contact force at support surpassing is avoided, and the frequency response of the track around the `pinned-pinned' frequency is corrected. Moreover the TEEF formulation is extended in order to account for the sleeper pitch rotation, and evaluation of its influence over the track dynamics is performed. 

Place, publisher, year, edition, pages
KU Leuven - Departement Werktuigkunde, 2018
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-244300 (URN)2-s2.0-85060393553 (Scopus ID)9789073802995 (ISBN)
Conference
Leuven; Belgium; 17 September 2018 through 19 September 2018
Note

QC 20190220

Available from: 2019-02-18 Created: 2019-02-18 Last updated: 2019-02-20Bibliographically approved
4. Assessment of the influence of railway track periodicity, load speed and support modelling on the rolling noise emission
Open this publication in new window or tab >>Assessment of the influence of railway track periodicity, load speed and support modelling on the rolling noise emission
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The presented methodology jointly accounts for the railway track periodicity and the moving load nature at noise predictions. This modelling approaches rail and sleepers employing the Timoshenko beam theory, and it is formulated to be directly implemented into noise software based on irregularity strip technique. By means of precalculated time domain responses with an analytical track model, the periodicity and moving track dynamics are addressed. In the same way, the propagative behaviour in moving conditions of waves along the rail is characterised by comparison of the responses at several positions.Regarding track support modelling, the usual point modelling is substituted by a distributed representation in order to explore the advantages of accounting for the support length. A numerical model fulfils this task and avoids boundary effects utilising infinite elements. Distributed modelling achieves a more realistic representation of the track geometry. It prevents exaggeration of the amplitude at the `pinned-pinned' frequencies without resorting to overestimation of the steel loss factors. This improvement is especially useful when overvalued rail damping leads to predicted track decay rate (TDR) higher than the one experimentally measured.Finally, the impact of periodicity, load speed and support modelling are assessed through the sound power level (SWL) results.  The predictions are performed with a software package, CRoNoS (CAF Rolling Noise Software), developed by CAF S.A. Moving conditions has a limited impact on the SWL, while modelling of the foundation as periodic is important at tracks with hard pad types, and distributed support modelling becomes significant when realistic values of the steel loss factor are used.

Keywords
Rolling noise, Moving load, Periodic foundation, Distributed support, Steel loss factor
National Category
Mechanical Engineering
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-244296 (URN)
Note

QC 20190220

Available from: 2019-02-18 Created: 2019-02-18 Last updated: 2019-02-20Bibliographically approved

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