Ifsttar PhD subject

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Title : Contribution to the dynamical optimization of design of switches and crossings

Main host Laboratory - Referent Advisor   -

Director of the main host Laboratory   -

PhD Speciality mécanique numérique

Axis of the performance contract 2 - COP2017 - More efficient and resilient infrastructure

Main location Marne-la-Vallée

Doctoral affiliation UNIVERSITE PARIS-EST

PhD school SCIENCES, INGENIERIE ET ENVIRONNEMENT (SIE)

Planned PhD supervisor BOURGEOIS Emmanuel  -  Université Gustave Eiffel  -  COSYS - IMSE

Planned financing Thèse CIFRE   - ESI Group

Abstract

Switches and crossings (S&C or turnout) are railway devices providing support and guidance for rolling stock on a given route when other routes diverge or cross it. They are an important and fragile element in railway networks, and the wheel-rail contact is more complicated there than on a plain rail. The object of the presented work is the development of digital tools having in common to contribute to the mechanical optimization of S&C.
To process the vehicle/track interaction in a turnout, an approach developed by the host laboratory consists of a co-simulation between the «in house » railway dynamics code, called VOCO [1], and a third-party finite element software modelling the track. With this approach, called ‘IVOIE4’, the duration of a simulation can be of the order of one day. In this thesis, we developed a new approach, called ‘IVOIE5’, to deal with vehicle / track interaction more quickly. The new approach consists in avoiding frequent inputs / outputs in the co-simulation process by computing the track response directly in VOCO, using elementary matrices imported from the finite element software. The new approach has been tested with complex geometries: results show a good agreement between both approaches and a significant reduction of computation time.
During the thesis, an international Benchmark on the simulation of the passing of a turnout was organized by the Universities of Huddersfield (UK) and Chalmers (Sweden) between 2020 and 2021. In total, 19 teams participated in the benchmark, and 9 softwares have been used. In order to meet the Benchmark specifications, a mobile track model was implemented in VOCO: it allows very fast simulations, and will facilitate the development of new contact methods in VOCO. Besides, the modelling of the check rail was improved for the purposes of the benchmark. The results of VOCO are in good agreement with the average trend of those of the other participants.
Four participants of the benchmark then extended their work by substituting a 3D finite element model of the turnout for the mobile model. This allowed the ‘IVOIE4’ and ‘IVOIE5’ approaches to be compared to other approaches. Results obtained with VOCO are again consistent with those of the other participants.
In order to take into account the multiplicity of input parameters which have an influence on the dynamic response of an ADV, the Proper Generalized Decomposition (PGD) [2] was implemented for the first time in the context of railway dynamics, at least in a non-intrusiveway, in partnership with ENSAM/ESI Group Chair. One of the advantages of the PGD method is to treat a multivariate parametric problem as a series of one-dimensional sub problems. Thus, the method makes it possible to circumvent the "curse of dimensionality", and to take into account parameters generally not considered in design or maintenance. The resulting reduced model can be easily manipulated, which makes it possible to progress in the optimization of the dynamic design of turnouts.
Finally, we discuss a new approach for the search for the contact point between the wheel and the rail, in the case of variable profiles of the rail: the wheel can touch the rail ahead or behind the median plane of the wheel. The new procedure makes it possible to obtain a more realistic trajectory of the wheel, resulting in more realistic peaks of contact forces, while keeping the same calculation time.
The three developments carried out (‘IVOIE5’, PGD, 3D contact approach) should make it possible in the future to facilitate the optimization of S&Cs. The participation in the benchmark made it possible to make comparisons with the other multibody approaches of dynamic simulations of S&Cs, and to verify the relevance of our approach.

Keywords : Switch and Crossing (S&C), Wheel-rail contact, Railway dynamics, Finite element, Track model, Proper generalized decomposition (PGD), Contact point, Benchmark

Main host Laboratory - Referent Advisor	-
Director of the main host Laboratory	-
PhD Speciality	mécanique numérique
Axis of the performance contract	2 - COP2017 - More efficient and resilient infrastructure
Main location	Marne-la-Vallée
Doctoral affiliation	UNIVERSITE PARIS-EST
PhD school	SCIENCES, INGENIERIE ET ENVIRONNEMENT (SIE)
Planned PhD supervisor	BOURGEOIS Emmanuel - Université Gustave Eiffel - COSYS - IMSE
Planned financing	Thèse CIFRE - ESI Group
Abstract Switches and crossings (S&C or turnout) are railway devices providing support and guidance for rolling stock on a given route when other routes diverge or cross it. They are an important and fragile element in railway networks, and the wheel-rail contact is more complicated there than on a plain rail. The object of the presented work is the development of digital tools having in common to contribute to the mechanical optimization of S&C. To process the vehicle/track interaction in a turnout, an approach developed by the host laboratory consists of a co-simulation between the «in house » railway dynamics code, called VOCO [1], and a third-party finite element software modelling the track. With this approach, called ‘IVOIE4’, the duration of a simulation can be of the order of one day. In this thesis, we developed a new approach, called ‘IVOIE5’, to deal with vehicle / track interaction more quickly. The new approach consists in avoiding frequent inputs / outputs in the co-simulation process by computing the track response directly in VOCO, using elementary matrices imported from the finite element software. The new approach has been tested with complex geometries: results show a good agreement between both approaches and a significant reduction of computation time. During the thesis, an international Benchmark on the simulation of the passing of a turnout was organized by the Universities of Huddersfield (UK) and Chalmers (Sweden) between 2020 and 2021. In total, 19 teams participated in the benchmark, and 9 softwares have been used. In order to meet the Benchmark specifications, a mobile track model was implemented in VOCO: it allows very fast simulations, and will facilitate the development of new contact methods in VOCO. Besides, the modelling of the check rail was improved for the purposes of the benchmark. The results of VOCO are in good agreement with the average trend of those of the other participants. Four participants of the benchmark then extended their work by substituting a 3D finite element model of the turnout for the mobile model. This allowed the ‘IVOIE4’ and ‘IVOIE5’ approaches to be compared to other approaches. Results obtained with VOCO are again consistent with those of the other participants. In order to take into account the multiplicity of input parameters which have an influence on the dynamic response of an ADV, the Proper Generalized Decomposition (PGD) [2] was implemented for the first time in the context of railway dynamics, at least in a non-intrusiveway, in partnership with ENSAM/ESI Group Chair. One of the advantages of the PGD method is to treat a multivariate parametric problem as a series of one-dimensional sub problems. Thus, the method makes it possible to circumvent the "curse of dimensionality", and to take into account parameters generally not considered in design or maintenance. The resulting reduced model can be easily manipulated, which makes it possible to progress in the optimization of the dynamic design of turnouts. Finally, we discuss a new approach for the search for the contact point between the wheel and the rail, in the case of variable profiles of the rail: the wheel can touch the rail ahead or behind the median plane of the wheel. The new procedure makes it possible to obtain a more realistic trajectory of the wheel, resulting in more realistic peaks of contact forces, while keeping the same calculation time. The three developments carried out (‘IVOIE5’, PGD, 3D contact approach) should make it possible in the future to facilitate the optimization of S&Cs. The participation in the benchmark made it possible to make comparisons with the other multibody approaches of dynamic simulations of S&Cs, and to verify the relevance of our approach.
Keywords :	Switch and Crossing (S&C), Wheel-rail contact, Railway dynamics, Finite element, Track model, Proper generalized decomposition (PGD), Contact point, Benchmark

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