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  • 1.
    Liu, Zhendong
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Measures to Enhance the Dynamic Performance of Railway Catenaries2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The pantograph-catenary system is used in railways to transfer electric power from infrastructure to trainset. As the pantograph slides against the catenary, the contact between the two surfaces is not stable due to stiffness variation, propagating wave and other environmental perturbation, especially at high speeds or in multi-pantograph operation. Heavy oscillation can result in poor power-transmission quality, electromagnetic interference, severe wear or even structural damage. So the pantograph-catenary dynamics has become one of the key issues which limits the operational speed and determines the maintenance cost. There are many types of catenary systems in Sweden, which are relatively soft and sensitive compared with the systems in other countries. They work well at low operational speed and have strict limitations to multi-pantograph operation. It is possible to achieve an operational speed of 350 km/h on newly-built high-speed lines, but there is still a large demand for higher operational speed and more capacity on the existing lines.

        Many researchers and engineers have made progress to improve its dynamic performance. From the research aspect, many numerical models have been built up to demonstrate the dynamics of the pantograph-catenary system and to unveil the key influencing factors. There have been many applications developed in recent years. Regarding the catenary, high-tensile loads on the catenary and low-stiffness-variation designs are widely used to improve the dynamic performance. Regarding the pantograph, aerodynamic-friendly designs and active-control technique contribute to the development of high-speed pantograph. But all these methods need not only large investment but long out-of-service. Considering the large scale and heavy service duty of the existing lines, it becomes almost impossible to completely upgrade the existing pantograph-catenary systems. So it is necessary to find practical and efficient methods to exploit the potentials of the existing systems to enhance their dynamic performances.

        This thesis investigates the dynamic behaviour of the Swedish pantograph-catenary systems and proposes methods for better usage. A numerical study on multi-pantograph operation is performed and the relationships between dynamic performance and some key parameters is established. By studying the multi-pantograph operation at short spacing distance, a method to use the leading pantograph as auxiliary pantograph is proposed to increase the operational speed on the soft catenary system. To ensure operational safety in abnormal conditions, numerical studies on pantograph raising/lowering processes and in catenary overlap sections are performed. By studying the influence of the lumped-mass on the dynamic performance, it shows that it is even possible to implement some artificial tuned-masses on the catenary for dynamic optimization.

  • 2.
    Liu, Zhendong
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Numerical study on multi-pantograph railway operation at high speed2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Multi-pantograph operation allows several short electric multiple unit (EMU) trainsets to be coupled or decoupled to adapt to daily or seasonal passenger-flow variation. Although this is a convenient and efficient way to operate rolling stock and use railway infrastructure, pantographs significantly influence each other and even significantly change the dynamic behaviour of the system compared to single-pantograph operation in the same condition. The multi-pantograph system is more sensitive and vulnerable than the single-pantograph system, especially at high operational speeds or with pantographs spaced at short distances. Heavy oscillation in the system can result in low quality of current collection, electromagnetic interference, severe wear on the contact surfaces or even structural damage. The mechanical interaction between the pantograph and the catenary is one of the key issues which limits the maximum operational speed and decides the maintenance cost.

        Many researchers have paid a lot of attention to the single-pantograph operation and have made great progress on system modelling, optimizing, parameter studies and active control. However, how the pantographs in a train configuration affect each other in multi-pantograph operation and which factors limit the number of pantographs is not fully investigated. Nowadays, to avoid risking operational safety, there are strict regulations to limit the maximum operational speed, the maximum number of pantographs in use, and the minimum spacing distance between pantographs. With the trend of high-speed railways, there are huge demands on increasing operational speed and shortening spacing distance between pantographs. Furthermore, it is desirable to explore more practical and budget-saving methods to achieve higher speed on existing lines without significant technical modification.

        In addition to a literature survey of the dynamics of pantograph-catenary systems, this thesis carries out a numerical study on multi-pantograph operation based on a three-dimensional pantograph-catenary finite element (FE) model. In this study, the relationship between dynamic performance and other parameters, i.e. the number of pantographs in use, running speed and the position of the pantographs, are investigated. The results show that the spacing distance between pantographs is the most critical factor and the trailing pantograph does not always suffer from deterioration of the dynamic performance. By discussing the two-pantograph operation at short spacing distances, it is found that a properly excited catenary caused by the leading pantograph and the wave interference between pantographs can contribute to an improvement on the trailing pantograph performance. To avoid the additional wear caused by poor dynamic performance on the leading pantograph and achieve further improvement at high speeds, it is suggested to use the leading pantograph as an auxiliary pantograph, which does not conduct any electric current and optimize the uplift force on the leading pantograph. After a brief discussion on some system parameter deviations, it is shown that a 30% of speed increase should be possible to achieve while still sustaining a good dynamic performance without large modifications on the existing catenary system.

  • 3.
    Liu, Zhendong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Jönsson, Per-Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Rønnquist, Anders
    Dep artment of Structural Engineering, NTNU Norwegian University of Science and Technology, Norway.
    Implications of the operation of multiple pantographs on the soft catenary systems in Sweden2015In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 53, no 3, p. 341-346Article in journal (Refereed)
    Abstract [en]

    Trains operating with several pantographs are used in Sweden and other countries. The more complex operational conditions, however, cause additional difficulties, i.e. low quality of current collection, increased mechanical wear and electromagnetic interference, due to the poor dynamic behaviour of the system. In order to address these problems, a three-dimensional model for the computational analysis of the interaction between catenary and pantograph is presented and validated in this paper, and the dynamic behaviour of the multi-pantograph system, based on Swedish soft pantograph/catenary systems, is analysed. Parametric studies are performed to investigate cases with different distances between pantographs and with up to three pantographs in use. The relationship between dynamic performance and other parameters, i.e. the number of pantographs in use, running speed and the position of the pantographs, is studied. The results show that an appropriate distance between pantographs and a given type of catenary allow operation on the existing infrastructure with up to three pantographs while maintaining an acceptable dynamic performance at the desired speed.

  • 4.
    Liu, Zhendong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Jönsson, Per-Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Rønnquist, Anders
    Dep artment of Structural Engineering, NTNU Norwegian University of Science and Technology, Norway.
    Possible speed increase on soft catenary system with help of auxiliary pantograph2016In: The Dynamics of Vehicles on Roads and Tracks - Proceedings of the 24th Symposium of the International Association for Vehicle System Dynamics, IAVSD 2015, CRC Press, 2016, no 3, p. 927-936Conference paper (Refereed)
    Abstract [en]

    Stiffness variations and wave propagation in the catenary system cause high dynamic variations in the contact force between pantograph and catenary at high operating speeds. In order to increase the operational speed on an existing catenary system, especially on soft catenary systems, technical upgrading is usually required to keep the current collection quality within an acceptable range. Therefore, it is desirable to explore a more practical and costsaving method to achieve higher operational speed. With the help of a 3D pantograph-catenary finite element (FE) model, a parametric study on two-pantograph operation at short spacing distances is carried out. Results show that although the leading pantograph suffers from deterioration of dynamic performance, the trailing pantograph achieves a better dynamic behaviour by using a proper spacing distance between pantographs. To avoid the additional wear caused by poor dynamic performance on the leading pantograph, it is suggested to use the leading pantograph as an auxiliary pantograph, which does not conduct any electric current. In this way, the operational speed of the existing system can be increased while still sustaining a good dynamic performance without large modifications on the existing catenary system.

  • 5.
    Liu, Zhendong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Jönsson, Pär-Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Ronnquist, Anders
    On the implementation of an auxiliary pantograph for speed increase on existing lines2016In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 54, no 8, p. 1077-1097Article in journal (Refereed)
    Abstract [en]

    The contact between pantograph and catenary at high speeds suffers from high dynamic contact force variation due to stiffness variations and wave propagation. To increase operational speed on an existing catenary system, especially for soft catenary systems, technical upgrading is usually necessary. Therefore, it is desirable to explore a more practical and cost-saving method to increase the operational speed. Based on a 3D pantograph–catenary finite element model, a parametric study on two-pantograph operation with short spacing distances at high speeds shows that, although the performance of the leading pantograph gets deteriorated, the trailing pantograph feels an improvement if pantographs are spaced at a proper distance. Then, two main positive effects, which can cause the improvement, are addressed. Based on a discussion on wear mechanisms, this paper suggests to use the leading pantograph as an auxiliary pantograph, which does not conduct any electric current, to minimise additional wear caused by the leading pantograph. To help implementation and achieve further improvement under this working condition, this paper investigates cases with optimised uplift force on the leading pantograph and with system parameter deviations. The results show that the two positive effects still remain even with some system parameter deviations. About 30% of speed increase should be possibly achieved still sustaining a good dynamic performance with help of the optimised uplift force.

  • 6.
    Liu, Zhendong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Rønnquist, A.
    Application of tuned-mass system on railway catenary to improve dynamic performance2018In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 165, p. 349-358Article in journal (Refereed)
    Abstract [en]

    Finding a simple and practical method to improve the dynamic behaviour of a specific structure is always desirable in civil and mechanical engineering. The railway catenary system is the overhead power line above the track, interacting together with the train-based pantograph to transfer electric power. Due to vertical stiffness variation and a propagating wave along the catenary, the fluctuation of the contact force becomes significant with operational speed increasing. Therefore, this has become one of the key factors which limits the operational speed and service life of key components. Wire misalignment, structural errors and uneven mass distribution of the catenary can further deteriorate the contact stability. In order to achieve a higher speed on existing lines, the catenary needs large-scale modification implying long out-off-service time. From the designing aspect, all components directly fixed to the catenary, like clamps, steady arms and other fittings, are made as light and small as possible to minimize disturbances. However, in other engineering applications, some well-designed additional mass systems are adopted aiming to improve their dynamic performance. In order to take advantage of these unavoidable masses on the catenary, an investigation on lumped-mass distribution in single-pantograph and multi-pantograph operations is performed with help of a 3D pantograph-catenary finite element (FE) model. The results show that a rightly-tuned mass, here the implementing location and the elasticity of its connection, can positively change the dynamic performance without implementing large-scale modification to the existing system. Through a brief discussion on the mechanism of this positive effect, this paper proposes that applying some artificial tuned-mass system can be a possible method to overcome unfavourable working conditions or even allow speed increase on existing lines.

  • 7.
    Liu, Zhendong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Rønnquist, Anders
    NTNU Norwegian University of Science and Technology.
    Application of tuned-mass system on railway catenary to improve dynamic performanceIn: Article in journal (Other academic)
    Abstract [en]

    Finding a simple and practical method to improve the dynamic behaviour of a specific structure is always desirable in civil and mechanical engineering. The railway catenary system is the overhead power line above the track, interacting with the train-based pantograph to transfer electric power. Due to vertical stiffness variation and a propagating wave along the catenary, the fluctuation of the contact force becomes significant with operational speed increasing. Therefore, this has become one of the key factors which limits the operational speed and service life of key components. Wire misalignment, structural errors and uneven mass distribution of the catenary can further deteriorate the contact stability. In order to achieve a higher speed on existing lines, the catenary needs large-scale modification implying long out-off-service time. From the designing aspect, all components directly fixed to the catenary, like clamps, steady arms and other fittings, are made as light and small as possible to minimize disturbances. However, in other engineering applications, some well-designed additional mass systems are adopted aiming to improve their dynamic performance. In order to take advantage of these unavoidable masses on the catenary, an investigation on lumped-mass distribution in single-pantograph and multi-pantograph operations is performed with help of a 3D pantograph-catenary finite element (FE) model. The results show that a rightly-tuned mass, here the implementing location and the elasticity of its connection, can positively change the dynamic performance without implementing large-scale modification to the existing system. Through a brief discussion on the mechanism of this positive effect, this paper proposes that applying some artificial tuned-mass system can be a possible method to overcome unfavourable working conditions or even allow speed increase on existing lines.

  • 8.
    Liu, Zhendong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Rønnquist, Anders
    NTNU Norwegian University of Science and Technology.
    Dynamic optimization of railway catenary system by turning unwanted lumped-mass into tuned-mass2018In: Dynamic optimization of railway catenary system by turning unwanted lumped-mass into tuned-mass, CRC Press/Balkema , 2018, Vol. 2, p. 675-680Conference paper (Refereed)
    Abstract [en]

    The railway catenary is suspended to its supports with droppers, clamps and oth-er fittings. These lumped-masses are made light and small to minimize disturbances. The mass-es cannot be completely removed but can be adjusted during maintenance. In other technical systems, artificial mass is used to improve the dynamic behaviour. Therefore, in this study the relationship between the lumped-mass distribution and its dynamic behaviour is investigated. Based on a 3D pantograph-catenary finite element (FE) model, a parametric study on the lumped-mass distribution on the Swedish soft catenary system is performed by applying addi-tional lumped-mass to different positions. It is shown that the mass distribution affects the dy-namic performance and in some cases, can improve the dynamic performance. The influence becomes stronger in multi-pantograph operation. Installing these masses on the messenger wire can avoid hard-point effects. In this way, the artificial mass can be used to improve the dynamic performance or correct some structural defects.

  • 9.
    Liu, Zhendong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Rønnquist, Anders
    Dep artment of Structural Engineering, NTNU Norwegian University of Science and Technology, Norway.
    Numerical study on pantograph raising and lowering in multi-pantograph operationIn: The international Journal of railway technology, ISSN 2049-5358, E-ISSN 2053-602X, no 3Article in journal (Other academic)
    Abstract [en]

    Multi-pantograph operation is a convenient and efficient way to operate railway rolling stock, but the influence between the pantographs makes the system more sensitive and vulnerable than a single-pantograph system. When a train passes through special sections or in an emergency condition, it is necessary to lower one or all of the pantographs and then raise them up again. In these circumstances, the motion of the pantographs can introduce a sudden impact to the catenary that may change the pantograph configuration, then disrupting the dynamic stability. To address the dynamic performance during pantograph raising and lowering, a numerical study on multi-pantograph operation is carried out with help of a 3D pantograph-catenary finite element (FE) model under the conditions: up to three pantographs, various pantograph raising/lowering orders and different operating positions in a span. The results show that the leading pantograph is little influenced by the raising and lowering movement of any pantograph behind it. However, any trailing pantograph is significantly affected by any operation taking place ahead of it. The dynamic performance of the system depends on the pantograph spacing distance and the operational speed, but is little affected by the operating position in a span. To study auxiliary-pantograph operation where the leading pantograph works as an auxiliary pantograph, this paper shows how an optimal setting of the leading pantograph benefits the trailing pantograph and suggests specifying the speed where the leading pantograph gets into or out of service to avoid disruption.

  • 10.
    Liu, Zhendong
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Stichel, SebastianKTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.Rønnquist, AndersNTNU Norwegian University of Science and Technology.
    The influence of pantograph raising and lowering on multi-pantograph operation2016Conference proceedings (editor) (Refereed)
    Abstract [en]

    Multi-pantograph operation is widely used in many countries. Although it is a convenient and efficient way to operate railway rolling stock and infrastructure, the multi-pantograph system becomes more sensitive and vulnerable than the singlepantograph system. When trains pass through special sections or in emergency conditions, it is necessary to lower one or all of the pantographs intentionally or unintentionally. In these circumstances, the motion of the pantographs introduces a sudden impact to the catenary and the dynamic stability is therefore disrupted. To address the dynamic performance during pantograph raising and lowering, a parametric study on multi-pantograph operation with various pantograph raising/lowering orders and different positions in span has been carried out using a 3D pantograph-catenary finite element (FE) model. The results show that the leading pantograph is little influenced by the raising and lowering movement of any pantograph behind it. For every trailing pantograph, the motion of any pantograph ahead of it not only introduces an impact into the system but also significantly changes the dynamic behaviour by the new configuration of the pantograph combination. The dynamic performance is only to a small extent determined by the position where the motion takes places. This paper shows that it is necessary to define the speed range where an auxiliary pantograph can join or leave the operating system to avoid disrupting the operation of the trailing pantograph.

  • 11.
    Zhendong, Liu
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Anders, Rønnquist
    NTNU Norwegian University of Science and Technology.
    Numerical Study on the Dynamic Behaviour of Railway Catenary Overlap Section for Higher Speed2017Conference paper (Refereed)
    Abstract [en]

    The dynamic behaviour in the contact between pantograph and catenary decides the quality of power transmission, the component service life and the maximum operational speed. The catenary system is desired to be built smooth and uniform in geometry and elasticity along the train-running direction, but due to electric concerns and tensile force retention, the entire catenary is made up by many tensioning sections. To make a pantograph smoothly shift between the neighbouring sections, an overlap of several spans is introduced to work as a transition zone. However, when the pantograph is passing through the overlap section, its dynamic behaviour can be heavily changed and cannot sustain as good contact as in the middle spans of each tensioning section. To clarify the dynamic behaviour in this special section and to ensure a stable contact between pantograph and catenary, a numerical study on catenary section overlap is performed based on a 3D pantograph-catenary finite element (FE) model. The following issues are discussed in this paper: operational speed, wire gradient, damping ratio, and spacing distance in multi-pantograph operation. The results show that the gradient of wires in overlap sections and the damping ratio have great influence on the dynamic performance, especially at high speed and in multi-pantograph operation. In practice, in the overlap section the gradient should be properly designed and some additional damping is beneficial to ensure good dynamic performance for higher speed.  

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