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  • 1.
    Andersson, Evert
    et al.
    KTH, Superseded Departments, Vehicle Engineering.
    Haggstrom, J
    Sima, M
    Stichel, Sebastian
    KTH, Superseded Departments, Vehicle Engineering.
    Assessment of train-overturning risk due to strong cross-winds2004In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 218, no 3, p. 213-223Article in journal (Refereed)
    Abstract [en]

    This paper describes the methodology for safety assessment related to the risk of a train overturning in strong cross-winds. As an example, this methodology is applied on the high-speed line Botniabanan being built for a maximum speed of 250 km/h in the northeast coastal region of Sweden. The process starts with a systematic identification of locations along the line having a potential high risk of overturning due to cross-winds. This is followed by a cross-disciplinary study. The first step is to estimate the probabilities of wind velocity and wind directions. The next step is aerodynamic computation of overturning forces and moments acting on relevant types of train. Further, the critical overturning wind velocity is determined by a multi-body simulation technique. Finally, the overturning accident frequency is calculated. The calculated risk is compared with generally accepted risk levels in modern train operation.

  • 2. Bhiwapurkar, M. K.
    et al.
    Saran, V. H.
    Harsha, S. P.
    Goel, V. K.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Effect of magnitudes and directions (mono-axis and multi-axis) of whole body-vibration exposures and subjects postures on the sketching performance2011In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 225, no F1, p. 71-83Article in journal (Refereed)
    Abstract [en]

    Whole-body vibrations in trains are known to affect the performance of sedentary activities such as reading, writing, sketching, working on a computer, etc. The objective of the study was to investigate the extent of disturbance perceived in sketching task by seated subjects in two postures under mono-and multi-axis Gaussian random vibration environment. The study involved 21 healthy male subjects in the age group of 23-32 years. Random vibrations were generated both in mono-and multi-axial directions in the frequency range of 1-10 Hz at 0.5, 1.0, and 1.5 m/s(2) rms (root mean square) amplitude. The subjects were required to sketch given geometric figures such as a circle, triangle, rectangle, and square with the help of ball-point pen under given vibration stimuli in two postures (sketch pad on lap and sketch pad on table). The deviation in distortion with respect to the given figure is represented in terms of percentage distortion. The influence of vibrations on the sketching activity was investigated both subjectively and by two specifically designed objective methods, namely, RMS (root mean square methodology) and area methods. The judgements of perceived difficulty to sketch were rated using seven-point semantic judgement scale. The percentage distortion and difficulty in sketching activity increased with an increase in vibration magnitude. Both subjective evaluation and the RMS method revealed that the task was affected more while sketching on the table. The percentage distortion was affected similarly and maximum in all the vibration directions except for the vertical, while sketching difficulty was found to be higher only with longitudinal and multi-axis vibration direction. The subjective evaluation also revealed that there was no effect of the type of entity chosen on the sketching difficulty.

  • 3.
    Brabie, Dan
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology.
    Andersson, Evert
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology.
    On minimizing derailment risks and consequences for passenger trains at higher speeds2009In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 223, no 6, p. 543-566Article in journal (Refereed)
    Abstract [en]

    The first part of this article deals with the possibility of preventing wheel climbing derailments after an axle journal failure by implementing mechanical restrictions between the wheelsets and the bogie. A multi-body system (MBS) computer model is developed to account for such an axle failure condition, which is successfully validated by comparing the pre-derailment sequence of events with two authentic cases. An extensive parameter analysis on the maximum vertical and longitudinal play between the wheelset and the bogie, required to prevent a highspeed power or trailer car to derail, is performed for various combinations of running conditions in curves. Once an actual derailment has Occurred on conventional passenger trains at 200 km/h, extensive MBS simulations are performed on the feasibility of utilizing alternative substitute guidance mechanisms, such as low-reaching parts of bogie frame, axle box, or brake disc, as means of minimizing the lateral deviation. Results are presented in terms of geometrical parameters that lead to a successful engagement with the rail for a total of 12 different derailment scenarios. These are caused by an axle journal failure, an impact with a small object on the track, or a high rail failure. Minimizing the lateral deviation is also investigated by means of restraining the maximum Coupler yaw angle and altering the bogie yaw stiffness. Time-domain simulations are also performed in terms of lateral track forces and derailment ratio when negotiating a tight horizontal 'S-curve'. Further, the articulated train concept is investigated in terms of the post-derailment vehicle behaviour after derailments on tangent and curved track at a speed of 200 km/h. In this respect, a trainset consisting of one power car and four articulated passenger trailer cars is modelled in the MBS software. Results in terms of lateral deviation and maximum carbody roll angle are presented as a function of different inter-carbody damper characteristics and running gear features. The feasibility of these damper characteristics is also tested in terms of lateral track forces and derailment ratio when negotiating a tight horizontal S-curve.

  • 4.
    Casanueva, Carlos
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology.
    Alonso, Asier
    CEIT and TECNUN, University of Navarra, Spain.
    Eziolaza, Ibon
    R&D Department, Construcciones y Auxiliar de Ferrocarriles, S.A., Spain.
    Giménez, José Germán
    TECNUN, University of Navarra and R&D Department, Construcciones y Auxiliar de Ferrocarriles, S.A., Spain.
    Simple flexible wheelset model for low-frequency instability simulations2014In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, no 2, p. 169-181Article in journal (Refereed)
    Abstract [en]

    As a general rule, the multi-body simulation models used by railway vehicle designers consider the wheelsets to be fully rigid, thus leading to possible errors when calculating the critical speed of the vehicle under study. This article suggests a wheelset model that takes into account wheelset flexibility for the study of dynamic stability. The model is simple to implement, easily parameterised, and can be applied to both conventional and variable gauge wheelsets. The parameters corresponding to wheelset flexibility that most influence the critical speed of high-speed and variable gauge vehicles are also analysed.

  • 5.
    Casanueva, Carlos
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Enblom, Roger
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    On integrated wheel and track damage prediction using vehicle-track dynamic simulations2017In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 231, no 7, p. 775-785Article in journal (Refereed)
    Abstract [en]

    The renewal costs for wheels and rails are a substantial part of the costs for rolling stock operators and infrastructure managers all over the world. The causes for reprofiling or grinding are, in most cases, related to the following: (1) wheel or rail profiles with unacceptable wear, (2) appearance of rolling contact fatigue cracks in the surface, and (3) wheel flats caused by locking wheels during braking. The first two causes are related to the dynamic behavior of the vehicle-track system, and can be predicted using multibody simulations. However, there are several limitations that restrain the usefulness of these prediction techniques, such as simulation time constraints, necessary simplifications, and lack of experimental data that lead to educated assumptions. In this paper, we take the end-user perspective in order to show whether the latest developments in wheel-rail damage prediction can be integrated in a simplified framework, and subsequently used by the different stakeholders for an improved management of the different assets involved in the operation of rail vehicles.

  • 6.
    Cha, Yingying
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Abbasi, Saeed
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Indoor and outdoor measurement of airborne particulates on a commuter train running partly in tunnels2018In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 232, no 1, p. 3-13Article in journal (Refereed)
    Abstract [en]

    Wear processes from mechanical braking, rail/wheel contact, the railway electrification system and re-suspended materials due to the turbulence of passing trains in tunnels and stations have been suggested to be the main contributors to particulate matter levels inside trains. In this study, onboard monitoring was performed on a commuter train stopping at underground and aboveground stations. The concentration and size distribution of particulates were monitored for both indoor and outdoor levels. The results show that the levels of PM10 and PM2.5 inside the train were about one-fifth of the outdoor levels. Significant increases in indoor particulate number concentrations were observed in tunnel environments and there was a slight increase when the doors were open. Differences in the size distributions of micro- and nano-sized particulates could be identified for different tunnels.

  • 7. Diedrichs, Ben
    On computational fluid dynamics modelling of crosswind effects for high-speed rolling stock2003In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 217, no 3, p. 203-226Article in journal (Refereed)
    Abstract [en]

    This work addresses crosswind stability exemplified for the German Railway Deutsche Bahn AG high-speed train ICE 2. The scope of the work is to describe the flow by means of computational fluid dynamics past the leading two cars of the train for yaw angles in the range 12.2-40.0degrees. Three track formations are utilized. The basic results are the set of independent aerodynamic coefficients for the lead and subsequent cars. The results are to some extent compared with experimental data for ICE 2 and also with data obtained for the Swedish high-speed train X2000.

    A numerical sensitivity study is undertaken to quantify differences in the above results dependent on the grid density and quality, turbulence model, numerical scheme, location of inlet and outlet boundaries, turbulence intensity and flow simulation software.

  • 8.
    Diedrichs, Ben
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology.
    Stichel, S.
    Krajnovic, S.
    Vehicle dynamics of a high-speed passenger car due to aerodynamics inside tunnels2007In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 221, no 4, p. 527-545Article in journal (Refereed)
    Abstract [en]

    High train speeds inside narrow double-track tunnels using light car bodies can reduce the ride comfort of trains as a consequence of the unsteadiness of the aerodynamics. This fact was substantiated in Japan with the introduction of the series 300 Shinkansen trains more than a decade ago, where the train speed is very high also in relatively narrow tunnels on the Sanyo line.

    The current work considers the resulting effects of vehicle dynamics and ride comfort with multi-body dynamics using a model of the end car of the German high-speed train ICE 2. The present efforts are different from traditional vehicle dynamic studies, where disturbances are introduced through the track only. Here disturbances are also applied to the car body, which conventional suspension systems are not designed to cope with.

    Vehicle dynamic implications of unsteady aerodynamic loads from a previous study are examined. These loads were obtained with large eddy simulations based on the geometry of the ICE 2 and Shinkansen 300 trains.

    A sensitivity study of some relevant vehicle parameters is carried out with frequency response analysis (FRA) and time domain simulations. A comparison of these two approaches shows that results which are obtained with the much swifter FRA technique are accurate also for sizable unsteady aerodynamic loads. FRA is, therefore, shown to be a useful tool to predict ride comfort in the current context.

    The car body mass is found to be a key parameter for car body vibrations, where loads are applied directly to the car body. For the current vehicle model, a mass reduction of the car body is predicted to be most momentous in the vicinity of 2 Hz.

  • 9. Diedrichs, Ben
    et al.
    Ekequist, M.
    Stichel, Sebastian
    Tengstrand, H.
    Quasistatic modelling of wheel-rail reaction due to crosswind effects for various types of high-speed rolling stock2004In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 218, no 2, p. 133-148Article in journal (Refereed)
    Abstract [en]

    This work describes a quasi-static tool developed to assess the performance swiftly of crosswind stability for three types of rolling stock with conventional, semi-trailer and Jacobs bogie running gear configurations. The prediction accuracy of the results returned by the tool for the quasistatic assumption is fair in comparison with results of more advanced multibody simulation software that is commercially available. The codes, which are based on steady equilibrium equations for the wheels and axles, bogie frames and vehicle body/bodies, handle arbitrarily canted embankments and circular curves. To a large extent the accuracy hinges on the bodies' lateral displacements relative to the contact points between the wheels and rails; therefore proper modelling of the suspension systems and bump stops are found to be important. Examples are given of the limitations associated with the quasi-static approach, studying the following: (a) the combined wind and track scenario in Deutsche Bahn AG's guideline, (b) the effects of typical track irregularities for high-speed transportation as a function of train speed and (c) the effects of oscillating crosswind. It has also been found relevant to demonstrate some of the large differences regarding provisions regulating crosswind safety. To this extent the present results are compared with those derived with the British Group Standard and also with results presented in the guideline of Deutsche Balm AG. In addition, examples are given of the differences found of the permissible crosswind speed using calculated (with CFD-RANS) and experimentally obtained aerodynamic loads.

  • 10. Diedrichs, Ben
    et al.
    Sima, M.
    Orellano, A.
    Tengstrand, H.
    Crosswind stability of high-speed train on a high embankment2007In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 221, no 2, p. 205-225Article in journal (Refereed)
    Abstract [en]

    This work presents aerodynamic results of crosswind stability obtained numerically and experimentally for the leading control unit (class 808) of Deutsche Bahn AG's high-speed train Inter-CityExpress 2. The train model is on top of a 6 m high embankment in accordance with the proposed European code for interoperable trains, the so-called technical specifications for interoperability. The purpose of the study is to convey the predictive accuracy that typical steady-state computational fluid dynamics-Reynolds average Navier-Stokes methods (industry standard) return and to contribute to the understanding of the aerodynamics for the current application.

    Attention is drawn to the aerodynamics around the train and embankment when subjected to a steady block profile crosswind of 30 degrees yaw angle on the basis of the onset velocity far upstream the embankment. The Re (Reynolds number) of the embankment cases is 4.6 x 10(6). Calculated results are obtained with the commercial code STAR-CD, with exclusively hexahedral meshes with a total cell count of 13.5 x 10(6). Results are obtained when the train stands on the windward and leeward tracks on top of the embankment. These results are first compared with a flat ground case from a previous study.

    Then experimental data are obtained in a high-pressure wind tunnel with a model scale of 1:100. Re effects are compensated by raising the ambient pressure by a factor of 60, which increases the air density and thus the Re by a similar factor. Calculated results are in fair agreement with the experiments, where both the calculations and the experiments predict the leeward case to be the more critical one.

    In addition, the related consequences on the mechanical behaviour, i.e. the stability of the car, are briefly addressed by means of a quasi-static mechanical analysis. The results of the present study indicate that the 6 m high embankment concerning the current train reduces the permissible crosswind speed with approximately 20 per cent.

  • 11. Dominguez, M.
    et al.
    Fernandez, A.
    Cucala, A. P.
    Lukaszewicz, Piotr
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Optimal design of metro automatic train operation speed profiles for reducing energy consumption2011In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 225, no F5, p. 463-473Article in journal (Refereed)
    Abstract [en]

    Trains equipped with automatic train operation (ATO) systems are operated between stations according to the speed commands they receive from balises. These commands define a particular speed profile and running time, with associated energy usage (consumption). The design of speed profiles usually takes into account running times and comfort criteria, but not energy consumption criteria. In this article, a computer-aided procedure for the selection of optimal speed profiles, including energy consumption, which does not have an effect on running times, is presented. To this end, the equations and algorithms that define the train motion and ATO control have been modelled and implemented in a very detailed simulator. This simulator includes four independent modules (ATO, motor, train dynamics, and energy consumption), an automatic generator of every possible profile and a graphical assistant for the selection of speed commands in accordance with decision theory techniques. The results have been compared with measured data in order to adjust and validate the simulator. The implementation of this new procedure in the Madrid underground has led to a 13 per cent of energy saving. As a result, the decision has been taken to redesign all the ATO speed profiles on this underground.

  • 12. Enblom, Roger
    Two-level numerical optimization of ride comfort in railway vehicles2006In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 220, no 1, p. 1-11Article in journal (Refereed)
    Abstract [en]

    This article addresses the interaction between and tuning of different mechanical subsystems in railway vehicle design. Application of numerical methods in a two-ievel optimization process, involving multi-body vehicle dynamics simulation and finite-element structural analysis, is proposed. The focus is on vibration ride comfort and tuning of dynamic properties of the vehicle, running gear, and carbody structure. As a background, a brief overview of multi-disciplinary and structural optimization methods is given. The selected solution based on the loosely coupled collaborative optimization approach, here implemented as a two-level structure, is presented. Numerical examples are provided to illustrate the choice of optimization algorithms suitable for this type of resonant systems and to demonstrate the performance of the numerical procedures on a realistic engineering problem. The leading coach of a three-car train-set is successfully optimized in terms of mass reduction and reduced natural frequency requirements, despite an infeasible initial design.

  • 13.
    Enblom, Roger
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Proposed procedure and trial simulation of rail profile evolution due to uniform wear2008In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 222, no 1, p. 15-25Article in journal (Refereed)
    Abstract [en]

    A procedure for numerical simulation of rail wear and the corresponding profile evolution has been formulated. The wear is assumed to be uniform in the sense that the profiles remain constant along the track portion to be investigated. A simulation set is selected defining the vehicles running on the track, their operating conditions, and contact parameters. Several variations of input data may be included together with the corresponding occurrence probability.

    Simulation of multi-body dynamics is used to calculate contact forces and positions, and Archard's wear equation is applied for the calculation of wear depth. Wear coefficients as a function of contact pressure and relative sliding velocity are collected from different test results.

    Trial calculations of four non-lubricated and two lubricated curves with radii from 303 to 802 m show qualitatively reasonable results in terms of profile shape development and difference in wear mechanisms between gauge corner and rail head. The wear rates related to traffic tonnage are, however, overestimated and the lubrication efficiency underestimated.

    It is expected that model refinements in terms of environmental influence and contact stress calculation are useful to improve the quantitative results.

  • 14.
    Gebretsadik, Elias Kassa
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Nielsen, Jens
    Chalmers University of technology.
    Ekh, Magnus
    Chalmers University of technology.
    Iwnicki, Simon
    Manchester Metropolitan University.
    Nicklisch, Dirk
    DB.
    Geometry and stiffness optimisation for switches & crossings, and simulation of material degradation2010In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 224, p. 279-292Article in journal (Refereed)
    Abstract [en]

    A methodology for simulatingwear, rolling contact fatigue, and plastic deformation for a mixed traffic situation in switches and crossings (S&C) has been developed. The methodology includes simulation of dynamic vehicle-track interaction considering stochastic variations in input data, simulation of wheel-rail contacts accounting for non-linear material properties and plasticity, and simulation of wear and plastic deformation in the rail during the life of the S&C component. To find means of improving the switch panel design, the geometry of a designed track gauge variation in the switch panel has been represented in a parametric way. For traffic in the facing and trailing moves of the through route, an optimum solution was identified and then validated by evaluating a wide set of simulation cases (using different wheel profiles). The optimum design includes a 12 mm maximum gauge widening. Several crossing geometries were investigated to find an optimal geometric design for the crossing nose and wing rails. The MaKuDe design showed the best performance for moderately worn wheel profiles in both running directions (facing and trailing moves). In connection with reduced support stiffness (e. g. elastic rail pads), this crossing design is predicted to lead to a significant reduction of impact loads and consequently provide a high potential of life-cycle cost reduction.

  • 15. Hardwick, Christopher
    et al.
    Lewis, Roger
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Low adhesion due to oxide formation in the presence of salt2014In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, no 8, p. 887-897Article in journal (Refereed)
    Abstract [en]

    This paper outlines work carried out to assess how, during winter months, adhesion may be influenced by contamination of the rail head by the salt/grit that is applied to road surfaces as a preventative method to stop ice formation. Twin-disc testing was carried out in which a mechanically formed oxide layer was produced on the disc specimens prior to assessing adhesion levels under realistic contact pressures and slips in the following conditions: dry, wet, dry salt and two salt/water solutions. Under dry conditions adhesion levels differ little from reference tests without an oxide layer, however, the presence of an oxide layer under wet conditions can be seen to further reduce adhesion from a reference level (0.2) to below 0.1. When salt is entrained into the contact it increases adhesion levels above that seen under wet conditions in the presence of an oxide layer, however, the presence of salt is most likely to affect the generation of rail head oxides in the first place and in turn influence adhesion.

  • 16. Harell, P.
    et al.
    Drugge, Lars
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Reijm, M.
    Study of critical sections in catenary systems during multiple pantograph operation2005In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 219, no 4, p. 203-211Article in journal (Refereed)
    Abstract [en]

    To improve the dynamic behaviour of a catenary system, the sections that limit the speed have to be found. A survey was made to gather information about critical sections of the catenary-pantograph system. Interviews with personnel at the Swedish National Rail Administration were performed and problem areas that need consideration were found and are presented. The purpose of this study was to find out how much of these critical sections affect the system and to suggest improvements to the design. Section overlaps and section insulators, both in combination with the usage of multiple pantographs, were modelled, and simulations have been performed at different speeds and for different catenary systems. As a result of this research, a better base could be built on how to ease the operation with multiple pantographs.

  • 17.
    Hossein Nia, Saeed
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Jönsson, Per-Anders
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Wheel damage on the Swedish iron ore line investigated via multibody simulation2014In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, no 6, p. 652-662Article in journal (Refereed)
    Abstract [en]

    The Swedish iron ore company LKAB uses freight wagons with three-piece bogies to transport iron ore from its mines in Kiruna and Malmberget to the ports at Lulea and Narvik. A simulation model of the freight wagon is built using the multibody simulation code GENSYS. The objective is to investigate possible sources of rolling contact fatigue (RCF) of the wheels given the high level of observed damage. A parameter study is performed on the effects of vertical track stiffness and viscous damping that occur as a result of seasonal variations of the track condition. Another parameter study is carried out on the influence of the wheel/rail friction coefficient as in winter time the climate is very dry along most parts of the Malmbanan line. The impact of track gauge, track quality and cant deficiency on RCF is also studied. Comparing the calculated and observed RCF locations on wheels, attempts are made to find a relation between wear number and RCF damage. To detect the surface-initiated fatigue a so-called shakedown map is used. It is shown that RCF occurs on the tread of the inner wheels while negotiating curves with below an approximately 450 m radius. It is also shown that cant deficiency can be helpful for the vehicles to negotiate curves and to reduce the risk of RCF, however, on the other hand it may increase the track forces and in severe cases result in flange climbing. Lateral track irregularities and a large track gauge result in small contact areas and can lead to a higher risk of RCF. In cold dry climate conditions, as the water content in air drops significantly, the wheel/rail friction coefficient increases and when the material in the wheel begins to behave in a brittle manner, the risk of RCF is significantly increased, especially when the wear rate is not high enough to remove the initiated cracks.

  • 18.
    Jönsson, Per-Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Andersson, Evert
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Experimental and Theoretical Analysis of Freight Wagon Link Suspension2006In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 220, no 4, p. 361-372Article in journal (Refereed)
    Abstract [en]

    Link suspension is the most prevailing suspension system for two-axle freight wagons and still frequently used for four-axle freight wagons in central and western Europe. The system design is simple and has existed for more than 100 years. However, still, the characteristics are not fully understood. This article focuses on the lateral characteristics of the link suspension. First, results from stationary measurements on freight wagons and laboratory tests on single links are presented. Then, a simulation mathematical model is proposed. Finally, the influence of various parameters on the link characteristics is investigated. With the developed simulation model, many of the stability problems of link suspension running gears can be explained, but further research is needed to fully understand the characteristics and to be able to recommend improvements. From the tests, it also becomes obvious that the characteristics of different links can vary significantly from each other depending on age and maintenance status.

  • 19.
    Kari, Leif
    KTH, Superseded Departments, Vehicle Engineering.
    Audible-frequency stiffness of a primary suspension isolator on a high-speed tilting bogie2003In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 217, no 1, p. 47-62Article in journal (Refereed)
    Abstract [en]

    The preload-dependent dynamic stiffness of a primary suspension isolator on a high-speed tilting bogie is examined via measurements and modelling within an audible frequency range. The stiffness is found to depend strongly on both frequency and preload. The former displays some resonance phenomena, such as stiffness peaks and troughs, while the latter exhibits a steep low-frequency stiffness increase in addition to an anti-resonance peak shifting to a higher frequency with increased preload. The problems of simultaneously modelling the preload and frequency dependence are removed by adopting a frequency-dependent waveguide approach, assuming incompressible rubber with an Abel operator kernel as its shear relaxation function. The preload dependence is modelled by a non-linear shape factor based approach, using a globally equivalent preload configuration. All the translational stiffnesses are modelled, including the vertical, longitudinal and lateral directions, and the vertical stiffness results are compared to those of measurements in a specially designed test rig. Good agreement is obtained for a wide frequency domain-covering 100600 Hz-using a minimum number of parameters and for a wide preload domain-from vanishing to the maximum in service, 90 kN.

  • 20.
    Karis, Tomas
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Analysing the correlation between vehicle responses and track irregularities using dynamic simulations and measurements2019In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017Article in journal (Refereed)
    Abstract [en]

    Track irregularities play a key role in vehicle response, but it is not uncommon to find irregularities with similar statistical characteristics giving very different vehicle behaviour. It is therefore important to find a consistent way of describing track irregularities, which better matches the vehicle behaviour to facilitate an efficient track maintenance and vehicle acceptance testing. Various proposals have been made to resolve this issue, although with limited success. In the present paper, a methodology to break down the track–vehicle interaction into steps, by analysing the irregularity–response correlation in detail, is applied to both the measured and simulated data of a passenger coach. The results show a very good agreement and a high correlation coefficient between the vertical axle box acceleration and the second spatial derivative of the vertical track irregularities when analysing the simulated data, but not for the measured data. Parameter variations are carried out through simulations, in which the vertical track stiffness, vehicle unsprung mass, vertical primary suspension and different combinations of track irregularities are varied. The results show that track stiffness mainly affects the axle box acceleration whereas the primary vertical suspension stiffness and unsprung mass predominantly affect the vertical wheel–rail forces. Therefore, it is important to understand the influence of track stiffness, especially with the help of the measured data, and the methods that reduce its influence should be investigated in future works.

  • 21.
    Krishna, Visakh V
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Tolerable longitudinal forces for freight trains in tight S-curves using three-dimensional multi-body simulations2019In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017Article in journal (Refereed)
    Abstract [en]

    With the need for increasing length of freight trains, Longitudinal Train Dynamics (LTD) and its influence on the running safety becomes a key issue. LTD is a complex issue with contributions from both the vehicles and the operating conditions such as infrastructure design, braking regimes, etc. Standards such as the UIC Code 530-2 and EN-15839 detail the procedure for on-track propelling tests that should be conducted to determine the running safety of a single wagon. Also, it only considers a single S-curve and specifies neighbouring wagons and buffers. The resulting LTD would hence not be able to judge the effects of various heterogeneities in the train formation such as the adjacent wagons, buffer types, carbody torsional stiffnesses, curvatures, etc. Here, there is a potential of using three-dimensional multi-body simulations to develop a methodology to judge the running safety of a train with regards to its longitudinal dynamic behaviour, subjected to various heterogeneities. A tool based on three-dimensional multi-body simulations has been developed to provide Longitudinal Compressive Force (LCF) limits, tolerable LCF for wagon combinations passing through S-curves of varying curvatures and assess the sensitivities of the various heterogeneities present in the train. The methodology is applied to open wagons of the ‘Falns’ type on tight S-curves by calculating the corresponding tolerable LCF and the effect of various parameters on the same is discussed.

  • 22. Lewis, R.
    et al.
    Dwyer-Joyce, R. S.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Pombo, J.
    Ambrosio, J.
    Pereira, M.
    Ariaudo, C.
    Kuka, N.
    Mapping railway wheel material wear mechanisms and transitions2010In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 224, no F3, p. 125-137Article in journal (Refereed)
    Abstract [en]

    In order to develop more durable wheel materials to cope with the new specifications being imposed on wheel wear, a greater understanding of the wear mechanisms and transitions occurring in wheel steels is needed, particularly at higher load and slip conditions. The aim of this work was to draw together current understanding of the wear mechanisms, regimes, and transitions (particularly with R8T wheel material) and new tests on R7T wheel material; to identify gaps in the knowledge; and to develop new tools for assessing wear of wheel materials, such as wear maps, that can be used to improve wear prediction. Wear assessment of wheel materials, as well as wear rates, regimes, and transitions, is discussed. Twin disc wear testing, used extensively for studying wear of wheel and rail materials, has indicated that three wear regimes exist for wheel materials: mild, severe, and catastrophic. These have been classified in terms of wear rate and features. Wear rates are seen to increase steadily initially and then level off, before increasing rapidly as the severity of the contact conditions is increased. Analysis of the contact conditions in terms of friction and slip has indicated that the levelling off of the wear rate observed at the first wear transition is caused by the change from partial slip to full slip conditions at the disc interface. Temperature calculations for the contact showed that the large increase in wear rates seen at the second wear transition may result from a thermally induced reduction in yield strength and other material properties. Comparisons made between discs and actual wheels have provided some support for the theories relating to the transitions observed. Wear maps have been produced using the test results to study how individual contact parameters such as load and sliding speed influence wear rates and transitions. The maps are also correlated to expected wheel-rail contact conditions. This improved understanding of wheel wear mechanisms and transitions will help in the aim of eventually attaining a wear modelling methodology reliant on material properties rather than on wear constants derived from testing.

  • 23. Lewis, R.
    et al.
    Magel, E.
    Wang, W. -J
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Lewis, S.
    Slatter, T.
    Beagles, A.
    Towards a standard approach for the wear testing of wheel and rail materials2017In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 231, no 7, p. 760-774Article in journal (Refereed)
    Abstract [en]

    An examination of the literature for the wear testing methodologies for wheel and rail materials reveals that while only a few different techniques have been used, there is a wide variety in exactly how the tests have been conducted and the resulting data reported. This makes comparison of the data very difficult. This work, carried out as part of the International Collaborative Research Initiative which is aiming to bring together the wheel–rail interface researchers from across the world to collate data and knowledge to try to solve some of the common problems that are faced, has examined the different approaches used and has attempted to pull together all the good practice used into a test specification for future twin-disc testing for wheel and rail materials. The adoption of the method will allow data to be compared reliably and eventually enable data to be compiled into wear maps to use as input, for example, to multi-body dynamics simulation wear prediction tools.

  • 24.
    Lewis, Roger
    et al.
    Department of Mechanical Engineering, University of Sheffield.
    Lewis, S.
    Department of Mechanical Engineering, University of Sheffield.
    Zhu, Yi
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Abbasi, Saeed
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    The Modification of a Slip Resistance Meter for Measurement of Railhead Adhesion2013In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 227, no F2, p. 196-200Article in journal (Refereed)
    Abstract [en]

    The aim of this work was to find a quick, flexible and localised method for determining railhead adhesion. The proposed method is a pendulum rig, which has a rubber pad at the base of a swinging arm. The arm is released and as the rubber pad slides across the contact surface, energy is lost. This loss can be translated into a friction coefficient. Tests have been performed under dry and contaminated conditions, including water, oil and leaf layers both in the laboratory on extracted rail and in the field on live rail. Friction modifiers were also tested. The results of these tests are compared with data obtained using a hand-pushed tribometer. The performed study shows that the pendulum is a viable way to test adhesion levels in the field.

  • 25. Lewis, Stephen R.
    et al.
    Lewis, Roger
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Eadie, Don T.
    Cotter, John
    Lu, Xin
    Effect of humidity, temperature and railhead contamination on the performance of friction modifiers: Pin-on-disk study2013In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 227, no F2, p. 115-127Article in journal (Refereed)
    Abstract [en]

    Commercially available friction modifiers are used in many different countries that have widely different atmospheric conditions. These variations in atmospheric conditions lead to varying levels of railhead oxidation and debris build-up. Friction modifiers can be applied to the rail without any prior cleaning of the rail and this can lead to varying friction modifier/iron oxide ratios potentially affecting the performance of the friction modifier. This paper reports the results of an investigation that was performed to determine the effects of varying atmospheric and oxide conditions on the performance of friction modifiers. A pin-on-disk test rig with an attached environmental chamber was used for the study. Results show that relative humidity has a pronounced effect on the way in which the friction modifier affects friction levels, and also the amount of time it remains on the disk. This also depends on the concentration of oxide in the friction modifier. Glow discharge optical emission spectroscopy analysis was also carried out to assess the effect of the friction modifier and atmospheric conditions on the chemical composition of the surface of the disk. Results show that the depth of surface modification is vastly different depending on the conditions and level of railhead debris.

  • 26. Li, M. X. D.
    et al.
    Berggren, E. G.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Assessment of vertical track geometry quality based on simulations of dynamic track-vehicle interaction2009In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 223, no 2, p. 131-139Article in journal (Refereed)
    Abstract [en]

    A study assessing vertical track geometry quality based on simulations of dynamic track-vehicle interaction is presented in this article. The dynamic model is composed of track, vehicle, and wheel-rail contact with moving irregularities and is solved in the frequency domain by fast Fourier transform or in the time domain by constructing a filter function based on system identification. Frequency-dependent stiffness and loss factor of railpads are used in this study. Numerical simulations are carried out for a 120 km long track to demonstrate the potential benefits of enhancing track quality assessment by calculating wheel-rail forces.

  • 27.
    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.

  • 28.
    Lukaszewicz, Piotr
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    A simple method to determine train running resistance from full-scale measurements2007In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 221, no 3, p. 331-338Article in journal (Refereed)
    Abstract [en]

    This article proposes a simple method to determine train running resistance. The resistance is determined by calculating the change in kinetic and potential energy of a coasting train between successive measurement positions. The strength of this method is that the measuring equipment needed is kept at a minimum and it is not limited to a track having a constant grade, thus making this method suitable, in particular, for long freight trains running in mountain areas. An error analysis is performed for this method and the probable error sources are discussed.

  • 29.
    Lukaszewicz, Piotr
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Running resistance - results and analysis of full-scale tests with passenger and freight trains in Sweden2007In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 221, no 2, p. 183-193Article in journal (Refereed)
    Abstract [en]

    This paper presents experimental results of running resistance tests. Running resistance is determined for conventional passenger trains, freight trains, and the X2 high-speed train. The influence of variables such as speed, number of axles, number of coaches, axle load, track type, and train length is studied. The running resistance is expressed in a general form by a second degree polynomial. The three terms in the polynomial are functions of these variables. The magnitude of the first term is speed independent and varies with number of axles, axle load, and type of track. The second term varies with speed and train length. No influence of axle load is distinguished. The third term is related to the air drag and varies with the speed squared and train configuration. It can be divided into two parts. One part is constant and depends upon the front and rear of the train, and another part increases approximately linearly with train length.

  • 30.
    Lukaszewicz, Piotr
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Running resistance and energy consumption of ore trains in Sweden2009In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 223, no 2, p. 189-197Article in journal (Refereed)
    Abstract [en]

    Running resistance of ore trains consisting of Uad-type wagons is determined from full-scale measurements on Malmbanan. Tests are also run in curves with the Uad equipped with three piece bogies where the axles are non-steerable and an ore wagon equipped with bogies allowing the axles to better align themselves on straight track and more radially in curves, thus making them steerable. Influence of speed, axle load, curve radii, and train length is studied and quantified. The running resistance is parameterized and expressed in a general way so that it can be calculated for any Swedish ore train consisting of Uad-type wagons. The study shows that the increase in running resistance is linear due to the increasing axle load on tangent track and train length. The increase in resistance due to curves is significant and increases as the curve radius decreases. If the axles align themselves radially, the curve resistance reduces by 40 per cent, compared with the Uad. The results show which parameters in a running resistance formula should be paid extra attention when constructing a train model for simulation purposes. A comparison is made between ore trains and ordinary Swedish loco-hauled freight trains. The energy consumption of an ore train is not much affected if the operational speed increases from 50 to 60 km/h. Also, a reduced aerodynamic drag has a very little effect on the consumption due to the low operational speed. In this article, a review of the study is made with conclusions.

  • 31. Mazzola, Laura
    et al.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Railway Technology.
    Secondary suspension of railway vehicles - air spring modelling: Performance and critical issues2014In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, no 3, p. 225-241Article in journal (Refereed)
    Abstract [en]

    This paper shows the importance of modelling the components of the suspension when performing dynamics simulations of a railway vehicle. Focusing on the air spring secondary suspension, a process to define an accurate component model is proposed based on a combination of laboratory tests and model identification techniques. Six models for the air spring secondary suspension are discussed and assessed based on comparison with experiments.

  • 32.
    Muld, Tomas W.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Efraimsson, Gunilla
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Henningson, Dan S.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Wake characteristics of high-speed trains with different lengths2014In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, no 4, p. 333-342Article in journal (Refereed)
    Abstract [en]

    Three different train configurations with different numbers of cars are analysed in order to investigate the effect of the train length on wake structures. The train geometry considered is the aerodynamic train model and the different versions have two, three and four cars. Due to the different lengths of the trains, the boundary-layer thickness will be different at the tail of each configuration. The flow is simulated using detached eddy simulation, and coherent flow structures are extracted via proper orthogonal decomposition and dynamic mode decomposition. As a result of reconstruction of the flow field using coupling of the mean flow and the first fluctuating proper orthogonal decomposition mode, it is found that the dominant flow structure in the wake is the same for all three cases. However, this structure has different frequencies and wavelengths depending on the boundary-layer thickness in front of the separation. It is shown that the frequency decreases as the boundary-layer thickness increases for these train configurations.

  • 33. Navik, Petter
    et al.
    Ronnquist, Anders
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    The use of dynamic response to evaluate and improve the optimization of existing soft railway catenary systems for higher speeds2016In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 230, no 4, p. 1388-1396Article in journal (Refereed)
    Abstract [en]

    An increasing demand for reduced travel times requires the exploitation of the full capacity of existing overhead railway catenary systems. This need has become an issue in Norway, as the majority of existing catenary systems are designed for a maximum speed of 130km/h. In many regions, plans to reconstruct the railway line do not exist. Therefore, existing catenary sections must be optimized to increase a train's velocity and reduce the total travel time. In this paper, the dynamic response is evaluated in an optimization investigation of an existing soft catenary system. A dynamic investigation that considers finite element models of existing soft railway catenary sections with original tension forces, current tension forces and suggested new tension forces for velocities at and above the design speed is conducted. The dynamic response is quantified by the interpretation of spectral densities and variations in their peak values. Due to more movement at mid-span than at the pole support, the effects from altering the tension forces and increasing the speed can be more accurately described and estimated by considering the dynamic content of the response at mid-span instead of the peak uplift at the pole support. A 23% increase in speed is possible for the system with the best tested new tension force setting, in which only the dynamic response and uplift at the pole support are considered.

  • 34.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    A multi-layer model of low adhesion between railway wheel and rail2007In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 221, no 3, p. 385-389Article in journal (Refereed)
    Abstract [en]

    The current paper presents a new multi-layer model of low adhesion between railway wheel and rail. The model proposes that when leaves are crushed between railway wheels and rail, both a coated slippery layer and a chemically reacted, easily sheared surface layer are formed. Elemental depth profiling reveals that the chemically reacted, easily sheared surface layer contains substances such as P and Ca. Both the coated slippery layer and the chemically reacted, easily sheared surface layer must be removed to get proper adhesion between railway wheel and rail.

  • 35.
    Olofsson, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Nilsson, Rickard
    KTH, Superseded Departments, Machine Design.
    Surface cracks and wear of rail: a full-scale test on a commuter train track2002In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 216, no 4, p. 249-264Article in journal (Refereed)
    Abstract [en]

    Damage mechanisms such as surface cracks and wear on a rail can reduce the service life of a railway track. The purpose of this investigation was to study the development of these two damage mechanisms on new and 3-year-old rails in a commuter railway track over a period of 2 years. Four curves were studied with radius between 303 and 616 m. In two of the curves, two different kinds of rail steel grade (UIC 900A grade with ultimate strength 900 N/mm2 and UIC 1100 grade with ultimate strength 1100 N/mm2) were used in each curve. In the other two curves, only the lower-strength rail was used. Four pieces of new rail, each 20 m long, were inserted in the two curves with both UIC 900A and UIC 1100 grade rail. Lubrication was applied on the high rail of one of the curves with both UIC 900A and UIC 1100 grade rail and on one of the curves with only UIC 900A grade rail. The two remaining curves were not lubricated. Surface cracks in the form of headchecks could be noted on the surface of the new 1100 grade rails after 1 month of traffic. By contrast, the surface of the UIC 900A grade rails showed visible surface cracks in only two of four curves and that after approximately 2 years of traffic. Both materials seemed to be similarly sensitive to crack initiation but the 1100 grade rail was more sensitive to crack propagation and also more sensitive to the formation of headcheck cracks. Lubrication, as expected, reduced the profile change. A less expected outcome was that lubrication also reduced the rate of crack propagation; however, the lubricated UIC 1100 grade rail was as sensitive to crack initiation as the unlubricated UIC 1100 grade rail. By comparing the wear depth in the headcheck zone with the crack length, equilibrium between these two damage mechanisms was found for the lubricated UIC 1100 grade rail. Both the crack length and the wear depth showed low values. By using a lubricant with friction modifiers the stresses was low enough to prevent crack propagation; at the same time, the rail was hard enough to reduce the wear rate. This is probably the most favourable state in terms of rail maintenance cost.

  • 36.
    Olofsson, Ulf
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sundh, Jon
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Bik, Ulf
    Nilsson, Ricard
    The influence of snow on the tread braking performance of a train: A pin-on-disc simulation performed in a climate chamber2016In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 230, no 6, p. 1521-1530Article in journal (Refereed)
    Abstract [en]

    In trains with tread brakes, the coefficient of friction between the brake block and the railway wheel determines the stopping distance. The blocks have traditionally been manufactured from cast iron. Although these blocks have good braking capacity, their use is often restricted due to the squealing noise they emit. Tests of alternative composite block materials have been successful under summer conditions; however, in regions with snowy winters the use of such materials has been limited due to problems with braking capacity under snowy conditions. This research aims to develop a laboratory-scale test methodology for evaluating the braking capacity of tread brake materials under winter and snowy conditions. A pin-on-disc machine placed in a climate chamber was used for testing, and a block of standard cast iron was compared with blocks of standard composite materials. The results indicated that the blocks of standard composite materials generate a much smoother surface on the counter wheel and a significantly lower friction coefficient under snowy conditions. A second test series evaluated blocks of alternative composite materials, and a candidate material with low noise and a sufficiently high sliding friction coefficient was selected for further study. A third test series examining geometrical changes in the contact surface in terms of milled parallel tracks was performed; it revealed that the braking capacity under winter conditions can be increased by milling actions if the parallel tracks are properly oriented - in this case, at an angle of 45 degrees to the sliding direction.

  • 37.
    Olofsson, Ulf
    et al.
    KTH, Superseded Departments, Machine Design.
    Sundvall, Krister
    KTH, Superseded Departments, Machine Design.
    Influence of leaf, humidity and applied lubrication on friction in the wheel-rail contact: pin-on-disc experiments2004In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 218, no 3, p. 235-242Article in journal (Refereed)
    Abstract [en]

    A novel test method has been used to study how applied and natural lubrication (leaf and humidity) influences the coefficient of friction in the wheel-rail contact. A pin-on-disc tribometer placed in a climate chamber was used as the test equipment. The pin-on-disc contact simulates the wheel-rail contact caused by commuter train traffic on straight track. The results show that the coefficient of friction decreases when the relative humidity increases and decreases even more when a leaf is used as a lubricant. By using an elm leaf as the lubricant, the coefficient of friction is reduced by a factor of four compared with the unlubricated case. However, the coefficient of friction decreases even more when a rail lubricant is used.

  • 38.
    Orvnäs, Anneli
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Persson, Rickard
    Aspects of Using Active Vertical Secondary Suspension to Improve Ride ComfortIn: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017Article in journal (Other academic)
    Abstract [en]

    This paper presents various aspects of using active vertical secondary suspension in arail vehicle to improve ride comfort. Dynamic control of the vertical and roll modes ofthe carbody is achieved by means of actuators replacing the conventional vertical dampersin the secondary suspension. Active damping improves vertical ride comfort, compared toa passive system. Besides dynamic control, the actuators are able to generate quasi-staticroll control between the carbody and bogies in curves. This allows for higher speeds incurves, without negatively affecting ride comfort. Furthermore, the anti-roll bar is removedto reduce the number of components.

  • 39.
    Persson, Rickard
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Tilting trains: benefits and motion sickness2010In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 224, no F6, p. 513-522Article in journal (Refereed)
    Abstract [en]

    Carbody tilting is today a mature and inexpensive technology that allows higher speeds on curves, thus shortening travel time. The technology has been accepted by many train operators, but some issues are still holding back the full potential of tilting trains. This paper focuses on improving the benefits and limiting the drawbacks of tilting trains. This is done by quantifying the possible running time benefits compared with today's tilting trains, identifying what motion components have an influence on motion sickness, and finally quantifying the influence from the increased speed on these motion components.

    A running time analysis was made to show what potential there is to further improve running times by optimizing tracks and trains. Relations between cant deficiency, top speed, tractive performance, and running times are shown for a tilting train. About 9 per cent running time may be gained on the Stockholm-Gothenburg (457 km) main line in Sweden if cant deficiency, top speed, and tractive performance are improved compared with existing tilting trains. Introduction of non-tilting high-speed trains is not an option on this line due to the large number of 1000 m curves.

    However, tilting trains run a greater risk of causing motion sickness than non-tilting trains. Roll velocity and vertical acceleration are the two motion components that show the largest increase, but the amplitudes are lower than those used in laboratory tests that caused motion sickness. Higher curve speeds will increase carbody motions still further, but there are some possibilities to trade between vertical and lateral carbody acceleration by increasing or decreasing roll.

  • 40. Polach, Oldrich
    et al.
    Böttcher, Andreas
    Vannucci, Dario
    Sima, Juergen
    Schelle, Henning
    Chollet, Hugues
    Götz, Gernoth
    Garcia Prada, Mayi
    Nicklisch, Dirk
    Mazzola, Laura
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Osman, Martin
    Validation of simulation models in the context of railway vehicle acceptance2015In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 229, no 6, p. 729-754Article in journal (Refereed)
    Abstract [en]

    The evaluation of a reliable validation method, criteria and limit values suitable for model validation in the context of vehicle acceptance was one of the objectives of the DynoTRAIN project. The presented investigations represent a unique amount of testing, simulations, comparisons with measurements, and validation evaluations. The on-track measurements performed in four European countries included several different vehicles on a test train equipped to simultaneously record track irregularities and rail profiles. The simulations were performed using vehicle models built with the use of different simulation tools by different partners. The comparisons between simulation and measurement results were conducted for over 1000 simulations using a set of the same test sections for all vehicle models. The results were assessed by three different validation approaches: comparing values according to EN 14363; by subjective engineering judgement by project partners; and using so-called validation metrics, i.e. computable measures developed with the aim of increasing objectivity while still maintaining the level of agreement with engineering judgement. The proposed validation method uses the values computed by analogy with EN 14363 and provides validation limits that can be applied to a set of deviations between simulation and measurement values.

  • 41.
    Qazizadeh, Alireza
    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.
    Persson, Rickard
    Rolling Stock Central & Northern Europe and Asia, Sweden.
    Proposal for systematic studies of active suspension failures in rail vehicles2018In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 232, no 1, p. 199-213Article in journal (Refereed)
    Abstract [en]

    Application of active suspensions in high-speed passenger trains is gradually getting more and more common. Active suspensions are primarily aimed at improving ride comfort, wear or stability. Failure of these systems may not only just deteriorate the performance but it may also put vehicle safety at risk. There are not many studies that explain how a thorough study proving safety of active suspension should be performed. Therefore, initiating this type of study is necessary for not only preventing incidences but also for assuring acceptance of active suspension by rail vehicle operators and authorities. This study proposes a flowchart for systematic studies of active suspension failures in rail vehicles. The flowchart steps are solidified by using failure mode and effects analysis and fault tree analysis techniques and also acceptance criteria from the EN14363 standard. Furthermore, six failure modes are introduced which are very general and their use can be extended to other studies of active suspension failure. In the last section of the paper, the proposed flowchart is put into practice through four failure examples of active vertical suspension.

  • 42. Six, Klaus
    et al.
    Mihalj, Tomislav
    Trummer, Gerald
    Marte, Christof
    V Krishna, Visakh
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Hossein Nia, Saeed
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, Superseded Departments (pre-2005), Vehicle Engineering.
    Assessment of running gear performance in relation to rolling contact fatigue of wheels and rails based on stochastic simulations2019In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, p. 1-12Article in journal (Refereed)
    Abstract [en]

    In this work, the authors present a methodology for assessing running gear with respect to rolling contact fatigue of wheels and rails. This assessment is based on the wheel/rail contact data of different wheel profile wear states obtained from a wheel profile prediction methodology. The approach allows a cumulative assessment of the rolling contact fatigue of rails in different curve radii (e.g. the sum of damage over the lifetime of wheel profiles). Furthermore, the assessment of the rolling contact fatigue can be undertaken at different wear states of the wheel profiles to provide an insight on how the rolling contact fatigue of wheels and rails varies depending on the evolution of wheel wear. The presented methodology is exemplarily applied to two bogie types, the UIC-Y25 standard bogie and the so-called FR8RAIL bogie with a mechanical wheelset steering device. The presented methodology has been shown to be a useful tool for the optimisation of vehicles already in an early stage of the vehicle development process.

  • 43.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles.
    On freight vehicle dynamics and track interaction.1999In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 213, no 4Article in journal (Refereed)
  • 44. Telliskivi, T.
    et al.
    Olofsson, Ulf
    KTH, Superseded Departments, Machine Design.
    Contact mechanics analysis of measured wheel-rail profiles using the finite element method2001In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 215, no 2, p. 65-72Article in journal (Refereed)
    Abstract [en]

    A tool has been developed for contact mechanics analysis of the wheel-rail contact. Using measurements of wheel and rail profiles as input, the toot is based on the finite element (FE) code ANSYS. Traditionally, two methods have been used to investigate the rail-wheel contact, namely Hertz's analytical method and Kalker's software program Contact. Both are based on the half-space assumption as well as on a linear-elastic material model. The half-space assumption puts geometrical limitations on the contact. This means that the significant dimensions of the contact area must be small compared with the relative radii of the curvature of each body. Especially in the gauge corner of the rail profile, the half-space assumption is questionable since the contact radius here can be as small as 10 mm. By using the FE method (FEM) the user is not limited by these two assumptions. The profile measurement system Miniprof was used to measure the wheel and rail profiles that were used as input when generating the FE mesh. As a test case, a sharp curve (303 m radius) in a unidirectional commuter train track used by X1 and X10 trains was chosen. The results of two contact cases were compared with the results of the Hertz analytical method and the program Contact. In the first contact case the wheel was in contact with the rail gauge corner. In the second case the wheel was in contact with the rail head. In both contact cases Hertz and Contact presented very similar results for the maximum contact pressure. For the first contact case, a significant difference was found between the FE method and the Hertz method and the program Contact in all of output data. The Hertz and Contact methods both presented a maximum contact pressure that was three times larger (around 3 GPa) than the FE solution. Here, the difference was probably due to the combination of both the half-space assumption and the elastic-plastic material model. For the second contact case, there was no significant difference between the maximum contact pressure results of the three different contact mechanics methods employed.

  • 45.
    Thomas, Dirk
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Diedrichs, Ben
    Bombardier Transportation.
    Rail vehicle response to lateral carbody excitations imitating crosswind2015In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 229, no 1, p. 34-47Article in journal (Refereed)
    Abstract [en]

    Repeatable field tests to measure the vehicle response to unsteady crosswinds are not practical due to safety and economic reasons. Simulations are therefore necessary to gather information on the vehicle response to crosswind. However, in turn, these simulations need to be validated. This study presents results of measured quasi-static and dynamic responses of a stationary rail vehicle due to defined lateral carbody excitations imitating unsteady crosswind, which are reflected by multibody simulations. The vehicle responses are measured in terms of suspension deflections, lateral carbody accelerations and vertical wheel/rail forces. The vehicle dynamic response to a gust-like event results in an overshoot of wheel unloading. In general the measurements and simulations show good agreement. However, the simulations partly overestimate the responses slightly and an influence due to airspring levelling can be observed in the measured values of quasi-static load cases.

  • 46.
    Thomas, Dirk
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Diedrichs, Ben
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Berg, Mats
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Dynamics of a high-speed rail vehicle negotiating curves at unsteady crosswind2010In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 224, no F6, p. 567-579Article in journal (Refereed)
    Abstract [en]

    Rail vehicles in everyday operation experience large lateral influences from curves and track imperfections, yielding large suspension deflections and displacements of the carbody relative to the track. Aerodynamic loads caused by crosswind may deteriorate the conditions that can result in vehicle overturning. This study investigates the influence of crosswind on a highspeed rail vehicle negotiating a curve. A multi-body simulation model of a high-speed rail vehicle is subjected to unsteady aerodynamic loads. The vehicle response is studied for different gusts, and variations of some vehicle parameters are performed.

  • 47.
    Wennberg, David
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Stichel, Sebastian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Rail Vehicles. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Wennhage, Per
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. KTH, School of Engineering Sciences (SCI), Centres, VinnExcellence Center for ECO2 Vehicle design.
    Substitution of corrugated sheets in a railway vehicle's body structure by a multiple-requirement based selection process2014In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, no 2, p. 143-157Article in journal (Refereed)
    Abstract [en]

    To simplify construction, reduce weight and improve mechanical properties, a sandwich panel substitution process is performed on corrugated sheets in the floor and roof of a rail vehicle car body. A requirement based selection is used to design the sandwich panels with the corrugated sheet mechanical characteristics as boundaries. Car body stiffness is evaluated by modal analysis. The derived panels reduce the mass of the car body by 600-700kg. Results show the varying importance of the longitudinal, transverse and shear properties of the floor and roof panels, as well as how efficient the corrugated sheets actually are.

  • 48.
    White, B. T.
    et al.
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Nilsson, R.
    SLL, Stockholm, Sweden..
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Arnall, A. D.
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Evans, M. D.
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Armitage, T.
    Arup, Sheffield, S Yorkshire, England..
    Fisk, J.
    Arup, Sheffield, S Yorkshire, England..
    Fletcher, D. I.
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Lewis, R.
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Effect of the presence of moisture at the wheel-rail interface during dew and damp conditions2018In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 232, no 4, p. 979-989Article in journal (Refereed)
    Abstract [en]

    Incidents involving low levels of adhesion between the wheel and rail are a recurrent issue in the rail industry. The problem has been mitigated using friction modifiers and traction enhancers, but a significant number of incidents still occur throughout the year. This study looks at the environmental conditions that surround periods of low adhesion in order to provide an insight into why low adhesion events occur. Network Rail Autumn data, which provided details on the time and location of low adhesion incidents, were compared against weather data on a national and then local scale. Low adhesion incidents have often been attributed to contamination on the rails, such as organic leaf matter, but these incidents also occur when no contamination is visible. The time, date and location of incidents were linked to local weather data to establish any specific weather conditions that could lead to these events. The effects of precipitation, temperature and humidity on rails were analysed in order to further the understanding of low adhesion in the wheel-rail contact, which will lead to adopting better methods of mitigating this problem.

  • 49.
    Zhu, Yi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Nilsson, R.
    Stockholm public transport AB, Stockholm, Sweden.
    A field test study of leaf contamination on railhead surfaces2014In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, no 1, p. 71-84Article in journal (Refereed)
    Abstract [en]

    Leaves on railway tracks affect the level of adhesion between the wheel and rail, especially in autumn. When crushed by wheels, leaves form a tarnished, low level of adhesion layer that sticks to the railhead and often requires mechanical removal. A Stockholm local traffic track with a long history of adhesion problems was subjected to field tests on railhead contamination. On five occasions under different conditions, spaced over a year, the friction coefficient was measured using a tribometer and samples of the rail were taken. The techniques of electron spectroscopy for chemical analysis and glow discharge optical emission spectrometry were conducted to determine the composition of the top layer of rail contaminants and hardness was measured using the nano-indentation technique. The tarnished layer contains much higher contents of calcium, carbon and nitrogen than do leaf residue layers and uncontaminated samples. These high element contents are generated from the leaf material, which chemically reacts with the bulk material. The hardness of the tarnished layer is one-fifth that of the non-tarnished layer of the same running band. A chemical reaction occurs from the surface to a depth of several microns. The thickness of the friction-reducing oxide layer can be used to predict the friction coefficient and extent of leaf contamination.

  • 50. Öberg, J.
    et al.
    Andersson, Evert
    Determining the deterioration cost for railway tracks2009In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 223, no 2, p. 121-129Article in journal (Refereed)
    Abstract [en]

    The cost of maintaining and renewing railway tracks affected by traffic-dependent deterioration is considerable. It is important not only to have proper maintenance regimes, but also to have knowledge of the interaction between vehicles and track in order to reduce the deterioration of both. In a joint project between Banverket (Swedish Rail Administration) and KTH (Royal Institute of Technology, Stockholm), a model for track deterioration is developed, considering track settlement, component fatigue, abrasive wear, and rolling contact fatigue of rails. The basis of the model is taken from what is considered as state-of-the-art knowledge. The model is used as a basis for a proposed new track access charging regime for Banverket, able to differ between vehicle types based on their characteristics and tendency to deteriorate the tracks. The model is implemented in an Excel (R) environment and applied to Swedish mainline traffic and vehicles. Using representative vehicle characteristics in determining track deterioration, it is predicted that there are large differences between different vehicles regarding their deterioration of the tracks. The model predicts axle load, unsprung mass, and wheelset steering capability as decisive for track deterioration. The model is believed to predict realistic results also for heavy-haul rail operations.

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