Pad Stiffness

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Pengfei Liu - One of the best experts on this subject based on the ideXlab platform.

Jens C. O. Nielsen - One of the best experts on this subject based on the ideXlab platform.

  • Multi-objective optimisation of transition zones between slab track and ballasted track using a genetic algorithm
    Journal of Sound and Vibration, 2019
    Co-Authors: Emil Aggestam, Jens C. O. Nielsen
    Abstract:

    The vertical dynamic vehicle–track interaction in a transition between ballasted track and slab track is simulated in the time domain using an extended state-space vector approach. A complex-valued modal superposition technique is applied for the linear, time-invariant and non-periodic finite element model of the railway track. By considering a multi-objective optimisation problem solved by a genetic algorithm, the maximum dynamic loads on the track structure are minimised with respect to the selected design variables. To reduce the risk of long-term degradation of track geometry due to ballast/subgrade settlement, the transition zone is designed to minimise the influence of the track Stiffness gradient between the two different track forms. The methodology is demonstrated by minimising the maximum wheel–rail contact force and the maximum pressure between sleeper/panel and foundation, while the selected design variables are distributions of rail Pad Stiffness and sleeper spacing adjacent to the transition. From the solution of the optimisation problem, non-dominated fronts are obtained illustrating potential for a significant reduction of the dynamic loads. It is shown that the optimised design leads to a more uniform distribution of load on the foundation reducing the risk of differential track settlement. The influences of the length of the transition zone and direction of travel on the maximum dynamic loads are investigated. Prescribed irregularities in longitudinal level may be accounted for but have been neglected in the optimisation as the optimised design would be more influenced by the given irregularity than by the Stiffness gradient.

  • Multi-objective design optimisation of transition zones between different railway track forms
    2018
    Co-Authors: Emil Aggestam, Andreas Andersson, Jens C. O. Nielsen, Martin Li
    Abstract:

    The vertical dynamic interaction between vehicle and railway track is simulated in the time domain using an extended state space vector approach. The track model includes a transition zone between slab track on a bridge and ballasted track on an embankment. By considering a multi-objective optimisation problem, solved using a genetic algorithm, selected vehicle and track responses are simultaneously minimised by optimising the distributions of rail Pad Stiffness and sleeper spacing in the transition zone. It is shown that the magnitudes of the maximum dynamic loads in the optimised transition zone can be reduced to be similar as the magnitudes far away from the transition zone.

  • Simulation of vertical dynamic vehicle-track interaction in a railway crossing using Green's functions
    Journal of Sound and Vibration, 2017
    Co-Authors: Peter Torstensson, Jens C. O. Nielsen
    Abstract:

    Vertical dynamic vehicle-track interaction in the through route of a railway crossing is simulated in the time domain based on a Green's function approach for the track in combination with an implementation of Kalker's variational method to solve the non-Hertzian, and potentially multiple, wheel-rail contact. The track is described by a linear, three-dimensional and non-periodic finite element model of a railway turnout accounting for the variations in rail cross-sections and sleeper lengths, and including baseplates and resilient elements. To reduce calculation time due to the complexity of the track model, involving a large number of elements and degrees-of-freedom, a complex-valued modal superposition with a truncated mode set is applied before the impulse response functions are calculated at various positions along the crossing panel. The variation in three-dimensional contact geometry of the crossing and wheel is described by linear surface elements. In each time step of the contact detection algorithm, the lateral position of the wheelset centre is prescribed but the contact positions on wheel and rail are not, allowing for an accurate prediction of the wheel transition between wing rail and crossing rail. The method is demonstrated by calculating the wheel-rail impact load and contact stress distribution for a nominal S1002 wheel profile passing over a nominal crossing geometry. A parameter study is performed to determine the influence of vehicle speed, rail Pad Stiffness, lateral wheelset position and wheel profile on the impact load generated at the crossing. It is shown that the magnitude of the impact load is more influenced the wheel-rail contact geometry than by the selection of rail Pad Stiffness.

  • dynamic vehicle track interaction in switches and crossings and the influence of rail Pad Stiffness field measurements and validation of a simulation model
    Vehicle System Dynamics, 2015
    Co-Authors: Bjorn Palsson, Jens C. O. Nielsen
    Abstract:

    A model for simulation of dynamic interaction between a railway vehicle and a turnout (switch and crossing, S&C) is validated versus field measurements. In particular, the implementation and accuracy of viscously damped track models with different complexities are assessed. The validation data come from full-scale field measurements of dynamic track Stiffness and wheel-rail contact forces in a demonstrator turnout that was installed as part of the INNOTRACK project with funding from the European Union Sixth Framework Programme. Vertical track Stiffness at nominal wheel loads, in the frequency range up to 20 Hz, was measured using a rolling Stiffness measurement vehicle (RSMV). Vertical and lateral wheel-rail contact forces were measured by an instrumented wheel set mounted in a freight car featuring Y25 bogies. The measurements were performed for traffic in both the through and diverging routes, and in the facing and trailing moves. The full set of test runs was repeated with different types of rail Pad to investigate the influence of rail Pad Stiffness on track Stiffness and contact forces. It is concluded that impact loads on the crossing can be reduced by using more resilient rail Pads. To allow for vehicle dynamics simulations at low computational cost, the track models are discretised space-variant mass-spring-damper models that are moving with each wheel set of the vehicle model. Acceptable agreement between simulated and measured vertical contact forces at the crossing can be obtained when the standard GENSYS track model is extended with one ballast/subgrade mass under each rail. This model can be tuned to capture the large phase delay in dynamic track Stiffness at low frequencies, as measured by the RSMV, while remaining sufficiently resilient at higher frequencies.

  • ACOUSTIC OPTIMIZATION OF RAILWAY SLEEPERS
    Journal of Sound and Vibration, 2000
    Co-Authors: Jens C. O. Nielsen
    Abstract:

    Abstract A mathematical model of vertical wheelset/track interaction is developed and adopted for minimization of sound power generated by railway sleepers (mono-bloc or bi-bloc). The influence of sleeper material properties, sleeper shape and properties of ballast and rail Pads on sleeper sound power can be investigated. The wheelset/track interaction is simulated in the frequency domain by using a so-called moving irregularity model with a given displacement amplitude spectrum. Boundary element models of the acoustic medium (air) are developed for mono-bloc and bi-bloc sleepers. Radiation efficiencies are calculated and compared for the different sleeper designs. From the results obtained in a parametric study, it is concluded that the sound power generated by the sleepers is strongly influenced by ballast Stiffness and damping and by rail Pad Stiffness. Further, it is concluded that a bi-bloc sleeper with appropriate dimensions of the connecting bar can lead to a 2–3 dB(A) reduction of sound power compared to a reference mono-bloc sleeper.

Xiaolin Song - One of the best experts on this subject based on the ideXlab platform.

Hugh B. Thompson - One of the best experts on this subject based on the ideXlab platform.

  • Dynamic Vehicle–Track Model to Study the Effects of Track Geometry and Vehicle–Track Interaction on Concrete Tie Rail Seat Load Environment
    Transportation Research Record, 2016
    Co-Authors: Mike Mchenry, Adam Klopp, Hugh B. Thompson
    Abstract:

    Rail seat deterioration (RSD) of concrete ties is manifested by the loss of concrete material in the rail seat area supporting the rail. This failure mode can lead to track that performs poorly and, in extreme cases, can result in the loss of rail clip hold down, reverse rail cant, and rail rollover derailments. This paper describes the use of a multibody vehicle–track dynamics model developed to study the load environment of concrete tie rail seats, specifically addressing the failure mode of RSD. Vehicle–track interaction simulations were conducted to determine the effect of track geometry perturbations on the overall load environment. Various types and magnitudes of track geometry perturbations, including combinations of surface (vertical) and alignment (lateral) perturbations were considered. Fastening system parameters such as clip hold-down force, tie Pad Stiffness, and broken insulator conditions were also considered. Results of these simulations suggest that concrete crushing, a hypothesized mecha...

Yu Qian - One of the best experts on this subject based on the ideXlab platform.

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