4,648 research outputs found

    Study of Track Irregularity Time Series Calibration and Variation Pattern at Unit Section

    Get PDF
    Focusing on problems existing in track irregularity time series data quality, this paper first presents abnormal data identification, data offset correction algorithm, local outlier data identification, and noise cancellation algorithms. And then proposes track irregularity time series decomposition and reconstruction through the wavelet decomposition and reconstruction approach. Finally, the patterns and features of track irregularity standard deviation data sequence in unit sections are studied, and the changing trend of track irregularity time series is discovered and described

    Advanced finite element modelling of coupled train-track systems : a geotechnical perspective

    Get PDF
    Abstract unavailable please refer to PD

    Solitonic State in Microscopic Dynamic Failures

    Full text link
    Onset of permanent deformation in crystalline materials under a sharp indenter tip is accompanied by nucleation and propagation of defects. By measuring the spatio-temporal strain field nearthe indenter tip during indentation tests, we demonstrate that the dynamic strain history at the moment of a displacement burst carries characteristics of formation and interaction of local excitations, or solitons. We show that dynamic propagation of multiple solitons is followed by a short time interval where the propagating fronts can accelerate suddenly. As a result of such abrupt local accelerations, duration of the fast-slip phase of a failure event is shortened. Our results show that formation and annihilation of solitons mediate the microscopic fast weakening phase, during which extreme acceleration and collision of solitons lead to non-Newtonian behavior and Lorentz contraction, i.e., shortening of solitons characteristic length. The results open new horizons for understanding dynamic material response during failure and, more generally, complexity of earthquake sources

    Train Tribometer Design and Feasibility

    Get PDF

    Wheel-rail contact force measurement. A comparison between distance laser and strain gauges measuring technology

    Get PDF
    The development of this PhD thesis is focus on the wheel/rail contact force measurement on a 1 : 10 scaled railway vehicle. To that end, the author has designed and manufactured a dynamometric wheelset instrumented with several sensors for the direct measurement of forces applied on the instrumented wheel. Two di erent technologies have been used for the wheelset instrumentation: On the one hand, a set of strain gauges measure the radial strains experienced by the wheel-web when a lateral load is applied on the wheel. On the other hand, three high precision lasers have been installed on the axel that measure the lateral de ection experienced by the wheel due to the applied lateral loads. Normal contact forces are measured independently throughout the de ection experienced by the primary suspension. This is also measured with laser distance sensors. After being instrumented, the wheelset has been submitted to a calibration process. A calibration test bench where controlled loads can be applied to the wheelset has been also designed and manufactured. Finally the instrumented wheelset has been installed on the scaled vehicle and tested on a 5 inches wide scale track. The force measurements obtained in the experiments with both set of sensors have been compared with numerical results drawn from a computational model of the vehicle. A novel procedure to measure the track irregularities applied to the scaled track has been also include as part of this thesis.El desarrollo de esta tesis se centra en la medici on experimental de fuerzas de contacto rueda carril en un veh culo ferroviario a escala 1 : 10. Para ello, el autor ha dise~nado y fabricado un eje dinamom etrico instrumentado con multiples sensores para la medici on directa de las fuerzas aplicadas en las ruedas. Para la instrumentaci on del sistema se han utilizado dos tecnolog as distintas: Por un lado se dispone de un conjunto de bandas extensom etricas que miden las deformaciones radiales experimentadas por el velo de la rueda debidas a la carga lateral aplicada en la misma. Por otro lado se han instalado tres l aseres de alta precisi on que miden la de exi on experimentada por la rueda debidas tambi en a las cargas lateral aplicadas. Las fuerzas normales a las que se ve sometida la rueda son calculadas a trav es de la medici on de la de exi on experimentada por la suspensi on primaria del veh culo, siendo tambi en medida mediante sensores de distancia l aser. Tras la instrumentaci on el eje dinamom etrico ha sido sometido a un proceso de calibraci on, para el cual se ha dise~nado y fabricado un banco de pruebas a escala donde puden aplicarse cargas al eje de forma controlada y conocer la respuesta de los sensores. Finalmente el mencionado eje dinamom etrico ha sido instalado en el veh culo a escala y su funcionamiento ha sido probado en una v a a escala de 5 inches de ancho. En los experimentos realizados se han contrastado las mediciones de fuerzas realizadas por ambos sensores y comparado con resultados num ericos obtenidos de un modelo multicuerpo de simulaci on del veh culo. Como parte de esta tesis se incluye tambi en la descripci on del novedoso proceso de auscultaci on y c alculo de irregularidades realizado en del trazado ferroviario a escala

    Slab track optimisation considering dynamic train–track interaction

    Get PDF
    Slab track is a type of railway track that is frequently used e.g. in high-speed applications as an alternative to ballasted track. Slab track is also well suited on bridges and in tunnels since no ballast is required and the cross-section of tunnels can be reduced. Slab tracks generally have lower maintenance demands than ballasted track. However, if maintenance is required it may be expensive and intrusive. On the other hand, overdimensioning of slab track will lead to high environmental impact and monetary cost. This thesis aims to increase the knowledge and improve the understanding of the dynamic interaction between vehicle and track in order to allow for the optimisation of slab track.To this end, both two-dimensional (2D) and three-dimensional (3D) slab track models, and a transition zone model between slab track and ballasted track, have been developed. These models are used to simulate the vertical dynamic vehicle–track interaction in the time-domain. The computational cost of the simulation is reduced by using a complex-valued modal superposition technique for the finite element model of the track. In the 3D model, both rails are represented by beam elements, while the concrete parts are described using shell or solid elements. The simulations employ a mix of in-house and commercial codes. The influence of different irregularities, e.g. variations in track support conditions and irregularities in longitudinal level, on significant track responses such as wheel–rail contact forces, stresses in the concrete parts and pressure on the foundation is assessed. From Single-Input-Multiple-Output (SIMO) measurements carried out in a full-scale test rig, the 3D model has been calibrated and validated. The developed models have been used to improve the designs of slab track and transition zones. Based on a multi-objective optimisation problem that is solved using a genetic algorithm, the transition zone design has been optimised to minimise the dynamic loads generated due to the stiffness gradient between the two track forms. The slab track design has been optimised to minimise the environmental footprint considering the constraint that the design must pass the static design criteria described in EN\ua016432-2. This design is then employed in the dynamic model where it is shown that there is a further potential for design improvements and related CO2 savings. In particular, there may be possibilities to reduce the thickness of the concrete layers and the amount of concrete between the rails. Finally, a model of reinforced concrete has been implemented and combined with the dynamic model to assess consequences of cracking in the concrete panel and to evaluate stresses in the reinforcement bars
    corecore