1,721,564 research outputs found
Author Correction: IRE1α-XBP1s pathway promotes prostate cancer by activating c-MYC signaling
No full textSheng X, Nenseth HZ, Qu S, et al. Author Correction: IRE1alpha-XBP1s pathway promotes prostate cancer by activating c-MYC signaling. Nature Communications . 2024;15(1): 6190
A theoretical model for ground vibration from trains generated by vertical track irregularities
No full textA model is developed for predicting ground vibrations due to vertical track irregularities. This model incorporates vehicles, a track and a layered ground, and uses the moving axle loads and the vertical rail irregularities as its inputs. Outputs include the dynamic wheel–rail forces and the displacement power spectra of the track and the ground surface. Results from this model are presented for a single-axle vehicle model and a British Mark 3 passenger coach running on different tracks (a ‘lighter ballasted track’, a ‘heavier ballasted track’ and a slab track) at different speeds (25, 60 and 83 m/s). Based on these results, the effects of track structure, vehicle speed and frequency range on the observed vibration levels are identified. The different roles of the moving axle loads and the roughness-induced dynamic loads are indicated, at different frequencies and for train speeds below and above the lowest ground wave speed
The roles of track roughness and axle-load time history in the generation of ground vibration from surface-running trains
No full textA theoretical study on the influence of the track on train-induced ground vibration
No full textAn investigation is presented on the nature of train-induced ground vibration propagation. It is based on a theoretical model for the track and a layered ground. Results are given of the responses of the ground and track to a moving harmonic or quasi-static load on the rails. The dispersion characteristics of the propagating modes of vibration in the track and the ground are presented and the excitation of vibration in the ground via the track is discussed in relation to these propagating wavenumbers. An important feature of the coupled system is the coincidence of a propagating wavenumber in the track and the ground that gives rise to the main peak in the vibration spectrum in the frequency range of interest. It has been observed, in some cases, that when the train speed reaches a value close to the speed of propagating waves in the ground, the response to the quasi-static axle loads of the train reaches a peak. The relationship between this critical speed and the wave speeds in the track and ground is considered in order to investigate the effectiveness of controlling this peak response load speed by increasing the bending stiffness of the track/embankment structure or by reducing its mass. It is found that such treatments may, or may not, have a significant effect depending on the ground stiffness and layering. For the multiple quasi-static moving axle loads of a train the loading has strong, closely spaced harmonic components. The effect on the vibration spectrum of the superposition of vibration from multiple axles is shown to lead to the reinforcement or suppression of some frequencies as a function of axle spacing and speed. This is demonstrated with calculated results
A comparison of a theoretical model for quasi-statically and dynamically induced environmental vibration from trains with measurements
No full textSimulation of ground vibrations from a moving harmonic load on a railway track
No full textA sequence of results is presented from a model of an oscillating load moving on a track on a layered ground. The results allow a visualization of the effect of the relative speeds of the load and the propagation speeds in the ground structure. This is useful in developing the understanding of the interaction of train speed, track structure and ground properties for high-speed trains. The simulation shows the excitation of high amplitudes of vibration in the track, the "bow wave" angle of propagation of vibration in the ground and the transfer of vibrational energy to a higher order mode as the speed of the load exceeds that of the first mode of propagation in the layered ground
Responses of infinite periodic structures to moving or stationary harmonic loads
No full textFormulae are derived for the computation of the response of periodically supported structures subject to a moving or stationary harmonic load. They are expressed in terms of an integral over the wavenumber in the longitudinal direction. The structures may be described using either a multiple-beam model, or more generally, a two-and-half-dimensional finite-element model. The supports, described by a receptance matrix, may have arbitrary degrees of freedom, either translational or rotational. Equations for free vibration propagation constants are yielded straightforwardly. Results are produced for a conventional ballasted track, showing the effects of the load speed and the modelling of the supports
Prediction of ground vibration from trains using discrete wavenumber finite and boundary element methods
No full textGround vibration is an important aspect of the environmental impact of rail traffic. Vibration from about 2–200 Hz is caused by trains moving on the ground surface or in tunnels. The wave field thus created must be modelled in three dimensions because of the excitation under each axle and the movement of the train. For arbitrary geometry of structures and ground surface to be allowed in the analysis, numerical models are required. In most practical situations, the ground and built structures, such as tunnels and tracks, can be considered to be homogeneous in the track direction and may be modelled using the wavenumber finite/boundary element method which is formulated in terms of the wavenumber in that direction. Compared with a conventional, three-dimensional finite/boundary element model, this model is more computationally efficient and requires far less memory since discretization is only made over the vertical–transverse section of the ground and/or built structures. With this model it is possible to predict complete vibration spectra. In this paper, the wavenumber-based modelling approach is outlined and then the applicability of the method to surface vibration and tunnel vibration analyses is demonstrated
- …
