This paper reports on fundamental research to investigate the influence of wheelset flexibility on the development of wheel polygonization of a locomotive. After preparing a flexible wheelset model ...by importing a FE (Finite Element) model into the MBS (Multi-Body System) environment, the investigation work proceeded in 3 steps. Firstly, FRF (Frequency Response Function) of the contact responses against the track irregularity is analysed for a free wheelset and an on-track wheelset, with consideration of rotation effect. Secondly, the influence of the wheelset flexibility on the contact responses excited by white noise is investigated for straight and curved tracks. The final step is to check the influence of the wheelset flexibility on the development of wheel polygonization based on a developed prediction program for railway wheel polygonization. 6 scenarios are investigated with comparison between rigid and flexible wheelsets. Results show that, the wheelset flexibility cannot dominate the railway wheel polygonization in a general sense, unless some prerequisites are fulfilled to provide a suitable environment for the wheelset flexibility to be effectively and continually excited to fluctuate the contact responses, and thereby initiate wheel polygonization. The torsional mode of the wheelset can be effectively excited by stick-slip vibration due to saturated contact adhesion that can occur on track with small curve radii or by large traction torque. In this case, the developed wheel polygonization order will be exactly determined by the wheelset torsional modal frequency and the vehicle speed.
•The influence of wheelset flexibility on wheel polygonal wear is identified based on a prediction program.•All the investigated wheelset flexible modes can be excited to influence the contact responses, but in very different way.•The wheelset flexibility cannot dominate the wheel polygonization unless some prerequisites are fulfilled.•The torsional mode of wheelset can be excited by stick-slip vibration to initiate the wheel polygonization.
This paper presents a comparative study on the applicability of existing popular wear models in simulation of railway wheel polygonization. Four representative wear models developed by BRR (British ...Rail Research), KTH (Royal Institute of Technology), USFD (University of Sheffield), and Professor Zobory respectively, are selected for the comparison with consideration of global and local methods. All the wear models are converted to calculate the instantaneous wear of one contact patch. Uniform expression of the converted wear functions is derived analytically with the equivalent wear coefficient as a useful index to identify the proportional relationship among the wear models quantitatively. Several scenarios grouped by harmonic excitation and random excitation are adopted to assess the fluctuation of the instantaneous wear depth calculated by different wear models. The evolved polygonal wear around the wheel circumference is also compared among the wear models based on a developed prediction program. Simulation results show that all the wear models being investigated in this paper present a similar ability to reflect the fluctuation of the instantaneous wear under various circumstances. Specifically, all wear models can correctly reflect the frequency characteristics of the excitation in a general sense, and the fluctuation phase of the instantaneous wear is obtained with almost the same result among the wear models. There is a very good consistency of trend for all local wear models to simulate the evolved polygonal wear. The mean value and the fluctuation amplitude of the instantaneous wear, as well as the roughness level of the evolved polygonal wear, are all determined by the original wear coefficients used. Besides, the global method is not suitable for calculating the polygonal wear of railway wheels as some sharp points might be generated by the absolute operation for the global WI (Wear Index).
•A uniform expression is analytically derived for four widely used wear models developed by BRR, KTH, USFD, and Professor Zobory respectively.•The derived equivalent wear coefficient is a useful index to identify the quantitative relationship among the wear models.•All of the wear models present a similar ability to reflect the fluctuation of the instantaneous wear depths under various circumstances.•The global method is not suitable for calculation of instantaneous wear depth of railway wheels.
This paper reports fundamental research on the general conditions for railway wheel polygonal wear to evolve. A common workflow for prediction of railway wheel polygonization is presented including ...assumptions, simulation scheme, and wear models. Based on this workflow, some rules for the evolution of railway wheel polygonization are proposed providing innovative perspectives to understand the basic mechanism of railway wheel polygonization. After summarising these rules, the general conditions for railway wheel polygonal wear to evolve are established. The phase between the instantaneous wear depth and the excitation is the key indicator determining the wheel OOR (Out-Of-Roundness) evolution direction (to grow or to diminish). The evolution tendency curve obtained from the instantaneous wear FRF (Frequency Response Function) is a useful tool to predict the OOR evolution, especially for predicting the OOR order that would grow predominantly at a given speed. If one or more structural modes can dominate the evolution tendency curve, and the energy distribution of track excitation allows this/these structural modes to be excited effectively, corresponding OOR orders can occur dominantly.
Having Your Say Shackleton, J. R; Oderberg, David S; Booth, Philip ...
2021, 2021-07-01
eBook
Today should be a Golden Age for free speech - with technology providing more ways of communicating ideas and opinions than ever before. Yet we're actually witnessing a growing wave of restrictions ...on freedom of thought and expression. In Having Your Say a variety of authors - academics, philosophers, comedians and more - stress the fundamental importance of free speech, one of the cornerstones of classical liberalism. And they provide informed and incisive insights on this worrying trend, which threatens to usher in a new, intolerant and censorious era.
To achieve high performance monitoring of the electric transmission powerpack for a diesel multiple unit (DMU), the dynamic responses of the rotor system inside the powerpack with dynamic spatial ...misalignment (DSM) and base motions from car body are investigated through structural modeling and numerical analysis. A three-dimensional coupled model, including public framework, diesel engine, electric generator and rotor system, is developed. Vibrations under deterministic and random base motions are numerically calculated using the Newmark Method. The simulation results show that vibration responses of the coupled model are evidently different from those of rotors with a fixed base. DSM is more nonlinearly sensitive to the deterministic base motion than rotor vibrations, and the converse is true when the base pitch motion is random in frequency. Additionally, results show that DSM may vary significantly in different axial positions, with large base motions in some extreme situations. These findings lay the primary foundations for implementing vibration-based condition monitoring of DMU diesel-generator systems.
•We compared the failure of railway thermite welds through real field-testing.•We simulated the dynamic impact force induced by the weld geometry.•We reported the progression of the surface hardness ...of welds in track condition.•We discussed the noticed failures; wear and cracks.
This paper details the field-testing approach and results of thermite welds used in railway applications. Rail steels made from R260 grades are welded by two different processes: the standard process according to the European standards, and a recent technology. Welds are introduced in the same testing location to ensure comparable loading conditions in the aim of studying their degradation behaviours. The total testing-period is 6 months. During the in-service period, the surface hardness of the running band, in the welded area, is recurrently measured. For an accurate assessment of field results, a vehicle/track interaction (VTI) model evaluated the expected dynamic loads induced by the initial vertical irregularities.
The simulations show that the highest dynamic load at the wheel/rail contact happens at the location of the maximum absolute gradient, in accordance with previous research. Particularly, dipped welds show relatively high dynamic forces inducing a high loss of the transversal profile. In respect of the field results, the comparison of initial and final surface hardness indicates a significant increase for ‘ALFONS’ welds over the welded areas. Additionally, all welds depicted a cyclic increase and decrease of the running band hardness. This result is discussed according to the ratcheting susceptibility of welds and eventual wear progression. For a testing-period of 10 weeks, the gauge corner of one ‘ALFONS’ weld developed a crack. The assessment of the longitudinal profiles revealed changes of the vertical irregularities that may modify the dynamic loads, and further the rolling contact fatigue mechanisms and degradation rates.
This study covers the parametric variations of vehicle and track characteristics to inform on the requirements for an optimum and yet pragmatic control of longitudinal rail weld profile. A ...statistical study has been carried out using a large set of measured weld profiles (arbitrary mix of flash butt welds and aluminothermic welds) in order to establish relationships between degradation mechanisms and the longitudinal geometry of the finished weld. The potential benefits which would be expected from improved controls over the welded profile, with respect to not only rail running surface damage but also susceptibility to rail breaks and ballast degradation, are demonstrated. Finally, recommendations for the review of the geometric controls of finished weld geometry in the relevant Euro Norms are made.
•The first-derivative assessment method is confirmed suitable in context of standard.•Light rail section on low track quality may be susceptible to rail foot fatigue.•Tighter weld geometry controls based on total bending stresses are proposed.
The minor mode is best understood as a tension between two scales, ascending and descending, and as a tension/ambiguity between two tonalities, the minor and its relative major. Analytical techniques ...include observing when composers switch between the two scales (for the most part when tendency tones resolve), and the ways the scales are occasionally combined. The explanatory power of the “harmonic minor scale” is subsumed in the two-scale approach. The only chord “requiring” the “harmonic minor scale” is the vii°7, and it is better understood as an ascending-scale functional harmony (an incomplete dominant) with a descending-scale color tone (the “incomplete dominant 9th”) that has no effect on its function. Melodic appearances of “harmonic minor” are usually coloristic devices to embellish ascending-scale dominant harmony, using the minor-6th scale degree from the descending scale. The two-scale analytical approach explains virtually all harmonic practice that is explained by the “harmonic minor” scale, and elevates “exceptions” to a grammatical status of less common “parts of speech”. These are used frequently enough to require explanation and integration into the overall harmonic model, as opposed to treating them as essentially ungrammatical utterances that connect “real words”. Teaching implications for harmony classes follow. Both the descending and ascending forms of each chord should be taught in the same lesson from the first exposure. The two-scale approach to analysis is to compare the method, location and frequency with which a composer has switched between ascending and descending scales (occasionally combining them), always considering the role of tonal ambiguity in the listener's perceptions. From their first assignments in the minor mode, students should be encouraged to compose exercises using both forms of each minor mode “diatonic” chord. Students should be encouraged to seek minor mode examples outside of the conventional anthologies used for teaching music theory, since anthologized selections tend to be chosen for optimal reinforcement of conventional approaches. Harmony texts/anthologies should contain a higher percentage of minor mode examples/explanations than major mode ones. These materials should fully cover the range of minor mode common practice, instead of being chosen for reinforcement of standard teaching models.
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