1,721,124 research outputs found
The mechanism of railway curve squeal
No full textRailway is an energy-efficient means of transport and it is also an important solution to traffic congestion. However, the noise and vibration problems caused by railways attract more and more attention now. One particularly severe problem is curve squeal noise, which is an intense tonal noise that arises in tight curves under certain running and environmental conditions. The mechanism behind this squeal noise is still the subject of controversy. Two causes have been proposed over the last several decades: falling friction and mode coupling. The first one supposes that a decrease of the friction coefficient with increasing lateral sliding velocity occurs and this is equivalent to introducing negative damping into the system, which then feeds energy into the system. In the mode coupling phenomenon, coupling occurs between the vibration in two different directions and energy can be transferred between them.In this thesis, firstly, these two mechanisms are explored by using an existing curve squeal model to predict the curve squeal in both the frequency domain and the time domain. This model is improved by including a track model based on mass-spring systems, which is more physical and easier to use in the time domain. The results show that both falling friction and mode coupling can lead to instability. Also, the inclusion of the rail dynamics is found to play an important role in the generation of curve squeal. Moreover, it is found that the inclusion of wheel rotation in the model affects the results for different wheels to different extents. To illustrate the findings in terms of wheel mode coupling and wheel-rail coupling instability from this model, several further studies are then performed.A two-mode model is developed to assess the respective roles of the mode-coupling and falling-friction instability mechanisms in the generation of curve squeal. Different pairs of modes from different wheels are considered. A parametric study is performed including investigation of the effect of the adhesion coefficient, contact angle, lateral offset of the contact point, wheel damping and friction curve slope. Two basic features are found to be characteristic of the wheel vibration in the presence of mode coupling. The first is a frequency shift meaning that the squealing frequency can be different from the natural frequency of the corresponding wheel mode. The second is a phase difference between the vibration in vertical and lateral directions. Previous wheel vibration measurements are used to give a qualitative comparison with the model to identify these features.To study the effect of rail dynamics on curve squeal, the rail is firstly modelled as an infinite beam over a continuous elastic foundation. In contrast with the wheel, it is not characterised by vibration modes. Results show that the presence of the rail plays a role in the instability. Various effects are then considered that may change the resonant behaviour contained in the rail dynamics. These include the effect of varying the rail pad stiffness, the influence of the periodic support of the rail, reflections between multiple wheels on the rail, rail cross-section deformation and the inclusion of rail cross mobility. Finally, a reduced model is developed to identify the essential elements of the dynamic behaviour of the rail that can cause instability. In this model, a single wheel mode is included and the rail is represented as a mass, a spring or a damper. It is found that it is not necessarily the introduction of ‘modes’ in the rail that causes the wheel modes to couple with the rail; instead the equivalent mass and/or damper behaviour of an infinite rail is the origin of a wheel-rail coupling phenomenon.Finally, a laboratory measurement is performed by modifying an available machine originally designed to perform pin-on-disc friction measurements. By using a 1:5 scale model of a railway wheel, squeal noise is observed at two different frequencies. During the measurements the wheel is stationary and is set in the vertical plane while the rotating disc lies in the horizontal one. The axis of the wheel is tangent to the rotating disc. Lateral force and wheel vibration in radial and axial direction are recorded. From the vibration data it is found that the response of the wheel in the vertical and lateral directions are almost in phase and that the squealing frequencies is always almost coincident with a natural frequency of the wheel. For the friction, a mild falling trend can be observed when the sliding velocity increases. For sliding velocities below 0.15 m/s the peak axial vibration velocity is found to be equivalent to the velocity of the rotating disc at the contact point. These observations suggest that stick-slip and/or falling friction can be responsible for the squealing in this testrig while there is no evidence of mode coupling in this specific situation. <br/
Effects of rail dynamics and friction characteristics on curve squeal
No full textCurve squeal in railway vehicles is an instability mechanism that arises in tight curves under certain running and environmental conditions. In developing a model the most important elements are the characterisation of friction coupled with an accurate representation of the structural dynamics of the wheel. However, the role played by the dynamics of the rail is not fully understood and it is unclear whether this should be included in a model or whether it can be safely neglected. This paper makes use of previously developed time domain and frequency domain curve squeal models to assess whether the presence of the rail and the falling characteristics of the friction force can modify the instability mechanisms and the final response. For this purpose, the time-domain model has been updated to include the rail dynamics in terms of its state space representation in various directions. Frequency domain and time domain analyses results show that falling friction is not the only reason for squeal and rail dynamics can play an important role, especially under constant friction conditions
Dataset for paper "Effect of rail dynamics on curve squeal under constant friction conditions"
No full textDataset supports:
Ding, B., Squicciarini, G., & Thompson, D. (2019). Effect of rail dynamics on curve squeal under constant friction conditions. Journal of Sound and Vibration, 442, 183-199</span
Effect of rail dynamics on curve squeal under constant friction conditions
No full textCurve squeal noise is a severe railway noise problem that can occur when a railway vehicle negotiates a sharp curve. It is usually characterised by a very loud tonal noise and can be very annoying for people in the vicinity. It is generally attributed to friction-induced instability, either due to a falling friction characteristic with increasing sliding velocity or to a mode coupling mechanism which can lead to instability even for a constant friction coefficient. The squeal frequency is usually associated with one or more wheel modes. However, the wheel is coupled dynamically to the track and insufficient attention has been paid in previous research to the role played by the rail dynamic behaviour. In this paper, the effect of the rail dynamics on curve squeal under constant friction conditions is investigated by means of different modelling approaches. The rail is firstly modelled using a waveguide finite element (WFE) model and it is found that the inclusion of the rail dynamics in the model can lead to squeal in some situations where it would otherwise not occur. Various effects are then considered that may introduce additional resonant behaviour into the rail dynamics. These include the effect of the rail cross mobility, rail cross-section deformation, the influence of the periodic support of the rail and reflections between multiple wheels on the rail. The effect of the rail pad stiffness is also explored. However, the results show that all these factors have little influence on the predicted curve squeal instabilities. By means of a reduced model, the main characteristics of the rail dynamics that can result in squeal are then assessed. It is shown that the mass and damping-like behaviour of the infinite rail are at the origin of the instabilities rather than any modal behaviour of the track. Curve squeal may occur for a single wheel mode even if the rail is represented by a damper, which is a close approximation to the vertical mobility of the track at high frequencies. This forms a third possible mechanism for curve squeal in addition to falling friction and wheel mode coupling.</p
Dataset for paper "An assessment of mode-coupling and falling-friction mechanisms in railway curve squeal through a simplified approach"
Full text linkDataset supports:
Ding, B. et al. (2018). An assessment of mode-coupling and falling-friction mechanisms in railway curve squeal through a simplified approach. Journal of Sound and Vibration, 423, 126-140.</span
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
