A state-of-the-art review of curve squeal noise: Phenomena, mechanisms, modelling and mitigation

[EN] Curve squeal is an intense tonal noise occurring when a rail vehicle negotiates a sharp curve. The phenomenon can be considered to be chaotic, with a widely differing likelihood of occurrence on different days or even times of day. The term curve squeal may include several different phenomena with a wide range of dominant frequencies and potentially different excitation mechanisms. This review addresses the different squeal phenomena and the approaches used to model squeal noise; both time-domain and frequency-domain approaches are discussed and compared. Supporting measurements using test rigs and field tests are also summarised. A particular aspect that is addressed is the excitation mechanism. Two mechanisms have mainly been considered in previous publications. In many early papers the squeal was supposed to be generated by the so-called falling friction characteristic in which the friction coefficient reduces with increasing sliding velocity. More recently the mode coupling mechanism has been raised as an alternative. These two mechanisms are explained and compared and the evidence for each is discussed. Finally, a short review is given of mitigation measures and some suggestions are offered for why these are not always successful.Squicciarini, G.; Thompson, D.; Ding, B.; Baeza González, LM. (2018). A state-of-the-art review of curve squeal noise: Phenomena, mechanisms, modelling and mitigation. Notes on Numerical Fluid Mechanics and Multidisciplinary Design. 139:3-41. https://doi.org/10.1007/978-3-319-73411-8_1S341139Anderson, D., Wheatley, N., Fogarty, B., Jiang, J., Howie, A., Potter, W.: Mitigation of curve squeal noise in Queensland, New South Wales and South Australia. In: Conference on Railway Engineering. pp. 625–636, Perth, Australia (2008)Hanson, D., Jiang, J., Dowdell, B., Dwight, R.: Curve squeal: causes, treatments and results. 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Engineering model for curve squeal formulated in the time domain

Curve squeal is a type of railway noise that may arise when a railway vehicle negotiates a relatively tight curve. Squeal is common in curves of a radius lower than 200 meters. A single frequency dominates the radiated sound, which makes squeal a very tonal noise. The high number of tight curves in cities and urban areas, the tonal nature and high noise levels, make squeal a serious source of noise pollution. The rising awareness of the impact of noise on public health increases the need to address the squeal problem. Consequently, there is a need for practical squeal simulation tools. The aim of this thesis is to develop a computationally fast squeal model in the time domain suitable for practical use. For this purpose, an existing squeal model is modified. The tangential contact is modelled using a point-contact model, which considers the contact variables in a global manner. This is in contrast to Kalker’s variational contact model which discretizes the contact area into elements. The friction model and contact compliance are defined in a stringent way in relation to Kalker’s model. In this way, the point-contact model is able to describe the transition of contact conditions from full stick to full slip. Although the proposed contact model is steady-state, it performs well at high frequencies. An upper limit of applicability of at least 5 kHz was found in the validation of the contact model within the squeal model. Compared to the classical validation with prescribed motion, the inclusion of the system dynamics puts different demands on the contact model. This indicates that contact models should be validated/compared in conditions that replicate their specific application as closely as possible. The engineering model is completed by implementing an existing model for sound radiation from the railway wheel, the implementation of which is validated against BEM results. A parameter study involving lateral creepage, wheel/rail contact position and friction is performed using the proposed squeal model. The investigated parameters show a strong influence on squeal occurrence and amplitudes. With the wheel being an important factor in squeal, the influence of the wheel modal damping is also investigated. Results indicate that increasing only the damping of the mode excited in squeal may not be sufficient. Squeal may then occur involving another mode with another frequency and amplitude. The amount of modal damping required to prevent squeal is relatively low

Engineering model for curve squeal formulated in the time domain

Curve squeal is a type of railway noise that may arise when a railway vehicle negotiates a relatively tight curve. Squeal is common in curves of a radius lower than 200 meters. A single frequency dominates the radiated sound, which makes squeal a very tonal noise. The high number of tight curves in cities and urban areas, the tonal nature and high noise levels, make squeal a serious source of noise pollution. The rising awareness of the impact of noise on public health increases the need to address the squeal problem. Consequently, there is a need for practical squeal simulation tools. The aim of this thesis is to develop a computationally fast squeal model in the time domain suitable for practical use. For this purpose, an existing squeal model is modified. The tangential contact is modelled using a point-contact model, which considers the contact variables in a global manner. This is in contrast to Kalker’s variational contact model which discretizes the contact area into elements. The friction model and contact compliance are defined in a stringent way in relation to Kalker’s model. In this way, the point-contact model is able to describe the transition of contact conditions from full stick to full slip. Although the proposed contact model is steady-state, it performs well at high frequencies. An upper limit of applicability of at least 5 kHz was found in the validation of the contact model within the squeal model. Compared to the classical validation with prescribed motion, the inclusion of the system dynamics puts different demands on the contact model. This indicates that contact models should be validated/compared in conditions that replicate their specific application as closely as possible. The engineering model is completed by implementing an existing model for sound radiation from the railway wheel, the implementation of which is validated against BEM results. A parameter study involving lateral creepage, wheel/rail contact position and friction is performed using the proposed squeal model. The investigated parameters show a strong influence on squeal occurrence and amplitudes. With the wheel being an important factor in squeal, the influence of the wheel modal damping is also investigated. Results indicate that increasing only the damping of the mode excited in squeal may not be sufficient. Squeal may then occur involving another mode with another frequency and amplitude. The amount of modal damping required to prevent squeal is relatively low

Time-domain modelling of curve squeal: a fast model for one- and two-point wheel/rail contact

Curve squeal is a type of railway noise that may arise when a railway vehicle negotiates a relatively tight curve. A single frequency, corresponding to a wheel mode, dominates the radiated sound, which makes squeal a very tonal noise. The high number of tight curves in cities and urban areas, its tonal nature and high noise levels make squeal a significant source of noise pollution. The rising awareness of the impact of noise on public health increases the need to address the squeal problem. Consequently, there is an increased need for practical simulation tools. In this thesis, a computationally fast squeal model formulated in the time domain is proposed. The computational efficiency is achieved by modelling the tangential contact with a point-contact model, which considers the contact variables globally. The friction model and the contact compliance are defined in a rigorous manner using Kalker\u27s variational theory. Validation results show that the contact model is valid up to at least 5 kHz. The proposed model is further extended to include the effects of spin creepage, contact angle and two-point wheel/rail contact. Spin creepage is treated as a contact property with its influence included in the friction model. Additionally, the model is also extended with an existing model for sound radiation from the railway wheel. Parameter studies show a strong influence of parameters that influence the dynamics coupling responsible for squeal: the contact angle, friction and the wheel/rail contact position. These parameters influence both squeal occurrence, amplitudes and frequency. Spin, however, influences only squeal amplitudes. With the wheel being a significant factor in curve squeal, the influence of the wheel modal damping is also investigated. To mitigate squeal in a specific case, all modes that are susceptible to squeal in that case have to be damped. Otherwise, squeal may shift to another mode and develop even higher amplitudes. The amount of modal damping required to prevent squeal is relatively low. Finally, a two-point wheel/rail contact case is analysed. Results show that squeal can occur on curve-outer wheels. The two-point-contact case is relatively complicated: squeal is the result of a combination of the dynamic interplay of the two contact points and the presence of two closely spaced wheel modes

Modelling of port container terminal using the queuing theory

The paper demonstrates application of the queuing theory in modelling a port container terminal As a port container terminal is a complex system, it is possible to achieve operational efficiency of the terminal through coordination of particular subsystem capacities, Le determination of optimal terminal capacity accommodation. A port container terminal can be considered as a queuing system defined with basic parameters: the ship or container arrival rate and the ship or container service rate, in an observed time unit. Appropriate indices of port container terminal operations are computed on the basis of these parameters. A model of total ship waiting and berth unoccupancy costs has been established through the introduction of costs as optimization criteria thus facilitating decision-making on optimal capacity of a port container terminal

Influence of spin creepage and contact angle on curve squeal: A numerical approach

Curve squeal is a loud tonal sound that may arise when a railway vehicle negotiates a tight curve. Due to the nonlinear nature of squeal, time-domain models provide a higher degree of accuracy in comparison to frequency-domain models and also enable the determination of squeal amplitudes. In the present paper, a previously developed engineering time-domain model for curve squeal is extended to include the effects of the contact angle and spin creepage. The extensions enable the evaluation of more realistic squeal cases with the computationally efficient model. The model validation against Kalker\u27s variational contact model shows good agreement between the models. Results of studies on the influence of spin creepage and contact angle show that the contact angle has a significant influence on the vertical-lateral dynamics coupling and, therefore, influences both squeal amplitude and frequency. Spin creepage mainly influences processes in the contact, therefore influencing the tangential contact force amplitude. In the combined spin-contact angle study the spin creepage value is kinematically related to the contact angle value. Results indicate that the influence of the contact angle is dominant over the influence of spin creepage. In general, results indicate that the most crucial factors in squeal are those that influence the dynamics coupling: the contact angle, wheel/rail contact positions and friction

An engineering time-domain model for curve squeal: Tangential point-contact model and Green's functions approach

Curve squeal is a strong tonal sound that may arise when a railway vehicle negotiates a tight curve. In contrast to frequency-domain models, time-domain models are able to capture the nonlinear and transient nature of curve squeal. However, these models are computationally expensive due to requirements for fine spatial and time discretization. In this paper, a computationally efficient engineering model for curve squeal in the time domain is proposed. It is based on a steady-state point-contact model for the tangential wheel/rail contact and a Green's functions approach for wheel and rail dynamics. The squeal model also includes a simple model of sound radiation from the railway wheel from the literature. A validation of the tangential point-contact model against Kalker's transient variational contact model reveals that the point-contact model performs well within the squeal model up to at least 5 kHz. The proposed squeal model is applied to investigate the influence of lateral creepage, friction and wheel/rail contact position on squeal occurrence and amplitude. The study indicates a significant influence of the wheel/rail contact position on squeal frequencies and amplitudes. Friction and lateral creepage show an influence on squeal occurrence and amplitudes, but this is only secondary to the influence of the contact position