Curve Squeal Research Articles

Effects of rail dynamics and friction characteristics on curve squeal

Curve 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.

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 5kHz. 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.

Tram squealing noise and its impact on human health.

Introduction:Tramway has become a serious urban noise source in densely populated areas. The disturbance from squealing noise is significant. Curve squeal is the very loud, tonal noise emitted by tram operation in tight radius curves. Studies had reported a relationship between noise levels and health effects, such as annoyance, sleep disturbance, and elevated systolic and diastolic blood pressure.Materials and Methods:This study aimed to analyze the wheel squeal noise along the tramway line in Košice, Slovakia, review the effects on human health, and discuss its inclusion in the design method. To observe the influence of a track curve on noise emission, several measurement points were selected, and the noise emission was measured both in the curve and in the straight lines employing the same type of permanent way.Results:The results in the sections with the radius below 50 m were greatly affected by the presence of a squeal noise, while the resulting noise level in the sections with the radius above 50 m depended on their radius. The difference between the average values of LAeq with and without the squeal in the measurement points with the radius below 50 m was 9 dB. The difference between the measurements in the curve sections with the radius below 50 m and those in the straight line was 2.7 dB.Conclusion:The resulting noise level in general was influenced by the car velocity and the technical shape of the permanent way. These results can be used in noise prognoses and in the health effect predictions.

At-Source Control of Freight Rail Noise: A Case Study

Controlling freight rail noise at-source can be more effective than seeking to treat either the noise path or the receiver. This paper presents a framework for at-source noise control of freight rail noise. This framework is discussed in the context of the complete system through which the noise is generated, and explained through a case study focused on curve squeal. The application to curve squeal includes considerations of the track, the wheel–rail interface and the rolling stock. It is shown how addressing each system in parallel can not only mitigate curve squeal, but can also lead to the more efficient operation of the railway. Other primary freight rail noise sources are also discussed, and opportunities for addressing these impacts through the proposed noise control framework are outlined. These include locomotive exhaust noise, locomotive idling noise, brake squeal and bunching/stretching noise.

Modelling Curve Gain in NSW

Noise from curve squeal is often a challenge for those preparing noise impact assessments for rail projects. This paper presents data to support a new modelling approach that better represents curve noise impact. Curve squeal can generate high levels of noise, and until recently there has been limited data available about how curve noise varies for different radius curves across the rail network in NSW. This paper presents comprehensive analysis of curve noise data measured at two tight radius curves and shows how the curve noise output relates to noise from nearby straight track. The NSW results are compared with the curve noise modelling approach outlined in the German standard Schall 03, which has been applied in noise assessments for several rail projects in areas with tight radius curves.

A numerical investigation of curve squeal in the case of constant wheel/rail friction

Curve squeal is commonly attributed to self-excited vibrations of the railway wheel, which arise due to a large lateral creepage of the wheel tyre on the top of the rail during curving. The phenomenon involves stick/slip oscillations in the wheel/rail contact and is therefore strongly dependent on the prevailing friction conditions. The mechanism causing the instability is, however, still a subject of controversial discussion. Most authors introduce the negative slope of the friction characteristic as a source of the instability, while others have found that squeal can also occur in the case of constant friction due to the coupling between normal and tangential dynamics. As a contribution to this discussion, a detailed model for high-frequency wheel/rail interaction during curving is presented in this paper and evaluated in the case of constant friction. The interaction model is formulated in the time domain and includes the coupling between normal and tangential directions. Track and wheel are described as linear systems using pre-calculated impulse response functions that are derived from detailed finite element models. The nonlinear, non-steady state contact model is based on an influence function method for the elastic half-space. Real measured wheel and rail profiles are used. Numerical results from the interaction model confirm that stick/slip oscillations occur also in the case of constant friction. The choice of the lateral creepage, the value of the friction coefficient and the lateral contact position on the wheel tread are seen to have a strong influence on the occurrence and amplitude of the stick/slip oscillations. The results from the interaction model are in good qualitative agreement with previously published findings on curve squeal.

Investigation of the effect of relative humidity on lateral force in rolling contact and curve squeal

Curve squeal is the result of the lateral force in rolling contact of rail and wheels along curves. Recently, field measurements of wheel squeal occurrences at a site in Australia showed an increasing possibility for a squeal event to occur as the relative humidity increases. To verify these results, a new method to measure the lateral and normal force simultaneously was developed on a test rig, so as to determine the friction-creep curves. To investigate the effect of relative humidity on squeal and friction creep curves, the relative humidity inside the acoustic enclosure of test rig was adjusted under controlled conditions of 50%, 70% and 90%. The test rig results show that the lateral adhesion ratio decreases slightly with the increase of relative humidity and that squeal is more likely in high relative humidity. The modelling analysis shows that the critical creepage decreases with the increase of the relative humidity, which means negative damping occurs for lower angle of attack.

The Impact of External Environments and Wheel-Rail Friction on Noise inside a Train Car

Trains travel through various environments typically on tracks above ground or in tunnels. When trains pass through different environments, the perceived noise inside a train car can change. For example, there are three main types of noise caused by wheel-rail interaction, namely, rolling, impact, and curve squeal. Each type can be perceived differently. To consider appropriate remedial measures, the effects of the external environment and wheel-rail interaction on noise inside train cars were investigated. Spectral analysis of noise from inside a train car traveling through tunnels featured a noticeable sound frequency around 250 Hz. More reflections enter train cars from tunnels with circular cross-section, namely those constructed by a boring machine. Impact noise had larger components at lower frequencies. Curve squeal noise had larger components at frequencies between 125 and 500 Hz.

Measurements of curve squeal from Oslo's subway

Curve squeal from the subway line at Brattlikollen, Oslo, has led to severe noise complaints through the years. Two important steps have been taken to reduce the problem. An automatic rail lubrication system has been installed on the critical spot, and Oslo's old subway trains (1300 series) are being replaced. One of the new trains (MX) has also been fitted with wheel dampers. Continuous measurements during 16 days and nights with 2238 train passages have been analyzed to verify the effectiveness of these steps to reduce noise. The main results are as follows: 1300 series trains without rail lubrication give severe curve squeal during 18% of the train passages. 1300 series trains with rail lubrication give severe curve squeal during less than 1% of the train passages MX trains give substantially less curve squeal than 1300 series trains, with or without lubrication The MX trains with wheel dampers gives no curve squeal, even without lubrication

Curve squeal of urban rolling stock—Part 1: State of the art and field measurements

This is the first part of a series of three papers dealing with curve squeal of urban rolling stock such as metros and trams. After a brief review of the present state of the art, the key parameters involved in curve squeal generation are discussed. Then, some results of field measurement campaigns, on metro and on tramway systems, are presented. A specific measurement methodology is applied for both campaigns in order to record the main key parameters: rolling speed, axle angle of attack, wheel/rail lateral position and modal damping of relevant wheel modes. On-board microphones are mounted close to each wheel of the instrumented bogies in order to locate the squealing wheels. No squeal occurs on the outer wheel of the leading axle in flange contact with the rail. The highest squeal levels are generally found on the front inner wheel. Pure tone frequencies are related to wheel axial modes for metro (undamped steel wheel) and for tramway (resilient wheels). Squeal occurrence is also observed on a bogie with independent wheels.

Curve squeal of urban rolling stock—Part 2: Parametric study on a 1/4 scale test rig

This paper is the second of a series of three, dealing with curve squeal of urban rolling stock such as metros and tramways. Measurements were carried out on a 1/4 scale test rig; they include parametric variations on a mono-block wheelset, and tests of anti-squealing solutions. The parametric variations show little influence of load and lateral contact position, except in the case of contact between the wheel flange and the rail, which prevents squealing. A relation between noise level and two kinematic parameters, rolling speed and angle of attack, is confirmed experimentally. The test of solutions leads to the determination of the damping value of the main wheel mode which is needed to suppress curve squeal. The average friction coefficient as a function of lateral creep is measured in dry conditions and with water.

Curve squeal of urban rolling stock—Part 3: Theoretical model

After a brief literature review on friction-induced vibrations and rolling contact, a model of curve squeal generation is presented. Both tangential and normal wheel–rail contact forces as well as axial and radial wheel dynamics are taken into account. For initial conditions close to the quasi-static equilibrium, the squeal occurrence is predicted through the stability analysis of wheel modes (linear analysis). In unstable cases, the squeal level and spectrum are determined through the numerical study of limit cycles in the time-domain (nonlinear analysis). The model is used to study the effect of the friction–velocity relationship and the coupling between tangential and normal dynamics on the stability of the system, especially for large lateral offsets of the wheel–rail contact point. A parameter study is also performed. Results on critical angles of attack, critical wheel damping factors, excited wheel modes and vibration levels are presented. Finally, the results are compared with laboratory and field measurements and the validity of the model is discussed.

Combating Curve Squeal: Monitoring existing applications

Curve squeal is the intense high frequency tonal noise that can occur when a railway vehicle traverses a curve or a switch. The high noise level causes annoyance for people who live in the neighbourhood of the squealing railway track as well as for the passengers waiting in stations with curves. The Combating Curve Squeal project is sponsored by the International Union of Railways (UIC) in order to develop tools to reduce curve induced squealing. The focus is to obtain applicable solutions. In phase 1, an overview of the extent of the noise problem for railways and a toolbox with methods and solutions to combat squeal noise were produced. In addition, work on a theoretical model was further advanced. As a conclusion, it was found that in principle solutions do exist, but several questions connected to their application have not yet been answered. Phase 2 of the project addresses these questions by concentrating on noise monitoring of existing solutions against squeal noise. Mainly infrastructure-based solutions to combat squeal noise in hot spots such as friction modification and asymmetric grinding will be assessed for further analysis. The aim is to obtain a preliminary design manual for practical solutions for the railways to reduce squeal noise. A measurement protocol and rig tests support these efforts. This paper focuses on the presentation of the applications and the development of the test procedure.

Transient models for curve squeal noise

The paper deals with numerical models of railway wheel noise occurring in narrow curves. Curve squeal is presumed to issue from a lateral creepage of the wheels on the rail head. The frequency range is from around 400 to almost 8000 Hz, with noise levels up to 120 dB close to the wheel. Lateral friction forces are induced on the wheel–rail contact area (typically stick-slip forces). Due to nonlinearities of friction forces, a transient analysis of the lateral creepage of the wheel is performed by using an axi-harmonic model. Results give a reduced number of excited modes. It is shown that squealing modes have 3, 4 and 5 nodal diameters. These results agree with experimental investigations of squeal noise measurements. An extension of the transient model is finally discussed. It consists to study the efficiency of a noise attenuation system made of a metallic ring inserted into grooves machined into the wheel.

The Harmonoise/IMAGINE model for traction noise of powered railway vehicles

Traction noise is one of the noise sources of powered railway vehicles such as locomotives, electric- and diesel-powered multiple unit trains and high-speed trains. Especially at speeds below 60 km/h and at idling, but also at acceleration conditions for a wide range of speeds, traction noise can be dominant. This is relevant for noise in residential areas near stations and shunting yards, but in some cases also along the line. The other relevant sources are rolling noise, often dominant between 100 and 250 km/h, aerodynamic noise, which can be dominant above 300 km/h, braking noise, curve squeal and impact noise. The braking system can often technically be considered part of the overall traction system, although acoustically it will often have separate noise sources. In the Harmonoise and IMAGINE EU projects, a generalised prediction model for railway traction noise has been proposed to cover a broad range of powered railway vehicles. The model is one of the prediction modules for overall rail traffic noise, which also covers the other main sources. The traction noise model includes the main operational parameters such as driveshaft speed and power settings, and also takes individual auxiliary components and their duty cycles into account, such as compressors, valves and fans. Source height is included in the model. The level of modelling detail in the many potential traction noise sources has been kept to a minimum, as for the purpose of rail traffic noise prediction it often suffices to model only the dominant sources. Measurement methods are outlined to determine the noise emission spectra, from which extrapolations are made to obtain estimates for different operating conditions.

Top-of-rail friction control for curve noise mitigation and corrugation rate reduction

Top-of-rail friction modifiers are designed to control frictional characteristics at the wheel–rail interface that influence noise, corrugations, and lateral forces. Key characteristics of the resulting thin film are: (1) controlled intermediate coefficient of friction and (2) positive friction, to reduce roll–slip oscillations related to both curve squeal noise and short pitch corrugation development. Practical results are presented on the effect of friction modifiers on curve squeal and flanging noise generation at a range of European mass transit sites. Reductions in A-weighted noise ranging from 6.3 to 22.8 dB were recorded, with an average reduction across the different test sites of 12 dB. Both top-of-rail squeal and flanging components of noise were reduced. The effect of friction modifier on short pitch corrugation development was evaluated over several years at two curves at Metro Bilbao. Under conditions where corrugations grew from 0.1 to 0.5 mm in 18 months under baseline conditions, with application of friction modifier essentially no corrugation growth occurred in an equivalent time period.

Introduction of falling friction coefficients into curving calculations for studying curve squeal noise

In this paper, a method of introducing falling friction coefficients into curving simulations for studying curve squeal noise is presented. Generation of squeal at the wheel of a railway vehicle in a curve is caused by unstable vibration, caused in turn by a lateral wheel/rail force which reduces with increasing lateral creepage. To model vehicle curve squeal, the wheel/rail tangential force in the curving simulation is calculated by a modified version of FASTSIM, which uses a sliding velocity-dependent friction characteristic. Using the falling friction characteristics, a UK passenger vehicle is modelled with SIMPACK. Curving behaviour is simulated for a range of curve radii and cant deficiencies. The wheel/rail contact properties are then obtained to study the possibility of the occurrence of squeal using a frequency-domain method. The methodology in this paper allows various curves, wheel/rail profiles, vehicle speeds and friction characteristics to be taken into account.

On the Design of Running Gears with Radial Steering Wheel Sets

Noise reduction of railway vehicles can be reached by suitable design of their bogies and running gears. Radial steering wheel sets avoid curve squeal. Besides they reduce lateral forces between the wheel and rail and their wear. Design principles for the development of interconnected self-steering wheel sets are introduced on examples of bogies for new articulated vehicles TEĹ˝ and coupled single-axle running gears FEBA for commuter trains NSB Class 72 from Bombardier Transportation Winterthur.

Curve squeal of train wheels: unstable modes and limit cycles

When a train goes round a curve, a transverse friction force may act at the contact points between the wheels and the rail in such a way that the wheels are excited to perform bending oscillations and to radiate a high–pitched squeal noise. This phenomenon has been modelled theoretically and simulated numerically. The wheel, which is a linear system, is described by a superposition of bending modes. It is excited transversely at one point along its edge by a stick–slip friction force, which depends nonlinearly on the wheel velocity. The growth rates of individual wheel modes are calculated, revealing the linearly unstable modes. The time history of the oscillation is also calculated, and this shows limit cycles dominated by the frequencies of some, but typically not all, of the linearly unstable wheel modes. Whether a mode is selected for the limit cycle depends on the time it takes for its velocity to reach a particular threshold and on its frequency relationship with other modes.

CURVE SQUEAL OF TRAIN WHEELS, PART 1: MATHEMATICAL MODEL FOR ITS GENERATION

A mathematical model is presented for the squeal noise generated by trains when traversing tight curves. Curve squeal is presumed to arise from lateral crabbing of the wheels across the rail head. This induces a lateral friction force acting at the contact of each wheel with the rail. An individual wheel then performs out-of-plane oscillations which are radiated and heard as squeal. This phenomenon is modelled by considering a flat round disc, with several out-of-plane modes, excited at one point along the edge by a dry-friction force (typically a stick/slip force) which is dependent on the disc velocity. An iteration scheme is developed which gives the time history of the disc velocity. The iteration is straightforward and only requires the impulse response (or the Green's function) of the disc and the functional dependence between friction force and disc velocity (friction characteristic). The numerical simulations produce time histories that show transient phenomena, such as exponential amplitude growth and the onset of limit cycles. The way these phenomena are influenced by some parameters, in particular the modal loss factors of the disc and its crabbing speed, will be examined. Practical methods to reduce or eliminate curve squeal will be discussed.