Squeal Noise Research Articles

Railway curve squeal detection and tonal analysis

Railway curve squeal is a loud tonal noise generated by instabilities in the wheel-rail contact of railway vehicles while negotiating tight curves. The emitted noise is perceived as highly disturbing and contributes to noise problems in urban environments. Traditional monitoring of squeal occurrence involves analyzing train pass-by sound measurements. Such monitoring system is sensitive to high background noise which can pose a problem in urban environments with limited possibilities for suitable microphone placement. To overcome these issues, an alternative approach to detect curve squeal from rail vibration measurements is investigated. This comprises a simple and practical monitoring solution virtually unaffected by sound disturbances from the surroundings. Furthermore, this method can identify whether squeal noise occurs on the low or high rail. Field measurements involve a two-part analysis: 1) the development and validation of a method for detecting squealing events from rail vibrations, and 2) identifying tonal components from the measured signals. Results from the first part suggest that curve squeal can be detected from rail vibrations and the specific rail where squeal is generated can be identified. In the second part, specific frequency regions where squeal tonal components tend to emerge are recognized.

A case study of railway curve squeal radiated from both the outer and inner wheel

This case study is presented after observations were made that partially contrast the prevailing picture of railway curve squeal given in the literature. These are observations with significance both for modelling and condition monitoring. The current case study will be followed by a subsequent investigation focused on the validation and application of a simulation model to investigate root-causes for curve squeal at the Stockholm metro. Curve squeal in a 213 m radius curve on the Stockholm metro is studied. Data includes track characteristics (rail profile, rail roughness and gauge width) and noise measured at the trackside as well as by two vehicles equipped with an on-board mounted noise monitoring system. The current case study contrasts field measurements of curve squeal reported in the literature by a relative shift of emitted noise towards higher frequencies. Wayside noise measurements in the studied curve during a few hours showed squeal generation for all vehicle passages with dominating 1/3 octave band centre frequencies in the range between 6.3–15.8 kHz. Noise data measured during one year of regular traffic of two vehicles equipped with a monitoring system were obtained. The occurrence of curve squeal was analysed through an implementation of the curve squeal detection algorithm in operation at the Stockholm metro. This algorithm was also applied to search for events of squeal noise radiation from the outer wheel. Results show emissions of squeal noise from the inner and outer wheel for 65 % and 8 % of the vehicle passages through the studied curve, respectively. Further, the occurrence of curve squeal radiated from the inner wheel was found to increase by 10 % after rail grinding. In the literature, squeal radiated from the outer wheel is described as having an intermittent character with magnified spectral components in the frequency range between 5–10 kHz. In contrast, the current work presents sustained tonal squeal generated from the outer wheel with similar noise characteristics as typically related to ordinary curve squeal.

Parametric analysis of the relationship between squeal and friction wear in motorcycle disc brakes

Squeal is a noise problem that affects all types of automotive brake systems and may affect the health of the population living in heavy traffic areas. Parameters such as pressure, friction, and Young’s Modulus are crucial in determining brake noise generation. Notably, wear on rubbing surfaces emerges as a key contributor to squeal, affecting the overall brake system functionality and necessitating frequent maintenance and parts replacement. This study conducted a detailed analysis of the influence of material and operational factors on squeal generation, specifically examining their relationship with friction wear in motorcycle disc brakes. To achieve this goal, a parametric study was conducted using finite element analysis software ANSYS. Thus, the study involved subjecting the geometry to static and modal analyses to verify the generation of unstable modes. Additionally, two models were built to analyze the influence of wear on noise: one with Archard wear activated, which calculated the worn volume, and another with this option disabled. The results of the study suggest that wear is a crucial parameter that must be considered in numerical models, given its significant impact on stability attributes. Moreover, since material and operational parameters play a substantial role in generating squeal noise, this study provides valuable insights into the causes and effects of brake noise, offering practical recommendations for mitigating this common problem in motorcycle disc brakes. The model developed also serves as foundational framework for configuring simulations for similar systems, automotive or train disc brake, to study the noise and lifespan of pads.

Friction-Wear and Noise Characteristics of Friction Disks with Circular Texture.

The reduction of friction-induced noise is a crucial research area for enhancing vehicle comfort, and this paper proposes a method based on circular pit texture to achieve this goal. We conducted a long-term sliding friction test using a pin-on-disc friction and a wear test bench to verify the validity of this method. To compare the friction noise of different surfaces, texture units with varying line densities were machined on the surface of friction disk samples. The resulting friction-wear and noise characteristics of the samples were analyzed in conjunction with the microscopic morphology of the worn surfaces. The results indicate that surfaces with textures can delay the onset of squeal noise, and the pattern of its development differs from that of smooth surfaces. The noise reduction effect is most evident due to the proper distribution of textures that can form furrow-like wear marks at the wear interface. The finite element results demonstrate that this morphology can improve pressure distribution at the leading point and reduce the tendency of system instability.

Numerical analysis of brake squeal noise – Application to the disk brake systems

Exploring Noise Reduction in Automotive Disc Brake Systems: Investigating the Impact of Viscoelastic Core Sandwich Plates. This study delves into the phenomenon of brake squeal noise generated by automotive disc brake systems. It focuses on analyzing the response of sandwich plates with viscoelastic cores, which are employed within brake systems to mitigate squeal noise arising from friction between brake pads and the brake disk. Through a series of finite element analyses conducted under varying operational conditions, including friction coefficient and angular velocity, the research aims to ascertain the complex eigenvalue of the disc brake system in order to identify unstable modes. The findings underscore that the incorporation of viscoelastic layers within preloaded, slender sandwich plates introduces nonlinear dynamic characteristics that contribute to the reduction of squeal noise within braking systems.

Automotive disc-brake squeal noise modeling for shape optimization under uncertainties

Disc-brake systems in automotive vehicles tend to exhibit undesirable squeal noise during braking operations. Although this noise does not affect braking efficiency, it creates noise pollution and poses problems from a sales point of view since noise is commonly associated with malfunction by consumers. Squeal noise can be minimized by optimizing the shape of the system's mechanical parts. However, uncertainties related to manufacturing processes inevitably affect the system's response, and must be considered. The presented work aims at numerically quantifying and minimizing disc-brake squeal noise in the presence of uncertain parameters. A simplified disc-brake model is constructed using the novel Isogeometric Analysis method which is well-suited to shape optimization problems. The prediction of squeal noise propensity is based on the fact that squeal noise is directly related to unstable structural modes and uses Complex Eigenvalue Analysis to determine the extent of squeal occurrences. A surrogate-based optimization strategy is used to handle the high computational cost in the context of optimization, as well as to propagate uncertainties. The constructed model shows good capability for representation and quantification of squeal noise phenomena. A Pareto front of robust squeal minimizing shapes is obtained through the proposed approach.

Flanging, squeal and corrugation-induced noise: Insights from recent measurement campaigns at interconnected tight curves

High noise events at tight curves often comprise of squeal, flanging and corrugation-induced noise. All noise types have the potential to cause annoyance at sensitive receivers in close proximity to the rail line. The presence of squeal, flanging and other high noise events at three interconnected sharp passenger curves on the metropolitan network in Sydney, New South Wales is investigated in the context of measured parameters. Rail and noise parameters were measured at ten locations in 2021, with a repeat of the measurements undertaken at three locations in 2022. Differences in high noise events were analysed and quantified to understand the underlying causes of curving noise in this area. The role of the wheel-rail interface contact conditions, train type, rail roughness, friction and speed is investigated to provide insights into the mechanisms leading to curving noise events at this site.

Development of analytical model for a wheel and rail vibration associated with curve squeal noise of railways

In this study, an analytical model for the vibrations of both a railway wheel and rail related to curve squeal noise was developed. The model was based on lumped parameter systems from the vibration characteristics of the wheel and rail and contact forces between them. Moreover, this model included two coupling factors between a wheel and rail, and between two vibration directions. The parameters of an actual wheel and track were applied to the model and their vibrations were estimated. The measurement of the curve squeal was also carried out at a curved section in an actual railway test line. From these measurement results, the peak frequencies in the estimated wheel vibration when passing through a curve are well simulated. Although the model needs to be improved in terms of the vibration magnitude, it has sufficient potential to simulate the vibration related to squeal noise.

Study on the noise generated in curved sections of railways

When trains run on a curved track, wheel and rail vibrations sometimes cause squeal noise (below 10 kHz) and high-frequency noise (above 10 kHz), contributing greatly to overall wayside noise and often causing complaints from residents. The measurements of noise and vibrations were conducted in commercial lines to understand the mechanisms underlying the generation of these noises and develop methods to reduce them. It is found that the occurrence of these noises varied from train to train, and the magnitude and dominant frequency at which they occurred varied greatly from wheel to wheel. Furthermore, the analysis of the results showed that these noises become prominent both inside and outside when outer wheel flanges contact outer rail.

Brake Squeal Investigations Based on Acoustic Measurements Performed on the FIVE@ECL Experimental Test Bench

Radiated noise is a major topic of interest regarding the brake squeal phenomenon as it is directly linked to the noise generated which can be potentially detrimental to user comfort and perception. However, very few studies offer in-depth and comprehensive insight into the analysis and understanding of acoustic noise during squeal events. This study is intended to provide an original contribution to this issue by investigating acoustic phenomena occurring during the squeal phenomenon via a digital antenna composed of 117 microphones. Experiments are performed on the Friction-Induced Vibration and noisE test bench at Ecole Centrale de Lyon (FIVE@ECL). The first main aim is to investigate the characteristics of the acoustic radiated field during brake squeal and more particularly to describe the evolution of the radiated field patterns per revolution of the disc system. The second major aim is to illustrate the possibility of reconstructing the radiated acoustic field everywhere in the space surrounding the brake system, leading to the construction of a robust representation of 3D acoustic patterns, providing acoustic squeal events in the physical space around the brake system. Results show that the vibratory signature remains identical during squeal event braking test. The acoustic signature of squeal noise consists mainly of a fundamental frequency and its harmonic components, with secondary lower contributions from other fundamental frequencies. The associated radiated acoustic field during squeal events are characterized by different directivities and intensities of the acoustic radiated field for each squeal frequency, with potential changes in these directivities and intensities over short times corresponding to the rotation period of the disc.

The Numerical Study for the Effect of Stiffness Matching on Wheel–Rail Curve Squeal Noise

This study delves into the phenomenon of high-frequency squeal noise occurring as trains traverse small-radius curved tracks and investigates the factors influencing wheel–rail curve squeal noise, particularly focusing on stiffness matching. To achieve this, we initially construct a finite element model of the wheel–rail friction system using finite element software ABAQUS 2022, validating its accuracy against Coulomb’s friction law. Subsequently, we employ complex eigenvalue analysis to extract the complex eigenvalues and vibration modes of the wheel–rail system, enabling us to study the positions and vibrational patterns associated with squeal noise by analyzing the amplitudes of unstable modes. Finally, we assess the impact of wheel–rail stiffness matching on curve squeal noise, using wheel–rail material stiffness and rail support stiffness as key variables. The outcomes of this study reveal the following insights: (1) Unstable modes closely align with the resonant frequency and mode shape of the wheel and rail. (2) Curve squeal noise primarily emanates from vibrations at the rim, railhead, and rail foot. (3) Wheel and rail stiffness significantly affect squeal noise, with a significant deviation in the elastic modulus between rail and wheel increasing the likelihood of squeal noise, while an optimal ratio of about 1.2 is observed. (4) Rail support stiffness plays a discernible role in controlling curve squeal noise. Theoretically, maintaining an appropriate support stiffness level can minimize the negative damping ratio of unstable modes, providing a viable avenue for curve squeal noise control.

Orthogonal binary singular value decomposition method for automated windshield wiper fault detection

For automobile manufacturers, reducing vehicle interior noise is essential for increasing customer satisfaction and vehicle quality. Windshield wipers are one of the major components that generate such noises, and faulty wipers could negatively affect passengers’ psychological and physiological perceptions while driving. Thus, identifying faulty wipers during the manufacturing process would improve the driving experience and vehicle and road safety as well as reduce driver distraction. However, the existing windshield wiper noise-detection process is entirely manual, relies upon human subjectivity, and is time-consuming. Accordingly, this paper develops a novel automated windshield wiper fault-detection system. First, a novel binarization approach is used to effectively binarize the transformed spectrograms of sound signals from windshield wiper operation to segment nAoisy regions. Then, a new matrix-factorisation approach called orthogonal binary singular value decomposition is proposed to decompose binarized mel spectrograms into uncorrelated binary eigenimages to extract meaningful features and identify faulty wipers. Then, the k -nearest neighbour classifier is utilised to classify the extracted features into normal or faulty windshield wipers. Finally, to demonstrate the effectiveness of the proposed system, it was validated on real-life windshield wiper reversal and squeal noise datasets, where it outperformed existing methods and achieved accuracies of 95% and 94%, respectively.

Influences of CrFe granularity and proportion on braking performance and dynamic response of Cu-based pads

In this study, the effects of granularity and proportion of CrFe on both braking performance and dynamic characteristics of copper-based friction materials were investigated. Braking tests and analyses of microstructure, elements, and vibration were conducted. Braking performance was evaluated using a scale pin-on-disc testing machine. Dynamic response was investigated by piezoelectric accelerometer and vibration signal analysis. Results show that the material containing 10% fine ferrochrome particles has the most stable friction coefficient and the lowest wear rate, particularly at high speeds (300–350 km/h). Moreover, by increasing the fine chromium iron content, high-frequency vibration and squeal noise are suppressed. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and laser scanning confocal microscopy were also conducted. Vibration signals were analyzed using fast Fourier Transform. These tests reveal the mechanism of the appropriate CrFe size and content to improve the braking ability and steadiness of pads for high-speed trains. This research is anticipated to be used as a beneficial reference for the design and manufacture of high-performance and environmentally friendly brake pads.

The effect of braking conditions on the particular matter emissions and brake squeal

Particular matter (PM) and squeal noise emitted from disc brakes are essential research subjects in the automotive industry. This study investigates the effect of braking conditions on the PM emissions and brake squeal of low metallic (LM), semi-metallic (SM) and non-asbestos organic (NAO) brake friction materials (BFMs) with a pin-on-disc tester. Braking conditions significantly affect the total number concentration (TNC) for all three BFMs. Generally, the geometric mean diameter (GMD) for NAO BFM is smaller than that for SM and LM BFMs. Moreover, the effect of braking conditions on the GMD for SM and LM BFMs is higher than that for NAO BFM. The speed has a more significant effect on GMD than contact load. The braking conditions can significantly affect the PMC. SM and LM BFMs exhibit larger particle mass concentrations (PMCs) than NAO BFM in most cases. All three BFMs show comparable A-weighted sound pressure levels (SPLs). The influence of braking conditions on brake squeal for SM and LM BFMs is stronger than that for NAO BFM.

Investigation of wheel squeal noise under mode coupling using two-disk testrig experiments

Wheel squeal noise is a common problem that occurs in railway systems especially on curved tracks. These tonal noises are usually found at high frequency, typically over 1 kHz. The cause of the squeal noise remains unclear and could be different under varied conditions. Several mechanisms that could cause wheel squeal, including falling friction and mode coupling, have been proposed in literature. Most existing lab experimental investigations were focused on the squeal noise caused by falling friction with vertical contacts. As a result, the squeal noise generated by mode coupling could be missed due to the absence of a non-vertical contact angle. In this work, a two-wheel test rig has been designed with curved wheel profiles to achieve adjustable contact angles with lateral components. Experimental and numerical modal analysis of the two-disk system was conducted to determine the dynamic characteristics for exploration of mode coupling effects. Using a set of benchmark parameters predicted to be the cause of significant mode-coupled instability, squeal noise was found at frequencies higher than the existing falling friction experimental tests as reported in the literature. The frequency and amplitude measured in the experiments agreed with the predictions of the analytical mode coupling model. Further experiments varying control parameters, contact angle, angle of attack and direction of rotation were performed, confirming that the new squeal noise was caused by mode coupling.

Study on reduction of squeal noise of disc brake system considering braking temperature of urban railway vehicle

Study on reduction of squeal noise of disc brake system considering braking temperature of urban railway vehicle

A Review of Wheel-Rail Dynamic Behavior on Curved Tracks

With a speedy advancement in vehicle speed and transport capability, a huge challenge has been imposed to improve railway vehicle dynamic behaviour and track design to ensure the optimum performance of railway vehicles and tracks. To safely negotiate the vehicle speed on circular and transition curve tracks several aspects such as wheel-rail wear, smooth ride and vehicle stability need to be analysed. The investigators have paid great attention to exploring the compatibility among vehicle stability and curving ability, parametric analysis and optimization of curving performance, minimising the wheel-rail wear and curve squeal noise etc. The present paper focuses on reviewing these past efforts made by the researchers.

Experimental Study on Reduction of Curve Squeal Noise on Mountain Tram Wheels on Sharp Curves Using Lubricant

Curve squeal noise is an intense tonal noise that occurs when a train goes through a narrow curve and is generated by the wheel contacting the rail. The squealing noise is an issue in mountain tram development projects. In this study, 1:7.5 scaled equipment is proposed to produce the squealing noise based on rolling speed, rolling direction, angle of attack, and preload ratio. Solid-stick lubricant is used as a mitigation method. The similarity law is applied and a finite element analysis code is used to compare the natural frequency of full-scale and small-scale results. The results show that the scaled equipment can generate squealing noise and that rolling backward direction has a higher possibility of generating squealing noise. Moreover, the frequency similarity approach is verified, and the solid stick lubricant is found to successfully mitigate the squealing noise even at high rolling speed and angle of attack.

Modelling of wheel/rail squeal noise in curves from mono-harmonic vibratory limit cycles

Most of the works in the literature agree to attribute the generation of wheel/rail squeal noise in curves to the important lateral slip imposed in the curve and the resulting instabilities. In models, the occurrence of the phenomenon is thus generally studied through a stability analysis based on the linearization of the contact forces. Despite its undeniable interest, the stability analysis does not allow the prediction of the amplitudes of the nonlinear self-sustained vibrations resulting from the instabilities. These nonlinear vibrations are most often calculated using a numerical integration of the dynamic equations of the system in the time domain. Some authors have proposed simplified methods allowing a direct calculation of stationary regimes, but limited to a reduced modal description of the system dynamics. In this presentation, an original method is proposed to determine approximate limit cycles from the wheel/rail contact mobilities expressed in the frequency domain. The contact condensation allows to be both more general and more functional to describe the dynamics of structures, in particular the one of the rail. Assuming a mono-harmonic vibratory cycle, the corresponding amplitude is determined from a power balance and the squeal level at the considered pulsation is obtained from analytical radiation factors.

State of the art about solutions for tram noise reduction in the framework of the Life SNEAK project

The LIFE SNEAK project, started in September 2021, aims at the reduction of noise from road traffic that mainly affects densely populated urban areas where the noise and vibrations produced by the tram overlap with noise produced by road traffic. Applicative measures will be designed and tested in a pilot case of the city of Florence, such as low-noise and vibration surfaces, with life cycle costs comparable to those of traditional surfaces, and measures to reduce tram noise aiming to obtain substantial reductions in noise and annoyance. Referring to tram noise, in the first phase of the project, specific attention has been dedicated to the state-of-the-art analysis concerning possible measures to perform noise reduction with specific attention to noise due to wheel-rail contact and "squeal noise" phenomena that mainly occur in urban environments close to curves with small radius. In this paper, the results of the state-of-the-art analysis are presented with particular attention to the use of sound-absorbing panels to be applied on the tram (bogie skirts).