Time-domain prediction of impact noise from wheel flats based on measured profiles

Railway impact noise is caused by discrete rail or wheel irregularities, such as wheel flats, rail joints, switches and crossings. In order to investigate impact noise generation, a time-domain wheel/rail interaction model is needed to take account of nonlinearities in the contact zone. A nonlinear Hertzian contact spring is commonly used for wheel/rail interaction modelling but this is not sufficient to take account of actual surface defects which may include large geometry variations. A time-domain wheel/rail interaction model with a more detailed numerical non-Hertzian contact is developed here and used with surface roughness profiles from field measurements of a test wheel with a flat. The impact vibration response and noise due to the wheel flat are predicted using the numerical model and found to be in good agreement with the measurements. Moreover, compared with the Hertzian theory, a large improvement is found at high frequencies when using the detailed contact model.     

The effects on noise of changes in wheel/rail system parameters

An analytical model has been developed that simulates the generation and propagation of wheel/rail noise. In the model, wheel/rail vibrations are induced by running surface roughness. The vibration responses are determined from considering contact stiffness effects and wheel/rail impedance interactions. Near field sound power levels are then calculated by combining the responses with radiation efficiencies, space-averaging the velocity squared on the wheel, and accounting for the decay of vibration along the rail. Finally, the noise levels predicted for the wayside are obtained from an analysis of the propagation that includes the effect of finite ground impedance. Good agreement exists between the analytical model and a series of validation measurements taken at DOT's Transportation Test Center in Pueblo, Colorado. A sensitivity analysis conducted for the parameters of a typical baseline system achieved significant changes in rolling noise only for reductions in wheel/rail contact stiffness, increases in wheel/rail contact area, and decreases in wheel/rail roughness through wheel truing and rail grinding.     

Wheel/rail noise—Part III: Impact noise generation by wheel and rail discontinuities

This paper is part of a series of publications dealing with wheel/rail noise [1–4]. Except for comparing the relative importance of impact noise with rolling noise, this paper concerns itself exclusively with the impact noise generated by such discontinuities as rail joints, frogs, switches, and wheel flats.Studies show that above a certain critical train speed the wheel separates from the rail when the interface encounters certain types of discontinuities. This critical train speed is an important acoustical parameter, because the noise generation process obeys completely different laws in the speed ranges below and above it. From the geometry, the kinematics, and the dynamics of the wheel/rail system, analytical models have been developed to identify the major variables controlling the generation of impact noise. The validity of these models has been confirmed by both scale-model and full-scale experiments.The results of the study show the following: (1) at rail joints, the height difference—and not the width of the gap—is the controlling parameter; (2) below critical train speed, impact noise increases with increasing train speed and does not depend on the direction of travel; (3) above critical train speed, the intensity of impact noise increases with increasing train speed for travel in the step-up direction but is independent of the train speed for travel in the step-down direction; (4) in generating impact noise, wheel flats are equivalent to step-down rail joints, provided flat height equals height difference at the joint; (5) both the magnitude and spectrum of impact noise produced by wheel and rail discontinuities can be predicted from a simple wheel drop test. With the knowledge gained from both the analytical and the experimental studies, we have been able to identify feasible measures for the control of impact noise.     

Wheel/rail noise generation due to nonlinear effects and parametric excitation

Two models are developed, one in the time domain and another in the frequency domain, to explain when a wheel/rail noise generation model requires the inclusion of discrete supports, parametric excitation, and the nonlinear contact spring. Numerical simulations indicate the inclusion of discrete supports to describe low frequency response, and also at higher frequencies, especially where the rail is very smooth or has a corrugation/wavelength corresponding to the pinned-pinned frequency. With a corrugation, it may become essential to include the nonlinear contact spring, as contact loss occurs at high corrugation amplitudes. As nonlinearity causes force generation over a broad frequency range, some contributions excite wheel resonances, resulting in high radiation levels, that require the inclusion of wheel/rail nonlinear effects and parametric excitation for accurate prediction.     

A HYBRID MODEL FOR THE NOISE GENERATION DUE TO RAILWAY WHEEL FLATS

A numerical model is developed to predict the wheel/rail dynamic interaction occurring due to excitation by wheel flats. A relative displacement excitation is introduced between the wheel and rail that differs from the geometric form of the wheel flat due to the finite curvature of the wheel. To allow for the non-linearity of the contact spring and the possibility of loss of contact between the wheel and the rail, a time-domain model is used to calculate the interaction force. This includes simplified dynamic models of the wheel and the track. In order to predict the consequent noise radiation, the wheel/rail interaction force is transformed into the frequency domain and then converted back to an equivalent roughness spectrum. This spectrum is used as the input to a linear, frequency-domain model of wheel/rail interaction to predict the noise. The noise level due to wheel flat excitation is found to increase with the train speed V at a rate of about 20 log₀V whereas rolling noise due to roughness excitation generally increases at about 30 log₀V. For all speeds up to at least 200 km/h the noise from typical flats exceeds that due to normal levels of roughness. When the wheel load is doubled the predicted impact noise increases by about 3 dB.     

On the sources of wayside noise generated by high-speed trains

A linear array of 14 microphones was used to measure radiated noise generated by a four-carriage electric train travelling at speeds between 160 and 250 km/h. Most of the results given in this paper pertain to apparent source locations of wheel/rail interaction noise, although preliminary data collected in a concurrent study of railway aerodynamic noise are briefly mentioned. An analysis of the measurements suggests that apparent sources of wheel/rail interaction noise are located (i) in the rail or substructure at low frequencies, (ii) on the wheel rim just below the axle at intermediate or peak frequencies, and (iii) on the lower part of the wheel and possibly in the rail at high frequencies.     

On the role of aerodynamically generated sound in determining wayside noise levels from high speed trains

The relative contributions of aerodynamic and wheel/rail noise to railway wayside noise levels are not well understood. Methods for predicting these contributions discussed in this paper include (i) an equation for turbulent boundary layer noise (the minimum wayside noise), (ii) an empirical formula for total aerodynamic noise based on airframe noise studies, and (iii) the Peters equation for wheel/rail interaction noise. Comparisons are made between predicted and measured noise levels for (i) a buoyant vehicle, (ii) the Linear Induction Motor Research Vehicle (LIMRV), and (iii) a magnetically levitated vehicle. Analysis of these results indicates that aerodynamic fluctuations could become the dominant source 3f wayside noise at train speeds of 240–280 km/h. This prognosis is for new high speed railway vehicles equipped with disc brakes and other innovations that reduce the wheel/rail noise contribution.     

Wheel/rail noise—means for control

Wheel/rail noise is one of the primary sources of noise from rail system operations—in many cases, the primary source. This paper is a review of the methods available for controlling all three types of wheel/rail noise: squeal, impact, and roar (rolling noise). The acoustical performance, non-acoustical benefits, problems, constraints, and additional research and testing requirements for each noise control treatment are presented.     

On the impact noise generation due to a wheel passing over rail joints

Impacts occur when a railway wheel encounters discontinuities such as rail joints. A model is presented in which the wheel/rail impacts due to rail joints are simulated in the time domain. The impact forces are transformed into the frequency domain and converted into the form of an equivalent roughness input. Using Track-Wheel Interaction Noise Software (TWINS) and the equivalent roughness input, the impact noise radiation is predicted for different rail joints and at various train speeds. It is found that the impact noise radiation due to rail joints is related to the train speed, the joint geometry and the static wheel load. The overall impact noise level from a single joint increases with the speed V at a rate of roughly .     

Vibration of a rolling wheel— preliminary results

Preliminary results are presented of the axial vibration of a railway wheel on a vehicle travelling at speeds of up to 100 miles/h. Frequency analysis shows that the wheel response is resonant, at modes of vibration which have been identified from static tests. Further developments of measurement and analysis techniques will be necessary before a more complete picture of the importance of wheel vibration on wheel/rail noise radiation can be determined.     

Evaluation of wheel dampers on an intercity train

Pass-by noise from high-speed trains is one important area that has to be handled in all new train projects. For the new line between Oslo and the Gardemoen Airport which opened in 1998, very stringent requirements were set out regarding external noise. To reach the target it was decided that the train should be equipped with wheel dampers. Two different types of wheel dampers were used on the train; a ring damper was mounted on the wheels of the driven bogies, whilst plate dampers divided into tuned absorber fins were mounted on the wheels of the trailer bogies.During the type testing of the Airport Express Train, additional measurements were performed in order to evaluate the acoustic effect of the plate wheel dampers. Two test series were performed with the same train set; first with the train in standard configuration and secondly with the wheel dampers removed from the second and third bogie. The external noise was measured at 5 and 25 m distance from the centre of the track at speeds ranging from 80 to 200 km/h. The third-octave filtered time histories were analyzed to calculate the effect of the wheel dampers. As expected, there was a significant reduction of 4-6 dB at frequencies above 2000 Hz, but there was also a reduction of 2 dB for frequencies as low as 800 Hz. This reduction was also found in the parts of the time histories when the rail should be dominating. This implies that the wheel dampers also reduce the rail noise. The total rolling noise reduction for the trailer bogie was 3 dB at 200 km/h and 1 dB at 80 km/h. From comparison with TWINS-calculated sound power levels it was estimated that the wheel noise would be reduced by 5 dB and the rail noise would be reduced by 1 dB at 200 km/h.     

The noise behavior of the wheel/rail-system— some supplementary results

Acoustical measurements were carried out on railroad coaches, on standard tracks and in the free field during test runs. In particular the influences of noise parameters like train speed, track condition, wheel type or locomotive propulsion were examined. Among other things, it appeared that the track conditions can vary considerably, a fact that has a great influence on all measurement values. One obtains a kind of “track profile” relatively independent of the train speed. Measurements both on the parts of the rail and in the free field during the pass-by of a train wheel, just as do the measurements of the wheel levels at the same time, indicate that the rail in the frequency range between 500 and 1200 Hz is the most important factor with regard to sound radiation. Only above this range is the wheel the essential radiator, mainly in the range around 2000 Hz. Further it could be ascertained that the total acceleration levels of the wheel rim have a greater speed exponent than the total acceleration levels of the rail. This can be important if one makes an extrapolation for high train speeds. Additional damping of coach wheels results in a greater noise reduction not only for the radiated sound but also for the structure-borne sound at the rails. This fact indicates the relatively strong coupling between rail and wheel. Furthermore it was ascertained that the levels generated by a locomotive in the upper frequency range are similar to those produced by damped coach wheels. A propulsion influence of an electrical locomotive on the radiated total sound level could not be ascertained. In the last section possible noise generating mechanisms are pointed out with regard to their importance as indicated by our present state of knowledge.     

瓦状阻尼橡胶块对高铁车轮减振降噪的影响分析

依据声学测试标准,为了评价某型高铁车轮在安装不同形式橡胶块装置后的减振降噪效果,在半消声室内基于B&K振动噪声测试分析系统,对裸轮和橡胶块车轮开展振动声辐射室内测试实验,并基于有限元方法对车轮模态进行了仿真分析。测试结果可知:相比裸轮,WA、WB车轮模态阻尼比显著增加,车轮的减振效果明显,其中WA车轮的减振效果略优于WB车轮。径向激励下,WA车轮声功率级降低了8 dB(A),WB车轮声功率级降低了5.5 dB(A);轴向激励下,WA车轮声功率级降低了8.2 dB(A),WB车轮声功率级降低了6.2 dB(A)。分析可知橡胶块装置能有效抑制车轮的滚动噪声和曲线啸叫,对车轮的减振降噪有积极作用。     

The influence of the contact zone on the excitation of wheel/rail noise

Rolling noise is excited by surface roughness at the wheel/rail contact. The contact patch is known to attenuate the excitation at wavelengths that are short in comparison with its length. A distributed point-reacting spring (DPRS) model is used with measured roughness data to determine the contact filter effect, and this result is compared with analytical predictions. It is found that the analytical model gives an attenuation that is too large at short wavelengths but is usable for wavelengths down to somewhat smaller than the length of the contact patch. Additionally, variations in the detailed geometry of the profile can cause the contact point on the wheel and rail to oscillate laterally. This introduces an oscillating moment that can induce additional vibration and noise. The DPRS model and rolling noise prediction model are both extended and used together to allow an estimate of the contribution to the radiated noise. It is found that, while the direct roughness excitation is still more important, the moment excitation can be significant, particularly for conforming profiles.     

A dynamic model for an asymmetrical vehicle/track system

A finite element model to simulate an asymmetrical vehicle/track dynamic system is proposed in this paper. This model consists of a 10-degree-of-freedom (d.o.f.) vehicle model, a track model with two rails, and an adaptive wheel/rail contact model. The surface defects of wheels and rails can be simulated with their geometry and an endless track model is adopted in the model. All time histories of forces, displacements, velocities and accelerations of all components of the vehicle and track can be obtained simultaneously. By using this model, one can study the effect that wheel/rail interaction from one side of the model has on the other. This can be done for many asymmetrical cases that are common in railway practice such as a wheel flat, wheel shelling, out-of-round wheel, fatigued rail, corrugated rail, head-crushed rail, rail joints, wheel/rail roughness, etc. Only two solutions are reported in this paper: steady state interaction and a wheel flat.     

Development of elastic force model for wheel/rail contact problems

In this investigation, a new formulation for the wheel/rail contact problem based on the elastic force approach is presented. Crucial to the success of any elastic force formulation for the wheel/rail contact problem is the accurate prediction of the location of the contact points. To this end, features of multibody formulations that allow introducing additional differential equations are exploited in this investigation in order to obtain a good estimate of the rail arc length travelled by the wheel set. In the formulation presented in this paper, four parameters are used to describe the wheel and the rail surfaces. In order to determine the location of the points of contact between the wheel and the rail, a first order differential equation for the rail arc length is introduced and is integrated simultaneously with the multibody equations of motion of the wheel/rail system. The method presented in this paper allows for multiple points of contact between the wheel and the rail by using an optimized search for all possible contact points. The normal contact forces are calculated and used with non-linear expressions for the creepages to determine the creep forces. The paper also discusses two different procedures for the analysis of the two-point contact in the wheel/rail interaction. Numerical results obtained using the elastic force model are presented and compared with the results obtained using the constraint approach.     

Local control of noise and vibration with KELTRACK™ friction modifier and Protector trackside application: an integrated solution

Wheel squeal is a source of continuing concern for many railroads and transits, as well as for their neighbours. The underlying mechanism for squeal noise has been well understood in the literature for some time. However an integrated abatement method addressing the underlying cause of the problem has not previously been reported.This paper describes practical experience using a water-based liquid Friction Modifier (KELTRACK™) applied using a top of rail trackside applicator (Portec Protector^®). The Friction Modifier and delivery equipment have been co-developed to provide an optimized product/delivery system that gives significant reduction of wheel squeal in curves.Wheels experiencing lateral creep in curves are subject to roll-slip oscillations as a result of the frictional characteristics of the interface layer between the wheel and rail. These roll-slip oscillations are amplified in the wheel web leading to the familiar squeal. Providing a thin film of material between the wheel and rail with positive friction characteristics can both in theory and practice greatly reduce the magnitude of these oscillations. The controlled intermediate friction characteristics of KELTRACK™ allow the material to be delivered to the top of both rails without compromising traction or braking.The positive friction aspects of the friction modifier are illustrated by published laboratory studies. Delivery of KELTRACK™ to the contact patch is achieved with a proprietary top of rail electric trackside applicator, the Portec Protector^®. The material is delivered to the top of both rails for optimum friction control.The integrated product/equipment technology is now successfully controlling noise at more than twenty transit sites. Typical sound level reduction is 10-15 dB, in some cases as high as 20 dB, depending on the initial sound level. Two case studies are presented illustrating the technology.     

Correlation between rolling noise generation and rail roughness of tangent tracks and curves in time and frequency domains

Despite considerable advantages of the railway track over other means of transportation, noise pollution is the main adverse consequence of railway transportation. The basic cause of railway noise is rail corrugation. Although characteristics of railway noise have been considerably studied in the literature, rail corrugation effects on rolling noise generation in tangent tracks and the curves have not been sufficiently investigated. This research addresses the limitations of the current understanding of the rolling noise generation by investigating rail corrugation effects on rolling noise in tangent tracks and curves. This research was made based on the results obtained form a thorough field investigation carried out in a railway line which includes tangents tracks and sharp curves. A track geometry recording car was used to measure rail corrugations. For this purpose, an indirect method was developed in this research to obtain rail corrugation patterns from the data recorded by the track recording car. The effectiveness of the new method was shown. The induced noises were recorded using two particular types of microphones and implementing the method suggested by the ISO 3095 Standard. The rolling noise signal was distinguished from the total noise, using Butterworth Band-Pass Filtering. The role of rail corrugations in the rolling noise was discussed. Correlations were made between various types of corrugations and the induced noises. The results were presented and discussed in the spatial and frequency scales. Results obtained have led to new findings in rail corrugation effects on rolling noise generation. This research paves a way toward a better understanding of rolling noise sources and the parameters influencing the noise.     

Application of MetaRail railway noise measurement methodology: comparison of three track systems

Within the fourth RTD Framework Programme, the European Union has supported a research project dealing with the improvement of railway noise (emission) measurement methodologies. This project was called MetaRail and proposed a number of procedures and methods to decrease systematic measurement errors and to increase reproducibility. In 1999 the Austrian Federal Railways installed 1000 m of test track to explore the long-term behaviour of three different ballast track systems. This test included track stability, rail forces and ballast forces, as well as vibration transmission and noise emission. The noise study was carried out using the experience and methods developed within MetaRail. This includes rail roughness measurements as well as measurements of vertical railhead, sleeper and ballast vibration in parallel with the noise emission measurement with a single microphone at a distance of 7.5 m from the track. Using a test train with block- and disc-braked vehicles helped to control operational conditions and indicated the influence of different wheel roughness.It has been shown that the parallel recording of several vibration signals together with the noise signal makes it possible to evaluate the contributions of car body, sleeper, track and wheel sources to the overall noise emission. It must be stressed that this method is not focused as is a microphone-array. However, this methodology is far easier to apply and thus cheaper. Within this study, noise emission was allocated to the different elements to answer questions such as whether the sleeper eigenfrequency is transmitted into the rail.