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.     

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.     

Prediction of aerodynamic noise reduction by using open-cell metal foam

As the speed of high-speed train (HST) increases continuously, aerodynamic noise has become more remarkable compared with the wheel/rail noise, which affects the inhabited environment along the railway and the riding comfort. This paper preliminarily investigates the feasibility of using open-cell metal foam covering layer to reduce the low Mach number aerodynamic noise generated by the flow around a circular cylinder which is the typical section of pantographs. The aerodynamic noises radiated from the circular cylinder with and without metal foam are calculated. The hybrid method combining two-dimensional large eddy simulation (LES) with Ffowcs Williams–Hawkings (FW–H) equation is employed. The calculated Strouhal number, time-averaged drag coefficient, base pressure and overall sound pressure level agree well with some available experimental data. Then, the influences of metal foam porosity, pore density, thickness of covering layer and the speed of train on the aerodynamic noise and the aerodynamic forces are investigated, and some detailed comparisons of flow field are made. The numerical results indicate that as a passive scheme, the open-cell metal foam with high porosity can modify the flow, adjust the vortex shedding frequency and regularize the wake, leading to a significant reduction of aerodynamic noise. The results are expected to provide useful information for the control of aerodynamic noise using this new material.     

Sources and mechanisms of wheel/rail noise: state-of-the-art and recent research

A review is presented of wheel/rail research studies, published since 1978. Additionally a study is presented which is focussed on the magnitudes and relative importance of vertical and horizontal forces in the wheel/rail contact zone. In the specific case and the frequency range 50–2000 Hz the vertical force appeared to be 3–10 times larger than the lateral (axial) force. Nevertheless radiation due to axial excitation of the wheel dominates the wayside sound pressure level in several one-third octave frequency bands. Another significant contribution to the wayside A-weighted sound pressure level is attributed to vertical excitation of the rail.     

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 .     

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.     

Laser measurement of torsional vibrations/longitudinal creepage of a railway wheel set on a scaled test bench

Since more than one century, test benches remain an essential tool to study various aspects of the railway dynamics such as for instance running stability, safety or even ride comfort. For each of these applications, the knowledge of the contact conditions (forces and relative displacements) between the wheel and the rail is a necessary condition to develop a sound understanding of the physical phenomena. More specifically, as soon as the longitudinal dynamics of the vehicle-track system is involved in the study (like for the performance of a locomotive, the rolling noise or rail corrugation), a precise measure of the longitudinal creepage between the wheel and the rail is needed to verify numerical predictions from theoretical models. In this paper, we focus on the measurement of torsional vibrations of a scaled wheel set which is rolling on a roller (representing infinite rails). First, a theoretical overview of the conditions under which these torsional vibrations are excited is given. Then, the experimental set-up used to study the phenomenon is presented. During the experiment, the wheel set torsional vibrations are measured using the rotational laser Doppler vibrometer, and the measure is used to calculate the longitudinal creepage of the wheel. Results are compared with outputs of a multi-body model of the test bench.     

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.     

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.     

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.     

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.     

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.     

A reduced-scale railway noise barrier's insertion loss and absorption coefficients: comparison of field measurements and predictions

In situ testing determined the insertion loss (IL) and absorption coefficients of a candidate absorptive noise barrier (soundwall) to abate railway noise for residents of Anaheim, CA. A 4000 m barrier is proposed south of the tracks, but residential areas to the north have expressed concerns that barrier reflections will increase their noise exposure. To address these concerns, a 3.66 m high by 14.6 m long demonstration barrier was built in the parking lot of Edison Field, Anaheim, as part of a public open house, thereby allowing for acoustical measurements.Insertion loss (IL) was measured in third-octave bands assuming 1/2-scale construction. The IL for three, scaled railway noise sub-sources (rail/wheel interface, locomotive, and train horn) was measured at six, scaled distances. The highest total, A-weighted IL, after corrections for finite-barrier and point-source speaker effects was 22 dB(A) for rail/wheel noise, 18 dB(A) for locomotive noise, and 20 dB(A) for train horn noise. These results can be compared favourably to IL predictions made using algorithms from the US Federal Rail Administration (FRA) noise assessment guidelines. For the actual barrier installation, shielded residential receivers located south of the project are expected to see their future noise exposures reduced from an unmitigated 78 CNEL to 65 CNEL.Absorption coefficients were measured using time delay spectrometry. At lower frequencies, measured absorption coefficients were notably less than the reverberation room results advertised in the manufacturer's literature, but generally conformed with impedance tube results. At higher frequencies the correspondence between measured absorption coefficients and reverberation room results was much improved. For the actual barrier installation, unshielded residential receivers to the north are expected to experience noise exposure increases of less than 1 dB(A). This factor of increase is consistent with a finding of no impact when assessed using FRA guidelines for allowable increases of noise exposure.     

Recent developments in wheel/rail noise research

A review is presented of wheel/rail noise research studies, published since 1976. The indications are that a forced vibration model for the mechanism of wheel/rail noise generation is consistent with the results obtained by various researchers. Further work is needed on the parameters governing the magnitudes of the forces in the wheel/rail contact zone, however, before a complete understanding of noise generation can be achieved, and hence control at source.     

The differing annoyance levels of rail and road traffic noise

The results of a study on the relative annoyance by rail or road traffic noise in urban and rural areas are reported. Fourteen areas with rail and road traffic noise with differing levels of loudness (L_eq) were investigated. The annoyance was assessed by means of a questionnaire. The analysis of the relationship between annoyance and L_eq—performed separately for rail and road traffic noise—shows that the same amount of annoyance is reached for railway traffic noise at L_eq levels 4–5 dB(A) higher than for road traffic noise (railway/traffic noise “bonus”). The estimation for the difference values vary for the different variables of annoyance. Furthermore, the difference levels tend to be higher in urban than in rural areas.     

Materials for noise reduction in food processing environments

Government standards for noise levels in industrial environments including the food processing industry have led to a program of materials selection for noise reduction. In addition to traditional architectural considerations, the constraints of sanitation and cost were factors. Primary materials systems studied were: (i) metal/polymer composites for impact noise reduction, (ii) polymer film/foam composites for sound absorption and (iii) transparent polymer barrier/enclosures. Of these three material systems, the third appears to be the most effective choice for reducing noise in the canneries.     

On measurements of aerodynamic noise generated by a high-speed electric train

Noise measured above a high-speed railway train indicates that aerodynamically generated noise may be quite significant at high vehicle speeds. A comparison of experimental and predicted noise levels demonstrates the similarity between the levels of aerodynamic noise produced by aircraft (airframe noise) and railway vehicles.     

Geometric Origin of Physical Constants in a Kaluza-Klein Tetrad Model

An important feature of Kaluza-Klein theories is their ability to relate fundamental physical constants to the radii of higher dimensions. In previous Kaluza-Klein theory, which unifies the electromagnetic field with gravity as dimensionless components of a Kaluza-Klein metric, i) all fields have the same physical dimensions, ii) the Lagrangian has no explicit dependence on any physical constants except mass, and hence iii) all physical constants in the field equations except for mass originate from geometry. While it seems natural in Kaluza-Klein theory to add fermion fields by defining higher-dimensional bispinor fields on the Kaluza-Klein manifold, these Kaluza-Klein theories do not satisfy conditions (i), (ii), and (iii). In this paper, we show how conditions (i), (ii), and (iii) can be satisfied by including bispinor fields in a tetrad formulation of the Kaluza-Klein model, as well as in an equivalent teleparallel model. This demonstrates an unexpected feature of Dirac's bispinor equation, since conditions (i), (ii), (iii) imply a special relation among the terms in the Kaluza-Klein or teleparallel Lagrangian that would not be satisfied in general.     

A full-scale test rig for railway rolling noise: simulation and measurement of dynamic wheelset-track interaction

A new outdoor rolling-noise test rig on a 25 m stretch of full-scale track will enable the study of vibrations of wheel and rail and of the pertinent noise emission under controlled conditions. The arrangement can be seen as a physical realization of the Track-Wheel Interaction Noise Software (TWINS) computer software. The track and wheel, which are not in mechanical contact, are excited in vertical and lateral directions using electrodynamic actuators. The track can be statically pre-loaded by up to 30 tonnes. The use of the rig is presently under development. The aim is that the radiated noise from separate railway components could be found as the wheel and the track can be excited both together and separately. Amplitude and phase of the applied forces are predetermined by use of an algorithm taking into account the real wheel-rail interaction properties. In that way different wheel-rail contact conditions can be simulated. Eight partners have co-operated in the development and operation of the CHARMEC/Lucchini Railway Noise Test Rig in Surahammar, Sweden.In ongoing experiments, the dynamics of both the wheel and rail have been examined in the frequency domain. For the track, comparisons have been made between data obtained from the rig and those from field measurements on a standard Swedish line. Both dynamic response and spatial decay rates have been studied. The performance of the rig has also been compared to results from TWINS and to results from the literature. Good agreement was obtained in the frequency range from 100 to 5000 Hz. Some results from preliminary measurements of noise emission will be given.