Track Decay Rate Research Articles

Assessment of measurement-based methods for separating wheel and track contributions to railway rolling noise

The noise produced during a train pass-by originates from several different sources such as propulsion noise, noise from auxiliary equipment, aerodynamic noise and rolling noise. The rolling noise is radiated by the wheels and the track and is excited by the wheel and rail unevenness, usually referred to as roughness. The current TSI Noise certification method, which must be satisfied by all new mainline trains in Europe, relies on the use of a reference track to quantify the noise from new vehicles. The reference track is defined by an upper limit of the rail roughness and a lower limit of the track decay rate (TDR). However, since neither the rail roughness nor the track radiation can be completely neglected, the result cannot be taken as representing only the vehicle noise and the measurement does not allow separate identification of the noise radiated by wheel and track. It is even likely that further reductions in the limit values for new rolling stock cannot be achieved on current tracks. There is therefore a need for a method to separate the noise into these two components reliably and cheaply. The purpose of the current study is to assess existing and new methods for rolling noise separation. Field tests have been carried out under controlled conditions, allowing the different methods to be compared. The TWINS model is used with measured vibration data to give reference estimates of the wheel and track noise components. Six different methods are then considered that can be used to estimate the track component. It is found that most of these methods can obtain the track component of noise with acceptable accuracy. However, apart from the TWINS model, the wheel noise component could only be estimated directly using three methods and unfortunately these did not give satisfactory results in the current tests.

A detailed experimental study of the validity and applicability of slotted stand-off layer rail dampers in reducing railway vibration and noise

This paper is concerned with an experimental study of improved slotted stand-off layer rail dampers in reducing railway vibration and noise. To achieve the goal, based on the idea of molecular design, polyurethane/vinyl ester resin interpenetrating polymer network damping materials with high damping properties was developed in the laboratory for the material of the damping layer. The effects of vinyl ester resin and organic small molecule hybridization on the damping properties of the polyurethane/vinyl ester resin interpenetrating polymer network material were investigated. The structural style of the damper was improved for ease of installation and removal in situ. Then, these improvements of damping material and structural style were used to make optimized slotted stand-off layer dampers, which were applied in a test section. The measurements indicate that the structural style improvement could improve the application convenience while also maintaining the noise reduction effect. The improved rail dampers could greatly increase the track decay rate at frequencies above 100 Hz and reduce noise levels by up to 6 dB at the speed of 60 km/h.

Dynamic response of a curved railway track subjected to harmonic loads based on the periodic structure theory

In this study, the authors have analysed the dynamic response of a curved railway track that is subjected to moving and non-moving harmonic loads. The track is considered as a curved Timoshenko beam supported by periodically spaced discrete fasteners. The displacement and rotation of the curved rail are expressed as the superposition of track modes in the frequency domain. Periodic structure theory is applied to the equations of motion of the curved track, allowing the dynamic response of the track to be calculated efficiently in a reference cell. The effect of the stiffness and damping of the fasteners, the fastener spacing and the radius of curvature on the mobility and decay rate of the track are analysed for non-moving loads on the rail head. The vibration of the rail due to moving loads is also discussed. It is found that the dynamic response of a curved rail with a large radius has the same characteristics as that of a straight track. However, the dynamic response of the track is significantly affected when the radius of curvature becomes small. The radius affects the mobility; it also has an effect on the track decay rate below 2000 Hz and the velocity of the rail in the vertical direction when the radius is smaller than about 15 m and for the lateral direction when it is less than about 30 m. Moreover, the curvature has a significant influence on the vertical/lateral cross mobility, the magnitude of which increases as the radius is reduced. When the radius is larger than 10 m, the amplitude of the lateral vibration under a moving vertical load and the vertical response to a moving lateral load are inversely proportional to the radius.

Vibro-acoustic performance of newly designed tram track structures

Rail vehicles in interaction with a railway structure induce vibrations that are propagating to surrounding structures and cause noise disturbance in the surrounding areas. Since tram tracks in urban areas often share the running surface with road vehicles one of top priorities is to achieve low maintenance and long lasting structure. Research conducted in scope of this paper gives an overview of newly designed tram track structures designated for use on Zagreb tram network and their performance in terms of noise and vibration mitigation. Research has been conducted on a 150 m long test section consisted of three tram track types: standard tram track structure commonly used on tram lines in Zagreb, optimized tram structure for better noise and vibration mitigation and a slab track with double sleepers embedded in a concrete slab, which presents an entirely new approach of tram track construction in Zagreb. Track has been instrumented with acceleration sensors, strain gauges and revision shafts for inspection. Relative deformations give an insight into track structure dynamic load distribution through the exploitation period. Further the paper describes vibro-acoustic measurements conducted at the test site. To evaluate the track performance from the vibro-acoustical standpoint, detailed analysis of track decay rate has been analysed. Opposed to measurement technique using impact hammer for track decay rate measurements, newly developed measuring technique using vehicle pass by vibrations as a source of excitation has been proposed and analysed. Paper gives overview of the method, it’s benefits compared to standard method of track decay rate measurements and method evaluation based on noise measurements of the vehicle pass by.

Experimental study of the treatment measures for rail corrugation on tracks with Egg fasteners in the Beijing metro

Rail corrugation occurring on tracks fitted with Egg fasteners has become a serious problem on the newly operated lines of the Beijing metro in recent years. Investigations and field measurements show that the dominant wavelengths of corrugation are 63–100 mm, inducing dominant frequencies of vibration on the rail in the frequency range of 160–310 Hz for train speeds at 60–70 km/h. Due to the influence of the dynamic behaviour of tracks on the formation of rail corrugation, various options for changing the dynamic behaviour of the track structure can be considered as possible solutions to treat corrugation. Four treatment measures have been considered: rail grinding, adding a rubber pad within the fastener, replacing the fastener with a compression-type fastener, and installing rail dampers on the rail. Field experiments have been carried out to evaluate the effectiveness of these rail corrugation treatment measures on two lines of the Beijing metro. Frequency response functions, track decay rates, and pass-by acceleration on the rail were measured, and the development of rail roughness was monitored. Experimental results show that all the four measures are effective to control or at least slow down the development of rail corrugation on tracks with Egg fastener. Rail grinding is mostly used to limit the effects of corrugation; here, it was noted that low-amplitude corrugation on some straight lines did not reappear after rail grinding. After adding a rubber pad within the fastener, the existing corrugation reduced in amplitude, while corrugation did not reappear on a newly ground rail. Replacing the fastener with a compression-type fastener and installing rail dampers on the rail were found to slow down the development of corrugation.

Prediction of rail and bridge noise arising from concrete railway viaducts by using a multilayer rail fastener model and a wavenumber domain method

Concrete viaducts are an important part of urban rail transit systems but they produce considerable noise, thereby affecting the communities living nearby. The vibration generated at the wheel–rail interface is transmitted along the rail and also onto the bridge; hence, noise is radiated from both the rail and the bridge. To facilitate noise prediction, it is desirable to develop a model that takes into account the generation and transmission of vibration in the train–track–bridge system. The vibration and the associated noise of the track–bridge system are computed with a unified vibroacoustic model using a wavenumber domain finite element and boundary element method. An important aspect to note is the frequency-dependent stiffness of a typical rail fastener utilized on bridges due to the resonance of the baseplate between the two rubber pads. In this study, to allow for this effect, a multilayer fastener model is proposed. The proposed procedure is applied to a viaduct with a U-shaped section and compared with field measurements during the passage of trains. The elastic modulus and damping of the rubber pads and the equivalent loss factor of the rail are chosen by fitting the calculated track decay rates to those estimated from the measured rail accelerations under train passages. The wheel–rail combined roughness is also derived from the measured rail vibration. A comparison is then made between the simulated and measured bridge vibration to verify the proposed method as well as the parameters used in the track–bridge system. The predicted noise levels are also compared with the measured results. The effects of the fastener model, fastener stiffness, bridge damping, and interference between multiple wheels are then discussed. It has been found that the bridge noise has a non-negligible effect on the total A-weighted noise levels in the region beneath the bridge and up to 30 m away from the track.

Estimation of track parameters and wheel–rail combined roughness from rail vibration

Rolling noise from running trains is significantly influenced by the wheel–rail combined roughness and the dynamic properties of the track. To facilitate predictions of vibration and noise, it is desirable to be able to determine these parameters accurately from field measurements. In this study, an inverse method for the determination of these parameters is adopted and enhanced. A track model that is based on a wavenumber finite element model of the free rail coupled to discrete supports, which allows for the pinned–pinned mode and cross–sectional deformation of the rail, has been used. The rail vibration induced by hammer impacts and the vibration during train passages are simulated using this model, and these results are then applied to illustrate the accuracy of the direct and indirect methods for the estimation of track decay rate. These methods are compared in a case study for a ballasted track for which hammer impact and train pass–by measurements have been obtained. Other track parameters can also be extracted from the measured data by using the advanced track model. Thereafter, a more complete method is adopted to estimate the wheel–rail combined roughness from the measured rail vibration under train passages. A comparison is made among the estimated roughness levels obtained from this full method, an existing simplified method and the direct measurement method. It is found that the simplified method overestimates the roughness around the pinned–pinned resonance frequency, but gives a good estimation if the track decay rates of the loaded track are used.

Internal noise reduction in railway vehicles by means of rail grinding and rail dampers

Interior noise reduction has become an important concern in railway operating environments due to the influence of increased speeds and reduced vehicle weights on energy efficiency. Two types of measures, rail grinding and rail dampers, were proposed to reduce the internal noise within railway metro vehicles on a particular curve section of a Chinese metro line where the internal noise within metro vehicles is so excessive when the train passes that drivers and passengers complain. The dynamic property and track decay rate of the track system were carried out through mechanical shock method first. Then the measurement of rail vibration performance, external noise and internal noise were conducted when the metro train passed through this track section at the required speed. The rail corrugation with a wavelength of 0.06 m is a major cause of the excessive internal noise. After the application of rail grinding, the overall A-weighted sound pressure levels reduced from 85 to 82 dB due to the removal of the rail corrugation and other short-wave irregularities. Moreover, after the further use of rail dampers, the overall A-weighted sound pressure levels within the carriage further decreased from 82 to 74 dB, resulting from the reduction of the wheel/rail external noise transmitted into the vehicle body through leaks in the vehicle body. Therefore, the noise reduction effect of the two presented measures is significant.

Study on Transmission Characteristics of Vertical Rail Vibrations in Ballast Track

A plane half-track model and a periodic track-substructure model are established. The spectral element method and spectral transfer matrix method are developed and applied to investigate the track decay rate (TDR) and transmission rate (TR) of the vertical rail vibrations, which can reflect the transmission characteristics in the longitudinal and downward directions, respectively. Furthermore, the effects of different track parameters on TDR and TR are investigated. The results show that the antiresonance frequency of the rail and the out-of-phase resonance frequency of the rail and sleeper form the boundary frequencies of the high-attenuation zone for longwise vibration transmission, where the vibration absorption of the sleeper is significant. The downward transmissibility of vertical rail vibrations is greatest around the antiresonance frequency of the rail. Vertical rail vibrations are primarily transmitted in the downward direction at low frequencies, while they are mainly transmitted along the rail at high frequencies. Stiffer rail pads can make more vibrations transmitted downwards to the sleeper above the antiresonance frequency of the rail, while the changes of other track parameters have different effects on the transmission characteristics. Additionally, a field measurement is performed for verification, and the simulations are well consistent with measurements.

The Effect of Rail Fastening System Modifications on Tram Traffic Noise and Vibration

Tram system is a backbone of public transportation in the City of Zagreb. In the last decade, its fleet has been renewed by 142 new low-floor trams. Shortly after their introduction, it was observed that they have a negative impact on the exploitation behavior of tram infrastructure, primarily on the durability of rail fastening systems. Because of that, it was decided to modify existing rail fastening systems to the new track exploitation conditions. When the (re)construction of tram infrastructure is carried out by applying new systems and technologies, it is necessary to take into account their impact on the future propagation of noise and vibration in the environment. This paper gives a short overview of the characteristics of the two newly developed rail fastening systems for Zagreb tram tracks, their application in construction of experimental track section, and performance and comparison of noise and vibration measurements results. Measured data on track vibrations and noise occurring during passage of the tram vehicles is analyzed in terms of track decay rates and equivalent noise levels of passing referent vehicle. Vibroacoustic performance of new fastening systems is evaluated and compared to referent fastening system, in order to investigate their ability to absorb vibration energy induced by tram operation and to reduce noise emission.

Experimental procedures for testing the performance of rail dampers

Rail dampers work by increasing the attenuation with distance of vibration transmitted along the rail, a quantity known as the track decay rate. Currently, there are no standardized procedures to measure their effectiveness in reducing rolling noise without the need for in-track installation and time-consuming tests. This paper describes and evaluates experimental procedures for assessing rail dampers. Instead of field measurements it is proposed to use laboratory measurements of vertical and lateral decay rates on a free rail equipped with dampers. These are combined with in-situ measurements on an undamped track. The decay rates of a damped track can be approximated by adding the results of the damped free rail to those of the undamped track.Three different methods are studied to measure the decay rates of damped free rails: (i) using a long rail, in the present work 32m long, from frequency response functions measured at intervals along the rail; (ii) using a short rail, in the present work 6m long, from the modal properties of the rail; and (iii) directly from the point and transfer frequency response functions at both ends of the short rail. The latter two are complementary: the modal method is more suited to low frequencies while the direct method is more suited to high frequencies. These methods are evaluated theoretically and by comparison with experimental results.Good agreement is found between the various methods, for vibration in both vertical and lateral directions, between 300Hz and 5kHz. In practice, the direct short-rail method is likely to be sufficient for most applications. The limitations of the methods are identified and corrections are proposed for the effect of near-field waves in the rail.

Application of Polyurethane Polymer and Assistant Rails to Settling the Abnormal Vehicle-Track Dynamic Effects in Transition Zone between Ballastless and Ballasted Track

This paper describes tests on a transition section between ballasted and ballastless tracks in the Liupanshui-Zhanyi railway in China. The originally unsettled transition zone is exposed to sudden car shaking and a series of track transition problems during train passage. As an example, the influences of polyurethane polymer and a combination of polyurethane and assistant rails to increase track stiffness distribution and track transition decay rates on the dynamic vehicle and track behaviour were investigated. The measured results indicate using only polyurethane and using both polyurethane and assistant rails not only effectively makes the track stiffness change more even but also increases the track decay rate at the target frequencies. These positive effects further reduce the wheel-rail interaction forces and vehicle and rail vertical acceleration, which decreases more when combining polyurethane and assistant rails than when using only polyurethane because the former outperforms the latter for smoothing the track stiffness distribution and increasing the track decay rate. Based on abating wheel-rail impact during the transition from ballasted to ballastless track and improving traffic operation and passenger comfort, combining polyurethane and assistant rails had the greatest effect and may be an effective remedy.

Vibration properties of slab track installed on a viaduct

A model of the vibration behaviour of a discontinuous slab track installed on a viaduct is presented. It is represented by a three-layer Euler–Bernoulli beam model subjected to a harmonic load. Analytical equations are derived using the receptance method, and they are used to determine the vibration properties of the system. Comparisons are made between the vibration behaviour under various parameter conditions of the Chinese CRTS I slab track and a typical floating slab track installed on a viaduct. Attention is focused on the mobility, vibration isolation and track decay rates. The results show that, as expected, the floating slab track generates significantly lower viaduct vibrations than the CRTS I slab track. A slab track fitted with a relatively stiff rail pad and soft bearing layer is recommended for consideration during the engineering design phase; appropriate choices can lead to the optimization of the vibration isolation performance of a railway track on a viaduct, thus avoiding the creation of excessive rail vibrations. It is also shown that the average response of the viaduct gives a more representative assessment of the vibration isolation effect than if the average force transmitted to the viaduct is used. Moreover, in terms of insertion loss, these results are relatively insensitive to the choice of viaduct parameters.

Predicting the effect of temperature on the performance of elastomer-based rail damping devices

Damping devices for railway tracks have been developed in recent years in which a tuned mass-spring absorber system is formed by an elastomeric material and embedded steel masses. The loss factor and stiffness of the elastomer are very important for the performance of the system but, unfortunately, both properties are sensitive to changes in the temperature. Although having a high loss factor gives good noise reduction, it also means greater variation of stiffness, and consequently tuning frequency, with temperature. Conversely, with lower loss factors the tuning frequency can be kept close to the target but a smaller noise reduction is achieved.To investigate the effect of the temperature on the performance of a generic rail absorber, a simple Timoshenko beam model of the track is used. To this is added a single-frequency continuous tuned absorber. The noise reduction at each frequency is estimated from the ratio of the track decay rates of treated and untreated rails.There is a physical link between the damping loss factor and the stiffness variation with temperature, of which account must be taken. The rate of change of stiffness with log frequency is established by assuming a constant value of loss factor. Using the time-temperature superposition principle, this is expressed in terms of temperature dependence. This is used in the prediction of decay rates and thereby noise reduction at different temperatures. This leads to an assessment of the relative importance of using a high damping loss factor or a temperature-independent stiffness.Finally, a method of weighting the noise reduction at different temperatures is investigated. A distribution of rail temperatures at a site in the UK is used to develop a weighting procedure. This is extended to account for temperature variations at other locations, where less data are available.