Rapporteur's report,session 3: Other sources of railway noise

A method of finding the flexural and torsional normal modes of beams which have straight stiffness axes is given. The Lanzcos method of minimized iterations, based on the integral equation of beam vibrations, is used to obtain intermediate modes with the distributions along the beam of its mass and rigidity as data. The inertia matrix appropriate to the intermediate modes is theoretically tridiagonal and the stiffness matrix is unit. The dominant eigenvalues and vectors of the inertia matrix give very good approximations to the frequencies and shapes of the graver normal modes. Results of test calculations are given.     

The STAIRRS project, work package 1: a cost-effectiveness analysis of railway noise reduction on a European scale

Noise control is a major economic factor for the railways as national and European Union environmental legislation is being enacted. In an effort to determine optimal strategies on a European level, the EU fifth framework programme has co-financed the Strategies and Tools to Assess and Implement noise Reducing measures for Railway Systems (STAIRRS) project. Work package 1 developed the necessary software to undertake large-scale cost-effectiveness analyses. The acoustically relevant geographic, traffic and track data were collected for 11 000 km of lines in seven European countries. Standard cost-benefit methodologies were adapted to fit the requirements of the project. An extrapolation mechanism allowed studies on Europe as a whole and, in an approximate manner, also on individual countries. Major conclusions are that the highest cost-effectiveness can be achieved by combining measures; freight rolling stock has a high cost-effectiveness on its own as well as in combination with other measures, especially when combined with track measures; noise barriers, in particular high ones, have a low cost-effectiveness. The conclusions for Europe as a whole are also true for individual countries. The STAIRRS project co-ordinator is the European Rail Research Institute, the work package leader is the Swiss Federal Railways with the participation of AEAT Technology (NL), German Railways, French Railways, PSI-Akustik (A), the Swiss Federal Institute of Technology and the Free University of Brussels.     

Symmetry breakdown of stochastic potential by noise cross-correlations among colored noise sources

A nontrivial phenomenon in stochastic zero-dimensional systems, namely, the symmetry breakdown of stationary probability function due to the correlation between the noises is studied. As a model system to study this effect, we consider a generalized synergetic system of Lorenz type with Gaussian colored noise of each mode. In the frameworks of theoretical approximation and numerical simulations it is shown the fluctuation cross-correlations break the symmetry of bistable synergetic potential, producing an asymmetric effective potential. At that, cross-correlations play the twofold role: cross-correlations are the reason of symmetry breaking at small cross-correlation times on the one hand, and the reason of symmetry restoring at large values of cross-correlation times on the other hand. Moreover, it is shown that symmetry breakdown occurs only if one of multiplicative function is odd. Any other combinations of noises restore the symmetric form of potential.     

Pressure Leq and multiple noise sources: A comparison of exposure-response relationships for railway noise and road traffic noise

Exposure-response relationships vary with different noise sources when conventional L_eq is used as the noise exposure measure. Further, reported annoyance to multiple noise source environments can be higher than predicted by conventional L_eq. Pressure L_eq is proposed as a superior unified noise index and some evidence is presented in support of this proposal.     

Identification of noise sources on a residential split-system air-conditioner using sound intensity measurements

This paper presents the results of experimental studies of the noise of a residential split-system air-conditioner unit. The compressor and condenser and associated fans were removed from the unit and did not form part of the studies. Care was taken with the unit to separate the inlet and exhaust noise from the noise radiated from the cabinet. The measurements were made with a two-microphone sound intensity probe and these resulted in sound power level data. The sound power levels produced by radiation from the inlet, exhaust and cabinet were obtained for five different volume flow rates. The effect on the sound power generated by removing the coil was investigated. Measurements and subjective studies show that the low frequency sound is predominantly radiated from the exhaust and inlet. At high frequency, the cabinet noise dominates.     

An inversion modelling method to obtain the acoustic power of the noise sources in a large factory

A common problem for large factories that wish to decrease their environmental acoustic impact on neighbouring locations is to find out the acoustic power of every noise source. As these factories cannot stop their activity in order to measure each source individually, a procedure is needed to obtain the acoustic powers with the factory under normal operating conditions. Their contribution to the overall sound pressure level at each neighbouring location can then be found and it is possible to calculate the improvements obtained after any modification of the sources. In this paper an inversion modelling method is used to do so. Acoustic powers are obtained by means of field sound pressure level measurements and with the use of a sound propagation software. A careful analysis of the solution has been carried out by simulating errors on the measured data in order to detect possible correlations between the acoustic power of different sources and avoid misleading interpretations of the results. The whole methodology has been applied to a liquid-gas production factory.     

传声器阵列对高频弱声源的声成像识别方法

研究了传声器阵列对高频弱声源的识别定位方法。该方法根据高频声源的指向性和阵列探测特性等特点,提出了利用信噪比加权方法提高有效阵元对声成像的贡献,根据信噪比的大小对每个阵元添加不同的权值,可以显著提高传声器阵列对高频弱声源的声像清晰度。仿真分析了阵元加权和不加权两种方法对阵列声成像结果的影响,以某型号笔记本电脑电路板噪声为对象进行的实验表明,在阵列测量中充分利用有效阵元信号可以实现对声压级低达10~20dB的微弱噪声源的精确测量。     

传声器阵列对高频弱声源的声成像识别方法

研究了传声器阵列对高频弱声源的识别定位方法。该方法根据高频声源的指向性和阵列探测特性等特点,提出了利用信噪比加权方法提高有效阵元对声成像的贡献,根据信噪比的大小对每个阵元添加不同的权值,可以显著提高传声器阵列对高频弱声源的声像清晰度。仿真分析了阵元加权和不加权两种方法对阵列声成像结果的影响,以某型号笔记本电脑电路板噪声为对象进行的实验表明,在阵列测量中充分利用有效阵元信号可以实现对声压级低达10~20 dB的微弱噪声源的精确测量。     

EURailNoise: a study of European priorities and strategies for railway noise abatement

The European Union is developing its noise policy by using a number of expert groups on specific noise issues. One of the most relevant noise problems is railway traffic which is dealt with by Working Group 6 (WG 6). The Commission of the European Union appointed a consortium of six consultants and experts in railway noise to prepare a study on European priorities and strategies for railway noise abatement. The main purpose of this study was to support the work within WG 6 and to create an inventory of measures for future railway noise abatement policy of the European Union. The EURailNoise study was to be completed in autumn 2001. The countries included the European Union member states, together with Norway, and Switzerland, and three prospective members (Hungary, the Czech Republic, and Poland).The EURailNoise study consisted of three main parts. The baseline was a review of current European legislation on railway noise generation as well as noise perception. In parallel a documentation of cases, where technical measures against railway noise had been successfully applied, was prepared using a classification of “good practice”, “promising new technology”, and “promising research results”.The second part covered the potential for further noise reduction demonstrated for High Speed Passenger Traffic, S-Trains, Locomotives, Trams, Freight Traffic, Track Design and finally Wheels and Track Monitoring and Maintenance. Thirdly, a strategy for future activities of the Commission concerning the reduction of rail noise was to be proposed including a proposal for noise emission limits. This paper summarizes the results of the EURailNoise study.     

Vibro-acoustic modelling of a railway bridge crossed by a train

This paper presents a vibro-acoustic modelling of a railway bridge excited by a moving train. The modelling of the bridge-train system is carried out by the modal superposition method taking into account the train mass, the viscoelastic suspension of the vehicles with an unlimited number of trucks and spans of the bridge. The numerical resolution of the coupled equations of motion is carried out by the Newmark’s method with an iterative process. we studied on one hand the influence of the track irregularities on the dynamic behaviour of the bridge-train system on the other hand the noise radiated by the bridge due to the passage of the train. The acoustic pressure is obtained by solving the wave equation which has as excitations source the bridge acceleration, they are considered as acoustic monopoles.     

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 d B(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。     

Experimental study of the effect of viscoelastic damping materials on noise and vibration reduction within railway vehicles

Interior noise and vibration reduction has become one important concern of railway operating environments due to the influence of increased speeds and reduced vehicle weights for energy efficiency. Three types of viscoelastic damping materials, bitumen-based damping material, water-based damping coating and butyl rubber damping material, were developed to reduce the vibration and noise within railway vehicles. Two sleeper carriages were furnished with the new materials in different patterns of constrained-layer and free-layer damping treatment. The measurements of vibration and noise were carried out in three running carriages. It is found that the reduction effect of damping treatments depends on the running speed. The unweighted root-mean-square acceleration is reduced by 0.08–0.79 and 0.06–0.49 m/s² for the carriage treated by bitumen-based as well as water-based damping materials and water-based damping material, respectively. The first two materials reduce vibration in a wider frequency range of 63–1000 Hz than the last. It turns out that the damping treatments of the first two reduce the interior noise level by 5–8 dBA within the carriage, and the last damping material by 1–6 dBA. However, the specific loudness analysis of noises shows that the noise components between 125 and 250 Hz are dominant for the overall loudness, although the low-frequency noise is noticeably decreased by the damping materials. The measure of loudness is shown to be more accurate to assess reduction effect of the damping material on the acoustic comfort.     

Traffic noise survey of Turin,Italy

This paper describes an objective traffic noise survey of Turin, an industrial town in north Italy. The main objects of the investigation were to determine the nature and level of outdoor traffic noise in an actual urban situation and to verify the relationships between level of traffic noise, traffic volume and traffic composition.Noise measurements were performed at 70 locations uniformly distributed over the town, in the autumn of 1974. A ten-minute record was made at each site every hour for 23 hours.The results are presented and compared with published data from previous surveys carried out in other European and North American towns.     

Video coding technique with a parametric modelling of noise

This paper presents a video encoding method in which noise is encoded using a novel parametric model representing spectral envelope and spatial distribution of energy. The proposed method has been experimentally assessed using video test sequences in a practical setup consisting of a simple, real-time noise reduction technique and High Efficiency Video Codec (HEVC). The attained results show that the use of the proposed parametric modelling of noise can improve the subjective quality of reconstructed video by approximately 1.8 Mean Opinion Scope (MOS) points (in 11-point scale) related to the classical video coding. Moreover, the present work confirms results attained in the previous works that the usage of even sole noise reduction prior to the encoding provides quality increase.     

Characterisation of tram noise emission and contribution of the noise sources

The recent expansion of French tram networks and the related local residential complaints mean that a better knowledge of the situations leading to negative reactions from the local inhabitants is required. Hence a research project has been conducted to evaluate and describe noise and vibration emission of trams as well as the perception by the local residents. This paper investigates tram noise emission on common straight track sections, involving two vehicle scales. First the acoustic power and the mean vertical directivity of the total tramset is assessed using an arc of microphones. Then the localisation and the analysis of the main noise sources are performed by means of a cross array during the tram pass-by. Two tram types representing two generations of French rolling stock, both running on two sites with distinct track characteristics, have been investigated considering the effect of speed, tram type, and track type on the noise source contributions and spectral features. Most sources are located in the lower part of the trams, mainly related to rolling noise, with a strong dependence on speed and track type. The tram type dependency, although globally of second importance, influences greatly the noise spectral distribution and behaviour. The HVAC was the only roof-mounted source which could be detected; its contribution towards building storeys becomes significant in configurations of low rolling noise. A tram noise emission model based on the various noise sources has been developed.     

Time reversal of noise sources in a reverberation room

Usually, time reversal is studied with pulsed emissions. Here, the properties of time reversal of the acoustic field emitted by noise sources in a reverberation room are studied numerically, theoretically, and experimentally. A time domain numerical simulation of a two-dimensional enclosure shows that the intensity of a time-reversed noise is strongly enhanced right on the initial source position. A theory based on the link that exists between time reversal of noise and the "well-known" time reversal of short pulse is developed. One infers that the focal spot size equals half a wavelength and the signal to noise ratio only depends on the number of transceivers in the time reversal mirror. This last property is characteristic of the time reversal of noise. Experimental results are obtained in a 5 X 3 X 3 m3 reverberation room. The working frequency range varies from 300 Hz to 2 kHz. The ability of the time reversal process to physically reconstruct the image of two noise sources is studied. To this end, care is given to the technique to separate two close random sources, and also to the influence of temperature fluctuations on the focusing quality.     

Identification of noise sources in factory’s sound field by using genetic algorithm

Noise control is important and essential in factory, where the noise level is restricted by the Occupational Safety and Health Act. Before noise abatement being performed, the identification work in searching for the location and sound power level (SWL) of noisy sound sources is absolutely prerequisite. Several researches on new techniques of single noise control have been well addressed and developed; however, the research work on sound identification for the existing multi-noise plant is hardly found sufficient. Under the circumstance of unrecognized noises, the noise control work will expectedly be extravagant and fruitless. Therefore, the numerical approach in distinguishing noises from a multi-noise plant becomes crucial and obligatory.In this paper, the novel technique of genetic algorithm (GA) in conjunction with the method of minimized variation square will be adopted and used in the following numerical optimization. In addition, various sound monitoring systems in detecting the noise condition within the plant area will also be introduced. Before noises identification, the accuracy of mathematical model has then been proved to be in good agreements comparing to the simulated data of SoundPlan, a commercialized simulation package in sound field. Moreover, three kinds of multi-noise plants have been fully discussed and acknowledged by GA optimization. The results reveal that the relevant locations and sound power levels (SWLs) of noises can be precisely recognized. This paper surely provides a rapid methodology in the noise identification work for a multi-noise plant.