When finishing the master study on acoustics at Chalmers I began to work at SP Acoustic Laboratory as a researcher. In 2000 I took part in the 5-year-long Nord2000 project and had worked for the project in the period of its last one and half years (the Nord2000 model was the first engineering method capable of predicting sound propagation under different meteorological conditions). Afterwards I joined the European projects Harmonoise (2001 Aug. - 2004 Dec.) and Imagine (2004 Jan. - 2006 Dec.). I have most been working on the source modelling of traffic noise but also handling sound propagation issues. It is a challenge to develop reliable measurement methods for determining the acoustical characteristics of traffic noise sources, which requires wide knowledge and deep understandings on the problem both theoretically and practically. So, I am here again to take the PhD study.
Reliable measurement methods to determine the acoustical characteristics of traffic noise sources, specially focusing on railway noise.
Peer reviewed papers
Abstract Some errors behind the Eyring formula have been discovered. By using a new probability description, which is also based on area law, a new formula for reverberation time has been proposed. The example calculations show that the new formula will give a result with its value between the result by the Eyring formula and the result by the Sabine formula.
Abstract In the Harmonoise project the description of vertical and horizontal directivities of railway noise sources has been required. Other features of the source description are sound power level spectra in third octave bands as a function of speed and the physical location of the different sound sources.
Based on systematic investigations methods to measure and to determine the directivities of railway noise sources are presented in this paper. The determination of the directivity of rolling noise is discussed in detail. For the directivities of traction noise and aerodynamic noise the discussion is more analytical because of limited access to relevant data.
For each type of main railway noise source, i.e. rolling noise, traction noise and aerodynamic noise, default directivity functions are proposed for the use in the source description of railway noise. These default directivity functions will be subject to revisions when more accurate data become available.
Abstract Traction noise is one of the noise sources of powered railway vehicles such as locomotives, electric- and diesel-powered multiple unit trains and high-speed trains. Especially at speeds below 60 km/h and at idling, but also at acceleration conditions for a wide range of speeds, traction noise can be dominant. This is relevant for noise in residential areas near stations and shunting yards, but in some cases also along the line. The other relevant sources are rolling noise, often dominant between 100 and 250 km/h, aerodynamic noise, which can be dominant above 300 km/h, braking noise, curve squeal and impact noise. The braking system can often technically be considered part of the overall traction system, although acoustically it will often have separate noise sources.
In the Harmonoise and IMAGINE EU projects, a generalised prediction model for railway traction noise has been proposed to cover a broad range of powered railway vehicles. The model is one of the prediction modules for overall rail traffic noise, which also covers the other main sources. The traction noise model includes the main operational parameters such as driveshaft speed and power settings, and also takes individual auxiliary components and their duty cycles into account, such as compressors, valves and fans. Source height is included in the model. The level of modelling detail in the many potential traction noise sources has been kept to a minimum, as for the purpose of rail traffic noise prediction it often suffices to model only the dominant sources. Measurement methods are outlined to determine the noise emission spectra, from which extrapolations are made to obtain estimates for different operating conditions.
Abstract Based on the assumption that railway noise can be modeled as a group/line of incoherent point sources a calculation scheme has been proposed for determining the horizontal directivity of a train pass-by: with any directivity function(s) given for the individual point sources, the model will determine the horizontal directivity of the train pass-by.
The sample calculations show that, (1) if all point sources behave as monopoles the horizontal directivity of the train pass-by will have a monopole pattern, for any measurement distance; (2) if all point sources have the same directivity but not like a monopole, the horizontal directivity of the train pass-by will have the same directivity pattern when the measurement distance not less than 3 times the train length, otherwise directivity pattern of the train pass-by will vary with the distance; (3) the horizontal-directivity function used in some existing national models can be derived when some reasonable assumptions applied.
Abstract Noise immission level depends not only on the sound power level of noise source(s) but also the associated propagation attenuation, which in turn depends on the distance, the source height(s), the receiver height, the terrain profile, the ground impedance(s), and the weather conditions. To collect all these information for determining the propagation attenuation will lead to a complicated measurement procedure, which is desired to simplify.
In the European Imagine project we propose a practical method to determine the sound power of railway rolling noise using one-microphone recordings. With a standard measurement position (7.5m from the track center and 1.2m above railhead) the time history of the sound pressure level of a train passage will be recorded. When choosing the special time interval Tp and calculating the equivalent sound pressure level for this time period, the corresponding sound power level can easily be obtained by using the tabled constants. Applying this method to determine the sound power level one needs only to record the sound pressure level of train passages. The measurement procedure is much simplified.
To limit errors this method requires a railway bed of a height between 0 and 2m above a roughly flat terrain that the ground impedance value(s) is not less than 200 kPas/m^2. Wind speed should be less than 5 m/s and a train length not shorter than 70m. In real life these requirements can easily be satisfied so the method is really practical.