Wavenumber–domain separation of rail contribution to pass-by noise

Abstract

In order to counteract the problem of railway noise and its environmental impact, passing trains in Europe must be tested in accordance to a noise legislation that demands the quantification of the noise generated by the vehicle alone. However, for frequencies between about 500 Hz and 1600 Hz, it has been found that a significant part of the measured noise is generated by the rail, which behaves like a distributed source and radiates plane waves as a result of the contact with the train's wheels. Thus the need arises for separating the rail contribution to the pass-by noise in that particular frequency range. To this end, the present paper introduces a wavenumber-domain filtering technique, referred to as wave signature extraction, which requires a line microphone array parallel to the rail, and two accelerometers on the rail in the vertical and lateral direction. The novel contributions of this research are: (i) the introduction and application of wavenumber (or plane-wave) filters to pass-by data measured with a microphone array located in the near-field of the rail, and (ii) the design of such filters without prior information of the structural properties of the rail. The latter is achieved by recording the array pressure, as well as the rail vibrations with the accelerometers, before and after the train pass-by. The performance of the proposed method is investigated with a set of pass-by measurements performed in Germany. The results seem to be promising when compared to reference data from TWINS, and the largest discrepancies occur above 1600 Hz and are attributed to plane waves radiated by the rail that so far have not been accounted for in the design of the filters.

On modified wavenumber filters for rail contribution estimations

“…However, at the moment of comparing the WSE results with the reference data, the rail spectra is underestimated for frequencies above 1.6 kHz. 4 This underestimation has been attributed to the presence of additional waves that are not captured by the WSE filters, and the novelty brought by this letter is the use of other filter families that can capture such waves.…”

“…The wave signature extraction (WSE) method has been recently introduced with the aim of separating the rail contribution to pass-by noise. 4 The method entails filtering wavenumber-domain spectra of microphone array measurements of the passby, and the output is the rail sound level spectra in 1/3 octave frequency bands. However, at the moment of comparing the WSE results with the reference data, the rail spectra is underestimated for frequencies above 1.6 kHz.…”

Sound Source Localisation for a High-Speed Train and Its Transfer Path to Interior Noise

“…They concluded that whether or not the rolling noise is the most important source, it depends on not only the train speed but also the wheel/rail surface conditions. Zea et al [16] introduced a wavenumber-domain filtering technique, referred to as wave signature extraction, to separate the rail contribution to the total pass-by noise. The advantage of the method is that, in principle, no prior knowledge of the structural properties of the track is needed.…”

Implications of the directivity of railway noise sources for their quantification using conventional beamforming

“…Moreover, the distribution of the sound intensity in the horizontal plane consists of sound propagating at a specific angle, which depends on the ratio between the structural and acoustic wavenumbers [2]. This feature was recently adopted to quantify the rail noise contribution by applying a wavenumber filter to the signals from a line array of microphones [9,10].…”