Hajime Takami

Field Measurement of Wayside Low-Frequency Noise Emitted from Tunnel Portals and Trains of High-Speed Railway:

In order to determine the actual circumstances of wayside low-frequency noise and infrasound generated by high-speed trains (Shinkansen), field measurements were performed at two sites, one near a tunnel portal and the other in a fully open section. The measurements were based upon the manual issued by the Ministry of the Environment of Japan in October 2000 and conducted to obtain G-weighted SPL, 1/3-octave band spectra, velocity dependence and distance attenuation of SPL. The measured results show that major components of the low-frequency noise from the tunnel portal are impulsive micro-pressure waves and continuous pressure waves, while those in the open section are near-field hydrodynamic pressure variations and far-field acoustic pressure waves.

Continuous Pressure Waves Generated by a Train Running in a Tunnel

This research describes several characteristics of tunnel continuous waves (TCW), which are a kind of low-frequency pressure wave radiated from railway tunnel portals. Several theoretical results are presented and measurement data obtained in field tests. Ratios of the amplitude and the frequency of the TCW radiated in the forward direction to those radiated backward have been obtained. Also described is a method for separating an incident wave from pressure data measured in a tunnel and this method is applied to data obtained in field tests. As a result, the separation method is shown to be applicable to the field test data.

Infrasound Generated by a High-Speed Train Running through a Short Tunnel

This paper deals with the pressure waves generated by a train running through a short tunnel and radiated from its portals to surrounding areas as infrasound. First described are the results of a field measurement conducted at a short, 93 m-long, Shinkansen tunnel to present the generation mechanism of the infrasound. Next an acoustic analysis is made of the infrasound radiated to the outside by applying a method for predicting the compression wave in the tunnel generated by train entry. The calculated and measured results of the waveform of the infrasound are consistent despite considerable simplification in geometric modeling in the analysis. Comparison of the spectra shows that the acoustic analysis is capable of calculating the components below about 10 Hz of the infrasound, including the harmonics of the fundamental frequency of 1.7 Hz determined from the tunnel length.

Visualization of the Structures in a Plane Mixing Layer

Direct numerical simulation of time-developing mixing layers has been performed. The structure of the mixing layer is visualized by means of the vorticity contour and passive scalar. Numerical results were compared with the smoke patterns. Mixing layer was generated behind a splitter plate towed in a straight long tunnel. Acoustic forcing was applied to excite the shear layer and also to induce wave resonance in the free shear layer. We found that scalar distributions is similar to smoke pattern in the vortical structure in prior to pairing. This paper describes the structure recognition by visualization technique.