Katsuhiro Kikuchi

Optimization of Train Nose Shape for Reducing Micro-pressure Wave Radiated from Tunnel Exit

When a compression wave generated by a high-speed train entering a tunnel propagates through the tunnel and arrives at the tunnel exit, an impulsive pressure wave (micro-pressure wave) is radiated from the tunnel exit. Improving the train nose shape is one of the techniques for suppressing the micro-pressure wave. Furthermore, tunnel entrance hoods are required for long concrete slab tunnels in order to suppress the micro-pressure wave. The effect of the tunnel entrance hood on the compression wave generated by the train can be evaluated by means of a rapid computational scheme devised and validated experimentally by Howe et al. In this study, the optimal longitudinal distribution of the cross-sectional area of the train nose shape was determined by using the rapid computational scheme and a genetic algorithm. The effect of the nose shape optimization was confirmed through experiments using scale models.

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.

Model Experiments on the Tunnel Compression Wave Using an Axisymmetric and Three-Dimensional Train Model

Generation of the compression wave by a train entering a tunnel is investigated by model experiments. In the model experiments, the train and the tunnel are represented by an axisymmetric model, a three-dimensional mirror image model and a three-dimensional model. The experimental results indicate that the effect of the three-dimensionality of the train nose shape is approximately 2 % for the pressure gradient of the compression wavefront when the train nose is streamlined, hence without large flow separation around the train nose. Furthermore, the relationship between the pressure gradient of the compression wavefront and the train position in a cross-section at the tunnel portal is clarified.

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.