Tokuzo Miyachi

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.

Distortion of Compression Wave Propagating through Shinkansen Tunnel

When a compression wave generated by a train entering a tunnel is propagated through the tunnel and reaches the exit portal, a pressure pulse (‘micro-pressure wave’) is radiated from the exit portal. The distortion of the compression wave during propagation in the tunnel is important for estimating the magnitude of the micro-pressure wave radiated from the exit portal. In this paper, the dependence of the distortion of the compression wave on the initial waveform at the tunnel entrance is investigated. First, a simple system of equations concerning the wave propagation in the tunnel is described. Secondly, theoretical and numerical investigations into the effects of nonlinearity and unsteady friction on the tunnel wall on the distortion of the compression wave are made.

Propagation characteristics of tunnel compression waves with multiple peaks in the waveform of the pressure gradient: Part 2: Theoretical and numerical analyses

This paper is the second part of a two-part study on the propagation characteristics of compression waves generated by a train entering a long slab track tunnel with a tunnel entrance hood, which generates a tunnel compression wave with multiple peaks in the waveform of its pressure gradient. In Part 1, we described field measurements on the propagation characteristics of the compression waves generated by Shinkansen trains in a 9.7-km-long tunnel, and we compared the results with those of simulations. It was shown that initial waveforms whose pressure gradient waveforms have shallower valleys tend to steepen more easily, and a mathematical model of the distortion based on the field measurements using a quasi-laminar friction model was proposed. This follow-up report describes the theoretical and numerical analyses conducted on the basis of the mathematical model. Initial waveforms of the pressure gradient that have no valleys and are higher on their right-hand side grow up easily during propagation; this is due to the unsteady friction being small in the region where the magnitude of the second time derivative of the pressure is small. This results in a dependence of the propagation characteristics on the initial waveform of the compression wave.

Propagation characteristics of tunnel compression waves with multiple peaks in the waveform of the pressure gradient: Part 1: Field measurements and mathematical model

A high-speed train entering a tunnel generates a compression wave. When the compression wave reaches the exit portal of the tunnel, a micro-pressure wave radiates outward. The magnitude of the micro-pressure wave is approximately proportional to the pressure gradient of the compression wave arriving at the exit portal. As the micro-pressure wave can cause environmental problems, tunnel entrance hoods have been installed at many portals of long slab track tunnels on the Japanese high-speed railway, the Shinkansen to reduce the magnitude of the micro-pressure wave. In this study, field measurements were taken in a Shinkansen long slab track tunnel with a hood at its entrance. The compression wave distorts during its propagation through a long slab track tunnel. The dependence of the propagation characteristics on the initial compression waveform was clarified on the basis of field measurements on different trains and hood window configurations. It was shown that compression waves with a waveform of the pressure gradient that has shallow valleys tend to steepen more easily and that the optimum window pattern of the hood depends on the length of the tunnel. Furthermore, a mathematical model corresponding to the results of the field measurements was proposed to describe the distortion of the compression waves.

1119 Model Experiment and Analysis of the Micro-pressure Wave Emitted from a Tunnel Hood with Openings

Hirokazu ATSUMI, Railway Technical Research Institute, 2-8-38 Hikari-cho, Kokubunji-shi, Tokyo Tokuzo MIYACHI, Railway Technical Research Institute, 2-8-38 Hikari-cho, Kokubunji-shi, Tokyo Sanetoshi SAITO, Railway Technical Research Institute, 2-8-38 Hikari-cho, Kokubunji-shi, Tokyo Takashi FUKUDA, Railway Technical Research Institute, 2-8-38 Hikari-cho, Kokubunji-shi, Tokyo Shinya NAKAMURA, Railway Technical Research Institute, 2-8-38 Hikari-cho, Kokubunji-shi, Tokyo An impulsive pressure wave emitted from a tunnel portal, called a micro-pressure wave, is one of the important wayside environmental problems in high-speed railways. A tunnel hood with openings on its side wall installed at the portal of the train entrance side is the principal countermeasure for reducing the micro-pressure wave. However, the micro-pressure wave tends to have large peak value around openings of the hood when the micro-pressure wave is emitted from the tunnel exit portal with the hood. In this study, we carried out the model experiment focused on the effects of the tunnel hood with openings installed at the portal of the train exit side. In addition, we developed a simple theoretical model simulated the micro-pressure wave around openings of the hood.

A Simple Scheme for Calculating Distortion of Compression Wave Propagating through a Tunnel with Slab Tracks

A high-speed train entering a tunnel generates a compression wave that propagates through toward its exit.When the compression wave reaches the tunnel exit, a pressure pulse (“micro-pressure wave” [1, 2]) is radiated from the exit portal, and it causes an environmental problem. The magnitude of the micro-pressure wave is approximately proportional to the maximum pressure gradient ∂ p/ ∂ t max (p: acoustic pressure, t: time) of the compression wave arriving at the tunnel exit [1].