Yutaka Sakuma

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.

A Study on Vehicle Response to a Sudden Gust of Wind

In order to analyze the behavior of a railway vehicle that is subjected to a sudden gust of wind, we have conducted wind tunnel tests and running tests using a 1/10th scale train model. The feature of this model is that its spring stiffness is chosen considering the law of similarity between external forces and the resultant displacement of the car body. Using this model, we have examined aerodynamic forces acting on the surface of the car body and the behavior of the model in detail. Moreover, using the full-vehicle simulation program that we have developed in order to analyze the behavior of railway vehicles under crosswinds, we have examined the effects of the rapid changes of wind forces on overturning or wheel unloading ratios. As a result, it has been revealed that a sudden increase in wind force of less than 3 seconds can affect vehicle dynamic response considerably. On the other hand, a conventional static analysis is sufficient to evaluate a vehicle response for a slow increase in wind force of more than 3 seconds.