Shinichiro Nakao

Attenuation and Distortion of Pressure Wave Propagating in a Constant Area Tube : 1st Report, Characteristics of a Weak Shock Wave

In order to clarify the attenuation and distortion of a pressure wave propagating in a constant area tube, experimental study has been carried out. Weak shock waves (Ms<1.1) were created using an open end shock tube. Experimental results show that the strength of a shock wave decreases exponentially with distance. The attenuation rate of wave strength is affected by the initial strength of the shock wave and by the unsteady boundary layer induced by the wave front. The shape of a weak shock wave becomes different with the propagation distance; that is, a compression wave appears just behind the shock wave front. And an overshoot is observed behind the shock wave front, because of the transition of the boundary layer.

The performance of a fast-opening gate valve for a railway tunnel simulator

When a high-speed train enters a tunnel, a compression wave is generated in front of the train. This compression wave propagates to the tunnel exit and spouts as a micro pressure wave, which causes a blast sound. To solve the noise pollution at the tunnel exit, we have to know how the compression wave propagates in the tunnel. Because it is very difficult to collect data from a real tunnel, we have to use a railway tunnel simulator to investigate the mechanism of the propagating compression wave. To accomplish the railway tunnel simulator, a fast opening gate valve was developed. In this present paper we have analyzed the performance of the fast opening gate valve by using a super high-speed video camera. The results show that the opening time of the gate valve decreases when the initial pressure in the actuating chamber increases. And the relation between the initial pressure in the actuating chamber(or opening time) and the characteristics of the compression wave such as the maximum pressure gradient was made clear.