Field Measurement of Pressure Waves Radiated from Tunnel Portals at Train Entry/Exit.

Abstract

When a train enters or leaves a tunnel at high speed, several pressure waves are radiated from the portals, of which we are especially concerned with two pressure waves in this paper. One is that radiated from the entrance when the train enters the tunnel, and the other radiated from the exit when the train leaves. Here, we call the former a tunnel entry wave, and the latter a tunnel exit wave. This paper reports the results of a field measurement performed at a Shinkansen tunnel to investigate the fundamental characteristics of tunnel entry/exit wave. The results of the field measurement show a good agreement with those of simple acoustic analysis regarding velocity dependency and distance attenuation. However, the agreement regarding directivity is not so good although qualitative tendency is consistent. The tunnel entry/exit wave is weaker when the train has a smaller crosssection and a slender nose shape. The peak pressure magnitude of the tunnel entry/exit wave is proportional to the pressure gradient of pressure wave in the tunnel and low frequency components below 10Hz are dominant, which is a similar tendency to that of the micro-pressure wave.