Study on a Method of Separating Incident and Reflected Waves from a Combined Pressure Wave in a Pipe

When a train is running in a tunnel, a pressure wave is continuously radiated from both end portals to the outside. We herein call this a “tunnel continuous wave”. Though some characteristics of the tunnel continuous wave have been revealed from previous research, the relation between the tunnel continuous wave radiating to the outside and the pressure wave inside the tunnel has not yet been obtained. The pressure wave measured at a fixed point in the tunnel is the superposition of two kinds of waves (an incident wave and a reflected wave) propagating in the opposite directions. Therefore, to investigate the relation between the tunnel continuous wave and the pressure wave inside a tunnel, it is necessary to separate the incident wave and the reflected wave from the measured combined pressure wave. In this paper, we propose a method of separating the incident wave and the reflected wave from the pressure waves measured inside a tunnel. The validity of this method is confirmed by numerical and experimental investigation.