Active Control of Incident Wave Front of Compression Wave in Tunnel to Reduce the Level of Micro-Pressure Wave

When a high speed train dashes into a tunnel, a compression wave is generated. The compression wave propagates through the tunnel at the sound speed. When it arrives at the exit of the tunnel, a MPW (micro-pressure wave) is emitted outward from the tunnel exit. The MPW has a positive impulsive pressure and the residents around the portal of the tunnel are put to annoyance. Several ways of passive control of micro-pressure wave have been investigated. The typical counter-measures are the installation of a hood at the entrance of a tunnel and side branches in a tunnel. Although they are effective, a quite long hood is required if the train speed is more than 350 km/h and the side branches cause low frequency noise around the portal if the train speed is more than 400 km/h at the Japanese MAGLEV test line. Therefore, an active control method is desired to apply with passive methods. In this paper, two dimensional MOC (Method of Characteristics) is applied and the active control of incident wave front of compression wave in a tunnel is numerically simulated to reduce the level of MPW.