It is well known that when a compression wave generated by a high-speed train entering a tunnel propa- gates through the tunnel and arrives at the distant exit, a micro-pressure wave is radiated from the exit portal toward the surrounding area. In addition, several pressure waves are radiated toward the outside area from the entrance when a train enters the tunnel and from the exit when the train leaves it. We call the former a tunnel entry wave, and the latter a tunnel exit wave.
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