China Solves 'Tunnel Boom' Problem With Maglev Trains

Ancient Slashdot reader Epeeist shares a report from The Guardian: The newest version of the maglev train is capable of traveling at 600km/h (about 370mph). However, the train's engineers have wrestled with the problem of the shock waves which occur as the train exits the mouth of a tunnel. When a high-speed train enters an enclosed space such as a tunnel, air in front is compressed, like in a piston. The resulting fluctuations in air pressure coalesce at the tunnel mouth, generating low-frequency shock waves. These are colloquially known as a "tunnel boom" -- a related, albeit different phenomenon to the "sonic boom" heard as aircraft pass the speed of sound. Tunnel booms pose serious challenges to operational safety, as the shock waves can disturb humans and animals nearby, as well as causing structural damage. Now, however, researchers have discovered that placing innovative soundproofing buffers at tunnel mouths can reduce shock waves by up to 96%. This promises improvements in operational safety, noise pollution and passenger comfort, as well as safeguarding animals in the vicinity of future lines. [...] The porous structure of the new 100-meter long buffers, combined with porous coatings on the tunnel body, allow the trapped air to escape before the train reaches the tunnel mouth, suppressing the boom in the same way as a silencer fitted to a firearm.

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