Kingfisher birds to solve one of the biggest problems of the Japanese bullet train
The Shinkansen bullet train travels along high-speed railways throughout Japan at speeds of 240–320 km/hr. (150–200 mph), carrying millions of passengers every year. However, when it was first designed, the high speeds caused an atmospheric pressure wave to build up in front of the train.
When it would travel through tunnels, the wave would cause a loud “sonic boom” at the exit, disturbing nearby residents. The engineers had to find a way for the train to travel more quietly without sacrificing speed or using more energy.
Like a piston in a cylinder, the train was forcing the fluid air out of the other end of the tunnel. The air exited in low-frequency waves (under 20Hz) that produced a large boom and aerodynamic vibrations.
This problem was particularly troublesome because it was tied to both the geometry of the tunnel and the speed of the train. The micro pressure of the wave was in proportion to the ratio of the cross-section of the trainset to that of the tunnel. Moreover, every unit increase in speed was producing an increase in pressure to the power of three.
Eiji Nakatsu was the general manager of the technical development department for the so-called “bullet” trains of Japan, famed for their speed and safety record. After attending a 1990 lecture on birds by an aviation engineer, Nakatsu, who is also an engineer, realized studying the flight of birds could bring his train, and us, into the future.
Enter, the kingfisher, who is noted for, among other things, their spectacular ability to dive into the water to catch fish, crustaceans, amphibians, and reptiles—especially impressive because they do it with no or very little splash.
When the bird makes the transition from flying through the air (a low-resistance medium) to diving into the water (a high-resistance medium), its long beak increases in diameter gradually from the tip to the back as it plunges to catch its next meal.
Nakatsu and his team measured the pressure waves that arose when shooting bullets of various shapes into a kingfisher beak-shaped pipe, confirmed their observations, and then ran a series of tunnel simulations with trains outfitted with this shape. Data analysis showed that the ideal shape for this series of Shinkansen is identical to that of a kingfisher’s beak.
Not only did this help to reduce noise and eliminate tunnel booms, but it also allowed the train to travel 10% faster using 15% less electricity. Less power needed; less fuel consumed; less money spent. The Japanese bullet train story is an object lesson in how we can look to nature to make our designs faster, cleaner, and — oh, yes, quieter.
Sources:
- https://youtu.be/YVU6YBPaaB8
- https://asknature.org/innovation/high-speed-train-inspired-by-the-kingfisher/
- https://www.greenbiz.com/article/how-one-engineers-birdwatching-made-japans-bullet-train-better
- https://medium.com/design-voices/looking-deeper-into-biomimicry-how-nature-inspires-design-55c6f881241d
- https://us-east-2.console.aws.amazon.com/polly/home/SynthesizeSpeech
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