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Home page > Nature & Technology > Birds’ Flight Methods as a Model for:High-speed Trains

HIGH-SPEED TRAINS
Nature & Technology


When Japanese engineers and scientists were designing their high-speed 500-Series electric trains, they encountered a major problem: Examining wild birds for the perfect solution, soon they found the design they were seeking and implemented it successfully.

Owl Flight and High-Speed Train Noise
In the high-speed trains developed by the Japanese, safety is one of the most important factors. A second is compatibility with Japanese environmental standards. Japan’s noise regulations regarding railway operators are the strictest in the world. Using current technology, it’s not actually that difficult to go faster, though it’s hard to eliminate noise while doing so. Under Japanese Environment Agency regulations, a railway’s noise levels must not exceed 75 decibels at a point 25 meters (82 feet) away from the center of railway track in urban areas. At a crossing in a town, when cars start to move all at once on the green light, they create more than 80 decibels. This goes to show just how quiet the high-speed Shinkansen train must be.
The reason for the noise that a train produces up to a certain operation speed is the rolling of its wheels on the tracks. At speeds of 200 kmph (125 mph) or over, however, the sound source becomes the aerodynamic noise caused by its movement through the air.

owl
high-speed_train


The major sources of aerodynamic noise are the pantographs, or current collectors, used to take in electricity from overhead catenary. Engineers, realizing that they couldn’t reduce noise levels with the conventional rectangular pantographs, concentrated their research on animals that move quickly, yet silently.
pantographOf all birds, owls make the least noise during flight. One of the ways they manage this is through the plumes of their wings. In addition, an owl’s wings have many small saw-toothed feathers (serrations) visible even to the naked eye, which other birds lack. These serrations generate small vortexes in the air flow. Aerodynamic noise stems from vortexes forming in the air flow. As these grow in size, the noise increases. Since owls’ wings feature many saw-toothed projections, they form smaller vortexes instead of large ones, and the owls can fly very quietly.
When Japanese designers and engineers tested stuffed owls in a wind tunnel, they once again witnessed the perfection of these birds’ wing design. Later, they succeeded in efficiently reducing train noise by using wing-shaped pantographs based on the principle of the owl’s serrations. Thus the pantograph system developed by the Japanese, inspired by nature, became the quietest functioning. (1)

The Kingfisher’s Dive and High-Speed Trains’ Entry into Tunnels

high-speed_trains
kingfisher


waves_in_tunnelThe tunnels on the lines used by high-speed trains represented another problem for engineers to solve. When a train enters a tunnel at a high speed, atmospheric pressure waves rise up and gradually grow up to be like tidal waves that approach the exit of the tunnel at the same sonic speed. At the exit, the waves then return. At the tunnel’s exit, part of the pressure waves is released with a sometimes explosive noise.
Since the pressure of the waves is about one thousandth of atmospheric pressure or less, they're referred to as tunnel micro-pressure waves, which form as shown in the diagram.
The very disturbing noise created under the influence of the pressure waves can be reduced by widening the tunnel, but the task of altering the cross-sectional area of tunnels is very difficult and expensive.
At first, engineers thought that reducing the cross-sectional area of trains and making the forefront shape sharp and smooth might be a solution. They put these ideas into action in an experimental train, but remained unable to eliminate the micro-pressure waves it created.
Wondering if similar dynamics arose in nature, the designers and engineers thought of the kingfisher. In order to hunt its prey, the kingfisher dives into water, which has greater fluid resistance than air, and it experiences sudden changes in the resistance like a train does when it enters a tunnel.
Accordingly, a train traveling at 300 kmph (186 mph) needs to have a forefront shape like a kingfisher’s beak, which facilitates the bird’s diving.

kingfisher
To catch its prey, the kingfisher dives from low-resistance air into high-resistance water. Just as the bird’s beak facilitates such a dive, it also prevents its body from harm. But the kingfisher still needs to be able to see its prey as it dives into the water. God has created the bird with a protective mechanism to protect its eyes without hindering its ability to see and seize its prey underwater. When one bears in mind the fact that underwater objects appear to be somewhere else than where they really are when one looks at them from above the water, the importance of this becomes even clearer.

Studies conducted by the Japanese Railway Technical Research Institute and the University of Kyushu revealed that the ideal shape to suppress tunnel micro-pressure waves was a shape of revolving paraboloid or a wedge. A close-up cross-section of a kingfisher’s upper and lower beak form precisely this shape. (2) The kingfisher is yet another example of how all living things are created with exactly what they need to survive—and whose designs can serve as models for human beings.

References:

1 Eiji Nakatsu, "Learning From Nature - A Flight of Wild Birds and Railways,"
http://www.wbsj.org/birdwatching/contribution/97_910e.html
2 Ibid.

 
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