JFS Biomimicry Interview Series: No.6 “Shinkansen Technology Learned from an Owl?” – The story of Eiji Nakatsu


 

JFS Newsletter No.31 (March 2005)
Technologies Learned from Living Things: Concepts and Examples – Front Line Reports

The train that runs between Tokyo and Hakata is, like the TGV in France, one of the fastest trains in the world. This train is the 500-Series Shinkansen, operated by JR West and known for futuristic design and characteristic long “nose” on the front of the train. The Shinkansen enables us to move comfortably and quietly at 300 km/h, but you will no doubt be surprised to learn that a bird inspired Shinkansen technology. We interviewed Mr. Eiji Nakatsu, an engineer and the director responsible for the test runs of this Shinkansen series. He is also an active member of the Wild Bird Society of Japan.

Q. How did you end up learning from a bird?

You might assume that the challenge for the Shinkansen is how to make it run faster, but thanks to current technology it is now not so hard to make it run faster. In fact, the greater challenge for us is how to make it run quietly.

The faster the train runs, the more noise it makes. And, a large aerodynamic noise is generated when air hits pantographs, the current collectors that receive electricity from the overhead wires.

Noise standards for the Shinkansen are one of the worlds strictest for railway operation, so we cannot run the train without solving this noise issue. We, as the engineers responsible for developing the technology, were searching for solutions to this challenge.

One day, I happened to see a notice for a lecture in a newspaper; attending the lecture, I had the honor of meeting Mr. Seiichi Yajima, then an aircraft design engineer and also a member of the Wild Bird Society of Japan. From him I learned how much of current aircraft technology has been based on studies of the functions and structures of birds.

I learned that the owl family has the most silent fliers of all birds. Some hawk species even make large noises on purpose when hunting – the sound functions to freeze their prey with fear. But somehow, an owl’s feathers emit virtually no noise. It seems that the owl family has acquired the function of “quiet flying” so that prey such as mice, will receive no warning that the owl is about to strike.

Inspired by this fact, we conducted wind tunnel tests* to analyze the noise level coming from a flying owl, using a stuffed owl courtesy of the Osaka Municipal Tennoji Zoo. We learned that one of the secrets of the owl family’s low-noise flying lies in their wing plumage, which has many small saw-toothed feathers protruding from the outer rim of their primary feathers. Other birds do not have these feathers.

These saw-toothed wave feathers are called “serration feathers,” and generate small vortexes in the air flow that break up the larger vortexes which produce noise. It took 4 years of strenuous effort by our younger engineers to practically apply this principle. Finally, “serrations” were inscribed on main part of the pantograph, and this succeeded in reducing noise enough to meet the world’s strictest standards. This technology is called a “vortex generator;” it has already been applied to aircraft and is now being applied to the caps and boots of professional skaters.

From this experience, I was struck by the amazing functions that have been developed by living things. I learned first hand that truth can be found in the way life exerts itself in order to persist and carry on in this world. From then on, “learning from nature” became a recurrent theme for me.

Q. I had no idea that “technology” developed by an owl had been applied to the Shinkansen. Are there other examples in which learning from Nature has been applied to the Shinkansen?

In fact, we had another challenge that we pursued to the test run phase. Half of the entire Sanyo Shinkansen Line (from Osaka to Hakata) is made up of tunnel sections. When a train rushes into a narrow tunnel at high speed, this generates atmospheric pressure waves that gradually grow into waves like tidal waves. These reach the tunnel exit at the speed of sound, generating low-frequency waves that produce a large boom and aerodynamic vibration so intense that residents 400 meters away have registered complaints. For this reason, we gave up doing test runs at over 350 km/h.

Then, one of our young engineers told me that when the train rushes into a tunnel, he felt as if the train had shrunk. This must be due to a sudden change in air resistance, I thought. The question the occurred to me – is there some living thing that manages sudden changes in air resistance as a part of daily life?

Yes, there is, the kingfisher. To catch its prey, a kingfisher dives from the air, which has low resistance, into high-resistance water, and moreover does this without splashing. I wondered if this is possible because of the keen edge and streamlined shape of its beak.

So we conducted tests to measure pressure waves arising from shooting bullets of various shapes into a pipe and a thorough series of simulation tests of running the trains in tunnels, using a space research super-computer system. Data analysis showed that the ideal shape for this Shinkansen is almost identical to a kingfisher’s beak.

I was once again experiencing what it is to learn from Nature, seeing first hand that a solution obtained through large-scale tests and analysis by a state-of-the-art super-computer turned out to be very similar to a shape developed by a living creature in the natural world. The nose of our new 500-Series Shinkansens has a streamline shape that is 15m in length and almost round in cross section.

This shape has enabled the new 500-series to reduce air pressure by 30% and electricity use by 15%, even though speeds have increased by 10% over the former series. Another benefit has been confirmed through a favorable reputation among customers that these trains give a comfortable ride. This is due to the fact that changes in pressure when the trains enter tunnels are smaller.

Q. You have learned from Nature and succeeded in reducing significant environmental impacts. This is a wonderful achievement.

Through these experiences, I came to a clear realization that answers or clues can be found in nature.[…]

Source: JFS Japan for Sustainability

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About agogo22

Director of Manchester School of Samba at http://www.sambaman.org.uk
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