March 31, 2005


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

Keywords: Newsletter 

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. It is possible to imagine other lines of inquiry using this approach. For example, there are spaces between the cars of rolling stock. It must be possible to reduce air resistance and aerodynamic noise further by virtually "connecting" these rolling stock cars.

However, connecting the trains with conventional materials won't work, because of stresses that occur when the train goes through a tight curve. Would it then be possible to develop a "train skin" that learns from the skin of seals, which stretches without wrinkling? I asked our partner manufacturers to look into the potential for developing this kind of technology, but it did not happen because the market would be too limited even if it were technologically feasible.

Yet, technology development using this approach is entirely possible, and there are more and more cases emerging. I know that there are other products already on the market, such as swimming suits developed through studies of shark skin and kingfisher feathers.

Q. How can we see nature in such a way that we can learn from it, as you do?

The most important thing, I think, is to observe. I myself have observed a lot about birds. Inspiration comes from building up a stock of observations over the years. So, one important factor is whether you were taught to observe nature during childhood. It is said that students nowadays tend to feel less attracted to science. I think that students have too little time to actually touch and feel nature. I would like to see more time set aside for children to observe nature and nurture such abilities, both in school and at home.

I studied engineering at school and worked as an engineer, but when I look back at my school days I wish I had studied biology more. One of the reasons why I did not take an interest in biology was that my teacher concentrated too much on memorizing details. I would like to urge schools and universities to teach students, especially engineering students, more about the survival strategies of living things as expressed in their shapes and functions.

For example, how did birds become birds, and fish become fish? For birds, why do some migrate? Why did whales return back to the ocean after living on land? Engineering Professor Nobuaki Kumagai, a former chairman of University of Osaka, echoes this thinking by saying "all college students should study biology."

My recommendation to young engineers is not to get stuck in their own fields, but to have reliable advisors in completely different fields. A railroad engineer tends to think only about trains. I was lucky enough to have a mentor in the field of aircraft, and I applied what I learned from him.

My mentor, Seiichi Yajima, had me read a book, "Aircraft Designing Theory" by Dr. Masao Yamana and Dr. Hiroshi Nakaguchi. This book says, "A tree, a blade of grass, a bird or a fish, all can be brilliant and everlasting teachers." This philosophy continues to inspire my work as an engineer.

I would also like to add that learning from nature ultimately leads to the knowledge that nature is a society with sound material cycles. Global environmental issues are now my major concern and I am currently helping start a citizen's movement "Be Modest to the Earth." (Japanese only)

After the Interview--What JFS Learned

Mr. Nakatsu's experience teaches us the following. To practice "learning from nature," it is important to start with our own needs and have a wide-angle view in looking for answers in the natural world. Here are concrete steps you can take.

1. Understand the needs and problems occurring in the human world (e.g.. Shinkansen noise)

2. Have a wide-angle view that takes in other fields (e.g.. Air pressure is an issue for aircraft)

3. Look for answers in the natural world (e.g.. Owls fly silently)

4. Repeatedly analyze data and conduct experiments and simulations (e.g.. Why and how do an owl's feathers erase noise?)

5. Consult experts in other fields (ex. Aircraft aerodynamic engineering, material sciences, physics, ecology of wild birds)

6. Apply the principles learned (ex. Putting triangular vortex-generator on pantograph)

7. Refer to and create application in other fields (boots and hats for skaters)

In the future, not only engineers, but also product designers, urban planners, and architects may go through these steps to learn from nature and actually put the principles they learn into practice.

(Staff Writer: Kazunori Kobayashi)

*This interview series is supported by the Hitachi Environmental Foundation.