![]() The design team would have to find a way to redesign the shape of the train to go faster without creating the boom. Moreover, every unit increase in speed was producing an increase in pressure to the power of three. The micro pressure of the wave was in proportion to the ratio of the cross-section of the trainset to that of the tunnel. This problem was particularly troublesome because it was tied to both the geometry of the tunnel and the speed of the train. The air exited in low-frequency waves (under 20Hz) that produced a large boom and aerodynamic vibrations. Like a piston in a cylinder, the train was forcing the fluid air out of the other end of the tunnel. Whenever a train sped into a tunnel, it generated atmospheric pressure waves that reached the tunnel exit at the speed of sound. The sonic boom problem was much more complex than the pantograph noise. The train could now run at 320 km/hr and meet the stringent 70dBa noise standard set by the government. In 1994, a new “wing-graph” replaced the traditional pantograph and was a great success. ![]() He set his team to testing prototype shapes that mimicked these forms. The fimbriae serve to break down the air rushing over the wing foil into micro-turbulences, and this muffles the sound that typically occurs in wings without this feature. These comprise a comb-like array of serrations grown on the leading edge of the primary wing feathers. Nakatsu became intrigued with the noise-dampening feather parts (fimbriae) of the owl. Vortex streets are a basic dynamic and indeed, some animals, such as bees, are thought to take advantage of it in their flight. Placing a leeward fin on a cylinder is an example. This turbulence is a major consideration in the design of any lone tower or vertical mast, and various ways have been devised to counteract it. Alternate and opposite eddies swirl downstream of the obstruction, swinging back and forth as the force of one dominates and then the other. Karman vortices are created at all scales, from islands in the ocean to car aerials, and are manifested wherever a single bluff body separates the flow of a fluid. In the case of the pantograph noise, air rushing over the struts and linkages in the mechanism was forming into so-called Karman vortices, also known as a Karman vortex street, and this turbulence was causing most of the noise. This dynamic was so forceful that it was creating sonic booms heard by residents 400 meters away. The loudest noise came from the connections to overhead wires (pantographs), and the emergence of the trains from the tunnels on the line. The trains ran through dense neighborhoods and many tunnels. Making his trains faster was one of Nakatsu’s goals, but to do that, he needed to first make them quieter. Indeed, more people move by train in Japan - an estimated 64 million a day - than anywhere else in the world. The 515-kilometer Tokaido Shinkansen is the world’s busiest high-speed-rail line, having moved 4.9 billion passengers from its opening in 1964 (for the Toyko Olympiad) to 2010. The Sanyo and Kyushu Shinkansen Lines, operated by Japan Railway West, connect western Japan’s two biggest cities, Osaka and Fukuoka, and are an extension of the older Tokaido Line from Tokyo to Osaka. 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. ![]() I will write about all these things in this series on transportation, but first let’s take a look at a how a couple of interesting birds inspired a sleek design.Įiji 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. The common thread in all these scenarios: Deep observation and analysis of the natural world can lead to amazingly creative innovations. ![]() ![]() Or, what does catching flies have to do with preventing plane crashes? How will locust swarms change the nature of our highways? Can a mold do a better job of plotting our mass transit systems than a team of engineers and planners? What is the connection between an engineer going bird watching and his saving millions of dollars for his company? ![]()
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