Cutting edge

September 29, 2000

Being able to swim like a shark is a question of drag, and scientists at Mie University have the means to measure this factor precisely

Humans have long dreamt of being able to swim like fish, despite the fact that we are not physically well suited to swimming. When a human swims, the water around the body undergoes a transition to turbulent flow, and drag dramatically increases. Swimming is a battle against drag, and only those who can beat the drag factor will become champions.

At Mie University in Japan, we have developed a device to measure fluid force in the direction of swimming, regardless of the yawing, pitching and rolling movements of the swimmer. It has thus been possible to measure active drag more precisely.

To reduce drag, swimmers originally concentrated on improving their stroke or form, but now there is considerable work being done to improve swimsuits.

Before the Atlanta Olympics in 1996, swimsuits were developed that repelled water. They were light, thin and fitted the body as closely as possible. A great deal of emphasis was placed on minimising the area of contact with the water and on materials that would expel any water that entered the suits.

After Atlanta, however, there was a radical change in swimsuit development. Application of the theory of boundary layer control of hydrodynamics gave birth to a new approach. The theory says that when a surface is uneven, such as the surface of a golf ball, the flow over it is disturbed. As a result, the flow moves parallel to the shape of the object and resistive drag is reduced.

Experiments on the efficiency of products manufactured in line with this concept were conducted at Tsukuba University in Japan more than ten years ago. However, the dimpled suits developed at the time did not yield the expected results and were extremely uncomfortable. Ten years later, a swimsuit that imitated the skin of a shark was created.

These swimsuits use a material that has minute V-shaped riblets set lengthways on its surface, just like the skin of a shark. In addition, the cutting and sewing of the material make it possible for the suit to cover the whole body without impeding the movement of the swimmer.

Mizuno Corporation Japan was the first sportswear manufacturer to develop the material. The scientific grounds for the effectiveness of sharkskin had already been established by the Nasa Langley Research Center. However, even though the principle of the effect was understood, a great deal of technological innovation was necessary before a product could be developed. It took more than four years before the new material was perfected.

Speedo England was largely responsible for the design of the new swimsuit. To keep the suits from impeding the muscle contractions of swimmers, it was necessary to take detailed measurements that allow for the build of each swimmer.

A three-dimensional body scanner is used to measure body shape. The data from this is combined with the movement analysis data of the swimming action to make a swimsuit. The swimsuits improve streamlining while allowing a full range of motion. The vibrations on the surface of the body caused by strong water currents are controlled, resulting in more reductions in drag.

According to the manufacturers of the new swimsuits, the result is a 7.5 per cent reduction in drag compared with other suits.

Hideki Takagi is associate professor in the health and physical education department of Mie University in Japan and a member of the scientific committee of the Japanese Swimming Federation.

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