Scientists discover secret of dolphin speed

05/14/04

How dolphins evolved to fly like birds under water

Physicists in Japan have discovered how the surface of a dolphin's skin reduces drag and helps them glide smoothly and quickly through water. These findings could help scientists design faster, energy-efficient boats, ocean liners, and submarines. This research is published in the Institute of Physics journal, Journal of Turbulence.

Scientists have known for some time that dolphins have evolved streamlined bodies which help them reduce the pressure of water against their skin (known as the 'form drag') as well as reducing friction (or 'friction drag'). Until now, no-one knew whether the soft flaky skin of a dolphin, which they shed once every 2 hours, also plays a vital part in helping them reduce these 'drags' and travel faster.

To try and understand the role of the soft, flaky skin, researchers from the Kyoto Institute of Technology in Japan devised a detailed computer simulation which models the flow of water over a dolphin's skin, modelling every individual flake of skin itself, and the way it peels off.

Professor Yoshimichi Hagiwara and colleagues found that the 'softness' or 'waviness' of the skin helps reduce drag caused by friction. They also discovered that the shedding of the skin itself reduces drag by disturbing tiny whirlpools of water called vortices, that occur in the flow around the surface of the dolphin and slow it down.

To test their simulation, they built a laboratory experiment which mimics dolphin skin using a 'wavy' plate covered in tiny pieces of film that gradually peel off as water moves over the surface.

Professor Hagiwara said: "It's really difficult to measure flow near swimming dolphins, so we designed an experiment that accurately reflects the way the surface layer of dolphin skin interacts with water flow over and around the dolphin".

He continued: "This research is important because it gives us greater insight into the mechanisms dolphins have evolved to cope with travelling through water, which is much harder than travelling quickly through air like birds do. This research could help us build boats, ocean liners and submarines using technology based on these natural solutions".

Professor Hagiwara and his team are now improving their models, and building a new test apparatus using a soft silicon-rubber wall, in the hope of mimicking dolphin skin even more precisely.

Source: Eurekalert & others

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