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Friday, August 24, 2012

The jellyfish - jet propulsion or what?

  • Jellyfish have been described as being at least 95% water and ranging in size from less than three centimetres to over two metres in diameter. Muscles propel many species along by rhythmic contraction and relaxation of their bell-shaped body - something like the opening and closing of an umbrella. Scientists who study fluid dynamics have discovered that certain jellyfish, while not fast swimmers, have an intriguing method of propulsion. With each contraction of their body, they create a doughnut-shaped vortex, like a smoke ring, which they push away from themselves. The momentum of the rings creates an opposite reaction that propels the jellyfish forward, somewhat like a jet but with pulses of energy instead of a constant thrust. "It sounds simple," said 'New Scientist' magazine. "But the act of forming a vortex ring is very difficult to model mathematically." That in itself is quite incredible. Evolution or design, you may wonder?
    "Not so for 30 year-old bioengineering professor John Dabiri, whose fluid dynamics laboratory at the California Institute of Technology is studying the dynamics and mechanics of biological propulsion. Their subject? The moon jellyfish because of its simple morphology and complex patterns of motion.
    By exploring these dynamics, Dabiri hopes to create more efficiently engineered systems of propulsion and energy technologies that could harness wind and wave power.
    Through his research, Dabiri has observed that moon jellyfish don't move through water simply by using jet propulsion. Instead, they create complex vortex rings in the wake of their motion that allow them propel themselves forward.
    Cracking the code to how jellyfish create these currents has the potential to inform the development of future propulsion models. On the horizon are possible advances in underwater transportation or medical technologies administered through the blood stream."
  • http://huttriverofnz.blog.co.uk

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