We found a match
Your institution may have rights to this item. Sign in to continue.
- Title
What dolphins tell us about hydrodynamics.
- Authors
Ungerechts, Bodo E .; Daly, Dan; Zhu, J. P.
- Abstract
Dolphins are superbly adapted to fast swimming, and the study of how they gracefully propel themselves through water requires the interdisciplinary collaboration of zoologists, hydrodynamicists, and biomechanists. Such studies have in fact been done, and there are aspects of dolphin propulsion beyond the simple comparison to the butterfly kick that will be of interest to swimming scientists. Although dolphins can swim three times faster than humans, they cannot deliver more power per kg of muscle mass. This phenomenal performance is made possible by a hydrodynamically optimal body shape, the oscillatory movement of the tail, and the phase coupling of the heaving and pitching of the semilunate shaped fluke. The streamlined body reduces the pressure drag to a minimum, and the combination of heaving and pitching motions transfers momentum to the surrounding water. The rate at which momentum is transferred determines the amount of thrust generated. The fluke sets water into rotation, called a vortex. Momentum is transferred and thrust is obtained either by canceling out the vortex rotation at each fluke reversal point, or by the creation of a propulsive jet from a combination of clockwise and counterclockwise vortices. Although human swimmers will not be able to set water into rotation as effectively as dolphins because of the shape and inflexibility of their ankles, this deficit can be lessened by swimmers emphasizing the reversal action of the kick, using as much as possible, a whip-like action. Part of dolphin propulsion research has involved the examination of the water after it leaves the dolphin's surface. Similar studies could be performed with human swimmers, using entrained air bubbles to reveal wake size or vortex formation. This would provide coaches useful feedback on how effective their swimmer's streamline or stroke technique might be. For example, a wide wake might indicate a high drag or wasted energy spent by the swimmer "fighting" the water, rather than cooperating with it.
- Subjects
DOLPHINS; HYDRODYNAMICS; FLUID dynamics; ANIMAL swimming; ANIMAL locomotion; ZOOLOGISTS; UNDERWATER propulsion; MOMENTUM (Mechanics); OSCILLATIONS
- Publication
Journal of Swimming Research, 1998, Vol 13, p1
- ISSN
0747-5993
- Publication type
Article