Dynamics of dolphin porpoising revisited |
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Authors: | Weihs D |
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Institution: | 1 Faculty of Aerospace Engineering Technion, Haifa 32000, Israel |
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Abstract: | Porpoising is the popular name for the high-speed surface piercingmotion of dolphins and other species, in which long, ballisticjumps are alternated with sections of swimming close to thesurface. The first analysis of this behavior (Au and Weihs,1980) showed that above a certain "crossover" speed this behavioris energetically advantageous, as the reduction in drag dueto movement in the air becomes greater than the added cost ofleaping. Since that publication several studies documented porpoisingbehavior at high speeds. The observations indicated that thebehavior was more complex than previously assumed. The leapswere interspersed with relatively long swimming bouts, of abouttwice the leap length. In the present paper, the possibilityof dolphins using a combination of leaping and burst and coastswimming is examined. A three-phase model is proposed, in whichthe dolphin leaps out of the water at a speed Uf, which is thefinal speed obtained at the end of the burst phase of burstand coast swimming. The leap is at constant speed and so theanimal returns to the water at Uf, goes to a shallow depth andstarts horizontal coasting while losing speed, till it reachesUi. At that point it starts active swimming, accelerating toUf. It then starts the next leap. Ranges of speeds for whichthis three-stage swimming is advantageous are calculated asa function of animal and physical parameters. Notation CConstant defined in equation (12) CDCoasting drag coefficient DDrag gGravitational acceleration HHeight of jump JEnergy required for jump kRatio of swim length to jump length lDistance LTotal distance (eq. 28) mAdded mass MAnimal mass M1Total mass rCoefficient defined in eq. (22) RRatio of energies, for three-phase swimming R2Ratio of energies, for burst and coast swimming tTime TThrust USpeed VBody volume WWeight |
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