In this chapter, let us look at the hydrodynamic aspects of fish and whales that swim with a “fanning” motion of the body, including pelvic, dorsal, anal, and caudal fins. These animals have developed streamlined bodies that are well adapted to their environment, mode of life, and movement. The body and the fin motion of slender fishes are accomplished by a rhythmic transverse oscillation of the entire body and can be treated as an unsteady motion of a slender body resembling the “snaking” or “anguilliform” motion discussed in the preceding chapter. On the other hand, a wide caudal fin can be better analyzed as an isolated wing performing a fanning motion consisting of a heaving and a feathering motion. In this case, the fanning motion can be divided into two types: “ostraciiform” and “carangiform” (Breder 1926; Gray 1968; R.W. Blake 1981c). In the former, the fanning motion is limited to the tail and is a rudderlike motion. It is seen typically in the Ostraciidae. The latter is, as seen in the Carangidae, performed by flexing the entire body with particular stress on the posterior part. The mechanical differences among these movements will be theoretically analyzed.
KeywordsDrag Coefficient Froude Number Drag Reduction Speed Ratio Vortex Sheet
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