Swimming by Snaking
Snaking is the most primitive way of swimming among animals. The young of most fishes swim in this mode, even though their adult locomotion may be very different. A sinusoidal deflection of either the whole body or a part of the body generates a lateral wave in the longitudinal direction. The mode of snaking used is strongly dependent on body size and body shape, because the viscous and inertial effects of the fluid surrounding the body are essentially related to the Reynolds number. The body length of microscopic organisms ranges from 1–5 μm for bacteria, to 300 μm for paramecia and spermatozoa, and their diameter is 1%–5% of the length or less. Thus, for microscopic organisms swimming in water or a slightly viscous fluid, the related Reynolds number and the reduced frequency are so small that the inertial effects of the fluid may be completely neglected. In such cases, the flow surrounding the body is said to be in the “Stokesian realm.” However, for large, elongate animals a few centimeters or meters in length swimming in fresh or salt water, the Reynolds number is large enough to introduce the inertial effects of the fluid into the hydrodynamic forces and moments. Streamlined bodies may coast for a considerable distance after having stopped their locomotion. The hydrodynamic aspects of a large, elongated body in unsteady motion can be treated either by the “slender body theory” or by the “two-dimensional flexible-wing (ribbon) theory.” In this chapter various snaking motions of different animals are presented, along with their modes of life.
KeywordsInertial Force Hydrodynamic Force Speed Ratio Body Element Friction Drag
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