Science of Swimming and the Swimming of the Soft Shelled Turtle
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Science of Swimming and the Swimming of the Soft Shelled Turtle Shinichiro Ito1 1
Department of Mechanical Engineering, Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo, 1680065, Japan
ABSTRACT Swimming is dynamically a part of the hydrodynamic field and can be considered as a field of the optimal control motion. Animals move by instinct according to the situation which they are confronting with. Therefore, their instinctive motion is optimal most of the time. The movement of animals can be classified roughly into two kinds: the fast motion with the maximum speed and the motion with the minimum energy consumption. Considering the foreleg of the soft shelled turtle as a flat plane, several sets of movement of the foreleg were observed and calculated theoretically. The theoretical results agreed the observation results in the both cases with the maximum speed and the minimum energy consumption. Applying the theoretical movement of the soft shelled turtle foreleg to human movement in swimming, the general Sshaped pull stroke is the minimum energy consumption motion in free-style. It became clear that there was a different stroke for generating the maximum speed in free-style. That was the soft shelled turtle style of fast swimming, the I-shaped pull strokes. In 2002 when the author announced this theory, there was only one fast swimmer whose free-style swimming strokes coincidentally accorded with the I-shaped pull with fewer numbers of strokes at that time. He was the Olympic gold medalist Ian Thorp. Now the I-shaped stoke has become main stream in free style. INTRODUCTION Advancing movement of an animal in water can be roughly divided into two categories, locomotion of the maximal efficiency (the minimal energy consumption mode) for a usual motion and that of the maximal speed (the maximal thrust mode) for an urgent evacuation or a predatory action instinctively. James Counsilman [1] is one of the first to apply physical principles to try to understand the mechanism of propulsion. His study, where underwater cameras were used for the first time, showed a skillful swimmer moved his arms in an S-shaped pattern over the body axis in rolling motion. This arm motion produced lift like a propeller on an airplane. He suggested that propeller-like diagonal sculling motion, S-shaped pull stroke, was used by skilled swimmers, acknowledging the importance of lift forces. A speed is determined at the steady state of the body where the resistance of the whole body and propelling force are balanced. In order to reduce resistance of the body, a shark skin swimsuit has been developed. On the other hand, what affects the propulsion for its increase? In free style swimming, thrust force is mainly generated by movements of the arms (Hollander et al. [2]). They reported that the propelling force ratio of arms to legs was from 10:1 to 6:1. Moreover,
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the lift-drag characteristics of an arm are similar to those of a palm, says Berger et al [3]. Therefore, the lift-drag force characteristics of a palm can be considere
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