77,273 research outputs found

    MAGNITUDE OF MAXIMUM SHOULDER AND HIP ROLL ANGLES IN BACK CRAWL AT DIFFERENT SWIMMING SPEEDS

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    The purpose of this study was to identify the characteristics of maximum shoulder and hip roll angles in back crawl at different swimming speeds. Ten male elite swimmers performed back crawl at four different swimming speeds. The swimming trials were filmed by a total of six digital video cameras and three-dimensional coordinates of swimmer's anatomical landmarks were calculated using the three-dimensional direct linear transform. The data were input to a MATLAB programme to calculate linear and angular kinematics. Among the four speed trials, maximum shoulder and hip roll angles were unchanged, and maximum shoulder roll angle was significantly larger than maximum hip roll angle in all trials. In conclusion, the swimming speed does not affect swimmer's shoulder and hip roll angles in back crawl swimming

    Magnitude of maximum shoulder and hip roll angles in back crawl at different swimming speeds.

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    The purpose of this study was to identify the characteristics of maximum shoulder and hip roll angles in back crawl at different swimming speeds. Ten male elite swimmers performed back crawl at four different swimming speeds. The swimming trials were filmed by a total of six digital video cameras and three-dimensional coordinates of swimmer's anatomical landmarks were calculated using the three-dimensional direct linear transform. The data were input to a MATLAB programme to calculate linear and angular kinematics. Among the four speed trials, maximum shoulder and hip roll angles were unchanged, and maximum shoulder roll angle was significantly larger than maximum hip roll angle in all trials. In conclusion, the swimming speed does not affect swimmer's shoulder and hip roll angles in back crawl swimming

    Hydrodynamics of Micro-swimmers in Films

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    One of the principal mechanisms by which surfaces and interfaces affect microbial life is by perturbing the hydrodynamic flows generated by swimming. By summing a recursive series of image systems we derive a numerically tractable approximation to the three-dimensional flow fields of a Stokeslet (point force) within a viscous film between a parallel no-slip surface and no-shear interface and, from this Green's function, we compute the flows produced by a force- and torque-free micro-swimmer. We also extend the exact solution of Liron & Mochon (1976) to the film geometry, which demonstrates that the image series gives a satisfactory approximation to the swimmer flow fields if the film is sufficiently thick compared to the swimmer size, and we derive the swimmer flows in the thin-film limit. Concentrating on the thick film case, we find that the dipole moment induces a bias towards swimmer accumulation at the no-slip wall rather than the water-air interface, but that higher-order multipole moments can oppose this. Based on the analytic predictions we propose an experimental method to find the multipole coefficient that induces circular swimming trajectories, allowing one to analytically determine the swimmer's three-dimensional position under a microscope.Comment: 35 pages, 11 figures, 5 table

    Gyrotactic suppression and emergence of chaotic trajectories of swimming particles in three-dimensional flows

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    We study the effects of imposed {three-dimensional flows} on the trajectories and mixing of gyrotactic swimming micro-organisms, and identify new phenomena not seen in flows restricted to two dimensions. Through numerical simulation of Taylor--Green and ABC flows, we explore the role that the flow and the cell shape play in determining the long-term configuration of the cells' trajectories, which often take the form of multiple sinuous and helical `plume-like' structures, even in the chaotic ABC flow. This gyrotactic suppression of Lagrangian chaos persists even in the presence of random noise. Analytical solutions for a number of cases reveal the how plumes form and the nature of the competition between torques acting on individual cells. \note{Furthermore, studies of Lyapunov exponents reveal that as the ratio of cell swimming speed relative to the flow speed increases from zero, the initial chaotic trajectories are first suppressed and then give way to a second unexpected window of chaotic trajectories at speeds greater than unity, before suppression of chaos at high relative swimming speeds
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