| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 99 === Fast-start swimming of fish is a very special type of locomotion. Many existing studies involved using the DPIV flow-visualizing technique to measure the flow field around a steadily swimming fish and exploiting the basic fluid dynamic theories to interpret the source of the propulsion force. However, few researches had focused on the area of how fish utilize the dynamic of the flow field to produce large thrust in the fast-start motion. In this study, we model the body movement of a fast-start fish by a 2-D zero-thickness flat plate with prescribed undulating motions. For simplicity, a potential flow is assumed, along with the unsteady Kutta condition to simulate the vortex-shedding phenomenon at the end of the flat plate. The panel method is adopted to solve the flow field numerically, and the force acting on the flat plate is calculated by using the unsteady Bernoulli equation. In order to compare the thrust generated by an undulating plate with that by a rigid flat plate, three different standards of comparison are proposed. Calculated results show that under all standards, the propelling force and forwarding distance produced by a flat plate with undulating motion are larger than that produced by a rigid-body motion. The present research also compares and discusses several different types of flat-plate undulating motions, with a view to explain how a fish benefits from the impetus of the starting vortex generated by its swinging tail and properly adjusts its configuration to help accelerate itself through the fluid.
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