Motion Control and Propulsion Performance of Underwater Propulsion System by Using Traveling Wave Motion of Flexible Fins

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This report presents an experimental study of propulsion characteristics of an underwater propulsion mechanism by using traveling-wave motion of flexible fins. In the experiment, the flexible fins were attached at the side of an underwater vehicle, and the traveling-wave motion of the flexible plate was generated by a cam and follower mechanism. The effect of the wave number and frequency of the waving motion of the flexible fin on the propulsion characteristics was examined. As a result, following major things were obtained in this study.(1) The underwater propulsion mechanism can take both forward and backward motion by changing the direction of the traveling wave motion of the flexible fins.(2) The underwater propulsion mechanism can take smooth movement in water by the traveling wave motion with high wave number. On the other hand, the propulsion force becomes smaller with increasing wave number.(3) Propulsion force and swimming speed increase with increasing frequency of the traveling wave motion. Moreover, fluctuation of the propulsion force and swimming speed increase with increasing frequency of the traveling wave motion.(4) The underwater propulsion mechanism takes maximum swimming speed when the wave number is around 1.0.(5) The propulsion force and swimming speed decrease with increasing non-dimensional frequency, and fluctuation of the swimming speed takes constant value.(6) To realize the traveling-wave motion of flexible fins, the output feedback sliding mode controller to suppress the vibration and track the desired motion is presented and designed.