ABSTRACT

The purpose of this study is to develop a scheme to improve the stability and efficiency of the propulsion for a biomimetic autonomous underwater vehicle (BAUV). A three-segment BAUV propelled by a flapping tail fin is considered. The BAUV with actuated fin motions and sensors is capable of performing Carangiform locomotion. A controller based on an oscillator structure was used to control the BAUV propulsion in order to increase the stability of the BAUV. The motion of the tail fin was described by a system includes two nonlinear oscillators. The oscillators produce stable limit cycle oscillations by adjusting the nonlinear feedback in the system. Limit cycles of the oscillator controller generate swimming patterns that resist perturbations and therefore the BAUV could swim stably. Increasing the swimming efficiency could be achieved by using actuators that drive motions of the fin via springs. With proper spring compliances, wasted energy due to braking could be stored and reused; therefore, the amount of energy required to propel the BAUV could be reduced. Thus, the resulting propulsion mechanism is expected to be useful as a design guideline to build a BAUV with good swimming stability and efficiency.

INTRODUCTION

Autonomous underwater vehicles (AUVs) have been used in numerous undersea missions, such as underwater surveys and surveillance. Conventional AUVs have the drawbacks of low propulsive efficiency and poor maneuverability. Biomimetic autonomous underwater vehicles (BAUVs) are designed to mimick the motion of fish, given their ability to hover precisely and turn swiftly (Guo, 2009). A review of fish swimming modes for aquatic locomotion provides an overview of the swimming mechanisms of fish (Sfakiotakis, et al., 1999; Colgate and Lynch, 2004). Fish swim using (a) body and/or caudal fin (BCF) locomotion, or (b) median and/or paired fin (MPF) locomotion.

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