ABSTRACT:

An undulatory stingray-inspired fin, which will serve as a propulsor on a new AUV, has been designed and fabricated. A simple design is achieved through use of a single actuator to generate a travelling wave down the chord of the fin. The hydrodynamic performance is studied through use of flow visualizations, which indicate that thrust is produced between a Strouhal number of ~0.5–3. This range is higher than the expected value from literature, showing a need for further investigation of the effect of undulation on the performance of low aspect-ratio fins.

INTRODUCTION

Current state-of-the-art autonomous underwater vehicles (AUVs) do not match the high maneuvering performance exhibited by many marine animals. Gliders are a promising addition to the AUV fleet, since they have no external propellers and therefore use extremely low power. They require, however, an average turn radius of 3–15 times the body length. It is proposed that a robotic stingray-inspired AUV be built to bridge the gap between marine animals and existing AUVs by combining advantages from both groups. It will function in two modes:

  1. with rigid fins in a low-power, delta wing, glider mode and

  2. with undulating fins for efficient propulsion and navigating complex environments. The method used to develop this new propulsion is explained in this paper. It follows these steps: identify useful mechanisms employed in stingray swimming, apply them in an engineering design solution, and tune the system parameters to achieve an optimal swimming gait.

BACKGROUND
How does it move?

The key to propulsion in the stingray is the travelling wave. The undulations generate semi-circular fluid structures along the body that are shed at the sharp trailing edge into the wake as vortices. It has been shown (Wolfgang et al., 1999) that fish do this in a controlled manner for optimum vortex strength.

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