Aquatic flight inspired propulsion for autonomous underwater vehicles

Abstract

Modern Autonomous Underwater Vehicle (AUV) technology has a number of limitations and one of these is vehicle manoeuvrability. Conventional flight style AUVs generally have turning circle diameters of five or more vehicle lengths, but most marine animals can turn in under one body length. This shows there is merit in looking at marine animals for inspiration to improve the manoeuvrability of AUVs. Aquatic flight propulsion is one marine animal propulsion strategy that was identified early in the research as having the potential to full fill this role.

Aquatic flight propulsion has been studied experimentally in the past, but most of the past research focused in one or two axis aquatic flight (foil pitch and dorsoventral roll). However, marine animal literatures show animal aquatic flight is a three axis problem and there is an additional motion component in anteroposterior yaw. The effect of this yaw motion is not well understood and this will be the focus of this thesis’s research.

The effect of aquatic flight yaw motion is investigated using a combination of computation modelling and experimental studies. It found two-axis aquatic flight is better for producing propulsive thrust for most scenarios, but three-axis aquatic flight is useful for producing additional off axis force. In particular, the three axis slanted foil actuation path can produce a sizeable vertical force with very little change to the horizontal thrust coefficient, which would be very useful for a positively buoyant AUV to control its depth.

The experiment verified the model’s results and many of the experiment data points were within 30% of the model prediction. The experiment has a relatively large uncertainty due to turbulences in the recirculating water channel, so 30% is a reasonably good fit. Whilst there is room for improvement for both the model and the experiment, the current model is sufficient to produce provisional estimates for actuator and control system design as well as identification of various cases of interest for further in depth analysis.

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