A fully actuated tail propulsion system for a biomimetic autonomous underwater vehicle

In recent years that has been a worldwide increase in the utilisation of Autonomous Underwater Vehicles (AUVs) for many diverse subsea applications. This has given rise to an increase in the research and development of these vehicles, with a particular focus on extending operational capability and longevity. Consequently, this activity has resulted in the design of many different types of AUVs that employ a variety of different propulsion and manoeuvring mechanisms. One particular area that has yielded promising results involves the vehicles designs that are biologically inspired or biomimetic. This class of AUV replicates the anatomical features of aquatic species in order to exploit some of the benefits associated with this type of swimming e.g. higher efficiency at low speeds, improved manoeuvrability. The study presented in this thesis considers the design and performance analysis of a unique biomimetic AUV design based on the physiology of an adult Atlantic salmon. This vehicle, called RoboSalmon, is equipped with a multiple jointed, fully actuated tail that is used to replicate the undulatory swimming gait of a real fish. The initial stage of this design process involves the development of a mathematical model to describe the fusion of the dynamics and electro-mechanics of this vehicle. This model provides the design specifications for a prototype vehicle, which has been used in water tank trials to collect data. Forward swimming and manoeuvring experiments, e.g. cruise in turning and turning circle swimming patterns, have been conducted for performance analysis and validation purposes. This part of the study has illustrated the relationship between the vehicle surge velocity, tail amplitude and tail beat frequency. It was found that the maximum surge velocity has been measured at 0.143 ms-1. Also, the vehicle has been shown to accomplish turning circle manoeuvres with turning radius just over the half of its body length. The final stage of this study involved the design of a heading control system, which changes the course of the vehicle by altering the tail centreline. This study allowed the course changing performance of the vehicle to be analysed. Furthermore, a line of sight guidance system has been used to navigate the vehicle through a multiple waypoint course in order to show autonomous operation within a simulated environment. Moreover, the vehicle has demonstrated satisfactory performance in course changing and tracking operations. It is concluded that the RoboSalmon biomimetic AUV exhibits higher propulsive efficiency and manoeuvrability than propeller based underwater vehicles at low speeds. Thus the results of this study show that mimicking biology can improve the propulsive and manoeuvring efficiencies of AUVs