Design, Modeling, And Control Of Bionic Underwater Vehicle Propelled By Multiple Undulatory Fins

The propulsion mode of fish's undulatory fin has advantages on less swimming disturbance, generations of vector thrust and convenience of being transplanted to underwater vehicles. Generally speaking, such a bio-propulsion mode provides a novel scheme for future aquatic robots, so it possesses values of theoretical research and prospective for wide applications. This thesis presents the fish-inspired robot which is propelled by cooperative undulation of the multi-fin bio-propulsor, including bionic design scheme, dynamic modeling of the undulatory multi-fin propulsion system and the cooperative control mechanism of the multi-fin propulsor. And we may draw the following innovative points.1. The thesis proposes the design scheme for a novel bionic underwater vehicle which is propelled by undulatory multiple fish-like fin. In terms of existing reports and published literature, it is the first time to imitate propulsion mechanism of undulatory fins and apply that into the design and implementation of propulsion and control system for the novel underwater vehicle. This propulsion and control scheme with four orthogonal-parallel-deployed undulatory fins has been verified to generate thrust as well as yawing and pitching moments via active multi-fin undulations. In addition, the thrust and moments can be controlled by coordinating undulatory parameters of each fin or varying cooperative undulations among the four fins. This bionic multi-fin propulsor can actively generate thrust and operational moments without any rudders, so it may not only be applicable in propulsion and gesture control, but also it is good at enhancing maneuverability at low speed and high-speed agility. The propulsion and control system design scheme based on the undulatory multi-fin propulsor provides an innovative idea and another choice for the bionic design of underwater vehicles.2. The kinematic and dynamic models are established on the basis of bionic inspirations in Balistiform fish's undulatory fins and the drag model in fluid mechanics. The kinematic model can describe morphological and kinematic characteristics of the undulatory fins under a uniform expression, and is more feasible with comprehensive considerations in morphology in company with locomotion of the fin base line, the natural shape, the fin ray oscillation, and the lateral as well as vertical displacements. Additionally, the dynamic model of bionic undulatory fin can uncover the relation between the forces/moments and propulsive wave parameters, geometric parameters as well as swimming velocity. And it has been used to construct the dynamic model of the propulsion and control system and to analyze its motion velocity, energy consumption and propulsion efficiency. To be more important, this undulatory fin dynamic model has been validated by experimental tests in thrust, moments and propulsive velocity of the underwater vehicle.3. In terms of the incorporation between propulsion and control in the bionic underwater vehicle, we present the multi-fin cooperative control mechanism for applying the undulatory fin mode into propulsion and gesture control. To be concrete, this method classifies the robotic control system into two levels: multi-fin cooperative control and motion/gesture control. On the level of multi-fin cooperation control, we propose and design the corresponding control algorithms to generate appropriate thrust in company with moments and to eliminate or decrease disadvantageous influences of the periodic moments, so as to satisfy manipulation requirements at low speed or others. The motion/gesture control system adopts the dual loop architecture to cope with various objectives in motion and gesture control. We select velocity, yawing and pitching as the three basic control channels in view of the fact that the multi-fin propulsor may only actively generate thrust, yawing moment and pitching moment. All the three basic control channels in the inner loop utilize fuzzy adaptive PID controller for non-coupling departure. The mission decomposition module in the outer loop answers for converting or decomposing the non-basic objectives into the basic objectives in velocity, yawing angle and pitching angle according to expert PID strategies. In succession, we propose corresponding forward-feedback compensatory algorithms and rolling correcting algorithms based on the dynamic model of the multi-fin propulsor. It is validated that the cooperative undulatory multi-fin propulsion and control approach is applicable into the motion/gesture control of underwater vehicles through abundant simulation in step responses, anti-disturbance and tracking performance of velocity, yawing, pitching and depth-keeping control systems.