A Study On Self-Powered System Of Robotic Fish Based On Wave Energy Harvesting

With the rapid development of human society, marine resources have been exploited frequently. Due to the limitations of human body, it is impossible for human to accomplish the underwater work. As a result, people turn to develop a variety of underwater robots to carry out underwater works. However, the traditional propulsive methods greatly limit the propulsive performance, efficiency and maneuvering of underwater robots. People are seeking for novel propulsive type for underwater robots. Fish possesses the excellent swimming performance of high efficiency which can be up to80%, and it also performs high maneuverability after millions of years evolution in the nature. Therefore it is very important to develop biomimetic robotic fish following the swimming propulsion mode of the real fish.It is hard to obtain energy supply for the underwater robots since they tend to work in the marine and other outdoor environments. So the energy problem has become a vital factor which limits the development of the underwater robot. Fortunately, oceans contain inexhaustible wave energy. So it would be important to design a novel structure to capture the wave energy to solve the energy problem.This thesis develops a multi-joint biomimetic robot fish based on Carangidae fish and solve the energy problem by utilizing the fish joints to obtain the wave energy. The main research contents and contributions of this thesis are listed as follows:(1)The structure design of the robot fish energy self-sufficient system. Firstly, the structure and propulsive mode is analyzed in detail, it is found out that the Carangidae can be approximated seen as a multi-joints system, and the fish relies on multi-joint system to realize the fluctuations. Based on the results, we first design a multiple rotary joints robot fish to improve propulsive efficiency, meanwhile, the joints is designed for dual purpose for which can drive the fish and can capture the wave energy to solve the energy problem. Then we raise the ideas of the overall structural design of the dual-use multi-joint robot fish and the basic design principle. Moreover, the detail manufacture of the robot fish is provided. And at last, we present a prototype of the multi-joint robot fish.(2) The theoretical research of the robot fish energy self-sufficient system. The slight wave function and the wave velocity potential equation are firstly solved based on the potential flow theory with slight wave assumption. We study the velocity and trajectory of water particle in the fluid field and obtain the pressure of any point of the field and the energy of waves. Then we build the dynamic function of the floating body based on its stress and moment. At last, by combining the floating body dynamic equation with the electromechanical equations of generator, we establish the mathematical model for two floating bodies.(3)The numerical simulation of the self-powered system of the robotic fish. Based on the above mathematical model for two floating bodies, we analyze the robot fish self-powered system combining the finite element method with the classical multi-body system dynamics simulation software ADMAS, and analyze the robot fish self-sufficient system. We simulate several situations including:the rotation moment of the floating body by disturbance force in still water, the linear motion of the floating body free falling into the water, and the composite motions of floating body in the waves. We analyze the computation results and verify them with the experiments results. At last, we research the effect of a variety of kinematic and structural parameters including the wave frequency, wave amplitude, the fish unit length and so on and detailed study their influence on the energy obtain.(4) The experiment study of the robotic fish self-powered system. We firstly compare and analyze the existed wave making systems and calculate the system based on the potential flow theory. Based on that, we build a push plate wave experiment platform. Then we design and manufacture a prototype of robotic fish joints equipped with various sensors and a signal acquisition system. Based on the experiment platform and system, we first conduct experiment on the motors to drive the joint to confirm that it can meet the torque and speed requirements. And then, we obtain the test joint image sequence in the waves with a high-speed camera. After that, experiments on the test joints for wave energy capturing are conducted. The charging current and charging power are detailed analyzed. And the effect of the wave parameters and structure parameters such as wave height, wave frequency, the floating body cell length, floating body cell width, joint transmission ratio, weight block location are studied.