Study On Micro Scale Wave Energy Absorption Mechnism And Conversion System Based On Buoy’s Rolling Motion

As is known to us, wave energy is one of the most significant renewable energy resources. And it is becoming more and more important to be developed and exploited in the days of energy shortage. Generally speaking, wave energy utilization can be classified into two sorts, the large scale utilization and the micro scale utilization. The former one is mainly to satisfy the need of resident lives, and the developments of according techniques are gradually matured. The latter one is specially to power some small or mini ocean mobile vehicles, such as small navigation buoys, UUVs, USVs and some monitoring buoys. Comparably, the techniques and the devices are less concentrated, and fewer efforts are put on the issue. The application of wave energy for these vehicles can improve the endurance and the working ability.To solve the power supply for small ocean vehicles, the dissertation has proposed a novel concept of micro wave energy conversion(Mi WEC) based on buoy rolling motion. In the WEC, the buoy’s rolling motion is utilized as the basic type to capture the wave energy, and a novel power take-off(PTO) system is designed to convert it into electrical energy. Concerning about the micro wave energy absorption mechanism and conversion system, the main contributions and innovations are concluded as follows:1. The power supply techniques for small ocean vehicles are summarized in a comprehensive way, and a concept of Mi WEC is concluded and proposed. Combining the applications and the relevant research on the WEC, techniques for power supplies, wave energy absorption and conversion are represented in details in the thesis. It is concluded that the micro wave energy can be absorbed, converted and restored, in order to power these vehicles.2. The practicality of micro wave energy absorption is analyzed, and a micro wave energy absorption mechanism based on buoy’s rolling motion is thus concluded. The characteristics of wave motion and energy distribution are researched, and Linear Wave Theory is utilized to depict regular waves and irregular waves. Through the comparison between rolling and heaving motion of buoys, the rolling motion is selected to be the type to capture wave energy. On the basis of Momentum Theorem, the mathematical model of buoy rolling model in waves is then derived, according to the Euler equation.3. A rolling Mi WEC system with a single buoy is simplified and obtained, and the key factors on micro wave energy absorption(Mi WEA) are thus deeply analyzed. The dynamic model and energy model of the Mi WEC system is established and solved by the analytical method, considering the nonlinearity in the model. The rolling buoy’s natural frequency and the influencing factors are emphasized. The wave energy absorption of the system in regular wave and irregular wave are analyzed through numerical method, and these factors are discussed. The results show that the MWEC system maximizes the power absorption by the buoy’s synchronism in regular wave; and increasing the rolling natural frequency can promote the absorption in irregular waves.4. A two-body Mi WEC system is proposed which utilizes the relative rolling motion between two buoys. The working mechanism is researched, and the effects by the reference buoy which is positioned beneath water are specially analyzed. The kinetic characteristics of the reference buoy and the influencing factors are analyzed, in order to control the rolling amplitudes. The two body system mathematical model is established and solved, and effects by the factors from the reference buoys are obtained. A general guideline for designing a two-body WEC system is then concluded, and examples are given. The results show that the reference buoy underwater has complicated effects on the power absorption due to the phase difference between the buoys, and an optimized way is to control the reference buoy’s rolling amplitude, to avoid the adverse effect and gain more stable energy absorption.5. A Mi WEC system based on inner inertia pendulum(IIP) system and its working mechanism are researched, and the effects on power absorption by IIP system design are specially analyzed. Dynamic characteristics of the single-DOF and the two-DOF inertial pendulum systems are analyzed, to find out its response when there is excitation. The model of a single-DOF WEC system is established, it is then solved through numerical simulation, and the influencing factors of the pendulum are obtained and analyzed. A guideline for designing an IIP WEC system is then concluded, and examples are given. The results exhibit that the length in IIP has an effect on the angular frequency, and well-chosen length will enable the reference more stability; the pendulum weight will make the MWEC have more PTO systems, which can maximize the power absorption.6. An energy conversion system(ECS) for Mi WEC is researched, and a PTO system is proposed and designed. The PTO system is an elastic energy storage device(EESD), which utilizes the mechanical flat spiral spring. A clockwise ECS system and its working principle are discussed, and the key parts of spiral spring and the controlling mechanism are designed and analyzed. The mechanical and the finite element models of the spiral spring are established, and the static and modal analysis are carried on. The deformation, stress distribution and natural frequency are derived. Then, the prototype of clockwise ECS is designed and manufactured. The electricity generations in different working conditions are measured through experiments, and the time-averaged powers are estimated. The test results show that the time-averaged power measured from the ECS without power matching is related to the rolling periods, it gains more with a smaller period. And the power matching part is necessary to ECS, according to different rolling condition.