This study aims to search the optimal system structure for a specific type of oscillatory wave-energy acquisition system, which owns the highest efficiency in acquiring the energy from sea wave. The system is mainly consisted of a float, a generator and several oscillators that are connected to the float or to each other by the elastic springs. In addition, all the components are capsulated in the float. For the purpose of comparison, when aided with an active control, the acquiring efficiency of the system with a near optimal structure is analyzed. Under the assumption of random sea wave, three steps are adopted to investigate the optimal system structure. First, the mathematical model of the capsulated float that can acquire the maxima power from sea wave is derived by the spectrum analysis. They offer the messages that what the dynamic properties of an optimal structure should be in order to acquire the maxima power. Second, the dynamic properties of the general system are analyzed. It is to examine the effect of increasing system¡¦s degrees of freedom in offering the flexibility of varying system dynamics to match the desired ones. The limitation of increasing the degrees of freedom is especially examined. Then, the maxima attainable powers for the systems with different degrees of freedom are simulated by the genetic algorithm. It is to support the inference made from the analysis about the effect of increasing the system¡¦s degrees of freedom. Finally, a preliminary examination of the effect of active control in power acquisition is done. The study indicates that an oscillatory system structure with two degrees of freedom is a near optimal structure for energy acquisition. An increase of system¡¦s degree of freedom shows little effect in improving system¡¦s dynamic characteristics in the main frequency range of sea wave. The proposed active control scheme is shown to be effective in improving the system¡¦s dynamic characteristics to enhance the energy acquisition from sea wave. However, the extra-energy consumed in the control action makes the increase of net energy acquisition negligible.

The purpose of this thesis is to develop a novel design of the oscillatory type of wave-energy acquisition system. It is aimed to increase the efficiency of wave-power acquisition from random sea. The main feature of the new system structure is its flexibility to adjust the system dynamics to satisfy two optimal criteria. The effects of various system parameters on the system dynamics and acquired power were analyzed. To find the set of system parameters to acquire the highest power, an optimization searching method was adopted. Finally, a regression model was established to help the user to calculate the optimal system parameters under various application conditions. The study first indicated that to acquire high power from sea wave the dynamic characteristics of the system should satisfy two criteria. However, the study also revealed that the dynamic properties of a traditional acquisition system are difficult to fulfill the two criteria in a wide frequency band. Accordingly, a new system structure was proposed. It is composed of a traditional acquisition system and a vibrating platform. The platform is linked to the acquisition system through a spring. Because of the coupling effect, the dynamic characteristics of the acquisition system are altered. The effects of varying different system parameters on the locations of pole or zero of the transfer function of acquisition system were examined. It was shown that with a proper choice of system parameters, the frequency bandwidth satisfying or close to the two criteria may be increased. The study indicated that acquired power of the proposed system is higher than the traditional one by 34%.

This study aims to develop an oscillatory wave-energy acquisition system with adjustable system characteristics. The system is designed to efficiently acquire energy from the sea waves with a wide frequency band. Based on the past studies, the oscillatory wave-energy acquisition system, designed previously, can only acquire energy from the sea waves with a narrow frequency band. Such a limit causes the system to have a low efficiency in acquiring power if the wave has a large frequency band. The main goal of this novel design to allow the system adjusting its system characteristics, based on the dynamic characteristics of sea wave, to attain the optimal power acquisition. In the study, different types of oscillatory systems are first examined whether they are effective to transform their dynamic characteristics when the system parameters are varied. The effectiveness of such transformation is evaluated through an optimization procedure. This procedure is to evaluate whether the frequency response of system can acquire the highest power from a given property of sea wave. Through a detailed analysis, the system structure of a three degree-of-freedom oscillatory wave-energy system is chosen for current purpose. A careful study about the effectiveness of dynamic transformation, via the adjustment of different system parameters, is then studied. The study shows that the selected system with adjustable capability can effectively acquire energy from a sea wave with large frequency band. The acquired efficiency can increase up to 70% compared to the earlier system.