Investigation on the Oscillating Buoy Wave Power Device

An oscillating buoy wave power device (OD) is a device extracting wave power by an oscillating buoy. Being excited by waves, the buoy heaves up and down to convert wave energy into electricity by means of a mechanical or hydraulic device. Compared with an Oscillating Water Column (OWC) wave power device, the OD has the same capture width ratio as the OWC does, but much higher secondary conversion efficiency. Moreover, the chamber of the OWC, which is the most expensive and difficult part to be built, is not necessary for the OD, so it is easier to construct an OD. In this paper, a numerical calculation is conducted for an optimal design of the OD firstly, then a model of the device is built and, a model test is carried out in a wave tank. The results show that the total efficiency of the OD is much higher than that of the OWC and that the OD is a promising wave power device.

Application of the state space model to the system of wave energy conversion Analytical method for wave forces on singleoscillating rectangular buoy

A new analytical method is proposed to analyze the force acting on a rectangular oscillating buoy due to linear waves.In the method a new analytical expression for the diffraction velocity potential is obtained first by use of theeigenfunction expansion method and then the wave excitation force is calculated by use of the known incident wavepotential and the diffraction potential. Compared with the classical analytical method, it can be seen that the presentmethod is simpler for a two-dimensional problem due to the comparable effort needed for the computation ofdiffraction potential and for that of radiated potential. To verify the correctness of the method, a classical example inthe reference is recomputed and the obtained results are in good accordance with those by use of other methods,which shows that the present method is correct.

Hydrodynamic Response and Power Performance of A Heave and Pitch Buoy Wave Energy Converter Under Bimodal Ochi-Hubble Wave Spectrum

In coastal sea areas with the bimodal Ochi-Hubble wave spectrum, such as parts of the China Sea and Indian Ocean,wave energy is the superposition of wind wave and swell. Traditional heaving buoy wave energy converters developed with narrowband wave spectrums suffer from big energy loss in these areas, leading to lower power absorption efficiency and higher generating costs. In contrast, multi-freedom buoy has different resonant frequencies and maximal power capture wave frequencies in different degrees of freedom(DOFs). Therefore, this study proposed using two DOFs to capture the energy of wind wave and swell correspondingly. A heave and pitch buoy model was established by potential flow theory and validated by experimental data. Coupling effect on the motion and power absorption, power capture frequency distribution and power absorption with different linear power takeoff system damping coefficients were analyzed to reveal the hydrodynamic response and the power performance of the two DOFs. The results indicate that by using heave and pitch DOFs, the wave energy components of wind wave and swell were captured in a targeted manner. It demonstrates that the 2-DOF buoy is an effective tool to avoid the energy loss and realize the efficient power absorption in coastal sea areas with bimodal Ochi-Hubble waves.

Wave Energy Study in China: Advancements and Perspectives

The history and current status of research and development of wave energy in the world is briefly introduced. The main problems existing in these studies are pointed out. The description is focused on the current status and the advancements achieved in China. After analysis of the wave energy resources and practical situations in China, it is pointed out that the studies on wave energy should be not only concentrated on the conversion efficiency and costs of wave energy devices, but also focused on the technology of independent operation and stable output of electricity. Finally, the perspectives of application of wave energy in China are discussed.

Hydrodynamic Performance of A Dual-Floater Integrated System Com-bining Hybrid WECs and Floating Breakwaters

The high investment and low return of wave energy converters(WECs)seriously hamper their large-scale commercial application.The integration of WECs and floating breakwaters is conducive to enhance the competitiveness of wave energy conversion.The objective of this paper is to investigate the hydrodynamic performance of a WEC-breakwater integrated system combining an upstream oscillating water column(OWC)and a downstream oscillating buoy(OB)via numerical simulations and physical experiments.A nonlinear numerical wave flume using Star-CCM+software is employed to obtain calculated results,where a tiny transverse gap is set between the flume wall and the block surface to simulate a similar two-dimensional(2D)model.The corresponding physical experiments are also carried out in a practical wave flume to verified the numerical results.The comparison of the isolated and hybrid system shows that the hybrid design leads to the decreased conversion efficiency of each WEC,but improves the transmission performance of the hybrid system.The wave resonance between two devices causes the abrupt reduction of OWC efficiency and a positive correlation exists with the OB efficiency.The total efficiency of the hybrid system is raised by an optimal opening ratio,a shallow OWC draft and a short spacing distance.Except for the OWC draft,other design parameters have weak effect on the wave attenuation of the hybrid system.This paper can help understand hydrodynamics of the hybrid WECs integrated with breakwaters and improve their performances.