| As an important renewable energy type,wave energy has attracted wide interest due to its wide distribution,abundant reserve and little negative environmental impact.In recent decades,many different devices for wave energy extraction have been developed.Among these devices,the Oscillating Water Column(OWC)device is probably the most potential wave energy extraction technology in coastal areas.However,suffering from the high costs of construction,installation,maintenance and operation,relatively few OWC devices fully achieve the commercial operation.In this paper,a dual cylindrical caisson(DCC)breakwater integrated an annular sector Oscillating Water Column(AS-OWC)device is proposed.The hydrodynamic performance of the proposed integrated device is investigated experimentally and numerically.The physical model tests are carried out in the nonlinear wave flume at the State Key Laboratory of Coastal and Offshore Engineering,Dalian University of Technology.A pressure method is proposed to estimate the air flow rate through the air duct using the dynamic air pressure in the air duct.The dynamic air pressure is calculated using the total air pressure and the environmental pressure,which is directly measured from the pressure sensors installed in the middle and on the sidewall of the air duct.The developed pressure method can remove the influence of uneven water surface in the complicated chamber and it can also describe the asynchronous phenomenon of the water and air motions in the device.The experimental results indicate that the proposed AS-OWC integrated system has a good performance on wave energy capture and the maximum hydrodynamic efficiency of 80.7% is obtained within the test range.Based on the open source OpenFOAM software package,a computational fluid dynamic model for two-phase incompressible flow(air and water)is developed to optimize the underwater geometrical parameters of an onshore OWC device.An exponential fitting formula is proposed to describe the correlation between the optimal relative chamber width and the relative front wall draught,and wavelength is also included in the fitting formula to consider the effect of wave conditions.A 3D numerical model is further developed for predicting the performance of the AS-OWC.The wave energy conversion efficiency and the water-gas movement state inside and outside the chamber are studied under the different water depths and wave periods.The wave load on the structure,the optimization of PTO damping coefficient as well as the proportional relationship between the reflected,conversional and loss wave energy are discussed.Both the experimental and numerical results show that the wave energy conversion efficiency of the OWC device with an annular sector cross-section is larger than that with a rectangular cross-section under the same conditions.Furthermore,the wave energy conversion efficiency of the AS-OWC device can be further improved by optimizing the PTO damping coefficient.Research work is of great significance to promote the commercialization of wave energy and the development of environmentally friendly hydraulic structures in China. |
