| Oscillating-buoy becomes a main kind of wave energy coverter(WEC) which could extract wave energy from its oscillating motion, as its advantages of simpler construction, better adaptability and high efficiency, compared with other kinds of WECs.The higher efficiency of an oscillating-buoy WEC could reduce the production cost of the wave energy utilization. So we should make a comprehensive study on the operating characteristics of oscillating-buoy WECs through theoretical analysis,numerical simulation and physical experiment in order to improve the capture width ratio of the device.Firstly physical tests of a single-buoy converter, a two-buoy converter composed of two coaxial-cylindrical buoys and another two-buoy converter consisted of a rectangular middle buoy and a rectangular surrounding buoy were carried out in order to investigate the effect of the wave climate, external load, geometric arrangement and mooring system on the dynamic responses of buoys and capture width ratio of the device.Based on the linear potential theory and three dimensional diffraction-radiation theory, a mathematical model of oscillating-buoy WECs was given. And numerical simulations of the operating characteristics of a single-buoy converter, a two-buoy converter composed of two coaxial-cylindrical buoys and another two-buoy converter consisted of a rectangular middle buoy and a rectangular surrounding buoy were carried out, respectively, in order to investigate the main influence factors of the hydrodynamics, dynamic response and wave energy capture width ratio of the oscillating-buoy WECs.The numerical results of single-buoy converters showed that the influence of the diameter and draft of a cylindrical buoy, and the length-width ratio of a rectangular buoy were significant. And a numerical comparison between a cylindrical buoy and a rectangular buoy revealed that the peak value of the capture width ratio corresponding to the optimal load damping coefficient of the cylindrical buoy WEC is larger than that of the rectangular one by 19%.In this paper we proposed a two-buoy wave energy converter composed of a heaving semi-submerged-cylindrical buoy, a fixed submerged-cylindrical buoy and a power take-off(PTO) system.Our numerical results revealed that the influence of the fixed submerged-buoy on hydrodynamic properties, dynamic response and capture width ratio can be significant and varies considerably,depending on vertical distance between the heaving semi-submerged-buoy and the fixed submerged-buoy, diameter and mass ratio of the fixed submerged-buoy to the heaving semi-submerged-buoy, height of the fixed submerged-buoy and water depth.A numerical simulation about a two-buoy WEC which consists of a rectangular middle buoy and a rectangular surrounding buoy was firstly made,and the influence of the wave climate, external load, horizontal distance between two buoys and draft of the surrounding buoy on the hydrodynamics and wave energy capture width ratio were analyzed.A numerical comparison between different types of oscillating-buoy WECs was made in order to find a larger capture width ratio of an oscillating-buoy WEC, and the results showed that the two-buoy converters could achieve a higher capture width ratio when the submerged or surrounding buoy was fixed,and the peak capture width ratios of two kinds of two-buoy converters were both larger than that of the single-buoy converter. The two-coaxial buoy converter had a higher capture width ratio for wave climate with lower frequency, and the two-surrouding buoy converter had a higher capture width ratio for larger frequency wave. |
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