The Concept Design And Performance Analysis Of A New Type Floating Hybrid Wind-wave System

With the running out of traditional fossil energy and accompanying problems of environmental pollution, people have been paying great attention to exploit renewable energy in the ocean, such as wind, wave, thermal energy and so on. Taking advantage over a single wind or wave energy device, the floating hybrid energy system not only improves power generation efficiency in the vast sea area, but also reduces manufacturing cost by sharing the same fundamental structures. Thus, it is of great economic and environmental significances to propose a reasonable and efficient combined system.By the support of the national Natural Science Foundation of China, this paper presents a new concept of hybrid wind-wave energy system (H2W) based on the existed floating wind turbines (FWTs) and wave energy coverters (WECs). Compared with the only semi-submersible type FWT without wave energy bouy, the numerical simulation and model test on hydrodynamic performance and power output are carried out for the proposed concept.The main research including the following several aspects:1. Based on the existing concepts of floating wind turbines, wave energy converters, a floating hybrid wind-wave energy system including structural style and main dimension is designed considering sea characteristics around China. The mooring system, the wave energy take-off system and the combination between the floaters and the platform are also designed.Based on the potential theory, the numerical simulation in frequency domain is performed by the hydrodynamic analysis software named Sesam and the hydrodynamic parameters are achieved, such as the added mass,damping and the response amplitude operators.2. A suitable stability calculation method is used for the specific combined concept and the stability check is performed on the floating wind turbine system and the hybrid system respectively. The results reveal that the design can meet the stability requirements of DNV.Also, a conclusion that the wave floaters can improve the stability performance of the whole system can be drawn by comparing the two results above.3. Models on a scale of 1:40 are made and the scale tests including the free attenuation test, regular wave test and irregular wave test are performed for both FWT and H2W.Through the corresponding processing of the experimental statistics, the natural period,motion RAOs and short term forecast of the motion time series both in operational and extreme conditions can be obtained, which have been compared with the results of the numerical simulation.4. Based on the numerical simulation and model test of the motion of the wave energy bouy, the average output power performance of the PTO system is estimated. The result shows that the maximum output power of a single WEC is to be about 200kW. What's more,the influences of wave period and PTO damping coefficient are discussed in this paper, as well as the relationship between the power output and the relative motion between the wave floater and the wind turbine platform.