Dynamic Response And Overall Strength Analysis Of Semi Submersible Floating Foundation

As a clean energy,wind energy has been paid more and more attention by all countries.Compared with the land,the offshore wind energy resources are more considerable.However,with the increase of offshore wind farms,there are less and less offshore exploitable areas.Therefore,it is an inevitable trend to develop the offshore wind energy resources.Compared with offshore,far-reaching sea has more abundant wind energy resources,but the traditional fixed wind turbine foundation is not suitable for deep sea,so the majority of scholars focus on the research direction of floating foundation.The semi submersible floating foundation is an excellent carrier of deep-sea floating fan because of its small draught,convenient transportation and installation.The 12 th Five Year Plan of national energy science and Technology issued by China National Energy Administration and the 12 th Five Year special plan of wind power science and Technology issued by the Ministry of science and technology clearly put forward the development direction of large-scale single unit capacity of wind turbine.First of all,it is necessary to break through the technical difficulties of 10 MW offshore wind turbine.However,most of the semi submersible floating foundations are mainly aimed at 5MW wind turbines.Therefore,it is of great significance for the further development of offshore wind power industry to study the semi submersible floating foundation with 10 MW wind turbines,analyze its hydrodynamic performance and overall strength,and evaluate its reliability.The main contents of this thesis include the following aspects:(1)According to the existing structural forms of semi submersible floating foundation,a four pontoon semi submersible floating foundation is established.The model is built by using Aqwa software.Then,the frequency domain calculation is carried out based on the three-dimensional potential flow theory to analyze its hydrodynamic performance.The additional mass coefficient,additional damping coefficient and first-order wave force of the four pontoon semi submersible floating foundation in frequency domain are obtained At the same time,the influence of different incident angles on the amplitude response function is analyzed.The results show that the four buoy semi submersible floating foundation has good hydrodynamic performance,which can meet the requirements of the code.It is found that the wave incidence angle has a great influence on the amplitude response function of the four buoy semi submersible floating foundation at low frequency,and has little influence at high frequency,while the water depth has little influence on the amplitude response function.(2)The common mooring modes and mooring line materials of ships and offshore engineering structures are introduced.Two mooring modes are designed.The time domain analysis method is used to analyze the motion response and mooring line tension under rated conditions.It is found that compared with the tensioned mooring system,the catenary mooring system has smaller motion response amplitude of the floating foundation,and the mooring line tension is also consistent Therefore,the catenary mooring system is selected.Then,the motion response and mooring line tension of the floating foundation under rated condition,stall condition and limit condition are calculated respectively.The results show that the motion response and mooring line tension of the floating foundation meet the requirements of the code.(3)The design wave parameters are determined by long-term prediction method,and then the total strength of floating foundation under the limit environment is analyzed.The results show that the overall strength of the four buoy semi submersible foundation meets the requirements of the specification.