Study On Motion Behaviors Of New Submerged Floating Platform For Offshore Wind Turbine

With the development of offshore wind power industry,offshore wind power development gradually change from inshore waters to deep sea.At present the foundation of offshore wind turbine based on the main type of single pile foundation,pile group foundation and gravity foundation,the increase of water depth will lead to the rapid increase of the cost of the fixed foundation,so fixed foundation will no longer be applicable.The cost of the floating platform is not limited by the water depth,which is suitable for the development of deep sea wind power.At present,the study of floating platform for offshore wind turbine is still in the exploratory stage,only a few prototype have built in Europe.The study based on the advantages of TLP and semi-submerged floating platform,designed a new submerged floating platform for offshore wind turbine,which is suitable for moderate water depth(50-200m),and the study of kinematic characteristics is based on numerical analysis and model test.Firstly,the 5MW wind turbine published by NREL was used for the design of wind turbine parameters.Based on the advantages of TLP and semi-submerged platform,a new floating platform for offshore wind turbine was designed,which is suitable for moderate water depth and have a small waterplane.The structural dimensions of the foundation structure and the parameters of the mooring system are given.Based on the design parameters,a finite element model is established to analyze the motion characteristics of the new submerged floating platform in frequency.The transfer function curve of the floating foundation and the amplitude-frequency response of heave,surge and pitch are obtained.And the motion characteristics of the floating platform under different wave conditions are analyzed.The main frequency of heave and surge is the natural frequency of the platform itself,which is less affected by the wave frequency.The pitch is affected by surge and the wave frequency,but the main frequency is still the natural frequency.Furthermore,the motion characteristics of the new submerged platform are analyzed in time domain.The heave,surge and pitch time domain curves under the operating condition and the ultimate condition are obtained.It is found that the new submerged platform can maintain good stability under both conditions.The influence of wave condition and water depth on the motion characteristics is further discussed,with the increase of wave height and water depth,the motion amplitude will increase,the influence of water depth is more obvious.Then,the program file of the fourth-order Runge-Kutta method was compiled and the time history response curve of the six-degree-of-freedom coupled motion equation of the floating platform was obtained.The results of software simulation and numerical calculation of surge and pitch are compared and analyzed,and the results are in good agreement with each other.Finally,the 1:80 size test model was made and the model test is carried out.The motion characteristics of the floating platform are studied under steady wind and random wave condition.The results of model test and software simulation are in good agreement with the results of the operating condition and the ultimate condition.The results show that the software simulation method is correct.The new submerged floating platform for offshore wind turbine is designed in this paper,combines the advantages of the existing floating platform,and the type is novel.Based on the study on motion characteristics of the platform,the results show that the hydrodynamic performance is good.This paper provides a new idea for the design and research of floating platform for offshore wind turbine in China.