Research On Dynamics Response And Structural Properties Of Floating Wind Turbines Under Wind-Wave Condition In South China Sea

In recent years,a rapid development has taken place in wind energy industry.Compared with onshore wind resources,offshore wind resources are far more stable and abundant,which indicates the main site for wind energy exploitation would move from onshore to offshore gradually in the near future.But most of the potential offshore wind resources are distributed in deep waters where depth are generally over 30 m,the traditional fixed-bottom wind turbines may not be suitable for operation in such deep waters.Thus offshore wind turbines become a preferred design because of its relatively inexpensive cost and wide applicability for operational water depth.Most of offshore wind turbines proposed today are designed for operation in specific sea areas,since sea condition,including wind condition and wave condition,varies from site to site,they may not be suitable for operation in South China Sea.Three different configurations of floating wind turbine are selected for analysis in this thesis.Corresponding operation situations in South China Sea are designed based on the applicable water depth of each configuration.A joint computing method using WAMIT and FAST is applied to analyze the dynamics response of each configuration,and the response amplitude operators(RAOs)of each configuration under different wind conditions or different incident wave angles are compared.Besides,response spectral analysis and maximum motion calculation under different wind-wave conditions are implemented with a JONSWAP spectrum model,which has been modulated to match the wave characteristics found in the South China Sea,as an input.Furthermore,many modified floating wind turbine models with different configuration parameters are built,and comparisons of maximum motion response between those models under design situation in South China Sea are made to analyze how the configuration parameter affects the dynamic response of selected floating wind turbines.Results shows that,none of the three selected floating wind tur bines is sensitive to incident wave angles,and also the increasement of aerodynamic damping decreases the surge and pitch peak RAOs of the whole system while heave motion is not affected.Calculation of maximum motion response for three selected floating wind turbines under given load cases in South China Sea shows that the hydrodynamics stability of OC3-Hywind Spar floating wind turbine is superior to the other two configurations,and also the maximum heave displacement of OC4-DeepCwind semi-submersible floating wind turbine under corresponding survival condition is too large for the original configuration to operate in South China Sea.A research focusing on the impact of different configuration parameters on the dynamics performance of selected floating wind turbine system is also conducted.The result shows that the platform bottom diameter and length of the main column is the key configuration parameters that affects the dynamics performance of OC3-Hywind Spar wind turbine;and for the ITI Energy Barge wind turbine,draft and platform length are the key dynamics response-associated structural parameters;the excessive heave maximum displacement of the DeepCwind floating wind turbine under survival condition can be reduced by altering some structural par ameters such as column draft and thickness of base column.