The Research On Dynamic Responses For Offshore Wind Turbine Structures

Nowadays, the offshore wind power technology is developing rapidly due to its advantages for stable, high-speed and pollution-free wind resources. Plenty of progress have been achieved both technically and practically. Though practical programs for fixed wind turbines have been carried out domestically, the technology is not mature yet, while floating wind power is still in the stage of theoretical research.Wave force is one of the most significant loads to which offshore structures are subjected. It is a considerable factor that affects the design for offshore wind turb ines. Hydrodynamic load has a remarkable effect on dynamic responses and stabilities for offshore wind turbines. The paper investigate s these issues, the main content are presented as below:(1)The model for a 5MW monopile wind turbine built by the Nationa l Renewable Energy Laboratory(NREL) is selected as an example in this study. The wave force is determined using the Morison equation. Two cases are considered in this study, namely, the case that considers the effect of fluid-structure interaction(FSI) and the case in which the effect of FSI is neglected. Kinematic equations and numerical models under the two cases are developed respectively, and the comparison between the two cases is made to investigate the effect of FSI. The results indicate that disti nct deviations affected by the intensity of the wind and wave exists in both wave force and dynamic responses in the two situations.(2)A design formula for setting the limit of metacentric height(GM) of a semi-submersible platform for floating wind turbi nes is proposed according to steady-state heel angles and rolling periods based on stability theory in marine engineering. Then, the most critical heeling axle of the floater is analyzed by theory. Finally, a numerical simulation for a 5WM floating wind tu rbine is performed using the Sesam software to investigate how three main factors, including the distance between pontoons, the radius of pontoons and the height of freeboard, influence the stability of platforms. The results indicate that these factors af fect the stability in different ways, corresponding with various effects on GM, center of gravity and displacement. These results can be used as reference for the design of semi-submersible platforms for floating wind turbines.(3)A novel reinforced concrete floating platform for offshore wind turbines is selected as an example in this study. The finite element model is simulated by Sesam software, and the response amplitude operators(RAOs) of the floating platform are computed to analyse the hydrodynamic characteristic. Finally, impacts on hydrodynamic performance of the floating platform by heave plates, connecting structures and ballast water are investigated respectively. The results indicate that the natural periods of the floating platform locate out of the main wave bandwidth. These factors affect the hydrodynamic characteristic of the floating platform in different ways, and the measures to improve hydrodynamic performance are proposed according to the conclusion.