Dynamic Response Analysis of a 5-MW Jacket-type Bottom-fixed Offshore Wind Turbine in Korean Nearshore Areas

초록

Global warming is a serious problem worldwide, which is increasing the demand for wind power, one of the renewable energy sources. Studies on offshore wind turbines to convert offshore wind into electrical energy are being actively conducted. In the case of bottom-mounted offshore wind turbines, the foundation plays an important role in the stability of the structure. Among the foundation concepts, the monopile concept is currently dominant, but the jacket foundation is also one of the preferred concepts. In this study, the dynamic response analysis of a National Renewable Energy Laboratory (NREL) 5-MW reference turbine supported by a jacket substructure was performed. The tower and jacket substructure consisted of beam elements. The natural frequencies of the jacket-tower structure were evaluated through modal analysis considering the self-weight of the Rotor-Nacelle-Assembly (RNA). The aerodynamic loads acting on the blades and hub were calculated using the AeroDyn module of OpenFAST developed by NREL. These loads and the weight of the RNA act as external loads on the tower top. The wave forces acting on the jacket substructure was calculated using modified Morison equation. The Newmark-beta method was employed to perform time integration. Stresses acting on the tower base and jacket substructure were calculated for environmental conditions in four Korean nearshore areas to evaluate the stability of the structure.