Structural analysis of a gravity substructure for 5MW offshore wind turbines

The offshore wind power generation especially has gained attention from many countries because of its huge amount of energy and infinite growth potential of application of its energy. The substructure for offshore wind turbines is strongly influenced by the effect of wave forces since the size of a tower and a rotor-nacelle becomes larger to increase the gross generation of wind turbines. Therefore, it is very important to accurately calculate the wave force acting on substructures. In the present study Eigen-function expansion method with using three-dimensional linear potential theory is used to evaluate the wave forces. The comparison between wave forces obtained from Morison equation and wave forces obtained from this study is made to compare the diffraction theory with Morison equation in case of the small substructure compared to the wave length. The wave run-up acting on the substructure is also presented. Using the wave forces obtained from this study, the structural analysis of the gravity substructure is carried out through ANSYS mechanical. The structural behaviors of the strength and deformation are evaluated to investigate an ultimate structural safety and serviceability of gravity substructure. Moreover, the modal analysis is carried out to investigate the resonance between the wind turbine and the gravity substructure. It is found that the suggested gravity substructure can be an effective substructure for 5MW offshore wind turbines.