Numerical analysis of a hybrid substructure for 3MW offshore wind turbines due to soil conditions

摘要

The offshore wind energy has gained attention from many countries tofind alternative and reliable energy sources. Therefore, many offshorewind farms are in the planning phase. In order to increase the grossgeneration of wind turbines, the size of a tower and a rotor-nacellebecomes larger. In other words, the substructure for offshore windturbines is strongly influenced by the effect of wave forces as the sizeof substructure increases. In the present study the hybrid substructure,which is composed of a multi-cylinder having different radius near freesurface and a gravity substructure at the bottom of multi-cylinder, issuggested to reduce the wave forces. In addition, since a large offshorewind turbine has a heavy dead load, the reaction forces on thesubstructure become severe, thus very firm foundations should berequired. Therefore, the dynamic pile-soil interaction has to be fullyconsidered. In the present study the ENSOFT Group V7.0 is used tocalculate the stiffness matrices on the pile-soil interaction conditions.Using the stiffness matrices and the loads at TP, which is obtained fromGH-Bladed, the structural analysis of the hybrid substructure is carriedout through ANSYS ASAS. The structural strength and deformation isevaluated to investigate an ultimate structural safety and serviceabilityof hybrid substructure for various soil conditions. The first few naturalfrequencies of substructure are heavily influenced by the wind turbine.Therefore, the modal analysis is carried out through GH-Bladed toinvestigate the resonance between the wind turbine and the hybridsubstructure.