Coupled rigid-flexible dynamics modeling and validations of floating offshore wind turbine

Abstract

Floating offshore wind turbine (FOWT) is a complex dynamical system, and reasonable dynamic model is significant to the structural response analysis and reliability evaluation of FOWTs. In this paper, a coupled rigid-flexible modeling method is proposed to predict the dynamic response of spar-type FOWTs and validated by experimental results. The dynamic modeling framework of the method is firstly presented, including the multi-rigid-body (MRB) module and the flexible tower module. The integrated kinematics formulation of MRB module considering the servo control mechanism is derived based on the quasi-coordinates Lagrange's equation. The equation of motion of the flexible tower is established by synthesizing the finite element method (FEM) and Kane's approach. Next, the external loads modules including gravity effects, hydrostatic and hydrodynamic loads, aerodynamic and mooring loads are addressed and incorporated into the equations of motion of the system. The proposed method is then validated against a scaled experiment and full-scale numerical results of FAST, and the aerodynamic performance, the hydrodynamic performance, the MRB module, the flexible analysis module, the mooring system and the servo control mechanism are systematically valuated. The results indicate that the proposed method has a satisfactory ability to predict the dynamic responses of FOWTs under different conditions.