A Simulink Model for the Dynamic Analysis of Floating Wind Turbines

The drive to maximize the wind-energy harnessing capabilities of modern societies is gradually leading toward the design of floating wind turbines (FWT). To guide such designs, accurate numerical models that predict the dynamic behavior of the systems are crucial to ensure their structural reliability. This chapter presents a new Simulink implementation of the FWT modeling with a focus on the wave-platform interaction. The hydrostatic and hydrodynamic forces applied to the floating platform are calculated using a numerical and an analytical approach. The numerical approach makes use of the open-source boundary element method (BEM) code, Nemoh. In the analytical approach, which is initially limited to a planar response of the FWT, a matched eigenfunction expansions method is examined to evaluate closed-form solutions of the velocity potential and the resulting force. This second approach offers deeper insights into the dynamic system and potentially higher computational efficiency compared to Nemoh. Both approaches are implemented as Simulink subsystems that are integrated with the remaining system in the time domain. The large variety of libraries in Simulink also enables the detailed modeling of other physics including aerodynamics, structural dynamics, and controls. The aerodynamic loads are applied at different cross-sections along the blade using the unsteady blade/element momentum method. While their flexibility can be accounted for, the blades and tower are modeled as rigid bodies in the present study, and the effect of the mooring lines is taken into account as a resulting stiffness matrix. The industry-standard ROSCO controller is also employed. Validation against the most popular tool OpenFAST is carried out on the 5-MW ITIBarge FWT, and the overall agreement demonstrates the capability of the developed Simulink model to perform accurate dynamic analysis for FWTs.