Abstract Summary
Floating wind turbines (FWT), which enable access to substantial wind resources in deep waters, have been anticipated to contribute significantly to achieving the carbon-neutral target. Popular simulation tools for this relatively new offshore technology adopt the linear potential flow theory borrowed from the offshore oil and gas industry to evaluate the hydrodynamic forces, which are calculated about the equilibrium position of the platform. However, the compliance of the floating platform can potentially lead to large displacements and rotations under combined wind and wave actions. In this case, the validity of the system’s description through its original linearization should be reinvestigated. The present work proposes a new piecewise linearization approach that can capture the nonlinearity by re-linearizing the wave-platform interaction system at instantaneous platform positions (operating points). An open-source boundary element method code, Nemoh, is utilized to calculate the hydrodynamic force for the linearized wave-platform system at each operating point. In addition, the blades-controller-platform coupling effect is investigated in this work by interfacing the wave-platform re-linearization scheme with a wind turbine model developed in Simulink with robust aerodynamics and controller simulation modules. The integrated model can be used to conduct a fast evaluation of the full-system nonlinear dynamics for operating FWTs. The results obtained by this method are compared versus the common practice of linearizing around the equilibrium and comparisons are drawn.
