Reduced nonlinear model of a spar-mounted floating wind turbine

Abstract

Floating offshore wind turbines (FOWTs) are complex dynamic systems requiring a thorough design for optimal operating performance and stability. Advanced control strategies, like model predictive control, are part of the integrated development of new concepts. This paper presents a simplified and computationally efficient model of the spar-mounted OC3-Hywind FOWT. Applications are, e.g., the real-time integration within the controller or an assessment during conceptual design, possibly within an optimization algorithm. Symbolic equations of motion of a multibody system are available as a set of ordinary differential equations. Aerodynamic forces are computed based on a rotor effective wind speed at hub height using data tables for thrust and torque coefficients. Hydrodynamic impacts on the floating body are modeled in a way that only the wave height serves as the disturbance signal. This estimation is based on potential flow theory and Morison’s formula for slender cylinders. The reduced model code is fully compiled and has a real-time factor of approximately 100. Various simulations of common load cases with a comparison to the certified FAST code have shown to be promising.