HAWC2 Interfacing Framework

Floating Offshore Wind Turbines (FOWTs) are inherently interdisciplinary systems that are excited by a multitude of non-linear external disturbances. Figure 1 provides an overview of the main sub-systems that comprise a FOWT and the environment in which they operate. The current generation of wind turbines has rotor diameters exceeding 240 m and rated powers of at least 15 megawatts. The large rotor-swept areas of such turbines cause their structures to experience vastly different aerodynamic conditions and highly variable loadings depending on the rotor azimuthal positions of the blades. At the same time, floating structures are exposed to linear and non-linear wave excitation that potentially cause resonance. The aerodynamic and hydrodynamic forces cause the floating substructure to move within its rigid-body degrees of freedom (DOFs), most prominently in surging (movement forwards and backwards) and pitching (tilting forwards and backwards) motions. FOWTs are therefore prone to negative aerodynamic damping, whereby the magnitude of oscillations increases rather than decreases if the controller of a FOWT is not co-designed together with other sub-components such as rotor aero-elastic design, tower design, floater design, etc. The continuous motion of the platform adds to the loadings that are experienced by a FOWT, compared to their fixed-bottom or onshore counterparts (e.g. on the intersection between the floating sub-structure and the tower).