The influence of gyroscopic effects on dynamic responses of floating offshore wind turbines in idling and operational conditions

The present paper investigates the significance of gyroscopic effects on responses of floating offshore wind turbines (FOWTs). A 17-degree-of-freedom (DOF) FOWT model is rigorously developed using the Euler-Lagrange approach. Based on rational approximation of the radiation loads, an extended state-space formulation is then established for the coupled mechanical-hydrodynamic-controller system, enabling very efficient time-domain simulations. Different strategies for deriving linear system equations of motion (EOMs) within the Euler-Lagrange framework are evaluated, with the focus of highlighting the correct procedure for capturing the full gyroscopic couplings in linear EOMs. Monte Carlo simulations are performed on three scenarios, i.e. no aerodynamics, idling FOWTs and operational FOWTs. It is observed that gyroscopic couplings significantly influence the tower torsion (and possibly foundation yaw depending on the foundation type) of FOWTs without aerodynamic loads, and the spar-type FOWT is most sensitive to gyroscopic effects among the three concepts considered (although the TLP can be similarly sensitive). The aerodynamic loads are the dominating loads for both idling and operational FOWTs, and the gyroscopic effect becomes less significant although it still plays a more important role in operational FOWTs than idling FOWTs. Excluding the gyroscopic effect leads to non-negligible overestimation of the tower torsion of the operational FOWT. This study unfolds the correct derivation procedure, the mathematical formulas, the physical mechanism and the influence/significance regarding the gyroscopic effects in FOWTs, which also acts as a useful guideline for developing in-house reduced-order FOWT models.