Evaluating Different Approaches for Modelling Rotor Aero-servo-dynamics
in Frequency-Domain Analysis of Floating Wind Turbines
Abstract
Computationally efficient frequency-domain models can play a very
important role in facilitating conceptual design optimization of
floating wind turbines (FWTs). However, achieving sufficient accuracy in
such models is challenging due to the nonlinear variation of the
aerodynamic loads, particularly the interaction between the floating
platform motions and the controller. Building on previously proposed
approaches from the literature, this work implements and improves upon
three methods to evaluate the influence of rotor dynamics on FWTs
dynamics in frequency domain. The investigated methods rely on: coupled
fixed-nacelle simulations in turbulent wind; decay tests in steady wind;
and linearized analytical expressions of the steady state aerodynamic
loads. The main objective is to assess the suitability of these methods
for future optimization of the floating platform and the mooring system.
The various techniques are compared through a case study of three
semi-submersible FWTs with increasing rotor size. While all approaches
have good accuracy below-rated wind speed, only the decay test approach
provide good estimates of the wind-induced global responses across all
tested conditions.