Frequency-Dependent Aerodynamic Damping and Inertia in Linearized Dynamic Analysis of Floating Wind Turbines

Abstract

In frequency-domain (FD) models of floating wind turbines (FWT), it is common to regard the interaction between nacelle motions and thrust by means of a constant aerodynamic damping coefficient. This approach is effective at higher motions frequencies, but does not consider interactions between nacelle motions and the blade pitch control system. As a result, the motions and loads at frequencies closer to the controller bandwidth may be underpredicted. A remedy for this problem is to include the linearized thrust expression in the FD model, such that the dynamic effects related to control are considered. In this paper, these dynamic effects are related to frequency-dependent damping and inertia terms. Expressions for damping and inertia coefficients are obtained with two different methods, and then included in the FD model. The resulting responses are compared to those obtained with the constant damping coefficient method, and also with coupled time-domain simulations of a semi-submersible 10 MW FWT. The better performance of the FD model with frequency-dependent inertia and damping coefficients encourages the adoption of the linearized thrust approach for representing the interaction between nacelle motions, thrust and control system.