Abstract

In this study, we demonstrate the ability of adjustable tuned mass dampers (TMDs) to reduce the platform motion of floating offshore wind turbines (FOWTs). The TMDs are located in the hull and provide control authority by varying the amount of water ballast and compressed air in a reservoir over time. The optimal TMD settings depend on the wind and wave conditions of the FOWT. We present an open-loop control scheme that changes the TMD natural frequency based on sea state and a simple method for estimating the peak wave period and significant wave height. The performance of this open-loop control is compared to ideal control of the TMDs (set knowing the exact sea state), a TMD with a constant natural frequency targeting the design load case with the greatest platform motion, and a baseline set of simulations of the platform without TMDs. The constant natural frequency case performs nearly as effectively as the actively controlled case, suggesting that the TMDs can be simply designed for extreme load conditions and provide consistent control over a range of environments; however, the methods used to find the optimal TMD parameters and estimate sea state statistics could be used in other aspects of FOWT control and design.

Introduction

This study examines the effect of tuned mass dampers (TMDs) on the performance of floating offshore wind turbines (FOWTs) using aeroelastic simulations. In an effort to improve system dynamics and structural loading on the tower and substructure, several control schemes for improving FOWT performance are presented. The control schemes use wave information to estimate sea state statistics that determine the natural frequency of the TMDs.

FOWTs can use the vast offshore wind resource located in water depths of more than 60 m (Musial et al., 2019). A challenge in the development of FOWTs has been the mitigation of wind- and wave-induced vibrations and responses on the turbine platforms. Traditionally, blade pitch control is used to regulate both the platform motion and generator power of the turbine. Because floating platforms can induce rotor motion, a non-minimum phase control problem prevents both the generator power and platform pitch motion from being adequately controlled (van der Veen et al., 2012); however, by using an additional actuator, better control solutions can be realized.

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