Characterizing and mitigating ice-induced vibration of monopile offshore wind turbines

Abstract

Offshore wind turbines (OWTs) are vulnerable to ice-induced vibrations (IIV) when they are located in ice-prone regions with drifting sea ice. The ice-induced frequency lock-in (FLI) phenomenon will cause excessive vibration and fatigue damage of OWTs. The present study characterizes the ice-induced FLI of OWTs under various ice conditions through coupled analysis and mitigates the significant FLI response using a three-dimensional pendulum tuned mass damper (3D-PTMD). Based on the National Renewable Energy Laboratory (NREL) 5 MW baseline monopile OWT model, a numerical model of the OWT with a 3D-PTMD is established wherein the interaction between the blades and the tower is modeled and soil effect is considered. Aerodynamic loading is computed using the Blade Element Momentum (BEM) method where the Prandtl's tip loss factor and the Glauert correction are considered. A coupled simulation program based on Määttänen–Blenkarn model is developed to simulate ice-structure interactions. Different ice velocities, thicknesses, and attack angles in the Bohai Sea are chosen to study the ice-structure interactions and characterize the FLI. Research results show that the FLI of the monopile OWT occurs when the ice velocity is between 0.01 m/s to 0.06 m/s and the ice thickness is 7 cm, and 0.03 m/s to 0.09 m/s when the ice thickness is 32 cm. When the FLI happens, the 3D-PTMD has significant effectiveness in mitigating the root mean square and peak response of the nacelle/tower and the foundation in fore-aft and side-side directions. The present study enhances the understanding of ice-induced FLI and provides a feasible solution for vibration control of OWTs in ice-prone areas.