Classification of Ice-Induced Vibration Regimes of Offshore Wind Turbines

Abstract Ice-induced vibrations of offshore wind turbines on monopile foundations were investigated experimentally at the Aalto Ice Tank. A real-time hybrid test setup was developed allowing to accurately simulate the motion of a wind turbine in interaction with ice, incorporating the multi-modal aspects of the interaction and the effect of simultaneous ice and wind loading. Different vibration patterns were observed where some could be described based on the common terminology of intermittent crushing or continuous brittle crushing. However, not all resulting vibrations could be described accordingly. A combination of several global bending modes interacting with the ice resulted in high global ice loads and structural response. Such response is likely typical for an offshore wind turbine, owing to the dynamic characteristics of the structure. The type of interaction observed during the tests would be most critical for design as the largest bending moments in critical cross-sections of the foundations occur for this regime. A classification of ice-induced vibrations is proposed which encompasses the experimental observations for offshore wind turbines on the basis of the periodicity in the structural response at the ice action point.