Sensitivity of the Dynamic Response of Monopile-Supported Offshore Wind Turbines to Structural and Foundation Damping

Abstract

The prediction of ultimate and fatigue demands for the design of offshore wind turbines (OWTs) requires accurate simulation of the dynamic response of OWTs subject to time-varying wind and wave loads. The magnitude of damping in an OWT system significantly influences the dynamic response, however, some sources of damping, such as foundation damping, are not explicitly considered in design guidelines and may increase damping significantly compared to commonly assumed values in design. Experimental and analytical studies have estimated the magnitude of foundation damping to be between 0.17% and 1.5% of critical, and this paper investigates how increased damping within this range affects load maxima and fatigue damage for a hypothetical 5MW OWT subjected to a variety of wind, wave, and operational conditions. The paper shows that increased damping effects the greatest percentage reduction of ultimate moment demands and fatigue damage when the OWT rotor is parked and feathered. In such cases, the aerodynamic damping is relatively low, allowing for additional damping from the foundation to account for a relatively larger proportion of the total system damping. Incorporating foundation damping in design guidelines may lead to more efficient structures, which is a crucial factor in overcoming the high cost barrier associated with offshore wind development.