Prediction of Tower Loading of Floating Offshore Wind Turbine Systems in the Extreme Wind and Wave Conditions

Abstract

The analytical formulae of wind-induced load, wave-induced load and their combination are proposed for the tower of floating offshore wind turbine systems by quasi-steady analysis. Sway-rocking model (SR model) is employed as the equivalent calculation model. The formulae of wind-induced load are in the same format as those of fixed-foundation wind turbine, but have different values for some critical parameters in resonant standard deviation. For wave-induced load, the standard deviations due to surge and pitch motions are proposed separately and their combination is calculated with complete quadratic combination (CQC) rule. For the total tower loading under wind and wave, the mean value depends on the wind only, and the combination without considering any correlation can predict the standard deviation accurately. The Gaussian peak factor is applicable to both wave-induced load and the total tower loading. All the proposed formulae are verified by full dynamic simulation.