An efficient rotational sampling method of wind fields for wind turbine blade fatigue analysis

Both the operational and ultimate load conditions should be considered in the structural design and reliability assessment of wind turbine systems. In the operational condition, the fatigue load experienced by wind turbine blades is of great concern in design which highly relies upon the rotor's rotation. Three kinds of methods have been developed to explore the rotational sampling effect of wind speeds on wind turbine blades, which, however, are somewhat inconvenient in practical applications. In view of the recent developments in wind field simulation, a novel rotational sampling method allowing for the analytical expression of fluctuating wind speeds on rotating blades is proposed in the present paper. In contrast to the existing methods, the proposed method circumvents the decomposition of cross power spectrum density (PSD) matrix and the interpolation in spatial and temporal dimensions. In particular, a closed-form expression of the rotational sampling spectrum is provided, thereby the mechanism of transfer of turbulent kinetic energy in frequency domain is quantitatively revealed. For illustrative purposes, fatigue analysis of the blades of a 5-MW offshore wind turbine is carried out, demonstrating the non-negligible influence of the rotational sampling on the fatigue load of blades and the competitive efficiency of the proposed method.