Performance analysis of monopile-supported wind turbines subjected to wind and operation loads

This paper presents an experimental study on the effects of joint wind and operating loads (JWOLs) on the long-term performance of monopole-supported wind turbines (MWTs) standing on soils. In this paper, a novel loading method that can apply ambient excitation without constraints and generate random fluctuating loads around a non-zero mean is proposed to simulate JWOLs. The method was realized using a wind tunnel. A series of wind tunnel tests with different JWOLs were designed and performed on a 1:100 MWT model of the NREL 5 MW wind turbine. The effects of the average load in the fore-to-aft (F–A) direction and the fluctuating loads in the F–A and side-to-side (S–S) directions on the long-term performance of MWTs (including the variations in the natural frequency, damping ratio, and the accumulated deformation) were studied. The test results show that the variation in the natural frequency is marginal (within −2.1% to 3.6%), whereas that in the damping ratio is within −63.9% to 38.4%. The accumulated deformation curve under different conditions can be represented using a power function. The long-term performance problems (the frequency shift and the accumulated deformation) of MWTs observed under simple harmonic loads may be high to an extent compared with those observed under certain JWOLs.