Short-term wind process is normally assumed to be a Gaussian distribution, such as TurbSim, the widely used 3D wind field tool. Nowadays, newest researches indicate that non-Gaussian wind model is believed to be more accurate according to the field observation data. A new numerical method is proposed to generate non-Gaussian wind filed using translation process theory and spectral representation method. This study presents a comprehensive investigation on power production and blades fatigue damage of floating offshore wind turbines (FOWTs) to the non-Gaussian wind field. The comparisons of Gaussian and non-Gaussian simulation results indicate that the non-Gaussian wind fields will cost obviously worse power performance and severe fatigue damage of FOWTs.
Floating offshore wind turbines (FOWTs), which are deployed in the nature ocean environment, are working under huge number of cyclic external loads. A typical wind turbine, during its 20 years life time, may experience more than 108 cycles loads with an approximately 30 rpm rotation speed and 4000 hours operation time per year (Manwell, et al, 2010). Capital expenditures for offshore wind developments are typically one and a half to two times more than for onshore developments (Watson, et al., 2005), and maintenance costs are likely to be 5–10 times higher than onshore (Van Bussel, & Zaaijer, 2001, March). Accurate estimation of fatigue damage is critical important to offshore wind industry.
Fatigue damage of FOWTs is the process in which an accumulation of damages is caused by a repeating environmental load of variable magnitude applied on their structures. Once sufficient damage is accumulated, fatigue fracture will initiate and propagate through the plasticized regions. Fatigue damage calculations and fatigue life predictions of offshore wind turbines are quite complicated.
Fatigue life of a medium scale horizontal axis wind turbine system was estimated by using the well-known S–N damage equation with load spectrum confirmed with at least 20-30 years’ operating life (Kong, et al, 2006). Reliability-based calibration of a design code for wind-turbine rotor blades is developed considering the fatigue failure in flapwise bending (Ronold, et al, 2001). Hu use 10-min mean wind speed and 10-min turbulence intensity based on long-term wind speed distribution to simulate the random wind field and analyze the fatigue reliability of a composite wind turbine blades considering wind load uncertainty (Hu, et al, 2012). A stochastic approach is employed to develop a computer code in order to simulate wind flow with randomness in its nature on the blade and subsequently each load case is weighted by its rate of occurrence using a Weibull wind speed distribution (Shokrieh and Rafiee, 2006).
