Fatigue load and life estimation of composite turbine blades under random ocean current

In the present study, the fatigue load and the fatigue life of the composite ocean current turbine (OCT) blade were estimated under random ocean current. Since the OCT blade is submerged into the water that has relatively high fluid density compared to that of air, the conventional design technique for wind turbine blades, i.e. blade element momentum (BEM) theory was modified. The modifications in terms of the section modulus and mass density of the core, buoyancy, and the added mass were applied to a set of BEM codes developed by National Renewable Energy Laboratory (NREL). On the other hand, a statistical approach was implemented to characterize randomly fluctuating ocean current. The representative model for the average velocity as well as for the power spectral density was developed through the statistical analysis, and the time history of the current magnitude was simulated. Using the simulated current history and the fatigue analysis procedure, the fatigue life of the OCT blade was estimated. The estimated current history and the fatigue life were compared with those of collected data, and a good agreement was observed.