Wind and Wave Misalignment Effects on Fatigue Load Assumptions for 5MW Offshore Wind Turbine

Abstract

Growing the oil prices, people concerned to solve the energy depletion problem. Many countries have suggested an alternative way of using the renewable energy. Wind energy promising renewable energy is getting attention as a clean energy does not emit pollutants indefinitely. Especially offshore wind turbines have great advantage of geographical conditions such that wind speed and quality are more favorable than those at onshore. Offshore wind turbines are exposed to the environment of wind, sea wave, current and so on. Typically, wind and sea wave make large portion of fatigue loads of wind turbine. From a economical perspective, wind turbines should be designed to endure various extreme conditions and fatigue during the designed life. The NREL Baseline 5MW model is chosen for the analysis. In this paper, fatigue analysis of meteorological data in the South-Western sea where 2.5GW offshore wind farm plan would be established is executed using the measured wind and wave data in the marine environment. Wind and wave loads are calculated using FAST and Crunch, Fatigue program used by post processor. Additionally, load analysis of each wind speed considering difference of wind and wave direction was performed. Lumping and Exact method was used to figure out misalignment effect of fatigue. First of all, damage equivalent loads of lumping method compared alignment to misalignment of wind and wave direction. The Fx, Mx, Mx1, Mx2, Mx3 damage equivalent loads of misalignment are much bigger than results of alignment. Secondly, choosing biggest damage equivalent load of Exact method results compared with Lumping method results. This comparison is aimed to investigate possibility of the wind and wave misalignment effect on fatigue analysis though Lumping method. As a result, there is a substantial divergence of damage equivalent load. Thus, more research is needed to decrease the number of simulations.