Application of the FAST2 Code to Prediction of Fatigue Loads for Two-Bladed Teetering Hub Wind Turbines

Designing wind turbines to be fatigue resistant and to have long lifetimes at minimal cost is a major goal of the federal wind program and the wind industry. To achieve this goal, we must be able to rapidly predict the fatigue spectra of wind turbines operating under extreme conditions. The structural dynamics codes used for such calculations must be able to adequately represent the machine witha minimal set of degrees of freedom and yet be able to model those characteristics of the machine that have the most influence on fatigue loads and response. In this report, we demonstrate the application of the FAST (Fatigue, Aerodynamics, Structure, and Turbulence) code, developed by Oregon State University under subcontract to the National Renewable Energy Laboratory (NREL), in predictingmachine fatigue loads. In particular, we focus attention on validation of the two-bladed teetering hub version of this code, called FAST2. We compare predicted blade loads and machine response from the FAST2 code with actual test data. These comparisons provide at least a partial validation of the code for two-bladed teetering hub wind turbines. We input various types of three-dimensional windturbulence to the code, representing turbulence associated with smooth, homogenous terrain as well as within a large, multirow wind park. We show the sensitivity of predicted loads and response to these various inflow cases. We also examine the sensitivity of these predictions to certain key turbine design parameters. Finally, we outline future case studies and code refinement steps.