Aeroelastic instability problems have become an increasingly important issue due to the increased use of larger horizontal axis wind turbines. To maintain these large structures in a stable manner, the blade design process should include studies on the dynamic stability of the wind turbine blade. Therefore, fluid-structure interaction analyses of the large-scaled wind turbine blade were performed with a focus on dynamic stability in this study. A finite element method based on the large

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... on beam theory is used for structural analysis considering the geometric nonlinearities. For the stability analysis, a proposed aerodynamic approach based on Greenberg's extension of Theodorsen's strip theory and blade element momentum method were employed in conjunction with a structural model. The present methods proved to be valid for estimations of the aerodynamic responses and blade behavior compared with numerical results obtained in the previous studies. Additionally, torsional stiffness effects on the dynamic stability of the wind turbine blade were investigated. It is demonstrated that the damping is considerably influenced by variations of the torsional stiffness. Also, in normal operating conditions, the destabilizing phenomena were observed to occur with low torsional stiffness. OPEN ACCESS Energies 2013, 6 2243 Keywords: blade element momentum method; dynamic stability; fluid-structure interaction; Greenberg's extension of Theodorsen's strip theory; wind energy The transformation matrix, T represents the functions of the curvilinear axial coordinate x 1 ; and Ψ, β, and θ indicate sweep angle, precone angle and initial pitch angle, respectively. Assuming that the initial curvatures and shearing strains are much smaller than unity in the Green-Lagrangian strain components, the strain-displacement relations are represented the same as those in the literature [24] . If higher-order strain components and initial curvatures are neglected and general warping displacements