Examination of Wind Turbine Blade Dynamics Considering Large Deformation and Including All Aeroelastic Load Couplings

Many researchers have studied the structural dynamics behavior of the blade of the horizontal axis wind turbine using different approximate theories where they considered some assumptions that other researchers ignored. In a previous study, the authors considered all the extensional, torsional and flexural loadings acting on the blade with their couplings, variable airfoil cross sections with warping effects, shear deflection, rotary inertia and with or without blade’s pretwist. That previous study was performed for the linear small displacement case. In the present study, the new contribution is considering all the inclusions of the previous study but for the nonlinear large deformation case instead of the small deformation case. To the best knowledge of the authors the simultaneous inclusion of all these factors has not been done so far. The external work that acts on the blade, the total strain energy and total kinetic energy for all the different load couplings were defined (all the important strain higher order terms are kept since large deformation is considered) and used to obtain the Lagrange equations of motion. Then the load vector R, mass and linear and nonlinear stiffness matrices were deduced from the derived Lagrange equations of motion to build the nonlinear dynamic equations of motion that was solved for the three unknown displacements in the directions of x, y and z axes and the three unknown rotations about the x, y and z axes at the required stations along the length of the given blade using the Newmark implicit iteration scheme for a 14m long pretwisted blade that has a linearly decreasing NACA4415 airfoil cross section from hub to tip.