Developing the Aeroelastic model of a Composite Wind Turbine Blade and Analyzing the Effects of Rotation and Length Increase on Natural Frequencies

The linear aeroelastic equation of motion of a wind turbine blade considering the length increase and rotation terms of the blade is derived. The blade is a composite cantilever beam. The Euler-Bernoulli theory is the fundamental theory in developing the equations. Because of the compatibility of the finite element and BEM, the blade is modeled with the finite element method. Applying Hamiltonian leads to the aeroelastic equations of motion. The finite element matrices are derived by considering linear and Hermitian shape function in axial and transverse deflection, respectively. We consider the linear equation of motion with length increase term. Simulation and analyzing the natural frequency and mode shapes validate the equations of motion. Besides, the effects of the length increase of the blade and rotation of blade on both short and long composite blades are investigated. Analysis of natural frequencies implies that the first and second frequencies of long blade ore affected by length increase and rotation of the blade. However, higher modes are affected by less than one percent.