STATIC AND DYNAMIC ANALYSIS OF WIND TURBINE-BLADES USING THE FINITE-ELEMENT METHOD

Analysis of forces and stresses of horizontal axis propellers and turbines has been the subject of increased interest in recent years because of the need to develop adequate analytical tools for the design and evaluation of wind turbine rotors. Most of the structural failures of wind turbines occur in the blade root section. Hence, a three-dimensional analytical model to compute the deflection, stresses and eigenvalues in the rotor blades is proposed using bending triangular plate finite elements. Both membrane and bending stiffness are considered in deriving the element stiffness matrix. The consistent mass matrix is used in generating the overall mass matrix. Lift and drag forces created in steady wind conditions are analysed as normal and tangential forces on the blade sections at certain angles of attack. These forces are applied as boundary loads to the computer program to analyse statically and dynamically rotor blades of symmetrical aerofoil NACA 0015 series. Constant chord, tapered and twisted blades were analysed at rated and survival wind speeds. The validity of the computer program used was verified by applying it to a standard cantilever box beam using the beam theory. The results showed that maximum stresses occurred at the root of the blades for all configurations in the spanwise direction and that a tapered blade, in addition to saving material weight, diminished the stresses obtained. The twisting of the blade leads to an increase in stiffness and a decrease in the stresses.