The wind energy is observed as an essential and powerful energy resource for the socio-economic development. It is proposed that the small-size wind turbines can demonstrate the innovative solution for the wind energy conversion for low speed regions. An innovative design, control, and monitoring processes require accurate and validated dynamic model of such turbines. In this investigation, the flexible multibody dynamics approach is used to extend the traditional method of dynamic modeling of small-size wind turbines. A systematic approach is developed based on Floating Frame of Reference formulation (FFR) that includes the dynamics of the flexible blades as well as the aerodynamic loads. Beam element is used to model the blade structure with variable twist angle and the corresponding generalized aerodynamic forces are developed. In order to counteract the effect of the geometric stiffening, the coupling terms in the expression of axial strain energy are taken into account. An experimental test-rig equipped with wind generator is used for the FFR model validation. The equipment gives a maximum discharge flow of 10 [m/s] in a 500 [mm] diameter duct. The dynamic effect of the twist angle of 30 [cm] diameter of rotor blades is studied based on the measured rotor speed of the wind turbine. High sensitivity multi-axis accelerometers are used to measure the induced vibration and the data points are collected via data acquisition card of 16 bit resolution. The comparison of experimental results and numerical solution shows a very good agreement and consequently the wind turbine model obtained is suitable for stress analysis, structural and control design. It is concluded that the FFR formulation is best suited for large rotation and small deformation problems, which coincide with the operational conditions of small-size wind energy systems.

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