This paper presents a 4-rigidbody segment model to describe a generic flexible blade of a horizontal axis wind turbine (HAWT). The element is made up of four rigid bodies in a chain structure fashion. The bodies of each element are connected by two universal joints at two ends, and one cylindrical joint in the middle. So each element possesses six degrees of freedom, including four degrees of freedom for bending, one degree of freedom for axial stretching, and one degree of freedom for torsion. A spring is applied for each degree of freedom to describe the stiffness of the component. Through potential energy equivalence between a Timoshenko beam and these springs, the stiffness of each spring is calculated. A blade can then be simplified to several such elements connecting together.

With the 4-rigidbody segment model, blades of a HAWT are built up. Their equations of motion are then derived through Kane’s equations. The commercial computational multibody dynamic analysis software Autolev is applied for motion and vibration simulation of blades under given initial conditions. Simulation results indicate that the 4-rigidbody segment model is appropriate to analyze dynamic loads, modal, and vibration of HAWT blades for fixed and moving references at high computational efficiency and low simulation costs. The method can also be served as a good solution to simulate dynamical behaviors of wind turbines and avoid their fatigue failures in time domain.

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