A Four-Rigid-Body Element Model and Computer Simulation for Flexible Components of Wind Turbines

In this paper, a four-rigid-body element model is presented for description of flexible components of a horizontal axis wind turbine (HAWT). The element consists of four rigid bodies arranged in a chain structure fashion. The bodies of each element are linked by two universal joints at two ends, and one cylindrical joint at the middle. Thus each element has six degrees of freedom. They are four degrees of freedom for bending, one degree of freedom for torsion, and one degree of freedom for axial stretching. For each degree of freedom, a spring is used to describe the stiffness of the component. Stiffness of each spring is obtained by using potential energy equivalence between a Timoshenko beam and these springs. With these considerations, flexible components of a HAWT such as blades and tower may then be represented by connecting several such elements together. Based on four-rigid-body element model, the tower and blades of a HAWT are constructed. Their equations of motion are then derived via Kane’s dynamical method. Commercial computational multibody dynamic analysis software Autolev has been used for motion simulation of tower and blades under given initial conditions. Simulation results associated with the tower indicate that four-rigid-body element model is suitable for analysis of dynamic loads, modal, and vibration of wind turbines with respect to fixed and moving references at high computational efficiency and low simulation costs. The approach is also a good candidate for simulating dynamical behaviors of wind turbines and preventing their fatigue failures in time domain.