Abstract
As wind turbine blades continue to evolve toward longer and more flexible designs, they undergo significant nonlinear damping effects during fatigue testing. This damping inhibits the response amplitude of the blades, thereby placing higher demands on the performance of fatigue loading equipment. To assess fatigue testing loading schemes for large blades, this paper considers both linear and aerodynamic damping, establishes a nonlinear dynamic model of the blade testing system, and analyzes the amplitude-frequency characteristics under nonlinear damping. Based on the principle of functional equivalence, it further constructs mathematical relationships between the blade’s equivalent damping ratio, response amplitude, and exciting amplitude. The results show that the response characteristics under nonlinear damping are influenced by the equivalent damping ratio, response amplitude, and vibration frequency. Experiments on four large blades verify the nonlinear mapping relationship between response and exciting amplitude. The equivalent damping ratio exhibits segmented characteristics, showing a near-linear positive correlation with the blade response at large amplitudes and remaining almost unchanged at small amplitudes. This paper provides a theoretical basis for selecting fatigue loading equipment and designing testing schemes. Additionally, the work offers significant experimental cases and theoretical support for further refining full-scale blade fatigue testing theories.
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