Finite Element Modeling and Modal Testing of a Wind Turbine Lattice Tower Component with Interference Pin Connections

Abstract

Fatigue failures at fastener holes in operating structures are undesirable as it can lead to catastrophic mechanical failures and casualties. Interference pins create interference fits with joined components to reduce stresses around fastener holes and extend the fatigue life of operating structures. In this paper, a novel finite element modeling method is developed for accurate dynamic analysis of a wind turbine lattice tower component with interference pin connections. Installation of interference pins is modeled as a multi-stage process. It causes local changes in stiffness in joined members of the component. The local stiffness changes are accounted for in the finite element model of the component through creation of cylinders to represent interference pins. An experimental setup including a three-dimensional scanning laser vibrometer and a mirror was used to measure out-of-plane and in-plane natural frequencies and mode shapes of the component. Ten out-of-plane modes and one in-plane mode of the component from its the finite element model are compared with their experimental results to validate its accuracy. The maximum percent difference between theoretical and experimental natural frequencies of the component is 3.27% and modal assurance criterion values between its theoretical and experimental mode shapes are all over 91%.