Finite Element Modelling of CFFT Small-Scale Wind Turbine Towers

Abstract

Wind energy has emerged as a promising and renewable solution to reduce reliance on fossil fuels in remote off-grid locations. Conventional wind turbine towers are made from concrete or steel, which present several significant drawbacks in certain applications. The use of lightweight and corrosion-resistant fibre reinforced polymer (FRP) tubes as permanent structural formwork can mitigate these challenges. Existing literature has highlighted the performance of concrete-filled FRP tubes (CFFTs) through experiments and successful applications in the field. However, only a few cantilever CFFTs have been tested, and their sizes were much smaller than required for wind turbine towers. In consequence, this thesis focuses on relatively large cantilever CFFTs at a scale representative of small wind turbine towers. The finite element (FE) method was adopted to simulate the behaviour of CFFT towers using the commercial software ABAQUS. The first part of this thesis presents the development and validation of CFFT FE models under bending and axial loading conditions, as well as hollow FRP tubes under bending. The models were compared to experimental results reported by Fam (2000) to ensure the selection of appropriate material properties. Good agreements were observed, and the accuracy of the FE modelling approach was proved. Subsequently, a parametric study was conducted to explore the feasibility of CFFTs for wind turbine towers. The analyses of cantilever towers with different geometric properties and reinforcement configurations under concentrated lateral load were performed first. Then, a cantilever CFFT tower under different loading configurations was tested. It is noted that towers subjected to concentrated load had the lowest load capacity and stiffness. Conclusions were made that with or without axial load, lateral load eccentricity does not affect the behaviour of cantilever CFFTs significantly. Meanwhile, the increase in height-to-diameter ratio decreases the load capacity and stiffness of cantilever CFFTs. Finally, the CFFT tower results were compared with concrete and steel tubular models with similar geometry. The results suggest that CFFTs have better overall performance than the other two types of towers. They are also superior with respect to flexibility in installation and their durability.