Concrete wind turbine towers in Southern Africa

[摘要] ENGLISH ABSTRACT: Exponential growth of the global wind turbine market has led to a significant increase in the capacity of wind turbine generators. Modern turbines require higher support structures as higher wind speeds combined with longer blades are necessary to increase their generating capacity. The standard 80-90 m tower is thus not economically viable anymore. Transportation logistics of large steel towers has led to concrete towers becoming a viable option. There are currently no design codes dealing exclusively with the design of concrete wind turbine towers. The aim of this project is to investigate and highlight important aspects of the design process of a normally reinforced high strength concrete wind turbine tower. The tower was designed using nonlinear finite element modelling as a design tool to accurately design the tower for various loads and load cases. An analytical design method was developed that can be used in the preliminary design stage. Finally, the importance of the soil-structure interaction was investigated through a sensitivity analysis.It was found that the formation of cracks greatly affected the stiffness of the structure and that the reduction in stiffness increased the deflection significantly. It was also found that a structure that has sufficient strength to resist the ULS loads may not necessarily comply with the maximum deflection limit for the SLS. The concrete strength class required was not only determined by the maximum compression stress the concrete would experience, but also by the stiffness required to ensure that the tower frequency is within the turbine's working frequency. The dynamic behaviour of the tower was also affected by the formation of cracks. The fundamental frequency of the tower was reduced by 46% after the SLS loads were applied. It was found that the soil preparation for the foundation plays a vital role in ensuring that the tower frequency is not reduced to a level where it falls outside the turbine working frequency.

[发布机构] Stellenbosch University