Keywords: fatigue analysis, welded joint, wind turbine towers, numerical analysis, modelling, finite element.

The wind energy sector has evolved drastically in recent years and the structural optimization of wind turbine towers is considered important for the construction of more robust and economical structures. The most common tower configuration, and the one under investigation, is the tapered steel wind turbine tower, where consequent tower subparts are welded together in the factory.

Welded connections constitute areas of stress concentration and have been proved to be prone to fatigue failure. Welding design and verification towards fatigue loading is often the driving criterion for the whole tower structural design.

The aim of this paper is to numerically investigate the possible weld failures arising from fatigue loading and a comparative study of two different wind turbine towers is conducted. The fatigue life of the two towers is calculated and compared based on the damage accumulation method and more specifically the Palmgren-Miner rule. Unlike similar studies using experimental data, the method introduced in the present study uses artificial wind time-histories produced by National Renewable Energy Laboratory (NREL) software. The loading time histories are produced for different wind mean speeds and the rainflow cycle counting method is used to produce the stress spectra.

At the end of this paper comments are made on the comparison of the two towers with respect to the determination of tower shell thicknesses and on the effect of fatigue loading towards the material amount used for the construction of the towers.

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