Abstract
Increased contemporary energy needs have led to multiple investments on wind power plants and structural improvements are considered necessary for the construction of taller, more robust and more economical structures. Tubular steel wind turbine towers that are the prevailing structural configuration, demand welding of circular subparts to construct the tower structure. These circumferential welds between tower subparts and between the tower and the connecting flanges are proved to be prone to fatigue failure, since cracks are observed in these areas of already constructed wind towers. The aim of the present work is to enlighten weld design procedures of wind turbine tower welds using damage accumulation methods. For the purposes of the comparative study, two towers of same height differing in shell thickness distribution are taken into account. The towers are compared numerically and analytically following two methods of calculating fatigue loads for structures; the first is an analytical method proposed in design codes and the second is by using artificial loading histories produced by the National Renewable Energy Laboratory software. In both methods, shell thickness is proved to be a decisive factor for the fatigue life of the structure and it is often a challenge to design an economic structure with sufficient fatigue life. From the comparison of the tower’s welds fatigue life, useful outcomes have been found on the precision of the methods compared and the relation of fatigue life and material used for construction.
Highlights
The challenge of constantly constructing taller wind turbine towers imposes the analytical and detailed structural design of such structures
The present study evaluates the effect of shell thickness reduction on the fatigue life calculation of steel tubular wind turbine towers
In both analyses methods and for both structural details, Tower-1 with thicker shell thicknesses appears to have a longer fatigue life compared to Tower-2 indicating that shell thickness is an important factor in the determination of the tower behavior against fatigue loading
Summary
The challenge of constantly constructing taller wind turbine towers imposes the analytical and detailed structural design of such structures. Lavassas et al (2003) after performing the analysis and design of a prototype wind turbine tower concluded that detailed finite element analysis is appropriate for the determination of the ultimate capacity of the structure. In their study it is proved that in unstiffened shell structures initial imperfections affect their post-buckling behavior. Valuable conclusions on their structural response have been derived from the post-collapse analysis of structures like the work of Lee and Bang (2013), which focused on the simulation of structural failure that led to a collapse of a wind turbine tower in Korea. Comments on the finite element simulation of the structures are made and lessons learnt from existing structures are introduced in contemporary structural guidelines
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