Finite element modelling of tubular bolted connection of a lattice wind tower for fatigue assessment

Abstract

One of the biggest challenges in front of the growing wind energy industry is to build higher towers for wind energy converters. In order to deal with such a problem a new hybrid tower, comprising a steel lattice lower part and a steel tubular upper part solution was proposed. The solution is targeted at tall onshore applications which are more effective in energy generation in situations where wind shear profile is clearly benefiting higher turbines, for example near forests. As part of this project, this thesis is focused on the fatigue assessment of tubular bolted connection of lattice tower. In first chapter, commercial towers for wind energy converters are briefly introduced, namely, concrete towers, welded steel shell towers, concrete/steel hybrid towers, lattice towers and hybrid lattice-tubular towers. In the second chapter, developments in fatigue analysis during the last decades and fatigue life prediction methods are given. Moreover, special emphasis is given to multiaxial fatigue life criteria which was used in fatigue life calculation of the connection used in this thesis. In the third chapter, numerical finite element modelling steps for stiffness calculation, global beam element model, and local connection model are given in detail. Additionally, finite element stress-strain results and fatigue life calculations using these results are also explained. In the last chapter, conclusions are drawn and further possible improvements of this work is suggested.