Optimisation of a steel tower for a wind turbine structure

The purpose of the research presented in this paper is to obtain a design that will minimise the cost of a steel tower for a wind turbine. The wind turbine tower investigated is constructed from a slightly conical ring-stiffened welded steel shell. This 45 m high shell is modelled by three stacked cylindrical shell segments, each 15 m in length and each having constant average diameter and thickness. The wind load is calculated according to Eurocode 1 Part 2–4. Design constraints on shell buckling and local buckling of flat ring-stiffeners are considered. The ring-stiffeners are necessary to prevent ovalisation. To calculate the manufacturing costs, the processing cost to form the shells into near cylindrical shapes, as well as the cost to assemble and weld the segments, is taken into account. The cost function to be minimised includes material and manufacturing costs. The optimum shell thickness, number of stiffeners and dimensions of the stiffeners are calculated using Rosenbrock’s direct search method for function minimisation complemented by an additional discretisation to account for available profiles. The results indicate that the minimum cost solution corresponds to the minimum number of ring-stiffeners. The procedure proposed can be treated as a baseline for determining least cost designs of slightly conical towers that meet the structural requirements of slender structures predominantly loaded by bending due to dynamic loads.