Cross-Section Optimization of Sandwich-Type Cylindrical Wind Turbine Towers

As wind energy is aggressively expanding within the alternative sources' part of modern world's energy pie, the need of addressing various obstacles that limit further wind utilization becomes all the more urgent. From a structural engineering point of view, surmounting the tower-base diameter limitation, dictated by the current transportation capabilities, is one of the industry's primary issues. The concept presented in this study, as a means to address this issue, is the implementation of a composite, sandwich-type tower section instead of today's predominant, conventional steel-only tubular section. The proposed section consists of two steel faces and a core of some lightweight material, binding and keeping them at a specified distance, thus providing significantly improved mechanical properties with minimal additional weight and cost. As an initial step towards a feasibility investigation of the proposed section, the analytical expressions that govern its behavior under either axial or bending loads are formulated in the current study. The results are verified by comparison with those obtained from a specialized composite section software, as well as a general purpose finite element software. The analytical solution is then employed to carry out extensive parametric analyses, involving a wide range of material qualities and layer thicknesses, leading to the optimization of the section, in terms of either elastic bending strength or initial stiffness. Finally, the determination of the optimal section-properties, which provide the most efficient solution regarding both criteria, is addressed, resulting in a preliminary design tool for sandwich-type, wind-turbine-tower sections.