Abstract
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.
Highlights
The ambitious goals set by governmental organizations worldwide, regarding the contribution of wind energy to global energy supply, are hindered by several, practical difficulties
In order to remain transferable through narrow roads and under overhead obstructions, tower sections cannot generally exceed a maximum diameter of 4.5m, which limits total tower heights to approximately 110 m (Burton et al, 2001; DNV, 2002; Hau, 2006; Twele et al, 2012; NREL, 2014)
The concept investigated in the current research endeavor is, instead, that of a composite tower section consisting of two steel faces and a core made of some lightweight material, resembling a sandwich form
Summary
The ambitious goals set by governmental organizations worldwide, regarding the contribution of wind energy to global energy supply, are hindered by several, practical difficulties. The concept investigated in the current research endeavor is, instead, that of a composite tower section consisting of two steel faces and a core made of some lightweight material, resembling a sandwich form The advantage of such a solution is increased stiffness and strength with relatively small disadvantages in terms of mass and cost addition. The sandwich concept has been implemented in various cases and is not a novel one whatsoever, the idea of utilizing it as a wind turbine tower section is still at research level and is only mentioned in the literature in limited works In their preliminary investigation, Schaumann and Keindorf (2008) compared three different sandwich shells with solid steel ones (“monocoque”) on the basis of ultimate limit state calculations and concluded that sandwich shells are more efficient with respect to buckling. From Equation 9 and 10, assuming that the whole section is plastified, the plastic neutral axis position and the plastic resistance moment Mpl can be calculated, respectively:
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