Buckling Verification of Manhole Area of Tubular Steel Wind Turbine Towers via Non‐linear Finite Element Analysis

Abstract

As wind turbine towers grow in height and their blades become longer, actions on the towers are also increased and their safe and cost‐effective design becomes critical for the further development of the wind energy sector. One potential failure mechanism of tubular steel towers is shell local buckling between ring flanges. In the present paper, the buckling behavior of a 120m tall wind turbine tower under realistic wind loads is investigated numerically, focusing on the buckling response near the man‐hole opening. To that effect, nonlinear finite element analyses accounting for geometrical and material nonlinearity and imperfections (GMNIA) is employed. GMNIA is performed taking into account initial geometric imperfections with the most unfavorable shapes resulting from the three primary buckling modes, determining the imperfection size according to EN1993‐1‐6 depending on the assumed fabrication quality class A, B or C. Numerical results are compared to analytical verification according to EN1993‐1‐6. Different wind directions are considered. Moreover, to investigate the influence of the stiffening of the manhole to the tower buckling strength, a comparison between three alternatives of stiffened and an unstiffened manhole is performed.

Nonlinear Finite Element Analysis of Tubular Steel Wind Turbine Towers near Man Door and Ventilation Openings to Optimize Design against Buckling

“…Due to the above reasons, a numerical treatment of the tower's buckling response is pertinent. The buckling behavior of wind turbine towers was investigated by some of the authors in [26,27], placing emphasis on the numerical modeling of the ring flanges away from the openings, while a very comprehensive investigation was published recently [28,29].…”

“…Hence, unstiffened openings are investigated, where the stiffness and strength reduction caused by the opening are addressed by increased plate thickness. Some initial efforts to compare stiffened and unstiffened man door openings were attempted in [42], while a preliminary version of the present paper, also involving ventilation openings, was presented by the authors in [43].…”