Hybrid towers for offshore wind energy converters

A new kind of tower construction, calling hybrid tower, is developed for offshore wind energy converters. The tower sections consist of two steel shells which are bonded together with a core material. The core between the inner an outer steel face increases the stability of the shells. In comparison with linear buckling analyses the validity of a laminate composite shell theory was proven. With model scale tests the stability of sandwich shells was analyzed against shell buckling due to axial compression and compared to tests with steel shells. Optical measurements were used to record the geometrical imperfections and to import the imperfect geometry of such shells in FE-models. Furthermore, a comparison of critical buckling loads was carried out with numerical solutions. The test series show a significant increase in bearing capacity for sandwich cylinders, which depends on the compressive strength of the core materials. The sandwich shells with a grout as core material show a catastrophic post buckling like steel shells. In contrast to this the elastomer core supports a ductile post buckling. The failure criteria for all variants of tested sandwich shells is more a local failure due to the steel faces called face wrinkling and not a global shell buckling.