Hybrid towers for offshore wind energy converters

A new kind of tower construction, calling hybrid tower, was developed for offshore wind energy converters. The tower sections consisted of two steel shells that were bonded together with a core material. The core between the inner an outer steel face increased the stability of the shells. Compared 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. The test series showed a significant increase in bearing capacity for sandwich cylinders, which depended on the compressive strength of the core materials. The sandwich shells with a grout as core material showed a catastrophic post buckling like steel shells. In contrast to this, the elastomer core supported a ductile post buckling. The failure criteria for all variants of tested sandwich shells was more a local failure due to the steel faces called face wrinkling and not a global shell buckling. The consideration of additional bearing capacities due to the core materials was valid, and in combination with high-strength steels, it could offer a new alternative solution for tower sections of offshore wind energy converters. This is an abstract of a paper presented at the Eighteenth International Offshore and Polar Engineering Conference (Vancouver, Canada 7/6-11/2008).