Design, fabrication, and testing of a composite tower for floating offshore wind turbines
The University of Maine and Ershigs, Inc. have designed, developed, and tested an innovative composite tower for floating offshore wind turbines. The composite tower is an alternative to a significantly heavier steel tower, resulting in a smaller hull with equivalent stability. This paper details research, design, manufacturing, and testing of a composite tower prototype at 1:2 scale. The composite tower offers operation and maintenance advantages and significant weight savings for new floating foundation technologies as compared to traditional steel towers resulting in overall reduction in the levelized cost of energy. This half-scale composite tower was part of front-end engineering and design for a full-scale multi-megawatt floating offshore wind turbine. This tower was made of two 9.09 m (29’10”) long tower sections 3.15 m (10’4″) in diameter utilizing full-scale production techniques. The two sections were bolted together to form a single 18.19 m (59’8″) long section. The structural testing regime included determination of the bending natural frequency, bending stiffness, ability of base connection to endure fatigue bending loading with a spectrum equivalent to 60 years, torsional stiffness and capacity, and ultimate bending capacity. The half-scale composite tower passed all testing requirements, thereby confirming design techniques and the manufacturing processes for use on full-scale offshore floating wind turbine platforms. The research activities help to transition the composite tower technology to full-scale projects currently underway.