Offshore support structure optimization by means of integrated design and controls

Support structures are one of the main cost drivers offshore, and since other offshore rules apply with regards to design and site conditions, different methodologies have to be developed to mitigate the loads on the support structure and therefore to reduce the associated component costs. Detailed onshore studies and field tests have already shown that advanced control algorithms can be an effective way to reduce fatigue and extreme loading on a wind turbine. Still, the overall cost-effectiveness for large offshore wind farms has not been studied in detail yet. In the scope of this paper, studies of new controller concepts are integrated within the design process of offshore support structures in order to stretch the applicability of monopiles to larger water depths or simply to reduce the structural weight and associated costs. A reference design of the support structure is made for a site in the Dutch North Sea. The focus is on reducing the dominant hydrodynamic excitation on the support structure. The implemented load mitigation concept leads to significant reductions in loading, allowing considerable material savings and therefore a more cost-effective design. The presented approach allows material reductions of more than 9% for the studied support structure. Undesired side effects, such as increased wear of turbine components, are unlikely, as other system loadings and characteristics remain within an acceptable range. Even if some of the rotor–nacelle assembly loads are slightly increased by the applied controller, the increases are low and probably still within the margins of the type-class fatigue loads. Copyright © 2012 John Wiley & Sons, Ltd.