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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.

This paper describes some effects on the load level of state-of-the-art multi-megawatt wind turbines introduced by the new edition of the

The first issue of the DNV Offshore Standard, DNV-OS-J103 Design of Floating Wind Turbine Structures, was published in June 2013. The standard was based on a joint industry effort with representatives from manufacturers, developers, utility companies and certifying bodies from Europe, Asia and the US. The standard represented a condensation of all relevant requirements for floaters in existing DNV standards for the offshore oil and gas industry which were considered relevant also for offshore floating structures for support of wind turbines, supplemented by necessary adaptation to the wind turbine application. The development of the standard capitalized much on experience from development projects going on at the time, in particular the Hywind spar off the coast of western Norway, the WindFloat off the coast of Portugal and the Pelastar TLP concept. In July 2018, DNV GL published a revision of DNV-OS-J103 as a part of the harmonization of the DNV GL codes for the wind turbine industry after the merger between Det Norske Veritas (DNV) and Germanischer Lloyd (GL) in the fall of 2013. The standard was re-issued as DNVGL-ST-0119 Floating wind turbine structures. This new revision reflects the experience gained after the first issue in 2013 as well as the current trends within the industry. Since 2013, numerous guidelines addressing the design of floating structures for offshore wind turbines have been published by various certifying bodies, and an IEC technical specification on the subject is under way. In addition, several prototypes have been installed and the first small array of floating wind turbines, Hywind Scotland pilot park, are currently in operation. The most important updates in the revision of the standard include formulation of floater-specific load cases, requirements to be fulfilled to support the exemption for design of unmanned floaters with damage stability, and replacement of current consequence-class based requirements for design fatigue factors with low-consequence based factors dependent on the accessibility for inspection and repair, the aim being a safety level against fatigue similar to that which is currently targeted for bottom-fixed structures. Other topics which have been considered in the revision are the floater motion control system and its possible integration with the control and protection system for the wind turbine, the issue of how to deal with slack in tendons in the station keeping system, corrosion, anchor design and power cable design. In parallel to the revision of the standard, a new service specification for certification of floating wind turbines has been developed by DNV GL, identified as DNVGL-SE-0422 Certification of floating wind turbines. For technical requirements, the service specification refers to the revised standard, DNVGL-ST-0119. The technical paper summarizes the updates and changes in the revised standard, in addition to the content of the new service specification.

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