Stability requirements for floating offshore wind turbine (FOWT) during assembly and temporary phases: overview and application

The renewable energy targets set by the EU governments is pushing the wind industry toward deeper and further sites, making the floating option the preferred technical and economic choice. Certification authorities are developing new guidelines, recommended practices and standard specific for this industry, starting to recognize the importance, beside the operational phases, of the temporary phases such as sea transport and installation on site (DNV, 2013). The aim of the present work is to propose an approach to analyse the assembly and temporary phases, namely when the turbine is assembled on the floating support structure and the following transport phase from the shipyard to the operational site. After a review of the approaches for industries near to the offshore wind industry, a framework is proposed where criteria, standards and environmental and loading conditions are discussed. Taking the FOWT NOVA as a case study, the proposed framework is focused on semi-submersible FOWT, assessing the design of this floating support structure, highlighting the impact of these rules and evidencing an overall good performance. The proposed approach can be used as a starting point by administrations and certification authorities and as guidelines in the conceptual/preliminary design phases of the design of an FOWT structure.