Comparative Analysis of Industrial Design Methodologies for Fixed-Bottom and Floating Wind Turbines

Abstract

The floating offshore wind turbine (FOWT) market is currently dominated by single unit demonstration projects and first pre-commercial wind farms such as the Hywind Scotland wind farm. Today’s FOWT substructure design process is therefore not yet at a level of industrialization comparable to fixed-bottom substructure design methodologies, where standardized design and realization procedures are well established throughout the industry. Aligned with work performed in the Ramboll and University of Stuttgart-led work packages “Concept Industrialization” and “Design practice” of the European H2020 LIFES50+ project, the ambition of this paper is to define state-of-the-art fixed-bottom and floating design methods and based on these identify key differences through comparative analysis. In the first part of the paper the scope and selected details of today’s industrialized design process for fixed-bottom substructure design is presented, including e.g. load iteration schemes and applied numerical methods, risk assessment incorporation, optimization, and cost modelling. In the second part, the key elements of this industrialized procedure which are different to FOWT design are identified and described: This is done based on a review of the current FOWT common design practice, where elements are identified that are unique and/or different for FOWTs — this includes e.g. the requirement to adapt the controller to the specific platform behaviour, as well as a tower and/or selected rotor-nacelle assembly (RNA) component redesign, and also includes differences in terms of defining and performing load case simulations. Another observation that is described relates to the floating specific required numerical methodologies applied for the detailed structural and mooring design, where challenges exist regarding the interface between coupled global loads analyses tools and detailed structural, mooring, and geotechnical tools. A further key item discussed in this respect is the industry-common load exchange practice for fixed-bottom design, where only a limited data exchange between WT manufacturers and platform designers is done; a procedure that is challenging to be applied for FOWTs. Compared with fixed-bottom design, the consideration of manufacturability, fabrication constraints, serial production, design complexity reduction, assembly, supply chain, installation, geotechnics, O&M and risk is often limited and these items will also be briefly discussed. Overall the paper is intended as a technical review of existing fixed-bottom design procedures and, facilitated through the comparative analysis with these established design methodologies, identifies and presents the key differentiating design elements and challenges for an industrialized FOWT design. The content of the paper will provide input for the focused development of design processes for industrialized detailed design of FOWTs to guarantee the demanded technology-readiness and manufacturing-readiness levels (TRL and MRL) and ultimately improve their CAPEX and OPEX by applying industrial design procedures. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 640741 (LIFES50+ project, www.lifes50plus.eu).