Concrete substructure for floating offshore wind turbines

The main objective of this R&D project is to develop the OO-Star Wind Floater into a feasible, cost effective and competitive solution for floating wind turbines. The first phase, focusing on the conceptual sizing and establishing a froze n concept, was completed Q1 2014. This concept was basis for a basic design phase where all relevant technical and economical aspects were analysed more in detail. The intention was to develop and document the feasibility and competitive strength of a full size 6 MW floating wind turbine for harsh environment. Some of the work has been to follow up of Master projects related to the development activities. One of the Master activities included model tank testing of the concept. Another part of the work was related to further development of the analysis and simulation tool 3DFloat (IFE-tool) able to perform fully coupled time domain analyses. It has also been an objective to further develop the design tool for reinforced concrete structures, ShellDesign, which has been used for structural design of the concrete hull.

Over the past five years Dr.techn.Olav Olsen AS (OO) have developed foundation solutions for offshore wind, bottom fixed and floating. As the market for bottom fixed solutions have grown rapidly, floating wind is relatively new and the number of publicly known floating solutions is limited. The need for innovative and cost effective floating solutions is emerging in countries with lack of shallow waters. OO believes that a concrete floating solution will be very competitive due to the nature of offshore wind which require foundations with long design life and not sensitive to fatigue. In response to this OO has over the last year developed a concrete semisubmersible floater with the following characteristics: -simple construction -structurally robust - can be designed for harsh water -can support large turbines -long design life, no maintenance -completion (including WTG) in shallow water alongside a quay -simple operation OO and IFE want to document the feasibility and advantages with such a solution through this proposed R&D project, split in two phases: 1.Feasibility study 2.Basic Engineering The aim of the project is to achieve the following: -Document feasibility and competitiveness of this new concept compared to existing solutions -Develop a fo undation technology which will be perfect for Norwegian waters and which can also be exported to other deepwater areas worldwide -Optimize the concept based on use of the Norwegian developed analysis and simulation tool 3DFloat (developed by UFE), specifi cally made for floating offshore wind -Design the concrete floater based on the most advanced design software for offshore concrete structures, Shelldesign (developed by OO). This software is today the only code checking program which allow for non-linear design with stiffness reductions due to cracking and corresponding stress distributions -To engage Master students in a number of master thesis over the next two years, related to structural and marine issues