The REFOS Project
"Life-cycle assessment of a Renewable Energy multi-purpose Floating Offshore System" REFOS is an innovative project, aiming at the development, design and life-cycle assessment of a multi-purpose floating TLP steel platform, suitable for combined offshore wind/wave energy resources exploitation. It involves a multi-discipline partnership, which covers all aspects of REFOS platform analysis and design, through a systematic, integrated and state-of-the-art approach, validated through structural and hydrodynamic testing.
The ultimate target is the final design of REFOS platform and its components, in form of a detailed design report and specific drawings, suitable for two typical locations (one in the Mediterranean and one in the North Sea) and adjustable to the environmental conditions and design requirements of a specific offshore site. The final design is accompanied by a techno-economic analysis, demonstrating the feasibility of the proposed solution. Towards this target, detailed structural analysis is performed, together with hydro-elastic dynamic analysis of the floating system, accounting for the wind turbine (W/T) and cylindrical Oscillating Water Column (OWC) devices. The work in REFOS continues and extends the results of a national project, where a multi-purpose floating platform, suitable for the Aegean Sea, has been studied at a preliminary stage, but without structural design considerations.
The project has three phases: (a) definition of design parameters and environmental conditions at selected locations; hydro-aero-elastic analyses; air turbine design for wave energy; (b) structural design of the steel tower, platform, and tendons; mechanical testing and numerical simulations; testing of a scaled-down physical model in the Wave Tank; (c) final design & techno-economic life-cycle analysis; dissemination of results.
The proposed floating solution will constitute a breakthrough in renewable energy technology, allowing for cost-efficient exploitation of combined offshore wind/wave energy in Europe, towards new market opportunities for the steel- and the renewable-energy-industry.
Μanufacturing of the integrated scaled – down physical model of the developed REFOS platform and conducting of extensive experimental campaign in the wave tank to simulate its dynamic behaviour for the operational and extreme sea state conditions at the selected locations.
Advanced numerical calculations to simulate the dynamic response of the floating platform under combined wind and wave loading conditions.
The final design of the REFOS platform.
Μechanical testing of key structural steel components under extreme loading and fatigue loading conditions.
Extensive simulations of the mechanical behaviour of key structural details using nonlinear finite element tools, to calculate local stresses and strains at critical locations.
A dedicated workshop at the end of the project for dissemination of the REFOS results.
Scientific and Technical feasibility of the REFOS project
REFOS aims at investigating a multi-discipline topic, using advanced experimental and numerical tools. The consortium is composed by offshore, wind, structural, mechanical and welding engineers with expertise and experience in
performing high-quality experiments and calculations of offshore structures under various loading conditions.
conducting demanding calculations on the behaviour of large wind turbines through the development of nonlinear aero-elastic models.
designing, constructing and inspecting of structural steel tubular structures, with emphasis on welded tubular connections.
manufacturing of high-quality pipes suitable for TLP tendon applications.
The experimental work will be conducted in very well-equipped laboratories (with expertise in large-scale testing) and the numerical analyses will be performed with state-of-the-art simulation tools for hydro-dynamic, aero-elastic and structural calculations. The relevant experience and capabilities of the partners guarantees the successful completion of the project.
Innovative aspects and originality of the REFOS proposal
REFOS is characterized by both innovation and originality:
It is the first RFCS project on floating renewable energy, considering the behaviour of the entire platform and its interaction with wind and waves. The proposal, using advanced experimental and numerical tools, aims at developing innovative methodologies towards developing an efficient solution for floating energy production. Previous RFCS projects on the applications of steel in wind energy structures [P1], [P2], have focused on onshore (land) wind energy applications, whereas the new RFCS project JABACO [P3] refers to bottom-fixed (not floating) offshore platforms.
It combines offshore, wave and wind engineering concepts with structural engineering practice, towards an “integrated” (“holistic”) approach, to achieve an optimum structural solution for the platform. The project results will be original and are expected to make a breakthrough in the area of offshore renewables, improving the current state-of-the-art significantly.
The floating platform concept to be developed will be both novel and unique, aiming at expanding existing energy production solutions, towards new horizons in cost-efficient renewable energy production.
The tests to be conducted within REFOS are novel and original. In particular, the testing equipment developed by NTUA for the hydrodynamic testing of the scaled-down model, as an improvement of existing NTUA facilities will be a novel set-up to study the wave-wind-platform interaction, leading to innovative and original results on the dynamic behaviour of the floating energy platform.
Progress beyond the state –of-the-art
The innovative character and features of REFOS, will lead to breakthrough progress in the area of offshore renewable energy, well beyond the state-of-the-art. More specifically, the REFOS project targets on the development of a new technological product, the REFOS platform, through a significant progress in the existing technological know-how. It is believed that the proposed floating production energy concept broadens the horizons of constructional steel sector.
[P1] RFCS Project FATHOMS “Fatigue behaviour of high strength steels welded joints in offshore and marine systems.” Completed: (1/07/2005 to 30/06/2008); RFSR-CT-2005-00042. FATHOMS project aimed to contribute to the knowledge on the fatigue behaviour of welded joints in high strength steels (minimum yield strength ≥ 420 MPa) and to improve the design criteria for welded structures and components for offshore applications, in terms of both weight and cost.
[P2] Three RFCS projects (“HISTWIN” projects) have been performed for onshore steel wind towers: (a) HISTWIN (RFSR-CT-2006-00031), High-strength steel tower for wind turbines (2006-2009); (b) HISTWIN2 (RFSR-CT-2010-00031), High steel tubular towers for wind turbines (2010-2013); (c) HISTWIN_Plus (RFS2-CT-2014-00023), High-Strength Steel Tower for Wind Turbine (2014-2015); innovative solutions for onshore wind turbine towers have been developed, with emphasis on the use of high-strength steel material, the optimal connection between the different parts of the tower and the optimization of the tower foundation.
[P3] RFCS (Research Fund for Coal and Steel), Project JABACO: “Development of Modular Steel Jacket for Offshore Windfarms” (July 2015 – December 2018). Using advanced numerical and experimental methodologies, it is aimed at developing a modular design concept for a bottom-fixed offshore steel tubular platform (jacket) for wind energy exploitation.