We have submitted our final report, and this concludes our feasibility study on the applicability of a new concrete suction anchor for floating wind. In the course of this project, FWTC devised innovative solutions encompassing buoyancy chamber, spiral post-tensioning, and padeye connection, that are now all patent-pending. We believe that there is ample potential for further exploitation of these technologies that lower LCOE for floating offshore wind. We want to thank the entire team for their contributions, and particularly Ramboll and Cathie for helping FWTC with design basis, load assessments, and steel suction anchor designs. Please reach out to us to know more about how we can help your floating offshore wind project make use of these new technologies.
We are grateful for working with Colorado School of Mines (CSM) on this project that Dr. Rick Damiani had led while at NREL.
With CSM, we are optimizing the structural design of the SpiderFLOAT, an innovative substructure invented by Dr. R. Damiani (FWTC), Mr. S. Sirnivas (NREL), and Mr. F. Wendt (Ramboll).
The project is part of ARPA-e's ATLANTIS program, is led by NREL and Colorado School of Mines, and seeks to use control-co-design techniques to minimize costs in the OWT floating substructure. Other partners include the University of Colorado at Boulder, the University of Virginia, and the American Bureau of Shipping.
Tasks include optimization of concrete structures and aero-hydro-servo-elastic simulations of the entire OWT.
Rationale for a new anchor design
Mooring accounts for around 15-20% of total floating wind costs. We have optimized an anchoring system for floating offshore wind by combining the versatility and low-cost of concrete materials with the efficiency of a suction anchor. Concrete can be cast in many forms and can leverage the existing local supply chain. Moving away from heavy steel-use for offshore wind structures is a trend that other experienced players in this field, e.g., Equinor and Ideol, have already embraced. Additionally we envisioned adding flotation capabilities to the anchor to allow for wet-towing. With this new design, we propose to cut costs by 80% in the anchoring systems CaPEx while maintaining all the advantages of a suction-assisted installation anchor (omni-directional loading capacity, installation accuracy, and environmentally friendly instillation and removal).
The suction anchor is made of two chambers. The main suction chamber sits at the bottom. At the top of the anchor, a special buoyancy chamber (FWTC, patent pending) is realized via a pair of dome-shape walls. The domes and the hatches are designed to keep the domes at rest or under compression at all times during installation, operation, and removal. This structural arrangement allows for the minimization of the necessary reinforcement and for the creation of additional buoyancy. With an air bag creating a water-tight seal at the bottom, and with the buoyancy chamber evacuated, the anchor can be wet-towed to the installation site with inexpensive vessels.
This new, patent-pending, three-dimensional post-tensioning arrangement allows us to mitigate longitudinal, radial, and circumferential tensile stresses that would otherwise arise in the suction skirt under certain loading conditions. This system allows for an efficient use of concrete and reduced use of steel reinforcement in the anchor, making it very economically attractive.
At the padeye, loads from the mooring line fairlead give rise to stress concentration and localized shear and bending in the concrete walls that must be overcome with an ad-hoc structural design. FWTC conceived three patent-pending solutions: an external steel fascia with load-transferring pins fastened to a recess in the suction skirt; a tendon assisted load distribution strategy; an integrated plate that uses existing tendons.
We designed the anchor for both a 10-MW and a 15-MW OWT system at sites offshore Scotland. We have also carried out a sensitivity analysis showing a wide range of soil and water conditions for this new anchor applicability. From a design standpoint, the anchor is structurally efficient and reliable; from an economic standpoint, the new anchor shows a great cost-cutting advantage for developers of floating offshore wind.
The next steps in the anchor design will require structural testing, sea-trials, and 3rd-party certification.
If interested in this technology, please contact us.
We are grateful to the Scottish Government and Carbon Trust’s Floating Wind Joint Industry Project (Floating Wind JIP) for selecting The Floating Wind Technology Company (FWTC) and RCAM Technologies among the winners of the technology acceleration competition.
FWTC, RCAM Technologies, and their supporting partners will collaborate to develop a concrete suction anchor, fabricated using novel 3D printing techniques. This consortium will focus on developing the design of the anchor, identifying transport and installation options, and establishing the expected cost savings relative to conventional anchors.
This project is led by RCAM Technologies that received an award by The National Offshore Wind Research and Development Consortium to develop an innovative substructure for offshore wind turbines. This project will develop and assess the feasibility of innovative concrete additive manufacturing methods, and more conventional methods for building an offshore wind turbine tower and integrated foundation on-site.
Scope of The Project
FWTC supported this project by generating an aero-hydro-servo-elastic model and performing load assessments of this innovative substructure supporting the IEA 15-MW OWT. We calculated SLS and ULS loads and performed detailed load extrapolations (probabilities of 10-2, 10-4, and 3.8e-7 per DNVGL-ST-0437) for the tower-substructure interface loads and the loads at the mudline. The two-year project scope includes the conceptual design, preliminary design, and feasibility assessment of the fixed-bottom, suction-bucket support structure, and heavy-lift-vessel alternative for a 15-MW class turbine.