Design, Validation, and Certification of a Synthetic Mooring Line System for a 15+ MW Floating Wind Turbine in the Humboldt Bay Wind Energy Area
University of Maine System acting through the University of Maine
Recipient
Orono, ME
Recipient Location
$308,908
Amount Spent
Active
Project Status
Project Update
A 25% Front-End Engineering Design (FEED) of a Taut-Synthetic mooring system has been developed using a preliminary set of Design Load Cases, and has been reviewed and approved by the American Bureau of Shipping. The design conforms to the Basis of Design that was completed earlier this year. The mooring system was sized for a 22 MW VolturnUS-S hull configuration with 22 MW IEA reference wind turbine, and subjected to load cases ranging from day-to-day operational fatigue during operation, to the 500-year extreme loads, to seismic shaking of the anchor points.
The 25% FEED mooring design will be validated through a 1:47 scale model basin test using an actuated mooring system to replicate the nonlinear behavior of the full scale mooring. The scale model basin test will confirm that the global performance of the floater is appropriately captured by the mooring model. The 1:47 scale model of the 22 MW VolturnUS-S hull will be the largest floater model tested at the UMaine wind-wave basin to date.
The 25% FEED design is also being put through an installation philosophy exercise in which an installation storyboard will be created. The design will then be put through a HAZID workshop to address risks of the mooring system to FOWT deployment, and a mooring integrity management report will be written.
The Issue
California’s goals of 5,000 megawatts (MW) of offshore wind by 2030 will require approximately 1,000 km total length of mooring lines, while 25,000 MW of offshore wind by 2045 will require upwards of 4,500 km total length of mooring lines. The current worldwide supply of mooring chain cannot meet such demand, and therefore the adoption of synthetic rope mooring systems will be necessary to accelerate the deployment of Floating Offshore Wind Turbine (FOWT) mooring systems. The current state of the art of synthetic mooring systems is limited to oil and gas installations and shallow to intermediate FOWT deployments. Deepwater taut-synthetic mooring systems deployed in California WEAs will need to be optimized to reduce hardware and connections while also increasing ease of installation due to significant weather window constraints present in the California offshore environment. In addition, any mooring system in a California WEA must withstand site-specific and technology-specific conditions, including length due to water depths between 550 and 1,300 meters, handling, and installation of the moorings with commercially available vessels, weight of the platforms, forces due to wind speed and storms, and seismicity.
Project Innovation
The University of Maine and its subcontractors will develop a novel mooring system design to tackle the unique challenges of floating offshore wind energy sites off the coast of California, including deep water, seismicity, and utility scale life cycle and supply chain constraints. Collaboration with synthetic rope suppliers and industry leading permanent mooring installers and suppliers will allow for detailed representation of synthetic rope properties in early design loops to achieve realistic life-cycle performance of the system. Project objectives include design of a deep-water synthetic mooring system to 50% Front-End Engineering Design level, validation of mooring system through scale modeling in a state-of-the-art wind wave basin facility, de-risking mooring systems through life cycle assessments, including mooring integrity management (MIM) and risk managements, increasing technology readiness level (TRL) from 3 to 4, verified by Approval in Principle letter from certification agency, development of cost estimates to allow comparison to contemporary deep-water mooring systems, and assessment of environmental impacts relative to the proposed mooring system.
Project Goals
HAZID workshop/installation storeyboard
1:70th scale basin test to verify design
Project Benefits
This project looks to develop a framework to design and certify under-water mooring systems for arrays that have large ranges of bathymetry, such as the California Wind Energy Lease Areas. By providing a topology that uses nylon synthetic ropes the global performance of floating wind turbines can be held nearly constant despite the changes in bathymetry across a project site, satisfying requirements of turbine OEMs during coupled analyses in the integrated loads assessment phase of commercial projects. Consistent mooring geometry, level global performance, and lower pretension loads also simplify mooring installation and floater hookup and unlock smaller handling vessels, which ultimately leads to decreased operations costs and timelines. The fully taut mooring system also has a smaller environmental impact than a more conventional semi-taut alternative, decreasing the total volume of ocean space impacted, benthic impacts in the touchdown zone, as well as smaller footprint impacts to fisheries.
Affordability
The taut synthetic system uses less mooring material overall, with large reductions in the amount of steel chain used. Capital costs of the proposed mooring system could decrease by up to 15% when compared with a conventional semi-taut alternative, and operational expenses could extend even further.
Environmental Sustainability
Decreased environmental impacts from the proposed taut-synthetic mooring included reduced ocean space utilization, decreased impact to the benthic environment, as well as reduced footprint for fisheries interaction.
Key Project Members
Spencer Hallowell
Jacob Ward
Anthony Viselli
Match Partners
University of Maine System acting through the University of Maine
American Bureau of Shipping
Delmar Systems, Inc.
Bridon Bekaert - The Ropes Group
