IEA Research Study Extended To Improve Accuracy of Offshore Wind Systems Design Tools

Researchers from the National Renewable Energy Laboratory (NREL) received a four-year extension of International Energy Agency (IEA) research that will advance the overall accuracy of offshore wind computer modeling tools.

The IEA Wind Technology Collaboration Program's Executive Committee awarded the extension of Wind Task 30 research and by doing so created the Offshore Code Comparison Collaboration, Continuation, with Correlation and unCertainty (OC6) project. This new project will dig deeper into differences between computer simulations and experimental measurements, building off of previous Task 30 research OC4 and OC5.

According to Amy Robertson, NREL project leader, the purpose of OC6 is to refine the accuracy of engineering tools used to design offshore wind turbines by improving their ability to estimate structural loads. The tools used to design offshore wind systems need to consider the coupling between the aerodynamic and hydrodynamic loading on the system, which is vital to optimization and stability.

Designing an offshore wind system involves running tens of thousands of simulations, which requires modeling tools accurate enough to provide realistic load results, but also fast enough to perform design iterations in a reasonable time frame.

"Coupled engineering-level tools (such as OpenFAST) that consider both the wind and wave loading simultaneously on the structure fit that need," Robertson said. "Improving these tools to better predict the actual behavior of offshore wind systems enables further design optimization and, therefore, cost reductions. Unvalidated models increase costs because the technology must be overdesigned to accommodate for large uncertainties in loading and operating conditions predicted by the numerical models."

The offshore code comparison projects are important for designers, certifiers, and research institutes that apply modeling tools for design, research, and instruction. In addition, many researchers have learned how to effectively model and simulate offshore wind turbines using information provided from these projects.

Including participants from the offshore wind industry as well as OC5 members (see Member chart), the OC6 project has the following objectives:

• Perform more focused validation projects based on the issues identified in previous IEA Wind Task 23 and Task 30 projects (Offshore Code Comparison [OC3], OC4, and OC5)
   
• Develop and employ more rigorous validation practices following American Society of Mechanical Engineers guidelines, with a strong emphasis on quantifying uncertainty in test campaigns used for validation
   
• Include higher-fidelity modeling solutions in the validation process (when possible), performing a three-way validation among engineering-level tools and measured data.

The OC5 participants have already identified validation projects that are the most relevant to focus on within the extension and organized them into five projects, or "work packages" (see OC6 Validation Projects Identified). The objectives will be investigated through measurement data obtained across multiple test campaigns, including testing of several offshore turbine support structure types, including two floating semisubmersibles, a spar, and a monopile. When possible, multiple phenomena will be investigated using the data sets.

OC5 Active Membership

OC6 will feature members of the offshore wind industry, as well as members of OC5.