International Effort Advances Offshore Wind Turbine Design Codes

September 12, 2014

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For the past several years, the U.S. Department of Energy’s National Renewable Energy Laboratory has teamed with the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) in Germany to lead an international effort under the International Energy Agency’s (IEA) Task 30 to improve the tools used to design offshore wind energy systems.

The computer-aided engineering tools used to design offshore wind systems are based on the same design tools used for land-based wind turbines. Land-based design tools use aero-servo-elastic codes, which incorporate aerodynamic (aero), control system (servo), and structural-dynamic (elastic) models; however, because offshore wind turbines are installed in marine environments, they require modeling tools that can also consider the hydrodynamic loads on a variety of substructure types as well as their mooring systems. To design these systems, engineers need design codes that can simulate incident waves, sea current, hydrodynamics, foundation dynamics of the substructure, and mooring loads and dynamics. The complex nature of the design codes required for these systems underscores the need to verify and validate their accuracy. 

The purpose of the IEA Task 30 Offshore Code Comparison Collaboration Continuation (OC4) project is to verify the accuracy of these design codes through code-to-code comparisons. For the last phase of the OC4 project, the research teams ran analyses using a reference model based on a 5-megawatt turbine on a floating semisubmersible foundation. Twenty-one organizations from 11 countries submitted results using 19 different simulation codes for this phase. In June, NREL hosted a meeting in conjunction with the Ocean, Offshore, and Arctic Engineering Conference in San Francisco, California, to present the final results of the OC4 project and launch the next phase of this important research effort. Thirty-two people from around the world, representing universities, laboratories, and commercial companies, attended the meeting.

Although the results of the code-to-code comparisons contribute to a greater understanding of the dynamics of offshore floating wind energy systems and the techniques used for modeling them, the code comparisons only identified differences—they did not determine which solution is the most accurate. To address this limitation, IEA launched an extension of the OC4 project:  Offshore Code Comparison Collaboration Continuation, with Correlation (OC5). The focus of this project is to validate offshore wind modeling tools through the comparison of simulated responses to physical response data from actual measurements. This project will examine three structures using data from both floating and fixed-bottom systems, and from both scaled tank testing and full-scale, open-ocean testing.

Read more about the results of the OC4 code-to-code comparison effort in Offshore Code Comparison Collaboration Continuation Within IEA Wind Task 30: Phase II Results Regarding a Floating Semisubmersible Wind System.