Abstract The main objective of the Offshore Code Comparison Collaboration Continuation, with Correlation (OC5) project is validation of aero-hydro-servo-elastic simulation tools for offshore wind turbines (OWTs) through comparison of simulated results to the response data of physical systems. Phase III of the OC5 project validates OWT models against the measurements recorded on a Senvion 5M wind turbine supported by the OWEC Quattropod from the alpha ventus offshore wind farm. The following operating conditions of the wind turbine were chosen for the validation: (1) idling below the cut-in wind speed, (2) rotor-nacelle assembly (RNA) rotation maneuver below the cut-in wind speed, (3) power production below and above the rated wind speed, and (4) shutdown. A number of validation load cases were defined based on these operating conditions. The following measurements were used for validation: (1) strains and accelerations recorded on the support structure and (2) pitch, yaw, and azimuth angles, generator speed, and electrical power recorded from the RNA. Strains were not directly available from the majority of the OWT simulation tools; therefore, strains were calculated based on out-of-plane bending moments, axial forces, and cross-sectional properties of the structural members. The simulation results and measurements were compared in terms of time series, discrete Fourier transforms, power spectral densities, and probability density functions of strains and accelerometers. A good match was achieved between the measurements and models setup by OC5 Phase III participants.

Floating wind solutions have developed significantly in the recent years, moving from single demonstrators to having several floating wind pilot wind farms currently under development and even in operation. This is an important step for the industry allowing the market to gain confidence in these solutions for offshore wind. Ideol is a leading floating platform designer and they have been working on a demonstration project for their innovative platform in France. The Floatgen demonstration project consists of a 2MW wind turbine mounted on the Damping Pool platform. During the design phase of the project, the coupled analysis of the full system — turbine, tower, floating platform and moorings needs to be carried out to verify the loading on the turbine and platform, adapt the turbine controller for the floating application and re-design the tower and transition piece. For this project, DNV GL performed the aforementioned analysis in Bladed whilst Ideol performed parallel analysis in OrcaFlex, focusing on the platform and mooring design. It is crucial that both numerical models used in the different software tools and parallel analysis workflows are equivalent and lead to the same overall system behavior. This paper describes the numerical model used for coupled analysis in Bladed and its verification against Ideol’s OrcaFlex model, with emphasis on the aspects related to the platform modelling. For the hydrodynamic loading of the platform, boundary element method was considered together with global and local viscous drag terms. To compare and verify the coupled model results in Bladed to Ideol’s own numerical results, a set of static and dynamic tests were run and the resultant kinematics were compared. Ideol’s model was previously validated against tank test experiments giving confidence in its behavior. The viscous drag coefficients in the Bladed model were adjusted to ensure a good agreement between the kinematics of Ideol’s model of the system and the Bladed model. This paper summarizes the results of this verification exercise, along with some recommendations on areas of further research in the floating wind modelling domain.

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The main objective of the Offshore Code Comparison Collaboration Continuation, with Correlation (OC5) project is validation of aero-hydro-servo-elastic simulation tools for offshore wind turbines (OWTs) through comparison of simulated results to the response data of physical systems. Phase III of the OC5 project validates OWT models against the measurements recorded on a Senvion 5M wind turbine supported by the OWEC Quattropod from the alpha ventus offshore wind farm. The following operating conditions of the wind turbine were chosen for the validation: (1) Idling below the cut-in wind speed; (2) Rotor-nacelle assembly (RNA) rotation maneuver below the cut-in wind speed; (3) Power production below and above the rated wind speed; and (4) Shutdown. A number of validation load cases were defined based on these operating conditions. The following measurements were used for validation: (1) Strains and accelerations recorded on the support structure; (2) Pitch, yaw, and azimuth angles, generator speed, and electrical power recorded from the RNA. Strains were not directly available from the majority of the OWT simulation tools. Therefore, strains were calculated based on out-of-plane bending moments, axial forces, and cross-sectional properties of the structural members. Also, a number of issues arose during the validation: (1) The need for a thorough quality check of sensor measurements; (2) The sensitivity of the turbine loads to the controller and airfoil properties, which were only approximated in the modeling approach; (3) The importance of estimating and applying an appropriate damping value for the structure; and (4) The importance of wind characteristics beyond turbulence on the loads. The simulation results and measurements were compared in terms of time series, discrete Fourier transforms, power spectral densities, probability density functions of strains and accelerometers. A good match was achieved between the measurements and models set up by OC5 Phase III participants.