Session: 09-02-08 Wind Energy: System Testing

Submission Number: 179767

Hybrid Model Testing of Floating Offshore Wind Turbines Using Software-In-The-Loop 

Floating offshore wind is set to play an important role in the future energy mix, with installed capacity expected to reach 40GW by 2040 (DNV, 2025). Sustaining cost reductions of floating wind will help bolster industrialization, scale-up, and competitiveness of offshore wind energy.

Physical model testing of floating turbines is key to de-risk design and reduce CAPEX+OPEX costs. However, accurately representing both turbine and platform dynamics is challenging due to scaling limitations—most facilities can simulate either wind or wave forcing, but not both without compromise. A Software-in-the-Loop (SiTL) approach addresses this by omitting the rotor or the floater and applying instead computed aerodynamic or hydrodynamic loads. This setup not only overcomes scaling challenges but also enables agile testing, such as assessing floating turbine response with different rotors. Therefore, SiTL is a practical and flexible solution for testing floating wind turbines.

Several studies have investigated SiTL applications (e.g., Sauder et al., 2016; Bayati et al., 2017; Chabaud et al., 2018). However, to the best of the author’s knowledge, none have validated a SiTL setup under combined wind and wave conditions. This study addresses that gap by validating a SiTL setup against physical model tests involving both wind and wave forcing.

The SiTL validation campaign was conducted in the DHI deep-water basin in 2025. The facility features a 3D wave maker and a new open-jet wind generator, jointly developed by DHI and DTU Wind. The wind generator can create a vertical wind shear and turbulent wind coherent with the Mann model. The floater was a variant of the TetraSub by Stiesdal Offshore. The turbine was the IEA 22 MW RWT, with scale 1:70. 

The experiment comprised two sets of tests: with rotor (reference) and without rotor (SiTL). The controller was either set to provide constant blade pitch and rotor speed, or to react to the external conditions by adjusting the blade pitch and torque. The same open-loop and closed-loop settings were replicated in the SiTL setup.

For the SiTL experiment, the rotor was removed and replaced with a structure able to pull the tower top in 3 degrees of freedom: surge, floater pitch, and floater yaw, using pre-tensioned cables. Floater motions were recorded in real-time and fed to the HAWC2 multi-body software. HAWC2 provided rotor loads in real-time, which were transmitted to the servos that pulled the cables via HexaWire. The wind recorded during the reference experiment was used for the HAWC2 simulation. Unlike other SiTL experiments, the HAWC2 model is the downscaled IEA 22 MW, allowing an exact match with reference results.

The SiTL system was validated under different conditions, including wind-only, wind and waves, uniform or Mann-based turbulence, open-loop or closed-loop. Three setups were compared: reference (with rotor), SiTL and a HAWC2 simulation including floater and hydrodynamic loading. Results show that floater motions matched well in the actuated degrees of freedom, proving the validity and reliability of the developed SiTL setup. Furthermore, the HexaWire system reacted quickly to the rotor loads from HAWC2.

Future work will focus on adding sway and roll degrees of freedom, thus improving the SiTL setup.
 

Presenting Author: Pietro Danilo Tomaselli DHI A/S, Marine & Hydraulic Structures Department

Presenting Author Biography: Dr. Pietro Danilo Tomaselli has been working in the offshore industry for 10+ years. He received the M.Sc. degree in Civil Engineering from the University of Palermo, in 2011. In 2016, he concluded his Ph.d. study at the Department of Mechanical Engineering, Technical University of Denmark. He is currently Senior Hydraulic Engineer at the Marine & Hydraulic Structures Department of DHI A/S (Denmark), working on consultancy and research projects in the marine field.

Authors:

Søren Løgstrup Sørensen DHI A/S, Marine & Hydraulic Structures Department
Riccardo Riva Technical University of Denmark, Department of Wind and Energy Systems
Pietro Danilo Tomaselli DHI A/S, Marine & Hydraulic Structures Department
Ignacio Johannesen Technical University of Denmark, Department of Wind and Energy Systems
Rasmus Sode Lund Technical University of Denmark, Department of Wind and Energy Systems
Henrik Bredmose Technical University of Denmark, Department of Wind and Energy Systems