| 25 Aug 2025
Hydro-elastic coupling effect on the dynamic global response of a spar-type floating offshore wind turbine
Abstract. Designing floating wind turbine systems requires integrated load assessments (ILA) using fully coupled hydro-servo-aero-elastic models. Although potential flow models are commonly employed for floater hydrodynamics in mooring design and floating offshore wind turbines movement estimation, such models usually assume a rigid body floater. This assumption can significantly impact tower eigenfrequency calculations, especially for large floaters. This study demonstrates these impacts using in-situ sensor data from the Zefyros 2.3 MW spar wind turbine. We detail the methodology used to accurately determine tower eigenfrequency. A rigid floater without added mass resulted in a 37 % error compared to measured modes. Incorporating floater flexibility and added mass reduced this error to 5 %, and further to 3 % with blade flexibility. The observed eigenfrequency discrepancies necessitate modifications to the hydro-servo-aero-elastic model to align with the detailed finite element hydro-structure model eigenfrequencies. We present potential model adjustments and discuss their impacts. After implementing one model modification, we present the results and illustrate the updated model validation process.
This paper addresses a very interesting topic, investigating the hydro-elastic coupling effects of a spar-type floating wind turbine. The study on the tower eigenfrequencies of the FOWT system with inclusion of floater flexibility and added mass is well presented, with a valuable comparison between numerical results—using beam and shell element modeling in Homer—and full scale in-situ sensor data. This contributes significant value for both academic and industry community.
The authors have also developed a coupled model in OpenFAST by largely tuning the tower stiffness while maintaining a rigid-body assumption for the floater. However, in my view, this model is insufficient to capture the hydro-elastic effects on the global dynamic response of the system. For the stated objectives of the study, Updating the OpenFAST model to explicitly incorporate floater flexibility is recommended.
In the following sections, I provide some remarks that the authors may consider during revision:
Here are some minor comments:
(1). There should be a space between a number and the unit. Please ensure consistent formatting throughout the manuscript.
(2). In Table 1, the decimal separator should be corrected: "8,3 m" should be written as "8.3 m".
(3). The figure order in the text should be reviewed and updated to improve readability. For instance, Figure 4 is introduced before Figure 3, and Figure 9 appears before Figure 8.
(4). The in-text citation formatting should be checked for consistency and compliance with the journal's style guide.
(5). A proofreading for grammar is recommended. Several sentences contain awkward phrasing or are missing grammatical elements such as subjects.