the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Aerodynamic response of a floating wind turbine scale model with inclusion of reference control functionalities
Alessandro Fontanella
Elio Daka
Felipe Novais
Marco Belloli
Abstract. Design and verification of control strategies for floating wind turbines often makes use of aero-hydro-servo-elastic modeling tools. Aerodynamic loads calculation in these tools has been recently validated against experiments not including active wind turbine control. This work investigates the aerodynamic response of a floating wind turbine scale model with active control and platform pitch motion. This is done in wind tunnel testing and with modeling of the scaled system in the offshore tool OpenFAST. A control design framework is developed to include the reference wind turbine controller ROSCO in the wind tunnel experiment. With platform pitch motion, the turbine aerodynamic response is predicted by the numerical model with different accuracy depending on the turbine control regime. Below rated wind, oscillations of aerodynamic torque in simulations are of lower amplitude than in the experiment, also when dynamic inflow is considered in the aerodynamic model. Above rated wind, where the turbine is controlled with collective blade pitch actuation, the response is not quasi-steady, and differences between the experiment and simulation are larger than in below-rated wind, in particular for phase with respect to motion.
Alessandro Fontanella et al.
Status: final response (author comments only)
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RC1: 'Comment on wes-2023-29', Anonymous Referee #1, 11 May 2023
The manuscript is well-written, with very clear figures.
The subject is very relevant for the development of floating wind turbines.Â
We suggest to a clarify the title, because "with inclusion of reference control functionalities" was not clear to us to start with. We suggest the somewhat lengthy title: "Controller design for model-scale rotors, and numerical/experimental study using prescribed motions.".
Abstract: the statement "Aerodynamic loads calculation in these tools has been recently validated..." should be completed by "for low-frequency motions", as indicated in the introduction. This is important to pinpoint when dealing with floating wind turbines, experiencing large wave-frequency motions.Â
In the abstract, and more generally in the paper, it should be emphasized that only thrust and torque loads have been investigated in the present study. Some of the other four components of the aerodynamic loading are important for the response of some floater concepts. See for instance Bachynski et al. (2015) https://doi.org/10.1016/j.egypro.2015.11.400Â
In the introduction it is stated that "In the last decade, several scale model experiments about the wind-wave response of floating wind turbines have been carried out, and a review of them is presented by Gueydon et al. (2020). The large majority of tests involving a scaled wind turbine did not use active turbine control.". This statement is inaccurate. A large number (probably the majority) of today's concepts supporting 5MW-15MW turbines have been tested in wave tanks using a hybrid (cyber-physical) approach, at SINTEF, Marin, UHC, etc... with literature references easy to find. This approach models the actual full-scale wind-turbine controller. Even though the present work is of course targeting tests using physical wind (and a "performance-matching" rotor), it should be emphasized that this approach is not the only one, and particularly that the hybrid approach solves the issue related to the downscaling of the controller.
Related to the previous point, in the introduction:Â "The methodology we developed to integrate active control in experiments and simulations should benefit future scale model testing activities" should be completed by "using physical wind".Â
In section 2.1, it is indicated that the tower eigenfrequency associated to the fore-aft mode is 9.5 Hz. Can the authors ellaborate on how this corresponds to the full-scale frequency of current designs? Are the aerodynamic thrust and torque investigated here affected by possible difference in vibrations frequencies between current designs and the model used here?
Line 216, it is stated that "loads measured by the load cell are mostly due to inertia". The varying projection of the acceleration of gravity on the horizontal accelerometer is likely to be important too when the rotor is undergoing pitch motions?
To conclude with a minor comment: Typo "fro" line 182.
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Citation: https://doi.org/10.5194/wes-2023-29-RC1 -
RC2: 'Comment on wes-2023-29', Anonymous Referee #2, 24 May 2023
The topics and content of the manuscript are relevant for the journal and for the topic of unsteady aerodynamics of floating wind turbines. However, the current version of the paper will require some restructuring and rewriting before the paper can be considered for publication. The major points are listed here below.
The writing style and clarity of the writing need to be improved significantly. The subject of the manuscript is not easy to follow given the way it is explained in the paper. It would be beneficial to include a table of symbols due to the many symbols used in the derivation of the scaled controller, tuning, and modificaitons. The procedure how the controller is designed, scaled, and tuned is difficult to follow. It would be easier to simplify and remove some of the details that are not relevant to the paper.
The manuscript used often unprecise languages and words without giving a clear context, for example "reference value", the reader often struggle to understand what exactly the "reference value" is referring to. The same with terms like simulation results or estimates etc. where no clear context is given to help reader understand which simulation results the authors are referring to. Another example is the shortening of the terms, while clear for many, it is better not to speak about "below rated wind" instead of the complete term "below rated wind speed". This kind of shortening of terms gives the reader the impression of lack of precision in the writing.
The manuscript gives the impression that when the authors describe the results of the experiment and the simulations, it is presented in a kind of a very long laundry list without context and logical connection. The readers are overwhelmed with a lot of information without knowing which ones are actually relevant or are important. It would be good to restructure the results and discussion in a more logical way, and possibly discard observations that are , while interesting, have little practical or theoretical value. Instead expand the discuss the discrepancies in more details and explanations of possible causes of the discrepancies and the consequence when using the results of the study.Â
the manuscripts contains spelling mistakes and more specific comments can be found in the attached PDF file  Â
Alessandro Fontanella et al.
Data sets
Aerodynamics of a Floating Wind Turbine Scale Model with Active Control Alessandro Fontanella, Elio Daka, Felipe Novais, and Marco Belloli https://doi.org/10.5281/zenodo.7741358
Model code and software
Aerodynamics of a Floating Wind Turbine Scale Model with Active Control Alessandro Fontanella, Elio Daka, Felipe Novais, and Marco Belloli https://doi.org/10.5281/zenodo.7741358
Alessandro Fontanella et al.
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