the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Aug 2026
A Global POD Comparison of Surge- and Pitch-Induced Wake Dynamics of a Floating Offshore Wind Turbine
Abstract. The motion of floating offshore wind turbine platforms strongly affects wake development. Consequently, understanding motion-induced wake effects has become a key research topic, with implications for wind farm layout optimization and advanced control strategies. This work investigates the wake dynamics of floating offshore wind turbines operating under realistic atmospheric boundary layer inflow using Large-Eddy Simulations with an actuator line model. A comprehensive dataset including surge and pitch motions over a range of motion frequencies and amplitudes is analysed through a global proper orthogonal decomposition, providing a common modal basis for the consistent comparison of wake dynamics across all cases. The results identify the reduced frequency as the dominant parameter governing platform-induced wake dynamics. Although the time-averaged wake is only marginally affected under the investigated operating conditions, the coherent wake response strongly depends on the reduced frequency. Motions with a reduced frequency of fr = 0.2 produce a negligible coherent contribution, whereas fr = 0.5 generates energetic coherent structures that persist up to approximately 4–5 rotor diameters downstream. In contrast, fr = 0.8 leads to a more localized response confined to the near wake. Motion amplitude primarily influences the intensity of the coherent response, while the reduced frequency controls its spatial evolution. Surge and pitch exhibit similar overall trends, although pitch produces slightly stronger coherent energy in the upper wake close to the rotor. Finally, only a limited number of POD modes are required to reconstruct the coherent response in regions where the platform induced wake structures remain well organized and spatially coherent, highlighting the potential of the proposed global POD framework for reduced-order modelling of floating offshore wind turbine wakes.
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Status: final response (author comments only)
- CC1: 'Comment on wes-2026-141', Zhaobin Li, 19 Aug 2026
- RC1: 'Comment on wes-2026-141', Anonymous Referee #1, 07 Oct 2026
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RC2: 'Comment on wes-2026-141', Anonymous Referee #2, 12 Oct 2026
Short summary:
The paper investigates the effects of platform motion on the wake dynamics of floating wind turbines using the global proper orthogonal decomposition technique applied to large eddy simulations with actuator line method and atmospheric boundary layer inflow.
General comments:
The research topic addressed is relevant and timely and the work brings new interpretations. The manuscript is well-written and the figures are clear.
In general, the choices made, especially the one related to the test cases, should be better substantiated.
Specific comments:
-Title: The authors should mention in the title that the work is based on numerical simulations, e.g. by adding CFD or LES.
-Abstract: I suggest being more cautious with words like “strongly” (L1) and “comprehensive” (L4). The same applies to a few other points in the manuscript. I suggest that the authors double-check whether there are studies supporting the use of “strongly” and whether their dataset can be considered “comprehensive”, also with respect to similar datasets of others.
-L8: The authors stated that the wake recovery is only marginally affected…
-L41: Isn’t ROM typically used for optimisation (e.g.), and derived from the physical understanding, rather than being used to increase the physical understanding and interpretation?
-L68: The authors only consider surge and pitch in their study. An explanation of why surge and pitch are the most relevant for your study and why you are not considering other DOFs should be added. Surge, or surge and pitch, are typically the most relevant motions when studying wake recovery, but here you are studying the dynamic aspects of the wake that could possibly be induced by other DOFs, so an explanation is needed.
-L81: The authors chose the IEA 22MW. Did you also choose a floater? Considering the hydrodynamic characteristics of one or different floaters for that turbine size would allow you to link the reduced frequencies to the natural frequencies or wave response frequency range of the floater DOFs.
-L91: “possible correction strategies are not considered here”. Why, and how do you think you are not introducing significant error?
-L102: Why didn’t you perform some simulation with laminar inflow and no ABL with platform motions, to better decouple the effect of each on wake recovery and dynamics? Later in the paper, you analyse in depth the energy and velocity coherent with platform motion; however, also in view of the role of ambient turbulence on recovery and the fact that it could overshadow the recovery induced by platform motion that some studies show under laminar conditions, intermediate simulations with motion and laminar inflow would have been a nice addition.
-L128: The ABL profile, the wind speed and the TI are representative of what location, if any? The choice should be substantiated.
-L157: The choice of using a below-rated operating condition should also be substantiated.
-L191: What are the gravity effects?
-L194: Is it common practice to correct for deflection with twist? I understand the direct effect of correcting with twist the twist generated by bend-twist coupling, but I don’t know if normally the effect of deflection itself can be corrected with twist or it this is an idea of the authors.
-L223-228: This method is not entirely correct: under floating motions, the blades are deformed partially because of the velocity variation and partially (arguably in greater part, but this should be calculated) due to the inertia the blades. A motion of the hub will cause a deformation of the blades also without considering aerodynamic forces. Therefore, I suggest to either find a justification to consider only the deformation caused by the velocity variation, or include also the deformation due to the motion of the hub (not sure whether it is possible with HAWC2), or delete this part and state that you neglect dynamic deformation due to floating motion in the comparison HAWC2 vs your model.
-L230: I think that you can only conclude that it is “a suitable basis for blade load representation under floating condition”. But, to conclude it, the previous comment should be addressed.
-L251-258: (L257) are you sure that the platform motion rage is until fr=1.5? For some FOWT concepts, fr=1.5 is the lower value of the wave-induced motion response range, not the upper value. Is it different for the IEA 22MW? The authors should link the fr values to realistic motion ranges of a suitable floater for the wind turbine of choice. And (L258) fr = 0.5 is, for some FOWT, not in the high frequency range (wave frequency range) but in the low frequency or natural frequency range, close to the pitch natural frequency. Is it different for a bigger FOWT? Overall, the authors should substantiate the choice of fr non only based on one (or more) studies, but also making the connection with relevant floater motions for one (or more) floating concept of the chosen size.
-L254: The authors should justify the choice of not considering frequencies that are in the wave induced range (fr=1.5 or higher). Although the amplitudes are small, the effect on the wake dynamics could have been interesting (for example, you could have used higher amplitudes that are not realistic but allow you to see some phenomena.
-L279: do you have a possible explanation for the deviation of mean thrust?
-Table 3: The authors built their test matrix based on amplitude rather than on velocity variation at hub height, which is often preferred because the thrust variation, and therefore arguably the main effect on the wake, is proportional to it. Nevertheless, the velocity variation (normalised and, optionally, dimensional) should be added to the table, together with other missing parameters like the dimensional frequency and amplitude that would help linking the test cases to realistic full-scale conditions.
-L285: I suggest to change the title of this section. All the analyses from here onwards is based on LES results, so the title is misleading. I suggest a title like “wake main characteristics” or similar.
-L290-291: I suggest to add more references. There are recent experiments that, although with lower TI, showed clear effect of platform motion on wake recovery for fr around 0.6 (so close to your 0.5). Overall, you should acknowledge that other studies (I have experiments in mind it maybe also numerical ones) saw an (significant) effect of floating motion on wake recovery, and you should explain why in your opinion you don’t see it. I think it’s because of the ambient turbulence whose effect becomes predominant (especially because your TI is not on the lower side for offshore sites).
-L302: why do you have a lower thrust (connected to a previous comment)? Is it expected? How is the turbine controlled (I believe fixed rpm and fixed blade pitch: state it in case it’s not yet stated anywhere).
-L326: Is 1Hz enough to see the phenomena you are interested in? Again, a comparison with the (dimensional) floater motion frequency would help.
-L348: could you briefly say why you chose those specific cases?
-L373-374: This is interesting, because there are studies saying that fr=0.3 has high effect on the wakes. Do you have any comments about it?
-L578-581: this is not generally true but only with certain level of turbulence. Experiments with TI around 3% (therefore not exactly laminar) show effect on wake recovery.
-L590 and L612: what is the difference between wake engineering models and reduced order models here?
Technical corrections:
A few changes to the wording or sentences I suggest:
-L98: considered -> performed
-L103: surge -> surging; pitch -> pitching
-L238: … carried out for the simulations with floating motions
-L310-318: I would move this paragraph before section 4.3.1 starts.
-L379: I would remove “preliminary”, and maybe use e.g. “first”.
-Figure 18: check consistency of notation in figure axes and labels (e.g. how you write fr).
-L516: suggestion: I would leave high-level statements on advantages/limitation for the Discussion section.
A few typos:
-L176: ensemble(Céspedes -> ensemble (Céspedes
-L413: literature ((Andersen -> literature (Andersen
-L622: citation brackets missing
Citation: https://doi.org/10.5194/wes-2026-141-RC2
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I congratulate the authors on this insightful LES study using global POD to characterise surge‑ and pitch‑driven wake dynamics of floating offshore wind turbines. The key finding regarding the role of reduced frequency on coherent wake evolution is valuable for reduced‑order‑model development.
I would encourage the authors to discuss the applicability of their conclusions across different platform motion types. As shown by Messmer et al. (2024), streamwise and lateral motions trigger distinct wake instabilities with different sensitive reduced‑frequency ranges. Since this work only considers surge and pitch, a note on how results may transfer to lateral sway motion would help constrain the generality of their observations for full six‑DOF platform dynamics.
I also suggest considering the resolvent‑based motion‑to‑wake model from Li and Yang (2024, JFM 980, A48). This physics‑driven model predicts motion‑induced coherent wake structures, offering an interesting benchmark for the data‑driven global‑POD results presented here.
Short summary: This comment asks for discussion on result generality across streamwise/lateral platform motions and highlights a resolvent‑based wake model for potential benchmarking against the global‑POD outputs.