Aeroelastic Performance Analysis of Wind Turbine in the Wake with a New Elastic Actuator Line Model

Round 1

Reviewer 1 Report

This paper addresses a numerical simulation study of floating wind turbine, with proposing a new actuator line model method. The aeroelastic performance of the floating wind turbine is the key point of the research, especially the rotating beam solver. With the proposed method, OpenForm code is used to conduct simulations. The validation work is organized very well, with plenty of simulation outcomes. Several comparisons are made to verify the feasibility of the proposed method. This paper can be accepted for publication with minor revisions according to the comments listed as below.

1. The last sentences starting from ‘It is demonstrated that … more serious’ are recommended to be revised. The main research findings are expected to included in abstract, which will help others to understand the contribution of the research. The current two sentences are not sufficient to support the research findings at this moment.
2. 1 and Fig.2 couldn’t be seen in my PC Lab. But it might due to the format problem.
3. In Fig.5, is the part with ‘Solve structural deflection’ corresponds to the ‘rotating beam solver’? I think the rotating beam solver is written very well, but its section in Fig.5 is not clear indicated.
4. Why two wind turbines are included in the model shown in Fig.7? Is it due to the reason for including wake effect?
5. In Table 3, it is indicated that when wind speed is lower than 8m/s, the error becomes larger than 10%. Comparatively, with larger wind speed, the error is smaller. Can some explanation be added for this point?
6. In acknowledgement, there are too many funding numbers. I don’t think this is good for this paper, and would like to suggest no more than 4 funding number.

Author Response

We sincerely thank the referee for the constructive comments, the details of the repy to the review report are in the attachment, please check it.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper’s fundamental contributions seem two-fold. First, it compares the aeroelastic response of a turbine simulated by different existing simulation software/methods. This is a useful benchmark. Second, it describes a new method that may maintain accuracy while decreasing computational cost. This would be a promising development. Additionally, I recognize that a lot of care was taken in organizing a lot of data.

2 main revisions are needed to strengthen the paper’s value:

1. Organize the information more clearly (nuances of all the different software packages considered).
2. Add data on computational cost.

Below are additional comments, which include comments related to these 2 main revisions.

• Please correct the English grammar issues. Perhaps have someone with the expertise. proofread the manuscript.
• Introduction- Clearly state if the foundation is floating or fixed. I would expect that the blade bending effect on aerodynamic is much greater for a fixed foundation than for a floating foundation that already has the whole structure moving a significant amount.
• Introduction 2nd paragraph- add comment on how does computational efficiency of Vortex Lattice method compare to CFD and BEM?
• Introduction- the summaries of the different methods are clearly described. It sets up the rest of the paper nicely.
• Line 210- why did this study use LES instead of RANS?
• In Sections 3.1 and 3.2, the results EALM are compared to the results of different software packages/computation methods. Please add more information on how the existing methods couple the aerodynamics and deflection. What assumptions does each software package suite/method make, and what limitations does each one have? It would be extremely helpful if this information was summarized in a table or figure. Perhaps you could have a table where each row is for each software package. One column could be for the Aerodynamic method, another column for the elastic dynamics method, and a third column for how the solver couples them (one-way, two-way, not at all, same step, based on previous step, etc).
• Section 3- in its current form one big discussion point that I think is missing is a description of how the different cases might have used different software packages or different simulation settings- and how these may impact the results. That is, these results do not necessarily allow direct 1:1 comparisons of different mathematical formulations because many other variables may not be constant across all of them. Please add more information on how this was accounted for and how it might affect the results and conclusions. It seems like some results were obtained from other papers and not obtained by the authors running the simulations themselves.
• On a related note, it would be very useful to show the following result: how much does blade bending impact aerodynamic performance? That is, run the simulation with effectively rigid bodies and with the flexible bodies in the same exact software package and then compare the results of thrust and power. Currently, that piece of information is obscured.
• Table 2 and table 4- clarify what each case number corresponds to in the actual Table. It is difficult to go back-and-forth between the text describing each case and then remember which case # it is. Are the case #’s in Table 4 the same as the case #’s in Table 2? It would be much easier to compare results if you added a column with a case description. Also, add a column that mentions what parameters are the same and what are changed for each case.
• The paper states that one of the main motivations for this study is that the EALM model can maintain accuracy while reducing computational cost compared to other methods. However, the paper does not provide data on the computational cost results. Please add at least some data that comparing the computational cost (e.g. run time/simulated time efficiencies) of the different methodologies.
• Regarding Table 3- add an explanation for why does the error go down with wind speed?
• Figure 17- Was ALM run in the same software suite as EALM (OpenFAOM or SOWFA?)? Say so in the caption. If not, describe how can we be sure that the differences are due to including blade bending.
• Why is the power and thrust drop due to blade deflection more exaggerated for a wind turbine in a wake? Please add comments in the paper.
• Please add some comments in the paper regarding uncertainty in the results. What’s the amount of results uncertainty / sensitivity to uncertain model parameters?

Author Response

We sincerely thank the referee for constructive comments, the details of the repy to the review report are in the attachment, please check it.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript addresses the aerodynamics of wind turbines presenting an elastic actuator line model which combines the traditional actuator line model and a beam solver used in the blade design, as taken from ref. [17]. The proposed approach is implemented in OpenFOAM and results are compared with alternative ones in the literature, including those provided by the FAST software package. Accurate results are obtained in terms of power, thrust and tip displacement. The effects of blade elasticity are investigated on wake flows based on the proposed approach.

In the reviewer’s opinion the manuscript needs some improvements before publication. Here follows a list of issues to be addressed:

1. The authors should better clarify the advantages of the proposed approach versus the first elastic actuator line model introduced in ref. [16]. Is the advantage that a quick beam solver method is used by the authors in place of the finite difference method applied in ref. [16]?
2. Figure 5 is meant to clarify the differences between the proposed approach and the first elastic actuator model but more details are needed. Again the differences/advantages of the proposed approach w.r.t. the first elastic actuator line model should better be clarified (see point #1 of the review)
3. Figures 1 and 2 are missing
4. Please explain Eq.(8) and Eq.(9)

Minor issues

Please change symbol “g( )” in Eq.(13) to avoid confusion with the gravity acceleration

English needs careful and serious checking, here follow a few examples:

Page 1, lines 32-33: “to deformative” should “deformable” and “reduced the” should be “reduced”

Page 1, line 38: “It has highly efficiency and widely used in the industrial application” should be “It has high efficiency and is widely used in industrial applications

Page 1, line 44: these researches usually cost should be these researches are usually cost

Page 2, line 69: the concept “..and this loading which acts the body force…” is not clear

Page 12, line 315: please check “From the pictures ??,…”

Page 15, line 388: “To analyze the influence of elastic blade of the wake flows” should be To analyze the influence of elastic blade on the wake flows

Page 18, line 455: please check “The propose of this study is to propose…”

Finally, a few references could be added on current applications involving the 5MW NREL wind turbine on onshore and offshore supports:

Agarwal P., Manuel L. (2009) Simulation of offshore wind turbine response for long-term extreme load prediction. Engineering Structures, 31, 2236-2246.

Ghassempour M., Failla G., Arena F. (2019) Vibration mitigation in offshore wind turbines via tuned mass damper, Engineering Structures, Volume 183, Pages 610-636.

Kim D.H., Lee S.G., Lee I.K. (2014) Seismic fragility analysis of 5MWoffshore wind turbine. Renewable Energy 65, 250-256.

Santangelo F., Failla G., Santini A., Arena F. (2016) Time-domain uncoupled analyses for seismic assessment of land-based wind turbines, Engineering Structures, Volume 123, Pages 275-299.

Rendon E.A., Manuel L. (2012) Long-term loads for a monopile-supported offshore wind turbine. Wind Energy, 17, 209-223.

Alati N., Failla G., Arena F. (2015) Seismic analysis of offshore wind turbines on bottom-fixed support structures, Philosophical Transactions of the Royal Society A, 373, 20140086

Dong W., Moan T., Gao Z. (2011) Long-term fatigue analysis of multi-planar tubular joints for jacket-type offshore wind turbine in time domain. Engineering Structures, 33, 2002-2014.

Author Response

We sincerely thank the referee for constructive comments, the details of the repy to the review report are in the attachment, please check it.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have revised the paper according to the reviewer's suggestions. The paper can be published as is.