Multiple TLDs on Motion Reduction Control of the Offshore Wind Turbines

Round 1

Reviewer 1 Report

This present paper studies the damping effects of the Tuned Liquid Dampers on a mono-pile offshore wind turbine based on ANSYS simulation and further, the correctness of the numerical simulations was verified through simple experiments. The explored study and the topic are interesting to the recent trend of researchers and engineers. However, this reviewer thinks that the paper is lengthy, equations, and results are not consistent throughout the paper. In order to improve the quality of the manuscript, the following comments need to be taken care:

1. From Eq. (3) and also in other Equations (not assigned equation  number (for example subsection 2.3)), symbols are introduced in the equation but not explained in the text. Please revise them and also check throughout the manuscript.
2. Equation number should be inserted from page 7 on wards.
3. In Figure 6, both figures should be of same label.
4. Please explain, why peak is observed in Fig. 8.
5. Left side of Fig. 11 should be labeled.
6. Figures 9, 10, 13 should be same x-label (axis) limit in order to get more clarity of their differences (for example Fig. 9, 13).
7. Please remove last sub plots from Fig. (18) and Fig. (19).
8. Please reduce the x-axis limit of Figs. 20, 21, and 27 as they (the results) seem to very clumsy.
9. This reviewer realizes that there are some irrelevant references are in the reference list (for example Bauer 1984,…), please remove them from the text and as well as from the reference list.
10. Please clearly mention the future scope of the present study at the end of the conclusion.

This reviewer recommends for revision of the manuscript.

Author Response

Response to valued reviewer #1:

1. From Eq. (3) and also in other Equations (not assigned equation  number (for example subsection 2.3)), symbols are introduced in the equation but not explained in the text. Please revise them and also check throughout the manuscript.

Res: Thank you very much for the comments and we have properly added the description.

1. Equation number should be inserted from page 7 on wards.

Res: Thank you very much for the comments and we have added the equation number.

1. In Figure 6, both figures should be of same label.

Res: Thank you very much for the comments and we have properly amended the figure.

1. Please explain, why peak is observed in Fig. 8.

Res: We have properly added the description.

1. Left side of Fig. 11 should be labeled.

Res: Thank you very much for the comments and we have added the labels.

1. Figures 9, 10, 13 should be same x-label (axis) limit in order to get more clarity of their differences (for example Fig. 9, 13).

Res: Thank you very much for the comments. Since the amplitude of each case is quite different and the amplitude of OWT with TLD is much smaller than that without TLD. It will be hard to see the displacement-history of OWT with TLD and if they use same label limits. We, however, had properly amended the label limits.

1. Please remove last sub plots from Fig. (18) and Fig. (19).

Res: Thank you very much for the comments and we have properly amended the figure.

8. Please reduce the x-axis limit of Figs. 20, 21, and 27 as they (the results) seem to very clumsy.

Res: Thank you very much for the comments and we have properly amended the figure.

1. This reviewer realizes that there are some irrelevant references are in the reference list (for example Bauer 1984,…), please remove them from the text and as well as from the reference list.

Res: Thank you very much for the comments and the irrelevant references have been removed.

1. Please clearly mention the future scope of the present study at the end of the conclusion.

Res: Thank you very much for the comments and we have added possible future works can be made.

Author Response File: Author Response.pdf

Reviewer 2 Report

Extremely good work. More of a small thesis than a paper. But pleasant to read. Nothing excessive.

Can be used as an example of how to write papers properly. Very good.

Author Response

Response to reviewer #2:

Extremely good work. More of a small thesis than a paper. But pleasant to read. Nothing excessive.

Can be used as an example of how to write papers properly. Very good.

Res: Thank you very much for your affirmation and support.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors have evaluated the effectiveness of tuned liquid dampers (TLDs) on offshore wind turbines (OWT), extending previous studies to include studying the response to wind and water waves. The study is approached methodically and provides a necessary examination of environmental impacts on OWTs.

My comments largely concern the presentation, but one overarching comment is that this manuscript requires proof reading. Other comments are:

• The different vertical axes in Figure 13 makes the difference between the experiment and simulations appear greater in the lower panel. Is this the case? A comment should be made on the change in agreement of the simulation when including the TLD.
• The acronym RNA and CAE are used well before they are described.
• Table 1 is confusing, the grid structure isn't needed for just stating the different cases. Additionally, what is I_ref?
• Multiple equation parameters should still be explained even if their definition seems obvious, such as:
  
  • V_hub (Eq. 2,5)
  • d (Eq. 3)
  • mu, rho & delta_ij  (sec 2.3)
  • lambda, R, h (line 45)
• Each panel of Figure 33 must be labeled. It is currently impossible draw any conclusions from just the Figure as presented.
• Line 285: should there be a negative on the right hand side of the equation?
• The flow chart presented in Figure 5 appears to have an optimisation step designed to minimise OWT motion by tuning the TLD. This is not described in the text. Either the flow chart or main text should be edited.
• Line 170, what is the "hub", is it the nacelle? Terminology should be consistent.
• Line 172-173: the sentence "The standard turbine elevation, the longitudinal standard deviation is:" doesn't make sense.
• Line 191: it's stated that a water depth of 27.35m is used in this study, however 20m is used in all following work.
• Line 263-264: sentence beginning "The sloshing..." mixes tenses.
• Line 274: what is the AC motor attached to?
• Figure 8 is of a different style and lower quality compared to the other line graphs. Additionally, the caption does not describe the axes.
• Figure 10: the experimental results are multivalued, and therefore incorrect.
• Table 2: a little awkward to read. Maybe add a vertical separator between the wind and wave parts.
• Section 3.2.1: It would be nice if the reason why the wind direction of severe weather is 90 degrees was explained here instead of later.
• Section 2.3: This section should include the description of the implementation given in section 3.3, Lines 468 onward
• In Figure 29 the 3-TLD setup is the worst performer for DLC1.2, can the authors explain why this is? 
• Can the authors address the diminishing returns of the number of TLDs for the DLC 6.2 condition (Figure 29)?
• There should be consistency about whether equations are centred or not.

Minor fixes:

• There are many uses of acronyms without a preceding article or pluralisation where there should be one (eg. Line 63 "The working principle of TLDs are..." and Line 102 "...frequency of the TLD...")
• Line 26: "Coal is the earliest developed..." what?
• Line 30: sentence beginning "Taiwan government..." is incomplete.
• Line 59: Mass ratio of what to what?
• Line 142: Missing the word "and" when listing environmental conditions.
• Lines 174-176, 214-230: Different font size.
• Line 253: density value missing units.
• Figure 4, refers to subfigure (b) instead of (right).
• Figures 13, 16, 17, 20, 21, 25, 26, 27, 29, and 30, refer to "left" and "right" when all subfigures are vertically aligned. Also, there should be consistency about the use of parenthesis around "left" and "right"
• Figure 29 vertical axis Amplitude has incorrect units.

Author Response

Thank you very much for your valued comments. Please see the attached file. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have properly incorporated my comments in the revised manuscript. Therefore, I've no further comments.