Influence of the Drag Force on the Average Absorbed Power of Heaving Wave Energy Converters Using Smoothed Particle Hydrodynamics

Round 1

Reviewer 1 Report

This is a very detailed paper outlining new approaches and comparisons of numerical methods in an important renewable energy technology. The paper by a subset of the authors as was cited in Renewable Energy in 2020 was appreciated as it gave more background.

To highlight the substantial work done in this paper, I think it would be nice to have the abstract, paper outline (lines 77-80), and conclusions organized to better reflect the different tools created (modified equations, coupled codes), methodologies used, and results generated.  For example, the abstract listing of the three ways to find the absorbed power (lines 9-11) repeats wording in the case of the modification without the reader knowing what to expect.  Maybe change to something life "three ways were compared: normal and modified linear..., and DualSPHysics."  The conclusion could be broken up into paragraphs or bullet points, since now major findings are buried in the middle of one long conclusion paragraph.

The motivation for the need of this research was very good by identifying the limits of previous efforts especially in the dynamic boundary conditions, along with the potential and workarounds with the new method.  However, the methodology section starts off with that this study assumes linear potential theory and then talks about viscosity and effects of Reynolds numbers. I think this could be clarified with an introduction transition to the methodology to discuss how the various calculational methods will be approached. This would also include clarifying the term "artificial viscosity."

For facilitating use of this method, it might be nice to include availability status of the tools and data along with potential future research directions and applications.  For example, could this be also applied to not just heaving pint systems but also combined heaving and surging systems. Can this help with understanding current research of systems.

The language was fine.  The conclusions had quite a few acronyms that might be spelled out but there was a table defining them to help. (The only small typo I identified was the word "with" in the figure 4 caption.)

Thanks for the opportunity to review this nice paper.

 

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript presents an interesting research work which fully within the aims and scope of Water. The manuscript has been organized well and the authors have properly justified the subject in the Introduction Section. Therefore, I think that this manuscript can be accepted for publication after considering minor revisions.

 

1. Line 95. Explain briefly why Quintic Kernel was applied in this case of study.

 

2. Lines 234-236. Authors indicate: “the drag force contains a quadratic term, which can be approximated as follows by calculating its Fourier series and retaining only the first frequency component”. Authors should explain more in depth why these assumptions are appropriate.

 

3. Section 4. Test cases and numerical setup. Lines 266-275. Authors should explain why these particular configurations/dimensions/geometries of the WECs were selected. I understand that these configurations were previously used in other works, and therefore, this allows the comparison with previous numerical and experimental results. However, I assume that these concrete configurations/dimensions/geometries were previously selected attending to some implications. It would be nice for the reader if the authors briefly indicate the reasons behind the selection of these particular configurations.

 

4. Lines 285-292: Authors stated the use of an artificial viscosity value higher than the real one under some conditions. Authors maintain in some cases this artificial viscosity value (0.01) due to previous studies focused on simulations of waves proposed this value. Authors should justify more in depth the use of this viscosity value. In fact, authors explain in Results and discussion Section (lines 343-346) that a possible explanation of the slightly higher value of Cd obtained from DualSPHysics could be the fact of use the artificial viscosity value. This should be clarified.

 

5. Line 50: replace “with” by “being”.
6. Line 90: “equations”.
7. Line 234: replace “it´s” by “it is”
8. Line 268: “with”.
9. Line 361: replace “Now that” by “Once”.
10. Line 442: “… has been calculated and compared to results from DualSPHysiscs simulations”.
11. Figure 8: Values “0” and “3.5” are superimposed. Authors should correct it.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The paper "Influence of the drag force on the average absorbed power of heaving Wave Energy Converters using Smoothed Particle Hydrodynamics" reports an intersting application of SPH method for the study of the dynamics of floating point absorber WECs, focused on the drag coefficient evaluation.
The introduction is clear and reports a good description of the state of art
The methodological framework is widely described, even if it is no clear to me how the terms F_r and F_hs are threated when moving from equation (16) to equation (17) (and from eq.42 to eq.43). Since the theoretical framework of the WEC includes a number of models and definition, a graphical sketch of the involved modelling would be helpful for the understanding of the overal procedure applied in the paper.
Results are clearly presented, but I think their discussion can be improved, focusing on the difference between the results of the proposed method and the results of linear potential theory and emphasizeing the advantages and disadvantages of the proposed method.
I also suggest to use synthetic bullet points for the conclusion.

Finally, I think the paper is valuable for publication after a minor revision.

Author Response

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Author Response File: Author Response.docx