Numerical Study on Wave Dissipation Performance of OWC-Perforated Floating Breakwater under Irregular Waves

Round 1

Reviewer 1 Report

This paper investigates the wave dissipation performance of an Oscillating Water Column perforated floating breakwater under irregular wave conditions via simulations and showed that the wave dissipation performance of the OWC perforated floating breakwater surpasses that of similar structures. Results of this manuscript are very useful for the interested reader of the current engineering journal. Applying the following comments and suggestions will improve the current version of the manuscript.

·       At the end of introduction, add a brief para describing the paper organization.

·       Related works should include more latest references about the subject investigated.

·       The scientific novelty and specific contributions should be explicitly highlighted.

· The methodology section may be enhanced to facilitate understanding of wide audience.

·    Title of section 2 (Calculation model) should be replaced with a more accurate one.

·    What was the significance of the parameters used in the study (Table 1)?

·       Derivation/reference for equations (1) & (2) is missing.

·       Section 4.2 lacks the quantitative discussion.

·       Line 202: "…. is compared with results from existing literature". Authors needs to provide the details of the literature used for comparison.

·       Figure 5, while comparing, the authors needs to provide the %difference between the two data sets.

·       It is recommended to add reason on why the peak value of the irregular wave is smaller than that of the regular wave.

·       What was the effect of changing the spacing?

·       Conclusions should be curtailed summarizing only key points. Further study limitations should be added.

·       The linguistic quality of the paper also warrant improvement.

Minor editing of English language required

Author Response

Reply to Comments of Reviewers

We thank the editor for offering us the comments. We believe that these comments have enabled us to improve our manuscript. In the following, we offer item-to-item reply to each comment and list the associated changes in the manuscript to address the comment. For clarity, the changes of revision are marked up using the “Track Changes” function in revised version.

 

Replies to reviewer’s comments:

 

Reviewer #1:

1. At the end of introduction, add a brief para describing the paper organization.

Reply：

We gratefully appreciate for your valuable comment. In the revised manuscript, several sentences are added to describe the paper organization at the last paragraph of introduction.

last paragraph of Introduction The paper is organized as follows: Section 2 presents the underlying theory and numerical models. In Section 3, the amplitude response operator, mooring box, porous floating breakwater and wave energy conversion device breakwater are verified, which proves the accuracy of the numerical simulation. Section 4 studies the wave dissipation characteristics of the OWC-perforated floating breakwater under the action of irregular waves, and performs numerical simulation calculations on the floating breakwater, and simulates the floating breakwater by changing the parameters of the incident wave height, angle, and spacing of the box. According to the wave dissipation characteristics, the curve of the transmission coefficient changing with it is obtained. Finally, Section 5 presents the conclusion of this study.

 

2. 2. Related works should include more latest references about the subject investigated.

Reply：

We appreciate the reviewer’s important suggestion. In the revised manuscript, ten references of 2018 to 2023 are included in the 3rd and 7th paragraphs of introductory section.

Line 59 to 64 of Section 1 Wang et al. (2011) established through analysis of the time-domain motion equation that the spacing between the double-float breakwater elements exerts a considerable influence on the transmission coefficient.Sun et al. (2022) proposed a box-type floating breakwater with kelp, and found that kelp improved the wave dissipation capacity of the breakwater, especially for long waves, by establishing a numerical model.Zhang et al. (2023) propose a floating breakwater made of sponge material, and the results show that the breakwater has better wave-absorbing performance and range of motion re-sponse as the porosity of the sponge increases. Line 85 to 88 of Section 1 In wave energy development devices, oscillating water column (OWC) wave power generation devices are widely utilized. Many experts studied the OWC structure by experimental and numerical methods (Liu et al.2015, Tsai et al.2018, Masoomi et al. 2021, Li et al. 2023), and the research progression has laid the foundation for the integration of OWC devices with floating breakwaters. Line 100 to 117 of Section 1 Zhang et al. (2020a, b) calculated the energy capture and wave attenuation capacity of a triangular baffle heave float under linear PTO damping.It was found that the energy harvesting efficiency of the integrated system can be improved by increasing the width and draft of the buoy and reducing the distance between the buoy and the floating breakwater. Howe et al. (2020c) proposed an elbow-type OWC WEC (Figure 29) and carried out relevant model experiments. The results showed that the spacing between two WECs plays a more important role in wave-energy extraction. Line 140 to 144 of Section 1 However, BEM's application is most prevalent in solving the Laplace equation, where the volume-surface transformation, ensured by Green’s theorem, is complete [2008]. The Laplace equation calculations have provided acceptable results assuming the incompressible fluid and the irrotational flow in the wave structure interaction problems [2007]. References: 5.   Sun B, Li C, Yang S, et al. Experimental and numerical study on the wave attenuation performance and dynamic response of kelp-box type floating breakwater[J]. Ocean Engineering, 2022, 263: 112374. 6.   Zhang H, Sun B, Li Z, et al. Wave attenuation and motion response of floating breakwater with sponge material[J]. Ocean Engineering, 2023, 277: 114325. 17  .Zhang, H., B. Zhou, and C. Vogel. 2020a. “Hydrodynamic performance of a dual-floater hybrid system combining a floating breakwater and an oscillating-buoy type wave energy converter.” Appl. Energy 2020 (1): 114–212. https://doi.org/10.1016/j.apenergy.2019.114212. 18.  Zhang, H., B. Zhou, and C. Vogel. 2020b. “Hydrodynamic performance of a floating breakwater as an oscillating-buoy type wave energy converter.” Appl. Energy 257 (6): 113–996.https://doi.org/10.1016/j.apenergy.2019.113996. 19.  Howe, D., J. R. Nader, and G. Macfarlane. 2020. “Performance analysis of a floating breakwater integrated with multiple oscillating water column wave energy converters in regular and irregular seas.” Appl. Ocean Res.99 (Feb): 102147. https://doi.org/10.1016/j.apor.2020.102147. 24.  Li, X.; Yu, Z.; Qu, H.; Yang, M.; Shi, H.; Zhang, Z. Experimental Study on the Aerodynamic Performance and Wave Energy Capture Efficiency of Square and Curved OWC Wave Energy Conversion Devices. Sustainabilit. 2023, 15: 4963. 25.  Masoomi, M.; Yousefifard, M.; Mosavi, A. Efficiency Assessment of an Amended Oscillating Water Column Using OpenFOAM. Sustainability. 2021, 13: 5633. 26.  Tsai, C.-P.; Ko, C.-H.; Chen, Y.-C. Investigation on Performance of a Modified Breakwater-Integrated OWC Wave Energy Converter. Sustainability. 2018, 10: 643. 27.  P. Lin, Numerical Modeling of Water Waves, CRC Press, Boca Raton, FL, USA, 2008. 28.  J. Jin, “A mixed mode function-boundary element method for very large floating structure-water interaction systems excited by airplane landing impacts,” Doctoral Dissertation, University of Southampton, Southampton, UK, 2007.

 

3. The scientific novelty and specific contributions should be explicitly highlighted.

Reply：

We appreciate your valuable comment. In the revised manuscript, we added the characteristics of OWC perforated breakwaters in the introductory section, emphasizing on the combination of power generation and perforated wave dissipation in line 108 to 117.

 

4. The methodology section may be enhanced to facilitate understanding of wide audience.

Reply：

We truly appreciate the reviewer’s valuable comment. In the revised manuscript, we have reorganized the methodology section (Section 2) to make the content easier for readers to understand.

 

5. 5. Title of section 2 (Calculation model) should be replaced with a more accurate one.

Reply：

Thanks for your suggestion.We truly appreciate the reviewer’s valuable comment. In the revised manuscript, we revised the content of Section 2 and reorganized it in the text.

 

6. 6. What was the significance of the parameters used in the study (Table 1).

Reply：

We gratefully appreciate for your valuable comment. Table 4 in the original text has been revised and placed in section 4, introducing the size of the calculation model, wave conditions and corresponding symbol expressions.

Table 4. Calculation conditions. Parameter Symbol Content Water depth h 18m、25m、36m Significant wave height HS 1m、3m、5m Spacing d 6m、8m、10m、12m Period T 3.69s、4.49s、5.28s、6.08s、6.89s、7.69s Incident wave angle θ 0°、30°、45°、60°

 

7. Derivation/reference for equations (1) & (2) is missing.

Reply：

Thanks for your suggestion. Section 3 has been revised as a whole, with corresponding explanations for the formulas in the revised content.

 

8.Section 4.2 lacks the quantitative discussion.

Reply：

We appreciate the reviewer’s important suggestion. In the revised manuscript, we provided a detailed supplement to the validation section of the model, and added a separate section called “3 Validation” (line 306 to 354 of Section 3).

 

9. Line 202: "…. is compared with results from existing literature". Authors needs to provide the details of the literature used for comparison.

Reply：

We appreciate your valuable suggestion.We apologize for the careless writing. In the revised manuscript, we added case diagrams for comparison of results and examples, and that references to the literature for comparison and provided explanations in Section 3.2 to 3.5.

 

10. Figure 5, while comparing, the authors needs to provide the %difference between the two data sets.

Reply：

We gratefully appreciate for your valuable comment. In the revised manuscript, we listed comparison of data errors in Table 1 to Table 3.

 

11. It is recommended to add reason on why the peak value of the irregular wave is smaller than that of the regular wave.

Reply：

We appreciate the reviewer’s important suggestion. The validation section of the revised manuscript has added a comparison between the numerical simulation results and theoretical results of irregular wave spectrum curves, and removed the comparison between irregular and regular waves due to the fact that the paper mainly discusses the results of irregular wave situations.

Line 307 to 313 of Section 3 3.1 Simulation of irregular waves In order to correctly simulate the wave surface situation, this paper conducts numerical simulation on irregular waves. In this paper, the wave parameters with spectral peak period TP=6.89s and wave effective wave height HS=3m are selected for simulation.Figure 2 shows the simulation of irregular waves in the center of the calculation domain in the repetition period of 100T, and the simulation is in good condition.   Figure 2. Irregular wave simulation results.

 

12. What was the effect of changing the spacing.

Reply：

We appreciate your valuable comment. Changing the spacing means that the distance between the front and rear boxes changes, so the length of the whole breakwater system along the wave incident direction increases. Therefore, the change of the spacing should have a certain impact on the transmission coefficient, so this factor is calculated and discussed.

 

13. Conclusions should be curtailed summarizing only key points. Further study limitations should be added.

Reply：

We truly appreciate the reviewer’s valuable comment. In the revised manuscript, only the conclusion content has been retained for some conclusions, and the sentence on analyzing the reasons has been deleted. In addition, we added limitations and perspectives in conclusion.

Line 476 to 494 of Conclusion   2) The spacing between the floating breakwater components has a significant impact on the transmission coefficient, particularly for long-period waves.The width of the OWC opening influences the wave dissipation effect. A wider opening is more effective for long-period waves. The change in the opening width of the OWC perforated floating breakwater leads to a variation in its natural frequency. Consequently, this change significantly affects the transmission coefficient of the structure. 3) The water depth has a great influence on the wave dissipation performance of OWC perforated floating breakwater. A shallower water depth yields better wave dissipation; The significant wave height has little effect on the wave dissipation effect. The wave dissipation performance is better when the incident wave angle is 0°. In the numerical simulation research of this paper, the author believes that some of the research content still needs in-depth discussion and improvement, mainly reflected in the following aspects: (1) This paper only discusses the wave dissipation performance of the OWC-opening double-body floating breakwater. Further research is needed on factors such as anchor chain force and wave pressure, and the coupling effect between the mooring system and the floating breakwater also needs to be considered. (2) This paper does not simulate and calculate the conversion efficiency of the embedded OWC wave energy conversion device. The influence of different wave conditions and different OWC opening widths on the wave energy conversion efficiency can be further simulated and discussed.

 

14. The linguistic quality of the paper also warrant improvement.

Reply：

Thanks for your suggestion.In the revised manuscript, we checked and corrected English Language issues in the text.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

This article addresses a relevant issue in coastal engineering, which is breakwater design.  Although several important results are presented in the text, I believed the content of this paper should be better organized. More detailed information is missing in several parts of the text. Additional figures should be included. In virtue of this, I believe this article is not ready to be published at this moment.

The authors may find more detailed comments below. If the authors perform the following the corrections, I believe this article may be ready for publication in the future.

REVIEW COMMENTS:

- Line 40: To which country the expression "at home" refers to?

- Line 63 - 66: please explain in more details. What is the "relative width" parameter?

- Section 3.2.1 "Governing Equations": it would be interesting to briefly introduce, or cite, the equations apllied (Navier Stokes, Continuity and Turbulence). These equations simply appear along the text. All the equations' variables must be introduced.

- Sections 3.2.2 and 3.3: al the equations' variables must be introduced.

- Section "3.5 Meshing Method": it would be good to provide a figure presenting the applied mesh, as well as further information. How many mesh points were considered? What's the mesh resolution (spacing)? The model domain is not clear. Is it a wave tank?.

- Figure 4: it is not clear what does this figure refers too. Is it data simulated at a specific point of the modeling domain? Please provide better explanation on this figure.

- Chapter "4. Numerical Simulation": is this chapter the authors present comparisons of model results (preliminary results, I believe) with theoretical solutions and with results from other works. However, no further details are given on the works used for comparison. I believe chapter 4 must be extensively enhanced, since very few information is provided. Presenting additional figures would also be important, since this is a relevant part of the paper.

- Lines 254 - 256: this information, as well as Table 2, may be presented in Chapter 2. It was not clear, until now, that 4 structures would be analysed.

- Line 256: It is not clear what "spacing is 8 m" refers to.

- MEANINFULL Wave Height: this parameter seems mistranslated. I believe the correct expression is SIGNIFICANT Wave Height.

- Line 350: verify grammar(broken) 

The parameter Significant Wave Height (Hs) is a very important parameter regarding wave mechanics. The effect of the Hs parameter is analysed is this article. However, the authors refer to it as "Meaningfull Wave Height", which I believe to be incorrect. 

Author Response

Line 294 to 303 of Section 2.6 For the numerical simulation, the calculation domain is 100m × 100m, and the automatic mesh generation method of hydro-dynamic diffraction is employed to generate the element mesh. This method involves switching between tetrahedral and swept mesh, depending on the overall structure. Tetrahedron mesh is generated if irregular spatial structure is encountered, and hexahedron mesh is generated if regular spatial structure is encountered. The maximum size of the grid is 3m, and the setting tolerance is 1m. Figure 1 shows the model mesh, and the mesh number of total calculation domain is about 25000. The maximum allowable frequency. Set the maximum size of the mesh division should not be smaller than the maximum frequency of the waves.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Manuscript has been significantly improved. I would like to recommend it for publication. 

Minor editing of English language required

Author Response

Reply to Comments of Reviewers

We thank the editor for offering us the comments. We believe that these comments have enabled us to improve our manuscript. In the following, we offer item-to-item reply to each comment and list the associated changes in the manuscript to address the comment. For clarity, the changes of revision are marked up using the “Track Changes” function in revised version.

 

Replies to reviewer’s comments:

 

Reviewer #1-2:

Minor editing of English language required.

Reply：

We gratefully appreciate for your valuable comment. In the revised manuscript, we checked and corrected English Language issues in the text.Such as words in lines 59, 61 and so on.

Reviewer 2 Report

The text is fine, the authors performed all the requested revisions. However, in the first version of the manuscript, Figure 1 presented a very clear 3D model of the studied structure. In the revised version of the text, Figure 1 presents only the 3D mesh. It depicts well the mesh, but it shows not so clear the geometry of the structure.

I suggest the authors to present both the mesh and the 3D model, as presented in the first version of the manuscript. After performing this correction, I believe this article may be ready for publication.

Author Response

Reply to Comments of Reviewers

We thank the editor for offering us the comments. We believe that these comments have enabled us to improve our manuscript. In the following, we offer item-to-item reply to each comment and list the associated changes in the manuscript to address the comment. For clarity, the changes of revision are marked up using the “Track Changes” function in revised version.

 

Replies to reviewer’s comments:

 

Reviewer #2-2:

The text is fine, the authors performed all the requested revisions. However, in the first version of the manuscript, Figure 1 presented a very clear 3D model of the studied structure. In the revised version of the text, Figure 1 presents only the 3D mesh. It depicts well the mesh, but it shows not so clear the geometry of the structure.

I suggest the authors to present both the mesh and the 3D model, as presented in the first version of the manuscript. After performing this correction, I believe this article may be ready for publication..

Reply：

We gratefully appreciate for your valuable comment. Figure 1 presented in the first version of the manuscript was available in the submitted revised manuscript in July 11, we changed the position of it, which is now displayed in Second 4.1.