A Review of the Linear Generator Type of Wave Energy Converters’ Power Take-Off Systems
Round 1
Reviewer 1 Report
The abstract is too general. Please provide some specific results.
A table with acronyms would be good.
The advantages and disadvantages of the WEC have to be summarised in a table.
The paper is very long. You can withdraw the information which is too old. There are a lot of papers from before 2012.
The paper is rather a book, there is more theoretical information.
The discussion pros and cons would be better. Some results about the power generation, which system is better in a location, comparison between of the systems, and so on....
Author Response
Response to Reviewer 1 Comments
Point 1: The abstract is too general. Please provide some specific results.
Response 1: The abstract has been updated.
Point 2: A table with acronyms would be good.
Response 1: A table with acronyms has been added before the references section.
Point 3: The advantages and disadvantages of the WEC have to be summarised in a table.
Response 3: The advantages and disadvantages of the linear generator based WECs have been summarized in a table in the section 7.
Point 4: The paper is very long. You can withdraw the information which is too old. There are a lot of papers from before 2012.
Response 4: The number of pages has been reduced. Some old information has been removed.
Point 5: The paper is rather a book, there is more theoretical information.
Response 5: Half of the theoretical information has been removed.
Point 6: The discussion pros and cons would be better. Some results about the power generation, which system is better in a location, comparison between of the systems, and so on....
Response 6: The discussion of pros and cons has been added already in section 7. The power generation results and deployed location have been presented in a Table in section 6.
Reviewer 2 Report
The article reviews the latest development on linear generators for wave energy conversion. The subject of wave energy conversion is interesting, but my biggest remark goes to the excessive length (75 pages, 30 figures 266 literature references) and descriptive tone of the text. The literature references should be reviewed more systematically and critically, by pointing out only the most important results and possibly detect the disagreements. From the literature you should be able to identify: 1) the major achievements, 2) the general research approaches and methods, 3) the research problems and knowledge gaps, 4) the unsolved questions and debates, 5) the emerging research lines and 6) offer guidelines for future research. In my opinion, the mathematical model for the wave-body interaction of WEC linear generators (section 3) is not really necessary or it should be substantially reduced, all these equations can be found in the given literature references. Sections 2 and 4 give detailed descriptions of the reviewed literature references, however, the authors should be able to build in more of their critical assessment and focus their attention only to the results and conclusions of the referenced studies. I also have the following comments:
1. The article and the literature references should be formatted considering the Instructions for Authors: https://www.mdpi.com/journal/sustainability/instructions
2. Line 95 is repeating line 66 (H. Polinder et al. reference)?
3. For each of the cited literature reference, the most important results and findings should be pointed out. For example: line 59 - "Uppsala University and Oregon State University developed a number of WEC prototypes that were installed in the ocean for performance analysis" - but what was found/concluded in this study? Line 99 - "...where all types of linear generator have been summarized with their effectiveness (Khatri and Wang 2019)" - how much are these effectivenesses?
4. Table 5 classifies literature reference into experimental researches and computer simulation. For experimental studies measurement conditions and uncertainties should be reported while for computer simulations only validated models should be considered. My suggestion is to focus more on experimental studies.
5. The article contains 30 figures and almost all were taken from the referenced studies. This is unnecessary, all these figures can be accessed given the literature reference. Only figures concerning the general working approach (figures 1, 10, 11), the classifications (figure 8) should remain.
6. I have counted 266 literature references. This is an excessive number, you should identify only the most scientifically relevant references and those closely linked to the subject of your review. For instance, you use 10 references from Farrok et al., some being duplicates and others possibly overlapping, and all being conference papers?
Author Response
Response to Reviewer 2 Comments
Point 1: The article reviews the latest development on linear generators for wave energy conversion. The subject of wave energy conversion is interesting, but my biggest remark goes to the excessive length (75 pages, 30 figures 266 literature references) and descriptive tone of the text. The literature references should be reviewed more systematically and critically, by pointing out only the most important results and possibly detect the disagreements. From the literature you should be able to identify: 1) the major achievements, 2) the general research approaches and methods, 3) the research problems and knowledge gaps, 4) the unsolved questions and debates, 5) the emerging research lines and 6) offer guidelines for future research. In my opinion, the mathematical model for the wave-body interaction of WEC linear generators (section 3) is not really necessary or it should be substantially reduced, all these equations can be found in the given literature references. Sections 2 and 4 give detailed descriptions of the reviewed literature references, however, the authors should be able to build in more of their critical assessment and focus their attention only to the results and conclusions of the referenced studies. I also have the following comments:
Response 1: Noted with thanks and appreciation. The detailed comments by the reviewer have been used to improve the quality of the paper.
The mathematical model for the wave-body interaction of WEC linear generators (section 3) has been substantially reduced. Different researchers proposed different mathematical equations and symbols for the same types of linear generator-based wave energy converter (WEC) systems. Therefore, in section 3, the existing mathematical equations have been stated uniquely. The main equations are taken from different articles, but they are developed further in our way (such as the state space model with and without electromechanical coupling). In brief, the outcomes of this section will provide the mathematical foundation for the modelling and upcoming advancement of the linear generator-based WEC.
Point 2: The article and the literature references should be formatted considering the Instructions for Authors: https://www.mdpi.com/journal/sustainability/instructions
Response 2: The references have been appropriately formatted.
Point 3: Line 95 is repeating line 66 (H. Polinder et al. reference)?
Response 3: Line 95 has been removed.
Point 4: For each of the cited literature reference, the most important results and findings should be pointed out. For example: line 59 - "Uppsala University and Oregon State University developed a number of WEC prototypes that were installed in the ocean for performance analysis" - but what was found/concluded in this study? Line 99 - "...where all types of linear generator have been summarized with their effectiveness (Khatri and Wang 2019)" - how much are these effectivenesses?
Response 4: The findings/ conclusions for those studies have been added in the introduction sections. Line 99 (present line 97) has been updated.
Point 5: Table 5 classifies literature reference into experimental researches and computer simulation. For experimental studies measurement conditions and uncertainties should be reported while for computer simulations only validated models should be considered. My suggestion is to focus more on experimental studies.
Response 5: Table 5 has been explained further in sections 6.1 and 6.2.
Point 6: The article contains 30 figures and almost all were taken from the referenced studies. This is unnecessary, all these figures can be accessed given the literature reference. Only figures concerning the general working approach (figures 1, 10, 11), the classifications (figure 8) should remain.
Response 6: Maximum figures have been removed.
Point 6: I have counted 266 literature references. This is an excessive number, you should identify only the most scientifically relevant references and those closely linked to the subject of your review. For instance, you use 10 references from Farrok et al., some being duplicates and others possibly overlapping, and all being conference papers?
Response 6: The number of references has been reduced.
Round 2
Reviewer 1 Report
The authors improve the paper.
Author Response
We would like to thank the reviewer for his valuable and insightful comments on our manuscript and the opportunity for improvements.
Reviewer 2 Report
The authors have addressed my comments and improved the manuscript substantially. Now, the review article extends at 55 pages, and my suggestion is to even further reduce the number of figures, the equations in section 3 as well as the number of references, by keeping only those crucial to the subject of the review.
Author Response
Point 1: The authors have addressed my comments and improved the manuscript substantially. Now, the review article extends at 55 pages, and my suggestion is to even further reduce the number of figures, the equations in section 3 as well as the number of references, by keeping only those crucial to the subject of the review.
Response 1: Noted with thanks and appreciation.
The page numbers have been reduced to 48 by removing 9 figures from the total 15 figures. The number of references has been reduced to 190 from 210. There have been seven equations removed from section 3.
Author Response File: 
Author Response.docx
