Research on the Accumulative Damage of Flywheels Due to In-Space Charging Effects
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors researched flywheel bearing damage caused by electrical discharge currents under the influence of cosmic radiation. The problem of electrical discharges in bearings is better understood and can be recognized, monitored, and solved. One of the main challenges is early identification because many factors, such as voltage, load, speed, and lubricant type, can affect electrical damage. There is a need to implement a fast method for detecting electrical discharge currents in bearings because they can lead to electrical erosion over time. In the title of their work, the authors emphasized that these damages are cumulative. However, they did not present the laws describing the accumulation of these damages. Generally recalling, damages can occur suddenly or intermittently. Damages can also be cumulative. The stated goal of the work was to improve the reliability of on-board flywheels.
The work is interesting but, unfortunately, has many substantive shortcomings. I will focus on the most important ones and discuss them briefly.
In the first sentence of the introduction, the authors mentioned the construction of the flywheel. It may be better to emphasize this is the flywheel assembly intended for use in space.
In the last sentence, the authors mentioned "the life and reliability of flywheel." It would be better to replace the word life with the term lifetime or lifespan.
On the second page, there are no dots ending the sentences between the words: "overlooked Based," "big data Preliminary," and "flywheel shaft system Finally."
In ordinary rolling bearings, fatigue damage accumulates during the use. I believe that damage caused by electrical discharges is different than fatigue damage. The small amount of electrical energy needed to initiate them results primarily from the small contact area between the rolling elements of the bearing and their raceways.
On page three, incorrect designations of parameters such as Vsh3asym, Vsh-ESD, Va, Vb, Vc, Vno, ia, ib, and ic appeared without proper subscripts.
V_a, V_b, and V_c are stator terminal voltages of a star-connected three-phase induction motor. V_no are motor back-EMF_s. i_a, i_b and i_c are stator currents.
Figure 2 shows a schematic diagram of the voltage inverter with RLE-type load (resistor-inductor-electromotive force). The diagram lacks the switching logic block and the designation of the six IGBTs (insulated gate bipolar transistors). The two capacitors in this diagram are not needed. Equations (1) refer to a star connection. In the case of induction motors, such a connection is preferred only during start-up.
In the first sentence on page four, it is better to rewrite "Adding both sides of equations (1) gives ... ." In the second sentence, the authors should note that they have applied "Kirchhoff's first law." The authors should underline they have written Equation (4) for star-connected stator winding. In the description of the acronym EDM, replace Electro with Electrical or Electic.
Also, incorrect symbol designations without proper subscripts appear on page four, namely CWR, CWF, CRF, Vsh3 CM, and Vsh-CM. Such wrong designations also appear later in the manuscript text, so I ask the authors to read the manuscript carefully and correct them.
On page eight, the symbol HC with an incorrectly used subscript indicates central film thickness.
It seems that generalizing equation (5) using equation (6) is incorrect because H_c is primarily proportional to W^(γ_c), where W is the load parameter (expression for lubricant film thickness).
On page eight, there are also incorrect parameter designations. For example, I distinguish Edischarge and HC.
The authors have written Equations (7) and (8) incorrectly. They have made an obvious schoolboy error in equation (7).
Given the above, I cannot, with regret, recommend this work in its current form (also bearing in mind the personal good of the authors) for publication.
Author Response
Thank you for your valuable feedback. We have carefully reviewed the document and addressed the issues you mentioned. The changes have been highlighted in red in the manuscript. Specifically:
Comment 1: In the first sentence of the introduction, the authors mentioned the construction of the flywheel. It may be better to emphasize this is the flywheel assembly intended for use in space.
Response 1: According to the reviewer's comments, the first sentence of the introduction has been changed to “The flywheel designed for space applications, consists of a motor, bearing components, a wheel body, and a housing.”
Comment 2: In the last sentence, the authors mentioned "the life and reliability of flywheel." It would be better to replace the word life with the term lifetime or lifespan.
Response 2: According to the reviewer's comments, the first sentence of the introduction has been changed to “Therefore, the lifetime and reliability of flywheel bearing components have always been a research hotspot.”
Comment 3: On the second page, there are no dots ending the sentences between the words: "overlooked Based," "big data Preliminary," and "flywheel shaft system Finally."
Response 3: It has been modified in the manuscript.
Comment 4: In ordinary rolling bearings, fatigue damage accumulates during the use. I believe that damage caused by electrical discharges is different than fatigue damage. The small amount of electrical energy needed to initiate them results primarily from the small contact area between the rolling elements of the bearing and their raceways.
Response 4: According to the reviewer's comments, we added description of electrical discharge damage in bearings in the introduction, “Unlike traditional fatigue damage, which accumulates over time due to repeated load cycles, electrical discharge damage in bearings is primarily caused by the localized effects of electrical currents, often resulting from small contact areas between the rolling elements and raceways.”
Comment 5: On page three, incorrect designations of parameters such as Vsh3asym, Vsh-ESD, Va, Vb, Vc, Vno, ia, ib, and ic appeared without proper subscripts. V_a, V_b, and V_c are stator terminal voltages of a star-connected three-phase induction motor. V_no are motor back-EMF_s. i_a, i_b and i_c are stator currents.
Response 5: It has been modified in the manuscript.
Comment 6: Figure 2 shows a schematic diagram of the voltage inverter with RLE-type load (resistor-inductor-electromotive force). The diagram lacks the switching logic block and the designation of the six IGBTs (insulated gate bipolar transistors). The two capacitors in this diagram are not needed. Equations (1) refer to a star connection. In the case of induction motors, such a connection is preferred only during start-up.
Response 6: The Figure 2 has been modified, please refer to the manuscript for details.
Comment 7: In the first sentence on page four, it is better to rewrite "Adding both sides of equations (1) gives ... ." In the second sentence, the authors should note that they have applied "Kirchhoff's first law." The authors should underline they have written Equation (4) for star-connected stator winding. In the description of the acronym EDM, replace Electro with Electrical or Electic.
Response 7: It has been modified in the manuscript.
Comment 8: Also, incorrect symbol designations without proper subscripts appear on page four, namely CWR, CWF, CRF, Vsh3 CM, and Vsh-CM. Such wrong designations also appear later in the manuscript text, so I ask the authors to read the manuscript carefully and correct them.
Response 8: It has been modified in the manuscript.
Comment 9: On page eight, the symbol HC with an incorrectly used subscript indicates central film thickness.
Response 9: It has been modified in the manuscript.
Comment 10: It seems that generalizing equation (5) using equation (6) is incorrect because H_c is primarily proportional to W^(γ_c), where W is the load parameter (expression for lubricant film thickness).
Response 10: Equation 5 is referenced from the professional book Encyclopedia of Tribology. We have revised the description of this section, please refer to the manuscript for details.
Comment 11: On page eight, there are also incorrect parameter designations. For example, I distinguish Edischarge and HC.
Response 11: It has been modified in the manuscript.
Comment 12: The authors have written Equations (7) and (8) incorrectly. They have made an obvious schoolboy error in equation (7).
Response 12: It has been modified in the manuscript.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsAuthors conducted a study on the electrical damage to flywheel bearings caused by space charging effects, which pose a significant challenge to flywheel systems in space. Understanding space charging mechanisms and developing efficient recommendations is crucial for ensuring the reliability of flywheel-based energy storage in space. Given the limited existing research on this topic, this study is important for expanding understanding in the field.
However, the authors should review the entire document to ensure proper formatting of the expressions according to standard scientific conventions, where variables are italic, and units are in non-italic. Also, ensure proper formatting of indices and exponentials. For example, the unit for area should be written as cm2 (not cm2).
Author Response
Authors conducted a study on the electrical damage to flywheel bearings caused by space charging effects, which pose a significant challenge to flywheel systems in space. Understanding space charging mechanisms and developing efficient recommendations is crucial for ensuring the reliability of flywheel-based energy storage in space. Given the limited existing research on this topic, this study is important for expanding understanding in the field.
However, the authors should review the entire document to ensure proper formatting of the expressions according to standard scientific conventions, where variables are italic, and units are in non-italic. Also, ensure proper formatting of indices and exponentials. For example, the unit for area should be written as cm2 (not cm2).
Response: Thank you for your valuable feedback and for pointing out the importance of adhering to standard scientific conventions. We have carefully reviewed the entire manuscript and made the necessary revisions to address your comments. Specifically, we have:
Variable formatting: Ensured that all variables are presented in italic font, following standard scientific notation.
Unit formatting: Revised all units to non-italic font and corrected formatting inconsistencies, such as using "cm²" instead of "cm2" for area.
Indices and exponentials: Standardized the formatting of indices and exponents throughout the manuscript to ensure clarity and consistency.
We greatly appreciate your attention to these details, which significantly enhance the quality and readability of our manuscript. Please do not hesitate to let us know if there are any further adjustments required.
Author Response File: Author Response.docx
Reviewer 3 Report
Comments and Suggestions for AuthorsDear authors,
My review is attached.
Best regards.
Comments for author File: 
Comments.pdf
They are listed in the above document.
Author Response
Comment 1：In the title’s content should be included a “the” between on and accumulative. The abstract is relevant, but the sentence “Preliminary experiments are conducted to validate SOME of the research results.” sounds odd, at least. Research results are implicitly ALL validated. Otherwise, they are not results.
Keywords should be alphabetically given and scientifically relevant, I suggest to change “Flywheel; Bearing; Electrical Damage”, which are also presented in title, to some more relevant. Here is no need of capital letters, as well.
Response 1: It has been modified in the manuscript, please refer to the manuscript for details.
Comment 2: The number of subchapter 1.1.1. is wrong. Please insert some text between chapter 2 and 2.1 to present the chapter content, at least. (Please, check the whole paper for the same issue.)
Response 2: We have carefully reviewed the document and addressed the issues you mentioned. Specifically:
Subchapter numbering: The numbering for subchapter 1.1.1 has been corrected to ensure consistency throughout the manuscript.
Content between chapters: We have added introductory text between Chapter 2 and Subchapter 2.1 to provide a proper transition and overview of the chapter content.
Document-wide review: A thorough review of the entire manuscript has been conducted to identify and correct similar issues, ensuring structural coherence and clarity.
We appreciate your attention to these details and your suggestions for improving the quality of our manuscript. If you have any additional comments or recommendations, we would be happy to address them.
Comment 3. Please provide bigger dimensionally images in figures, and check them for clarity (6, 7, 8). Also, change “Motor Current, Motor Current Noise, Flux” etc. with simple symbols (suggestion) I, IN, Φ etc. (Please, check the whole paper for the same issue.)
Response 3: We have provided a clearer images, please refer to the manuscript for details.
Comment 4. Please explain all the equations terms and change their symbols with well-known ones, Wikipedia is enough clear in this aspect and it can help. Also, “x” symbol suggests vector multiplication, usually “ . ” is involved (even in text). (Please, check the whole paper for the same issue.)
Response 4: Each equation has been updated to include a clear explanation of all terms and variables, ensuring that their meanings are explicitly stated within the manuscript.
Comment 5. Please, leave space between symbols, values and units: “V=IR=0.38V” à V = I . R = 0.38 V etc. (Please, check the whole paper for the same issue.)
Response 5: It has been modified in the manuscript, please refer to the manuscript for details.
Comment 6. Page 10: “… according to equation 10/11/12 …” à … according to equations 10, 11 and 12 …, “ / ” suggests or meaning.
Response 6: It has been modified in the manuscript, please refer to the manuscript for details.
Comment 7. Please use all over the configuration 10-9 instead of 10e-8, 10^-8 or others. (Please, check the whole paper for the same issue.)
Response 7: It has been modified in the manuscript, please refer to the manuscript for details.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsGiven that the authors have corrected all the ambiguities pointed out by the reviewer that appeared in the first version of the manuscript, I think that the publishing house may submit the corrected manuscript for publication.
Author Response
Given that the authors have corrected all the ambiguities pointed out by the reviewer that appeared in the first version of the manuscript, I think that the publishing house may submit the corrected manuscript for publication.
Response：Thank you for the reviewer's review. We have made revisions to the manuscript.
Reviewer 3 Report
Comments and Suggestions for AuthorsDear authors,
My comments are attached.
Best regards.
Comments for author File: Comments.pdf
They are listed in the above attached document.
Author Response
Please see Reply.pdf and manuscript for details.
Author Response File: Author Response.pdf
