Numerical Investigation of Aerodynamic Interactions between Rigid Sails Attached to Ship
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe author describes the interaction between two sails installed on a commercial vessel and he optimise their distance and sail settings.
Contents
Grid convergence study
Has a grid convergence study be performed? Only checking one result against a singular value might create an illusion of confidence.
Wind gradient
Referring to Fig. 8 and Eqs (3), the wind gradient is not smooth (first order of the velocity distribution is not continuous). This strikes as not quite as observed in nature. Since this wind distribution over height is used as boundary condition, this sharp bend might have an effect on the velocity distribution in the area of interest. Has this been checked?
Introduction, second paragraph
What is the relevance of the observation regarding autonomous ship operation with regard to the topic investigated?
Reproducibility and Verifyability
It must be possible to reproduce and verify all results presented in a scientific paper. The author is therefore asked to present the section shape of the wing sail and a side view of the vessel in his paper. The sail geometry in Figure 2 might be better presented as a (simple) technical drawing. All geometries used should be made available and their availability given in the Data Availability Statement.
The definition of the Reynolds number should be added (at least the reference length mentioned) and the viscosity and density of the air used added.
The dimensions of the computational domain for the isolated sail without hull should be stated. The author might also want to show the boundary conditions in the relevant figure (at least in Figure 7).
The position of the Sail-1 is given with reference to AP, but nowhere the position of the AP in relation to the ship is given.
Author Contributions
The second and third authors contributed in the area of reviewing, editing and supervision. If reviewing and editing would entitle a person to claim authorship of any scientific paper they reviewed or edited, all scientific reviewers and final editors could claim authorship! The author might want to reconsider his choice.
References
The CFD software used should be included in the References section.
Please add a reference, where the deisgn of the hull came from - or who designed the hull.
Please include a (additional) reference to the ‘previous study’ mentioned in L.333.
Introduction, L.50
‘Thus, this method of setting angles might not yield the optimized angles.’ This observation is known by every keen sailor and thus cannot be seen as a new insight.
Results, L.146
‘Figure 10 shows the changes in CL, CD and Cx […]’: The Figure 10 does not show the changes, but the absolute values …
Results, L.188
‘The difference due to difference of Δl is up to 0.1 and the effects of Δl are not significant.’: Let us look at the values for γ = 60° – the average thrust coefficient for Δl = 2c is 1.4, hence the relative difference is 0.1/1.4 = 7%. In the field of ship propulsion, this is significant! Also that statement seems to be in contradiction to the results shown in Figures 14-17 and 21, where there can be seen an obvious difference in Cx for the left (Δl = 2c) and right (Δl = 4c) diagrams! Also it is later stated: ‘These results indicate a difference in behaviour depending on Δl.’ (L.236)
Ratio Cx (ave.) / Cx (single)
The author might want to explicitly clarify, if the value Cx (single) used for this ratio, is for the same value of γ, α1 or for α2. This is not clear from the text.
Downwind sailing
Has the author tried to set the secondary sail at an angle different to 90°?
Presentation
The SI units for angles is ° and not ‘deg’ and for forces N (and not kN as used in Table 1).
Please include the old goal of the IMO's GHG reduction target for the benefit of the user, who is not accustomed to it. Thanks.
Please include a sketch, how the forces F, D and Fx are orientated with regard to the vessel and the wind direction, e.g. as a second figure in Figure 1.
Please add the distance from AP (or bow) – a parameter used later – to Figure 1.
In the reviewers view, it would be easier to follow the flow of the article, if the part discussing Figure 21 (L.254ff) is moved to the start of the section 4.2.5.
Actually the findings presented in L.239ff is known to every respectable sailor …
All tables
- Traditionally the units are not set into parenthesis when standing in a column on their own.
- Dimensionless units are traditionally marked with a (long) hyphen: –
Table 1
- To aid readability, the author might want to use the traditional marker for average values: an overbar, hence CD (ave.) will become $\overline{C_D}$ in LaTeX. The author might also want to consider to use Cx0 (or just Cx?) instead of Cx (single). Since there is only one density used in the whole article, the author might drop the subscript in ρa.
Table 3
- Why is the symbol for the vessel's length given, but not for her beam, depth, draft and block coefficient? By the way, the block coefficient is irrelevant regarding the topic of this paper.
- It should be ‘Block coefficient’ (‘l’ instead of ‘r’).
All figures
- All axis need a label with the values displayed – and their units.
- Traditionally the units are set in square brackets and not (round) parenthesis.
- Since this article is made available online, the author might want to consider to use colours.
- The unit should be part of the label and not attached to the axis.
- Figures showing the corresponding data should have the same scaling for all axis to help the reader who wants to compare them, e.g. 3 and 10 to name one group.
Figures 3 and 10:
- The author might want to connect the single data points by lines to help reading those figures.
- The author might want to add a CL–CD diagram, which not only shows the section characteristics better, it will also show the position, where the drag becomes greater than the lift by including a line CL = CD.
Figures 6 and 11:
- The authors might want to use the same presentation for both figures (and remove the grey background in Figure 11).
- It would be really helpful in grasping these pictures, if the author could include a symmetry line along the deck of the vessel.
Figures 14-17, 21 and 28:
- Please use the same scale for the horizontal, vertical axis and the colour bar in all figures in this group to help in comparing these diagrams.
- The author only shows a small area out of the whole α1-α2 parameter space investigated. The author might want to show a broader overview of the behaviour of two rigid wings interacting with each other.
- Please give the actual values for α1 and α2 inside the diagram instead of ‘best’.
Figures 18 and 19:
- It is not clear, why settings for α1 and α2 are discussed in the text, which are not giving the best thrust coefficient. The author might want to argue his selection.
- It might be helpful to mark the four cases shown in Figures 18 and 19 in the diagrams of Figure 21 (e.g. by dashed horizontal and vertical lines).
- The case shown in Figure 18 (left) is on the very border of the diagram from Figure 21 (left).
- The case shown in Figure 19 (right) is not even inside the diagram from Figure 21 (right)!
Figures 20, 22, 24, 26 and 29:
- It would be immensely helpful, if the authors could include the shape of the vessel's deck as an outline and the symmetry line in these diagrams!
- The units are given in the legend and it is not necessary to repeat them in the caption.
Figures 23, 25 and 27:
- Should not these diagrams look like Figures 18 and 19?
Comments on the Quality of English LanguageSome sentences needs clarifications or rewriting:
- ‘The research findings indicate that the innovative optimized angle of attack for maximizing thrust is revealed for tailwind conditions.’ (L.16ff)
- '[…] thrust in the relative wind direction' (L.45f): Traditionally the thrust is in direction of the vessel, which is the only component helping to move the vessel in the desired direction.
- 'It shows that the thrust acting on the sails generally decreases compared to a single sail due to these mutual interference effects.' (L.52f): If the combined thrust acting on all sails is less than the thrust of one single sail, why bother to install more than one sail? The author probably means something along this line: ‘When combining multiple sails, the thrust generated by each single sail decreases compared when calculated for each sail isolated.’
- 'The wind direction changes along the sides of the vessel from the stern.' (L.149): It is not clear, what the author might want to tell the reader here.
- ‘In L-shaped arrangement, the absence of the fore side sail directly behind the aft side sail […]’ (L.337f): What does the author want to tell the reader? The fore sail is still there (not absent) …
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors1. There is no specific result of this paper in abstract. There should be clear results, conclusions, such as the general influence effect between the sail and the hull, and the particular best angle of two sails when the maximum thrust force occurs and so on.
2. The results shown in the abstract should be consistent with the conclusions of the study. One suggestion for the authors: As the CFD method is used in this paper, the side force caused by the sails can be considered, and the relevant analysis as well as discuss can be given. In fact, the side force may cause the whole different results.
3. Provide outline of the paper - before section 2.
4. It seems there are insufficient literature review in “Introduction” part. The introduction part should be more clearly about the background and the research status referring to this paper, most importantly, the limitation of current research, the significance, contribution, and innovation of this paper. The summary of literature should be presented in a tabular form. It will provide a clear direction for the research.
5. The meaning of x, y, X, and Y of the coordinate system in Figure 1 should also displayed in Table 1.
6. In part 2.2, there are lack of sufficient description about the validation of CFD accuracy, the initial condition, simulation process and the reason using reference [9] as comparison is not given. In fact, the accuracy of your CFD model is the foundation of the whole paper, this part is quite important.
7. At line 103, “This research assumes a near-future scenario of fully wind-powered, autonomously operated large cargo ships and does not consider any superstructures on deck.”. the words “fully wind-powered” is confusing, as the speed of the ship will cause the different relevant wind speed, and then the result of rigid sail, are the ship speed is not considered?
8. At section 3.1, is there the grid independence verification conducted?
9. It is suggested to increase the number of references.
Comments on the Quality of English LanguageNo comments
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn the paper entitled “Numerical Investigation of Aerodynamic Interactions between Rigid Sails attached to Ship”, the authors assessed the performance of two different configurations of rigid sails. In general, the language should be improved to enhance the clarity and reliability of the manuscript, technical terms should be revised, and the verification study should be performed to ensure the reliability of the obtained numerical results. The following issues should be addressed before the publication in the Journal of Marine Science and Engineering:
1. The technical terms should be in accordance with the ITTC nomenclature. There are some uncommon terms throughout the manuscript such as: ship’s body, brock coefficient, wing sails are acting as resistance, etc.
2. Please provide higher-quality figures.
3. The literature review is weak and it should be thoroughly revised. More relevant to the topic and recently published papers should be included to give an overview of the research carried out so far and provide a research gap.
4. Nomenclature should be given at the beginning or the end of the manuscript.
5. More details on the CFD calculation should be given. The mathematical and numerical model is missing. The applied boundary conditions, physical setup of the simulations, and details on the grid are missing as well both for the single sail and sail attached to the hull.
6. Revise the sentence “The vessel type is a Cape size Bulker because it doesn’t need higher speed than other ship types”.
7. Provide a more detailed body plan of the hull with an adequate number of the cross sections.
8. The novelty of the proposed research in comparison to the previously published similar studies should be highlighted.
9. The verification study is missing. The results of the numerical uncertainty should be provided in order to ensure the reliability of the obtained numerical results. Consider the following papers:
Saydam, A. Z., Küçüksu, G. N., İnsel, M., & Gökçay, S. (2022). Uncertainty quantification of self-propulsion analyses with RANS-CFD and comparison with full-scale ship trials. Brodogradnja, 73(4), 107-129.
Mikulec, M., & Piehl, H. (2023). Verification and validation of CFD simulations with full-scale ship speed/power trial data. Brodogradnja, 74(1), 41-62.
10. How were the configurations of sails determined?
11. There is a lot of space for the improvement of the Engish language to ensure the reliability and clarity of the manuscript.
12. The Y-axis title should be added to Figure 13.
Comments on the Quality of English LanguageThere is a lot of space for the improvement of the Engish language to ensure the reliability and clarity of the manuscript.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThe paper presents Numerical Investigation of Aerodynamic Interactions between Rigid Sails attached to Ship. Some comments can be found as follows:
1. The abstract must be focused on what is done in the paper, method, techniques, results without general sentences.
2. The introduction must be improved, by searching scopus, there are hundreds of papers published.
3. The novelty must be clear based on the previous point.
Otherwise, the paper is clear and easy to follow.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for Authorsno futher comment.
Comments on the Quality of English Languageno
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have addressed most of my comments. Therefore I recommend the publication of the manuscript.
Comments on the Quality of English LanguageThere is a lot of space for the improvement of the Engish language to ensure the reliability and clarity of the manuscript.
