Ship Bow Wings with Application to Trim and Resistance Control in Calm Water and in Waves

Round 1

Reviewer 1 Report

The paper presents the study of the dynamic wing application on the ship bow, especially on the effect of the wing’s attack angle in the ship resistance. The manuscript provides the comparison of experimental and numerical results on the ship resistance, trim, and sinkage for the case of bare hull and installation of dynamic wing with various angle of attack. The study results are quite interesting and valuable as a new concept of a future ship with reducing the energy consumption.

However, the authors still need to enrich the physical insights in the manuscript. The text also requires an extensive editing in English writing. Specific comments are presented below,

 

1. Page 4, line 147-149. It is applicable a method to avoid the transient effect, but it is needed to show why the authors chose the method. What is the reason to use the hyperbolic tangent function? And, how were the results changed with using the function? It would be better to show some figures which is comparing the results, with the hyperbolic and other functions, such as linear or square.
2. Page 4, line 156-168. Convergence test. The authors performed the grid and timestep convergence tests. However, the results were fragmentary, and just provided in qualitative comparisons. It is recommended to apply an uncertainty study methods suggested by ITTC, and provide more quantitative and specific analysis on the convergence test. Moreover, provide a specific CFL number, which was just written as small CFL number in the text.

• ITTC, 2017, Uncertainty Analysis in CFD Verification and Validation Methodology and Procedures.

3. Page 6, Chapter 4. It is recommended to divide the results chapter with several sub titles. I think the authors just missed to type the Chapter title of 4.1. and 4.2..
4. Ship speed. What is the design speed of the ship used in the study? (Please show the ship dimensions used in the study for the readers.) The hull form seems like a high-speed ship, but the studies were just done in the Frude number of lower than 0.3. I think the speed need to be faster to study the accurate wing’s effect considering the ship’s main purpose. Is there any reason to perform the studies in the relatively lower ship speeds?
5. Page 6, line 206-210. Foils. How did the authors determined the shape and dimensions of the foil?  
6. Page 7, line 222. What is the acceptable limit? Why did the authors think like that?
7. Page 7, Fig 6. The sinkage is very small magnitude, which seems also quite difficult to be measured in the experiments. Before to discuss the accuracy of the CFD results, it is needed to check the resolution of the sensors used in the experiments first.
8. Page 12, line 345-346. When the ratio of wavelength to ship’s length was 1, the ship motion might be the most severe. Is there any reason to pass the ratio of 1 in the study?
9. The authors adopted the experimental and numerical methods to study the effect of the dynamic wing, and provided the comparison of the two methods. However, it is not seemed that the necessity of the CFD methods in the study, except just to divide the component of the resistances for the skeg, wing, and vane. I think more analysis can be done with the CFD on the phenomena which cannot be measured in the experiments, using the advantages of the CFD simulation, like visualization in the vicinity of the wing to show the mechanism of the wing’s effect on the flow, or to show the free surface deformation around the ship’s bow when the slamming occurred in Fig. 15 and 16, and so on.
10. It is not a sufficient conclusion. The key things found in the study need to be summarized in the conclusions. I recommend rewrite the conclusion, in consideration with the other engineering papers.
11. It is strongly recommended to redraw the figures to distinguish the several data. It is difficult to separate the CFD and experimental results in this form. And, it would be better to show all the figures in normalized values.
12. The parameters in the results are not explained well in the manuscript. Please check, and it is recommended to put a nomenclature at the first page of the manuscript.

Author Response

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Reviewer 2 Report

In this paper the authors propose to use a wing with dynamic angle of attack as ship stabilizer. This stabilizer reduces the resistance and decreases the amplitude of pitch motions. They attach the wing to the ship bow and simulate ship motion in the towing tank with scaled ship model as well as in numerical wave tank. In their experiments the usage of the wing lowers the resistance up to 34% depending on the sea wave length. The authors conclude that the wing has overall positive effect on propulsion performance and reduces wave resistance.

I found the paper worth reading, however, there are some possibilities for the improvement.

First of all, the title of the paper mentions "dynamic wings", but after reading the abstract you realize that the wing is in fact in "in static mode". This is very confusing and I urge authors to define what "static wing" and "dynamic wing" means in their paper. Does "dynamic" mean that you can control the angle of attack automatically?

Second, it is not clear why the dimensions of the vane are not scaled with the size of the ship model. The vane has the significant effect on the experimental results and not scaling it with the model size means adding a lot of noise into the results.

I recommend to accept this paper after the aforementioned issues are resolved. 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have responded and revised well for the manuscript following the comments. The reviewer thinks the paper can be accepted in the present form.

Author Response

We thank the Reviewer for his/her positive opinion concerning the revised paper.