Biomimetics Design Optimization and Drag Reduction Analysis for Indonesia N219 Seaplanes Catamaran Float
Round 1
Reviewer 1 Report
The manuscript is about re-design and optimization of an existing seaplane catamaran float using hydrodynamic characteristics of sailfish. The manuscript has major issues which I'll try to summarize here.
1- The language needs major editing. There are unfinished and sometimes meaningless sentences which makes the reading difficult. For example, in line 36, "... there was no further research, and the idea to design a seaplane [1]." is not a complete sentence. Or lines 60-62, "Based on research ... a higher frictional force" does not express any meaning.
2- The manuscript is about "imitating the hydrodynamic characteristics of sailfish". However, those characteristics are never mentioned. Also, it is not clear if these characteristics are only specific to sailfish or other species of fish and aquatic animals also have these characteristics. Therefore, it is not mentioned why the authors try to imitate sailfish.
3- It is mentioned that "the research aims to increase aircraft efficiency"(see, for example, line 12). However, the mentioned efficiency is never defined. Since seaplanes spend most of their power for flying, it is not clear what the authors really mean by "efficiency".
4- To the best of my knowledge, CFD refers to Computational Fluid Dynamics, not Computerized Fluid Dynamics, as mentioned in line 85.
5- The parameters are not defined. For example, in Table 1, what are Lw1, Height, Width, etc? They must be clearly shown in pictures. Also, there are vague sentences such as "Deadrise angle is an angle at the bottom of the hull ..." (line 166). All of the used terms must be clearly defined.
6- Figures 1-6 are not clear. Besides, Figures 1-5 don't provide any particular information.
7- What are the effects of the new design on other aspects of the seaplane, such as, its landing on water surface and take off, forces and stresses on the body, passenger comfort, etc? They are not discussed in the manuscript. Based on your results, the new design reduces the drag force. However, can the seaplane still land on water surface smoothly? Does its body experience major stresses during landing and take off, which are not present in the original design?
There are also some minor issues, such as spelling errors (e.g., line 52), inconsistency in symbol formats (e.g., v and S, and v and S, in equation (1) and line 99), no reference for equations (e.g., equations (2)-(4)) etc.
Author Response
Dear, reviewer 1
Thankyou for your review, suggestions, and questions. Please see the attachment below for our response.
Best regards,
Prof. Dr. Ir. Yanuar, M.Eng., M.Sc.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The subject matter of the paper is interesting.
Overall, the paper is carefully and clearly written. Unfortunately, on deeper analysis of the assumptions and presented results, a number of questions arise due to imprecise descriptions included in the paper.
The idea presented by the authors is very interesting but its description is very laconic.
The positions of the aircraft axes relative to the water surface, and therefore the floats, are different during takeoff than during landing.
The drag of the floats is important during takeoff. With increasing speed the generated lifting force on the floats decreases, their draught decreases, trim angles also change. The issue is very complex. The authors present only some aspects of the problem.
The authors focus on presenting the results of numerical calculations of three shapes of floats. OK.
It is not clear how the shapes b (the catamaran model with the body of a sailfish;) and c (the floating pontoon with sailfish adaptation) shown in Fig.1. were created.
They are there, but it is not clear how they have been formed. The title suggests that the paper will contain information on how to form such shapes.
The shape b does not have a redan. Why?
The floats themselves are not that interesting. What is interesting are visualizations of flow around.
The quality of the drawings is insufficient.
Fig. 5. should contain an illustration of wave interference that occurs on the floats and should be in the text at point 3.4 Interference Factor Analysis
The authors base their analysis on the grid independence test, but do not present any results.
"Based on the grid independence test results above, at sizing 0.2, the maximum velocity value is 4.97 m/s. Then the maximum velocity value tends to be constant. Based on this, the value of 0.20 can be chosen as the sizing for future simulations."
No drawings showing the grid in the vicinity of the object.
Description of the numerical method very brief. Based on the laconic description provided, it appears to be correct.
The authors model turbulent flow but provide no information about the turbulence conditions at the inlet to the computational area.
I would have objections to the boundary condition in the inlet cross section. Rather, it should be a velocity condition in the case under study.
Figure 4: No redan at 30 deg angle. Why?
Analyzed floats have different capacities. Their displacement depends on the weight of the plane with floats and therefore the water line in each case will be different.
Non-closed system of equations 8-13.
lambda not defined,
H not defined,
Ca not defined,
AT not defined,
Rn not defined,
Lwl not defined,
B not defined,
T not defined.
Figure 7: What is the definition of the drag coefficient used in this figure?
Figures 2 and 3 would be more useful as an illustration of Figure 8.
Inconsistencies- Figures 2 and 3 are based on pitch angle and figure 8 is based on bow or stern height.
Results for trim-Figure 8.
"The effect is because every trim change that occurs will change the area and volume of the hull immersed in water and will affect the viscosity and wave resistance."
It seems that this approach is not very sensible. It means that in each of these cases the load capacity of the float is different.
Rather, floats should be trimmed at a constant load.
"Figure 9: Total drag vs. deadrise angle variation of the initial design compared to Wipeline® 13000 design."
Why is the new drag greater than the pattern drag (design compared to...)?
Figure 9, Shape with deadrise angle 30 deg has no redan.
Deadrise angle, if in this case also the load capacity of the float is different then it is difficult to compare this with each other.
The paper is interesting and contains a lot of relevant information. The problem is the inaccurate definition of the assumptions making it difficult to interpret the results.
The paper can be published after clarification of ambiguities shown by the reviewer.
Author Response
Dear, reviewer 2
Thankyou for your review, suggestions, and questions. Please see the attachment below for our response.
Best regards,
Prof. Dr. Ir. Yanuar, M.Eng., M.Sc.
Author Response File: Author Response.docx
Reviewer 3 Report
The manuscript reports a Computational Fluid Dynamics (CFD) study on the biomimetic design optimization via trim, deadrise angle, and clearance on the Indonesia N219 seaplane catamaran. The drag reduction analysis is also reported. The main goal, as clarified in the title and introduction, is to prove that with the adaptation of biomimicry design, a significant drag reduction may be generated. It is an interesting topic that may be applied to the future design of aircraft, and the presented results are highly novel.
However, the CFD results show that the drag reduction relative to the redesigned shape of the surface. There is no explanation of the uncertainty associated with the measurement of model dimensions, pressure drop, flow rate, and calculation of Reynolds number based on the measured variables.
Secondly, I don't see enough references and most advanced studies are cited in the Introduction section. General influence factors only are mentioned. For the citation of the findings, please align the statement rather than some using "research", some giving the real name of the author. And please cite more advanced studies.
Next, regarding the design of three different shapes, the parameter of Wipline might indicate a bit difference comparing with the other two models. So how these Lwl and Height may act on the flow resistance is still worthy considerations.
Next, Section 2.1 to 2.4 are more like hypotheses for the whole manuscript, however, no valid statement or evidence for its applicability for this study. And the reason why these values of angles for trim, deadrise, and clearance validation are chosen is not clearly stated. It would be better to refer to the particular citations so that the readers can follow the discussion.
Please elaborate more on why such boundary conditions, inlet and outlet sources, water/air pressure, flow conditions of fluids are selected. All these factors are all matter in your following discussion of the research as well as simulation works thru CFD. Besides, the description of the scenarios is not academic enough. I would recommend authors may improve the English language and style also during the revision.
Other than above mentioned critical issues, this manuscript has also a number of drawbacks, which must be eliminated, before it may be considered for publishing. The reviewer's comments and recommendations are brought below.
- Table 4 format is gone, the title is also not a finished sentence, please re-align.
- Line 213-219, please suggest whether relative ASDM could be applied for the simulation, and control factors are suggested to put into the table also, which is not limited to the density values, fluid temperature, viscosity, etc., as there is no reference here.
- Line 271-276, please change the writing styles instead of bullet point.
- The figures of ANSYS Fluent, a more explanatory figure, are highly recommended to put in for the elaboration for different factors of hypotheses, including trim, deadrise, and clearance validation.
- The discussion from 3.3 to 3.4 are difficult to match with the results obtained and indicated in Figure 8-10, subfigures e.g., (a) & (b) or tables are suggested to provide for better comparison as well as result statement.
- Other than the presented result from the CFD dynamic simulation, more discussion regarding the hypotheses given in Chapter 2 needed to be given. And before the Cconclusion section, there is suggested to have another individual paragraph for the discussion.
- The conclusion is a bit long, please reorganise as the last comment mentioned.
- Reference please try to include more recent publications in your Reference, and please double confirm the ref. 27 for its format.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
Thank you for the response and the changes you have made to the manuscript. I still have the following comments.
1) I think any change of the float without considering the seaplane equilibrium and performance during landing, take-off, and taxi on water surface is of no value. Besides, the results are obvious to me, and probably many others, that changing the shape of the float to a more hydrodynamic form, such as a fish body, will reduce the drag. I think the optimization must be done by considering the equilibrium and performance of the seaplane as a constraint.
2) I don't understand what is the point of rewriting the equations in the previous format, without any changes!
3) The language still needs major improvement.
Author Response
Thank you for the response and the changes you have made to the manuscript. I still have the following comments.
1) I think any change of the float without considering the seaplane equilibrium and performance during landing, take-off, and taxi on water surface is of no value. Besides, the results are obvious to me, and probably many others, that changing the shape of the float to a more hydrodynamic form, such as a fish body, will reduce the drag. I think the optimization must be done by considering the equilibrium and performance of the seaplane as a constraint.
2) I don't understand what is the point of rewriting the equations in the previous format, without any changes!
3) The language still needs major improvement.
Author Respond:
Thank you for your response and following comment. We would try to answer them in the best possible way.
Author Respond:
- Thank you for the comments and suggestions. Yes, we agree that changing the float must consider the effect and the equilibrium or even the performance of the seaplane. As a first step, we are currently trying to focus on the drag to validate our theory about the biomimetics approach for design engineering, and this manuscript represents those theories. If we try to include it on the effect and the state of the seaplane, it would have to cover a lot more intensive study such as; the strength of the structure, the aerodynamics performance of the float and the seaplane combine when landing, take off, and taxi, etc. We try to convince a better design than the commercial design used for a decade—many more to come for future studies.
- Thank you for the comment, we will replace it in the latest version.
- Thank you for the comment, we have tried our very best to improve the language for now. We decided to use author service from MDPI for English language editing after the reviewer process is final to meet the standard of MDPI processes.
Reviewer 3 Report
The new version has better improvement regarding the CFD stimulation, which makes the article structure more acceptable for the readers. Still some minor improvements must be made before further acceptance:
1) Please align the figure size and the labeling within the figures in a united format. Can refer from previous Process publications.
2) I suggest you can put one calculation progress to indicate the following result and how it is obtained with different parameters. Whereas currently is still with formula only, which is not valid for the supporting, or you also can put in your supplentary information and have 1-2 sentences for the instructions.
Overall, this new manuscript has more new input as well as insight comparing with the last version. Congrats!
Author Response
Author Respond:
- We tried our best to configure the figure size and labelling accordingly, but there is a case where the word file will be re-configured on its own, depending on the version. However, if there are any incorrect configurations, please let us know.
- Any supplementary information regarding the formula can be found in the different paragraphs (before and after the formula). As suggested in the paragraphs, the reader can read further information within the given reference.
Round 3
Reviewer 1 Report
Dear authors, you are optimizing a system without considering its application. Therefore, you do not consider all the constraints present in the system. This does not make sense. You can still use more and more optimum shapes and reduce the drag still further. However, what is the use of your design if the seaplane does not have equilibrium?
Author Response
Thank you for the questions and suggestions that have been given. In this case, all we can provide is a certainty that the research we are doing is an investigation that gives novelty to the float, which is the part of the seaplane and not the whole of the plane. However, to find out other aspects that deal with the equilibrium possessed by the aircraft, more cooperation is needed for the sustainability of the research. We have planned to collaborate with the Indonesian Agency for the Assessment and Application of Technology (BPPT) for the sustainability of the research so that the model can test it at the Nurtanio aircraft factory.
We have brought our discussion to experienced parties. If the multiphase factor changes in the floating pontoon design on the aircraft flight process, most of these variables are the pilot's level of familiarity with the environment and the aircraft itself. This variable is related to the interaction between the seaplane system and the aerodynamic system, which will regulate the stability when the airplane takes off and landing so that it involves other departments, considering that we are from the naval engineering department, collaboration is needed with the aerodynamics department for further research. Therefore we have planned the completeness of research in partnership with trusted institutions in Indonesia. However, this manuscript is the first step to further investigate the new design pontoon interaction with seawater as the primary focus by considering the dimension, trim angle, clearance, and deadrise angle.
Round 4
Reviewer 1 Report
None.
Author Response
Dear Reviewer,
Thanks for the comments and suggestions. Your input is very valuable for the continuation of our further research.
