CFD Simulation and Optimization of the Leaf Collecting Mechanism for the Riding-Type Tea Plucking Machine

Round 1

Reviewer 1 Report

1. Is the analysis of the trajectory of fresh leaves mentioned at line 18 of the article stated in the article?

2. The abstract section of the article introduces the problems and solutions of the tea picker.Additional relevant test findings are recommended.

3. This paper is a simulation and optimization of the leaf collecting mechanism, and it is suggested to add the introduction of the structure and working principle of the leaf collection mechanism in part 2.1.

4. Figure 2(c) is missing the caption description.

5. Is the text in the article header correct?

6. The article is entitled "CFD simulation and optimization of leaf collecting mechanism for riding-type tea plucking machine", and the cavity structure is optimized using the gas-solid coupling method in section 3.2.1. It is suggested to make relevant additions to the test conditions and methods.

7. In line 311 of the article, is it correct to select a three-factor, three-level test for cavity structure optimization?

8. Part 3.2.1 of the article through the orthogonal test to find the optimal combination of the test factors, should be combined with the results of the necessary analysis of the test factors, so as to highlight the value of the orthogonal test.

9. Suggest further explanation of the content of the picture in Figure 8.

Author Response

Thank you very much for your comments concerning our manuscript entitled “CFD simulation and optimization of leaf collecting mechanism for riding-type tea plucking machine” (ID: agriculture-2338725). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

BRIEF SUMMARY

The paper presents the study of leaf collecting mechanism based on a riding-type tea plucking machine made in Japan. The study intends to carry out CFD simulation and optimization to compare with experimental work.

The manuscript has a length of 18 single-spaced one-column pages including 9 figures, 7 tables and 20 equations. To the reviewer understanding, the paper could accomplish the instructions and standards of the journal in this matter. But please, check it.

Several authors do specify non-conventional email affiliations.

The reviewer believes that the work presented, despite not being a novel technique, it could help to understand tea plucking and leaf gathering machine mechanism. Nevertheless, several aspects of the manuscript could be improved or better addressed, and they are commented as follows. 

BROAD COMMENTS

The reviewer thinks the abstract in the current version could be more completed. It should be answering the question - why this issue is important and what is the purpose of the research? A sentence at the end with the major conclusion would be useful.

This reviewer believes the introduction section includes specific State of Art in order to place authors’ work and select, comment and refer the most significant ones to ensure that the authors are aware of similar research work performed by other researchers. Is this the first time working in this type of research? Is the list of references completed with previous related works of the authors?

Introduction CFD studies presented in references are not connected. Very difficult to assess how the list is completed. Solid explanations of a riding-type tea plucking machine has to be provided, flow dynamics of the leaf collecting, etc.

An important example: reference [10] is related to “catalytic monolith reformer for the production of hydrogen that could be used in fuel cell systems” and reference [11] is related to “the challenges facing CFD in aerospace products”. Both of them are presented in lines 57-58 of the introduction. The question arises: how are these two references an introduction to support the authors’ work, the CFD simulation of leaf collecting mechanism of a plucking machine? This is very important.

Authors have to clarify the new contribution of this work compared with, for instance, reference [15], since the title of this reference feels quite far from the presented manuscript.

In this first reading, the reviewer misses the main reason of this study. The reviewer misses to know the reason/explanation of this investigation, why the purpose of the article is to investigate this type of riding-type tea plucking machine, for instance. Is there any company interested? Why this Japanese machine and no other? The introduction section ought to better point out these matters.

The aim of the paper is not clear in the introduction section, being a brief summary of the references. Discussion from the review of existing studies has to be clearly presented. Please, openly state the hypothesis(es) to test and the research question(s) to answer with your work. For instance, is this one in page 9 line 293: “In the process of tea plucking and leaf gathering, the principle is to maximize the 293 velocity-outlet and stabilize the flow field.”?

ASPECTS TO BE REVISED

##Understanding how it works

Page 1 Lines 44-50: it is very difficult to understand the mechanism and functions of a plucking machine with just this word-by-word description. A scheme is totally necessary and Table 1 is not enough. For instance, how do fresh leaves cut from the tea leaf surface? Also, a whole and in-detail photography is necessary.

Figure 2, how much is l_2 or d, for instance? What is Figure 2(c) the cut of? Very very difficult to understand the air component to be simulated.

## Grid convergence / Mesh representative

Please show an image of the mesh. The mesh quality is necessary to be assessed. The sentence “The total number of grids is 599122, and the grid quality meets the requirements.” is not enough.

The examination of the spatial and temporal convergence of CFD simulations are commonly based on use of Richardson's extrapolation and the CGI calculation. Please, comment why not to use it.

##CFD simulation

It is totally necessary to describe the numerical method use, especially in a simulation and results: (i) The numerical method used must be at least formally accurate in space and specific boundary conditions, (ii) Grid/cell quality assessment and number: justify the element for a good grid quality, (iii) Grid convergence study of different sizes would be good (iv) Stopping criteria (v) Set up of the simulation (v) Software/code used: name and version. There is no evidence of the version used and no evidence of the existence of the appropriate licence to publish this work, if a commercial code is used. Then, I strongly suggest confirming these aspects. This is a weak point of the manuscript.

##Instrumentation

In the testing, Figure 9 and Table 6, how the velocity is measured in the velocity inlet and outlet? There is missing indispensable information regarding to instrumentation: brand, range, accuracy, technical data, etc. Then, this reviewer strongly encourages adding this information. For instance, range and accuracy of the velocity sensors. This reviewer recommends summarizing all in a table.

SPECIFIC COMMENTS

- Page 1 Line 39: What is “4000–5000 kg/person”?

- Section 2.2 is the well-known turbulence theory, it does not contribute much; on the other hand, the reasoning of why the k-epsilon model is used is missing. Please, complete it.

- Update the reference of the software used in the optimization framework.

- Page 10 Line 305: “… the gas-solid coupling simulation method is used to carry out orthogonal experiments” What is “gas-solid coupling”?

- A Nomenclature appendix would be very useful. It would help to understand the notation through the manuscript.

- Page 2 Line 81: “The operation principle of the tea plucking machine is to use the upper and lower serrated knife to repeatedly cut the fresh leaves on the tea tree and send them to the leaf collecting box (bag) on the car through the certain airflow. The use of effective air supply, can make cut down the tea is not damaged, to ensure the quality of plucking fresh leaves.” How does the serrated knife know where to cut? How does it know that they are fresh leaves ready to be plucked?

- Table 3, the units of all parameters should go into brackets. The basis of the Box-Behnken test principle has to be provided together with references, to prove the suitability of this methodology in this case.

- Figure 4, the x-axis is the distance of the outlet? Please, make it clear.

- Table 5 and, lines 316-324 have to be explained. How the interaction effects of factors are known, for instance X1X2? And the meaning of the square factors, X1^2?

- Is the equation (20) an appropriate measure for the uniformity of air velocity to state in line 399: “Under a certain velocity, the uniformity of each air outlet area is basically the same, and the quality of tea can be guaranteed.” . Please, comment it.

- How is the quality of fresh tea leaves after plucking evaluated in this presented work, lines 408-409?

- Page 17 Line 18, “… so the effect of blade collection can be controlled by adjusting the engine speed.” How the engine speed can have an effect of blade collection?

- The design of orthogonal test factors for experiments in the optimization remains “blurred”. A better explanation it would be necessary, and it may be good graphical support.

- In many applications, the industry and manufacturers seem to have reached the optimum in their geometries and properties. Then, my question, and probably an open question, how do manufacturers come to the optimum? And if they do, could they use a similar approach, apart from their own expertise?

QUESTIONS

Other issues and questions to note are:

** Experimental uncertainty analysis. There is no evidence of experimental uncertainty analysis. Then, the required velocity measurement and M calculation should report the uncertainty band, for instance in figure 9 and table 7. Hence, an answer related to this question reported in this rebuttal would be sufficient.

** Under what conditions do the authors consider that the experimental model will not be adequate? Under what conditions will require additional research for the reliability of the results? Hence, an answer related to this question reported in this rebuttal would be sufficient.

** The limitations of the methodology that become clear from the results should also be indicated.

** Which are the stakeholders of your research? What recommendations, guidelines, improvements can be made to stakeholders?

** How can research in the field be continued? There is no future work description.

OVERALL RECOMMENDATION

In general, in the opinion of the reviewer, this paper could bring insights to the field but the paper has to gain in quality and comprehension. The study of this fact can be of importance since it could unify academia and industry.

An improvement can be done to fully understand and have a general idea of the work, the methodology, results and conclusions. In some parts, it is too descriptive and difficult to understand the relation/correspondence of the different results presented in the figures. Specially, to researchers not working exactly with the riding-type tea plucking machine.

By reading de conclusions, it is quite difficult to understand what it is new in this research, since the machine is a commercial made in Japan machine, already used by the authors. It seems that the main contribution is the optimization, but with the CFD presented is very difficult to evaluate, being too scarce.

The complexity of the optimization framework and the use of CFD commercial software are a constraint. This reviewer wonders if manufactures and industry are ready to work in this direction, to use all the methodology presented in this manuscript. The question, then, would be if they would move to these new concepts.

The reviewer believes that the resulting version of the paper attending their comments will gain in understanding and value. In the current format, it is very intricate to get a whole picture in the review, and it would be more appropriate for a congress/conference paper than a research paper.

Author Response

Thank you very much for your comments concerning our manuscript entitled “CFD simulation and optimization of leaf collecting mechanism for riding-type tea plucking machine” (ID: agriculture-2338725). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches.  Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Paper: CFD simulation and optimization of leaf collecting mechanism for riding-type tea plucking machine, by authors: Xiaoxing Weng, Dapeng Tan, Gang Wang , Changqing Chen1, Lianyou Zheng , Mingan Yuan , Duojiao Li ,  Bin Chen , Li Jiang and Xinrong Hu presents numerical investigation of leaf collecting mechanism used in agriculture. The authors used CFD approach to determine internal flow-field of leaf collecting mechanism and the movement trajectory of fresh leaves.

This manuscript could be interesting for the engineers involved in numerical modeling, but this can also be useful for the engineers in agriculture. This paper is suitable for Agriculture journal.

In my opinion, the manuscript can be published, only MINOR review is recommended.

Comments:

1. The abstract reflects realistically the substance of the work. It covers the research context and background, motivation, hypothesis, method, main results, and conclusion, underlining the implications of the main findings. The title is a clear representation of the manuscript's content. In the introductory part, the authors give elaboration of the overall context stating the motivation and the objectives of the work.

2. What is the main contribution of this paper? You should emphasize more in the introduction section. Maybe you can compare your approach to the others previous research in other fields, terrain modeling….

3. You used commercial code for modeling and k-e turbulence model. Please, add some parameters used in modeling.

4. Could you be more specific regarding the accuracy of the proposed numerical model? What about verification of proposed model?

5. The results are presented in a logical sequence and the discussion and analysis of the results are properly elaborated.

6. The claims in the section "Conclusion" are reasonable and supported by the presented results.

7. Validation of the proposed model can be improved by adding some statistical analyses and showing the accuracy of your model. Could you be more specific regarding the accuracy of the proposed numerical model? Use some statistical method for interpretation of the results.

Author Response

Thank you very much for your comments concerning our manuscript entitled “CFD simulation and optimization of leaf collecting mechanism for riding-type tea plucking machine” (ID: agriculture-2338725). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches.  Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Thanks to the authors for your responses. The paper has gained in value, and several parts of it have been improved. The authors have properly answered several reviewer comments, but unfortunately not all of them. The new version of the manuscript is in the revision format of Word, which is difficult to read and not an appropriate format to read.

This reviewer cannot agree with the authors’ response regarding the main reason for this study. The authors do not explain how this investigation is related to their previous works, clarify the new contribution of this work, or indicate if there is any company interest. In lines of the manuscript, "However, there is little research on the structural design of plucking machinery, […]" should point out more vividly the inaccuracy and misinformation in plucking machinery and applications. Responses 2 and 3 are the same, but both questions refer to different subjects: the authors’ previous works and the general state-of-the-art to support the hypothesis to be tested in this work. There is no response: the introduction of CFD studies presented in references is not connected.

Question 3, adding a new reference [17] to the authors I reached it in Chinese, the English version did not work, and I am sorry, but I cannot read it. Then, it is necessary to explain the new contribution of this work compared with that one, because the sentence "However, there is little research on the structural design of plucking machinery [17]" does not seem enough.

The response to question 4 is not convincing. Question 6: Why is the purpose of the article to investigate this Japanese riding-type tea plucking machine? Is any company interested?

IMPORTANT: in the new Table 2, density (gas-air) and viscosity (gas-air), are the values correct? They appear to be mixed up and misplaced amongst themselves. Please, check it. In addition, scientific format and [Pa] is in capital letter.

Questions 10 and 11. There is no image of the mesh yet. This response does not appear to address a commonly accepted mesh quality assessment: ""The total number of grids is 599122, and the average unit mass is 0.7802. The closer the value is to 1, and the overall quality histogram is to the right, the better the grid quality is. So the grid quality meets the requirements."" The response is what COMSOL is and does, but nothing about grid convergence index calculation is discussed in the simulations presented in this paper.

Question 15. There is no answer as to why k-epsilon is used. There are different turbulence models, and it is necessary to tune the one that is most appropriate. For instance, the reasoning can be based on y+, but there is no mention of that.

Question 17, about the gas-solid coupling: "Deformed solids will deform or move under the action of fluid load." Where are the results of deformed solids caused by the action of air at 25 m/s presented in the paper?

IMPORTANT: in the new Table 6, answering question 13, the wind velocity range is up to 30 m/s (to measure 25 m/s) and the intrinsic error is up to 5 m/s, how can the results of Table 7 be one decimal point precise? Despite the detection precision? This has to be clarified. In addition, an image of the sensor and the location where it is installed in the experimental work would be useful and even necessary. And in tables 3, 4 and 7, should they not show the same number of decimals for the velocities?

This reviewer acknowledges the effort made by the authors in editing several figures and tables, adding a new figure 1, updating the abstract and keywords, and rewriting several sections. This reviewer also thanks the authors for their specific answers to several questions.

This reviewer still believes that the resulting version of the paper reflecting their comments will gain in understanding and value. In the current format, there are errors and missing information that can be added to complete it.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf