Optimization of the Housing Shape Design for Radiated Noise Reduction of an Agricultural Electric Vehicle Gearbox

Round 1

Reviewer 1 Report

The manuscript is very interesting. The results presented may be useful to other researchers. The presented topic is part of the solution to the current problems of mechanical engineering. There is currently a lot of pressure to introduce low-emission vehicles, also in agriculture.

However, the manuscript has several shortcomings:
1. The abstract should be expanded with the short purpose of the research.
2. The introduction is very concise and I have no major comments except one. The aim of the work at the end of the introduction should be moved to the section where the aim and methodology of the research are defined.
3. The aim of the research should be clearly emphasized and appropriate theses of the experiment should be defined.
4. The test methodology should be described in such a way that modeling can be reproduced in other conditions.
5. Many authors are engaged in research on noise emissions, so it is worth adding a section with a discussion on the results obtained.
6. Pay more attention to spelling. Not all phrases are understandable. Consider language proofreading by a native speaker.

The manuscript can be published after minor changes have been made.

Author Response

The manuscript is very interesting. The results presented may be useful to other researchers. The presented topic is part of the solution to the current problems of mechanical engineering. There is currently a lot of pressure to introduce low-emission vehicles, also in agriculture.

 

However, the manuscript has several shortcomings:

1. The abstract should be expanded with the short purpose of the research.

→ A sentence has been added at the beginning of the abstract to emphasize the purpose and background of the research (from line 17).

1. The introduction is very concise and I have no major comments except one. The aim of the work at the end of the introduction should be moved to the section where the aim and methodology of the research are defined.

→ Generally, the importance of research, the differentiation of previous studies and the objective of study are described in the introduction. In my opinion, it is correct that the aim of the work is located in the introduction before explaining the research method.

1. The aim of the research should be clearly emphasized and appropriate theses of the experiment should be defined.

→ In the last paragraph of the introduction, it has been revised to emphasize the research objectives and the detailed explanation for the methodology has been added (from line 88 to line 99)

4. The test methodology should be described in such a way that modeling can be reproduced in other conditions.

→ I have added the methodology for measurement of noise. Specifically, the utilization and placement of the sensor (from line 149 to line 155), the load condition (from line 158 to line 160), and the post processing (from line 169 to line171) used in the test have been added to make the methodology reproducible

1. Many authors are engaged in research on noise emissions, so it is worth adding a section with a discussion on the results obtained.

→ Discussions have been added to each section (from line 216 to line 222 & from line 384 to line 393). In the conclusion section, a discussion about the entire results of the study has been added (from line 402 to line 407).

6. Pay more attention to spelling. Not all phrases are understandable. Consider language proofreading by a native speaker.

→ This manuscript was proofread in English. Certification of English editing is attached below.

Reviewer 2 Report

The manuscript describes a process of shape design optimization of a gearbox housing in order to reduce radiated noise of an electrical vehicle. The proposed approach shows reduction of equivalent radiated power (ERP) of all operation conditions. The different research steps are presented in a very good level and the structure of the whole manuscript is clear and understandable. However, additional information or further development will significantly improve the work presented in this manuscript. In particular:

• 1. Introduction

Although, the development of the Introduction section has been done in a satisfactory degree, further improvements are necessary in order to better document the background of the research but also the innovation aspect of the research presented in this manuscript.

Although shape design optimization through topology optimization is one important aspect of this investigation not much work on this area has been mentioned in the introduction part.

Please check for more references regarding shape design and topology optimization. Additional and extra works currently undertaken in worth to be discussed.

The paragraph from line 52 to line 86 is too long. This could be broken down into smaller paragraphs and organized according to the subject discussed.

In the last paragraph of the Introduction, where an overview of the workflow and research approach conducted in this study is developed, discussion on topology optimization is not provided.

A clearer overview on the research methodology would provide better understanding of the different tasks undertaken. Also, the development of a diagram describing the workflow as a whole could be useful. This could be done in a subsection, dedicated to the research methodology.

• 2.3. Order Analysis

In lines 170-176 check the syntax of sentences for clarity. For instance, “…or more were the gear mesh component…”

Figure 7a and Figure 7b are in different pages and this makes reading and understanding difficult. Please add both images in the same page.

• 3.1. Finite Element Model Update and Validation

More explanations regarding the finite element method (FEM) applied in this manuscript are necessary, also software used. In general, check the whole manuscript and add additional information regarding software or tools applied for design and analysis.

Check citations in line 212 “Son, et al. [11]”

In line 222-224 a reference is needed.

•  4.1. Equivalent Radiated Power

In Figure 8 the caption is in the next page. This makes understanding of figure difficult. Please move the caption in the same page with images.

Also, the images presented in Figure 8 should be improved.

The images do not clearly describe the purpose of this figure. Other views might be more appropriate to describe the figure.

In Figure 9 graph values in the vertical axis are necessary for better understanding.

In lines 282-288 check the whole paragraph and shorten parts of it for better understanding.

• 4.3. Topology optimization

More information regarding software and tools for topology optimization are necessary. Initial configurations and generally the method applied are not mentioned. Detail descriptions are required.

In lines 326-327 is mentioned that “The weight of the housing before optimization was 4.84Kg, and the weight increased by approximately 12% to 5.44Kg after optimization”. More explanations and discussion on this aspect is necessary.

How the results derived from topology optimization influences shape design? Is the new design the one derived from the topology optimization? More clarifications are necessary.

Figure 16 is separated in two pages, see similar comment for Figure 7.

In Figure 16 and Figure 17 values in vertical axis are missing.

• 5. Conclusions

In lines 344-352 discussion on topology optimization as part of the suggested workflow is necessary. In general, discussion in all steps undertaken in this research should be included and clearly presented.

Author Response

The manuscript describes a process of shape design optimization of a gearbox housing in order to reduce radiated noise of an electrical vehicle. The proposed approach shows reduction of equivalent radiated power (ERP) of all operation conditions. The different research steps are presented in a very good level and the structure of the whole manuscript is clear and understandable. However, additional information or further development will significantly improve the work presented in this manuscript. In particular:

• 1. Introduction

Although, the development of the Introduction section has been done in a satisfactory degree, further improvements are necessary in order to better document the background of the research but also the innovation aspect of the research presented in this manuscript.

Although shape design optimization through topology optimization is one important aspect of this investigation not much work on this area has been mentioned in the introduction part. Please check for more references regarding shape design and topology optimization. Additional and extra works currently undertaken in worth to be discussed

→ In order to understand the research trend of topology optimization, I have added the recently written papers from line 74 to line 81 and discussed the limitation of them.

The paragraph from line 52 to line 86 is too long. This could be broken down into smaller paragraphs and organized according to the subject discussed.

→ The long paragraph has been divided into three parts. Part of an investigation about previous studies, which started from line 52, has been divided into two parts for applications (gearbox, electric vehicle) and a researcher for housing shape optimization.

In the last paragraph of the Introduction, where an overview of the workflow and research approach conducted in this study is developed, discussion on topology optimization is not provided.

→ In the last paragraph of the introduction, it has been revised to emphasize the research objectives and approach. By adding methodology to topology optimization, I described how this technique was used in this study (from line 93 to line 99).

A clearer overview on the research methodology would provide better understanding of the different tasks undertaken. Also, the development of a diagram describing the workflow as a whole could be useful. This could be done in a subsection, dedicated to the research methodology.

→ This study is composed of i) experimental analysis of excitation sources considering the characteristics of electric vehicles, ii) configuration of finite element models suitable for optimization of gearbox housing, and iii) design region definition and optimization considering dynamic response of the gearbox housing. To make this workflow easier to understand, the composition of the paper is different from the classic composition (introduction, materials and methods, results, conclusions). As you mentioned, it seems a good idea to use diagrams. A diagram has been added at the end of the introduction to make this paper easier to understand (Figure 1).

2.3. Order Analysis

In lines 170-176 check the syntax of sentences for clarity. For instance, “…or more were the gear mesh component…”

→ After checking the content of the text, the sentence has been corrected as follows.

“Two of the three main noises indicating a noise of above 60 dB (A) were the gear mesh components” (from line 191 to line 192)

Figure 7a and Figure 7b are in different pages and this makes reading and understanding difficult. Please add both images in the same page.

→ The figure or caption has been modified to the correct location.

• 3.1. Finite Element Model Update and Validation

More explanations regarding the finite element method (FEM) applied in this manuscript are necessary, also software used. In general, check the whole manuscript and add additional information regarding software or tools applied for design and analysis.

Check citations in line 212 “Son, et al. [11]”

→ I have added the software used for FE modeling and modal analysis (line 231). I also added the software used for internal machine element modeling in the next section (line 248).

For the FE model used in this study matches perfectly to the validated model in reference “Son, et al. [11]”. This paper was written by myself, and described the process and results for “Finite Element Model Update and Validation”. However, in this paper, it was judged that it was important to mention that there was a process about model validation, so I briefly mentioned it with reference.

The FEM based numerical analysis mentioned in the text is a very commonly used technique and it was judged that the description of the technique itself is not necessary.

In line 222-224 a reference is needed.

→ Reference has been added to support that bearing reaction force is affected by the housing structure (line 250).

•  4.1. Equivalent Radiated Power

In Figure 8 the caption is in the next page. This makes understanding of figure difficult. Please move the caption in the same page with images.

→ The figure or caption has been modified to the correct location.

Also, the images presented in Figure 8 should be improved. The images do not clearly describe the purpose of this figure. Other views might be more appropriate to describe the figure.

→ Depending on the direction of rotation of the input shaft, the direction of the axial reaction force acting at the bearing position changes the most. It was determined that the current view that can check the direction of the axial force is the most suitable. (Now, the figure number is 9)

In Figure 9 graph values in the vertical axis are necessary for better understanding.

→ The vertical axis of the graph is equivalent radiated power (ERP), which is a value that can approximately estimate the sound power of the sound source. The graphs related to ERP are used for finding the operating conditions at peak or for relative comparison on the dB scale before and after optimization, and the meaning of absolute values is not significant. Many papers using ERP do not display absolute values as in this paper, and compare and analyze them with relative values. (Now, the figure number is 10)

In lines 282-288 check the whole paragraph and shorten parts of it for better understanding.

→ In order to make the paragraph easier to understand, the development of the sentence has been modified (from line 314 to line 319).

First of all, I mentioned the rotational speed with the loudest noise,

The gear mesh frequency was described according to the excitation source at the speed,

Finally, I mentioned the natural frequencies that are affected by the corresponding excitation frequency.

The next paragraph (from line 328 to line 332), which was described in the same way, has been also modified.

• 4.3. Topology optimization

More information regarding software and tools for topology optimization are necessary. Initial configurations and generally the method applied are not mentioned. Detail descriptions are required.

→ The software used in this paper has been added, and the detailed methodology for topology optimization has been added with reference (from line 352 to line 361).

And the initial design (original shape of the housing) has been add (Figure 11).

In lines 326-327 is mentioned that “The weight of the housing before optimization was 4.84Kg, and the weight increased by approximately 12% to 5.44Kg after optimization”. More explanations and discussion on this aspect is necessary. How the results derived from topology optimization influences shape design? Is the new design the one derived from the topology optimization? More clarifications are necessary.

→ Since the gearbox used in this study is mounted on an agricultural electric vehicle, there are no weight restrictions. Since the gearbox is mounted on an electric vehicle for agriculture, there are no weight restrictions.

기어 박스는 농업용 전기차에 장착되어 있기 때문에 무게 제한이 없습니다.

Equipment gearbox is fitted has no constraints on farming because electric items.

기어 박스가 장착 된 장비는 전기 용품이기 때문에 농사에 제약이 없습니다.

전체 결과를 로드할 수 없음

다시 시도

재시도 중...

재시도 중...

In other words, there is no constraint on increasing the weight of the vehicle because an agricultural electric vehicle has to exert large traction forces as a a vehicle for the purpose of agricultural works.

→ In the previous sentence, it was mentioned that the optimized shape of the housing was modeled by considering the finite elements with a relative density of 0.8 or more as fully filled elements (Here, the value of the relative density can be seen as representing the degree to which the corresponding element is required to satisfy the optimization objective function.). This means that elements with a relative density of 0.8 or less were removed from the topology optimization result, and the corresponding figure is shown in Figure 17.

As you mentioned, the shape of the optimization result is the shape of the topology optimization result itself. The shape is a conceptual design and should be designed in detail in consideration of manufacturability in actual production. This paper aims to perform an objective and reliable optimization procedure. To achieve this, I have been added a discussion at the end of the section (from line 384 to line 393).

Figure 16 is separated in two pages, see similar comment for Figure 7.

→ The figure or caption has been modified to the correct location.

In Figure 16 and Figure 17 values in vertical axis are missing.

→ As a graph related to equivalent radiated power (ERP), the vertical axis was not displayed for the same reason as explained above (Now the figure numbers are 18 and 19).

• 5. Conclusions

In lines 344-352 discussion on topology optimization as part of the suggested workflow is necessary. In general, discussion in all steps undertaken in this research should be included and clearly presented.

→ Discussions have been added to each section (from line 216 to line 222 & from line 384 to line 393). In the conclusion section, a discussion about the entire results of the study has been added (from line 402 to line 407).

 

Reviewer 3 Report

The manuscript presents an interesting study, with a right methodology, and the manuscript is clear, well organized and structured and the authors has worked exhaustively, taking care of the technical details. In addition, the quality of the manuscript presentation is good.

However, it is opinion of the reviewer that, among others, some suggestions could improve the paper:

- The introduction section should be improved and more references should be added. This section should take into consideration the most relevant studies on the subject to build a complete scientific framework.

In other sections (Equivalent Radiated Power, Gear Whine Noise or Order Analysis) no reference is made to the documents from which these knowledge and techniques are extracted and others documents of high relevance on the subject.

For example, the following references are not included in the manuscript:

Bustos, A.; Rubio, H.; Castejon, C.; Garcia-Prada, J.C., EMD-Based Methodology for the Identification of a High-Speed Train Running in a Gear Operating State. Sensors. 2018, 18, 793.

Bustos, A.; Rubio, H.; Castejon, C.; Garcia-Prada, J.C., Condition monitoring of critical mechanical elements through Graphical Representation of State Configurations and Chromogram of Bands of Frequency. Measurement 2019, 135, 71-82.

- There are many acronyms in the manuscript, it would be advisable to make a list of acronyms.

- It is mandatory to specify which “topology optimization technique” was used and describe how it operates and detail some references.

For these reasons, the reviewer proposes to publish the manuscript after minor revision.

Author Response

The manuscript presents an interesting study, with a right methodology, and the manuscript is clear, well organized and structured and the authors has worked exhaustively, taking care of the technical details. In addition, the quality of the manuscript presentation is good.

 

However, it is opinion of the reviewer that, among others, some suggestions could improve the paper:

- The introduction section should be improved and more references should be added. This section should take into consideration the most relevant studies on the subject to build a complete scientific framework.

In other sections (Equivalent Radiated Power, Gear Whine Noise or Order Analysis) no reference is made to the documents from which these knowledge and techniques are extracted and others documents of high relevance on the subject.

For example, the following references are not included in the manuscript:

Bustos, A.; Rubio, H.; Castejon, C.; Garcia-Prada, J.C., EMD-Based Methodology for the Identification of a High-Speed Train Running in a Gear Operating State. Sensors. 2018, 18, 793.

Bustos, A.; Rubio, H.; Castejon, C.; Garcia-Prada, J.C., Condition monitoring of critical mechanical elements through Graphical Representation of State Configurations and Chromogram of Bands of Frequency. Measurement 2019, 135, 71-82.

→ The papers you mentioned were very interesting. I think it can be used by interest in frequency analysis or system diagnosis in my future research. Recognizing that there were insufficient references detailed explanations and references have been added about gear whine (line 125), order analysis (line 147) and topology optimization (line 355). The reference for equivalent radiated power was already attached (line 276).

- There are many acronyms in the manuscript, it would be advisable to make a list of acronyms.

→ In MDPI, there is no separate form to list the abbreviations. Instead, the journal's instruction is: “Abbreviations should be defined in parentheses the first time they appear in the abstract, main text, and in figure or table captions and used consistently thereafter.”

With this instruction, I checked once again to see if all abbreviations were indicated when they were first mentioned in the abstract, text, and figures or tables.

- It is mandatory to specify which “topology optimization technique” was used and describe how it operates and detail some references.

→ The software for topology optimization used in this study has been added, and the methodology for topology optimization has been added with reference (from line 352 to line 361).

Reviewer 4 Report

The authors modeled the shape of the drive gear housing of an electric agricultural vehicle. The information presented is quite interesting, however the manuscript lacks orderliness. Whenever possible, the manuscript should be divided into classic sections. I have no major comments regarding the abstract, introduction and conclusions. However, the purpose of the research should be precisely described and the research methodology used should be presented in detail. The results should be put in order and subjected to careful discussion. The manuscript is in some places unreadable as it stands. Linguistic proofreading should be considered.

Author Response

The authors modeled the shape of the drive gear housing of an electric agricultural vehicle. The information presented is quite interesting, however the manuscript lacks orderliness. Whenever possible, the manuscript should be divided into classic sections.

→ This paper analyzes the noise of each gear stage through noise and vibration measurement to find the gear noise order that has the greatest effect on the overall noise, and then modifies the shape of the housing using topology optimization through simulation. Rather than describing the classic method of introduction, materials and methods, results and discussion, and conclusion, it is thought that the description as it is now will enhance readers' understanding. Also, when checking a number of papers similar to the subject of this paper, most of them are described in this way.

 

I have no major comments regarding the abstract, introduction and conclusions. However, the purpose of the research should be precisely described and the research methodology used should be presented in detail.

→ In the last paragraph of the introduction, it has been revised to emphasize the research objectives and the detailed explanation for the methodology has been added.

I have added the detailed methods for noise measurement test through order analysis

[Utilization and placement of the sensor (from line 149 to line 155), the load condition (from line 158 to line 160), and the post processing (from line 169 to line171)].

And the detailed description of topology optimization for shape modification has been added with reference (from line 352 to line 361).

The results should be put in order and subjected to careful discussion.

→ Discussions have been added to each section (from line 216 to line 222 & from line 384 to line 393). In the conclusion section, a discussion about the entire results of the study has been added (from line 402 to line 407).

The manuscript is in some places unreadable as it stands. Linguistic proofreading should be considered.

→ This manuscript was proofread in English. Certification of English editing is attached below.

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

The authors corrected the shortcomings in the manuscript. I have no more comments.