Abstract

PurposeThis paper aims to numerically investigate the surface texturing effects on the main bearings of a three-cylinder ethanol engine in terms of the power loss and friction coefficient for dynamic load conditions.Design/methodology/approachThe mathematical formulation considers the Partir-Cheng modified Reynolds equation. The mass-conserving Elrod-Adams p-theta model with the JFO approach is used to deal with cavitation. A fluid-structure coupling procedure is considered for the elastohydrodynamic lubrication. Accordingly, a 3-D linear-elastic substructured finite element model obtained from Abaqus is appliedFindingsSimulations were carried out considering different dimple texture designs in terms of location, depth and radius. The results suggested that there are regions where texturing is more effective. In addition, distinct journal rotation speeds are studied and the surface texture was able to reduce friction and the power loss by 7%.Practical implicationsThe surface texturing can be a useful technique to reduce the power loss on the crankshaft bearing increasing the overall engine efficiency.Originality/valueThe surface texturing performance in a three-cylinder engine using ethanol as fuel was investigated through numerical experimentation. The results are supported by previous findings.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2019-0380/


Authors

Rodrigues, Gabriel Welfany;  Bittencourt, Marco Lucio

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  • 1 reviewer
  • pre-publication peer review (FINAL ROUND)
    Reviewer report
    2020/03/13

    No further comments.

    Reviewed by
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    Decision Letter
    2020/03/12

    12-Mar-2020

    Dear Rodrigues, Gabriel; Bittencourt, Marco

    It is a pleasure to accept your manuscript ilt-09-2019-0380.R2, entitled "SURFACE VIRTUAL TEXTURING OF THE JOURNAL BEARINGS OF A THREE-CYLINDER ETHANOL ENGINE" in its current form for publication in Industrial Lubrication and Tribology. Please note, no further changes can be made to your manuscript.

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    Guest Editor, Industrial Lubrication and Tribology
    ltm-henara@ufu.br, henara.costa@gmail.com

    Decision letter by
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    Author Response
    2020/03/11

    Campinas, March 10th 2020
    To
    Prof. Dra. Henara Costa
    Guest Editor, Industrial Lubrication and Tribology
    Resubmission of Manuscript: ilt-09-2019-0380

    Dear Prof. Dra. Henara Costa,

    I would like to thank reviewers for their review of our manuscript "Surface Virtual Texturing of the Journal Bearings of a Three-cylinder Ethanol Engine" submitted for consideration for publication in Industrial Lubrication and Tribology.
    Below we answer reviewers’ questions and the new version of our manuscript is uploaded on the journal’s website. The modifications on the new manuscript version are marked in red color.
    If there are still any questions and comments related to the revised version, we will be glad to answer them.
    Sincerely,

    Reviewer: 1

    • The number of equations should be reduced. Partially they are common knowledge and it may be sufficient to cite the respective research literature accordingly.
      Answer: The number of equations was reduced as suggested. For instance, the former equations (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 22, 23, 27, 28, 34) were deleted in the new version of the manuscript. The respective literature for the suppressed equations was cited.

    • The number of figures must be reduced. For instance, figure 8, 9 and 10 can be combined in one figure.
      Answer: The former figures 8, 9 and 10 were combined into Figure 3.

    • Figure 11 and 12 can be combined.
      Answer: Figure 11 and 12 were combined into Figure 4.

    • Figure 13, 14, and 15 can be combined. Figure 16 and 17 as well.
      Answer: Figures 13, 14 and 15 were combined into Figure 5. Figures 16 and 17 were combined in Figure 6. Figures 18 and 19 were combined in Figure 7. Figures 21, 22 and 23 were combined in Figure 9.

    • The overall goal should be to reach not more than 10 figures.
      Answer: The former Figures 1, 3, 5, 6, 7 and 26 were deleted in the new version of the manuscript. Further explanation and reference literature were indicated in red color to supply the absence of these figures. We tried to reach the goal of 10 figures, but we were afraid not to include important information and results. The final number of pictures is 12.

    • The conclusions should be shortened and streamlined.
      Answer: Modifications were carried out to attend the reviewer in the conclusion section.

    • The following manuscript “Influence of surface texturing on hydrodynamic friction in plane converging bearings-An experimental and numerical approach” may help with the discussion of the surface texture's position.
      Answer: The manuscript was cited in Section 4.1 pg. 16.

    • The following article of Gruetzmacher “From lab to application-improved frictional performance of journal bearings induced by single-and multi-scale surface patterns” related to surface textures applied to journal bearings fits perfectly with the scope of the article. However, it has not been mentioned.
      Answer: We agree with the reviewer. The manuscript was cited in the introduction section pg. 1.


    Reviewer: 2

    • Why was the 1.9 mm radius adopted to study the influence of dimple depth variation rather than 2.3 mm which showed a greater reduction in the friction coefficient and power loss?
      Answer: The objective was to investigate the dimple depth effect and the intermediate dimple radius was chosen. At this point, the goal was not finding the dimple texture with the lowest power loss but understand the dimple depth influence over the power loss. Using the intermediate dimple radius gave us a better insight of the dimple depth effect rather than use the best dimple radius, which could suppress the dimple depth influence.



    Cite this author response
  • pre-publication peer review (ROUND 2)
    Decision Letter
    2020/03/03

    03-Mar-2020

    Dear Prof. Bittencourt:

    Manuscript ID ilt-09-2019-0380.R1 entitled "SURFACE VIRTUAL TEXTURING OF THE JOURNAL BEARINGS OF A THREE-CYLINDER ETHANOL ENGINE" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments of the reviewer(s) are included at the bottom of this letter.

    The reviewer(s) have recommended major revisions to the submitted manuscript, before it can be considered for publication. Therefore, I invite you to respond to the reviewer(s)' comments and revise your manuscript.

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    Once again, thank you for submitting your manuscript to the Industrial Lubrication and Tribology and I look forward to receiving your revision.

    Sincerely,
    Prof. Henara Costa
    Guest Editor, Industrial Lubrication and Tribology
    ltm-henara@ufu.br, henara.costa@gmail.com

    Reviewer(s)' Comments to Author:
    Reviewer: 1

    Comments to the Author
    - The number of equations should be reduced. Partially they are common knowledge and it may be sufficient to cite the respective research literature accordingly.

    • The number of figures must be reduced. For instance, figure 8, 9 and 10 can be combined in one figure.

    • Figure 11 and 12 can be combined.

    • Figure 13, 14, and 15 can be combined. Figure 16 and 17 as well.

    • The overall goal should be to reach not more than 10 figures.

    • The conclusions should be shortened and streamlined.

    • The following manuscript may help with the discussion of the surface texture's position:

    Influence of surface texturing on hydrodynamic friction in plane converging bearings-An experimental and numerical approach

    • The following article of Gruetzmacher related to surface textures applied to journal bearings fits perfectly with the scope of the article. However it has not been mentioned.

    From lab to application-improved frictional performance of journal bearings induced by single-and multi-scale surface patterns

    Reviewer: 2

    Comments to the Author
    General comments:

    This is a technically work with a good contextualization in the virtual texturing and energy losses field. In general, the language level is good. The methodology is detailed well founded. Results are well connected and give an interesting insight into the development of new possibilities for technologies applied to this problem. Corrections increase the quality of work, making it more complete
    Detailed comments:

    Results

    • Why was the 1.9 mm radius adopted to study the influence of dimple depth variation rather than 2.3 mm which showed a greater reduction in the friction coefficient and power loss?
      Reviewer: 1

    Comments:
    - The number of equations should be reduced. Partially they are common knowledge and it may be sufficient to cite the respective research literature accordingly.

    • The number of figures must be reduced. For instance, figure 8, 9 and 10 can be combined in one figure.

    • Figure 11 and 12 can be combined.

    • Figure 13, 14, and 15 can be combined. Figure 16 and 17 as well.

    • The overall goal should be to reach not more than 10 figures.

    • The conclusions should be shortened and streamlined.

    • The following manuscript may help with the discussion of the surface texture's position:

    Influence of surface texturing on hydrodynamic friction in plane converging bearings-An experimental and numerical approach

    • The following article of Gruetzmacher related to surface textures applied to journal bearings fits perfectly with the scope of the article. However it has not been mentioned.

    From lab to application-improved frictional performance of journal bearings induced by single-and multi-scale surface patterns

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Please see comments below.

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: Please see comments below.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: Please see comments below.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: Please see comments below.

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: Please see comments below.

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: Please see comments below.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?: Please see comments below.

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: No, I would not like my name to appear with my report on Publons

    Reviewer: 2

    Comments:
    General comments:

    This is a technically work with a good contextualization in the virtual texturing and energy losses field. In general, the language level is good. The methodology is detailed well founded. Results are well connected and give an interesting insight into the development of new possibilities for technologies applied to this problem. Corrections increase the quality of work, making it more complete
    Detailed comments:

    Results

    • Why was the 1.9 mm radius adopted to study the influence of dimple depth variation rather than 2.3 mm which showed a greater reduction in the friction coefficient and power loss?

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Yes, the paper contains significant information and the publication is justifying. It Contains original and significant content, with direct applications that aim to improve the performance of a mechanical system, reducing losses.

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: The article focuses about surface texturing and energy losses. It presents relevant and fundamental publications for the understanding of the presented results with classic and recent references on the subject. I did not notice any relevant articles that were ignored.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: The proposed methods are appropriated. The modelling and simulation method are very well detailed, including describing the algorithms used to calculation of the pressure and fraction film fields and bearing displacement calculation.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: In the introductory chapter, the authors presented a contextualization in the energy loss problems. The simulation results are well connected and give an interesting insight into the development of new possibilities for technologies applied to this problem. The goal here is to reduce friction and power loss by increasing the efficiency of the mechanical system. The article presents effective results in this regard.

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: The paper identifies clearly how texture influences system efficiency by decreasing losses, as an alternative to improve real systems, such as the crankshaft studied.

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: In general, the language level is good. The paper has a clearly and technical language as expected of the journal’s readership. All precautions were taken with the writing of this paper by the authors.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: Yes, I would like my name to appear with my report on Publons

    Decision letter by
    Cite this decision letter
    Reviewer report
    2020/03/03

    General comments:

    This is a technically work with a good contextualization in the virtual texturing and energy losses field. In general, the language level is good. The methodology is detailed well founded. Results are well connected and give an interesting insight into the development of new possibilities for technologies applied to this problem. Corrections increase the quality of work, making it more complete
    Detailed comments:

    Results

    • Why was the 1.9 mm radius adopted to study the influence of dimple depth variation rather than 2.3 mm which showed a greater reduction in the friction coefficient and power loss?

    Reviewed by
    Cite this review
    Reviewer report
    2020/02/19

    • The number of equations should be reduced. Partially they are common knowledge and it may be sufficient to cite the respective research literature accordingly.

    • The number of figures must be reduced. For instance, figure 8, 9 and 10 can be combined in one figure.

    • Figure 11 and 12 can be combined.

    • Figure 13, 14, and 15 can be combined. Figure 16 and 17 as well.

    • The overall goal should be to reach not more than 10 figures.

    • The conclusions should be shortened and streamlined.

    • The following manuscript may help with the discussion of the surface texture's position:

    Influence of surface texturing on hydrodynamic friction in plane converging bearings-An experimental and numerical approach

    • The following article of Gruetzmacher related to surface textures applied to journal bearings fits perfectly with the scope of the article. However it has not been mentioned.

    From lab to application-improved frictional performance of journal bearings induced by single-and multi-scale surface patterns

    Reviewed by
    Cite this review
    Author Response
    2020/02/17

    To

    Prof. Henara Costa Guest Editor, Industrial Lubrication and Tribology

    Resubmission of Manuscript: ilt-09-2019-0380

    Dear Prof. Henara Costa,

    I would like to thank reviewers for their careful review of our manuscript "Surface Virtual Texturing of the Journal Bearings of a Three-cylinder Ethanol Engine" submitted for consideration for publication in Industrial Lubrication and Tribology.

    Below we answer reviewers’ questions and the new version of our manuscript is uploaded on the journal’s website.

    If there are still any questions and comments related to the revised version, we will be glad to answer them.


    Reviewer 1:

    Comments on the results section:

    1. The influence of the dimple radius on the friction coefficient and power loss behaves similarly to the influence of dimple depth on the friction coefficient and power loss, but less evidently. Is it possible to identify values at which it is unviable to increase the depth by defining, for example, a relative error in relation to the reduction rate?

    Answer: It is difficult to estimate a value where the dimple depth becomes unviable. Our results showed that the increment in the dimple depth has a positive effect in reducing the power loss for the considered values with a clear tendency. We could extrapolate the results to find the depth of dimples that does not affect anymore the power loss. However, this behavior can be totally different for larger dimple depths without physical meaning. Further investigation in this aspect is still necessary. In fact, it was pointed out that the aspect ratio (radius over depth) is the parameter that most influence the dimple efficiency.

    1. Why was the 1.9 mm radius adopted to study the influence of dimple depth variation rather than 2.3 mm which showed a greater reduction in the friction coefficient and power loss? Was it because it presented a larger reduction when compared to the previous value?

    Answer: The objective was just to investigate the dimple depth effect and the intermediate dimple radius was chosen. The objective was not finding the dimple texture with the lowest power loss but understand the dimple depth effect over the power loss.

    1. Explain why a density of 65% was used and show how density is calculated, dividing the ratio of texture area by cell area.

    Answer: Actually, the density of 65% was obtained as the ratio of dimple area (Ad) and the cell area (Ac), given in terms of the dimple radius (R) and cell dimensions (𝐿𝑡𝑥×𝐿𝑡𝑧). Fives dimples were placed in the axial direction for each row. Based on that, the texture density (TD) is calculated as 𝑇𝐷=𝐴𝑑𝐴𝑐=𝜋𝑅2𝐿𝑡𝑥×𝐿𝑡𝑧=𝜋(1.5)23.3×3.3 ≅0.65=65%.

    1. How the β parameter was calculated? If we take as an example the case with nx = 3 and nz = 5 illustrated in section 4.1, with the values of L and R present in Table 1 and the values of Ltx and Lty shown in table 2, it is not possible to obtain the values of β 60% and 100%.

    Answer: The bearing was divided into 6 regions and β is calculated for only one region and not to the entire bearing length. For nx = 3 and nz = 5, the considered region (1, 2, 3, 4, 5 or 6) is fully textured and β = 100%. From one cell to another, there gaps a and b on the radial and axial directions respectively.


    Reviewer 2:
    1. Introduction
    p. 1, line 47: The following review articles could also be cited:
    - Daniel Gropper, Ling Wang, Terry J. Harvey, Hydrodynamic lubrication of textured surfaces: A review of modeling techniques and key findings, Tribology International, v.94, p.509-529, 2016.
    - C. Gachot, A. Rosenkranz, S.M. Hsu, H.L. Costa, A critical assessment of surface texturing for friction and wear improvement, Wear, v. 372–373, p.21-41,2017.
    - Grützmacher, P.G.; Profito, F.J.; Rosenkranz, A. Multi-Scale Surface Texturing in Tribology Current Knowledge and Future Perspectives. Lubricants 2019, 7, 95.

    Answer: The papers were cited in the first paragraph of the Introduction.

    b) p. 1, line 54: The term 'lifting' could be replaced by 'additional hydrodynamic support'
    Answer: The term ‘lifting’ was replaced by ‘additional hydrodynamic support’ throughout the text.

    c) p. 2, line 25: The following publication could be cited throughout the manuscript instead of (or in addition to) Profito, 2015 where many aspects and formulations used in the present work were originally proposed:
    - F.J. Profito, D.C. Zachariadis, D. Dini, Partitioned fluid-structure interaction techniques applied to the mixed-elastohydrodynamic solution of dynamically loaded connecting-rod big-end bearings, Tribology International, v. 140, 2019.
    Answer: When our manuscript was first submitted, the given publication was not available yet. We added the given publication.

    2.2 Modified Patir And Cheng Reynolds Equation

    a) p. 4, Eq. 5: Why the contact factor (phi_c = h_T/h) was not considered in this version of P&C; Reynolds equation?

    Answer: In fact, the contact factor was considered. Equation (5) of the original manuscript was replaced. The contact factor of the P&C; Reynolds equation for the parameters used did not have great influence on the results for the simulated cases.

    b) p. 5, line 4: Why a transversely oriented roughness pattern was considered in the present work? More information about the surface topography of the investigated bearing should be provided.

    Answer: More specific information about the surface parameters were added in Table 1. We do not have the specific information about the surface topography for the case considered in the manuscript. The parameters were obtained from the literature. We adopted the parameters for a transversely oriented roughness pattern obtained in reference (Profito, 2015).

    c) Since the proposed model is used to predicted mixed lubrication, asperity contact pressure should have been considered in the model. Why was this not considered in the formulation, and how the neglecting of rough contact effects may have influenced the obtained results? Furthermore, the authors must make clear that thermal effects and angular misalignments (important in ICE main bearing applications) have also been neglected from the analysis.

    Answer: Actually, the asperity contact pressure was considered. We added section 2.3 in the revised version of the manuscript to describe the details about the Greenwood-Trip model considered in the work. For the simulated cases, the asperity contact pressure was null. At the end of section 2.1, we added the information that thermal effects and angular misalignments were not considered.

    2.3 Calculated Characteristics

    a) p. 6, line 6: The fact that the bearing surface is fixed could be mentioned in Sec. 2.1.

    Answer: This information was added in the second paragraph of Section 2.1.

    b) p. 6, Eq. 17: The plus-minus sign does not make sense here since only the friction force acting on the journal surface is considered in Eq. 17.

    Answer: The plus-minus sign was deleted in Equation (19) of the revised version of the manuscript.

    c) p. 6, Eq. 18: What is the 'psi' quantity? Check if the defined hydrodynamic CoF is dimensionless.

    Answer: Variable \psi is the dissipated power due to friction (please see the first sentence of Section 2.4). The units for the parameters in the ‘psi’ equation and the friction coefficient are given below

    omega_j ==> N
    omega_j x R_j ==> m/s
    psi ==> N x m/s
    U ==> m/s
    F_x,F_y ==> N

    Therefore, mu_friction = {N x (m/s)}/{(m/s) x N} is dimensionless.

    2.4 Surface Texturing

    a) p. 6, Eq. 19: To maintain consistency with Eq. 3, h(theta_b) could be written as h(theta_b,z_b)

    Answers: We agree with the reviewer and this modification appears now in Equation (21) of the revised manuscript.

    b) p. 6, line 50: What is a Cartesian difference system?

    Answer: The word “difference” has no meaning here and we have replaced by “Cartesian reference system” at the end of the first paragraph of Section 2.5.

    2.5 3d Elasto-Hydrodynamic Lubrication (EHL)

    a) p. 8, line 29: The term 'A 3D finite element model based on ...' could be replaced by '3D finite element substructuring approach based on ...'
    Answer: The term 'A 3D finite element model based on ...' was replaced for a '3D finite element substructuring approach based on ...'. in the first paragraph of Section 2.6.

    3.1 Solution of the Reynolds equation

    a) p. 9, line 37: The SOR algorithm proposed by Ausas is based on the finite volume discretization of p-theta Reynolds equation in which the (convective) Couette term is approximated by an upwind scheme. However, it was mentioned in p. 10 (and Fig. 6) that the finite difference method was used in the present manuscript. The authors should clarify this issue since the underlying requirement for the effectiveness of Ausas' algorithm to solve the p-theta model is the assurance of the local conservation of fluxes at each control volume of the discrete domain.

    Answer: The computational procedure used in this paper is based on the Ausas’s algorithm, which considers a convective approach using an upwind scheme for the wedge term in the Reynolds equation. In the paper “The impact of the Cavitation Model in Analysis of Microtextured Lubricated Journal Bearings”, Ausas also referred to the discretization scheme of the p-theta Reynolds equation as finite difference. To deal with the non-linearities Ausas used a Gauss-Seidel iterative process, in which no assembly of any linear system is needed. The scheme is based on the mass balance at each node with uniquely-defined fluxes.

    We added the information in Section 3.1, first paragraph, that the method is based on the Ausas´s algorithm, which considers a convective approach using an upwind scheme for the wedge term in the Reynolds equation.

    1. Results

    a) p. 15, line 28: crankshaft pf (???)
    Answer: This was a typo error and already fixed in the new version of the manuscript.

    b) p. 15, line 15: How were the forces calculated? Also, it should be mentioned that a quasi-static solution was adopted to solve the dynamic problem instead of a full transient one.
    Answer: The loads were calculated from the pressure curves using a dynamic model for the piston-conrod-crankshaft mechanism for one cylinder of the engine. The reference “Neves, G.; Bittencourt, M.L.; Villalva, S.G. ; Galli, L. A. F. . Comparison of Dynamical Models for Internal Combustion Engines. 18o. SAE Conference, São Paulo, Brazil 2009” was cited. This information and a sentence about quasi static solution was added in page 15 of the revised manuscript.

    c) p. 17, Table 1: What was the engine operating temperature?
    Answer: We used the same viscosity employed during the validation of our program obtained in one of referenced papers. The dynamic viscosity is approximately the same as for the oil SAE10W-60 at 45°C. We understand now that the value is about twice that one effectively used for the considered engine for the same temperature.

    d) More details about the simulations setup, i.e. mesh size, time steps, convergence tolerances, etc. should be provided for all simulation cases.
    Answer: The required information about time steps and convergence tolerances was included in the first paragraph of Section 4.1. The mesh size was added in Table 2.

    e) More detailed results showing the variations of the minimum oil film thickness, peak hydrodynamic and asperity contact pressures, power loss, CoF, shaft trajectory etc, over the engine operating cycle should be provided for all simulation cases. For instance, the knowledge of the magnitude of oil film thickness is important to assert the predominant lubrication regime at different instants of the engine cycle.
    Answer: More detailed results regarding these aspects were included in Sections 4.3 and 4. 4. However, providing the results for all simulated cases would make the manuscript too long. The results included in these sections can illustrate the overall results. Specifically, we added figures 24, 25 and 26 and the text in blue color.

    f) Furthermore, the mechanisms involved in the verified power loss and CoF deviations should be discussed. There are trends that are not given a physical explanation. Linking them to observations does not give a physical explanation.
    Answer: More physical information about the observed results were added in Sections 4.3 and 4.4. The modifications are in blue letters.

    4.1 TEXTURING LOCATION EFFECTS

    a) p. 18, Fig. 11: What is the z-axis scale?
    Answer: The scale is in millimeters and the z-axis is along the bearing length.

    b) p. 19, Tab. 2: How the texture parameters listed in Table 2 were defined?
    Answer: The objective was to place five dimples in the axial direction and three dimples in the radial direction for each piece of 60 degrees of the bearing surface. Therefore, the dimple cell size was chosen in a way that geometrically allowed the placement of the texture in the axial and radial directions. The dimple radius was chosen as approximately half of the dimple cell side. Thus, an increment in the dimple cell radius could be possible for the next simulations. The dimple cell depth was chosen based on some previous simulations to set the initial magnitude.

    4.2 DIMPLE RADIUS AND DEPTH

    c) p. 21, line 34: The use of the defined mean CoF can mislead the analysis of results since textures may be beneficial/detrimental at different instants/positions of the engine cycle. Therefore, it is strongly recommended to show all results as a function of the crank angle.
    Answer: The results of the friction coefficient for the different dimple depths and radiuses in terms of the crank angle are given in Figures 16 and 18. Please see also the sentences in blue color added in pages 20-22.

    d) p. 21, line 47: Why the reduction of the mean CoF would reach a limit and what would be the physical mechanisms involved to support such a statement.
    Answer: This affirmation was based on the tendency that was observed. As the dimple depth increases, the improvement fo the power loss became smaller if compared with the previous dimple depth. For example, from a texture depth of 5 µm to 10 µm an improvement of 0.26% was observed. For the dimple depth of 10 µm to 15 µm an 0.17% improvement was observed and for 25 µm to 30 µm only 0.08%. This suggests that the dimple depth can reach a limit. As this statement can be misunderstood, it was deleted in the new version of the manuscript.

    4.3 ELASTOHYDRODYNAMIC EFFECTS

    a) p. 23, line 54:
    Why the clamped boundary condition was chosen for all nodes on the external bearing surface? Does it make sense physically based on the configuration and assembly of the crankshaft system? If the displacements of all nodes on the external surface are restricted, practically no deformation associated with the bearing flexibility will occur in radial direction. This is not the case for this type of bearing in which EHL effects are significant. The authors should justify the used boundary condition and, if possible, cite other references that adopted similar constraints.
    Answer: We agree with the reviewer’s comments. The analysis presented was more qualitative than quantitative for taking into account the EHL. The objective was to first comprehend the texture behavior when the elastic deformation is considered. The program developed still has limitations in terms of performance and mapping of information between different meshes. In addition, the boundary conditions used were based on previous papers such as

    • Liu, H., Xu, H., Ellison, P. J., and Jin, Z. (2010). Application of computational fluid dynamics and fluid-structure interaction method to the lubrication study of a rotor-bearing system. Tribology Letters, 38(3):325–336.

    • Hili, M. A., Bouaziz, S., Maatar, M., Fakhfakh, T., and Haddar, M. (2010). Hydrodynamic and elastohydrodynamic studies of a cylindrical journal bearing. Journal of hydrodynamics, 22(2):155–163.

    We added some information in the first paragraph of Section 4.3

    We have optimized our software and intend to run the real geometry for one crankshaft throw in the near future.

    b) p. 24, line 50:
    Contour plots of the film thickness after deformation should be provided along with the journal orbits. For EHL analysis, it is very important to analyze the magnitude of the surfaces' displacements and the deviations of the journal orbits from the ideal trajectory locus.
    Answer: Figure 24 was added on page 25 and illustrates the contour plots for the surface displacements and the film thickness. Figure 26 shows the distribution of textures.



    Cite this author response
  • pre-publication peer review (ROUND 1)
    Decision Letter
    2019/11/03

    03-Nov-2019

    Dear Prof. Bittencourt:

    Manuscript ID ilt-09-2019-0380 entitled "SURFACE VIRTUAL TEXTURING OF THE JOURNAL BEARINGS OF A THREE-CYLINDER ETHANOL ENGINE" which you submitted to the Industrial Lubrication and Tribology, has been reviewed. The comments of the reviewer(s) are included at the bottom of this letter.

    The reviewer(s) have recommended major revisions to the submitted manuscript, before it can be considered for publication. Therefore, I invite you to respond to the reviewer(s)' comments and revise your manuscript.

    To revise your manuscript, log into https://mc.manuscriptcentral.com/ilt and enter your Author Centre, where you will find your manuscript title listed under "Manuscripts with Decisions." Under "Actions," click on "Create a Revision." Your manuscript number has been appended to denote a revision.

    You will be unable to make your revisions on the originally submitted version of the manuscript. Instead, revise your manuscript using a word processing program and save it on your computer. Please also highlight the changes to your manuscript within the document by using the track changes mode in MS Word or by using bold or coloured text.

    Once the revised manuscript is prepared, you can upload it and submit it through your Author Centre. The deadline for uploading a revised manuscript is 01-Feb-2020 from receiving this email. If it is not possible for you to resubmit your revision within this timeframe, we may have to consider your paper as a new submission.

    When submitting your revised manuscript, you will be able to respond to the comments made by the reviewer(s) in the space provided. You can use this space to document any changes you make to the original manuscript. In order to expedite the processing of the revised manuscript, please be as specific as possible in your response to the reviewer(s).

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    Please note that Emerald requires you to clear permission to re-use any material not created by you. If there are permissions outstanding, please send these to Emerald as soon as possible. Emerald is unable to publish your paper with permissions outstanding.

    Once again, thank you for submitting your manuscript to the Industrial Lubrication and Tribology and I look forward to receiving your revision.

    Sincerely,
    Prof. Henara Costa
    Guest Editor, Industrial Lubrication and Tribology
    ltm-henara@ufu.br, henara.costa@gmail.com

    Reviewer(s)' Comments to Author:
    Reviewer: 1

    Comments to the Author
    General comments:
    This is a technically work with a good contextualization in the virtual texturing and energy losses field. In general, the language level is good. The methodology is detailed well founded. Results are well connected and give an interesting insight into the development of new possibilities for technologies applied to this problem.

    Detailed comments:
    Results
    - Influence of the dimple radius on the friction coefficient and power loss behaves similarly to the influence of dimple depth on the friction coefficient and power loss, but less evidently. Is it possible to identify values at which it is unviable to increase depth by defining, for example, a relative error in relation to the reduction rate?
    - Why was the 1.9 mm radius adopted to study the influence of dimple depth variation rather than 2.3 mm which showed a greater reduction in the friction coefficient and power loss? Was it because it presented a larger reduction when compared to the previous value?
    - Explain why a density of 65% was used and show how density is calculated, dividing the ratio of texture area by cell area
    - How β parameter was calculated? If we take as an example the case with nx = 3 and nz = 5 illustrated in section 4.1, with the values of L and R present in Table 1 and the values of Ltx and Lty shown in table 2, it is not possible to obtain the values of β 60% and 100%.

    Reviewer: 2

    Comments to the Author
    --------------------------------------------------------------------------------------------------------------------------1. INTRODUCTION

    p. 1, line 47: The following review articles could also be cited:
    - Daniel Gropper, Ling Wang, Terry J. Harvey, Hydrodynamic lubrication of textured surfaces: A review of modeling techniques and key findings, Tribology International, v. 94, p. 509-529, 2016.
    - C. Gachot, A. Rosenkranz, S.M. Hsu, H.L. Costa, A critical assessment of surface texturing for friction and wear improvement, Wear, v. 372–373, p. 21-41, 2017.
    - Grützmacher, P.G.; Profito, F.J.; Rosenkranz, A. Multi-Scale Surface Texturing in Tribology Current Knowledge and Future Perspectives. Lubricants 2019, 7, 95.

    p. 1, line 54: The term 'lifting' could be replaced by 'additional hydrodynamic support'

    p. 2, line 25: The following publication could be cited throughout the manuscript instead of (or in addition to) Profito, 2015 where many aspects and formulations used in the present work were originally proposed:
    - F.J. Profito, D.C. Zachariadis, D. Dini, Partitioned fluid-structure interaction techniques applied to the mixed-elastohydrodynamic solution of dynamically loaded connecting-rod big-end bearings, Tribology International, v. 140, 2019.


    2.2. MODIFIED PATIR AND CHENG REYNOLDS EQUATION

    p. 4, Eq. 5: Why the contact factor (phi_c = h_T/h) was not considered in this version of P&C; Reynolds equation?

    p. 5, line 4: Why a transversely oriented roughness pattern was considered in the present work? More information about the surface topography of the investigated bearing should be provided.

    Since the proposed model is used to predicted mixed lubrication, asperity contact pressure should have been considered in the model. Why was this not considered in the formulation, and how the neglecting of rough contact effects may have influenced the obtained results? Furthermore, the authors must make clear that thermal effects and angular misalignments (important in ICE main bearing applications) have also been neglected from the analysis.


    2.3. CALCULATED CHARACTERISTICS

    p. 6, line 6: The fact that the bearing surface is fixed could be mentioned in Sec. 2.1.

    p. 6, Eq. 17: The plus-minus sign does not make sense here since only the friction force acting on the journal surface is considered in Eq. 17.

    p. 6, Eq. 18: What is the 'psi' quantity? Check if the defined hydrodynamic CoF is dimensionless.


    2.4. SURFACE TEXTURING

    p. 6, Eq. 19: To maintain consistency with Eq. 3, h(theta_b) could be written as h(theta_b,z_b)
    p. 6, line 50: What is a Cartesian difference system?


    2.5. 3D ELASTO-HYDRODYNAMIC LUBRICATION (EHL)

    p. 8, line 29: The term 'A 3D finite element model based on ...' could be replaced by '3D finite element substructuring approach based on ...'


    3.1 SOLUTION OF THE REYNOLDS EQUATION

    p. 9, line 37: The SOR algorithm proposed by Ausas is based on the finite volume discretization of p-theta Reynolds equation in which the (convective) Couette term is approximated by an upwind scheme. However, it was mentioned in p. 10 (and Fig. 6) that the finite difference method was used in the present manuscript. The authors should clarify this issue since the underlying requirement for the effectiveness of Ausas' algorithm to solve the p-theta model is the assurance of the local conservation of fluxes at each control volume of the discrete domain.


    1. RESULTS

    p. 15, line 28: crankshaft pf (???)

    p. 15, line 15: How were the forces calculated? Also, it should be mentioned that a quasi-static solution was adopted to solve the dynamic problem instead of a full transient one.

    p. 17, Table 1: What was the engine operating temperature?

    More details about the simulations setup, i.e. mesh size, time steps, convergence tolerances, etc. should be provided for all simulation cases.

    More detailed results showing the variations of the minimum oil film thickness, peak hydrodynamic and asperity contact pressures, power loss, CoF, shaft trajectory etc, over the engine operating cycle should be provided for all simulation cases. For instance, the knowledge of the magnitude of oil film thickness is important to assert the predominant lubrication regime at different instants of the engine cycle.

    Furthermore, the mechanisms involved in the verified power loss and CoF deviations should be discussed. There are trends that are not given a physical explanation. Linking them to observations does not give a physical explanation.


    4.1 TEXTURING LOCATION EFFECTS

    p. 18, Fig. 11: What is the z-axis scale?

    p. 19, Tab. 2: How the texture parameters listed in Table 2 were defined?


    4.2 DIMPLE RADIUS AND DEPTH

    p. 21, line 34: The use of the defined mean CoF can mislead the analysis of results since textures may be beneficial/detrimental at different instants/positions of the engine cycle. Therefore, it is strongly recommended to show all results as a function of the crank angle.

    p. 21, line 47: Why the reduction of the mean CoF would reach a limit and what would be the physical mechanisms involved to support such a statement.


    4.3 ELASTOHYDRODYNAMIC EFFECTS

    p. 23, line 54:
    Why the clamped boundary condition was chosen for all nodes on the external bearing surface? Does it make sense physically based on the configuration and assembly of the crankshaft system? If the displacements of all nodes on the external surface are restricted, practically no deformation associated with the bearing flexibility will occur in radial direction. This is not the case for this type of bearing in which EHL effects are significant. The authors should justify the used boundary condition and, if possible, cite other references that adopted similar constraints.

    p. 24, line 50:
    Contour plots of the film thickness after deformation should be provided along with the journal orbits. For EHL analysis, it is very important to analyze the magnitude of the surfaces' displacements and the deviations of the journal orbits from the ideal trajectory locus.
    Reviewer: 1

    Recommendation: Minor Revision

    Comments:
    General comments:
    This is a technically work with a good contextualization in the virtual texturing and energy losses field. In general, the language level is good. The methodology is detailed well founded. Results are well connected and give an interesting insight into the development of new possibilities for technologies applied to this problem.

    Detailed comments:
    Results
    - Influence of the dimple radius on the friction coefficient and power loss behaves similarly to the influence of dimple depth on the friction coefficient and power loss, but less evidently. Is it possible to identify values at which it is unviable to increase depth by defining, for example, a relative error in relation to the reduction rate?
    - Why was the 1.9 mm radius adopted to study the influence of dimple depth variation rather than 2.3 mm which showed a greater reduction in the friction coefficient and power loss? Was it because it presented a larger reduction when compared to the previous value?
    - Explain why a density of 65% was used and show how density is calculated, dividing the ratio of texture area by cell area
    - How β parameter was calculated? If we take as an example the case with nx = 3 and nz = 5 illustrated in section 4.1, with the values of L and R present in Table 1 and the values of Ltx and Lty shown in table 2, it is not possible to obtain the values of β 60% and 100%.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: Yes, the paper contains significant information and the publication is justifying. It Contains original and significant content, with direct applications that aim to improve the performance of a mechanical system, reducing losses.

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: The article focuses about surface texturing and energy losses. It presents relevant and fundamental publications for the understanding of the presented results with classic and recent references on the subject. I did not notice any relevant articles that were ignored.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: The proposed methods are appropriated. The modelling and simulation method are very well detailed, including describing the algorithms used to calculation of the pressure and fraction film fields and bearing displacement calculation.

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: In the introductory chapter, the authors presented a contextualization in the energy loss problems. The simulation results are well connected and give an interesting insight into the development of new possibilities for technologies applied to this problem. The goal here is to reduce friction and power loss by increasing the efficiency of the mechanical system. The article presents effective results in this regard.

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: The paper identifies clearly how texture influences system efficiency by decreasing losses, as an alternative to improve real systems, such as the crankshaft studied.

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: In general, the language level is good. The paper has a clearly and technical language as expected of the journal’s readership. All precautions were taken with the writing of this paper by the authors.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: Yes, I would like my name to appear with my report on Publons

    Reviewer: 2

    Recommendation: Major Revision

    Comments:
    --------------------------------------------------------------------------------------------------------------------------1. INTRODUCTION

    p. 1, line 47: The following review articles could also be cited:
    - Daniel Gropper, Ling Wang, Terry J. Harvey, Hydrodynamic lubrication of textured surfaces: A review of modeling techniques and key findings, Tribology International, v. 94, p. 509-529, 2016.
    - C. Gachot, A. Rosenkranz, S.M. Hsu, H.L. Costa, A critical assessment of surface texturing for friction and wear improvement, Wear, v. 372–373, p. 21-41, 2017.
    - Grützmacher, P.G.; Profito, F.J.; Rosenkranz, A. Multi-Scale Surface Texturing in Tribology Current Knowledge and Future Perspectives. Lubricants 2019, 7, 95.

    p. 1, line 54: The term 'lifting' could be replaced by 'additional hydrodynamic support'

    p. 2, line 25: The following publication could be cited throughout the manuscript instead of (or in addition to) Profito, 2015 where many aspects and formulations used in the present work were originally proposed:
    - F.J. Profito, D.C. Zachariadis, D. Dini, Partitioned fluid-structure interaction techniques applied to the mixed-elastohydrodynamic solution of dynamically loaded connecting-rod big-end bearings, Tribology International, v. 140, 2019.


    2.2. MODIFIED PATIR AND CHENG REYNOLDS EQUATION

    p. 4, Eq. 5: Why the contact factor (phi_c = h_T/h) was not considered in this version of P&C; Reynolds equation?

    p. 5, line 4: Why a transversely oriented roughness pattern was considered in the present work? More information about the surface topography of the investigated bearing should be provided.

    Since the proposed model is used to predicted mixed lubrication, asperity contact pressure should have been considered in the model. Why was this not considered in the formulation, and how the neglecting of rough contact effects may have influenced the obtained results? Furthermore, the authors must make clear that thermal effects and angular misalignments (important in ICE main bearing applications) have also been neglected from the analysis.


    2.3. CALCULATED CHARACTERISTICS

    p. 6, line 6: The fact that the bearing surface is fixed could be mentioned in Sec. 2.1.

    p. 6, Eq. 17: The plus-minus sign does not make sense here since only the friction force acting on the journal surface is considered in Eq. 17.

    p. 6, Eq. 18: What is the 'psi' quantity? Check if the defined hydrodynamic CoF is dimensionless.


    2.4. SURFACE TEXTURING

    p. 6, Eq. 19: To maintain consistency with Eq. 3, h(theta_b) could be written as h(theta_b,z_b)
    p. 6, line 50: What is a Cartesian difference system?


    2.5. 3D ELASTO-HYDRODYNAMIC LUBRICATION (EHL)

    p. 8, line 29: The term 'A 3D finite element model based on ...' could be replaced by '3D finite element substructuring approach based on ...'


    3.1 SOLUTION OF THE REYNOLDS EQUATION

    p. 9, line 37: The SOR algorithm proposed by Ausas is based on the finite volume discretization of p-theta Reynolds equation in which the (convective) Couette term is approximated by an upwind scheme. However, it was mentioned in p. 10 (and Fig. 6) that the finite difference method was used in the present manuscript. The authors should clarify this issue since the underlying requirement for the effectiveness of Ausas' algorithm to solve the p-theta model is the assurance of the local conservation of fluxes at each control volume of the discrete domain.


    1. RESULTS

    p. 15, line 28: crankshaft pf (???)

    p. 15, line 15: How were the forces calculated? Also, it should be mentioned that a quasi-static solution was adopted to solve the dynamic problem instead of a full transient one.

    p. 17, Table 1: What was the engine operating temperature?

    More details about the simulations setup, i.e. mesh size, time steps, convergence tolerances, etc. should be provided for all simulation cases.

    More detailed results showing the variations of the minimum oil film thickness, peak hydrodynamic and asperity contact pressures, power loss, CoF, shaft trajectory etc, over the engine operating cycle should be provided for all simulation cases. For instance, the knowledge of the magnitude of oil film thickness is important to assert the predominant lubrication regime at different instants of the engine cycle.

    Furthermore, the mechanisms involved in the verified power loss and CoF deviations should be discussed. There are trends that are not given a physical explanation. Linking them to observations does not give a physical explanation.


    4.1 TEXTURING LOCATION EFFECTS

    p. 18, Fig. 11: What is the z-axis scale?

    p. 19, Tab. 2: How the texture parameters listed in Table 2 were defined?


    4.2 DIMPLE RADIUS AND DEPTH

    p. 21, line 34: The use of the defined mean CoF can mislead the analysis of results since textures may be beneficial/detrimental at different instants/positions of the engine cycle. Therefore, it is strongly recommended to show all results as a function of the crank angle.

    p. 21, line 47: Why the reduction of the mean CoF would reach a limit and what would be the physical mechanisms involved to support such a statement.


    4.3 ELASTOHYDRODYNAMIC EFFECTS

    p. 23, line 54:
    Why the clamped boundary condition was chosen for all nodes on the external bearing surface? Does it make sense physically based on the configuration and assembly of the crankshaft system? If the displacements of all nodes on the external surface are restricted, practically no deformation associated with the bearing flexibility will occur in radial direction. This is not the case for this type of bearing in which EHL effects are significant. The authors should justify the used boundary condition and, if possible, cite other references that adopted similar constraints.

    p. 24, line 50:
    Contour plots of the film thickness after deformation should be provided along with the journal orbits. For EHL analysis, it is very important to analyze the magnitude of the surfaces' displacements and the deviations of the journal orbits from the ideal trajectory locus.

    Additional Questions:
    Originality: Does the paper contain new and significant information adequate to justify publication?: The manuscript does not contain solid new and significant information. Furthermore, there are figures in the manuscript that are very similar to ones already published in other references (e.g. Fig. 2 and Fig. 4). Also, it seems that to a great extent the present manuscript is a direct reproduction of other works with minor modifications.

    Relationship to Literature: Does the paper demonstrate an adequate understanding of the relevant literature in the field and cite an appropriate range of literature sources? Is any signficant work ignored?: The manuscript demonstrates acceptable understanding of the relevant literature.

    Methodology: Is the paper's argument built on an appropriate base of theory, concepts, or other ideas? Has the research or equivalent intellectual work on which the paper is based been well designed? Are the methods employed appropriate?: The manuscript is built on an appropriate base of theory and concepts, especially regarding the mathematical model used in the analysis. However, there are some issues in the solution procedure and simulation setup which must be addressed (see recommendations in 'Comments to the Author').

    Results: Are results presented clearly and analysed appropriately? Do the conclusions adequately tie together the other elements of the paper?: The presentation of the results should be improved to provide more explanations about the physical mechanisms responsible for the verified friction reduction (see recommendations in 'Comments to the Author').

    Practicality and/or Research implications: Does the paper identify clearly any implications for practice and/or further research? Are these implications consistent withthe findings and conclusions of the paper?: The manuscript identifies the implications for practice (friction reduction) and their consistency with the findings and conclusions.

    Quality of Communication: Does the paper clearly express its case, measured against the technical language of the field and the expected knowledge of the journal's readership? Has attention been paid to the clarity of expression and readability, such as sentence structure, jargon use, acronyms, etc.: The manuscript clearly expresses its case with a good and clear technical language. Only minor revision in the English language and a few typographical corrections should be addressed.

    Reproducible Research: If appropriate, is sufficient information, potentially including data and software, provided to reproduce the results and are the corresponding datasets formally cited?:

    This journal is participating in Publons Transparent Peer Review. By reviewing for this journal, you agree that your finished report, along with the author’s responses and the Editor’s decision letter, will be linked to from the published article to where they appear on Publons, if the paper is accepted. If you have any concerns about participating in the Transparent Peer Review pilot, please reach out to the journal’s Editorial office. Please indicate below, whether you would like your name to appear with your report on Publons by indicating yes or no: Yes, I would like my name to appear with my report on Publons

    Decision letter by
    Cite this decision letter
    Reviewer report
    2019/11/02

    --------------------------------------------------------------------------------------------------------------------------1. INTRODUCTION

    p. 1, line 47: The following review articles could also be cited:
    - Daniel Gropper, Ling Wang, Terry J. Harvey, Hydrodynamic lubrication of textured surfaces: A review of modeling techniques and key findings, Tribology International, v. 94, p. 509-529, 2016.
    - C. Gachot, A. Rosenkranz, S.M. Hsu, H.L. Costa, A critical assessment of surface texturing for friction and wear improvement, Wear, v. 372–373, p. 21-41, 2017.
    - Grützmacher, P.G.; Profito, F.J.; Rosenkranz, A. Multi-Scale Surface Texturing in Tribology Current Knowledge and Future Perspectives. Lubricants 2019, 7, 95.

    p. 1, line 54: The term 'lifting' could be replaced by 'additional hydrodynamic support'

    p. 2, line 25: The following publication could be cited throughout the manuscript instead of (or in addition to) Profito, 2015 where many aspects and formulations used in the present work were originally proposed:
    - F.J. Profito, D.C. Zachariadis, D. Dini, Partitioned fluid-structure interaction techniques applied to the mixed-elastohydrodynamic solution of dynamically loaded connecting-rod big-end bearings, Tribology International, v. 140, 2019.


    2.2. MODIFIED PATIR AND CHENG REYNOLDS EQUATION

    p. 4, Eq. 5: Why the contact factor (phi_c = h_T/h) was not considered in this version of P&C; Reynolds equation?

    p. 5, line 4: Why a transversely oriented roughness pattern was considered in the present work? More information about the surface topography of the investigated bearing should be provided.

    Since the proposed model is used to predicted mixed lubrication, asperity contact pressure should have been considered in the model. Why was this not considered in the formulation, and how the neglecting of rough contact effects may have influenced the obtained results? Furthermore, the authors must make clear that thermal effects and angular misalignments (important in ICE main bearing applications) have also been neglected from the analysis.


    2.3. CALCULATED CHARACTERISTICS

    p. 6, line 6: The fact that the bearing surface is fixed could be mentioned in Sec. 2.1.

    p. 6, Eq. 17: The plus-minus sign does not make sense here since only the friction force acting on the journal surface is considered in Eq. 17.

    p. 6, Eq. 18: What is the 'psi' quantity? Check if the defined hydrodynamic CoF is dimensionless.


    2.4. SURFACE TEXTURING

    p. 6, Eq. 19: To maintain consistency with Eq. 3, h(theta_b) could be written as h(theta_b,z_b)
    p. 6, line 50: What is a Cartesian difference system?


    2.5. 3D ELASTO-HYDRODYNAMIC LUBRICATION (EHL)

    p. 8, line 29: The term 'A 3D finite element model based on ...' could be replaced by '3D finite element substructuring approach based on ...'


    3.1 SOLUTION OF THE REYNOLDS EQUATION

    p. 9, line 37: The SOR algorithm proposed by Ausas is based on the finite volume discretization of p-theta Reynolds equation in which the (convective) Couette term is approximated by an upwind scheme. However, it was mentioned in p. 10 (and Fig. 6) that the finite difference method was used in the present manuscript. The authors should clarify this issue since the underlying requirement for the effectiveness of Ausas' algorithm to solve the p-theta model is the assurance of the local conservation of fluxes at each control volume of the discrete domain.


    1. RESULTS

    p. 15, line 28: crankshaft pf (???)

    p. 15, line 15: How were the forces calculated? Also, it should be mentioned that a quasi-static solution was adopted to solve the dynamic problem instead of a full transient one.

    p. 17, Table 1: What was the engine operating temperature?

    More details about the simulations setup, i.e. mesh size, time steps, convergence tolerances, etc. should be provided for all simulation cases.

    More detailed results showing the variations of the minimum oil film thickness, peak hydrodynamic and asperity contact pressures, power loss, CoF, shaft trajectory etc, over the engine operating cycle should be provided for all simulation cases. For instance, the knowledge of the magnitude of oil film thickness is important to assert the predominant lubrication regime at different instants of the engine cycle.

    Furthermore, the mechanisms involved in the verified power loss and CoF deviations should be discussed. There are trends that are not given a physical explanation. Linking them to observations does not give a physical explanation.


    4.1 TEXTURING LOCATION EFFECTS

    p. 18, Fig. 11: What is the z-axis scale?

    p. 19, Tab. 2: How the texture parameters listed in Table 2 were defined?


    4.2 DIMPLE RADIUS AND DEPTH

    p. 21, line 34: The use of the defined mean CoF can mislead the analysis of results since textures may be beneficial/detrimental at different instants/positions of the engine cycle. Therefore, it is strongly recommended to show all results as a function of the crank angle.

    p. 21, line 47: Why the reduction of the mean CoF would reach a limit and what would be the physical mechanisms involved to support such a statement.


    4.3 ELASTOHYDRODYNAMIC EFFECTS

    p. 23, line 54:
    Why the clamped boundary condition was chosen for all nodes on the external bearing surface? Does it make sense physically based on the configuration and assembly of the crankshaft system? If the displacements of all nodes on the external surface are restricted, practically no deformation associated with the bearing flexibility will occur in radial direction. This is not the case for this type of bearing in which EHL effects are significant. The authors should justify the used boundary condition and, if possible, cite other references that adopted similar constraints.

    p. 24, line 50:
    Contour plots of the film thickness after deformation should be provided along with the journal orbits. For EHL analysis, it is very important to analyze the magnitude of the surfaces' displacements and the deviations of the journal orbits from the ideal trajectory locus.

    Cite this review
    Reviewer report
    2019/11/01

    General comments:
    This is a technically work with a good contextualization in the virtual texturing and energy losses field. In general, the language level is good. The methodology is detailed well founded. Results are well connected and give an interesting insight into the development of new possibilities for technologies applied to this problem.

    Detailed comments:
    Results
    - Influence of the dimple radius on the friction coefficient and power loss behaves similarly to the influence of dimple depth on the friction coefficient and power loss, but less evidently. Is it possible to identify values at which it is unviable to increase depth by defining, for example, a relative error in relation to the reduction rate?
    - Why was the 1.9 mm radius adopted to study the influence of dimple depth variation rather than 2.3 mm which showed a greater reduction in the friction coefficient and power loss? Was it because it presented a larger reduction when compared to the previous value?
    - Explain why a density of 65% was used and show how density is calculated, dividing the ratio of texture area by cell area
    - How β parameter was calculated? If we take as an example the case with nx = 3 and nz = 5 illustrated in section 4.1, with the values of L and R present in Table 1 and the values of Ltx and Lty shown in table 2, it is not possible to obtain the values of β 60% and 100%.

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