Numerical Study on Improved Geometry of Outlet Pressure Ripple in Parallel 2D Piston Pumps
Nigel Johnston
Round 1
Reviewer 1 Report
The presented work is very relevant and interesting, has a certain scientific value. However, as a reviewer, I have the following remarks.
1. In the introduction, there is no review of structures that have two cylinders and a uniform supply of each of them in a certain area (see, for example, the patent of the Russian Federation for the invention No. There is no justification that the structure under study is better than the one indicated above.
2. The continuity equation (formula 1) does not take into account the change in the density of the liquid, while this account is taken below (see, for example, equation 5).
3. The authors confuse the "modernization" of the pump, which is performed in the article, with "optimization". In the event that optimization is carried out, then it is necessary to choose the objective function. In this case, as an objective function, I would recommend the sum of pressure deviations at the outlet of the pump per cycle from the nominal one, there is no definition of optimization parameters based on their influence on the objective function. There is no choice and justification of the non-linear implicit optimization method.
4. Insufficiently correct verification of the developed mathematical model was carried out. It is not clear why it was impossible to achieve full geometric correspondence between the developed mathematical model and the full-scale sample.
Author Response
Reviewer#1, Concern # 1: In the introduction, there is no review of structures that have two cylinders and a uniform supply of each of them in a certain area (see, for example, the patent of the Russian Federation for the invention No. There is no justification that the structure under study is better than the one indicated above.
Author response: We are very sorry, because of editorial or submission system reasons, we are unable to see the patent you provided. We acknowledge that the introduction is not sufficient, and we will add some more. We do not say that the 2D pump we developed is better than the any hydraulic pump, but to, in this paper, test and verify that this 2D pump doesn’t have structural flow ripple and found the first stone for the further research to reduce the ripple. The pros and cons of various structures include 2D pumps are covered in a paper published by my colleagues.
Zhang, C., Zhu, C., Meng, B., & Li, S. (2021). Challenges and Solutions for High-Speed Aviation Piston Pumps: A Review. Aerospace, 8(12), 392.
Author action: add in introduction
“
However, in aviation and aerospace fields, the outlet pressure ripple of axial piston pumps is needed to particular concern because it can cause vibration of pipelines, cause damage to hydraulic components, and endanger the stability of hydraulic systems [4-6].
Swarnava conducted an investigation of a novel positive displacement axial piston machine using a bent cylinder sleeve configuration, and groove geometry was chosen primarily to reduce flow ripple [19].
The output flow curve of the high-speed 2D piston pump is a triangular curve, and the working principle and output flow characteristics of the 2D pump have been described in detail in Reference [23] and will not be described here.
The parallel 2D piston pump, a hydraulic pump without structural flow ripple, is a great innovation, but unfortunately there is no research to measure its outlet flow and pressure ripples, and no solution to further reduce its ripples has been proposed [25].
- Battarra, M., Mucchi, E. On the relation between vane geometry and theoretical flow ripple in balanced vane pumps. Mechanism and Machine Theory 2020, 146, 103736.
- Mukherjee, S., Masia, A., Bronson, M., Shang, L., Vacca, A. A Novel Positive Displacement Axial Piston Machine With Bent Cylinder Sleeves. In Proceedings of ASME/BATH 2021 Symposium on Fluid Power and Motion Control, Online, 2021; p. V001T01A024.
- Zhang, C., Zhu, C., Meng, B., Li, S. Challenges and Solutions for High-Speed Aviation Piston Pumps: A Review. Aerospace 2021, 8, 392.
”
Reviewer#1, Concern # 2: The continuity equation (formula 1) does not take into account the change in the density of the liquid, while this account is taken below (see, for example, equation 5).
Author response: This is our mistake, and we have revised equation 1.
Author action:
Reviewer#1, Concern # 3: The authors confuse the "modernization" of the pump, which is performed in the article, with "optimization". In the event that optimization is carried out, then it is necessary to choose the objective function. In this case, as an objective function, I would recommend the sum of pressure deviations at the outlet of the pump per cycle from the nominal one, there is no definition of optimization parameters based on their influence on the objective function. There is no choice and justification of the non-linear implicit optimization method.
Author response: We took your suggestion and changed " optimization " to " improved geometry ".
Author action: The corresponding “optimization” has been revised to “improved geometry”.
Reviewer#1, Concern # 4: Insufficiently correct verification of the developed mathematical model was carried out. It is not clear why it was impossible to achieve full geometric correspondence between the developed mathematical model and the full-scale sample.
Author response: This was indeed our mistake. The geometry of the experiment and the simulation did not match. Of course, the simulation model is not fully established, such as the lack of leakage. This will be noted in our future simulations and experimental tests of the flow ripple in the parallel 2D piston pump.
Author action: added” Finally, measuring outlet flow ripple of the parallel 2D piston pump are also in progress, and the geometry of the numerical model of the parallel 2D pump will also more closely match the geometry of the experiment. ”in discussion and conclusion.
Reviewer 2 Report
The work is properly designed and the experimental assessment supports the numerical results. English language is appropriate, despite some improvements could be achieved. Based on this considerations, it is the reviewer's opinion that the manuscript may become worthy of publication after the following remarks have been fully addressed:
1 - It is somehow hard to understand the original contribution provided by this work. Originality must be clearly stated in the section introduction, highlighting the novelty of the proposed work.
2 - The literature survey is excessively restricted and it should be extended. Ripple attenuation in volumetric pumps is a well known subject with a lot of remarkable contributions already published. See for example:
- "On the relation between vane geometry and theoretical flow ripple in balanced vane pumps" (2020) Mechanism and Machine Theory, 146, art. no. 103736
- "A NOVEL POSITIVE DISPLACEMENT AXIAL PISTON MACHINE WITH BENT CYLINDER SLEEVES" (2021) Proceedings of ASME/BATH 2021 Symposium on Fluid Power and Motion Control, FPMC 2021
3 - How did the authors choose the refinement of the grid? A grid convergence plot should be included within the manuscript
4 - The authors use the term "optimization", however it is not clear if an optimization algorithm was used to improve the pump geometry or it is simply a trial&error improvement process. In the first case, the authors should provide more details about the optimization process. In the second case, the authors should avoid using the term "optimization", since it refers to a precise scientific approach. Better use the term "improved geometry" or similar.
5 - It is difficult to recognize a carrier frequency within the experimental data in Fig. 21(a). Please, provide also the FFT plot of the same data in order to have a more detailed view.
Author Response
Reviewer#2, Concern # 1: It is somehow hard to understand the original contribution provided by this work. Originality must be clearly stated in the section introduction, highlighting the novelty of the proposed work.
Author response: This is our mistake not to highlight the innovation of the article. The 2D piston pump is an innovative hydraulic pump, and there is little research about its unique characteristics. In particular, the 2D pump is designed for low outlet ripples, but the corresponding research has been missing, and this study tries to fill this blank. We will add descriptions of innovations in the article.
Author action: It is first pointed out in the introduction that reference 23 has a detailed description of the working principle of the high-speed 2D piston pump.
“The output flow curve of the high-speed 2D piston pump is a triangular curve, and the working principle and output flow characteristics of the 2D pump have been described in detail in Reference [23] and will not be described here.”
Secondly, in the last paragraph of the introduction, the innovation and importance of this paper are again raised.
“The parallel 2D piston pump, a hydraulic pump without structural flow ripple, is a great innovation, but unfortunately there is no research to measure its outlet flow and pressure ripples, and no solution to further reduce its ripples has been proposed [25].”
- Zhang, C., Zhu, C., Meng, B., Li, S. Challenges and Solutions for High-Speed Aviation Piston Pumps: A Review. Aerospace 2021, 8, 392.
Reviewer#2, Concern # 2: The literature survey is excessively restricted and it should be extended. Ripple attenuation in volumetric pumps is a well known subject with a lot of remarkable contributions already published. See for example:
- "On the relation between vane geometry and theoretical flow ripple in balanced vane pumps" (2020) Mechanism and Machine Theory, 146, art. no. 103736
- "A NOVEL POSITIVE DISPLACEMENT AXIAL PISTON MACHINE WITH BENT CYLINDER SLEEVES" (2021) Proceedings of ASME/BATH 2021 Symposium on Fluid Power and Motion Control, FPMC 2021
Author response: Many thanks for the references provided, which we will add to the article.
Author action: added “However, in aviation and aerospace fields, the outlet pressure ripple of axial piston pumps is needed to particular concern because it can cause vibration of pipelines, cause damage to hydraulic components, and endanger the stability of hydraulic systems [4-6].”
- Battarra, M., Mucchi, E. On the relation between vane geometry and theoretical flow ripple in balanced vane pumps. Mechanism and Machine Theory 2020, 146, 103736.
“Swarnava conducted an investigation of a novel positive displacement axial piston ma-chine using a bent cylinder sleeve configuration, and groove geometry was chosen primarily to reduce flow ripple [19].”
- Mukherjee, S., Masia, A., Bronson, M., Shang, L., Vacca, A. A Novel Positive Displacement Axial Piston Machine With Bent Cylinder Sleeves. In Proceedings of ASME/BATH 2021 Symposium on Fluid Power and Motion Control, Online, 2021; p. V001T01A024.
in the introduction.
Reviewer#2, Concern # 3: How did the authors choose the refinement of the grid? A grid convergence plot should be included within the manuscript
Author response: We did this research, and because the number of grids has little effect on the results, it was not added to the article. We will add it in the corresponding paragraph.
Author action:
Added ”
Figure 9. Relation between number of mesh elements and averaged outlet pressure.
Averaged outlet pressures are compared by increasing the number of mesh elements with similar quality of the mesh element, as shown in Figure 9. From 2.6×105 mesh elements to 4.9×105 mesh elements, the averaged outlet pressure changes by 0.625%. From 4.9×105 mesh elements to 7.5×105 mesh elements, the averaged outlet pressure changes by 0.25%. So, a grid with a number of 7.5×105 elements is chosen as the computational model.” in line 161.
Reviewer#2, Concern # 4: The authors use the term "optimization", however it is not clear if an optimization algorithm was used to improve the pump geometry or it is simply a trial&error improvement process. In the first case, the authors should provide more details about the optimization process. In the second case, the authors should avoid using the term "optimization", since it refers to a precise scientific approach. Better use the term "improved geometry" or similar.
Author response: This is a very good suggestion, and we choose the second option.
Author action: The corresponding “optimization” has been revised to “improved geometry”.
Reviewer#2, Concern # 5: It is difficult to recognize a carrier frequency within the experimental data in Fig. 21(a). Please, provide also the FFT plot of the same data in order to have a more detailed view.
Author response: We adopted this suggestion. Add this FFT plot in the experiment section.
Author action: The figure 23 is added and the similarities and differences between experiment and simulation are analyzed.
Figure 23. Frequency spectrograms of the test data and simulation result
Author Response File: 
Author Response.pdf
Reviewer 3 Report
Page 2: it is not clear how the pump operates. Figure 1 is not sufficient, and a clear diagram and explanation is needed. Without a clear explanation, the rest of the paper is difficult to follow. It is not clear what “2D” means in this context.
Several abbreviations, e.g. LLC, LRC, RNG. LLCMW are used without definition (some are defined much later in the paper).
Page 9: it is stated that the pressure decline is caused not by backflow but by the transition from acceleration to deceleration. Whilst this is a plausible explanation, there is no evidence for it. Some evidence for this claim should be presented, and there should be enough information in the simulation results to provide this evidence. Indeed the pressure decline corresponds to the delivery pressure decline due to compressibility (at 60 degrees in figure 16), so this is probably a contributing factor if not the only factor.
Lines 286-288 state that “there is no correlation between the chamber pressure and the pump outlet pressure” and “Their pressure declines seem to correspond, but this is just a coincidence”. I would argue that there is a correlation; the slight delay in the outlet pressure dip is simply due to the integrating effect of the compressible oil volume in the delivery line.
Line 362: It is claimed that “the experimental result and the numerical simulation are basically consistent”. I see little correlation here, even in the period of the pulsations.
The quality of the spectra in figure 23 is poor; I would like to see more data points in the important region up to 10 kHz (by taking data over a longer period). Frequency content above 10 kHz is largely irrelevant.
Two explanations for the differences between experiment and simulation: the different position of the pressure sensor, and the shape of the distribution windows. These differences could easily be rectified and then a more meaningful comparison could be drawn.
There are some errors of English, for example:
Line 29: “is needed to particular concern” –> “is of particular concern”
Author Response
Reviewer#1, Concern # 1: Page 2: it is not clear how the pump operates. Figure 1 is not sufficient, and a clear diagram and explanation is needed. Without a clear explanation, the rest of the paper is difficult to follow. It is not clear what “2D” means in this context.
Author response: We understand your opinion. However, the mechanical structure and working principle of this two-dimensional (2D) pump have been introduced in detail in earlier articles, and it takes a long text to introduce the relevant content. So we just listed a few related articles to give readers a better understanding of 2D pumps.
Author action: line 73: ”The output flow curve of the high-speed 2D piston pump is a triangular curve, and the working principle and output flow characteristics of the 2D pump have been described in detail in References [23] and [24] and will not be described here.”
- Huang, Y., Ding, C., Wang, H., Ruan, J. Numerical and experimental study on the churning losses of 2D high-speed piston pumps. Engineering Applications of Computational Fluid Mechanics 2020, 14, 764-777.
- Shentu, S., Ruan, J., Qian, J., Meng, B., Wang, L., Guo, S. Study of flow ripple characteristics in an innovative two-dimensional fuel piston pump. Journal of the Brazilian Society of Mechanical Sciences and Engineering 2019, 41, 1-15.
Reviewer#1, Concern # 2: Several abbreviations, e.g. LLC, LRC, RNG. LLCMW are used without definition (some are defined much later in the paper).
Author response: We accept your comment and revise the article. The corresponding definitions of LLC, LRC, CFD, and RNG have been supplemented. LLCMW is just a symbol sign without definition.
Author action:
Line 44: ”There are many studies on the flow ripple, such as the work by Ma where they optimized the design of the valve plate using the mathematical model and computational fluid dynamics (CFD) simulation to reduce the compressible flow ripple [13,14].”
Line 186: ”The renormalization group (RNG) k-ε model is used as the turbulence model for this simulation.”
Line 211: “For the convenience of understanding, the left chamber of the left pump unit is denoted by the symbol, LLC, and the left distribution part of the left pump unit is denoted by the symbol, LLDP, and so on.”
Reviewer#1, Concern # 3: Page 9: it is stated that the pressure decline is caused not by backflow but by the transition from acceleration to deceleration. Whilst this is a plausible explanation, there is no evidence for it. Some evidence for this claim should be presented, and there should be enough information in the simulation results to provide this evidence. Indeed the pressure decline corresponds to the delivery pressure decline due to compressibility (at 60 degrees in figure 16), so this is probably a contributing factor if not the only factor.
Author response: We originally thought that the pressure decline was caused by the acceleration change, but the simulation of a single pump unit found that the acceleration change would not produce such a large pressure decline, as shown in figures 13 and 14. The final analysis thinks it is caused by this parallel mechanical structure, as shown in figure 15. This pressure decline occurs as the oil flows back and forth between the left and right pump units.
Author action:
Reviewer#1, Concern # 4: Lines 286-288 state that “there is no correlation between the chamber pressure and the pump outlet pressure” and “Their pressure declines seem to correspond, but this is just a coincidence”. I would argue that there is a correlation; the slight delay in the outlet pressure dip is simply due to the integrating effect of the compressible oil volume in the delivery line.
Author response: We still believe that the outlet flow ripple is the main cause of the outlet pressure ripple. Because the two simulation images are fitted, compare figures 16 and 17. But we also agree with your mention of the effect of delivery pressure, which we added to the analysis.
Author action: Line 292: ” Their pressure declines seem to correspond, but this is not actually inferred from their maintained rotational angles. But the pressure declines in the chambers may be transmitted to the outlet and exacerbate the outlet pressure ripple due to the oil compressibility.”
Reviewer#1, Concern # 5: Line 362: It is claimed that “the experimental result and the numerical simulation are basically consistent”. I see little correlation here, even in the period of the pulsations.
Author response: We believe that in the amplitude-frequency graph, the two sets of data are relatively similar, especially in frequency. We modify our wording.
Author action: line 368: “Firstly, the experimental result and the numerical simulation are relatively consistent, especially in the prediction of the pressure ripple period.”
Reviewer#1, Concern # 6: The quality of the spectra in figure 23 is poor; I would like to see more data points in the important region up to 10 kHz (by taking data over a longer period). Frequency content above 10 kHz is largely irrelevant.
Author response: We accept your comments and revise the article.
Author action:
|
(a) |
(b) |
Figure 23. Frequency spectrograms of the test data and simulation result. (a) The range is 50 kHz and (b) the range is 10 kHz.
Reviewer#1, Concern # 7: Two explanations for the differences between experiment and simulation: the different position of the pressure sensor, and the shape of the distribution windows. These differences could easily be rectified and then a more meaningful comparison could be drawn.
Author response:
We accept your comment. The main purpose of our article is to measure and reduce the outlet pressure ripple of the pump. Through the test, the outlet pressure ripple of the pump is measured to be a small value that meets the requirement. Of course, our CFD model does have shortcomings, and the modeling of the distribution window is also relatively rough. We intend to put further work into the pump outlet flow ripple test to complete.
Author action:
Line 405: “Finally, measuring outlet flow ripple of the parallel 2D piston pump are also in progress, and the geometry of the numerical model of the parallel 2D pump will also more closely match the geometry of the experiment.”
Reviewer#1, Concern # 8: Line 29: “is needed to particular concern” –> “is of particular concern”
Author response: We accept your comments and revise the article.
Author action: “However, in aviation and aerospace fields, the outlet pressure ripple of axial piston pumps is of particular concern because it can cause vibration of pipelines, cause damage to hydraulic components, and endanger the stability of hydraulic systems [4-6].”
Author Response File: Author Response.pdf
Reviewer 4 Report
This work looks at the occurrence of pressure flow ripples in 2D piston pumps, performing a numerical simulation to understand the cause of these ripples and to determine an optimized design to reduce these pressure ripples. Finally an experimental prototype is constructed based on these optimized designs showing a reduction in the flow ripple. Overall the study is well conducted, technically sound and the results are of merit in the field, and worthy of publication in the journal. I think the writing could be improved, and so the manuscript would benefit from a thorough proof reading. Also on the numerical schemes used and the equations solved the authors should expand on what they have written (see comments below).
Comments:
line 13: 50 L/min, symbol "L" needs to be defined? This is important to define as it is used also later on in the manuscript.
line 29: this sentence does not make sense, "ripple of axial piston pumps is needed to particular concern because it can cause vibration". Do you mean something like "...piston pumps are of particular concern because...".
line 44: not clear what is meant by "such as Ma optimized...", better write something like "such as the work by Ma where they optimized..."
line 69: Not properly formed sentence beginning "The 2D pump ... deceleration proposed by our term", you need to insert the word "was" between deceleration and proposed.
line 85: remove the word "on" between the word "studied" and "the"
line 101: change "present" to "presented"
line 113: Change "Remaining oil" to "The remaining oil"
line 193-196: From the list of numerical schemes used and the equations presented its not clear exactly what you are solving here. You say you are using a second order scheme for to model the pressure, though you haven't presented an equation for the evolution of pressure? As pressure a crucial variable in this study it is important that its treatment, both in terms of the governing equation and how it is numerically solved, is stated clearly.
Also you only use a first order upwind scheme for the turbulence rather than second order as used for the momentum equations. Do you have a reason (or citation from previous works) motivating the choice of the schemes you use?
line 203: change "accurately control" to "accurately controlled"
line 220: It is strange to start a sentence with an equation, probably you should insert equation (9) directly after the line "expressed by equation 9" and then after the equation continue with "where the direction of rotation conforms to the right-hand rule and where n is the rotational speed...".
line 235 Figure 11: The caption needs to be expanded on and the figure needs to be better labeled. The small subplot on the left-hand-side has no labels on the x-y axis, and the overall meaning of the overlay of the right plot on top of the circle with the arrows needs to be explained clearly so that it can be properly interpreted.
line 279: change "as figure 15" to "as shown in figure 15"
line 281: change "can effect on" to "can have an effect on"
line 288: remove word "related" here
line 380: change "correctness of the..." to "the accuracy of the...". Though this statement that the accuracy/correctness is verified is somewhat questionable, seeing as there are differences, as you have identified in the last paragraph of the section before. Perhaps you can change the sentence stating more carefully that the model has been tested and has shown consistency with the optimized prototype.
Author Response
Reviewer#2, Concern # 1: line 13: 50 L/min, symbol "L" needs to be defined? This is important to define as it is used also later on in the manuscript.
Author response: We accept your comments and revise the article.
Author action: line 80: ” A pump with a rated flow rate of 50 L/min where L is the volume unit and 1 L is equal to 1 dm3, a rated load pressure of 8 MPa, and a small outlet pressure ripple is re-quired for a special working condition of the aerospace field.”
Reviewer#2, Concern # 2: line 29: this sentence does not make sense, "ripple of axial piston pumps is needed to particular concern because it can cause vibration". Do you mean something like "...piston pumps are of particular concern because...".
Author response: Your understanding is correct. We will correct this grammatical error.
Author action: line 28: “However, in aviation and aerospace fields, the outlet pressure ripple of axial piston pumps is of particular concern because it can cause vibration of pipelines, cause damage to hydraulic components, and endanger the stability of hydraulic systems [4-6].”
Reviewer#2, Concern # 3: line 44: not clear what is meant by "such as Ma optimized...", better write something like "such as the work by Ma where they optimized..."
Author response: We accept your comments and revise the article.
Author action: Iine44: “There are many studies on the flow ripple, such as the work by Ma where they optimized the design of the valve plate using the mathematical model and CFD simulation to reduce the compressible flow ripple [13,14].”
Reviewer#2, Concern # 4: line 69: Not properly formed sentence beginning "The 2D pump ... deceleration proposed by our term", you need to insert the word "was" between deceleration and proposed.
Author response: We accept your comments and revise the article.
Author action: line 69: “The 2D pump using the guiding rail with a uniform acceleration and a uniform deceleration was proposed by our team, in order to eliminate the structural flow ripple [21,22].”
Reviewer#2, Concern # 5: line 85: remove the word "on" between the word "studied" and "the"
Author response: We accept your comments and revise the article.
Author action: line 86: “Shentu studied the outlet pressure ripple of a parallel 2D pump by CFD simulations and experimental studies [24].”
Reviewer#2, Concern # 6: line 101: change "present" to "presented"
Author response: We accept your comments and revise the article.
Author action: line 100: “Finally, experimental results will be presented as an example to verify the simulation and the improved geometry design.”
Reviewer#2, Concern # 7: line 114: Change "Remaining oil" to "The remaining oil"
Author response: We accept your comments and revise the article.
Author action: line 113: “The remaining oil enters the cylindrical chamber in the middle through kidney-shaped channels and circular channels, and then enters the left pump unit through kidney-shaped channels.”
Reviewer#2, Concern # 8: line 193-196: From the list of numerical schemes used and the equations presented its not clear exactly what you are solving here. You say you are using a second order scheme for to model the pressure, though you haven't presented an equation for the evolution of pressure? As pressure a crucial variable in this study it is important that its treatment, both in terms of the governing equation and how it is numerically solved, is stated clearly.
Also you only use a first order upwind scheme for the turbulence rather than second order as used for the momentum equations. Do you have a reason (or citation from previous works) motivating the choice of the schemes you use?
Author response: We use the commercial software Fluent for simulation, and these need to be set in the solution methods. We will supplement this in the article.
The first-order upwind scheme is used for turbulence because it was used for the simulations in our previous article, so it was chosen to control the variable.
- Shentu, S., Ruan, J., Qian, J., Meng, B., Wang, L., Guo, S. Study of flow ripple characteristics in an innovative two-dimensional fuel piston pump. Journal of the Brazilian Society of Mechanical Sciences and Engineering 2019, 41, 1-15.
Author action: line 193: “The solution methods are required for solving the numerical calculation through the commercial software FLUENT.”
Reviewer#2, Concern # 9: line 203: change "accurately control" to "accurately controlled"
Author response: We accept your comments and revise the article.
Author action: line 204: “One disadvantage of using a throttle valve to modulate pressure is that it cannot be accurately controlled.”
Reviewer#2, Concern # 10: line 220: It is strange to start a sentence with an equation, probably you should insert equation (9) directly after the line "expressed by equation 9" and then after the equation continue with "where the direction of rotation conforms to the right-hand rule and where n is the rotational speed...".
Author response: We accept your comments and revise the article.
Author action:
Line 223: “
The LLDP, LRDP, RLDP, and RRDP also rotate at the angular velocity of ω that is expressed by equation 9,
|
, |
(9) |
where n is the rotational speed in rpm and the direction of rotation conforms to the right-hand rule.
”
Reviewer#2, Concern # 11: line 235 Figure 11: The caption needs to be expanded on and the figure needs to be better labeled. The small subplot on the left-hand-side has no labels on the x-y axis, and the overall meaning of the overlay of the right plot on top of the circle with the arrows needs to be explained clearly so that it can be properly interpreted.
Author response: We accept your comments and revise the article.
Author action:
Figure 11. The chamber pressure in the LLC.
Reviewer#2, Concern # 12: line 279: change "as figure 15" to "as shown in figure 15"
Author response: We accept your comments and revise the article.
Author action: line 283: “In order to study the outlet load of the pump unit in the parallel 2D piston pump, pressure distributions of the outlet flow zone are plotted as shown in figure 15.”
Reviewer#2, Concern # 13: line 281: change "can effect on" to "can have an effect on"
Author response: We accept your comments and revise the article.
Author action: line 287: “In the parallel 2D piston pump, the symmetrical distribution of the left and right pump units can cause the oil to move left and right, so that the outlet load fluctuation of the pump unit can have an effect on the pressure fluctuation in the chamber.”
Reviewer#2, Concern # 14: line 288: remove word "related" here
Author response: We accept your comments and revise the article.
Author action: line 290: “Their pressure declines seem to correspond, but this is not actually inferred from their maintained rotational angles.”
Reviewer#2, Concern # 15: line 380: change "correctness of the..." to "the accuracy of the...". Though this statement that the accuracy/correctness is verified is somewhat questionable, seeing as there are differences, as you have identified in the last paragraph of the section before. Perhaps you can change the sentence stating more carefully that the model has been tested and has shown consistency with the optimized prototype.
Author response: We accept your comments and revise the article. The numerical model is only a reference for the design of the prototype. We want to see more test results of the prototype. Therefore, the first highlight of the conclusion is the low pressure ripple test results of the prototype. Of course, for the improvement of the numerical model, we will further study in the future.
Author action: line 380: ”In the end, the accuracy of the numerical simulation is verified and the outlet pressure ripple rate of the parallel 2D piston pump is measured by testing the outlet pressure ripple of the optimized prototype.”
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
The authors are thanked for their response to my previous comments. I follow up those comments here.
Concern #1: I appreciate that a long explanation of the operation would be a repetition of previous papers. However the reader may not have access to these papers. I feel that inclusion of figure 2 from ref. (23) would be helpful, with a brief explanation.
Concern #2: addressed satisfactorily.
Concern #3: In the author’s response, it is stated that the pressure decline is caused not by the acceleration change, as stated in the previous version, but by the parallel mechanical structure. However the revised paper still states that it is caused by the acceleration change (lines 246 to 249). The “parallel mechanical structure” reason does not seem to be explained in the revised paper.
Concern #4: I think I may have misinterpreted this as I was focusing on the flow data, fig 17, instead of the pressure data, fig 16. This is now satisfactory.
Concern #5: Figure 23(b) has been added which is a zoomed-in version of figure 23(a). However it does not help much as the spectral points are coarsely spaced and do not seem to correspond to the harmonic frequencies of the data (from figure 22(b) the period is 1.5 msec corresponding to a fundamental frequency of 667Hz, whereas in figure 23 the data points are about 770 Hz apart). The fft needs to be applied on a longer data set to get a meaningful and detailed spectrum.
Author Response
Reviewer#1, Concern # 1: I appreciate that a long explanation of the operation would be a repetition of previous papers. However the reader may not have access to these papers. I feel that inclusion of figure 2 from ref. (23) would be helpful, with a brief explanation.
Author response: We accept your suggestion and make changes.
Author action:
|
(a) |
(b) |
Figure 1. (a) The mechanical design of a parallel 2D piston pump and (b) working principle of the rollers and the guiding rail.
line72: “Figure 1(a) demonstrates the mechanical design of a parallel 2D piston pump which consists of two high-speed 2D piston pumps mechanically connected in series. The transmission mechanism of the high-speed 2D piston pump is a mechanism composed of the rollers and the guiding rail, as shown in Figure 1(b). When the cone rollers of the driving roller and balancing roller are rolling on the guide rail, the rotation of the driving roller and balancing roller into a reciprocating linear motion.”
Reviewer#1, Concern # 2: addressed satisfactorily.
Author response: Thank you for your comment.
Author action:
Reviewer#1, Concern # 3: In the author’s response, it is stated that the pressure decline is caused not by the acceleration change, as stated in the previous version, but by the parallel mechanical structure. However the revised paper still states that it is caused by the acceleration change (lines 246 to 249). The “parallel mechanical structure” reason does not seem to be explained in the revised paper.
Author response: We agree with you after careful reading. The problem we wrote is that your understanding has deviated. We will improve this.
Author action:
Line 254: “However, this interpretation is not supported by corresponding research, so a single pump unit is simulated to verify this interpretation.”
Line 281: “Firstly, the pressure fluctuation disappears, and there is only a pressure decline of nearly 45 degrees, which is far less than the pressure decline in the previous parallel 2D piston pump simulation. This shows that the inertia caused by the change of acceleration is not the main reason for the pressure decline.”
Line 292: “In the parallel 2D piston pump, the symmetrical distribution of the left and right pump units can cause the oil to move left and right, so that the outlet load fluctuation of the pump unit can have an effect on the pressure fluctuation and pressure decline in the chamber. The influence of the symmetrical distribution of the left and right pump units on chamber pressure will continue to be concerned.”
Reviewer#1, Concern # 4: I think I may have misinterpreted this as I was focusing on the flow data, fig 17, instead of the pressure data, fig 16. This is now satisfactory.
Author response: Thank you for your comment.
Author action:
Reviewer#1, Concern # 5: Figure 23(b) has been added which is a zoomed-in version of figure 23(a). However it does not help much as the spectral points are coarsely spaced and do not seem to correspond to the harmonic frequencies of the data (from figure 22(b) the period is 1.5 msec corresponding to a fundamental frequency of 667Hz, whereas in figure 23 the data points are about 770 Hz apart). The fft needs to be applied on a longer data set to get a meaningful and detailed spectrum.
Author response: We have taken your suggestion. Redrawn for Figure 23.
Author action:
Figure 23. Frequency spectrograms of the test data and simulation result.
Line 375: “The comparison between the processed data and the original data is shown in figure 22(a). Then, the processed experimental data and the simulation are compared, as shown in figures 22(b) and 23, and the following conclusions are drawn.”
Author Response File: Author Response.pdf
Round 3
Reviewer 3 Report
Concern #1: now ok.
Concern #2: now ok.
Concern #3: explanation is now ok. I don’t think there’s any need to mention the previous explanation of it being due to a change in acceleration. If this explanation is mentioned, please say why it is not supported by your research – i.e. it would cause less pressure change that is observed.
Concern #4: now ok
Concern #5: The quality of the plot is much better. However the agreement between simulation and test is poor and this should be mentioned.
Author Response
Reviewer#1, Concern # 3: Explanation is now ok. I don’t think there’s any need to mention the previous explanation of it being due to a change in acceleration. If this explanation is mentioned, please say why it is not supported by your research – i.e. it would cause less pressure change that is observed.
Author response: Thanks for your comment. We simulated the single pump unit first, and found the phenomenon of this pressure decline, but it was not obvious. So we also put a simulation model of the pump unit below. We will modify the wording.
Author action: line 254: “However, this interpretation is not supported by previous simulation research of the 2D piston pump, so a single pump unit is simulated to verify this interpretation.”
Reviewer#1, Concern # 5: The quality of the plot is much better. However the agreement between simulation and test is poor and this should be mentioned.
Author response: Thanks for your comment. We will add this content.
Author action: line 379: “Secondly, after studying the amplitude-frequency characteristics of the test data and simulation result, it is found that the main frequency of the simulation result is 667 Hz and the main frequency of the experimental data is 600 Hz. The main frequencies of the two are relatively close, but their amplitudes are quite different, as shown in Figure 23.”
