Macro–Micro-Coupled Simulations of Dilute Viscoelastic Fluids
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsComments and suggestions:
1) In this manuscript, what is the "micro" of macro-micro coupled approach
? Is the FENE model? However, it more seems to be a macro model as shown in Sec. 2.3.2 and 2.4.2.
2) The author mentioned that, "the stochastic equations need to be fully decoupled". How much does this "fully decoupling" affect the numerical results?
3) Compared to macroscopic methods, the macro-micro approach leads to a substantial increase in computational demands. What is the difference in computational cost between the two methods? Also, the author should provide a clearer explanation of the calculation process of this macro-micro coupled method.
4) Please note the standardization of figure. Such as, Figure 2 is missing values on the x-axis and the variable "t" in Figures 5 and 7 should be in italics.
Author Response
We thank the reviewer for their comments. We are attaching our responses as a pdf file.
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors investigated the behavior of viscoelastic fluids using the FENE model, considering the microscale kinetic theory to reflect the non-Newtonian characteristics of the polymers. Their results are presented based on the dimensionless parameters that arise from the mathematical model and represent a contribution to computational techniques. However, the general structure of the manuscript must improve since there is no clear order for the solution methodology, in addition, the authors must appropriately address the following points:
1. The first part of the introduction related to the applications and examples of complex fluids has no references. In this sense, the authors must consider including relevant references that reflect the fundamental applications of the study phenomenon on a macro and micro scale, which is the focus of the investigation. As well as the types of fluids present at each scale, considering that these materials are different and can be described with different rheological models.
2. Correct the numbering of the equations since several equations do not have a number assigned. Furthermore, there is no equation (4).
3. Indicate the definition of each parameter according to its order of appearance. For example, the manuscript does not mention the definition of the parameters Re, n, B, and De that appear after equation 1(b). Review the entire document.
4. What are the boundary and initial conditions to solve the governing and constitutive equations? Also, how are these equations simplified since they are in vector form, i.e., what are the physical limitations of the problem?
5. How can you ensure the correct functioning of the solution obtained without adequate validation?
6. The manuscript does not indicate the range of the physical variables used to calculate the dimensionless parameters, in this sense, it is difficult to reproduce the numerical solution. Likewise, the results section does not describe the physical behavior of viscoelastic fluids, which should be the focus of the work, highlighting the difference between polymer solutions on a macro and micro scale.
Comments on the Quality of English LanguageThe quality is good, however, it can be improved by avoiding the use of excessively long sentences.
Author Response
We thank the reviewer for their comments. We are attaching our responses as a pdf file.
Author Response File: 
Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors
The paper is interesting.
1) Some more recent bibliography should be included such concerning several issues such as
For GPU simulation
Schram, R. D., & Barkema, G. T. (2018). Simulation of ring polymer melts with GPU acceleration. Journal of Computational Physics, 363, 128-139.
Behbahani, A. F., Schneider, L., Rissanou, A., Chazirakis, A., Bacova, P., Jana, P. K., ... & Harmandaris, V. A. (2021). Dynamics and rheology of polymer melts via hierarchical atomistic, coarse-grained, and slip-spring simulations. Macromolecules, 54(6), 2740-2762.
For alternative approaches coupling microscopic to macroscopic property calculation
Filippos Sofos, Karakasidis, Theodoros, Liakopoulos, Antonios, Giannakopoulos, Antonios, A quasi-continuum multi-scale theory for self-diffusion and fluid ordering in nanochannel flows, (2014) Microfluidics and Nanofluidics, 17 (6), pp. 1011 – 1023
Xu, X., & Yu, P. (2016). A multiscale SPH method for simulating transient viscoelastic flows using bead-spring chain model. Journal of Non-Newtonian Fluid Mechanics, 229, 27-42.
2) In Molecular dynamics simulations there is the possibility to fix the temperature using a thermostat like Nose or Nose-Hoover. Is there such possibility in this scheme to include such a feature
3) Does the model include slip at the walls of a channel in a flow?
4) In figs 1-3 in what units is the time represented?
5) More details on how many Gpus are employed how the problem scales with the number. Of Gpus as well as the real execution times would be welcome as well as a comparison wth parallel execution not on GPUs
6) A comparsn on the execution also with other works woul be welcome
Author Response
We thank the reviewer for their comments. We are attaching our responses as a pdf file.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe work has improved substantially with the modifications made to the manuscript.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have responded extensively and appropriately to the reviewers' comments, thus I recommend the paper for publication.
