Sensitivity Analysis of Simulation Parameters to Evaluate the Coarse-Grain DEM for Liner Wear Prediction

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Parameter calibration has always been an important issue in numerical simulation. In this study, a sensitivity analysis was conducted to determine whether calibrating simulation parameters is sufficient for predicting liner wear in tumbling mills using the coarse grain DEM. It is a good work. This can provide readers with parameter calibration references. I have some small suggestions as follows:

(1) Is the author's method limited to the engineering scale only? How to distinguish simulation accuracy at different scales？

(2)Did the author consider the influence of factors such as particle breakage and particle shape during the simulation process, for specific details, please refer to "Discrete element method simulation of granular materials considering particle breakage in geotechnical and mining engineering: A short review"

(3) The applicability of the author's method can be discussed.

(4) The author's references are relatively old, mostly papers from 10 or even 20 years ago. The author can refer to papers from the past five years.

Author Response

Please see attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors present an original approach to wear modeling. Unlike standard applied techniques such as the Ai test, the proposed approach allows to take into account the geometry of the lining, which will lead to more accurate results. However, the proposed solution is extremely labor intensive. To create a model requires the selection of a large number of parameters, an error in the selection of which will significantly affect the results. There are a number of comments on the paper:
- In the end, it is not clear what wear was determined? The authors should compare the modeling data with experimentally obtained data to verify the model.
-The purpose of the paper should be more clearly stated.
- The paper is overloaded with mathematical calculations, which significantly impairs its holistic perception.
- The results section needs revision as it mainly contains a description of the obtained patterns.
- A description of the research plan should be added to improve further perception of the results obtained.
- Data on the software used in modeling are not given. The time spent on modeling should also be given.
- In conclusion, the authors themselves agree that the approach needs to be finalized and needs additional research, perhaps to increase the practical significance should immediately make adjustments to take into account these comments.
- The graphic material is of poor quality.
Taking into account the mentioned remarks the article needs to be finalized and reconsidered.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

LANG:

 

Consistency in terminology:

Ensure consistent use of terms such as “coarse grain” and “coarse-grain” throughout the manuscript, including title and abstract.

 

Expression:

Improve the academic level of English throughout the manuscript.

Several sentences should be reconsidered, e.g. “DEM can accurately track the motion of every single particle, which also means that the industrial scale simulation can cost a large amount of computing resources. Therefore, a personal computer cannot finish a large scale calculation in an acceptable time.”, and “… whereas the cost of time is still not acceptable on a laptop using small coarse-grain ratio.” This could be rephrased.

Also, use formal expressions (no “we/our”).

In the abstract, leave the symbols after the terms “friction coefficient” and “restitution coefficient” for clarity.

 

 

 

 

Dear Authors,

 

Thank you for your submission. After review of your manuscript, I have several remarks and suggestions for improvement. Given the critical nature of some of these points, I recommend a major revision to ensure the clarity and scientific rigour of your work. In detail:

 

Particle Shape and Contact Models:

Clearly state the assumptions made, particularly regarding particle shape (spherical particles) and the contact models used. This should be addressed before going into the methodology. For that, providing a comprehensive overview-summary of the boundaries would help, such as including:

Intended large-scale simulation with hundreds of thousands/millions of particles;
Spherical particle shape;
Particle size around xxx mm;
Intended coarse-graining factor XXX;
Shear modulus adaptation (if applicable, and I believe so);
Contact models used (Hertz-Mindlin? Citation?);
Total simulation time intended;
Approx. timestep(s);
Software solver/code (Citation); (…)

 

References:

It would enhance the manuscript if the number of references in one single row could be reduced, especially to avoid overwhelming the reader. Focus on key representative works here instead of listing a lot of authors to gain a large number of references. On the other hand, include important references that were omitted, such as Kuwagi et al. (2004), who used a notable approach (particle assembly concepts), or others as mentioned further below.

 

Chapter 2.1:

This section can be significantly shortened. Basic DEM equations and concepts should be referenced rather than fully restated (unless they are specifically addressed later in the work). Equations 4 and 5, which pertain to a specific contact model, can be omitted if not directly relevant. Please also cite sources here.

 

Wear analysis and contact models:

Discuss the selection of contact models and consider the implications of using different ones. Clarify why the chosen models were selected and how others might perform differently.

Also, please address/show the resolution/triangulation of the parts on which the wear was analysed (can be relevant to a certain degree, e.g. regarding the rounded parts/edges of the components: low resolution leading to sharp edges vs. high resolution leading to small triangles that get penetrated to a relatively high degree by coarse-grained particles).

 

Particle count and size:

Can be seen as questionable:

110k spherical particles with a simple contact model is not a large number for DEM.

Also, the smallest particle size of 15 mm (not yet coarse-grained) and 45 mm coarse-grained is quite large for this type of application.

 

Geometrical and numerical effects of coarse-graining:

Clearly state the limitations of using spherical particles and how this affects the sensitivity study.

Please address the aspect that coarse-graining does not only affect the numerical side of the results, such as the ones you analysed – but also aspects that arise from the geometrical side of coarse-graining – simplest example: screening does not work as intended with coarse-graining, which is understandable – but also your application may be affected here, as some areas may just do not get included due to the larger particles (aside the fact that you assume oversimplified spherical particles for this type of analysis, which need to be pointed out very clearly; your approach is understandable, but this limitation needs to be stated – to make this visually clear: you want to do a detailed analysis on wear effects on coarse-graining particles and analyse effects here – but the fact that you simplify complex particles as spherical is probably more relevant in terms of your sensitivity study, but is not stated.)

 

Wear model description:

Provide a description of the wear model used. Several authors address that, e.g. combining normal and tangential types; consider citing relevant literature such as A. Katterfeld.

 

Chapter 3.1 - explanation:

Clarify the methodology for normalising wear rates using original level benchmark data.

Introduce the base model first and explain the normalisation process in detail.

(There are several literature references on coarse-graining analysis in various forms, from general contact mechanics, such as regarding your work, to very complex mechanics, such as bonded-particle breakage in mining, e.g. a very recent work on that was done by L. Koch (2024), comparing raise-caving mining simulations with different sizes of particles in the BPM.)

 

Calibration:

Common base calibration tests are missing / not addressed, such as static and dynamic angle of repose testing. (This regards the flow of the bulk material – it should be considered as the material’s behaviour should be calibrated and representable in the end for each level of coarse-graining.)

If you aim to analyse the sensitivity of coarse-graining only and in general, so more for a type of “generic/representative” material, this may be an approach, but then you would not refer to an industry/physical model as a base reference.

 

Visualisation of the first model’s setup:

Before presenting your first results (Chpt.3), include a visualisation of the simulated setup (similar to Figure 12, for the full-size mill model).

 

Introduce the benefits of coarse-graining:

State the overall benefits of coarse-graining, especially also the reduced stable timestep and thus the enhanced computational efficiency, at the beginning of the manuscript, not only towards the end (and not only the lower number of particles/contacts, which is obvious but important to mention, also as this affects non-linear). Mention the Raleigh timestep in that context, referencing to the (smallest) particle size as the computational bottleneck.

 

Conclusion and future work:

Clearly state that the conclusion is based on comparisons with the base model (without coarse-graining), and with several simplifications for the given application of the mill (particle geometry with spheres, neglecting particles below a certain size (15 mm), not including breakage mechanics (which is, in the end, the actual point of such a mill)) – to analyse the effects of coarse-graining vs. non-coarse-graining – not only stating the impacts on the results, but please also on the benefits gained (efficiency increase in numbers!).

 

A closer outline of the future work, the multi-level coarse-grain approach, would help to get clarity on what this means. This approach is basically available, so applying (instead of proposing) it to this type of application could be an idea; however, please clarify how/where: Typically, there are areas where the particles can be represented larger (commonly areas of lower interest, just to account for load forces due to a stack of particles, e.g. in a silo), however, inside a mill, it would be interesting where this could be the case, furthermore, as the transition from coarse-grained to actual size is a critical zone, requiring for some very defined aspects, e.g. a dense packing and more or less steady stream conditions – so one would wonder where and how this may be applied, ultimately adding an overall benefit in an application as this. If it is too vague yet, leaving this and probably making a future outline to some other aspects may be an idea, e.g. testing further particle shapes, enhancing your base simulation, or even advancing your setup with different contact models, may be a more concrete concept and more understandable for DEM-familiar audiences.

 

I hope these remarks and suggestions help improve the clarity and scientific rigour of your manuscript. I look forward to seeing the revised version.

 

Best regards

Comments on the Quality of English Language

Consistency in terminology:

Ensure consistent use of terms such as “coarse grain” and “coarse-grain” throughout the manuscript, including title and abstract.

 

Expression:

Improve the academic level of English throughout the manuscript.

Several sentences should be reconsidered, e.g. “DEM can accurately track the motion of every single particle, which also means that the industrial scale simulation can cost a large amount of computing resources. Therefore, a personal computer cannot finish a large scale calculation in an acceptable time.”, and “… whereas the cost of time is still not acceptable on a laptop using small coarse-grain ratio.” This could be rephrased.

Also, use formal expressions (no “we/our”).

In the abstract, leave the symbols after the terms “friction coefficient” and “restitution coefficient” for clarity.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have worked to improve the article and responded to all questions and comments. The work is theoretical, but has practical importance in the study of grinding processes.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for your detailed responses and the effort put into improving your manuscript. The revision made has addressed many of the remarks raised, significantly enhancing the clarity and scientific rigor of your work. I appreciate the enhancements made.

That being said, a few minor (in terms if effort for incorporation) but relevant remaining points still require attention before final publication. These are primarily minor refinements aimed at improving the completeness and clarity of the work:

 

1. Inclusion of figures from the response letter

A rather major point: The response letter contains useful visualisations, particularly the triangulation image and the initial simulation setup (Case 2). However, these figures do not appear in the revised manuscript itself (?).

These figures should correspondingly be included in the manuscript and addressed in similar form as in your letter.

1.1: For the Case 2 figure, it is recommended to enhance the visualisation by including the particles. This would allow readers to better identify the size ratio of coarse-grained particles relative to the mill details. (Given that the coarse-grained particles seem relatively large compared to the liner’s height and width).

1.2: The triangulation figure raises two remarks: There are the side walls included/triangulated – especially when considering efficiency, modelling those superfluous walls which never get in contact with particles could be a simple thing to leave out and enhance the overall setup with easy-to-do means as according a best practice (by only including those surfaces that are actually required). And secondly: The ratio of your triangles on the main surface show a not too high mesh quality for analyses like this as their aspect ratio is quite high (rather long and thin); you may want to consider that for future work.

 

2. Declaration of particle shape simplification

As you stated in your letter, the use of spherical particles as a simplification is a common and justified approach. While spherical particles are often used, employing a particle size distribution (PSD) is a common practice to capture the variety of bulk behavior when using sphere-simplification. A simple brief mention and statement in that regard in the beginning would help clarify this choice and ensure transparency for the readers, particularly showing that you are aware of the availability of complex particles as well.

 

3. Concise overview of simulation parameters

As suggested in the initial review, it would be beneficial to provide a quick-reference overview of (the mentioned) key simulation parameters, e.g. added in Table 3, thus further particularly including the shear modulus (Young’s modulus) used. (The authors note in the letter that the shear modulus was adjusted to enhance computational efficiency, which is an accepted practice in DEM. However, the specific values chosen and the rationale behind them should be explicitly stated in the manuscript. This is a critical simulation parameter, particularly in the context of computational efficiency (timestep). (No additional sensitivity study on shear modulus is requested (although probably interesting especially in terms of wear analysis), but transparency on the chosen values is necessary.))

Providing this information in a single, easy-to-locate section improves readability and aligns with common practices in similar studies.

 

4. Minor language aspect

Personal form (“our”) still appears, even in the abstract. Please revise these occurrences to maintain a formal, objective academic tone. (Line 16,74,77).

Author Response

Please see the attachment.

Author Response File: Author Response.pdf