-->PONE-D-25-31404-->-->Structural Optimization of the Excavator Boom Under Extreme Working Conditions Using EDEM–ADAMS Coupled Simulation�Structural optimization design-->-->PLOS ONE

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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Reviewer #1: Yes

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Reviewer #3: Yes

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Reviewer #1: REVIEW

of the Research Article entitled: "Structural Optimization of the Excavator Boom Under Extreme Working Conditions Using EDEM–ADAMS Coupled Simulation: Structural optimization design" (PONE-D-25-31404)

Authors: Huawei Wu, Xiaolong Ding, Gui Liu, Xiaoyuan Zhu, Hualiang Wang

The reviewed article contains 34 pages, 5 chapters, 21 figures, 28 formulas, 9 tables and 17 literature sources.

Тhe title of this study is correctly selected and brings new elements to this topic, because: Hydraulic excavators are extremely widely used machines in the mining, construction, agricultural and infrastructure sectors. Therefore, it is natural to strive for their continuous improvement in terms of structure, topology, strength characteristics, power capabilities, reliability and durability, under different operating conditions and when performing different tasks.

In the Abstract, the authors consistently describe the stages of the research. The methods and means for achieving the set goals are shown. The results obtained and their significance are correctly described.

In the Introduction, the authors review most of the latest and most relevant research on the above issues. Seventeen sources published in the last 5-6 years have are reviewed. It is found that recent research focuses mainly on the analysis of excavation resistance and digging force, with the development of dynamic models, using simulations and topological optimizations. Recent advances in virtual prototyping facilitate the modeling of coupled dynamics and discrete elements for the analysis of excavator performance.

Based on the review, the authors set themselves the goal of filling the missing link in the research, namely to create a systematic methodology for generating load spectra under multiple conditions, for identifying critical operating conditions, for optimizing strength and stiffness for structural improvement.

In Chapter II a kinematic analysis and dynamic modeling of excavation mechanisms are performed. For the purposes of this study, a multifunctional small machine (an excavator for excavation works) is designed and manufactured and a method for optimization under extreme operating conditions is proposed. The excavator’s manipulator is implemented according to the classical scheme: boom, arm and booked, driven by hydraulic cylinders and operating exclusively in the vertical plane.

The kinematic model of the three-linkage mechanism is constructed using the standard Denavit–Hartenberg (D-H) method. The D-H parameters and the homogeneous transformation matrix from the base frame to the bucket-end frame are correctly described. Forward kinematic computations for the determination of the basic angles θ are arranged based on the cosine formulae. This way all dimensions and angles of the excavator’s manipulator are described.

The proposed model of virtual prototyping enables rapid acquisition of hinge joint load data, significantly enhancing efficiency while reducing experimental resource expenditure. The geometric model is imported into Adams for multibody dynamics simulation to establish linkage kinematic relationships.

After elimination of redundant degrees of freedom and overconstraints, 22 essential kinematic joints are applied at critical hinge locations.

Based on the operating parameters of each cylinder and the kinematic analysis of the working conditions a rigid-body dynamics model is constructed and validated, from which the working range diagram under typical no-load conditions is obtained to verify the forward kinematic solution.

In chapter III - Development and Operating Condition Analysis of an EDEM-Coupled Model, the enhanced discrete element method (EDEM) is coupled with the multi-body dynamics simulation software ADAMS to effectively analyze the digging operation and to monitor in real time the contact forces between the bucket and the material, as well as the load variations at the hinge joints of the connecting rods.

An EDEM model is built for the mechanism and ore particles, describing contact parameters between materials - such as the static friction coefficient, rolling friction coefficient, and coefficient of restitution. Five models of particle unit are used – ellipsoidal, triangular pyramid, cylindrical, cubic and triangular prism.

A coupled EDEM–Adams simulation is conducted to evaluate two typical operating conditions: front digging and lateral digging. The corresponding digging resistance curves of the bucket under both scenarios are presented in excavation resistance diagrams. The load diagrams (force/time) are constructed for the four main boom joints ( Joints 11, 12, 13 and 14) under both digging conditions.

The simulation results indicate that, during the 15-seconds operation cycle, the hinge point loads under forward excavation exhibit two distinct peaks: one at 7.65 s and another at 8.9 s, which correspond to the peak moments of the digging resistance. In contrast, the peak velocity under lateral excavation appears at 7.96 s, which aligns with its corresponding peak load phase. The three positions described above are considered extreme working conditions with the heaviest load on the boom joints.

Based on the hydraulic cylinder driving functions in ADAMS and the cylinder stroke ranges, the load of each joint of the boom under the extreme loading condition is determined, and shown on the diagrams.

After completing the simulation setup, the equivalent stress contours and the total deformation distribution of the boom under each operating condition are obtained and shown on the diagrams.

The results of the finite element analysis (FEA) reveals significant differences in the mechanical response of the boom under three sets of extreme loading conditions. The forward excavation condition at t = 8.9 s represents the most critical scenario, exhibiting a peak equivalent stress and a maximum deformation. The lateral excavation condition at t = 7.96 s yields the lowest mechanical response.

In chapter IV a design optimization of the boom and comparative validation is performed.

The study employs topology optimization to achieve improved performance and lightweight design. The structural design task is as a material distribution problem, to maximize stiffness and minimize deformation. An objective function design variable and constraint conditions are used.

Images of boom topology optimization under extreme working conditions are shown before and after optimization.

To verify the reliability of the topology optimized boom model, a static simulation analysis is conducted on the boom under the same excavation conditions, applying identical loading and boundary conditions, with the results shown in stress and deformation diagrams.

The results after the boom optimization are very good: the mass is reduced by 13.8%, the stress by 26.12%, and the deformation by 29.11%.

Finally, a validation and comparison of the optimized design is made. To evaluate the effectiveness of the boom optimization under the most critical working condition identified through EDEM–ADAMS co-simulation, the optimized design is compared with the results obtained using a conventional optimization approach. The validation showed that the proposed method gives better results than the conventional optimization approach.

In the Conclusion, the authors show the contributions of this work and the applied method, defending them with the results obtained.

About the present article I can mention the following technical errors and remarks:

- in D-H transformation matrix (equation 1), in the first row, third column (i.e. element 1,3) there must be “sin.sin” instead of “sin.cos”;

- on page 33, after Fig.16, on the fourth row is written “Fig.3.15” – this figure does not exist;

- on page 20 is written “scrap-and-dig15” – what does 15 mean?;

- In the Fig.15. – e) and f), there must be 7,96 s.

- In the Table 3 the kinematic joints can be described more precisely;

- After the formulae (28) - the objective function f(x) can be described in more details with corresponding criteria.

CONCLUSION

The reviewed paper is obviously an original research paper with important topic, technical rigorous and meets the scientific and ethical standard for inclusion in the published scientific report.

This paper proposes a unique method for structural optimization of the extreme loading conditions of the excavator mechanism in dynamic environment.

High level of analysis and optimization methods are applied such as kinematic analysis of the D-H coordinates, the ADAMS multi-body dynamics software, EDEM–ADAMS Coupled Simulation. After determining the extreme operating conditions of the boom, force and deformation optimization is performed for these conditions, in order to achieve greater strength and lower deformations at a reduced weight of the excavator.

The conclusion is correctly done supported by the research results.

In conclusion, I recommend that this work be included for publication after the aforementioned technical errors are corrected.

Reviewer #2: The manuscript is well-structured and follows a logical progression from problem definition to methodology, results, and conclusions. The integration of EDEM–ADAMS coupling with topology optimization is a solid contribution, especially for excavator boom optimization under extreme conditions.

However, there are areas where the work could be clearer, more rigorous in validation, and more concise.

While the method is well-integrated, similar approaches (DEM–MBD + FEA optimization) exist in literature for other components. The novelty is more in application than in fundamental methodology.

1. Certain figures (e.g., FEA stress distributions) do not include numerical scale bars or units, which reduces clarity and makes interpretation more difficult.

2. Terminology Consistency – The manuscript uses multiple terms such as “pick-and-dredge,” “digging mechanism,” and “excavating mechanism” interchangeably without clear definitions, which may confuse readers.

3. Kinematics Section Detail – The derivations in the kinematics section are presented in excessive detail for the main text and could be shortened or moved to an appendix to improve readability.

4. No experimental validation – While simulations are comprehensive, there is no physical testing to confirm load cases, deformation magnitudes, or optimization effects.

5. The manuscript requires minor English revision in addition to the correction of typographical errors, such as "Loud image" instead of "Load image" in Fig. 18 caption, emoving the stray number in ‘scrap-and-dig15 transporter, etc.

Reviewer #3: Comments for improvement:

Section II-A: Prototype Development: Remove the word “diagram” from Fig. 1. Figure caption should be like “Fig. 1 Structural Assembly of the Loader-Excavator”.

Section II-A: Prototype Development: Please keep figure for the top view of the Loader-Excavator and change the figure numbers accordingly.

Section II-C: Forward kinematics formulation: In the present study the working range diagram under typical no-load conditions is obtained to verify the forward kinematic solution. But the working range represents the working space through which the bucket tip can reach within in this range. The simulation is also one of the tool to validate the forward kinematics but need to show case the comparison of the input joint angles with bucket tip pose. Recommended to perform comparison of results of simulation with forward kinematics or perform inverse kinematics to validate the forward kinematic model developed for loader-excavator.

In the section II-D, it is mentioned that “Following elimination of redundant degrees of freedom and overconstraints, essential kinematic joints were applied at critical hinge locations” but its methodology is missing to achieve the same. Please add the methodology or justify clearly that how it was achieved.

In Fig. 6: If possible increase the font size of the nomenclatures given to all the joints for better readability.

Fig. 7: Scope of work diagram: Generally, best suitable name for this figure 7 is “Working range diagram” in place of “scope of work diagram”.

Fig. 7: Presented working range diagram is overlapping with the shovel front of the loader-excavator. It is also visible in the Fig. 1 and Fig. 7. Might be the presented working range not be achieved as per the visual presentation given in the manuscript. Please justify exactly.

Table-6: Total mass of 780 kg and 1200 kg taken for particle types. Please justify that why different values taken for study?

Table-7: row -1, write F_z (N) in place of Fz (N). Do correction.

Table-8: row-1, unit of Modulus of elasticity should be MPa in place of Mpa. Do correction.

Para-1 (Content after the Fig. 16): Presently written last line: “This kinematic configuration corresponds spatially to the maximum digging depth condition illustrated in Fig. 3.15”.

Here, wrong figure number is written. Please write correct figure number. If might be Fig. 16.

Paragraph above Fig. 16 and paragraph below Fig. 17: To avoid repetition of statements.

[See Paragraph above Fig. 16: Notably, the forward excavation condition at t = 8.9 s represents the most critical scenario, exhibiting a peak equivalent stress of 131.42 MPa and a maximum deformation of 0.10777 mm. In contrast, the lateral excavation condition at t = 7.96 s yields the lowest mechanical response, with a peak equivalent stress of 104.13 MPa and a deformation of 0.072722 mm.]

[See Paragraph below Fig. 17: Finite element analysis of the boom under three sets of extreme loading conditions reveals that the equivalent stress and total deformation reach their maximum values at 8.9 s under the forward excavation condition, with respective peaks of 131.42 MPa and 0.10777 mm.

In contrast, the minimum mechanical response occurs at 7.96 s under the lateral excavation

condition, where the equivalent stress and total deformation are 104.13 MPa and 0.07272 mm,

respectively.]

Section IV: Design Optimization of the Boom and Comparative Validation: 3rd paragraph, “The boundary condition is defined as a mass retention ratio of 70%”. On what basis or consideration, the mass retention ratio taken as 70%? Justify.

Section IV-B: Validation and Comparison of the Optimized Design: In the present case, the conventional optimization approach adopted for comparison of equivalent stress and total deformation of optimized model of boom. There are two conventional approaches for optimization: size optimization and shape optimization. But in the present study, it is not defined that which approach adopted for conventional optimization (i.e. size or shape optimization) for comparison purposes. Also study does not shows any variation in thickness of plates or shapes of the boom. According to the given information in the manuscript, it reflects that only simple FEA performed for the boom and results were compared for equivalent stress and total deformation.

Please elaborate the justification perfectly and revise the content accordingly.

In the conclusion section: Add the future scope of the presented study. (What kind of extension of the study presented is possible?).

This will provide motivation and scope to the readers of the journal for their future research work.

Note: Minor Revision is Required. It is required to incorporate/justify the given comments.

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Reviewer #1: Yes:  Krasimir Ganchev

Reviewer #2: No

Reviewer #3: Yes:  Dr. Bhaveshkumar P. Patel

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Submitted filename: Review Comments.pdf

Structural optimization of the excavator boom under extreme working conditions using EDEM–ADAMS coupled simulation

PONE-D-25-31404R1

Dear Dr. 丁,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Carlos Alberto Cruz-Villar, Ph. D.

Academic Editor

PLOS ONE

Additional Editor Comments: The Academic Editor grants acceptance under the understanding that the Authors will comply with the PLOS One criteria for papers describing new methods or software for applications. Specifically, these reports must meet the criteria of utility, validation, and availability, which are described in detail at http://journals.plos.org/plosone/s/submission-guidelines#loc-methods-software-databases-and-tools.

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Reviewer #1: All comments have been addressed

Reviewer #3: All comments have been addressed

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-->2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. -->

Reviewer #1: Yes

Reviewer #3: Yes

**********

-->3. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #1: N/A

Reviewer #3: Yes

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The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #1: Yes

Reviewer #3: Yes

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-->5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.-->

Reviewer #1: Yes

Reviewer #3: Yes

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-->6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #1: The authors have satisfactorily addressed all my comments. I recommend this manuscript for publication.

Reviewer #3: A kinematic modeling and structural optimization analysis were performed for a Loader-Excavator as a digging transportation device, and attempt is made to improve the performance of boom under critical working condition. The dynamic simulation and working condition identified using the ADAMS software. As well as excavation resistance and hinge-point loads were obtained using EDEM-based excavation simulation. Ultimately achieved the reduction in weight of the boom, deformation and equivalent stresses through structural optimization. Also further reduced equivalent stress and deformation in comparison with the model optimized by conventional method.

I appreciate the efforts made by authors for the current state of the manuscript presented. The abstract is perfectly written. The flow of content presented in the manuscript is perfect and technically correct. Right methodology adopted to justify the title of the manuscript and objectives.

Within the revised manuscript, authors have incorporated all suggested comments and now no further correction is required in the current state of manuscript.

It is recommended to accept the manuscript for publication.

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Reviewer #1: No

Reviewer #3: No

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