Cross-Coupled Dynamics and MPA-Optimized Robust MIMO Control for a Compact Unmanned Underwater Vehicle
Round 1
Reviewer 1 Report
Please read the attachment. Thank you.
Comments for author File: 
Comments.pdf
The technical English of the manuscript appears to be quite strong. The language used is generally clear and concise, with appropriate terminology and scientific expressions.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
This article approaches the development of a robust controller for an under-actuated ROV in which there is strong coupling between surge and yaw that would probably make the vehicle unusable without mitigation. The authors approach the controller development in steps, clearly outlining the logic behind each components of their work. The introduction is clearly written and the motivation of the work and background to the approach are explained well. The development of the mathematical model is clear, although there appear to be some minor errors and the development relies on reference [24] for equations (11) to (13), which are not explained in the text.
The development of the data-driven transfer function in section 4.1 is explained clearly. The extension to an ARMAX approach is less explained and no references are given - was the Matlab toolbox used in this case as well? Also, Figure 13 shows cross-validation of the ARMAX model, but not the model of equation (17) that it replaces. This would be a useful comparison.
The development of the multi-parameter root locus controller in section 5.1 presents only the outcome of the process. It does not explain how the closed-loop transfer functions were derived, or what performance parameters were required for the derivation. For example, what overshoot would be considered acceptable, and what settling time is required?
Section 6 gives a brief and unconvincing explanation of the benefits of the Marine Predator Algorithm. Figure 17 does not have sufficient explanation to make the algorithm understandable and the results in Table 4 are not explained. Do T_p and T_s mean "peak time" and "settling time" and does %OS mean "percentage of overshoot"? What would unacceptable values of these quantities look like, from an operator's perspective?
The closed-loop experimental results in Figures 18 and 19 suggest that the MPA controller works well. The frequency analyses in Figures 20 and 21 suggest that the root-locus PI controller would have worked almost as well. It is difficult to conclude from Table 4 and figures that the difference is "significant" as claimed in section 7 and Figures 20 and 21, but clearly the process has been successful in developing robust control systems.
Finally, in section 7, there is mention that the effects of the umbilical are included in the controllers. This is true, but the extent is not clear. The umbilical is often a major limiter in ROV operations. Do the authors have plans to characterise how much the effects of drag on the umbilical can be mitigated?
In summary, this is a solid piece of work that could be improved with more detail about the different stages of the process.
Comments for author File: Comments.pdf
The quality of English expression is very good. The attached document suggests changes to address minor issues. There are also some mistakes in some of the equations and figures that are discussed in the document.
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
The project involves the development of a compact, low-cost unmanned underwater vehicle (UUV) or MicroROV with 3 degrees of freedom (DoF). It focuses on understanding the dynamics and cross-coupling effects of the MicroROV, developing high-fidelity transfer function models, designing baseline controllers using a multi-parameter root-locus (MPRL) technique, optimizing the controller gains with an innovative Marine Predator Algorithm (MPA), and validating the control strategy through pool tests. The goal is to create an efficient and affordable MicroROV that can be remotely operated while advancing the understanding of its physics and implementing effective control mechanisms.
Although the motivation and development of the project are fine. However, I think it is necessary to make some corrections, additions, and improvements to the paper to increase the impact of the paper and its contribution to the state of the art.
1. Line 99 begins the enumeration and brief description of the contributions. Objectives are being confused with contributions. I would appreciate a clear differentiation of objectives and contributions (An objective is something you want to achieve, but it is not strictly something that contributes to expanding the state of the art).
2. Once the differentiation between objectives and contributions is done, these contributions must be contrasted with state of the art, demonstrating how these contributions help to expand state of the art (This is done by comparing the contributions with similar works in state of the art).
3. Figure 1. should include images of the other points of view (perspectives) of the vehicle to make its structure clearer
4. Figure 2. should increase the size of the figure by at least 50%
5. Table 2 should be fixed. Header titles go out of bounds and blend into each other.
6. The sentence "the following equations are sufficient to model the coupled nonlinear dynamics of the vehicle" on line 145 could be rephrased as "Equations (1) and (2) model the coupled nonlinear dynamics of the vehicle". It is important to refer to the equations by their number to ease the reader to refer to them.
7. The sentence "of the vehicle 2 is simplified as" on line 147 could be rephrased as "of the vehicle 2 is simplified by (3) as". Please, reference every equation by its own numbers.
8. Figure 4 is pixelated. Please improve the resolution.
9. In Figure 5, the caption should be unbold. Please review this issue in the rest of the figures.
10. The paper directly jumps from section 6 (Marine Predator Algorithm - Optimization algorithm) to section 7 Conclusions. This is confusing because 1) section 6 should include experiments or results related to the convergence of the algorithm and tunning performance. 2) A new section should be added to show and evaluate the control experiments over the robot.
11. Figure 19 needs a deep explanation, including an analysis of Figure 19.c. Even Fig. 19.c should be zooming in, emphasizing the response region.
12. The sentence "Also modelled are the independent heave and yaw degrees-of-freedom as well as influence of umbilical cord is captured." in line 425 should be rephrased.
English presents some small grammar problems. I advise the authors to review the wording of the article carefully.
Author Response
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Author Response File: Author Response.docx
Reviewer 4 Report
Article is interesting, the subject is current and has useful value. In order to enhance the article quality, I suggest the following remarks be taken into account:
1. The authors should clearly indicate which in the presented idea is novel compared to the existing publications.
2. Why such a control scheme was proposed. Please refer to other methods, for example:
- Li, D.; Du, L. AUV Trajectory Tracking Models and Control Strategies: A Review. J. Mar. Sci. Eng. 2021, 9, 1020
- Borkowski P., Zwierzewicz Z. „Ship course-keeping algorithm based on knowledge base” Intelligent Automation & Soft Computing vol. 17, no. 2, 2011 (149-163)
3. Table 3: why is assumed this values?
4. The authors are suggested to have Discussion section to investigate the weakness, strength, and potential enhancement of proposed scheme.
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The new manuscript is a comprehensive update to the original version. It reads well and addresses previous concerns. This is clearly worthy of publication and is a valuable contribution to the literature.
Reviewer 4 Report
I accept the amendments made by authors.
