Collision Characteristics During Autonomous Underwater Vehicle Recovery with a Petal Mechanical Gripper

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Journal of Marine Sicence and Engineering

Manuscript title: Collision Characteristics during AUV Underwater Recovery with the Petal Mechanical Gripper

Reviewer’s comments:

The manuscript presents an innovative method for the recovery of AUV via a PMG. The authors concentrate on comprehending and enhancing the collision dynamics between the AUV and the PMG during recovery. They create a collision model utilizing Adams software and evaluate it experimentally in a tank with a scaled (3:1) model. A comparison is made between two recovery schemes - active and passive - while thoroughly examining the effects of characteristics such as the AUV's beginning velocity and the PMG's closure velocity. The study finds that well calibrated active recovery enhances recovery duration and motion stability while mitigating collision-induced impact forces.

The paper provides a detailed description of the collision model, including the dynamic equations of the AUV, hydrodynamic coefficient determination (via CFD and theoretical analysis) and experimental validation of the simulation with a scaled tank test, achieving a maximum impact force error of about 5.10%. The investigation into the effects of both the AUV’s initial speed and the PMG’s closure speed is systematic. The figures and diagrams are clear and helpful in understanding the concepts and results.

Specific points to be addressed:

1. The paper mentions that gravity and buoyancy moments are neglected during the short collision period. Although reasonable, the authors are advised to make a brief discussion of this assumption to help readers understand its limitations.
2. The authors should consider scaling effects: as the experimental validation employs a 3:1 scale model, a discussion on the potential impact of scaling on dynamic similarity (e.g., Reynolds number effects) and the extrapolation of results to full-scale systems would be advantageous.
3. The authors should clearer descriptions of the rectangular and annular fluid domains to help clarify why these specific geometries were chosen and how they relate to the AUV’s actual operating environment.
4. The authors should consider adding a table that compares the PMG to traditional docking or passive recovery systems based on key metrics like recovery time, number of collisions, impact forces, and operational complexity.
5. The authors are advised to expand the discussion how the PMG's performance compares to current state-of-the-art systems in real-world operational settings (for example, changing currents and irregular AUV paths) which would help make the contribution more clear.

 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The Authors need to revise the English for the manuscript.

Author Response

Response to Reviewer #1

General comment:

The manuscript presents an innovative method for the recovery of AUV via a PMG. The authors concentrate on comprehending and enhancing the collision dynamics between the AUV and the PMG during recovery. They create a collision model utilizing Adams software and evaluate it experimentally in a tank with a scaled (3:1) model. A comparison is made between two recovery schemes - active and passive - while thoroughly examining the effects of characteristics such as the AUV's beginning velocity and the PMG's closure velocity. The study finds that well calibrated active recovery enhances recovery duration and motion stability while mitigating collision-induced impact forces. The paper provides a detailed description of the collision model, including the dynamic equations of the AUV, hydrodynamic coefficient determination (via CFD and theoretical analysis) and experimental validation of the simulation with a scaled tank test, achieving a maximum I mpact force error of about 5.10%. The investigation into the effects of both the AUV’s initial speed and the PMG’s closure speed is systematic. The figures and diagrams are clear and helpful in understanding the concepts and results.

Thank you for your recognition of our manuscript and your valuable comments. We have carefully considered the reviewer’s comments and thoroughly revised manuscript accordingly. The point-by-point responses to the reviewer’s comments are provided below, and the relevant modifications in the revised manuscript are highlighted in red.

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Comment 1:

The paper mentions that gravity and buoyancy moments are neglected during the short collision period. Although reasonable, the authors are advised to make a brief discussion of this assumption to help readers understand its limitations.

Response:

Thank you for your careful review and valuable suggestions. We will add the relevant description in the paper to specifically discuss the reason and limitations of the assumption that gravity (moments) and buoyancy (moments) are neglected during the brief collision process.

Changes implemented (Section 2.3.1, Lines 150 - 154)

The effect of gravity and buoyancy moments during this period can be neglected, since their contribution to the collision dynamics is small during the brief collision process. This assumption is reasonable under the simulation and experimental conditions of the current study, but not applicable in cases with large relative motion after the collision and longer tangential collision time.

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Comment 2:

The authors should consider scaling effects: as the experimental validation employs a 3:1 scale model, a discussion on the potential impact of scaling on dynamic similarity (e.g., Reynolds number effects) and the extrapolation of results to fullscale systems would be advantageous.

Response:

Thank you for your constructive comment. Regarding the scaling effect you mentioned, it seems that there was a misunderstanding due to a wording issue. This study involves two sets of simulation models: a full-scale simulation model and a 3:1 scaled simulation model. The 3:1 scaled simulation model is only concerned in the experimental validation of the simulation method. After the accuracy of the simulation method was confirmed, all subsequent analyses were carried out based on the simulation results of the full-scale model. Therefore, the scaling effects (such as changes in Reynolds number) did not directly affect the final full-scale simulation results.

To avoid misunderstanding of the readers, we have refined the relevant description in the revised manuscript, as given below.

Changes implemented (Section 2.5, Lines 211-215)

A tank experiment is designed to verify the accuracy of the simulation results for the collision process during AUV recovery, and a 3:1 scaled prototype is applied for cost effectiveness and ease of operation. A 3:1 scaled simulation model is constructed, and the simulation results are compared with the experimental results to verify the simulation method.

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Comment 3:

The authors should clearer descriptions of the rectangular and annular fluid domains to help clarify why these specific geometries were chosen and how they relate to the AUV’s actual operating environment.

Response:

Thank you for your valuable suggestion. As suggested, we have added a paragraph in the manuscript to explain why rectangular and annular fluid regions were chosen, and provide a detailed explanation of how these geometric shapes simulate the fluid environments that the AUV may encounter during actual recovery operations.

Changes implemented (Section 2.5, Lines 160-164)

The rectangular and annular fluid regions are chosen to better simulate the flow field environment that the AUV may encounter during the recovery process. Specifically, the rectangular region simulates the linear and deflected operations of the AUV, while the annular region simulates the rotational motion environment of the AUV. These two geometries closely resemble the AUV actual underwater motion conditions.

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Comment 4:

The authors should consider adding a table that compares the PMG to traditional docking or passive recovery systems based on key metrics like recovery time, number of collisions, impact forces, and operational complexity.

Response:

We appreciate your valuable feedback and the suggestion to provide a more detailed table. In fact, the PMG cannot be directly compared with traditional passive recovery devices, mainly due to the significant differences in size and shape between the two, and the inability to standardize the AUV structural and motion parameters. Fortunately, the PMG also features a passive recovery mode, which just uses the traditional docking for AUV recovery. Therefore, we compared the collision parameters of the PMG in active and passive recovery modes, including key metrics such as recovery time, collision frequency, and impact force. For better understanding the reviewer and readers, we have modified the two tables that compare the performance of PMG system in the two recovery modes. The tables will clearly demonstrate the advantages of the PMG system in these metrics and the effectiveness of the active recovery.

Changes implemented (Section 3, Lines 275 and 276)

Table 6. The impact force of passive and active recovery

u (m/s)	Recovery mode	N	Impact force (kN)
			1	2	3	4	5	6
u1 = 1	P	6	2.634	6.77	6.466	5.228	1.501	7.71
	A	4	9.552	13.69	3.65	8.916
u2 = 1.5	P	5	1.347	5.898	11.682	7.098	12.045
	A	4	1.689	19.526	6.029	20.815
u3 = 2	P	5	5.064	6.033	22.159	12.162	21.765
	A	4	5.068	7.448	7.655	13.616

Table 7. The recovery time of passive and active recovery

u (m/s)	Recovery mode	Recovery time (s)	Collision time (s)
			1	2	3	4	5	6
u1 = 1	P	2.27	0	0.76	1.3	1.61	1.77	2.27
	A	2.03	0	1.29	1.62	2.03
u2 = 1.5	P	1.5	0	0.5	0.87	1.15	1.5
	A	1.41	0	0.93	1.1	1.41
u3 = 2	P	1.1	0	0.37	0.64	0.82	1.1
	A	1.04	0	0.71	0.82	1.04

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Comment 5:

The authors are advised to expand the discussion how the PMG's performance compares to current state-of-the-art systems in real-world operational settings (for example, changing currents and irregular AUV paths) which would help make the contribution more clear.

Response:

Thank you for your valuable comment. For the current study, the main focus is on the collisions during the AUV recovery with PMG and their impact on the AUV performance, under that premise that the AUV can accurately enter the PMG recovery range. In complex water environments with changing currents or irregular path, we need to first ensure that the AUV can enter the PMG recovery range accurately, and different flow field environments and trajectories may affect the AUV recovery rate. In fact, we have basically completely our new work on the AUV recovery with the PMG in the real-world operational settings. Thank you for your forward-looking instruction. We have also mentioned this in the manuscript in the future work.

Changes implemented (Section 4, Lines 498-502

In future research, we will focus on the recovery performance of the PMG system, particularly how the varying water flow and irregular AUV paths affect the performance and recovery rate of AUV recovery with the PMG. The goal is to enhance the recovery stability of the PMG system in dynamic environments and reduce the impact of environmental changes on the recovery.

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The submitted article "Collision Characteristics during AUV Underwater Recovery with the Petal Mechanical Gripper" deals with autonomous underwater vehicle recovery (AUV) using a petal mechanical gripper (PMG). The authors set up a collision model using Adams software to explore effects of different recovery modes and closure speeds on recovery efficiency and AUV's motion behavior. The study includes both simulations and experimental validation using a tank test, demonstrating that active recovery improves efficiency and stability. The results provide valuable insights into optimizing AUV recovery mechanisms. However, the following points in the manuscript require further clarification.

a) In Section 2.3.3, the impact function used in the collision analysis is presented with multiple parameters such as stiffness coefficient, damping coefficient, and penetration depth. However, the selection criteria for these values are not explicitly explained. The authors should clarify how these parameters were determined and provide any validation or reference to ensure their accuracy in modeling real-world conditions.

b) In Section 2.5, the experimental verification results are presented alongside the simulation data, showing a maximum impact force error of 5.10%. However, there is limited discussion on the possible sources of discrepancies between experimental and simulated results. The authors should elaborate on potential factors contributing to this error, such as environmental conditions, sensor accuracy, or modeling assumptions.

Author Response

Response to Reviewer #2

General comment:

The submitted article "Collision Characteristics during AUV Underwater Recovery with the Petal Mechanical Gripper" deals with autonomous underwater vehicle recovery (AUV) using a petal mechanical gripper (PMG). The authors set up a collision model using Adams software to explore effects of different recovery modes and closure speeds on recovery efficiency and AUV's motion behavior. The study includes both simulations and experimental validation using a tank test, demonstrating that active recovery improves efficiency and stability. The results provide valuable insights into optimizing AUV recovery mechanisms. However, the following points in the manuscript require further clarification.

Response:

We are grateful for the respected reviewer’s pertinent suggestions to our work. Reponses are made one by one according to the comments and listed below. The relevant modifications in the revised manuscript are highlighted in red.

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Comment 1:

In Section 2.3.3, the impact function used in the collision analysis is presented with multiple parameters such as stiffness coefficient, damping coefficient, and penetration depth. However, the selection criteria for these values are not explicitly explained. The authors should clarify how these parameters were determined and provide any validation or reference to ensure their accuracy in modeling real-world conditions.

Response:

Thank you for your valuable suggestions. When determining the parameter settings of the impact function used in the collision analysis (including stiffness coefficient, damping coefficient, and penetration depth), we mainly referred to the empirical values in the Adams/View Contacts and the relevant literature [26], and proper adjustments were made to the parameters based on the material properties and collision characteristics of the AUV and PMG.

We have also made modifications to the revised manuscript to make it clearer and easier to comprehend, as detailed below.

Changes implemented (Section 3.2, Lines 199-205)

The parameter settings in the table are mainly referenced from the Adams/View Contacts manual, and proper adjustments are made based on the material properties of the PMG and AUV. Specifically, the values of parameters such as stiffness coefficient, damping coefficient, and penetration depth are modified based on experimental data from a similar system [26]. These adjustments ensure that the model more accurately reflects the real-world collision behaviors, and the accuracy of the parameter settings will be further validated through comparison with experimental data.

 

References

[26] Guo, J.; Zheng, R.; Lu, H. AUV Underwater Docking Collision Analysis and Guidance Structure Optimization Based on ADAMS Simulation. Acta Armamentarii 2019, 40, 1058-1067.

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Comment 2:

In Section 2.5, the experimental verification results are presented alongside the simulation data, showing a maximum impact force error of 5.10%. However, there is limited discussion on the possible sources of discrepancies between experimental and simulated results. The authors should elaborate on potential factors contributing to this error, such as environmental conditions, sensor accuracy, or modeling assumptions.

Response:

Thank you for your constructive feedback. As suggested by the reviewer, we have elaborated on the potential sources of the maximum impact force error between the experimental verification results and simulation data, as detailed below.

Changes implemented (Section 2.5, Lines 229-233)

This discrepancy can be related to the positioning of force sensor in the experiment, which is located in the middle of the PMG main claw, potentially capturing higher or lower impact force than in the simulation. Additionally, the simulation does not account for the influence of the surrounding flow field on the AUV when the AUV approaches to the PMG.

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

No comment.