Design and Construction of Hybrid Autonomous Underwater Glider for Underwater Research

Round 1

Reviewer 1 Report

The authors present the design and construction of a underwater vehicle. This represents an application case interesting to the robotics community. Although the paper is more technically oriented, the introduction and references can be extended a liitle bit to increase the scientific background and contribution.

The conclusions directly addresses what has been done, however, they do not present drawbacks or limitations of the presented work that can be improved in the future. This will provide the readers also no not so good experience with this development.

Author Response

Response to Reviewer 1 Comments

Point 1:

The authors present the design and construction of a underwater vehicle. This represents an application case interesting to the robotics community. Although the paper is more technically oriented, the introduction and references can be extended a little bit to increase the scientific background and contribution.

Response 1: Thank you for this suggestion. We agree with the reviewer’s assessment. Accordingly, throughout the introduction and references, we have revised the introduction to address the main contribution and more references related to scientific background.

Point 2: The conclusions directly addresses what has been done, however, they do not present drawbacks or limitations of the presented work that can be improved in the future. This will provide the readers also no not so good experience with this development.

Response 2: Thank you for pointing this out. As suggested by the reviewer, we have added the drawbacks or limitations and some future works that can be improved in conclusion section.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript presents an underwater glider with a hybrid system containing a gliding mode and a propulsion mode to simultaneously achieve good moving durability and maneuverability. In addition to detailed mechanical and electrical designs, the navigation, communication, and underwater movement are investigated and elucidated by both simulations and field experiments. The proposed glider shows a horizontal velocity of 1 m/s and 0.2 m/s in AUG mode and glide mode, respectively. On whole, the authors describe the proposed glider in a thorough manner. I could not deny the plenty of efforts from them. Here I would like to ask several questions and look forward to furthering clarifications.

1.       From the perspective of technology, the manuscript structure is good enough. Can the authors explain what scientific meanings this manuscript can offer to the community? Any breakthroughs compared to others? What can other researchers learn from it?

2.       Page 2, line 75. It is the first time presenting “DVL”. Explain its full name for good readability.

3.       Page 9, line 182. I expect more explanations about the selection of KD and KL. The authors chose a number of 242 for KD, saying as low of it as possible, but a number of 395 for KL, saying as high of it as possible. I don’t see the logic here. 242 is in the same magnitude as 395.

4.       Page 15, line 276. Any thoughts on improving the performance by reducing the position errors and velocity errors?

5.       Some figures’ quality and font size need to be improved, like figure 22.

6.       The arrangement of sections seems not proper. Both mechanical and electrical designs are the prerequisite. Having the mechatronic system enables control, which is followed by other functions such as communication and navigation.  

Author Response

Response to Reviewer 2 Comments

This manuscript presents an underwater glider with a hybrid system containing a gliding mode and a propulsion mode to simultaneously achieve good moving durability and maneuverability. In addition to detailed mechanical and electrical designs, the navigation, communication, and underwater movement are investigated and elucidated by both simulations and field experiments. The proposed glider shows a horizontal velocity of 1 m/s and 0.2 m/s in AUG mode and glide mode, respectively. On whole, the authors describe the proposed glider in a thorough manner. I could not deny the plenty of efforts from them. Here I would like to ask several questions and look forward to furthering clarifications.

Point 1:

From the perspective of technology, the manuscript structure is good enough. Can the authors explain what scientific meanings this manuscript can offer to the community? Any breakthroughs compared to others? What can other researchers learn from it?

Response 1: Thank you for pointing this out. The scientific meaning of this manuscript is the design and construction of the mechanical system, electrical system, navigation system, control system, and communication system of a hybrid autonomous underwater glider for underwater research. In general, an autonomous underwater glider has actuators in the form of a buoyancy engine, a moving mass engine, and a rudder. The term hybrid in this paper states that there are additional actuators, such as bow, stern, and main thruster as well as a complete control surface: rudder and elevator.

This manuscript also describes the design of the moving mass engine and the buoyancy engine which are adapted to the modular hull design. Besides that, the addition of hybrid actuators increases the maneuverability and speed of the vehicle when compared to the design of an autonomous underwater glider in general.

In addition, the performance of the mechanical design, electronic systems, communication systems, control and guidance systems, and multi-sensor navigation systems in dual mode, AUG and AUV mode, are also shown in this manuscript in the form of simulation results and field experiments.

 Point 2: Page 2, line 75. It is the first time presenting “DVL”. Explain its full name for good readability.

Response 2: As suggested by the reviewer, we have added the full name of the DVL (Doppler Velocity Log) sensor on Page 2, Line 75.

Point 3: Page 9, line 182. I expect more explanations about the selection of KD and KL. The authors chose a number of 242 for KD, saying as low of it as possible, but a number of 395 for KL, saying as high of it as possible. I don’t see the logic here. 242 is in the same magnitude as 395

Response 2: Thank you for pointing this out. One of the important parameters related to HAUG Hydrodynamics is its Lift to Drag (L/D) ratio, which means the lift provided by the HAUG (not only the wing) divided by the drag produced by the HAUG (not only the wing). A Higher L/D ratio also correlates with the ratio between the distance traveled (dX) and depth traveled (dZ). HAUG with a higher L/D ratio will have a longer distance (dX) for the same depth travel (dZ). This also means that, with the same buoyancy setting to obtain a certain vertical speed (Vz), a higher horizontal speed (Vx) will be obtained for HAUG with a higher L/D ratio. Thus, a higher L/D ratio will be desirable for better HAUG performance.  KD describes the increase of the drag value as the angle of attack increases. This constant needs to be as low as possible which means of high L/D, while KL describes how much lift increases as the angle of attack increases. This constant needs to be as high as possible (high L/D)

In addition, the numbers 242 for KD and 395 for KL were not selected, yet, all values were found by using Computational Fluid Dynamics (CFD) methods.

The following table shows a list of drag constants for different vehicles.

1. Chunya Sun, Baowei Song, Peng Wang, Xinjing Wang, Shape optimization of blended-wing-body underwater glider by using gliding range as the optimization target, International Journal of Naval Architecture and Ocean Engineering, Volume 9, Issue 6, 2017, Pages 693-704, ISSN 2092-6782, https://doi.org/10.1016/j.ijnaoe.2016.12.003.
2. Afande, Nur & Chung, Ting & Arshad, Mohd Rizal & Mohd-Mokhtar, Rosmiwati & Abdullah, M.Z.. (2010). Design dasof an underwater glider platform for shallow-water applications. International Journal of Intelligent Defence Support Systems. Volume 3. 186-206. 10.1504/IJIDSS.2010.03709.
3. Muhammad Yasar Javaid, Mark Ovinis, Fakhruldin B.M. Hashim, Adi Maimun, Yasser M. Ahmed, Barkat Ullah, Effect of wing form on the hydrodynamic characteristics and dynamic stability of an underwater glider, International Journal of Naval Architecture and Ocean Engineering, Volume 9, Issue 4, 2017, Pages 382-389, ISSN 2092-6782, https://doi.org/10.1016/j.ijnaoe.2016.09.010.
4. Jianguo, W., Minge, Z., & Xiuju, S. (2011). Hydrodynamic Characteristics of the Main Parts of a Hybrid-Driven Underwater Glider PETREL. Autonomous Underwater Vehicles. doi:10.5772/24750

Point 4: Page 15, line 276. Any thoughts on improving the performance by reducing the position errors and velocity errors?

Response 4: Almost all AUVs use the Inertial Navigation System (INS) as their primary sensor. To produce a better solution (reducing position and velocity error), the data from INS is usually integrated with other sensors such as Doppler Velocity Log (DVL), Global Positioning System (GPS), acoustic based-sensors such as Long Baseline (Long Baseline) and Ultra-Short Baseline (USBL), or optical based sensor such as camera or lidar.

The results on Page 15, line 276 was showing the navigation system while only using the INS sensor (Inertial Measurement Unit Sensor).

Currently, in this paper, the navigation system design uses the Extended Kalman Filter(EKF), which fuses the INS with DVL, GPS, and depth sensor. And the results of integrating INS with other sensors, which produce a better solution, was shown in Figure 21 on Page 17.

Besides using EKF, there are some research shows other methods, that can be used for multi-sensor fusion, that as using Neural Networks and Error-state Kalman Filter­­⁵.

5. Shaukat, N.; Ali, A.; Javed Iqbal, M.; Moinuddin, M.; Otero, P. Multi-Sensor Fusion for Underwater Vehicle Localization by Augmentation of RBF Neural Network and Error-State Kalman Filter. Sensors 2021, 21, 1149. https://doi.org/10.3390/s21041149

Point 5: Some figures’ quality and font size need to be improved, like figure 22.

Response 5: Thank you for pointing this out. The reviewer is correct, and we have changed the picture quality in figure 22, which is now figure 15.

Point 6: The arrangement of sections seems not proper. Both mechanical and electrical designs are the prerequisite. Having the mechatronic system enables control, which is followed by other functions such as communication and navigation.  

Response 6: We agree with the reviewer’s assessment. Accordingly, throughout the manuscript, we have revised the arrangement, as follows: Mechanical and electrical design in the first order, followed by control and guidance, and other functions: navigation and communication.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have revised their manuscript according to reviews and the entire structure is improved a lot. Their responses address my questions and I don't have further concerns. The manuscript could be accepted in its current form in Robotics.