State-of-the-Art Review and Future Perspectives on Maneuvering Modeling for Automatic Ship Berthing

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

The article addresses a technical subject related to maritime technology and safety. While the paper has merits, there are several areas for improvement to meet academic publishing standards.

Specific Comments:

Introduction:

Quality: The introduction sets the stage but lacks coherence.

Issue: Fragmented and unclear presentation of the background and objectives.

Suggestion: Improve the flow and clarify the objectives to make the introduction more coherent.

Methodology:

Quality: The methodology section seems to discuss various tools and frameworks.

Issue: Insufficient detail about the methods and tools used, making it difficult for replication.

Suggestion: Provide a detailed, step-by-step explanation of the methods, including any software or tools used.

Discussion:

Quality: The discussion appears to cover various aspects but may not delve deep enough.

Issue: Lack of critical evaluation and context when discussing the results.

Suggestion: Include a more comprehensive evaluation and comparison of your findings with existing literature.

Recommendations:

1. Revise the article for better coherence and flow.

2. Enhance the methodology section by providing detailed explanations.

3.  Strengthen the discussion by incorporating deeper insights and contextual comparisons.

 

Author Response

Response to comment 1: Thanks for your suggestion. For better coherence and flow, the background and objectives are modified, the details are as follows:

‘According to statistics, 89%~96% of the collision accidents [1] are caused by human error, and nearly 70% of accidents are related to the bad ship skills of the opera-tors in the port [2]. To reduce or even eliminate the collisions caused by human errors, the maritime sector is moving rapidly towards autonomous shipping.

With the proposal of E-Navigation (IMO-2006, the eighty‑first session of the Maritime Safety Committee (MSC)), China Classification Society (CCS), Det Norske Veri-tas (DNV), Germanischer Lloyd (GL), Lloyd's Register of Shipping (LR), and other authority institutions successively published corresponding regulations and standards on autonomous ships. Regarded as the last-mils issue in ship operation, berthing maneuver is the most complicated and dangerous mission with comprehensive consideration on restricted and busy waterways, off-design ship performances, and strong external disturbances. In sum, automatic berthing is at the top level of autonomy [3-5].’

Response to comment 2: Thanks for your suggestion. In the methodology section, reference and citation database Web of Science, bibliometric software VOS-viewer are adopted to analyze the important issues and correlation of current references related to automatic berthing. To improve the readability and replication, modifications are made, and the details are as follows:

‘2.1. Literature search and visualization

In the present work, reference and citation database Web of Science (WoS), and bibliometric software VOS-viewer are adopted to collect references, and analyze the important issues and correlation of current references related to automatic berthing. The method and process of literature index [20] and visualization are as follow:

• The first step is to search literature in the WoS database, and KCI-Korean journal database, the following index keywords in the theme, abstract, and keywords: (“berthing*” OR “docking*”) AND (“ASV” OR “unmanned surface vessel” OR “unmanned surface vehicle” OR “autonomous surface vessel” OR “autonomous surface vehicle” OR “ship”) NOT (“underwater” OR “ROV” OR “UUV” OR “AUV” OR “aircraft” OR “drone” OR “car” OR “truck” OR “launch” OR “recovery” OR “cell” OR “actuator”);
• The second step is to go through the collected literature and remove the research that is out of this work’s scope, and 115 papers are retained;
• The third step is to supplement studies and papers that are the source of certain re-search or cited in the selected papers but not included in the database, and finally, 134 papers are added. With the literature collection and filter, a total of 249 articles consistent with the research scope are collected.
• The fourth step is to extract the research objects, methods, contents, and publication time from the titles, abstracts, and keywords section of the collected references, and establish a bibliometric database.
• In the fifth step, set up the threshold for the occurrence number in the extraction database, and then, plot the network illustration on automatic berthing studies, and density diagrams on the detailed research methods and techniques.’

Response to comment 3: Thanks for your suggestion. We strengthened the discussion section by incorporating deeper insights and contextual comparisons. The details are as follows:

‘2.4. Discussion of MMG model

Some studies [60-64] on ship berthing control adopt the conventional MMG mathematical model frame as the foundation of control algorithm. In these researches, a number of assumptions are proposed [16]:

• Hydrodynamic forces acting on the ship are treated quasi-steadily.
• Lateral velocity component is small compared with longitudinal velocity component.

Automatic berthing control studies [62-66] considering the berthing maneuver characteristic have shown satisfactory results with comparison of model tests. In these researches, the berthing maneuver specifications are concerned:

• Hydrodynamic forces acting on the ship are with strong non-linearity, the ship longitudinal velocity is small, and is in the same order with the lateral velocity and yaw moment.
• Thrust and steerage forces are with four-quadrant characteristics.
• Ship is vulnerable to external disturbances.
• Ship motion is assisted by auxiliary devices like side thrusters, tugs, cables, and anchors.

In sum, automatic berthing simulation results based on both methods are acceptable. However, there exists two ambiguous questions on the maneuver modeling frame for the berthing maneuver motion control:

• What are the similarities and differences between the conventional MMG maneuvering model and automatic berthing maneuvering model?
• How to establish an accuracy automatic berthing maneuvering model?

To answer the first question, similarities and differences between the conventional MMG model and berthing maneuver model are summarized in Table.2. With regard to the modeling methods, uniform methods (including data-based method, system-based method, and CFD-based method) are adopted to obtain the ship hydrodynamic performances for both the conventional model and berthing maneuver model. The main differences are found upon the hull motion characteristics, propulsion and steerage devices performances, external disturbances, and auxiliary devices. In conventional MMG model, moderate speed is concerned, the hydrodynamic forces are treated as linear, and the drifting angle should be smaller than 20 degrees, the resultant inflow angle to the thruster and rudder is small, and the ship motion is relatively insensitive to the external disturbances. However, in the berthing maneuver process [67,68], the ship undergoes conditions like low advance speed, large drifting, four-quadrant thrust and low rudder effect, and the ship is vulnerable and sensitive to external disturbances.

In brief, there exists distinct differences between the conventional moderate speed MMG model and the berthing maneuver MMG model, it is essential to build a proper and accurate maneuvering model for ship automatic berthing. What kind of effects do the differences lead to, and how to establish an accuracy model would be answered in the following sections.’

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Line 55-66

Indicate the seaports where automatic berthing was performed. If they belong to the ports of intensive shipping, this will increase the relevance of the research.

 

Line 90

Explanation "MMG model" is needed. Some sources refer to MMG as the Manoeuvring Mathematical Modeling Group.

 

Line 197-203

Doesn’t not considered, information received from ECDIS anti-grounding monitoring system.

 

Line 216

Doesn’t not considered factors such as:

a) determination and implementation of required safe margin distance between other moored vessels;

b) possibility of auto correction of final Pose B position, after receiving information from RADAR target, LIDAR and position sensors;

c) berthing bollard location;

d) accuracy of DGPS.

 

Line 234

The notation in Figure 6 needs to be improved.

 

Line 273-275

Need to add information about propeller reversal.

 

Line 287-288

The authors write that “Lateral velocity component is small compared with longitudinal velocity component”.

However, in the final phase of berthing, the lateral and longitudinal components of the speed become comparable, and in some cases the lateral component exceeds the longitudinal one (in the case of a vessel “pressing” to the berth with the help of a tug). This should be noted in the article.

 

Line 358

The upper part of Figure 9 refers to the circulation of the ship or for the case when the ship was denied berthing. I suggest the authors to change this figure.

Figure 9 (b) - you need to change the scale of the figure. This will improve its visualization.

 

Line 384

Figure 10 (a) - you need to change the scale of the figure. This will improve its visualization. It is also necessary to provide an explanation of the symbols on the axes.

 

Line 422

Figure 11 (a) - you need to change the scale of the picture. This will improve its visualization. It is also necessary to provide an explanation of the symbols on the axes.

The symbols KT, KQ, h0, Lpp are used in the figure (I believe that these are the thrust and moment coefficients, the efficiency coefficient, as well as the length between perpendiculars) for which there are no explanations.

It is also necessary to estimate the deviation between experimental values and simulation results. For example, for the case Sim x/Lpp»2.5, for the case Exp x/Lpp»3.3.

 

Line 502-506

You need to add the symbol r (I think this is the density of sea water).

“cross-flow resistance coefficient with drifting angle β=90°” is a very large value for berthing. Such angles correspond to the circulation or turn of the ship.

 

Line 515

The symbol NH in expression (1) denoted the hydrodynamic moment; in this expression, the authors refer to the hydrodynamic forces.

 

Line 530 Table 4

I suggest that the authors replace the symbols “+” and “-” for the designation U with the words “ahead” and “astern”; for the designation np the symbols “+” and “-” into the words “normal” and “reverse”. The “-” character for both U and np corresponds to a negative value.

 

Line 552

The symbol Jr must be added.

 

Line 656

Port tidal and current information, for vessels under automatic berthing control system, must be received online from port ODAS buoys.

This must be stated in the article.

 

Line 708

Vessels which use tug boats assistance for berthing and un-berthing, required permanently controlling and monitoring by ship’s operator Master or Pilot, which subsequently minimize operations of automatic berthing control system.

It is necessary to discuss this situation in the article.

 

 

 

 

Line 738-751

The article considers ships of small displacement. It is necessary to cite the opinions of the authors on how automatic berthing of large displacement ships, which are characterized by high inertia, will be carried out.

 

Line Reference

Refine Reference 8-17

Comments on the Quality of English Language

Author Response

The detailed responses are attached.

Response to comment 1: Thanks for your suggestion. Normally, the research, development, and application of automatic berthing follows the period: algorithm development → simulation analysis → model ship test → training ship test → test run → application. As far as we collected, by now, the present status of automatic berthing is mostly conducted on the simulation level and training ship test, the direct adoption is rare. Hence, the application of automatic berthing in seaports in the present work are missed. We will pay close and continuous attention to the development and application of automatic berthing.

Response to comment 2: Thanks for your suggestion. We added the explanation of ‘MMG model’, the details are as follows:

‘This paper aims to comb the hot issues in automatic berthing maneuver modeling, demonstrate the similarities and differences of conventional maneuvering modeling group (MMG) model [1] and berthing maneuver MMG model, and emphasize the significance of berthing maneuver modeling.’

[1]Yasukawa, Hironori, and Y. Yoshimura. "Introduction of MMG standard method for ship maneuvering predictions." Journal of marine science and technology 20 (2015): 37-52.

Response to comment 3: Thanks for your suggestion. The electronic chart display and information style system (ECDIS) anti-grounding monitoring system is an integrated aid system, gives an overall view on the status of the ship and port, and helps making up navigation courses. EDCIS is widely used in ship navigation, port and vessel traffic management, ship scheduling and dispatching. There are three main factors that the ECDIS is not involved in the present paper:

1. As described in subsection 2.1, the bibliometric analysis performs literature index based on autonomous ship berthing and docking, within the collected database, the branch of perception utilization mainly focuses on the wall distance, approaching angle, and berthing velocity of the target ship itself, the information provided by ECDIS is not efficient for ship berthing.
2. The density diagram of perception element and technique illustrated in Figure 6(b) is filtered by the occurrence number, however, the references related to ECDIS are with low quantity.
3. In the actual berthing maneuver process, it is the embedded monitoring system like IMU, RADAR, not ECDIS provides the essential information.

Response to comment 4: Thanks for your suggestion. The mentioned four factors are important for the realistic of automatic berthing and mooring. Follow your suggestion, we added the corresponding contents in the revised manuscript:

1) Determination and implementation of required safe margin distance between other moored vessels. In line 240, the modifications are: ‘Furthermore, it is reported that most marine accidents are caused by ship-ship collision and ship-shore collision [50]. In order to reduce the risk of collision accidents, collision avoidance algorithm [51] is embedded into the control system to determine and implement the required safe margin distance between the moored ships, moving ships, and the obstacles, which increases the system load, to some extent.’

2) Possibility of auto correction of final Pose B position, after receiving information from RADAR target, LIDAR and position sensors. In line 220, the modifications are: ‘The hidden scientific control problems are to position the target ship to the final pose B with real-time feedback of the perception elements (wall distance, lateral speed, and approaching angle) in the restricted water area and strong environmental disturbances [35].’

3, 4) Berthing bollard location, accuracy of DGPS. In line 204, the modifications are: ‘Among which, the approaching angle, lateral speed, and other own ship states are monitored through DGPS (differential global position system) and IMU (inertial measurement unit), the berth and bollard location and target ship detection are determined by the camera [30], millimeter wave RADAR [31], and other position sensors, while in severe weather conditions, 3D LIDAR [32], ultrasonic sensor, solar-blind ultraviolet and other measurement gages are employed to make up the deficiencies.’

Response to comment 5: Thanks for your suggestion. To improve the readability, the notation and scale of Figure 6 are modified.

Response to comment 6: Thanks for your suggestion. We added the information about propeller reversal in line 273-275, the detailed modifications are as follows:

‘However, during the berthing process, the ship undergoes much more complicated external conditions, such as extreme low speed, high drifting, propeller reversal, shallow water effect, bank effect, and heavy traffic flow, which eventually, lead to distinct changes on the hydrodynamic forces acting on the ship hull, propeller thrust, and rudder steerage force.’

Response to comment 7: Thanks for your suggestion. In line 287-288, the explanation is dedicated to the conventional MMG model with moderate ship speed. And the descriptions from line 292 to 295 indicate the characteristics of berthing maneuver. To avoid misunderstanding, modifications are made, and the details are as follows:

‘Automatic berthing control studies [62-66] considering the berthing maneuver characteristics have shown satisfactory results with comparison of model tests. In these re-searches, the berthing maneuver specifications are concerned:

• Hydrodynamic forces acting on the ship are with strong non-linearity, the ship longitudinal velocity is small, and is in the same order with the lateral velocity and yaw moment.
• Thrust and steerage forces are with four-quadrant characteristics.
• Ship is vulnerable to external disturbances.
• Ship motion is assisted by auxiliary devices like side thrusters, tugs, cables, and anchors.’

Response to comment 8: Thanks for your suggestion. In Figure 9, the data-based maneuver modeling methods including the experimental method and empirical method are illustrated. The upper part of Figure 9(a) indicates the turning maneuver sea trail, the lower part indicates the towing tank tests, Figure 9(b) represents the regression analysis. To improve the visualization, the scale of Figure 9(b) is modified.

Response to comment 9: Thanks for your suggestion. We modified the scale of Figure 10(a) and the corresponding explanation in subsection 3.3. The details are as follows:

‘The grey box model sets a prior model structure [75], some identification algorithms, such as maxi-mum likelihood (ML) [76], Kalman filtering (KF) [77], least squares method (LS) [78] or the improved algorithm are used to identify the experiment/simulation parameters like ship speed, yaw rate, propeller revolution, rudder angle, trajectories. And then, the maneuverability of the target ship is obtained (shown in Fig. 10(a)). However, these methods have some inherent disadvantages, the accuracy is sensitive to signal noise and initial estimations, and simultaneous drift is an-other critical issue.’

Response to comment 10: Thanks for your suggestion. Figure 11 indicates the research contents and comparisons between turning/zig-zag maneuvers of CFD-based methods, the comparison results here are not the main concern. And hence, to improve readability, explanation of the symbols and diagrams in Figure 11 were added, the details are as follows:

• ‘The virtual captive model tests method conducts specific maneuvering test simulations based on the maneuvering model [83,84] of the target ship, the hydrodynamic characteristics of which are obtained via the CFD method (shown in Fig.11(a), where upper left is the dimensionless longitudinal force X’, upper right the propeller thrust coefficient K_T, torque coefficient K_Q, thrust efficiency η₀, lower left the comparisons of turning maneuver trajectory, lower right the comparisons of heading angle ψ and rudder angle δ time histories).
• The direct simulation method indicates that the maneuvering model tests are performed with the CFD method directly (shown in Fig.11(b), where the upper is turning maneuver, and lower the zig-zag maneuver).’

Response to comment 11: Thanks for your suggestion. We are sorry to miss the explanation of the symbols, the details are as follows:

‘where X_H(r=0), Y_H(r=0), N_H(r=0) represent the hydrodynamic derivatives related to the lateral speed, u the longitudinal speed, v the lateral speed, r the yaw rate, C_d the cross-flow resistance coefficient with drifting angle β=90°, C_rY and C_rN the correction factor, L the ship length, d the ship draft, and x the longitudinal distance from the mid-ship point.’

Response to comment 12: Thanks for your suggestion. We modified the explanation of the symbol N_H, the detailed list is as follows:

‘where X_H, Y_H the hydrodynamic forces, and N_H the hydrodynamic moment acting on ship hull, R0 the resistance under straight moving condition, v the lateral component of ship velocity, r the yaw rate, and X_vv, Y_r, N_vvr, et al. the hydrodynamic derivatives.’

Response to comment 13: Thanks for your suggestion. Following your advice, we modified the descriptions of ship speed U and propeller revolution n_p in Table 4.

Response to comment 14: Thanks for your suggestion. We added the explanation of J_P in line 552, the details are as follows:

‘where J_P the propeller advance ratio.’

Response to comment 15: Thanks for your suggestion and expertise. Subsection 4.3.4 (line 652-688) mainly indicates that the wind and current effects on the are essential for ship berthing maneuver modeling, the wind and tidal current information collection methods are not involved. The ODAS buoys as well as ECDIS are necessary for ship navigation, but the introduction and technique development of such auxiliary systems are out of the theme of the present paper, and hence, are not stated in the article.

Response to comment 16: Thanks for your suggestion. As summarized on subsection 4.4.2, with the motion and tug specifications eliminated, the tugboats now in the maneuver modeling and motion control are simplified in two ways, one treats the tugboats as external azimuth thrusters taking effects direct and indirect methods, the other regards the tugboat and target ship as an integral. However, in the actual berthing process, tugboat assistance is significant for the berthing maneuver safety, it is complicate missions for the target ship’s master, pilot, and the tugboat operator. For the target ship, it is significant to manage the thrust allocation induced by the assistant tugboats. With regard to the tugboats, it is major to control the thrust through the adjustment on the touching angle, cable angle and tension. As for accurate ship automatic berthing, it is necessary to perform constant control and monitor on both the target ship and the assistant tugboats, minimize the operations and improve the robustness of the control system. In the future, as establishing the automatic berthing control system, we shall take the ship profiles, motion specifications, and thrust performances of the tugboats into account, for a more accurate and realistic control. The detailed modifications are as follows:

‘The automatic berthing process is described as: move the ship with low speed from pose A in the proximity of the harbor, to pose B lying right next to it, while simultaneously avoiding all static and dynamic obstacles. The hidden scientific control problems are to position the target ship to the final pose B with real-time feedback of the perception elements (wall distance, lateral speed, and approaching angle) in the restricted water area and strong environmental disturbances. In the berthing process, path planning, trajectory tracking, stabilization and robustness control are essential control targets. Furthermore, with regard to multi-tug assistance berthing control, it is necessary to perform constant control on the thrust allocation induced by the assistant tugboats, and monitor the status of target ship [1-3]. No matter for the self-berthing or tug-assistant berthing, wall distance, approaching angle, ship speed, and yaw rate are the control indices. Accordingly, ship berthing control is a low-speed low-frequency, and high-accuracy berthing control problem.’

[1] Bidikli, Baris, Enver Tatlicioglu, and Erkan Zergeroglu. "Robust dynamic positioning of surface vessels via multiple unidirectional tugboats." Ocean Engineering 113 (2016): 237-245.

[2] Du, Zhe, Vasso Reppa, and Rudy R. Negenborn. "Cooperative control of autonomous tugs for ship towing." IFAC-PapersOnLine 53.2 (2020): 14470-14475.

[3] Wu, Gongxing, et al. "Cooperative maneuvering mathematical modeling for multi-tugs towing a ship in the port environment." Journal of Marine Science and Engineering 9.4 (2021): 384.

Response to comment 17: Thanks for your suggestion. Modifications are made in subsection 4.4.2 to make clear the berthing methods for ships with small and large dimensions. The details are as follows:

‘In the berthing process, whether it’s for ships with small displacement, or ships with larger dimension, the essential indices for ship berthing are the same, namely the approaching angle, lateral speed, and wall distance. Tugs are utilized to release the berthing risk and improve efficiency. Based on the survey of 15 ports in China, 120m of the ship length is normally regarded as a boundary for tug usage [1], it is acceptable for ships with shorter ship lengths to conduct self-berthing. As for ships with greater dimensions, it is mandatory to change direction, turn around, pull up, and parallel berth with the assistance of tugboats [2]. However, when it comes to liquid cargo ships, engineering ships, ships with damage, extreme weather, and other conditions, ships are obligated to berth with tugs.’

[1] Song Zhang, et al. “System design and key technology of ship automatic berthing and unberthing.” China Ship Survey. 10 (2022): 42-47.

[2] Yadong Yang, and Qinglin Gao. “Shzip Maneuvering.” Wuhan University of Technology Press. 2015.

Response to comment 18: Thanks for your suggestion. Modifications are made on the reference structure, the details are as follows:

[8] Executive, T.M. Video: Japanese Demonstration of Autonomous Docking System. Available online: https://maritime-executive.com/article/video-japanese-demonstration-of-autonomous-docking-system

[9] Watch: World’s first successful trail of auto berthing and un-berthing system. Available online: https://safety4sea.com/watch-worlds-first-successful-trial-of-auto-berthing-and-un-berthing-system/

[10] Executive, T.M. First Autonomous Navigation and Berthing Test on a Containership. Available online: https://maritime-executive.com/article/first-autonomous-navigation-and-berthing-test-on-a-containership

[11] Project, K.A.S.S. Detailed task. Available online: https://kassproject.org/en/task/task.php

[12] Water test of the first domestic autonomous navigation system experimental ship. Available online: https://news.qingdaonews.com/qingdao/2019-05/17/content_20362302.htm

[13] Brilliance, N. The first unmanned container ship in China successfully undocked. Available online: http://www.brinav.com/pages/News/NewsDetails.aspx?ID=2022

[14] Rolls-Royce. Rolls-Royce and Finferries demonstrate world’s first Fully Autonomous Ferry. Available online: https://www.rolls-royce.com/media/press-releases/2018/03-12-2018-rr-and-finferries-demonstrate-worlds-first-fully-autonomous-ferry.aspx

[15] Corporation, W. World’s first Autodocking installation successfully tested by Wärtsilä. Available online: https://www.wartsila.com/media/news/26-04-2018-world-s-first-autodocking-installation-successfully-tested-by-wartsila-2169290

[16] MARITIME, K. Autonomous ship project, key facts about yara birkeland: the zero emission, autonomous container feeder. Available online: https://www.kongsberg.com/zh-hans/maritime/support/themes/autonomous-ship-project-key-facts-about-yara-birkeland/

[17] PENTA, V. Launching the first fully integrated Assisted Docking system. Available online: https://www.volvopenta.com/about-us/news-page/2021/jan/launching-the-first-fully-integrated-assisted-docking-system/

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper carries out a very interesting state-of-the-art review of maneuvering modeling for automatic ship berthing. Initially, it conducts a bibliometric analysis on automatic berthing, then shows similarities and differences between MMG maneuvering model and automatic berthing maneuvering model. Also, it explains berthing maneuver specifications and modeling procedures used nowadays. It is of interest to readers.

It could be of interest to improve the quality and size of  some figures, for example, figures 6.a, 6.b and 6.c

Author Response

Detailed responses are attached.

Response to comment 1: Thanks for your suggestion. We went through the main text, the qualities and sizes of Figures 6, 7, 9, and 10 are modified.

Author Response File: Author Response.pdf