Ship Domain Research Articles

Research on Autonomous Collision Avoidance of USV Based on Improved APF Algorithm

Abstract Aiming at the problem of Unmanned Surface Vessel (USV) avoiding dynamic vessels on the sea surface, an Artificial Potential Field method based on Velocity Obstacle Method (VO-APF) was studied. Under the premise of complying with the Convention on the International Regulations for Preventing Collisions at Sea (COLREGs), the overlapping of ship domains is minimized. The Quaternion ship domain was introduced into VO to make it more suitable for collision avoidance judgment in the ship domain, and the collision avoidance time of the ship was predicted, and the reasonable obstacle avoidance point was finally obtained. The attraction function of the obstacle avoidance target point and the repulsion function of the ship domain based on the APF are set, and the USV is subjected to the repulsion force and attraction in the APF, and finally completes the whole dynamic ship collision avoidance task. In the simulation environment, VO, APF and VO-APF were compared in three different encounter situations. The results show that VO-APF can help USV to complete the collision avoidance task under the premise of complying with COLREGs, and the overlap time between USV’s own ship domain and the other ship domain is the shortest, and the safety degree is the highest.

Autonomous collision avoidance decision-making method for USV based on ATL-TD3 algorithm

To address the issue of decision-making for ship collision avoidance in complex encounter situations, an Autonomous Collision Avoidance Decision-making (ACAD) model based on Attention Long Short-Term Memory Twin Delayed Deep Deterministic Policy Gradient (ATL-TD3) algorithm for Unmanned Surface Vessel (USV) is proposed in this study. The novelty of this method is: (1) Incorporating LSTM and multi-head self-attention mechanism into the existing TD3 algorithm network enhances its focus on pertinent historical state information. Furthermore, the generalization ability of the trained model is further enhanced through optimization of the accumulated experience. (2) A comprehensive reward mechanism is designed, incorporating ship domain, arena, yaw, and other relevant factors, which solve the encounters defined in clauses 13–17 in Chapter 2 of COLREGs and immediate danger. The experiment involved a comparative analysis of the average reward curve and success rate during training under different environments. Additionally, 20 cases of Imazu classic encounters and real navigation data from the Suez Canal were utilized to validate the proposed algorithm. It is highlight that the ACAD model trained by the ATL-TD3 algorithm exhibits remarkable performance in the generalization verification, surpassing conventional collision avoidance methods.

An integrated decision support system for ship collision avoidance

The ship encounter process is divided into the stages of free action, risk of collision, close-quarter, and immediate danger according to the four-stage theory of ship encounters. Current research on ship collision avoidance primarily focuses on the risk of collision stage, aiming to prevent ships from entering the close-quarter stage. However, various navigational equipment and environmental factors may cause ships to enter the close-quarter or immediate danger stages. Therefore, this paper establishes an integrated decision support system for the above stages to ensure that ships can handle all situations. First, the system includes a new collision risk detection module based on the ship domain model and the four-stage theory. Subsequently, in the collision avoidance strategy formulation module, two sets of avoidance strategies are established based on the convention on the COLREGs and the most effective avoidance principle for ships in different stages. Finally, in the avoidance action optimization module, a new fitness function is constructed based on ship maneuverability, and the sparrow search algorithm is introduced to solve for the optimal avoidance actions. The results demonstrate the capability of the decision support system presented in this paper to effectively avoid other ships in different stages of the encounter process.

Dynamic Calculation Approach of the Collision Risk in Complex Navigable Water

It is vital to analyze ship collision risk for preventing collisions and improving safety at sea. This paper takes Ningbo-Zhoushan Port, a typical complex navigable water, as the research object. Firstly, a probabilistic conflict detection method based on an AIS data-driven dynamic ship domain model is proposed to achieve effective ship conflict detection under uncertain environments. Then, a ship group identification method is proposed, which can extract the ship groups with conflict correlation and space compactness. Finally, according to the characteristics of ship traffic in complex navigable waters, the dynamic calculation of ship collision risk is carried out from individual, regional, and local multi-scale perspectives. The experimental results show that the proposed method can detect the collision risk in a timely, reliable, and effective manner under complex dynamic conditions. As such, they provide valuable insights into ship collision risk prediction and the development of risk mitigation measures.

USV Collision Avoidance Decision-Making Based on the Improved PPO Algorithm in Restricted Waters

The study presents an optimized Unmanned Surface Vehicle (USV) collision avoidance decision-making strategy in restricted waters based on the improved Proximal Policy Optimization (PPO) algorithm. This approach effectively integrates the ship domain, the action area of restricted waters, and the International Regulations for Preventing Collisions at Sea (COLREGs), while constructing an autonomous decision-making system. A novel set of reward functions are devised to incentivize USVs to strictly adhere to COLREGs during autonomous decision-making. Also, to enhance convergence performance, this study incorporates the Gated Recurrent Unit (GRU), which is demonstrated to significantly improve algorithmic efficacy compared to both the Long Short-Term Memory (LSTM) network and traditional fully connected network structures. Finally, extensive testing in various constrained environments, such as narrow channels and complex waters with multiple ships, validates the effectiveness and reliability of the proposed strategy.

A Study on A Novel Collision Risk Prediction Map for Maritime Traffic Surveillance Based on Ship Domain

A Study on A Novel Collision Risk Prediction Map for Maritime Traffic Surveillance Based on Ship Domain

An Integrated Maneuverability–Based Ship Domain at Close Quarters

An Integrated Maneuverability–Based Ship Domain at Close Quarters

Holistic collision avoidance decision support system for watchkeeping deck officers

The paper presents a 3-stage synthesis-based Decision Support System for watchkeeping deck officers. Its functional scope covers conflict detection, maneuver selection, and maneuver execution, all phases supplemented by collision alerts. First, a customized elliptic ship domain is used for checking if both OS and TS will have enough free space. A survey-based navigators’ declarative OS arena is then used to determine the time at which OOW would like to take evasive action. Next, a safety level is assigned to the current situation based on the predicted violations of the ship domain and the declarative arena. The safety levels are also attributed to potential evasive maneuvers (single actions combining course alteration and rudder deflection). For a selected maneuver, Collision Avoidance Dynamic Critical Area (CADCA) is displayed, which informs OOW about the time window when the maneuver remains feasible. All of the above contribute to a holistic system of multi-level safety assessment utilizing: empirical ship domain, survey-based declarative arena, and ship dynamics-based CADCA. These, in turn, take into account navigators’ knowledge and preferences, ship maneuverability, and the impact of environmental conditions. The system is presented in three real-life scenarios located in the southern part of the Baltic Sea around the Danish straits.

Risk Analysis and Visualization of Merchant and Fishing Vessel Collisions in Coastal Waters: A Case Study of Fujian Coastal Area

The invasion of ship domains stands out as a significant factor contributing to the risk of collisions during vessel navigation. However, there is a lack of research on the mechanisms underlying the collision risks specifically related to merchant and fishing vessels in coastal waters. This study proposes an assessment method for collision risks between merchant and fishing vessels in coastal waters and validates it through a comparative analysis through visualization. First of all, the operational status of fishing vessels is identified. Collaboratively working fishing vessels are treated as a unified entity, expanding their ship domain during operation to assess collision risks. Secondly, to quantify the collision risk between ships, a collision risk index (CRI) is proposed and visualized based on the severity of the collision risk. Finally, taking the high-risk area for merchant and fishing vessel collisions in the Minjiang River Estuary as an example, this paper conducts an analysis that involves classifying ship collision scenarios, extracts risk data under different collision scenarios, and visually analyzes areas prone to danger. The results indicate that this method effectively evaluates the severity of collision risk, and the identified high-risk areas resulting from the analysis are verified by the number of accidents that occurred in the most recent three years.

Research on Dynamic Quaternion Ship Domain Model in Open Water Based on AIS Data and Navigator State

During the process of establishing the analytical quaternion ship domain model, the impact of ship traffic conditions and navigator state was not taken into consideration. However, the significance of these factors in the ship domain cannot be ignored. To create a more realistic representation of changes in the ship domain in real navigation environments, this study further considers the influence of ship encounter course, waterway traffic intensity, relative ship velocity, and the navigator state based on the quaternion ship domain model. As a result, a new dynamic quaternion ship domain model is proposed. To assess the changes in the size and shape of the ship domain under various navigation environments, ship domain scaling and shape transformation functions are introduced. Specifically, this study focuses on analyzing the ship traffic near the Lao Tie Shan Waterway, simulating the size and shape changes of the ship domain during the navigation process in this area. The findings indicate that the size of the ship domain dynamically adjusts to the traffic conditions. Additionally, when the navigator state is excellent, the ship domain takes on an irregular diamond shape with the smallest area, whereas when the navigator state is poor, the shape approximates a rectangle with the largest area. Furthermore, the dynamic quaternion ship domain model proposed in this study is compared to the ship domain models put forth by Goodwin, Davis, and co-authors. The results demonstrate that the dynamic quaternion ship domain model is more compatible and suitable for open waters compared to the static quaternion ship domain model.

An Improved VO Method for Collision Avoidance of Ships in Open Sea

In order to effectively deal with collisions in various encounter situations in open water environments, a ship collision avoidance model was established, and multiple constraints were introduced into the velocity obstacle method, a method to determine the ship domain by calculating the safe distance of approach was proposed. At the same time, the ship collision avoidance model based on the ship domain is analyzed, and the relative velocity set of the collision cone is obtained by solving the common tangent line within the ellipse. The timing of starting collision avoidance is determined by calculating the ship collision risk, and a method for ending collision avoidance is proposed. Finally, by comparing the simulation experiments of the improved algorithm with those of the traditional algorithm and the actual ship experiment results of manual ship maneuvering, it is shown that the method can effectively avoid collisions based on safe encounter distances that comply with navigation experience in different encounter situations. At the same time, it has better performance in collision avoidance behavior. It has certain feasibility and practical applicability.

Autonomous collision avoidance method for MASSs based on precise potential field modelling and COLREGs constraints in complex sailing environments

Autonomous collision avoidance (CA) for maritime autonomous surface ships (MASSs) in complex navigational environments requires accurate environment modelling and efficient CA algorithms. This study proposes a fast construction method for complex environmental potential field models applicable to vector charts. It accurately represents all complex static obstacles, including concave polygons, and dynamically adjusts the range of influence of a potential field according to its danger level. For dynamic ships, a dynamic obstacle modelling method, based on the quaternion ship domain, is designed to highlight the uncertain motion characteristics of ships. Based on the coupled modelling of dynamic and static obstacles, the virtual potential field of target ships, constrained by the International Regulations for Preventing Collisions at Sea (COLREGs), was constructed. By combining the first-order Nomoto model and optimal field prediction strategy, an optimal CA path, satisfying ship dynamics and COLREGs constraints, was realised, and the local optimal problem of the traditional artificial potential field method was solved. Simulation results show that the proposed method accomplishes fast and accurate modelling of complex environments and realises autonomous path planning and real-time multivessel CA tasks for MASSs in complex water considering the COLREGs constraints. Thus, the proposed method can be implemented in actual ships.

Intelligent decision-making system for multiple marine autonomous surface ships based on deep reinforcement learning

This study addresses the issue of multi-ship collision avoidance and the requirements for autonomous navigation of Marine Autonomous Surface Ships. To address this challenge, we propose a collision avoidance decision-making system for multi-ship encounters that integrates the Proximal Policy Optimization (PPO) algorithm with the ship domain while considering ship manoeuvring characteristics. Moreover, the reward function designed for the PPO algorithm can effectively ensure the trained collision avoidance decision-making model adheres to COLREGs and to prioritizes the utilization of small angle steering whenever possible. Additionally, a neural network based on Bidirectional Gated Circulation Unit (BiGRU) is established, incorporating Layer Normalization to handle high-dimensional observation data and enhancing the algorithm's efficiency. Through simulation experiments, the results demonstrate the flexibility and safety of the proposed decision-making method in multi-ship collision avoidance and surface obstacle avoidance scenarios.

Modeling and application of ship traffic conflicts in nearshore waters with heavy traffic

Ensuring the safety of ship navigation is essential to support the sustainable development of the shipping industry, and maritime safety analysis has thus received much attention in the field of shipping. Traditionally, the safety evaluation is mostly performed with the help of accident data, which is thus limited by the insufficient amount of accident data and affects the evaluation effect. In order to overcome this limitation, a ship traffic conflict model is established, which consists of three sub-models: multi-risk ship domain model, ship traffic conflict preliminary screening model and ship traffic conflict detection model. The multi-risk ship domain model is the key foundation, combining the traditional ship domain model with the water traffic conflict severity model to fully consider the severity of ship traffic conflict. To validate the proposed model, three ships in the study waters are selected as the own ships, and the severity of traffic conflicts formed with their target ships within a certain conflict time range are analyzed separately. Then, the conflict datasets obtained from the training of the ship traffic conflict model are used to analyze the traffic conflict situation in the heavily trafficked waters near Tianjin Port. Specifically, the spatial distribution characteristics are obtained using the kernel density estimation (KDE) method and the water grid method, and the temporal distribution characteristics are verified with the help of the accident statistics method. The proposed ship conflict model can provide technical support for further research in the field of ship traffic conflict, and the experimental analysis results are of great significance for strengthening maritime traffic supervision.

Grounding risk quantification in channel using the empirical ship domain

Ship groundings in channels pose substantial risks to human safety and economic stability. Existing quantitative models inadequately factor in risks related to ship deviations from the channel and variations in ship grounding susceptibility. We propose a grounding risk quantification framework utilizing Automatic Identification System (AIS) data and empirical ship domain, designed to assess risks from channel deviations or shallow water approaches. We build an empirical ship domain model, then develop a spatial grounding risk function considering ship sensitivity variations across directions. By exploring spatiotemporal relationships between ships and unnavigable waters, we quantify and normalize grounding risk. We apply this framework to the Yangtze River Estuary channel, finding higher grounding risk in the main channel than in the small ship channel due to smaller widths, shallow water, and the small ship channel entrance’s proximity to the anchorage. This provides valuable support for channel management and shipping safety.

Ship collision avoidance control based on improved velocity obstacle method

The velocity obstacle method has extensive research in collision avoidance, which uses circles to represent robots or ships to find a collision-free velocity. To better describe the motion characteristics of ships, an improved velocity obstacle method based on elliptical ship domain is proposed in this paper. In the previous research on collision avoidance, the ship domains of the own ship and the target ship are seldom considered at the same time. This paper considers the ship domains of the own ship and the target ship at the same time and judges whether the ship domains of the two ships overlap based on the generalized characteristic polynomial. The heading angle is discretized to construct the velocity obstacle (VO) by calculating the collision velocity at different heading angles. Velocities on the boundaries of the velocity obstacle are used to find an optimal heading angle. The algorithm is tested in different encounter situations and successfully realizes collision avoidance.

Facile and eco-friendly fabrication of superhydrophilic and superhydrophobic SiC surfaces by nanosecond laser treatment

Superhydrophobic silicon carbide surfaces have garnered substantial attention for their potential applications in aerospace, ship domain, military, etc., fields. In this work, we used a nanosecond laser (λ = 1065 nm) and fluorine-free N-octyltriethoxysilane (OcTES) to fabricate SiC surfaces capable of transitioning from superhydrophilic to superhydrophobic. Superhydrophilic surfaces were produced within minutes through laser treatment, and the time required to convert it to superhydrophobic surfaces is only 1 h. The apparent water contact angle (WCA) of superhydrophilic SiC could reach the saturated Wenzel regime. The number of hydrophilic polar bonds on SiC surfaces increased while nonpolar bonds of hydrophobicity decreased due to oxidation during laser treatment. After OcTES treatment, the SiC surface transformed from superhydrophilic to superhydrophobic (WCA of 153° and roll-off angle of 0°). These results indicate that surface roughness and chemical compositions are critical for superhydrophobicity. It was discovered that Si–O–Si groups were formed on SiC surfaces in the atmosphere, thereby enhancing the material surface's hydrophobicity. Superhydrophobic SiC surfaces also have excellent low-adhesion and anti-icing properties, making them of potential interest for functional ceramic surface applications.

A COLREGs-Compliant Ship Collision Avoidance Decision-Making Support Scheme Based on Improved APF and NMPC

In this paper, combined with the improved artificial potential field (IAPF) method and the nonlinear model predictive control (NMPC) algorithm, a collision avoidance decision-making support scheme considering ship maneuverability and the International Regulations for Preventing Collisions at Sea (COLREGs) is proposed. First, to comply with the requirements of COLREGs, an improved repulsive potential field is presented for different encounter scenarios when the ship detects the risk of collision, and the coordinated ship domain is applied to provide safety criteria for collision avoidance. Then, by transforming the MMG model to a discrete-time nonlinear system, the NMPC is utilized to predict the future state of the ship according to the current state, and the IAPF method is incorporated to calculate the potential field in each future state as the objective function. Following this approach, the action taken to avoid collision is more effective, the ship motion in avoiding collision is more accurate, and the collision avoidance decision making is more reasonable. Finally, two simulation examples of multi-ship encounter scenarios are applied to illustrate the merits and effectiveness of the proposed collision avoidance decision-making support scheme.

An advanced decision-making model for determining ship domain size with a combination of MCDM and fuzzy logic

The ship domain is a critical and practical concept for both collision risk assessment and planning of collision avoidance action at sea. This study presents a new methodology that combines Fuzzy Logic and Analytic Hierarchy Process for determining the ship domain, especially for open waters.The model considers various factors such as ship speed, manoeuvrability, encounter type, etc., which are critical for determining ship domain size and shape. In order to verify the effectiveness of the proposed model, numerical experiments and comparative implementations with existing models were conducted. Through experimental analysis in different scenarios, the results demonstrate that the proposed model can be effectively used for collision risk assessment. Finally, the model will contribute to ship movement safety, collision risk assessment, and collision avoidance action planning. Moreover, the framework proposed in this study may provide a typical perspective for further research of ship domain.

Effects of ship domain shapes on ship collision risk estimates considering collision frequency and severity

This study aims to estimate ship collision risk considering the occurrence frequency and severity simultaneously, as well as to explore the influence of ship domain shapes on estimation results in the Yangtze River estuary waterway. In contrast to the circular ship domain, the elliptical domain may result in an overestimate for head-on collisions and overtaking collisions, while it may underestimate the small-angle and large-angle crossing collision frequency. Conversely, the sector domain may underestimate the occurrence frequency of all collision types. Results also reveal that overtaking encounters are the most common type with a relatively low severity degree, while large-angle crossing collisions are associated with a lower frequency but a higher potential for causing serious consequences. The collision occurrence likelihood and severity are a little higher for the passenger ship type. Furthermore, two high-risk areas are found to be located between longitudes of 121°33′E and 121°46′E, 121°50′E and 121°58′E, respectively. The results of this study are beneficial for a better understanding of the overall collision risk in the Yangtze River estuary waterway.