Browsing by Author "Du, Lei"

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Available-Maneuvering-Margins-Based Ship Collision Alert System
(2022-08-15) Du, Lei; Valdez Banda, Osiris; Sui, Zhongyi
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The timing of a ship taking evasive maneuvers is crucial for the success of collision avoidance, which is affected by the perceived risk by the navigator. Therefore, we propose a collision alert system (CAS) based on the perceived risk by the navigator to trigger a ship’s evasive maneuvers in a timely manner to avoid close-quarters situations. The available maneuvering margins (AMM) with ship stability guarantees are selected as a proxy to reflect the perceived risk of a navigator; hence, the proposed CAS is referred to as an AMM-based CAS. Considering the dynamic nature of ship operations, the non-linear velocity obstacle method is utilized to identify the presence of collision risk to further activate this AMM-based CAS. The AMM of a ship are measured based on ship maneuverability and stability models, and the degree to which they violate the risk-perception-based ship domain determines the level of collision alert. Several typical encounter scenarios are selected from AIS data to demonstrate the feasibility of this AMM-based CAS. The promising results suggest that this proposed AMM-based CAS is applicable in both ship pair encounter and multi-vessel encounter scenarios. Collision risk can be accurately detected, and then a collision alert consistent with the risk severity is issued. This proposed AMM-based CAS has the potential to assist autonomous ships in understanding the risk level of the encounter situation and determining the timing for evasive maneuvers. The advantages and limitation of this proposed method are discussed
Collision prevention of ship towing operation under environmental disturbance
(2022-12-15) Zhang, Lei; Du, Zhe; Valdez Banda, Osiris; Goerlandt, Floris; Du, Lei; Li, Xiaobin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Towing operations are highly reliant on the experience of the towing operators. Safety concerns arise when towing operations are subjected to environmental disturbances and dynamic traffic conditions. However, a systematic framework and approaches to enhance the safety and automation of towing operations remain lacking. This work proposes a framework of collision prevention of ship towing operations under environmental disturbance in near port waters. The focus is to prevent internal collisions between tug and assisted ship and provide early warning of possible collisions with other surrounding ships. A cooperative multi-agent control strategy is employed to specify the direction and magnitude of the towing force of the two tugs in real-time. Therefore, in the presence of environmental disturbance, the assisted ship can sail along the planned trajectory, and the acceptable safe geometric distance between each ship pair in the towing system is guaranteed. Further, a COLREGs-compliant collision alert system is designed to promptly remind the towing operators of a collision hazard with nearby ships, and different alert levels indicate different action obligations of towing operators. This proposed framework and developed methods are applied to a tandem towing system consisting of two tugs and one assisted ship to test its feasibility.
A COLREG-compliant ship collision alert system for stand-on vessels
(2020-12-15) Du, Lei; Valdez Banda, Osiris; Goerlandt, Floris; Yamin, Huang; Kujala, Pentti
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Bridge alarms are a plausible way to reduce the ship collision probability by timely alerting the officer on watch of a conflict. However, there currently are no dedicated methods for alerting a stand-on ship to compensate the unawareness of or inactive response of a give-way ship to dangerous encounter situations. Therefore, this article proposes a collision alert system from the stand-on ship perspective to trigger the stand-on ship's involvement in the conflict elimination. The developed method quantifies the terms of the COLREGs regarding the stand-on ship's responsibility for conflict elimination. The conflict severity is divided into 9 classes based on the ship intention estimation, conflict evolution analysis and COLREGs scrutiny. These are linked with the 4 stages of the encounter process to helps stand-on ship clarify her action responsibilities as per the rules and classify the alert into four levels. The available maneuvering margin of the stand-on ship is considered to improve the accuracy of severity ranking. The results of several case studies in open water with good visibility indicate that the proposed method can support the stand-on ship to correctly understand the rules and to fulfil her duties.
An empirical ship domain based on evasive maneuver and perceived collision risk
(2021-09) Du, Lei; Valdez Banda, Osiris; Yamin, Huang; Goerlandt, Floris; Kujala, Pentti; Zhang, Weibin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
This paper introduced a new ship domain concept and an analytical framework. The ship domain takes the point of the ship’s first evasive maneuver as a basis and correlates it with the navigator-perceived collision risk level. The first evasive maneuver of a ship is detected based on the ship turning point identification and ship intention estimation. The available maneuvering margin (AMM) is utilized as a proxy to measure the perceived collision risk by the navigator. Interpreting the first evasive maneuver in terms of this AMM over a large sample of vessel encounters taken from automatic identification system (AIS) data finally enables an empirical estimation of the size of this ship domain. The method is applied to AIS data in the Northern Baltic Sea, and separate ship domains are constructed for the give-way and stand-on vessels with different maneuverability characteristics. Compared to the existing proximity-based ship domain, this ship domain explicitly incorporates the dynamic nature of the encounter process and the navigator’s evasive maneuvers. Several advantages of this proposed ship domain concept and limitations of the presented modeling approach are discussed. Finally, possible future applications are explained, including waterway safety assessment and navigational decision support systems to reduce ship-ship collision risk.
Improving Near Miss Detection in Maritime Traffic in the Northern Baltic Sea from AIS Data
(2021-02-10) Du, Lei; Valdez Banda, Osiris; Goerlandt, Floris; Kujala, Pentti; Zhang, Weibin
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Ship collision is the most common type of accident in the Northern Baltic Sea, posing a risk to the safety of maritime transportation. Near miss detection from automatic identification system (AIS) data provides insight into maritime transportation safety. Collision risk always triggers a ship to maneuver for safe passing. Some frenetic rudder actions occur at the last moment before ship collision. However, the relationship between ship behavior and collision risk is not fully clarified. Therefore, this work proposes a novel method to improve near miss detection by analyzing ship behavior characteristic during the encounter process. The impact from the ship attributes (in-cluding ship size, type, and maneuverability), perceived risk of a navigator, traffic complexity, and traffic rule are considered to obtain insights into the ship behavior. The risk severity of the detected near miss is further quantified into four levels. This proposed method is then applied to traffic data from the Northern Baltic Sea. The promising results of near miss detection and the model validity test suggest that this work contributes to the development of preventive measures in maritime management to enhance to navigational safety, such as setting a precautionary area in the hotspot areas. Several advantages and limitations of the presented method for near miss detection are discussed.
Improving stand-on ship’s situational awareness by estimating the intention of the give-way ship
(2020-04-01) Du, Lei; Goerlandt, Floris; Valdez Banda, Osiris; Huang, Yamin; Wen, Yuanqiao; Kujala, Pentti
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The lack of situational awareness is a major cause of ship collisions. Thus, enhancing the situational awareness of the stand-on ship is a key for navigational safety, where the intention estimation of the give-way ship is crucial. According to COLREGs, the stand-on ship is not allowed to take evasive actions until the give-way ship does not take proper actions timely. The stage that needs the stand-on ship to take actions plays as the second protective layer for the ship, which is named as ‘Stand-on Ship as Second Line of Defense’ (SLoD). A method to estimate the intention of the give-way ship and to trigger SLoD is proposed in this article. Four modules of the proposed method include: “data pre-processing” collects all traffic information and determines the ships' obligations; “action identification” pinpoints the turning points; “action uncertainty” generates a bounded reachable velocity considering the give-way ship's maneuverability; “conflict assessment” judges potential collision by using non-linear velocity obstacle algorithm. Several typical encounter scenarios are simulated to demonstrate the feasibility of the proposed method. The results show that intention estimation of the give-way ship improves the situational awareness of the stand-on ship, which can support the stand-on ship to make collision avoidance decisions.
An intelligent method for real-time ship collision risk assessment and visualization
(2020) Du, Lei; Valdez Banda, Osiris; Kujala, Pentti
A4 Artikkeli konferenssijulkaisussa
Ship collision attracts prevalent attention due to its high occurrence frequency and severe potential conse-quence. It is therefore of pressing importance to prevent ship collision at sea for safe maritime transporta-tion. Non-linear Velocity Obstacle (NL-VO) algorithm has received increasing attention in maritime colli-sion avoidance by taking the dynamics of ship action during the encounter process into consideration. How-ever, one precondition of NL-VO algorithm is that the trajectory of target ship needs to be known in ad-vance, which makes the application of this algorithm limited in the historical ship collision risk analysis ra-ther than the in real-time collision avoidance. Although the generalized velocity obstacle algorithm over-comes this limitation using the trajectory prediction module, the trajectory uncertainty of the target ship is not discussed leading to the possible inaccurate collision risk assessment. Therefore, this paper presents a real-time collision risk assessment method based on an improved NL-VO algorithm by including the uncer-tainty analysis of the target ship’s predicted trajectory. The proposed method consists of two main modules: trajectory uncertainty module assumes that the increase in the radius of the circular restricted area is con-sistent with the Wiener process; collision risk assessment module utilizes the non-linear velocity obstacle algorithm combined with the dynamic circular restricted area to evaluate the potential collisions. Several encounter scenarios in a specific port channel are designed to demonstrate the feasibility of using this pro-posed method to assess ship collision risk in real-time. The result shows that this improved NL-VO algo-rithm can timely identify a ship that is in danger of colliding with the own ship and know when the collision will occur, which contributes to reducing ship collision occurrence probability.
LADRC-based Path Following Control for Cylindrical Drilling Platform Towing System
(2020-11-06) Tao, Jin; Du, Lei; Sun, Hao; Sun, Qinglin; Xie, Guangming; Zhou, Quan
A4 Artikkeli konferenssijulkaisussa
The towing process is the precondition to put a cylindrical drilling platform into use, which is saturated with risk due to the complexity of the towing environment, towing maneuvering, and the sudden and severity of accidents. Therefore, to control the cylindrical drilling platform towing system safely following a predefined course to reach the target see area becomes increasingly important. For environmental disturbances caused by wind and currents changing with time, a linear adaptive-disturbance-rejection-control (LADRC) based path following control method for cylindrical drilling platform towing system is proposed. Firstly, on the basis of both the mathematical modeling group model and the catenary model, three degrees of freedom nonlinear model of the cylindrical drilling platform towing system is built to obtain its real-time motion state. Then, a LADRC controller based on a two-dimensional trajectory tracking guidance law is designed for real-time path following control. Finally, simulation experiments of the path following control for the cylindrical drilling platform towing system is conducted. The results illustrate that the LADRC can effectively resist influences of the environmental disturbances and has a better path following performances than the traditional proportional-integral-derivative (PID) controller.
Maritime Traffic Risk Analysis in the Northern Baltic Sea from AIS Data
(2021) Du, Lei
School of Engineering | Doctoral dissertation (article-based)
Non-accident critical events, such as near misses, detected from AIS data have been widely utilized as a basis to assess the maritime traffic risk, thereby helping to achieve a safe maritime transport system. However, this method originated from other fields, such as road and aviation transportation, and its validity has not been fully verified. Therefore, the direct utilization of non-accident critical events as a basis to correctly understand the maritime traffic risk remains challenging. Further, increasingly crowded ship traffic also poses new challenges to these non-accident critical event-based methods. More attention needs to be paid to violations of Inter-national Regulations for Preventing Collisions at Sea (COLREGs) and multi-vessel encounters. The primary aim of this thesis is to improve maritime traffic risk analysis to support decision making for the prevention of and response to collision risk from the traffic management perspective, with a focus on advancing the latest methodology of utilizing non-accident critical events detected from AIS data as the basis to assess traffic risk. To this end, a review and analysis of these related works is firstly conducted to understand the state-of-the-art of this non-accident critical events-based methodology. The analysis shows the feasibility and challenges of using it as a basis for maritime traffic risk analysis. This thesis seeks to improve response to these identified challenges, including the inadequate consideration paid to the dynamic nature of ship manoeuvres, the utilization of the only ship attributes to detect near misses and the inadequate attention paid to multi-vessel encounters.Therefore, this thesis proposes a framework for near miss detection from AIS data based on ship manoeuvre characteristics. The implementation of this framework is based on the understanding of the process of a navigator formulating and executing her manoeuvre strategy for collision avoidance. This framework enables the consideration of the dynamic nature of ship manoeuvres and the impact of four contributing factors on ship manoeuvres. The framework is applicable for both ship-pair encounters and multi-vessel encounters and is well integrated with the rules in the COLREGs. Under the guidance of this framework, methods for analysing the collision risk represented by ship manoeuvres are developed, and then applied to assess traffic risk in the Northern Baltic Sea. The dangerous waters with high risks of ship collisions in the Northern Baltic Sea are identified and found to be highly consistent with those dealt with in other similar works in terms of the occurrence position and frequency/possibility of dangerous encounters. The results also call for more attention to be paid to the waterway crossing between Stockholm and Turku as many serious encounters were detected there. In addition, the results identify traffic complexity as one of the direct causes of serious encounters. The findings of this thesis contribute to the development of an intelligent traffic supervision system and decision support system to enhance maritime traffic safety.
Multi-ship following operation in ice-covered waters with consideration of inter-ship communication
(2020-08-15) Zhang, Weibin; Zou, Ziyao; Wang, Jin; Du, Lei
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
With the advancement of technology, the ship-to-ship communication plays an increasingly important role in fleet following operations. In this study, a new ship following model that considers communication conditions is constructed for convoys following icebreaking ships through sea-ice areas. The model combines the effects of ice and communication on speeds and inter-ship distances. Then, the linear stability of the model is analysed. Simulation and analysis using actual data reveal that modelling stability is improved compared to models that do not consider communication and the backward-looking effect. The model provides a theoretical basis for maritime traffic simulation software. Moreover, it can accurately predict changes in the velocities of following ships. Consequently, the high stability of the proposed following model can be utilized for risk mitigation for fleets navigating in ice-covered waters.
Path following control for towing system of cylindrical drilling platform in presence of disturbances and uncertainties
(2019) Tao, Jin; Du, Lei; Dehmer, Matthias; Wen, Yuanqiao; Xie, Guangming; Zhou, Quan
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Towing is a critical process to deploy a cylindrical drilling platform. However, the towing process faces a great variety of risks from a complex nautical environment, the dynamics in towing and maneuvering, to unexpected events. Therefore, safely navigating the towing system following a planned route to a target sea area is essential. To tackle the time-varying disturbances induced by wind, current and system parametric uncertainties, a path following control method for a towing system of cylindrical drilling platform is designed based on linear active disturbance rejection control. By utilizing Maneuvering Modeling Group model as well as a catenary model, we develop a three degree-of-freedom dynamic mathematical model of the towing system under external environmental disturbances and internal uncertainties. Furthermore, we design a linear active disturbance rejection control path following controller for real-time tracking error correction based on a guidance method combining cross-track error and parallax. Finally, the path following performance of the towing system is evaluated in a simulation environment under various disturbances and internal uncertainties, where the corresponding tracking error is analyzed. The results show that the linear active disturbance rejection control performs well under both the external disturbance and inherent uncertainties, and better satisfy the tracking performance criteria than a traditional proportional–integral–derivative controller.
Review and analysis of methods for assessing maritime waterway risk based on non-accident critical events detected from AIS data
(2020-08) Du, Lei; Goerlandt, Floris; Kujala, Pentti
A2 Katsausartikkeli tieteellisessä aikakauslehdessä
The safe navigation of ships is of high societal concern. A promising approach for analyzing waterway risks is using non-accident critical events as surrogate indicators of collision accidents. These are typically detected in data from the Automatic Identification System (AIS). Recognizing the significant interest in this approach, this article provides a review and analysis of methods based on the detection of non-accident critical events from AIS data, which aim to provide insight into maritime waterway risk. Considering also recent calls for increased focus on foundational issues in risk research and safety science, each method in the literature is critically reviewed based on five questions: How are non-accident critical events defined? What is the accident-theoretical basis of the method? How are non-accident critical events ranked? How is the method used? To what extent has the method been validated? Based on the results, it is concluded that focus is needed to build evidence of the validity of the models’ results, if these are to be effectively used for waterway risk analysis. As a prerequisite, more focus is needed on how exactly non-accident critical events are defined, and what factors are involved in the relation between their occurrence and accident involvement.