Deling Wang

Maritime autonomous surface ships (MASSs) are reshaping the organization of navigation, ship operation, remote control and maritime supervision. However, the transition from crewed navigation to autonomy also changes the structure of safety risk. Traditional ship risk assessment approaches rely heavily on historical accident records and crew-centered operational assumptions, whereas MASS operations involve coupled risks arising from perception systems, autonomous decision-making, communication links, cybersecurity, remote control centers, environmental uncertainty and management readiness. To address the scarcity of operational accident data and the need for a structured safety evaluation method, this paper develops a Formal Safety Assessment (FSA)-based risk evaluation framework for MASS operations. A hierarchical indicator system is established from five dimensions: ship machinery, human factors, environmental factors, information technology and management. A frequency-severity risk criterion is then constructed by defining the Frequency Index (FI), Severity Index (SI) and Risk Index (RI), and by introducing the ALARP principle to classify unacceptable, tolerable and broadly acceptable risk regions. On this basis, an integrated fuzzy analytic hierarchy process is proposed to determine factor weights, transform expert judgements into membership degrees, and calculate comprehensive risk scores. A case study using 50 expert questionnaires shows that the overall risk score of MASS operation is 5.64, located in the ALARP region. Among the first-level indicators, environmental factors, information technology factors and ship machinery factors present relatively high risk levels, with scores of 6.82, 6.60 and 6.25, respectively. At the secondary-indicator level, intelligent navigation system, weather conditions, hydrometeorological conditions, communication capability, equipment and systems, navigation decision-making, and environmental perception are identified as high-intensity risk indicators. Further contribution decomposition reveals that environmental perception, routine ship management, navigation decision-making, and communication capability contribute most substantially to the overall risk profile due to their higher systemic importance. The proposed framework provides an interpretable approach for MASS safety assessment and risk-control prioritization under limited operational data availability.

Side-by-side mooring alongside a quay is an effective strategy to enhance berth utilization and port efficiency. However, in confined waters, hydrodynamic interactions among adjacent ships and the quay wall can significantly alter ship motions, wave loads, mooring tensions, and fender reactions, thereby affecting operational safety. In this study, frequency- and time-domain numerical models of side-by-side moored ships at a quay were developed using the ANSYS AQWA 2025 R1 hydrodynamic analysis software (hereafter AQWA). The S175 and Wigley III hulls were selected as representative vessels. After model validation and mesh independence analysis, the hydrodynamic response of the inboard ship was examined under varying wave headings, water depths, quay boundary conditions, and outboard ship scales. Mooring loads were further analyzed under regular waves, irregular waves, and combined wave–current conditions. The results indicate that side-by-side mooring significantly modifies the sway, heave, and roll responses of the inboard ship. While the outboard ship generally provides a shielding effect, local response amplification may still occur within specific frequency ranges. The wave heading, shallow water, and quay wall effects play dominant roles in redistributing wave excitation forces, added mass, and radiation damping. Time-domain simulations reveal that ship-to-ship mooring lines S2 and S3 are the critical load-bearing components, especially under beam waves and certain oblique current directions. The use of polyester mooring lines effectively reduces peak tensions in critical lines but may increase fender reactions. These findings provide a reference for hydrodynamic safety assessment and mooring optimization in side-by-side berthing operations.

The maneuvering performance of ships in marginal ice zones is critical for navigational safety, yet most existing studies focus on icebreaking vessels. This study develops a coupled numerical framework that integrates the Non-Smooth Discrete Element Method (NDEM) for simulating ship–ice interactions with the three-degree-of-freedom MMG model for ship dynamics. The framework was applied to an S175 container ship, and numerical simulations were conducted for turning circle and Zig-Zag maneuvers under varying ice concentrations (0–60%), floe sizes, and rudder angles. NDEM efficiently handles complex, high-frequency multi-body collisions with larger time steps compared to conventional DEM or CFD–DEM approaches, enabling large-scale simulations of realistic ice conditions. Results indicate that increasing ice concentration from 0% to 60% reduces the turning diameter from 4.11L to 3.21L and decreases steady turning speed by approximately 53%. Larger floes form stable force chains that restrict lateral motion, while higher rudder angles improve responsiveness but may induce dynamic instability. These findings improve understanding of non-icebreaking ship maneuverability in ice and provide practical guidance for safe and efficient Arctic navigation.