Dong-Jin Kim

A reliable assessment of large-amplitude roll phenomena such as parametric roll requires an accurate characterization of roll damping. In this study, free roll decay model tests were conducted on the Duisburg test case container ship at large initial heel angles exceeding 30°, and linear and nonlinear roll damping coefficients were determined from the free decay results using the Froude energy method. The roll time series was reproduced with the fourth-order Runge–Kutta method using the estimated damping coefficients and compared with the experimental results. In addition, the speed dependence of the damping characteristics was examined using an equivalent linear damping coefficient. In the large-amplitude free roll decay tests, linear damping alone was insufficient to reproduce the measured response, whereas including a quadratic nonlinear damping term substantially reduced the prediction error. In addition, the damping coefficients identified from the small-amplitude region of the large-amplitude free roll decay tests underestimated the damping in the large-amplitude regime. The equivalent linear damping coefficients further showed that damping increased with the forward speed. These results suggest that an accurate prediction of large-amplitude roll responses requires nonlinear damping coefficients obtained from large-amplitude free roll decay tests.

This study introduces global path planning for autonomous ships in port environments, with a focus on the Port of Ulsan, where various environmental factors are modeled for analysis. Global path planning is considered to take place from departure to berth, specifically accounting for scenarios involving a need to navigate via anchorage areas as waypoints due to unexpected increases in port traffic or when direct access to the berth is obstructed. In this study, a navigable grid for autonomous ships was constructed using land, breakwater, and water depth data. The modeling of the Port of Ulsan’s traffic lanes and anchorage areas reflects the port’s essential maritime characteristics for global path planning. In this study, an improved A* algorithm, along with grid-based path planning, was utilized to determine a global path plan. We used smoothing algorithms to refine the global paths for practical navigation, and the validation of these paths was achieved through conducting ship maneuvering simulations from model tests, which approximate real-world navigation in navigational simulation. This approach lays the groundwork for enhanced route generation studies in complex port environments.

It is necessary to estimate manoeuvring characteristics of submerged bodies at the design stage in order to ensure the safe operations. In this study, added mass coefficients in the mathematical model of submerged bodies are estimated by captive model tests and numerical calculations. Two kinds of models, MARIN ‘BB2’submarine model and AUV (Autonomous unmanned vehicle) model are utilized in the forced oscillation tests. Compared to BB2 submarine, AUV with cylindrical type hull form shows relatively small added masses in roll, pitch, and yaw directions. Next, numerical calculations based on potential theory are performed under the assumption that viscous effects on inertia forces are negligible. Added masses obtained by numerical calculations are in good agreements with forced oscillation test results. And if slow manoeuvres of submerged bodies are presumed, some of velocity coupled terms can be approximated by combinations of added mass coefficients.