Nonlinear stability analysis of autonomous container ship under environmental disturbances using hardware-in-the-loop validation

This study investigates the course-keeping and maneuvering performance of an S-175 container ship under stochastic wind and current disturbances, utilizing a high-fidelity nonlinear 4-DOF model. Sliding mode control, integrator backstepping, and proportional-integral-derivative controllers are used for a comparative and integrated ship maneuvering simulation tool. We demonstrate that the standard C-index yields a false positive for stability during high-speed autonomous maneuvering. Consequently, this paper establishes a nonlinear energy-based framework as a requisite alternative to linear metrics, validated through rigorous HIL testing. Phase portraits, Lyapunov stability, trajectory-level eigenvalues, and hardware-in-the-loop benchmark PID, integral backstepping, and sliding mode control under wind/current using standard tracking and effort metrics are analyzed. Simulations are conducted along the Elbe River, with the ship maintaining constant speed during path-tracking to rigorously test controller performance under constrained conditions. The study evaluates three controllers, focusing on adverse roll motion during high-speed turns and employing eigenvalue analysis to validate stability. Results demonstrate that the sliding mode control outperforms the others, exhibiting minimal overshoot, faster settling time, and superior robustness in autonomous navigation through narrow, disturbance-exposed waterways. However, this enhanced stability imposes significantly higher mechanical stress on the steering actuators, despite reducing the total hydrodynamic energy expenditure compared to the oscillatory behavior of PID control. These findings suggest a domain-specific control strategy. Sliding mode control for high-risk, confined navigation where precision is paramount, and PID for open-sea transits where power efficiency takes precedence.