Adaptive Sliding Mode Control of a Mobile Harbor System

This paper presents an adaptive sliding mode (ASM) control scheme developed for a mobile harbor system, which transfers containers to/from container ships in the deep sea. The container ship is a big vessel and, due to its weight and size, cannot anchor at shallow water ports. Therefore, to save the cost and effort of expanding the existing port to the deep sea, the mobile harbor system (i.e., a small ship with a crane mounted on it) is utilized to transport containers between the container ship (in the deep sea) and the existing sea port. However, during the loading/unloading operation, the mobile harbor is exposed to large disturbances like the ocean waves. Consequently, due to the wave -induced movements of the mobile harbor, the load (i.e., the container) undergoes large pendulous movements (i.e., sway), which must be suppressed to increase both the safety and the time-efficiency of the transport process. In this paper, an adaptive sliding mode control scheme is designed for suppressing the sway movements of the load during the loading/unloading of the containers in the deep sea. Further, Lyapunov- function based analyses are performed to prove the asymptotic stability of the closed-loop system in the presence of sea waves. Finally, simulation results are provided to demonstrate the effectiveness of the proposed control scheme.