On investigating dynamic coupling in floating platform and overhead crane interactions: modeling and control

In offshore crane systems, the floating platform motion has a significant impact on the dynamics of the cart motion. Nevertheless, previous studies have ignored the dynamic coupling interaction between the crane and the floating platform induced by changes in hydrostatic, hydrodynamic, and mooring loads affecting the offshore platform-crane system response. To address this problem, this study presents, firstly, a comprehensive model of the crane-platform dynamic coupling under realistic surge-roll-heave motions of the floating platform induced by ocean waves. While the payload motion can be known, the surge-roll-heave motions of the floating platform are considered unknown. Therefore, secondly, we propose an output feedback control approach that combines a state feedback controller and an extended high-gain observer to primarily achieve desired trajectories of the cart motion under unknown payload mass, dynamic friction, dynamic coupling, and external disturbances. The extended high-gain observer uses the measured displacement of the cart to estimate the dynamic states and external disturbances, providing the state feedback controller with the necessary information and increasing the robustness of the control system. The effectiveness of the proposed model-based control approach under unknown dynamic and wave motion disturbances is verified through simulation.