Modeling and Control of an Offshore Container Crane

Quang Hieu Ngo
School of Mechanical Engineering, Pusan National University
December, 2011
Dr. Ngo now is a lecturer at the Department of Mechanical Engineering, Can Tho University.


This dissertation investigates control algorithms for controlling sway motions and orientations (trim, list, and skew) of an offshore container crane in the presence of ship motions induced by random wave. New mechanisms, equations of motion, and control systems have been analyzed. In designing the control algorithms for suppressing the sway motions of the spreader - a main part of the offshore container crane, the ship motions (rolling, pitching, and heaving) have been included into the dynamic equations as varying parameters. In this research, for the first time, the necessity of a new mechanism for controlling offshore container cranes is identified and treated, from a control point of view. Indeed, the lateral sway of the load caused by the pitching motion of the ship cannot be suppressed with the conventional type quay crane. The equations of motion are derived based on the new mechanism. The control algorithm has been developed consisting of generating the desired trajectories to compensate for the ship motions. Such trajectories for trolley motions are generated depending on ship motions. The trolley moves following the trajectories in X, Y directions with the anti-sway control algorithm. Based on the control system, the spreader can stay in the desired position even though the trolley always moves to compensate for the ship motions. Experiment results of sway control are also provided. Moreover, a new control system for controlling spreader orientation is also developed and applied to the offshore container crane. With the proposed control law, the spreader can be controlled in 6 degrees of freedom. The system is verified to show the efficiency of the skew motion control (the most critical issue in orientation control). The performance and functions of the control system can be improved when performance records of its application to real cargo work operation are accumulated.