Dynamics Analysis of an Offshore Ship-mounted Crane Subject to Sea Wave Disturbances

This paper analyzes the dynamics of an offshore ship-mounted crane subject to some regular sea wave disturbances. Considering that an offshore ship-mounted crane is a kind of typical underactuated system, which has less number of actuators than the degrees of freedom (DOFs) with strong-coupling characteristics, the modeling analysis and controller design for this kind of systems are both challenging tasks. Additionally, influenced by sea waves and currents, an offshore crane fixed on a ship always suffers from some persistent disturbances induced by the movement of the attached ship, which is different from an overhead crane fixed on land. Therefore, developing an accurate dynamics which contains the influence of the waves is of great importance for the control issue of these systems. In this paper, by applying the Lagrange's method in an attached frame and analyzing the motion responses of the ship under sea conditions, we first introduce the impact of sea waves's motion into the whole dynamics of this system, then the precise model of an offshore ship-mounted crane consisting of a trolley and a payload is obtained. Finally, experimental results compared with simulation results can verify the validity of this model effectively.