A Nonlinear 8-DOF Coupled Crane-Ship Dynamic Model

A nonlinear crane-ship dynamic model was developed. The 8-DOF dynamic model incorporates hull motions coupled with nonlinear large-angle load swings. We treated the ship and crane as one rigid body and included arbitrary, bi-angular swings of the suspended load coupled with the surge, sway, heave, roll, pitch, and yaw motions of the ship. Basic crane maneuvers, such as luff and slew angle trajectories and cable reeling and unreeling, are taken into consideration. The ship equations of motion are integrated simultaneously with the crane equations. The hydrodynamic and hydrostatic forces on the ship are obtained using the Large Amplitude Motions Program (LAMP). The motion response of the crane of the Auxiliary Crane Ship (T-ACS) lifting a 30-ton load was investigated. Simulations show that the coupling effect is unilateral; the cargo oscillations are dependent on the ship motion, while the ship motions are not affected by load pendulations. Large-amplitude responses occur at wave periods near the natural period of the hook load. In order to investigate the influence of realistic sea states on the excitation of crane loads, we applied irregular sea waves to the vessel based on the Brettschneider two-parameter spectral formula. Large-Amplitude load swings developed at sea state 5, which makes the operation of the crane ship at this sea state dangerous. Reeling and unreeling of the cable are investigated. The results show a hysteretic effect. The load-swing amplitude depends on the reeling or unreeling speed.