Experimental study on the low-speed manoeuvring capability of a twin-lift decommissioning system.

A simple dynamic positioning (DP) system has been developed for the scaled model of a novel twin-lift decommissioning operation. Such a decommissioning solution involves the two semi-submerged vessels transporting the topside to another vessel. And it requires the synchronised motion of the two topside-carried vessels at a low speed, under the environmental disturbances. In order to ensure efficiency and safety, model tests with a scaling factor of 1:37 have been carried out in the wave tank. The DP system in the experiment consists of a 3-Degree of Freedom (3DoF) motion equation, a Proportional–Integral–Derivative (PID) controller and a thrust allocation algorithm. This paper investigates the motion response of each vessel under the random wave and constant wind of different angles, to assess the low-speed manoeuvring performance. It is found that the given control scenarios allow the twin-lift decommissioning system to yield good motion performance under operational conditions. [ABSTRACT FROM AUTHOR]