The floating crane vessel can be applied to install the offshore topside module of the platform during the lifting operations. If the motions of the topside are large due to the severe ocean environments, the topside will frequently collide with the jacket structures, which will threaten the safety of lifting operations. As the coupled motions are not easy to be predicted accurately due to the complex coupling system, including the waves, the mooring system, the crane vessel, the crane sling and the topside, model tests are carried out to study the motions of the mooring vessel LANJING during lifting operations.
The model tests are carried out in the port and coastal basin of Tianjin University. The model scale is set to 1:60. Motions of LANJING and the topside, tension forces of the 8 mooring lines and waves are measured in regular and irregular waves. The coupled motions with resonance phenomena are clearly observed and the physical mechanism is revealed. The obtained experimental results can be used to validate the numerical results, and thus ensure the safety of lifting operations.
With the development of the offshore oil and gas exploration engineering in China, the topside module of the jacket platform is becoming heavier and its size is growing larger. The demand on the lift capability of the floating crane vessels for the lifting operations is increasing correspondingly. Up to now, the largest floating crane vessel operated by the China Offshore Oil Engineering Co., Ltd (COOEC) is the LANJING (2017), which is a self-propelled pipe laying & crane vessel, with test speed up to 12.55 knots and operation depth 300m. LANJING is equipped with an offshore engineering heavy crane with lifting capacity of 7,500T (fixed way)/4,000T (revolving way), whose single lifting capacity is largest in the world before 2016. The crane is located on the ship stern. Fig. 1 shows that LANJING is working for the lifting operation of one topside module using the stern fixed way. In order to ensure the safety of lifting installation and its operation efficiency, it is necessary to limit the motions of the topside under working sea states. According to the Nobel Denton Guidelines for Lifting Operations by Floating Crane Vessel (2006), the maximum offshore module movement during installation is suggested to be limited to, vertical movement, ±0.75 m, horizontal movement, ±1.50 m.
