Analyses on docking dynamic characteristics of the jack-up platform with two-piece units guide cable

To meet the requirements of deeper offshore oil and gas exploration, a two-piece units mode jack-up rig is employed to upgrade the existing cylindrical leg jack-up rig which works in shallow areas of 50 m deep. A set of mat support structure is added to the bottom of the cylindrical leg jack-up rig and the upper piece of rig and the bottom piece of rig are connected by a docking assembly, making the two pieces become a mat jack-up rig. This paper studies the equilibrium position and displacement response of the upper unit in docking procedure under different environmental condition and different ballast mode based on the three dimensional time domain linear potential flow theory and Morison theory, and analyses the dynamic response of the guide cable under different docking positions through physical models in laboratory. If the environment load acts from the stem direction, longitudinal oscillation affects mostly on the displacement of the guide cable. With the increment of water depth, the axial tension of the guide cable and the vertical angle of deviation decreases. Under the condition of separately floating, the guide cable is mostly affected by the mass of the platform; the forces acting on the guide cable of the lower unit is much smaller than that of the upper unit. Once one of the units was fixed, the towing force dropped obviously. The bearing force of the guide cable is obviously affected by the wave period and wave height and will increase with the increment of wave period and wave height in general.