分体式平台对接过程中牵引索动态响应分析

采用分体式平台模式,对现有作业水深(50 m)较浅的圆柱形桩腿自升式平台进行升级改造,即在其底部增加一套沉垫式刚性支撑结构,利用对接装置将上分体平台桩腿和下分体支撑桩腿对接,使上、下分体结合成一座沉垫型自升式平台。基于三维时域线性势流理论和Morison理论研究不同环境条件、不同压载模式下平台上分体对接过程中的平衡位置和位移响应,通过时域分析研究牵引索应力分布和位移响应情况;并通过实验室物理模型实验分析不同对接位置牵引索的动态响应。当环境载荷作用力从平台艏部入射时,纵荡对牵引索的位移响应影响最大。随着水深的增加,牵引索的轴向拉力值逐渐减小,竖向偏离角度逐渐减小。分体漂浮状态下牵引索受平台质量影响较大,下分体拖缆受力远小于上分体;一端分体固定时,牵引索牵引力下降明显。牵引索受力震摇幅值受波浪周期和波高影响显著,总的趋势是随着波浪周期和波高的增大而增大。

Analyses on docking dynamic characteristics of the jack-up rig 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.