Multi-body Structure Dynamic Analysis During Spar Block Sitting

Along with the global energy demand increasing gradually, the offshore oil mining alsomoves gradually from the shallow sea to the deep sea.In the oil fields of South China Sea,the installation of platform is different from offshore assignments, the environment of SouthChina Sea is harsh, and the wind, wave and current load has added great risk for the hoistingoperation. It is difficult to safely complete the installation, as to the cooperation of the cranevessel and platform. However offshore installation is an important part of the deep seaproject,and is the last of significant engineering before the platform is put into use,and plays adecisive role in successful completion of the petroleum mining project. In this paper, themodel test and numerical simulation was carried out about Truss Spar block sitting。Research mainly involved four aspects, the key technology, multi-body hydrodynamicinteraction, sea hoisting model test technical and practical engineering application. In view ofthe actual project, the key technology of the specific operation phases were analysis in detail;at the same time the way of the installation procedures were illustrated. For block in placeoperation, it needs to use crane vessel and deep-water floating platform in small gaps tocomplete the installation, research needs to consider mutual interference of two floatingbodies, also needs to consider mechanical coupling movement between crane vessel andblock. On the basis of extensive investigating the multi-floating-body hydrodynamicinteraction evolution, the hydrodynamic coefficient of the two barge vessel was calculatedand analysis in detail, which have the small gaps alongside in waves. The model test wasconduced to observe the multi floating body movement and the motion of block in sittingprocess, the test measured the6-DOF motion of two floating bodies in regular and irregularwave, and the movement of the block in state of hovering and sitting process. From thechange in wave direction、spectrum peak period and significant wave height, the three objectsmotions were obtained,and the model test result were compared with the simulation result,verified the reliability of simulating. Using the practical engineering application goal andselecting Li-Wan gas field background to study the motion between block and platform indifferent wave direction、wave height、period and wind speed, and also study the motionbetween crane vessel and platform in the wind、wave combined with current sea state.The results showed that the numerical simulation models were in accordance with the experimental data. Simulating took into account mechanical coupling and multi-bodyhydrodynamic interaction, which had considerable reliability to forecast the motion offloating body. Meanwhile to the Li-Wan gas field sea state, Spar was arranged stern by thecrane vessel, the wave direction of45°and315°were the safe working wave angle and thewave direction of90°and270°were the dangerous working wave angle. In the safe workingwave angle, the significant wave height should small than2m and the wind speed shouldsmall than13m/s, in this sea state the block sitting was smooth and steady. Research of sparblock sitting plays a decisive role in the deep sea hoisting. Research can provide reference forpractical engineering scheme, but also for providing technical reserves of the futureinstallation of deep water platform.