Mooring Analysis of Ultra Large Floating System

Liu, Jianhui (Offshore Oil Engineering CO., Ltd.) | Zhong, Wenjun (Offshore Oil Engineering CO., Ltd.) | Zeng, Hengyi (China National Offshore Oil Corp.) | Shen, Keli (CCCC First Harbor Consultants Co., Ltd.)



As the offshore industry move into deeper water, the logistic capacity to supply materials for work boats is challenged. The introduction of new floating concepts and systems with functions of material reserves and physical distribution is needed. During the course of exploitation of oil and gas in South China Sea with harsh environment and high frequency of typhoon, too far offshore will reduce the efficiency and extend the project period. In order to solve this problem, an ultra large floating system concept arising from the intermediate base is put forward with functions of material reserves, refuge harbor for work boats, and landing pad for helicopters. The ring ultra-large floating system with outer diameter of 400 m comprises eight same modules and each module has four columns with heavy draft. The wave chamber composed of horizontal perforated double breakwaters is positioned close to the water plane to reduce the reflection and dynamic pressures on the vertical hull. This paper focuses on mooring behavior of the ultra-large floating system by using a combination of physical and finite element models under South China Sea environment. Model tests were performed to investigate the hydrodynamic coefficients, such as added mass, damping ratio and natural period of the system, as well as hull/mooring coupled motions. The comparison of experimental results and numerical predictions of the responses of the ultra-large floating system are presented.


Geometrically there are two distinctive types of Very Large Floating Structure (VLFS) that have been investigated, namely Pontoon and Semi-Submersible (Phan, et al., 2002): (1) A pontoon type VLFS has a relatively simple geometrical shape designed for operation in protected waters. One distinctive feature of this type of VLFS is that it has very small draft compared to length and beam. As a result, when studying the hydroelastic behavior of this type of structure it is treated as a mat like object of either "very thin" or "zero" thickness.