Research On Motions And Green Water Of Large Fpsos In Shallow

The Bohai Bay is the main area for ocean oil production in China. There are 4 FPSOs (Floating Production, Storage and Offloading) operated in the recent large oil fields named QHD32-6, BZ25-1, CFD11-1 and PL19-3, respectively. All these oil fields are located in shallow water. Besides, increasing LNG carriers and LNG floating terminals will be moored in shallow water in the world. Therefore, the shallow water hydrodynamics such as 6-DOF motions, mooring loads, touching sea bottom and green water will still be the hot topics on large floating structures.A FPSO needs to be moored in a specific sea area for several years, so it is impossible to avoid severe environment, which often makes green water occur. In non-collinear directions of wind, wave and current, the FPSO does not always encounter head waves. It probably induces specialties in motions and green water especially because of the complexity of shallow water hydrodynamics. In the present paper, based on the 300kDWT PL19-3 FPSO operated in shallow water, investigations are conducted on motion performance and the green water of the FPSO encountering wind, wave and current.Firstly, time-domain numerical simulations based on 3-D linear potential theory, and model tests are carried out in order to analyze the motion performance of the moored FPSO encountering different sea conditions in shallow water. Secondly, the green water is analyzed according to the result in model test, and a quick method predicting the occurrence of green water is verified. Lastly, green water and wave run-up along the side of fixed and moving FPSOs are simulated in 3-D numerical wave tanks and compared with model tests.It is shown that the influence of the yaw angle on motions and green water of a FPSO is considerable. Green water occurs more frequently around the mid-ship when the FPSO encounters larger wave heading. The quick method predicting the occurrence of green water is not applicable to shallow water because of not considering the wave run-up. In the same wave situation, the motions of the FPSO in lower water depth are lower, but green water occurs more severely. In shallow water, water depth has an important influence on green water. Wave run-up and green water will be more severe in shallower water. It is remarkable especially when FPSOs encounter large wave heading.