Numerical Simulation And Model Experiment Of Green Water On Motion-Restricted FPSO

FPSO is the shortened form of Floating Production Storage and Offloading. Because of its economical efficiency, reliability and adaptability and so on, it is widely used in the offshore industry. Usually, single point mooring system is used on FPSO, in order to get smaller mooring line force. But this also makes the bow exposed to the effect of wave, and the risk of FPSO suffering from Green Water can be very high. In addition, FPSO needs to be moored in a specific sea area for several years, even more than ten years. So it is impossible for FPSO to avoid severe sea conditions, which makes the probability of Green Water increase. Furthermore, compared to normal ship, there are more difficulties in examining and repairing the FPSO. Severe Green water can not only affect the efficiency of FPSO, but also cause damages to the deck, structure and equipments on FPSO. Green Water on FPSO is resulted from steep wave and the motion of bow downward.The process of Green Water can be thought as four main stages, wave runs up along the bow, water comes over the freeboard onto the deck, water propagates on the deck and water hits the deck and deckhouse. These stages are connected, and can not be divided into separated parts.In harsh sea states, FPSO is in survival condition. Motion of ship, relative wave motion and drift force are obviously nonlinear functions of wave height. It is difficult to be solved mathematically and the physical phenomena of the occurrence of Green Water is also very complicated.A rough review and summarize about the investigations and recent research progress of Green Water is conducted in the paper. A numerical method to simulate the phenomena of Green Water on FPSO is established by using CFD software. Numerical simulations of Green Water on FPSO are made in some limited conditions. And then the wave height and impact loads on deck because of Green Water are analyzed, which can be used to predict the damage of the structures on deck.In this paper, a further development on the FLUENT software is did, in order to set up a 2-D numerical wave tank, and then extended to a 3-D tank. Dynamic boundary was used to make waves in the 3-D numerical wave tank, and free surface was captured by VOF method. Then, the regular waves needed are simulated successfully. The numerical simulations of Green Water on motion-restricted FPSO are made under three adjacent regular waves and bulwark of three different heights. Wave running up along the bow, wave deforming and wave breaking were recorded in these simulations. The wave height on deck and the impact loads on deck and deck house are also recorded. After knowing the peak values of the wave height and pressure of Green Water, we studied the effect of the wave parameters and the height of bulwark. It is found that the wave heights and pressures are greatly influenced by the wave parameters, and do not change much by altering the height of bulwark. Meanwhile, the relevant model experiment is also accomplished. Comparison is made between the results of simulation and experiment, and it is shown that the results agree well.