In this study, a numerical simulation was performed for a sidewall green water problem on a ship-shaped FPSO under oblique waves. The simulation results were directly compared with experimental data to verify the feasibility of the CFD method. The numerical simulation results of the relative wave heights along the side of the FPSO were compared with experimental data in order to check the accuracy of the numerical method for green water problems. By a comparison of still photos of the experiment and snapshots of the numerical simulation, a physical procedure of the sidewall green water was discussed.
In the design phase of offshore structures, it is very important to estimate the green-water occurrence/loads and to design the freeboard and forecastle properly. In particular, it is known that the impact load of the green water can cause fatal damage to the offshore equipment and the safety of operators. Basically, green water occurs when the relative wave motion becomes higher than the freeboard of the offshore structures. Here, the relative wave height is a function of the difference between the wave elevation and vertical motion responses of the offshore structure. Thus, accurate prediction of nonlinear wave height and the motion of a floating body are critical for the green water problem.
The primitive stage of green water research had been the focus on deck wetness to prevent flooding of cargo tank on merchant ship and destroyer under harsh weather condition. Most of the studies for the green water were performed by the experimental method (Newton, 1959, Hong et al., 1993). From the experimental results, many researchers suggested prediction methods for green water loads. Firstly, the estimation methods had been started from considering static water head of measured maximum water height on the deck (Fukuda et al., 1973). some methods were modified by taking into account the dynamic amplification of the pressure on the deck. Buchner (2002) presented a new prediction method combined with applying dam-break theory and Newton's momentum relations of a control volume.