Numerical Simulation Of Green Water Occurrence Of High Speed Vessels

Green water is a phenomenon which vessels encounter wave, and at the same time liquid surpasses freeboard and flush into deck. In general case, liquid flow out the deck without damage, but more liquid may flush into deck under severe sea state, which can damage equipments, cargos and superstructures on the deck. Especially for the high speed vessel, it capsizes to a great extent .Green water is one of the strongly nonlinear ship-wave interaction problems which is difficult to be solved mathematically. The physical phenomenon of the occurrence of green water is very complicated. The past investigations only can describe the phenomena at some extend, and it cannot give a reasonable explanation for the mechanism of green water. At present, with the high-speed development of computer and calculate technology, numerical simulation has been applied for forecasting and analyzing nonlinear fluid motion in order to instead of physics experiment. Therefore, the problem of ship building and ocean engineering can be solved by taking full advantage of existing theory, numerical research methods and traditional ship hydrodynamic methods.A comprehensive review about the investigations and recent research progress of green water is conducted in the present paper. Green water flow and its impact on the deck for a vessel advancing in waves with high forward speed are investigated by 3-D numerical simulation method which integrally considers the effects of bow flare, water swell-up, wave and body motions and takes advantages of CFD technique and potential flow theory. A Foredeck Simulation Model (FDSM) based on the simultaneous whole ship motions is established for the simulation of green water flow behavior and its impact loads on the deck structures for high speed vessels. The simulation is realized by the secondly development on the platform of the commercial software Fluent, in which the vessel motion is obtained by the potential flow theory. The green water flow behavior and impact load on deck are calculated and analyzed for the case of S175 ship advancing in head waves by taking advantage of relative motion theory method and dynamic grid method. Numerical results agree well with the corresponding experimental ones. It indicates the present method can be applied to predict and analyze the impact forces on floating structures due to green water. It also can be regarded as a good engineering approach to evaluate the green water effects. Meanwhile, it can be used for ship lines optimization, especially forward lines and strength design, and it is helpful to take measures to avoid the harm of green water.A ship hull section moving on transverse waves discussed in this paper and the phenomena is numerically simulated by using the module SDOF of Fluent and the secondly development on Fluent software. The gravity centre of floating body oscillating in head waves is traced. The simulation results indicate that the longitudinal movement and the vertical oscillation are induced by the drift force and the vertical wave force components. The simulation for the fully coupled ship motion and wave is realized. This method can clearly describe green water action on ship structure and it can be extended to analyze the destruction of floating body due to green water.