Mechanism Study Of Green Water Load On Ship Deck By Experiment

Warships have to experience many kinds of serious tests in various ocean environments from offing to open sea. Strong ocean waves induced by storms may cause ships vibrating nonlinearly in a large amplitude, and even enduring the green water, which may devastate structures of warships. However, rare studies are focused on the theory of green water in present China, and people know little about the essence of the generating and developing procedure when these impacts occur, especially about methods for predicting the impact pressure. Green water experiments have been carried out on the international standard ship model S-175, by which the essence of green water and prediction methods have been studied in this thesis.Firstly, the responses of pitch and heave, the values of wave heights and impact loads on the deck and vertical board of green water have been tested by the ship model experiment. During the experiment, the green water has been analyzed with different values of wave height, headings, speed and external floating or not. Secondly, the empirical formulas and mathematical model widely adopted in forecasting impact loads of green water have been verified by the experiment. The new method for forecasting has been presented by this paper. Thirdly, during the analyzing about the experimental phenomenon and the tested data, the mathematical models and rule of green water have been summarized. Finally, the motions of ships and the wave heights of green water have been computed by the N.S.M. program. And the wave loads of green water have been forecasted by empirical formulas, dam break model and flood wave model. The results have been verified by experimental data.As is shown in the results, the following conclusions can be obtained:the main cause of green water is the large amplitude pitching of the bow; green water is more easily to occur when the ship is advancing instead of stationary, waves are in the same scale of the ship length, and the ship is ahead the ocean waves; large flare of ship bow may reduce the occurrence of green water effectively in a low sea state, however, it will enhance the impact loads by the green water; it is efficient to predict the water shape flowing on the deck in a theory model coupled with experimental formulae, but inaccurate when predicting the green water.