The Numerical Simulation And Characteristics Research Of Air Cavity Craft Motion In Waves

Ship energy conservation is not only related to saving resources,environmental protection,but also affect the shipping industry's economic interests.In particular,the IMO's mandatory efficiency standards for new ship construction,the Energy Efficiency Design Index(EEDI),have made the ship's energy efficiency standards even more stringent.How to develop ship's energy-saving emission reduction technology has become the current problem demanding prompt solution for shipping industry.Therefore,to carry out the relevant scientific innovation and technology research is very necessary.It is an effective and environmentally friendly way to reduce drag by introducing air into the bottom of a ship.It is of important theoretical and engineering practical significance to reduce the air pollution,save energy and reduce emissions of ships and implement the new regulations of IMO(International Maritime Organization).At present,most scholars mainly study the problem of ship gas-layer drag reduction in still water,and little research has been done on the effect of wave on the gas-layer and motion performance of air cavity craft.The wave-on-gas effect is a key technical problem in the application and development of the air cavity craft.Therefore,this paper has important theoretical and practical significance for numerical simulation and characteristics research of air cavity craft motion in waves.For the wave problem,this paper studies the numerical wave-making method and the motion forecasting method of the ship in the wave respectively.Two types of typical ships are studied,which are displacement vessel and planing boat.The effect of wave on gas layer,influence of speed increase on gas layer and the influence of ship type on the layout of gas layer in wave are studied in this paper.In this paper,the effects of ventilation volume,wave length ratio,wave height and cavity on gas drag reduction and ship heave amplitude,pitch amplitude,and centroid acceleration are discussed for conventional displacement vessel and displacement vessel with cavity.And the influence of gas injection volume and wavelength on drag reduction about planing boat motion in waves is discussed,and the mechanism of the correlation is discussed through the surface shear stress distribution and gas distribution.The results show that the gas layer reduces the shear stress of the hull surface for the displacement vessel,so the frictional drag of hull is reduced.The existence of cavity in the bottom of the ship increases the distribution area of the gas layer,so that the drag reduction rate of the ship with cavity is relatively higher.The change of wavelength mainly affects the total drag reduction rate and has little effect on the friction drag reduction rate.When the wavelength changes,the gas layer at the bottom of the ship mainly affects the center of the gravity acceleration amplitude and has little effect on the pitch amplitude and heave amplitude of the ship.Meanwile the results of sdudy on planing boat show that in the range of lower ventilation,the increase of gas injection volume increases the fictional drag reduction rate and the total drag reduction rate.The change of wave length has little effect on the friction drag reduction and the total drag reduction.The gas layer at the bottom of the ship mainly affects the amplitude of gravity acceleration.