Study On The Configuration Of Air Cavity And Hydrodynamic Characteristics Of Air Cavity Craft

The effectiveness of the gas layer in reducing ship resistance has been recognized,and it is a hot and difficult issue for research in our country and abroad in recent years.The surface of the hull is isolated from the water by the gas layer,which greatly reduces the frictional resistance of the ship.The ship with heavy frictional resistance,can significantly reduce energy consumption,reduce carbon dioxide and other gas emissions,save energy and reduce emissions and protect the environment.Under the background of the enforcement of EEDI by the International Maritime Organization(IMO),the improvement of ship design and construction technology can bring huge economic and social benefits.For the planing craft,the resistance of the planing craft increases sharply during high-speed navigation,and reducing the resistance is an important way to improve the navigation performance of the planing craft.Through the gas layer drag reduction,the resistance of the planing craft can be greatly reduced,the speed of the planing craft and the comprehensive navigation performance can be improved,and the planing craft with the gas layer drag reduction is called an air cavity craft.Air cavity crafts have a wide range of application needs in marine rights maintenance,law enforcement,rapid search and rescue,anti-smuggling,landing and so on.In recent years,as people’s living conditions have improved,the demand for various types of high-performance yachts has increased.It can be seen that the study of air cavity craft has very important theoretical significance and practical value.When the speed of the planing craft is small,the hull is in a positive floating state.At this time,the weight of the hull is supported by the buoyancy of the hull.As the speed increases,the hull rises continuously,the buoyancy decreases,the lift increases,and the wet surface area of the hull keeps decreasing.When the planing craft is in the taxiing state,most of the hull is lifted out of the water,and the weight of the hull is mainly supported by the moving lift,and only a small part of the hull is in the water.During the above-mentioned changes in the navigational state,the volume of the hull under water constantly changes,which has an impact on the formation and layout design of the gas layer,which brings difficulty and challenge to the research of the bubble planing craft.Based on the existing planing craft,this study carried out ship type generation,air cavity configuration and ship type matching research.Using the theoretical method,the meshing technique,the air cavity craft resistance and the wave-making simulation method of the gas-water two-phase flow interface are studied.The resistance of the air cavity craft with different air cavities was studied.Numerically calculate the resistance and navigational attitude of a planing craft with or without a gas layer.The relationship between single-stepped round head,single-stepped square head,double-stepped cavity and drag reduction is studied.The relationship and law of gas layer stability with parameters such as cavity configuration,speed and ventilation are studied.The relationship between speed,ventilation and drag reduction and the effect of wave on gas layer stability and drag reduction were studied for the double-stepped air cavity craft.The ship model was made for the ship type developed,and the ship model test of gas layer formation,gas layer drag reduction and wave gas layer distribution was carried out.The research shows that the double-stepped cavity increases the distribution area of the gas layer,which is beneficial to the stability of the gas layer and the drag reduction in the wave.As the ventilation increases,the rate of drag reduction increases and there is a saturated ventilation.Increasing the ventilation after saturated ventilation does not result in an increase in the gas layer area and an increase in the drag reduction rate.