Experimental Research On The Ship Form Of High-speed Catamaran Drag Reduction By Microbubble

This project makes experimental research on "the resistance reduction by air curtain for high-speed air cavity vessel" which is one of the leading subjects in shipping industry. Because microbubble could effectively reduce the friction resistance between solid wall and other medium, if microbubbles are formed at the bottom of vessels, which makes the water close to the vessel's bottom become the mixture of water and microbubble and form a thin gas layer, the resistance of navigating vessel would be cut down and lead to the purpose of improving the velocity or decreasing the power of main engine while maintaining the velocity.In this article, we discussed the mechanism of reducing the friction resistance elementarily. Firstly, we analyzed the process of producing single microbubble out of the porous material and the relevant factor. Because the movement of microbubbles is always in the way of cluster, primary analysis of this content is carried in this article for knowing more about the main factors of friction resistance.In experiment study, according to the principal dimensions and ship form coefficients of three good performance high-speed catamarans designed by a domestic ship academe, we designed a new ship form of high-speed catamaran. The experiment of reduced resistance has been done under the condition of different navigating velocity, gas pressure and jetting area, the conclusion from the experiment is that: when the gas pressure is constant, the ratio of reduced resistance is improved with the increase of the velocity, but when the velocity reached a certain value, the ratio of reduced resistance could not be increased and could even be decreased. Because it is impossible for the microbubbles keep a thin gas layer stably close to the vessel's bottom when the velocity is too high. At the same velocity, the ratio of reduced resistance is improved with the increase of the gas pressure. If we still kept on increasing the gas pressure when it reached a certain value, the effectiveness of the ratio of reduced resistance is not obvious. When the jetting area is altered, there is almost no effect on the resistance of ship model, which illuminated that the jetting area is not the primary factor of reduce resistance. This conclusion is consistent with the result of domestic and overseas. When gas is jetted from the foreside and middle part of the ship model, the ratio of reduced resistance is as high as 23.85% under the condition of that the gas pressure is 0.12Mpa and the velocity is 4.160m/s. This result is consistent with the result of the experiment of high-speed catamaran carried out by Russia. Whether installing the aft wave-suppressing plate or not has also great influence on the ratio of reduced resistance. After the ship model is installed 10°aft wave-suppressing plate, the effectiveness of reduced resistance is greatly improved.When the ship length Froude numbers is 0.959, the resistance per unit displacement of the model in this paper is lower 10.89% and 15.03% compared with the two good ship forms with the same style.The size of the microbubble is not considered in this article. This factor needs further study in the future.