자유순환 공기윤활을 이용한 고속선 저항성능 개선에 관한 연구

Abstract

Abstract

A Study on Improvement in the Resistance Performance for High Speed Boat using Free-Ventilated Air Lubrication

Kim, Kyu-Sun Advisor : Prof. Park, Je-Woong, Ph. D. Department of Advanced Marine Transportation System Engineering Graduate School of Chosun University

Recently, the concerns for unstability of oil price and carbon dioxide regulation are increasing across the country and various countermeasures are being expanded to all industries. Especially, the amount of greenhouse gas emitted from vessels at every year is known to be about 600~800 million tons taking about 5% of the worldwide greenhouse gas emission which is about 2.5 times that of airplane.

The greenhouse gas from vessels is expected to be fully regulated soon. So it is time for Korea, as the number one in the world shipbuilding industry, needs to prepare various countermeasures to reduce greenhouse gas.

This study mentioned about the method to reduce frictional resistance by directly inducing the air coming to the bow of the ship during high speed running to the bottom of the ship and spraying an air film on the body of the ship for 30 knot class high speed small leisure boat.

Numerical analysis and model test for 2 dimensional model were carried out and the effects of the speed of the ship and the change of the air speed on the forming of the air film sprayed on the bottom of the ship and the resistance performance were analyzed through model test for 3 dimensional real ship model.

The conclusions derived through this study are as follows;

(1) As the air speed coming to the bow of the ship increases, the amount of the air flowing to the bottom of the ship increases.

(2) The assumption is supposed the speed of head wind is not changed, according to increase speed of ship inflow of air film is more prolonged toward the bottom of the ship. Especially, the assumption is given head wind is not existed, as the speed of the ship increases, the phenomenon in which the air film at the bottom of the ship spreading longer toward the stern of the ship. That is, according to principle of Bernoulli, as the water speed increase at the bottom of the ship the pressure is relatively lower. Then, it causes more inflow of the air from the atmosphere.

(3) For step installed at the exit of the air guide plate, there a large amount of reduction of frictional resistance. However, without air inflow, the resistance increases rather due to the turbulence occurred on the stairs. If the step is installed in the bottom of the ship, however, frictional resistance can be reduced as the air flew in from the bow forms air-cavity in the rear of the bottom stairs even at the lower speed.

(4) If there is no bottom step, the whole resistance can increase as the resistance by the air guide plate becomes bigger than the reduction of frictional resistance if the ship speed is relatively low.

(5) The air film is formed better if the exit of the air guide plate is extended to the after part of the ship. However, more studies are required to clarify to which extent of the bottom the intersection exit should be extended for better efficiency.

(6) For an application of the air guide plate to an actual ship, the enforced initial designed drag showed larger bow wave patterns by the air guide plate at a certain speed range compared to bare hull without an air guide plate but the resistance is reduced. The reason is that the reduction of frictional resistance by an air film became bigger than the increase of wave resistance. However, the ship doesn't glide well even at the high speed and there is a large trim by head because of the weight of the air guide plate and transformation of the bow. The resistance will rather increase if there is no enforced trim by stern.