연안어선의 선측부력부 형상 최적화 연구

Abstract

The Ministry of Oceans and Fisheries allows the installation of Side buoyancy box, which is an appendage to assist the buoyancy of the fishing vessel and improve its stability, up to 10% of the lower volume of the upper deck. However, in the fishery field, since the Side buoyancy box has been mainly manufactured on-site of the shipyard without design, there has been no consideration at the design stage for improving the stability and increasing the resistance. This study investigated the effect of the Side buoyancy box of the protruding shape on the stability, roll decay and resistance performance of a fishing vessel. And reviewed the shape that can improve the resistance performance while maintaining the roll motion based on the general shape. First of all, a representative shape was derived by analyzing the status of the Side buoyancy box of the existing fishing vessel. And the variation of static and dynamic stability was investigated by applying this to the target fishing vessel. Through this, it was confirmed that the Side buoyancy box increases the breadth of the fishing vessel , thereby increasing the static and dynamic stability. For evaluating the effect of the Side buoyancy box on the roll damping of the target fishing vessel, a study related to roll motion was conducted. In order to analyze the motion performance based on potential theory, it is necessary to estimate the roll damping coefficient, and in general, it is derived through roll simulation using CFD or a free roll decay model test. In this study, roll decay simulation using CFD has been conducted to estimate the roll damping coefficient. And based on this, the effect of the Side buoyancy box on the roll damping performance was analyzed through the roll RAO ​​analysis of the target fishing vessel and confirmed that the roll damping performance is improved due to the application of Side buoyancy box. In addition, through resistance analysis using CFD for the fishing ground departure condition, the effect of the Side buoyancy box shape on the increase in resistance compared to the bare hull was analyzed. As a result, the overall resistance increased due to the appendage protruding from ship's side shell, and the longer the length of the Side buoyancy box, the more the wetted surface area increased, which was disadvantageous in terms of resistance. Based on this performance analysis, it was tried to find the optimal shape to improve the resistance performance while maintaining the motion through the modification of the front end shape and the section of main body of the Side buoyancy box. The front end shape was designed respectively the general shape(front end angle of 45°), wedge shape, and a cone shape etc. And the section of the main body was reviewed the rectangular shape and the shape with bilge radius. Considering the resistance and the roll motion comprehensively, it was decided that it is advantageous to modify only the shape of the front end, so the angle of the front end was additionally reviewed for 15° and 30°. Through this case, it has been confirmed that the rectangular shape based on the same volume is effective in maintaining the roll motion compared to the shape with bilge radius, and the resistance is further reduced as the angle of the front end is lowered. Therefore, in the case of installing the Side buoyancy box to improve stability in coastal fishing boats, it is necessary to verify the shape that can minimize the resistance while maintaining the roll motion.