공액경사법을 이용한 LPG 운반선 화물창 내부구조물 중량최소화 설계

Abstract

Since the cargo tank of LPG carriers is made of expensive low-temperature steel that can maintain its function even at -50oC, the reduction of cargo tank materials has been a major concern for shipyards to improve price competitiveness. The purpose of this study is to minimize the weight of the web frames and stringers that form the interior of the cargo tank of the LPG carriers. A total of 92 design variables including 6 shape-related design variables were selected for the minimum weight design. In order to reduce the time required for the optimization process, the conjugate gradient method, which is a gradient-based optimization technique, was adopted. In addition, for the structural analysis, the cargo tank located at the second position in the bow was selected as the structural analysis target, and in order to improve the reliability of the analysis, a boundary condition considering the deformation of the entire ship for each loading condition was applied to the partial model. As a result of the study, it was confirmed that the error rate did not exceed the maximum 3% by comparing the maximum stress value generated in all internal structures for the entire model structure analysis and the partial model one. A total of 92 dimensions with the minimum objective function were determined, and the weight was reduced by about 39 tons per cargo tank.