Study On Local Structure Design For 50000DWT Oil Tanker Based On Common Structural Rules

In order to improve the oil tankers' safety and unify the evaluation flow, IACS weaved a new regulation called "Common Structural Rules for Double Hull Oil Tankers". Based on the design of the 50000DWT oil & crude oil tanker, the structure design applying CSR for Oil Tankers, are described in this dissertation. It settled the process for calculating the loads. The process is used to calculate the primary loads and primary structures scantlings of the aft end. The gained structure scantlings are compared with the scantlings gained by CCS rule. This dissertation calculates the primary structures scantlings of the cargo tank region. These scantlings are also compared with the scantlings of the cargo tank region of 50000DWT oil tanker. It is obvious to 50000DWT oil tanker that the scantlings from CSR are larger than the scantlings from CCS in the aft end and the cargo tank region.This dissertation analyses the relationship between continuing longitudinal structural components and longitudinal strength stress. This dissertation defines the conception that the changed stress per unit need to change how much the areas of deck structural components. The optimized model for getting the least areas of cross section components is established based on the first goal finding the best combinations of longitudinal stiffeners and the plate in stiffened panel. The local restrains are achieved further by increasing the requirements that the basic stiffened panel stress value is less than the permissible stress value.The ship's hull is a thin-walled box girder structure composed of stiffened panels. The overall failure of a ship hull girder is normally governed by buckling and plastic collapse of the deck, bottom, sometimes it depends on the side shell of stiffened panels. Therefore, the analysis of buckling strength of ship panels in deck, bottom, and side shells is very important and necessary for the safety assessment of ship structure. The oil tankers with the length over 150 meters have to be analyzed by Finite element method as design verification according to CSR. The dissertation describes basic methods and analytical approach for yield strength assessment and buckling strength assessment of oil tanker structure in detail, basing on technical specifications of yield strength and buckling strength in Common Rules. At the same time the FEM analyzing tool LR ShipRight SDA software is used to analyze both the yield strength assessment and buckling strength assessment by FEM method for middle three cargo tank in the cargo tank region. According to the analysis result, the yield strength satisfies the rules requirements in most cases. The buckling strengths of continuing longitudinal structural components such as deck plate, inner bottom plate, outer bottom plate that is further from the neutral axis in middle cross section are weaker. The dissertation also adjusts the structures in the right places where the scantlings have the weaker buckling strength.The first approach is to increase plate thickness of stiffened panel. Another approach is to decrease the short edge length of stiffened panel.