Study On Ultimate Strength And Residual Strength Of LNG Carrier Considering Low Temperature Effect

Natural gas is holding an important position in the world power system,there is a tendency that LNG carrier fleet become larger and the capacity of a single carrier become higher. On the other hand, the requirement raised by the rules and regulations for the assessment of ultimate strength is getting stricter and stricter. Thermal analysis must be made in advance to ensure the structural safety of LNG carrier because of the cryogenic cargo it transports.This thesis focuses on the ultimate strength and residual strength of a membrane LNG carrier considering the cryogenic effect. The main contents of this thesis are listed as follows:1) The methods to analysis the ultimate strength of the hull girder are introduced and summarized. Quasi-static method is emphasized, and case study is made to verify its feasibility.2) Heat transfer theory is reviewed, including the characteristic of the basic three kinds of heat transmission method. Simplified analysis model is obtained with reference to the heat transfer feature of LNG carriers. Iterative calculation code is developed with Patran Command Language, a typical case is analyzed and compared to the experiment result of GTT Company,and good agreement is found, which indicates the effectiveness of the calculation method.3) Temperature field under different operational mode is derived, with the Young?s modulus temperature relationship, yield stress temperature relationship, ultimate strength under different operational mode is obtained,and difference is quantified.4) Residual strength of several grounding scenarios is studied. Thelinear relationship between the RIF under sagging and dimensionless damaged width is derived. As for scenario leading to LNG leakage, thermal analysis is made to study the cryogenic zone with the guide of marine steel property under low temperature condition. The effect of low temperature brittleness is analyzed.5) With the distribution of still water bending moment and wave induced bending moment in damaged condition, the reliability is studied, and difference between different scenarios is analyzed.