Safety Assessment On SPB LNG Carrier Under Accident Condition

Natural gas has found an increasingly wide utilization in most countries and the demand for LNG carriers goes up.The cryogenic cargo go against the ship structural safety,so it is necessary to research this negative effect.This thesis conduct a research on the structure safety of SPB(Self-supporting type B)LNG carrier under accident condition,focus on the ultimate strength considering the cryogenic effect.The main contents are listed as follows:(1)A simplified heat-transfer model is built with reference to heat transfer theory and structural characteristic of SPB LNG carrier.A calculation program is written with PCL to solve the hull temperature field.The convective heat-transfer coefficient is determined by iterative computation in consideration of the coupling among structure temperature,air temperature,and convective coefficient.(2)The temperature field after the failure of liquid cargo containment system is analyzed.The air temperature field of convection space is calculated with CFD which is used to simulate LNG release and dispersion.The factor of temperature and the factor of area are proposed after discretizing the air temperature field.The factors are used to improve initial program to solve hull temperature field.(3)The longitudinal ultimate strength is calculated with ABAQUS/Explicit.The cryogenic effect on ultimate strength: 1.the cryogenic effect on material mechanics properties is researched,the hull load-carrying capacity weaken because of cold shortness.2.the thermal stress go against hull structure totally or locally.(4)The residual strengths are calculated in different damaged conditions.According to the distribution of still water bending moment and wave induced bending moment,the hull reliability is studied with FOSM method and the structure safety is assessed.This paper will provide certain reference significance for research of temperature field,ultimate strength and structural reliability of SPB LNG carriers.