A comprehensive structural analysis of a 80,000 ton oil production and storage vessel is presented. The contents of the project involves the analysis of longitudinal strength, transverse strength and local strength. Among them the analysis of transverse strength and local strength are carried out by the Finite Element Method.
The vessel is recently designed for offshore oil field of China. The principal dimensions of the vessel are: length L=210M, breadth B=32.8M, depth D=18.2M, draft T=11.7M. For this large vessel with complex loading conditions and particular operation requirements, it is difficult to meet the structural safety by checking the strength just simply by design Rules. Hence, it is necessary to carry out a comprehensive structural analysis by direct calculation in order to ensure the structural safety of the vessel. Based on this reason, the paper systematically deals with the structural analysis and calculation of the vessel. The ordinary-strength hull structural steel (yield stress: 235 N/mm2) is used in this vessel. In all cases, the check on stresses of the members is made according to the permissible stresses of DNV "Ship Rules"(l989).
The still water bending moment and shear force are calculated by an inhouse program "The Ship Structural Analysis and Design System"(SSADS). The program "SSADS" was approved by China State Shipbuilding Corporation for the standard program in China shipbuilding industry. 12 loading conditions are taken in the calculation. The largest still water bending moment and shear force of the vessel occur In loading condition l(Table 1). They are 20% and 60% larger than the corresponding values required by DNV "Ship Rules" respectively. Therefore, the modulus of the midship section should be determined by this calculated largest still water bending moment and wave bending moment worked out based on DNV "Ship Rules".