Dynamic Analysis and Design of LNG Tanks Considering Fluid Structure Interactions

Following a general description and analysis of the fundamental criteria for the dynamic design concerning dynamic stiffness, strength and environment issues, it is considered that the natural characteristics of the dynamic system and the dynamic responses of the system subject to various dynamic loads are two key critical issues in the dynamic design. Therefore, for the dynamic design of a LNG tank filled with liquid and operated on seaway, it is necessary to accurately predict its natural characteristics and dynamic response considering fluid structure interactions. To address these two key issues in the dynamic design stage, the developed computer software based on a mixed displacement–pressure finite element model to complete fluid-structure interaction analysis is introduced. An integrated internal liquid-tank-external water interaction system investigated by numerical simulations is summarised to consider the two issues involving the dynamic design of LNG tanks. The five studied cases include: i) 50% filled LNG liquid in a fixed rigid tank, ii) elastic tank only, iii) 50% filled LNG liquid-elastic tank interaction, iv) empty elastic tank-external sea water interaction and v) internally 50% filled LNG liquid-elastic tank-external sea water interaction. The calculated results are compared to reveal the coupling effects on the dynamic design of LNG tanks. To further demonstrate the effects of the natural characteristics affected by different interactions on the dynamic responses involving the dynamic strength, stiffness and vibration environment problems considered in dynamic design, the numerical simulations of the studied systems subject to regular sea wave excitations and earthquake excitations are carried out. The dynamic displacements for stiffness analysis, the dynamic stress for strength analysis and vibration level for dynamic environment analysis are presented and discussed. Guidelines provided in this paper maybe useful for dynamic designs of LNG tank operating in complex marine environments.