Study on Effects of Sloshing Loads on Fatigue Strength of Independent B-Type LNG Tank
摘要
The main objective of this thesis is to investigate the load effects due to sloshing on the fatigue assessment of an IMO independent type B LNG tank. The selection of the cargo containment system type and the number of cargo tanks of large LNG carrier or LNG FPSO (FLNG) is mainly related to the sloshing problem. In contrast to earlier design concept, nowadays the LNG carriers and FLNG are considered to be operating at intermediate loading condition in harsh environmental conditions. The most popular LNG containment system for the FLNG is an independent prismatic tank categorized as IMO (International Maritime Organization) type B tank, in which the ship hull supporting the LNG tanks. It is recognized that the independent prismatic tank type B is free from possible liquid sloshing inside the tank in the view point of the strength. However in the view point of fatigue assessment of the cargo tank, it needs careful verification in accordance with IMO type B independent tank requirements.\nThe sloshing pressures at the internal structures of DSME ACTIB (Aluminum Cargo Tank Independent type B) LNG cargo tank are predicted based on scaled sloshing model tests to calculate fatigue damage for the internal structures of the tank. The chaotic nature of the sloshing causes difficulties in the conventional spectral fatigue analysis method for the fatigue analysis of internal structures of the LNG tanks. \nIn this thesis, an experimental investigation of the load effects due to sloshing impact on the fatigue analysis of an independent type B LNG tank, DSME ACTIB, is carried out. A scaled model tests with 2D tank including internal structured are performed to predict the long-term responses of sloshing pressures near the internal structure at each cell of designated wave scatter diagram, IACS 34 North Atlantic wave scatter diagram.\nA schematic procedure for fatigue assessment of independent type B LNG tank based on sloshing model test is proposed, and applied to fatigue assessme