• Journal of the Society of Naval Architects of Korea
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• v.50 no.6
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• pp.390-398
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• 2013

In this paper, an experimental study on sloshing problems in an independent B-type tank of STX Offshore and Shipbuilding Co. is described. Recently STX Offshore and Shipbuilding Co. introduced a new design of an independent B-type tank in order to reduce sloshing impact loads on LNG CCS. This tank has many internal members, so that sloshing flow and the resultant hydrodynamic loads are very different from those in typical membrane tanks. In this study, a series of sloshing experiment have been carried out for 1/50 scale model, and the main characteristics of sloshing load on the independent tank are observed. The properly scaled internal members such as swash bulkhead, center bulkhead and stringers have been installed in the test tank model, but sloshing pressures are measured on the tank walls only. The forced excitation signals have been generated by using the predicted ship motion in irregular sea states. The characteristics of sloshing loads on this tank have been observed in different filling levels with various heading angles, and sea states. In this paper, some key findings from the model tests are discussed.

• Journal of the Society of Naval Architects of Korea
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• v.60 no.4
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• pp.213-221
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• 2023

The demand for Liquefied Natural Gas (LNG) carriers and LNG-fueled ships has significantly increased in recent years due to the sulfur-oxide emission regulations by the International Maritime Organization (IMO). The main goal of this paper is to introduce the process for the Engineering Critical Assessment (ECA) of IMO independent type-B cargo tanks made from 9% nickel alloy. A methodology proposed by the British Standard was used to conduct ECA for any structure with initial flaws. Based on this standard, a Matlab code was developed to perform ECA. Coarse mesh Finite Element Analysis (FEA) was performed on an independent type-B LNG cargo tank with a capacity of 15,000 m³. The location with the highest development of maximum principal stress was identified at the bottom of the cargo tank. Fine mesh FEA was performed to obtain the stress range required for ECA. The dynamic cargo tank loads used for FEA were determined using some ship rules presented by Det Norske Veritas. As a result of performing a 20-year long-term crack propagation analysis with a semi-elliptical surface crack, the fracture-to-yield ratio exceeded the Fracture Assessment Line (FAL) and some structural reinforcement was necessary. Performing a 15-day short-term crack propagation analysis, the fracture-to-yield ratio remained within the FAL, and no significant LNG leaks were expected. This paper is believed to provide a guide for performing ECA of LNG cargo tanks in the future by providing the basic theory and application sample necessary to perform ECA.