• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.394-399
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• 2019

Plywood is a laminated wood material where alternating layers are perpendicular to each other. It is used in a liquefied natural gas (LNG) carrier for an insulation system because it has excellent durability, a light weight, and high stiffness. An LNG cargo containment system (LNG CCS) is subjected to loads from gravity, sloshing impact, hydrostatic pressure, and thermal expansion. Shear forces are applied to an LNG CCS locally by these loads. For these reasons, the materials in an LNG CCS must have good mechanical performance. This study evaluated the shear behavior of plywood. This evaluation was conducted from room temperature ($25^{\circ}C$) to cryogenic temperature ($-163^{\circ}C$), which is the actual operating environment of an LNG storage tank. Based on the plywood used in an LNG storage tank, a shear test was conducted on specimens with thicknesses of 9 mm and 12 mm. Analyses were performed on how the temperature and thickness of the plywood affected the shear strength. Regardless of the thickness, the strength increased as the temperature decreased. The 9 mm thick plywood had greater strength than the 12 mm thick specimen, and this tendency became clearer as the temperature decreased.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.189-195
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• 2000

New concept of LNG-FPSO ship with moonpool and bilge step in bottom is considered and investigated in the point of motion reduction and sloshing phenomena of the cargo and operation tanks. The cargo capacity of the ship of which principle dimensions is L x B x D x t(design) =270.0 x 51.0 x 32.32 x 13.7(m) 16K at 98% loading condition. The two moonpools and rectangular step at bilge part are setted up specially for getting the effect of motion decrease. For the motion analysis, linearized three dimensional diffraction theory with the simplified boundary conditions is used. The six-degree of freedom coupled motion responses are calculated for the LNG-FPSO ship. Viscous effects on the roll motion responses of a vessel are taken into account in this calculation program using an empirical formula suggested by Ikeda, Himeno and Tanaka is used. The case study for the moonpool size had been carried out by theoretical estimation and experimental method. For the optimization of the moonpool size and effect of the step, 9 cases of its size and with and without step are considered. From the results of calculation and experiment, it can be concluded that this designed LNG-FPSO ship have possibility to carry out her missions in the rough sea as for the owner's demand waves condition. The motion responses, especially roll motion, for the designed LNG-FPSO ship are much lower than those of another drillship and shuttle tanker and limit criterions are satisfied. For the check of the cargo tank and operation tank sizes we have performed sloshing analysis in the irregular waves which focuses on the pressure distribution on the tank wall and the time history of pressure and free surface for No.2 and No5. tanks of LNG-FPSO with chamfers. Finally we got the tank size which has no resonance and no impact pressure in all filling in the bow quartering and beam sea.

• Journal of Welding and Joining
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• v.14 no.1
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• pp.99-106
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• 1996

Development of an automatic TIG welding system incorporating a vision sensor and torch control mechanism leads to an improved welding quality and greater production efficiency. The automatic welding system should be greatly restricted in its size and weight for the LNG(Liquefied Natural Gas) storage tank and also provide a unique torch rotating mechanism which keeps the torch tip in the constant position while the angle is changed continuously to maintain the welding torch substantially perpendicular to the weld line. The developed system is driven by two translation axes X, Z and one rotational axis. A moving line window method is adopted to the image recognition of the corrugated membranes with specular reflection. This method decides original laser stripe patterns in image which is affected by multi-reflection. A self-teaching algorithm, which guides the automatic welding machine with the information provided by the CCD camera without any previous learning of a reference trajectory, was developed for tracking the corrugated membrane of the LNG tank along the weld line.

• Journal of the Korean Institute of Gas
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• v.9 no.4 s.29
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• pp.1-5
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• 2005

An investigation was made on the fatigue characteristics of type 304 stainless steel membrane manufactured by plastic working. To investigate the effect of plastic deformation, tests were performed with 5 types of specimens having different amount of plastic deformation. Fatigue tests were executed under both room and LNG temperatures $(-162^{\circ}C)$. All the test results were compared with the fatigue data provided by RPIS (Recommended Practice for Inground LNG Storage Tank). On the basis of these results, it was confirmed that RPIS's design fatigue curve could be applied to evaluate fatigue life of KOGAS membrane manufactured by pressing.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.4
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• pp.74-82
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• 1993

The present paper deals with the structural safety assessment techniques for independent type B spherical LNG tank against fatique crack initiation and propagation, which contains fellowing 3 steps. 1) Prediction of long term distribution of wave induced stresses and fatique crack intiation life using cumulative damage theory which were described at the 1st report. 2) Surface crack propagation analysis to verify that initial defects cannot penetrate tank plate. 3) Passing-through fatigue crack propagation analysis was performed based on LBF(Leak Before Failure ) theory.

• Journal of Ocean Engineering and Technology
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• v.22 no.3
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• pp.96-102
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• 2008

As LNG tank is operated around $-162^{\circ}C$, an experimental approach on the cryogenic temperature tensile and fatigue strengths of SUS304L lap joint weld is very important at the design stage of membrane type LNG tank. In this study, in order to estimate the tensile and fatigue strengths of SUS304L lap joint weld at cryogenic temperature condition, tensile and fatigue tests were conducted. Also, S-N curves are presented with statistical testing method recommended by JSME. As a result of the experimental approach, the d￡sign guide of fatigue strength is proposed and that is expected to be useful for membrane type LNG tank design.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.6_2
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• pp.787-793
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• 2021

The global demand for Liquefied Natural Gas(LNG) continues to increase and is facing a big cycle. To keep pace with the increase in international demand for LNG, the demand for LNG fueled ships is also increasing. Since LNG fuel tanks are operated in a cryogenic environment, insulation technology is very important, and although there are various types of insulation applied to Type C tanks, multi-layer insulation and vacuum insulation are typically applied. Powder insulation materials are widely used for storage and transportation of cryogenic liquids in tanks with such a complex insulation structure. In this study, compression tests at room and cryogenic temperature were performed on closed perlite, glass bubble, and fumed silica, which are representative powder insulation material candidates. Finally, the applicability to the Type C fuel tank was reviewed by analyzing the experimental results of this study.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.8
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• pp.1192-1200
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• 2008

This paper is concerned with the thermal design of the $138,000m^3$ class membrane type LNGC. To predict the temperature distribution, BOG and BOR, 3-dimensional numerical calculation was carried-out for the quarter of No.3 LNG tank. These sequence analyses were performed under the standard conditions of IMO ship design condition, USCG ship design condition and the Korean flag LNGC's route condition according to the 6-voyage modes. As the results, temperature behavior, heat flux, total penetrating heat, BOG and BOR were obtained, and those were compared with the maneuvering results considering the real temperature variation of air and sea water temperature at noon time. For securing the safety of LNGC during the ballast voyage, optimum control patterns of pressure and temperature in LNG tank is suggested in this paper.

• Journal of Advanced Marine Engineering and Technology
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• v.21 no.5
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• pp.542-548
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• 1997

In this study an evaluation method of fatigue strength of membrane type LNG tank is presented with FEM analysis and experimental approach of seam and raised edge welds. The study contains the following : l)FEM analysis of test specimens 2)Fatigue tests of seam and raised edge welds 3)Estimation of cumulative damage factor of the welds on the basis of safe life design concept complying with the rules of classification society 4)Review of the effect of mean stress on the fatigue strength 5)Modelling of fatigue life of the welds which is changeable by weld heights With the results obtained in this study, a model ${\Delta}{\delta}/h^2=0.13553\;{N_{f}}^{-0.3151}$ for seam and raised edge welds having a given weld height is proposed to be useful for designers and inspectors.

• Transactions of Materials Processing
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• v.20 no.6
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• pp.409-419
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• 2011

Membrane structures are widely used for LNG(Liquefied Natural Gas) storage tanks. This study presents a membrane structure based on the Mark-III type. For its development, a series of numerical simulation was conducted using ABAQUS and experimental investigation was carried out. The manufacturing process of the membrane was simulated. The thickness distribution predicted by the numerical approach agreed well with the experimental results.