• Journal of Ocean Engineering and Technology
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• v.8 no.2
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• pp.93-104
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• 1994

Recently in the design of super tankers or LNG carriers which transport a large amount of liquid in the cargo holds, the structural damage due to liquid sloshing becomes an important problem. The impact pressure from sloshing is most violent when the liquid motion of a partially filled tank is in resonance with the motion of a ship. In this paper the sloshing natural periods in liquid cargo tanks are estimated for partially filled tanks with various geometries. Especially the sloshing periods of baffled tanks which are often installed to reduce liquid motion and sloshing forces are calculated. A variational method is adopted to analyze the baffled tank of arbitrary filling depth of liquid. In this approach the liquid domain is divided into several subdomains in which the analytic solutions are potential energy are calculated from the velocity potentials in eachsubdomain. By minimizing the Hamilton's functional, the sloshing natural periods are estimated and the results are compared with experimental and numerical results.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.4
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• pp.307-313
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• 2016

When liquefied natural gas (LNG) is stored in a tank, it is necessary to maintain low temperature. It is very important that insulation techniques are applied to the LNG cargo because of this extreme environment. Hence, laminated wood, especially plywood, is widely used as the structural member and insulation material in LNG cargo containment systems (CCS). However, fracture of plywood has been reported recently, owing to sloshing effect. Therefore, it is necessary to increase the strength of the structural member for solving the problem. In this study, compressed wood, which is used as a support in LNG independent type B tanks, was considered as a substitute for plywood. Compression and bending tests were performed on compressed wood under ambient and cryogenic temperatures to estimate the mechanical behaviors and fracture characteristics. In addition, the direction normal to the laminates surface was considered as an experimental variable. Finally, the feasibility of using compressed wood for an LNG CCS was evaluated from the test results.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.3
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• pp.342-347
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• 2015

Floating LNG is a new concept which is used as LNG regasification/receiving facility and for LNG production/export facility. LNG Floating Production Storage and Offloading(FPSO) concept will put vitality into marginal gas fields which were delayed because of excessive investment cost in the world. LNG Floating Storage Regasification Unit(FSRU) also provides commercially competitive and effective solutions to the areas where onshore infrastructure is not well established. LNG cargo containment system is one of the key functions for FLNG to store produced LNG on a floating structure. This paper presents a new technology related to a LNG containment system; a combined cargo containment system utilizing the advantages of iIndependent tank type and membrane system. Technical advantages have been validated through research work.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.1
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• pp.125-134
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• 2003

The present paper is concerned to the thermal analysis during the cool-down period of 138,000 m$^3$class GTT MARK-III membrane type LNG carrier servicing with LNG from the Middle East to Korea. It is the cool-down period that cools the insulation wall and the gas in LNG tank to avoid the thermal shock as the start of loading of -162$^{\circ}C$ LNG. For six hours of the standard cool-down period, the temperature of NG falls down from -4$0^{\circ}C$ to -13$0^{\circ}C$ and especially the mean temperature of the 1st barrier in the top side insulation wall falls down from -38.38$^{\circ}C$ to -122.42$^{\circ}C$ in case of IMO design condition. By the 3-D numerical calculation about the cargo tank and the cofferdam, the temperature variation in hulls and insulations is precisely predicted in this paper. And the mean temperature variation of gas is calculated as the function of the spraying rate by the heat balance model during the cool-down period.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.2
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• pp.162-169
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• 2016

A new concept of membrane type LNG CCS was proposed. Also, its static behavior was numerically analyzed considering the interaction between primary and secondary barrier together with securing device. Hull deflection was taken into account as an external load, together with temperature distribution across the barriers. The suggested numerical model considers both sliding and contact between the two mating surfaces of both the primary and secondary barrier, and anisotropic material behavior of plywood, R-PUF was also taken into account. Furthermore, detailed local strength was evaluated for the securing device, which is arranged between two barriers to hold the primary barrier. It was confirmed through the numerical analysis that the new concept of membrane type CCS was structurally safe under static loading condition and securing concept was structurally reliable.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.531-538
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• 2011

To ensure the structural integrity of membrane type LNG tank, the rational assessment of impact pressure and structural responses due to sloshing should be preceded. The sloshing impact pressures acting on the insulation system of LNG tank are typical irregular loads and the structural responses caused by them also very complex behaviors including fluid structure interaction. So it is not easy to estimate them accurately and huge time consuming process would be necessary. In this research, a simplified method to analyze the dynamic structural responses of LNG tank insulation system under pressure time histories obtained by sloshing model test or numerical analysis was proposed. This technique basically based on the concept of linear combination of the triangular response functions which are obtained by the transient response analysis under the unit triangular impact pressure acting on structures in time domain. The validity of suggested method was verified through the example calculations and applied to the structural analysis of real Mark III type insulation system using the sloshing impact pressure time histories obtained by model test.

• 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 KSME Conference
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• 2004.04a
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• pp.1346-1351
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• 2004

This study is concerned with the thermal analysis during the cool-down period of 135,000 $m^3$ class GT-96 membrane type LNG carrier under IMO design condition. The cool-down is performed to cool the insulation wall and the natural gas in cargo tank for six hours to avoid the thermal shock at the start of loading of $-163^{\circ}C$ LNG. During the cool-down period, the spraying rate for the NG cooling decreases as the temperature of NG falls clown from $-40^{\circ}C$ to $-130^{\circ}C$ and the spraying rate for the insulation wall cooling increases as the temperature gradient of the insulation wall is large. It was confirmed that there existed the largest temperature decrease at the 1 st barrier and 1st insulation, which are among the insulation wall, especially in the top side of the insulation wall. By the 3-D numerical calculation about the cargo tank and the cofferdam during the cool-down period, the temperature variation in hulls and insulations is precisely predicted.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.1
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• pp.132-150
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• 2014

In this study, the inertial properties of fully filled liquid in a tank were studied based on the potential theory. The analytic solution was obtained for the rectangular tank, and the numerical solutions using Green's 2nd identity were obtained for other shapes. The inertia of liquid behaves like solid in recti-linear acceleration. But under rotational acceleration, the moment of inertia of liquid becomes small compared to that of solid. The shapes of tank investigated in this study were ellipse, rectangle, hexagon, and octagon with various aspect ratios. The numerical solutions were compared with analytic solution, and an ad hoc semi-analytical approximate formula is proposed herein and this formula gives very good predictions for the moment of inertia of the liquid in a tank of several different geometrical shapes. The results of this study will be useful in analyzing of the motion of LNG/LPG tanker, liquid cargo ship, and damaged ship.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.103-108
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• 2020

Generally, the cargo tank of LPG carriers corresponds to an independent tank Type A defined by the International Maritime Organization (IMO). The outside of the tank is insulated by polyurethane foam, and the tank is made of expensive low temperature steel that can withstand temperatures as low as -50℃. The cargo tank is composed of outer shell plates, bulkheads, stiffeners, web frames, and stringers. Among them, the outer shell plates, bulkheads, and stiffeners can be designed without structural analysis by the Classification Rules and are constructed easily through optimal design. On the other hand, optimal design, including numerous structural analysis, is not performed because web frames and stringers should be designed and approved through structural analysis. Only adequate design, which determines the design dimensions through several dozen structural analysis, is performed. In this study, for finite element analysis, eight loading conditions were applied, and the deformation of the entire ship for each loading condition was considered. The minimum weight design was performed for the web frames of cargo tanks in the 82,000 ㎥ LNG carrier through the gradient-based optimization technique, and the weight was reduced by approximately 108 tons per ship.