• Special Issue of the Society of Naval Architects of Korea
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• 2005.06a
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• pp.22-30
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• 2005

Sloshing loads, produced by the violent liquid free-surface motions inside the cargo tank have become an important design parameter in ship building industry since there have been demands for the increased sizes of the cargo containment system of LNG carriers. In this study, sloshing impact pressure acting on the shell of the spherical cargo tank of an LNG carrier as well as dynamic pressure and flow behavior around the pump tower located at the center of the tank have been calculated. Comparative numerical sloshing simulations for a spherical LNG tank using 2-D LR.FLUIDS which is based on the finite difference method and 3-D MSC.DYTRAN which is capable of calculating nonlinear fluid-structure interaction have been carried out. A method of calculating sloshing-induced dynamic loads and the subsequent structural strength analysis for pump tower of a spherical LNG carrier using MSC. DYTRAN and MSC.NASTRAN have been presented.

• Journal of Ship and Ocean Technology
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• v.5 no.3
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• pp.36-44
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• 2001

The collision energy absorbing characteristics of side structure of the LNG carriers which have the cargo containment systems of the spherical and the membrane types are compared. A failure mechanism of the double hull side structures of 130, 000 $m^3$ class LNG carriers under sideways collision event has been simulated by using the detailed finite element calculations. In ship collision analysis, the finite element method based on explicit time integration has been use[1 with much success. Finite element modeling techniques for detail description of structural members antral ship motion regarding the dynamic behavior allowed to investigate the effect of bow shape and the initial contact position on side shell of collided ship. In the numerical simulations of the ship-to-ship sideways collision, the effect of the colliding bow shapes and the change of the colliding ship draft are investigated. The critical collision energy which is absorbed by a side structure of a collided ship until the fore-end of colliding ship arrives at the boundary of the cargo tank is calculated. The critical speed of specified colliding ships which can not penetrate the boundary of the LNG cargo tank of the collided ship under collision accident if evaluated.

• Journal of Ocean Engineering and Technology
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• v.28 no.2
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• pp.126-132
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• 2014

In this study, a method for analyzing the collision and interaction between ice bergy bits and a Mark III type liquid natural gas (LNG) carrier was considered, and the structural safety of a ship's hull and cargo containment system (CCS) was evaluated. In the analysis, a constitutive model implementing the strain rate dependant mechanical property was used to consider the typical material characteristics of ice rationally. A relatively simple and easy ice structure interaction analysis procedure, compared with the accurate but complicated FSI analysis scheme, was suggested. When the ice bergy bits collided with ship's side hull under the four assumed scenarios, the structural behaviors of the ship structure and LNG CCS were simulated by applying the suggested ice collision analysis procedure using the commercial hydro-code LS-DYNA. In addition, the effects of the shapes and colliding speed of the ice bergy bits on the ice-structure interaction and safety of the CCS were examined in detail.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.2
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• pp.114-121
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• 2014

Liquefied natural gas(LNG) cargo containment system(CCS) has the primary function of ensuring both adequate structural safety with respect to sloshing load which is defined as a violent behaviour of the liquid contents in CCS due to external forced motions and thermal insulation keeping natural gas below its boiling point. Among different LNG CCS types such as independent B-type and membrane ones, Mark III CCS is considered in this paper to perform its strength assessment. Mark III CCS plate is designed and constructed by stacking various non-metallic engineering materials such as plywood, triplex, reinforced PU foam that are supported by series of mastic upon inner steel hull structure. From the viewpoint of structural analysis, this plated structure is treated as a laminated composite structure showing complex structural behaviour under external load. Advanced finite element models of Mark III CCS plate is generated and used in conjunction with ultimate strength based failure criteria from laminated composite mechanics for the strength assessment. The strength assessment is performed within the initial failure state of Mark III CCS plate. Results provide failure details such as failure locations and loads. Finally obtained results are reviewed using the loads from acceptance criteria suggested by classification.

• Journal of Welding and Joining
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• v.12 no.1
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• pp.102-115
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• 1994

This paper is to evaluate the fatigue strength of lap joints of materials applied to LNG carrier cargo containment of GAZ-TRANSPORT(GT) type, which was welded by manual and automatic TIG welding process. The thicknesses of lapped members were 1.5mm/1.5mm or 1.5mm/0.7mm in Invar to Invar joint, and 1.5mm/8.0mm in Invar to stainless steel joint, respectively. These lap joints were mainly applied to the membrance fabrication of GT-LNG carrier. Fatigue tests of Invar/Inar lap joints were conducted under the stress ratio R=0 at room temperature. The effect of mean stress and cumulative fatigue damage on the allowable stress of Invar lap joint was evaluated on the basis of test results. Fatigue test was also conducted on Inver/Stainless steel lap joints welded by automatic TIG process without filler metals. The fatigue test of the joint was carried out under the same conditions as those of Invar/invar lap joints. The fatigue strength of the joint welded without filler metal was comparable to those welded with filler metal quoted from reference. The fatigue strength of Invar/stainless steel lap joint was only dependent on the lap throat thickness, and not on the welding process. Based on test results, the applicability of TIG welding process without filler metal in Invar/stainless steel lap joint was reviewed by controlling welding variables to assure the valid throat thickness of lap joints.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.6
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• pp.726-734
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• 2008

While the structural safety assessment of Cargo Containment System(CCS) in membrane type LNG carriers has to be carried out in consideration of sloshing impact pressure, it is very difficult to figure out its dynamic response behaviors due to its very complex structural arrangements/materials and complicated phenomena of sloshing impact loading. For the development of its original technique, it is necessary to understand the characteristics of dynamic response behavior of CCS structure under sloshing impact pressure. In this study, for the exact understanding of dynamic response behavior of CCS structure in membrane Mark III type LNG carriers under sloshing impact pressure, its wet drop impact response analyses were carried out by using Fluid-Structure Interaction(FSI) analysis technique of LS-DYNA code, and were also validated through a series of wet drop experiments for the enhancement of more accurate shock response analysis technique. It might be thought that the structural response behaviors of impact response analysis, such as impact pressure impulses and resulted strain time histories, generally showed very good agreement with experimental ones with very appropriate use of FSI analysis technique of LS-DYNA code, finite element modeling and material properties of CCS structure, finite element modeling and equation of state(EOS) of fluid domain.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.6
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• pp.735-749
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• 2008

For the development of the original technique of structural safety assessment of Cargo Containment System(CCS) in membrane type LNG carriers, it is necessary to understand the characteristics of dynamic response behavior of CCS structure under sloshing impact pressure. In the previous study, the wet drop impact response analyses of CCS structure in membrane Mark III type LNG carriers were carried out by using Fluid-Structure Interaction(FSI) analysis technique of LS-DYNA code, and were also validated through a series of wet drop experiments for the enhancement of more accurate shock response analysis technique. In this study, the characteristics of structural shock response behaviors of CCS structure were sufficiently figured out by careful examinations of the effects of specimen weight, drop height, incident angle, corrugation and stiffness of inner hull on its shock response behaviors. The shock response analysis of upward shooting fluid to inner hull was performed, and the reason of faster strain response than shock pressure one was also figured out.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.4
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• pp.265-271
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• 2014

304L stainless steel sheets are used as a primary barrier for the insulation of membrane-type liquefied natural gas(LNG) carrier cargo containment system. 304L stainless steel is a transformation-induced-plasticity(TRIP) steel that exhibits complex material behavior, because it undergoes phase transformation during plastic deformation. Since the TRIP behavior is very important mechanical characteristics in a low-temperature environment, significant amounts of data are available in the literature. In the present study, a uniaxial tensile test for 304L stainless steel was performed to investigate nonlinear mechanical characteristics. In addition, a viscoplastic model and damage model is proposed to predict material fractures under arbitrary loads. The verification was conducted not only by a material-based comparative study involving experimental investigations, but also by a structural application to the LNG membrane of a Mark-III-type cargo containment system.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.4
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• pp.206-213
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• 2021

Recently, although the size of the LNG Cargo Containment System (CCS) has been increasing, the secondary barrier is reported to remain unchanged, and the conventional Flexible Secondary Barrier (FSB) used in Mark-III type has been pointed out to be vulnerable to failure owing to thermal and cyclic loads. In this respect, a tensile test was carried out to verify the reinforcing effect of FSB using aramid fiber on weft compared to the conventional FSB. In order to consider the LNG leakage situation, a series of tensile tests were conducted from ambient to cryogenic temperature, and mechanical properties were evaluated for each fiber direction on account of anisotropy. Tensile behavior and fracture analyses were performed to confirm the mechanical properties of each material according to temperature. Tensile test results proved that replacing the aramid fiber instead of E-glass fiber used on weft is effective in enhancing the mechanical properties.

• Journal of Ocean Engineering and Technology
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• v.36 no.4
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• pp.217-231
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• 2022

Reinforced polyurethane foam (R-PUF), a material for liquefied natural gas cargo containment systems, is expected to have different mechanical properties depending on its stacking position of foaming as the glass fiber reinforcement of R-PUF sinks inside R-PUF under the influence of gravity. In addition, since R-PUF is not a homogeneous material, it is also expected that the coordinate direction within this material has a great correlation with the mechanical properties. So, this study was conducted to confirm this correlation with the one between the mechanical properties and the stacking position. In particular, in this study, R-PUF of 3 different densities (130, 170, and 210 kg/m³) was used, and tensile, compression, and shear tests of this material were performed under 5 temperatures. As a result of the tests, it was confirmed that the strength and modulus of elasticity of the material increased as the temperature decreased. Specifically, the strength and modulus of elasticity in the Z direction, which was the lamination direction, tended to be lower than those in the other directions. Finally, the strength and elastic modulus of different specimens of the material found at the bottom of their lamination compared to the specimens with these properties found at positions other than their lamination bottom were evaluated. Further analysis confirmed that as the temperature decreased, hardening of R-PUF occurred, indicating that the strength and modulus of elasticity increased. On the other hand, as the density of R-PUF increased, a sharp increase in strength and elastic modulus of R-PUF was observed.