• Ocean and Polar Research
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• v.25 no.3
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• pp.287-302
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• 2003

The seasonal variations in the circulation of the water mass in the East Sea/Japan Sea have been simulated using a free surface primitive ocean model, RIAMOM (RIAM Ocean Model), comparing the results from GFDL-MOM1 (Geophysical Fluid Dynamics Laboratory Modular Ocean Model, version 1.1, hereafter MOM) with the GDEM (Generalized Digital Environmental Model) data. Both models appear to successfully reproduce the distinct features of circulation in the East Sea/Japan Sea, such as the NB (Nearshore Branch) flowing along the Japanese coast, the EKWC (East Korean Warm Current) flowing northward along the Korean coast, and the NKCC/LCC (North Korean Cold Current/Liman Cold Current) flowing southwestward along Korean/Russian coast. RIAMOM has shown better performance, compared to MOM, in terms of the realistic simulation of the flow field in the East Sea/Japan Sea; RIAMOM has produced more rectified flows on the coastal region, for example, the narrower and stronger NKCC/LCC than MOM has. There is however obvious differences between the model results and the GDEM data in terms of the calculation of the water mass; both models have shown a tendency to overpredict temperature and underpredict salinity below 50m; more diffusive forms of thermocline and halocline have been simulated than noted in GDEM data.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.980-992
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• 2024

Steam line break accident (SLB) in the nuclear reactor is one of the representative Non-LOCA accidents in which thermal-hydraulics and neutron kinetics are strongly coupled each other. Thus, the multi-scale and multi-physics approach is applied in this study in order to examine a realistic safety margin. An entire reactor coolant system is modelled by system scale node, whereas sub-channel scale resolution is applied for the region of interest such as the reactor core. Fuel performance code is extended to consider full core pin-wise fuel behaviour. The MARU platform is developed for easy integration of the codes to be coupled. An initial stage of the steam line break accident is simulated on the MARU platform. As cold coolant is injected from the cold leg into the reactor pressure vessel, the power increases due to the moderator feedback. Three-dimensional coolant and fuel behaviour are qualitatively visualized for easy comprehension. Moreover, quantitative investigation is added by focusing on the enhancement of safety margin by means of comparing the minimum departure from nucleate boiling ratio (MDNBR). Three factors contributing to the increase of the MDNBR are proposed: Various geometric parameters, realistic power distribution by neutron kinetics code, Radial coolant mixing including sub-channel physics model.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.2
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• pp.102-109
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• 1996

Effects of frictional laws on finite element solutions in metal forming were investigated in this paper. A rigid-viscoplastic finite element formulation was given with emphasis on the frictional laws. The Coulomb friction and the constant shear friction laws were compared through finite element analyses of compression of rings and cylinders with different aspect ratios, ring-gear forging, multi-stage cold extrusion and hot strip rolling under the isothermal condition. It has been shown that two laws may yield quite different results when the aspect ratio of a process and the fractional contact region are large.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.8
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• pp.807-812
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• 2015

A microcapsule water slurry is a latent heat-storage material having a low melting point. In this study, the thermal properties of a microcapsule water slurry are measured. The physical properties of the test microcapsule water slurry, i.e., thermal conductivity, specific heat, latent heat, and density, are measured, and the results are discussed for the temperature region of solid and liquid phases of the dispersion material (paraffin). It is clarified that Eucken's equation can be applied to the estimation of the thermal conductivity of the microcapsule water slurry. Useful correlation equations of the thermal properties of the microcapsule water slurry are proposed in terms of the temperature and concentration ratio of the microcapsule water slurry constituents.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.3
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• pp.183-189
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• 2005

A modeling of a hydraulic-gun-aerator is proposed to set up a design procedure for such devices. The aerators are used to destroy any thermal stratification that are responsible for the degradation of water qualify of lakes. The aerator produces ascending flow by using air bubbies released instantly near the bottom of the lake into a cylindrical pipe installed vertically. Differently form the diffuser-aerators, they can pull up the cold, oxygen depleted water directly to the region of the free surface, and they are believed to work effectively especially for relatively deeper lakes. Their design procedure has not been established yet though, and we propose a model focusing on the exit flow velocity at the top of the aerator through the examination of presently operating devices.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.285-289
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• 2004

Oceanographic observation and qualitative analysis for deep ocean water in the East Sea were carried out from January 2003 to January 2004, in order to understand the characteristics of deep sea water in the East Sea. Temporal and spatial variation of water masses were discussed from survey of the study area including the coastal sea of Kwangwon province in where the polar front mixing cold and warm water masses were formed. On the basis of the vertical profiles of temperature, salinity and dissolved oxygen, water masses in the study area were divided into 5 major groups; (1) Low Saline Surface Water (LSSW) (2) Tsushima Surface water (TSW) (3) Tsushima Middle Water (TMW) (4) North Korea Cold Water (NKCW) and (5) East Sea Proper Water (ESPW). In winter, surface water in coastal sea of Kwangwaan Kosung region were dominated by North Korean Cold Water (NKCW). As Tsushima warm current were enforced in summer, various water masses were vertically emerged in study area, in order of TSW, TMW, NKCW and ESPW. It is highly possible that the LSSW which occurred at surface water of september is originated from influx of fresh water due to the seasonal rainy spell. Nevertheless water masses existed within surface water were seasonally varied, water quality characteristics of East Sea Proper Water (ESPW) under 300 m did not changed all the seasons of the year.

• Steel and Composite Structures
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• v.34 no.1
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• pp.123-139
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• 2020

The tube outward local buckling of Concrete-Filled Steel Tube (CFST) beam under high compression stress is still considered a critical problem, especially for steel tubes with a slender section compared to semi-compact and compact sections. In this study, the flexural performance of stiffened slender cold-formed square tube beams filled with normal concrete was investigated. Fourteen (14) simply supported CFST specimens were tested under static bending loads, stiffened with different shapes and numbers of steel stiffeners that were provided at the inner sides of the tubes. Additional finite element (FE) CFST models were developed to further investigate the influence of using internal stiffeners with varied thickness. The results of tests and FE analyses indicated that the onset of local buckling, that occurs at the top half of the stiffened CFST beam's cross-section at mid-span was substantially restricted to a smaller region. Generally, it was also observed that, due to increased steel area provided by the stiffeners, the bending capacity, flexural stiffness and energy absorption index of the stiffened beams were significantly improved. The average bending capacity and the initial flexural stiffness of the stiffened specimens for the various shapes, single stiffener situations have increased of about 25% and 39%, respectively. These improvements went up to 45% and 60%, for the double stiffeners situations. Moreover, the bending capacity and the flexural stiffness values obtained from the experimental tests and FE analyses validated well with the values computed from equations of the existing standards.

• Nuclear Engineering and Technology
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• v.25 no.1
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• pp.71-79
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• 1993

Positron annihilation characteristics and microhardness of 25% cold worked and isochronally annealed hafnium specimens were measured to study recovery and recrystallization stages of hafnium specimens. The annihilation lifetime of positrons in hafnium has been measured for the distinct cases of annihilation in the annealed lattice and annihilation after trapping at lattice defects generated by cold deformation at room temperature. The annihilation lifetime in the annealed lattice was 187 $\pm$3.7 psec, whereas it was 217 $\pm$ 4.2 psec for positrons trapped at deformation-induced defects (mostly dislocations). The changes in Doppler broadening and hardness showed similar trend in the recrystallization range, however, the measured value of Doppler broadening variation were quite sensitive to changes in the recovery region in which the variation in hardness value was completely insensitive. Recovery of cold worked hafnium initiated at about 623 K and recrystallization occurred at around 1023 K.

• Steel and Composite Structures
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• v.43 no.2
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• pp.201-219
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• 2022

This paper firstly proposed high performance composite columns for cold-region infrastructures using ultra-high performance concrete (UHPC) and ultra-high strength steel (UHSS) Q960E. Then, 24 square UHPC-filled UHSS tubes (UHSTCs) at low temperatures of -80, -60, -30, and 30℃ were performed under axial loads. The key influencing parameters on axial compression performance of UHSS were studied, i.e., temperature level and UHSS-tube wall thickness (t). In addition, mechanical properties of Q960E at low temperatures were also studied. Test results revealed low temperatures improved the yield/ultimate strength of Q960E. Axial compression tests on UHSTCs revealed that the dropping environmental temperature increased the compression strength and stiffness, but compromised the ductility of UHSTCs; increasing t significantly increased the strength, stiffness, and ductility of UHSTCs. This study developed numerical and theoretical models to reproduce axial compression performances of UHSTCs at low temperatures. Validations against 24 tests proved that both two methods provided reasonable simulations on axial compression performance of UHSTCs. Finally, simplified theoretical models (STMs) and modified prediction equations in AISC 360, ACI 318, and Eurocode 4 were developed to estimate the axial load capacity of UHSTCs at low temperatures.

• Journal of the Korean GEO-environmental Society
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• v.15 no.1
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• pp.35-41
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• 2014

Many infra suructure such as road, railway, building and utility foundations have been damaged by the repeated freezing and thawing of the soil during winter and spring every year in seasonal frost region. The frost penetration depth is most important factor in the design of structure such as road, railway and building in seasonal frost region. This paper presents the results of calculation of frost penetration depth and frost heaving in concrete track for railway construction. Model concrete track were installed near the railway track in Gangwon, Gyeonggi, Choongbuk province and frost penetration depth were measured using methylene blue frost penetration depth gauge. Model concrete track in Cheolwon, frost heaving of concrete track were also evaluated. The measure of maximum frost penetration depth and frost heaving can be applied to design railway track for cold region in Korea.