• Nuclear Engineering and Technology
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• 제51권6호
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• pp.1487-1503
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• 2019

The methods and performance of a pin-level nuclear reactor core thermal-hydraulics (T/H) code ESCOT employing the drift-flux model are presented. This code aims at providing an accurate yet fast core thermal-hydraulics solution capability to high-fidelity multiphysics core analysis systems targeting massively parallel computing platforms. The four equation drift-flux model is adopted for two-phase calculations, and numerical solutions are obtained by applying the Finite Volume Method (FVM) and the Semi-Implicit Method for Pressure-Linked Equation (SIMPLE)-like algorithm in a staggered grid system. Constitutive models involving turbulent mixing, pressure drop, and vapor generation are employed to simulate key phenomena in subchannel-scale analyses. ESCOT is parallelized by a domain decomposition scheme that involves both radial and axial decomposition to enable highly parallelized execution. The ESCOT solutions are validated through the applications to various experiments which include CNEN $4{\times}4$, Weiss et al. two assemblies, PNNL $2{\times}6$, RPI $2{\times}2$ air-water, and PSBT covering single/two-phase and unheated/heated conditions. The parameters of interest for validation include various flow characteristics such as turbulent mixing, spacer grid pressure drop, cross-flow, reverse flow, buoyancy effect, void drift, and bubble generation. For all the validation tests, ESCOT shows good agreements with measured data in the extent comparable to those of other subchannel-scale codes: COBRA-TF, MATRA and/or CUPID. The execution performance is examined with a mini-sized whole core consisting of 89 fuel assemblies and for an OPR1000 core. It turns out that it is about 1.5 times faster than a subchannel code based on the two-fluid three field model and the axial domain decomposition scheme works as well as the radial one yielding a steady-state solution for the OPR1000 core within 30 s with 104 processors.

• 한국해양공학회지
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• 제33권3호
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• pp.214-221
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• 2019

A series of model tests was performed to evaluate the survivability of an articulated tower-type buoy structure under harsh environmental conditions. The buoy structure consisted of three long pipes, a buoyancy module, and top equipment. The scale model was made of acrylic pipe and plastic with a scale ratio of 1/22. The experiments were carried out at the ocean engineering basin of KRISO. The performance of the buoy structure was investigated under waves only and under combined environmental conditions from sea state (SS) 5 to 7. A nonlinear time-domain numerical simulation was conducted using the mooring analysis program OrcaFlex. The survivability of the buoy was analyzed based on three factors: the pitch motion, submergence of the top structure, and anchor reaction force. The model test results were directly compared to the results of numerical simulations. The effects of the sea state and combined environment on the performance of the buoy structure were investigated.

• 한국인터넷방송통신학회논문지
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• 제19권2호
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• pp.181-186
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• 2019

수상태양광발전 시스템은 건물옥상이나 산지 등에 개발되는 육상 태양광 발전과는 달리 주로 댐이나 저수지 등 수면위에 부력체를 이용하여 태양광 모듈을 설치하는 새로운 개념의 발전기술로서 국내 저수지 수면의 약 5 % 정도만 활용하다라도 약 4,170 MW 규모의 발전시설 건설이 가능할 만큼 개발 잠재량이 풍부하여 환경에 대한 훼손이 없이 국토의 효율적 이용이 가능한 장점이 있다. 그러나 육상과 달리 수면위에서 태양광 발전을 하기 위해서는 부력체를 이용하여 모듈 등 발전시설을 수면 위에 설치하여야 하며, 이와 더불어 수위 및 유속의 변동 등에도 안정적으로 시설을 유지할 수 있는 기술이 요구된다. 이러한 수상태양광발전 시스템에 추가적으로 안전성을 평가할 수 있는 기술기준이 현재 정립이 되어 있지 않으며 본 논문을 통해 수상태양광발전 시스템의 표준화를 위해 고려할 사항들을 정리하였다.

• 한국발생생물학회지:발생과생식
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• 제22권4호
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• pp.369-378
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• 2018

We determined the morphologic characteristics (body weight and degree of abdomen inflation) of the red spotted grouper, Epinephelus akaara, mother fish producing healthy eggs. Experimental fish were chosen from fish reared in a sea cage. The fish were divided into four size groups by body weight: 400~600, 600~800, 800~1,000, and 1,000~1,200 g and four stages (I~IV) of the degree of abdomen inflation. After hormone treatment, we observed the amount of ovulation-induced eggs, and rates of buoyancy, fertilization, embryonic survival, and hatching. As a result, mother fish with a body weight of 600 g or more spawned, and the fertilization rate, embryonic survival rate, and hatching rate were high in the 800~1,000 g range, thus showing effective ovulation induction. As a result of dividing the degree of abdomen inflation based on the anal fin of the mother fish into I-IV stages and determining hormone treatment time, the GSI was $0.9{\pm}0.2%$ at stage I, $2.3{\pm}0.2%$ at stage II, $5.6{\pm0.2%$ at stage III, and $7.9{\pm}0.9%$ at stage IV. The flotation rate and hatching rate were highest at stage III, and the fertilization rate and embryonic survival rate were highest at stage IV. Therefore, in terms of egg quality, the amount of eggs collected per mother fish, maturation, and histology were different depending on the degree of abdomen inflation. At stage III, where the abdomen inflation degree of the mother fish was based on the basal part of the dorsal fin relative to the height of the anal fin was 1, the egg quality was highest.

• 한국물환경학회지
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• 제27권4호
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• pp.391-396
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• 2011

Recently it revealed that urban runoff was one of the major source that contaminates the river, lake and estuary because it contains toxic compounds such as heavy metals and Poly Aromatic Hydrocarbons (PAHs) as well as suspended solids, organic compounds and nutrients. The engineered polymetric media in this research were developed for reducing pollutants in urban runoff and would be used to be charged in the storm water treatment equipment. The engineered media that were composed of the polypropylene was foamed to have the buoyancy and then shattered by mechanical for the efficient filtration. In this study, Spherical Expanded Polypropylene Media (SEPM), Crushed Polypropylene Media (CPM), Large Crushed Expanded Polypropylene Media (LCEPM), Small Crushed Expanded Polypropylene Media (SCEPM) were made from polypropylene. Surface characteristics of the developed media were determined by scanning electron microscopy analyses. Also, removal efficiencies of SS, $COD_{Cr}$ in the artificial road runoff and the bed headloss by media and particle pollutants captured by media were examined. Results on the surface characteristics of media indicated that SCEPM had the largest specific surface area, $0.80m^2/g$, the lowest specific gravity, 0.091, and the biggest porosity, 0.63, because of crushing the media at the process of manufacturing. And the SCEPM's removal efficiencies of TSS and $COD_{Cr}$ in the artificial road runoff were 92.9% and 83.6%, respectively and the headloss of SCEPM was the least of them.

• Advances in nano research
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• 제10권3호
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• pp.221-234
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• 2021

During the previous few years, phenomenon of bioconvection along with the use of nanoparticles showed large number of applications in technological and industrial field. This paper analyzed the bioconvection phenomenon in magnetohydrodynamic boundary layer flow of a Powell-Eyring nanoliquid past a stretchable cylinder with Cattaneo-Christov heat flux. In addition, the impacts of chemical reaction and heat generation/absorption parameter are considered. By the use of appropriate transformation, the governing PDEs (nonlinear) have been transformed and formulated into nonlinear ODEs. The resulting nonlinear ODEs subjected to relevant boundary conditions are solved analytically through homotopy analysis method which is programmed in Mathematica software. Graphical and numerical results versus physical quantities like velocity, temperature, concentration and motile microorganism are investigated under the impact of physical parameters. It is noted that velocity profile enhances as the curvature parameter A and Eyring-Powell fluid parameter M increases but a decline manner for large values of buoyancy ratio parameter Nr and bio-convection Rayleigh number Rb. In the presence of Prandtl number Pr, Eyring-Powell fluid parameter M and heat absorption parameter ��, temperature profile decreases. Nano particle concentration profile increases for increasing values of magnetic parameter Ha and thermophoresis parameter Nt. The motile density profile has revealed a decrement pattern for higher values of bio-convection Lewis number Lb and bio-convection peclet number Pe. This study may find uses in bio-nano coolant systems, advance nanomechanical bio-convection energy conversion equipment's, etc.

• 한국과학교육학회지
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• 제40권6호
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• pp.583-594
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• 2020

본 연구는 기존의 밀도라는 개념은 현상에 대한 원인자를 제공하는데 한계점이 있으며, 부력이라는 개념은 많은 오개념을 갖고 있고 정량적 계산을 이해하기 위해 지나치게 어려운 개념이 필요함에 문제를 제기하여 지레의 원리를 적용한 과정적 관점의 새로운 설명방식을 제안하였다. 새로운 설명방식은 중력이라는 근본원리와 과정적 관점이 드러나도록 지레라는 가시적 도구를 활용하여 제안되었다. 연구결과, 교사들은 많은 대안개념에 머물러 있었으며 밀도가 중력과 관련됨을 인식하는 교사는 절반이상 되지 않았다. 뿐만 아니라 이 현상을 물질적 관점으로 이해하면서 관점과 불일치하게 인식하였으나 수업처치 후 유의미한 개념 변화를 하였다(p<.000). 또한, 기존의 설명방식에 비해 원리와 과정적 관점을 잘 인식할 수 있다는 평가를 하였다. 이를 통해 지레의 원리를 도입한 과정적 과점의 설명방식에 대한 교육적 가치를 확인할 수 있었다.

• Ocean Systems Engineering
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• 제11권1호
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• pp.17-42
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• 2021

Articulated loading platforms (ALPs) belongs to a class of offshore structures known as compliant. ALP motions have time periods falling in the wind excitation frequency range due to their compliant behaviour. This paper deals with the dynamic behavior of a double hinged ALP subjected to low-frequency wind forces with random waves. Nonlinear effects due to variable submergence, fluctuating buoyancy, variable added mass, and hydrodynamic forces are considered in the analysis. The random sea state is characterized by the Pierson-Moskowitz (P-M) spectrum. The wave forces on the submerged elements of the platform's shaft are calculated using Morison's Equation with Airy's linear wave theory ignoring diffraction effects. The fluctuating wind load has been estimated using Ochi and Shin wind velocity spectrum for offshore structures. The nonlinear dynamic equation of motion is solved in the time domain by the Wilson-θ method. The wind-structure interactions, along with the effect of various other parameters on the platform response, are investigated. The effect of offset of aerodynamic center (A.C.) with the center of gravity (C.G.) of platform superstructure has also been investigated. The outcome of the analyses indicates that low-frequency wind forces affect the response of ALP to a large extent, which otherwise is not enhanced in the presence of only waves. The mean wind modifies the mean position of the platform surge response to the positive side, causing an offset. Various power spectral densities (PSDs) under high and moderate sea states show that apart from the significant peak occurring at the two natural frequencies, other prominent peaks also appear at very low frequencies showing the influence of wind on the response.

• 한국가스학회지
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• 제26권1호
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• pp.20-26
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• 2022

대기 중으로 가스가 누출될 때, 누출구에서 비교적 가까운 위치에 누출 축을 따라 형성되는 인화성 증기운의 농도 및 속도에 관해 실험, 이론 및 수치해석을 이용한 결과를 비교하였다. 제트기류 확산(Jet dispersion) 과정에 대해 실험을 통해 농도를 측정하였고, 이론적 접근법으로써 자기유사성(Self-similarity) 이론을 적용하여 속도를 계산하였다. 그리고 두 가지 CFD 도구 - 서브그리드모델을 사용하는 FLACS와 범용 CFD 도구인 CFX-를 이용해 속도와 농도를 계산하여 각 결과와 비교하였다. 자기유사성 이론과 CFD의 가장 큰 차이점은 부력항에 의한 차이이며, 이는 누출원으로부터 거리가 멀어져 누출 모멘텀이 감소할 수록 영향력이 증가한다. 결과는 누출원 반경에 대한 무차원 거리와 최대 속도에 대한 무차원 속도를 이용하여 비교한다.

• 한국안전학회지
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• 제37권2호
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• pp.1-9
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• 2022

Most factories deal with toxic or flammable chemicals in their industrial processes. These hazardous substances pose a risk of leakage due to accidents, such as fire and explosion. In the event of chemical release, massive casualties and property damage can result; hence, quantitative risk prediction and assessment are necessary. Several methods are available for evaluating chemical dispersion in the atmosphere, and most analyses are considered neutral in dispersion models and under far-field wind condition. The foregoing assumption renders a model valid only after a considerable time has elapsed from the moment chemicals are released or dispersed from a source. Hence, an initial dispersion model is required to assess risk quantitatively and predict the extent of damage because the most dangerous locations are those near a leak source. In this study, the dispersion model for initial consequence analysis was developed with three-dimensional unsteady advective diffusion equation. In this expression, instantaneous leakage is assumed as a puff, and wind velocity is considered as a coordinate transform in the solution. To minimize the buoyant force, ethane is used as leaked fuel, and two different diffusion coefficients are introduced. The calculated concentration field with a molecular diffusion coefficient shows a moving circular iso-line in the horizontal plane. The maximum concentration decreases as time progresses and distance increases. In the case of using a coefficient for turbulent diffusion, the dispersion along the wind velocity direction is enhanced, and an elliptic iso-contour line is found. The result yielded by a widely used commercial program, ALOHA, was compared with the end point of the lower explosion limit. In the future, we plan to build a more accurate and general initial risk assessment model by considering the turbulence diffusion and buoyancy effect on dispersion.