• Coupled systems mechanics
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• 제2권4호
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• pp.375-387
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• 2013

Soils consist of an assemblage of particles with different sizes and shapes which form a skeleton whose voids are filled with water and air. Hence, soil behaviour must be analyzed by incorporating the effects of the transient flow of the pore-fluid through the voids, and therefore requires a two-phase continuum formulation for saturated porous media. The present paper presents briefly the Biot's basic theory of dynamics of saturated porous media with u-P formulation to determine the responses of pore fluid and soil skeleton during cyclic loading. Kelvin elements are attached to transmitting boundary. The Pastor-Zienkiewicz-Chan model has been used to describe the inelastic behavior of soils under isotropic cyclic loadings. Newmark-Beta method is employed to discretize the time domain. The response of fluid-saturated porous media which are subjected to time dependent loads has been simulated numerically to predict the liquefaction potential of a semi-infinite saturated sandy layer using finite-infinite elements. A settlement of 17.1 cm is observed at top surface. It is also noticed that liquefaction occurs at shallow depth. The mathematical advantage of the coupled finite element analysis is that the excess pore pressure and displacement can be evaluated simultaneously without using any empirical relationship.

• 한국전자통신학회논문지
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• 제12권4호
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• pp.561-568
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• 2017

저밀도 파장분할다중화 기술을 광 집적 소자에 효율적으로 활용하기 위하여 광섬유와 평면기판 내 광 도파로 사이의 파장 선택적 광 결합기 구조가 효율적인 수단으로 고려될 수 있다. 본 논문에서는 공기 도랑 격자를 지닌 실리콘 도파로와 단일 모드 광섬유 간 결합을 고려하였다. 격자의 깊이에 따른 결합 효율의 경향성과 그 한계점을 조사하였다. 이를 위해 결합 모드 이론에 기반을 둔 모델링을 통하여 설계된 결합기 구조의 결합효율을 예측하고, 유한요소법을 이용한 시뮬레이션 결과와 정량적으로 비교 분석 하였다.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.700-709
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• 2017

This work looks at the effect of changes in kinetic parameters on simultaneous reactivity insertions and beam tube flooding in a typical material testing reactor-type research reactor with low enriched high density ($U_3Si_2-Al$) fuel. Using a modified PARET code, various ramp reactivity insertions (from $0.1/0.5 s to $1.3/0.5 s) plus beam tube flooding ($0.5/0.25 s) accidents under uncontrolled conditions were analyzed to find their effects on peak power, net reactivity, and temperature. Then, the effects of changes in kinetic parameters including the Doppler coefficient, prompt neutron lifetime, and delayed neutron fractions on simultaneous reactivity insertion and beam tube flooding accidents were analyzed. Results show that the power peak values are significantly sensitive to the Doppler coefficient of the system in coupled accidents. The material testing reactor-type system under such a coupled accident is not very sensitive to changes in the prompt neutron life time; the core under such a coupled transient is not very sensitive to changes in the effective delayed neutron fraction.

• 대한건축학회논문집:구조계
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• 제34권11호
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• pp.81-87
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• 2018

Among various types of geothermal heat pump systems, Vertical Closed-Loop Geothermal Heat Pump (VGSHP) has received increasing attention due to a variety of advantages such as the potential to be installed in a relatively small space and improved energy efficiency. In this research, the performance of VGSHP system coupled with heat storage tank was evaluated, by analyzing operational behavior of heat storage tank, the variations of heat pump energy performance due to the connection with heat storage tank, part load ratios characteristics of heat pump and the corresponding energy cost, compared to chiller and boiler based conventional system. The results of this study showed that the VGSHP system coupled with heat storage tank showed an energy saving effect of about 18% for cooling and about 73% for heating, and annual heating/cooling energy cost reduction of 43,000,000 KRW ($ 39,000), compared to the conventional air conditioning system. In addition, after considering both energy cost and initial investment cost including equipment, installation and auxiliary device expenses, payback period of approximately 11.8 years was required.

• Journal of Mechanical Science and Technology
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• 제16권7호
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• pp.950-958
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• 2002

The combustion characteristics of a low NOx burner using reburning technology have been experimentally studied. The return burner usually has three distinct reaction zones which include the primary combustion zone, the reburn zone and the burnout zone by provided secondary air. NOx is mainly produced in a primary combustion zone and a certain portion of NOx can be converted to nitrogen in the rebury zone. In the burnout zone, the unburned mixtures are completely oxidated by supplying secondary air. Liquefied Petroleum Gas (LPG) was used as main and reburn fuels. The experimental parameters investigated involve the main/reburn fuel ratio, the primary/secondary air ratio, and the injection location of rebury fuel and secondary air. When the amount of return fuel reaches to the 20-30% of the total fuel used, the overall NO reduction of 50% is achieved. The secondary air is injected by two different ways including vertical and parallel injection. The injector of secondary air is located at the downstream region of furnace for a vertical-injection mode, which is also placed at the inlet primary-air injection region for a parallel-injection mode. In case of the vertical injection of the secondary air flow, the NOx formation of stoichiometric condition at a primary combustion zone is nearly independent of the rebury conditions (locations, fuel/air ratios) while the NOx emission of the fuel-lean condition is considerably influenced by the reburn conditions. In case of the parallel injection of the secondary air, the NOx emission is sensitive to the air ratio rather than the fuel ratio and the reburning process often coupled with the multiple air-staging and fuel-staging combustion processes.

• Journal of Microbiology and Biotechnology
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• 제26권12호
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• pp.2116-2126
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• 2016

Bacterial biofilms are spatially structured communities that contain bacterial cells with a wide range of physiological states. The spatial distribution and speciation of copper in unsaturated Pseudomonas putida CZ1 biofilms that accumulated 147.0 mg copper per g dry weight were determined by transmission electron microscopy coupled with energy dispersive X-ray analysis, and micro-X-ray fluorescence microscopy coupled with micro-X-ray absorption near edge structure (micro-XANES) analysis. It was found that copper was mainly precipitated in a $75{\mu}m$ thick layer as copper phosphate in the middle of the biofilm, while there were two living cell layers in the air-biofilm and biofilm-medium interfaces, respectively, distinguished from the copper precipitation layer by two interfaces. The X-ray absorption fine structure analysis of biofilm revealed that species resembling $Cu_3(PO_4)_2$ predominated in biofilm, followed by Cu-Citrate- and Cu-Glutathione-like species. Further analysis by micro-XANES revealed that 94.4% of copper were $Cu_3(PO_4)_2$-like species in the layer next to the air interface, whereas the copper species of the layer next to the medium interface were composed by 75.4% $Cu_3(PO_4)_2$, 10.9% Cu-Citrate-like species, and 11.2% Cu-Glutathione-like species. Thereby, it was suggested that copper was initially acquired by cells in the biofilm-air interface as a citrate complex, and then transported out and bound by out membranes of cells, released from the copper-bound membranes, and finally precipitated with phosphate in the extracellular matrix of the biofilm. These results revealed a clear spatial pattern of copper precipitation in unsaturated biofilm, which was responsible for the high copper tolerance and accumulation of the biofilm.

• 한국물환경학회지
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• 제26권1호
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• pp.81-88
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• 2010

This study was conducted to find the capability of comparison of overall oxygen transfer coefficient in the membrane coupled high performance reactor (MPHCR) in treating high organic loading wastewater. Effluent quality had been analyzed while the influent organic loading rate was changed from 2 to $7kg\;COD/m^3{\cdot}day$. The oxygen transfer coefficients had been investigated using two-phase nozzle for operating variables which were internal circulation flowrate (5~8 L/min), air flow rate (0.0125~0.2 L/min), liquid temperature ($10{\sim}20^{\circ}C$), and pure-oxygen flow rate (0.0125~0.2 L/min). The overall oxygen transfer coefficient was increased with flowrate of internal circulation and air and high temperature. Especially, internal circulation flow rate showed distinct effect on overall oxygen transfer coefficient due to an increase of gas holdup and air-liquid contract area by two-phase nozzle. In the high range of organic loading rate from 4 to $7kg\;COD/m^3{\cdot}day$, the removable efficiency of COD was 91%. Conventional activated sludge process usually treat organic loading from 0.32 to $0.64kg\;COD/m^3{\cdot}day$ however, the MPHCR can treat 10 to 20 times higher if it would be compared to the conventional activated sludge process. Foaming problem often happened and caused biomass wash out of the reactor, therefore, the foaming should be controlled for the enhanced operation.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제4권2호
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• pp.111-116
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• 2000

Transboundary air pollution has recently become an area of increasing scientific interest and political concern as countries are receiving air pollutants from their neighbors. In order to gain a better understanding of the long-range transport processes of air pollutants and the source-receptor relationships among neighboring countries, an atmospheric transport model coupled with a RAMS(Regional Atmospheric Modeling System) model was applied to the East Asia region during the entire month of January 1993. The scalar transport option of the RAMS model was used to calculate special atmospheric constituents such as trace gases or aerosols. The sulfate production in clouds and rainwater and its removal processes by dry and wet deposition were considered. The sulfate budget from source regions to receptor regions was estimated by analysing the source-receptor relationships. When a specific receptor site revealed a sulfate value higher than the sulfate concentration based on its own source origin, this was taken to indicate long-range transport from another source region. The contribution ratio from various source region was calculated. The contribution ratio of dry and wet deposition was higher on the main continent of the East region. Furthermore, the high deposition amounts were identified on the west coast of Korea and the East China Sea.

• 한국항공우주학회지
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• 제39권12호
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• pp.1097-1106
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• 2011

제자리 비행하는 헬리콥터 전기체 형상으로부터 발사되는 유도무기 운동을 모사하기 위해 비정렬 중첩격자기법을 6자유도 운동 기법과 연계하여 비정상 해석을 수행하였다. 주로 터, 꼬리로터, 그리고 유도무기를 포함하는 동체로 구성되는 헬리콥터 전기체 형상에 대한 비정상 해석을 수행하였으며, 6자유도 운동 기법을 이용하여 헬리콥터에서 발사되는 유도 무기의 초기 발사 거동을 예측하였다. 발사위치 및 유도무기의 추력크기에 따른 발사거동을 비교하였으며, 주로터에서 발생하는 비정상 내리흐름에 따른 유도무기의 비행 특성을 분석하였다.

• 설비공학논문집
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• 제29권12호
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• pp.628-637
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• 2017

This study was conducted to present an effective control method for the common duct system to uniformly discharge volume flow rate exhausted from the kitchen and bathroom of each household in an apartment regardless of the position of household. Since the common duct system is installed vertically and the ventilator is installed in the terminal, the static pressure of each household decreases when vertical height increases. Therefore, the volume flow rate exhausted from each household is different. In order to improve such a phenomenon, a constant air volume damper shall be installed in a branch duct coupled with a common vertical duct system. The selected ventilator should also be able to handle the maximum volume flow rate considering diversity factor. Therefore, a uniform volume flow rate must be exhausted from all households where the hood is operated. This paper mainly focuses on suggestion of an optimum exhaust control method by comparing exhaust performance of each household according to the presence or absence of a constant air volume damper.