• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.793-798
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• 2017

In modern naval ships, an infrared signature suppression (IRSS) system is used to reduce the metal surface temperature of the heated exhaust pipe and high-temperature exhaust gases generated from the propulsion system. Generally, the IRSS systems used in Korean naval ships consist of an eductor, mixing tube, and diffuser. The diffuser reduces the temperature of the metal surface by creating an air film due to a pressure difference between the internal gas and the external air. In this study, design variables were selected by analyzing the shapes of a diffuser designed by an advanced overseas engineering company. The characteristics of the design variables that affect the performance of the IRSS were investigated through the Taguchi experimental method. A heat flow analysis technique for IRSS systems established in previous studies was used analyze the performance of the diffuser. The performance evaluation was based on the area-averaged value of the metal surface temperature and exhaust gas temperature at the outlet of the diffuser, which are directly related to the intensity of the infrared signature. The results show that the temperature of the exhaust gas was significantly affected by changes in the diameter of the diffuser outlet, and the temperature of the diffuser's metal surface was significantly affected by changes in the number of diffuser rings.

• Journal of Korea Water Resources Association
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• v.43 no.11
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• pp.995-1009
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• 2010

Accelerated soil erosion due to extreme climate change, such as increased rainfall intensity, and human-induced environmental changes, is a widely recognized problem. Existing soil erosion models are generally based on the gross erosion concept to compute annual upland soil loss in tons per acre per year. However, such models are not suitable for event-based simulations of erosion and deposition in time and space. Recent advances in computer geographic information system (GIS) technologies have allowed hydrologists to develop physically based models, and the trend in erosion prediction is towards process-based models, instead of conceptually lumped models. This study aims to propose an effective and robust distributed rainfall-sediment yield-runoff model consisting of basic element modules: a rainfall-runoff module based on the kinematic wave method for subsurface and surface flow, and a runoff-sediment yield-runoff model based on the unit stream power method. The model was tested on the Cheoncheon catchment, upstream of the Yongdam dam using hydrological data for three extreme flood events due to typhoons. The model provided acceptable simulation results with respect to both discharge and sediment discharge even though the simulated sedigraphs were underestimated, compared to observations. The spatial distribution of erosion and deposition demonstrated that eroded sediment loads were deposited in the cells along the channel network, which have a short overland flow length and a gentle local slope while the erosion rate increased as rainfall became larger. Additionally, spatially heterogeneous rainfall intensity, dependant on Thiessen polygons, led to spatially-distinct erosion and deposition patterns.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.2
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• pp.79-85
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• 2018

A two-way pump can reduce costs by draining and circulating water out and into the drum of the washing machine using a single motor whereas a conventional one-way pump uses two motors for doing the same function. However, when the water is drained through the drainage outlet in the two-way pump casing, a backward or inhalation flow occurs and the water flows to the circulation outlet. Likewise, when the water is circulated, the backward flow or inhalation makes the water flow to the drainage outlet. In this study, design optimization of the two-way pump casing is performed to maximize its performance while improving backward flow and inhalation occurring inside of the pump casing. For this, design variables of the pump casing that mainly affect the performance of the pump such as flow rate and torque of the motor were selected through the analysis of mean. Using response surface models for the performances, the ratio of the flow rate to the torque was maximized with satisfying the constraints for the back flow and inhalation through design optimization.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.9
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• pp.599-608
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• 2022

Urban air mobility (UAM) equipped with rotor system is subject to ground effect at vertiport during takeoff and landing. The aerodynamic performance of the aircraft in ground effect should be analyzed for the safe operation. In this study, The ground effects on the aerodynamic performance and wake structure of the quadcopter electric vertical takeoff and landing (eVTOL) configuration equipped with coaxial counter-rotating propellers were investigated by using the lattice Boltzmann method (LBM). The influence of the ground effect was observed differently in the upper and lower propellers of the coaxial counter-rotating propeller system. There was no significant change in the aerodynamic performance of the upper propeller even if the propeller height above the ground was changed, whereas the averaged thrust and torque of the lower propeller increased significantly as propeller height decreased. In addition, the amplitude of the thrust fluctuation tended to increase as the propeller height decreased. The propeller wake was not sufficiently propagated downstream and was diffused along the ground due to the outwash flow developed by the ground effect. The impingement of the rotor wakes on the ground and a fountain vortex structure were observed.

• Journal of Nutrition and Health
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• v.12 no.2
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• pp.1-13
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• 1979

성장발육하는 시기에 영양과 성장하는 아동들의 체위와는 밀접한 관계가 있고 또한 영양부족과 그로 말미암아 자라나는 이학적 소견과도 불가분의 관계가 있기 때문에 그동안 우리나라에서 부분적, 단편적으로 연구 발표된 문헌을 중심으로 그를 검토 고찰하여 보았다. 그 결과를 요약하면 다음과 같다. 우리나라 아동들이 출생후 6개월까지는 주로 모유에 의존하고, 약간이 인공영양에 의존하고 있는데, 이 시기에는 다른 선진제국의 어린이들의 성장발육과의 별 차이가 없었다. 그러나 이유기인 $6{\sim}30$개월 사이에는 우리나라 어머니들의 이유에 대한 지식이 빈약하고 이들 음식물을 그대로 아기들에게 적용하기 힘든 이유등으로 아이들에게 보급해서 주는 음식물이 빈약함으로 말미암아 다른 선진제국 아이들에 비해서 이 시기에 체위가 많이 떨어지고 빈혈현상을 나타내는 것을 볼 수 있다. 이때 고양군에서 농민의 아동들에 대해서 시행한 영양조사 내용을 보면, 전체 칼로리도 부족되고 특히 단백질, 철분, 칼슘, 비타민 A, B복합제가 전반적으로 부족되는 것을 알았다. 이는 어머니들의 육아와 이유식에 대한 지식의 결집도 중요한 역할을 했겠거니와 더욱더 중요한것은 우리나라 어른들의 식습관이, 민족적 전통적으로 짜고, 매웁고, 딱딱해서 이를 아기들에게 그대로 적응해서 먹이기가 힘든 것도 더 중요한 이유가 된다. 어른들을 위한 음식물에도 맵지 않고, 짜지 않으며, 아기들도 즐겨 먹을 수 있는 유동식 혹은 반유동식으로 된 영양가치가 좋은 음식물을 발전시켜 애용하도록 하는 것이 민족적인 긴급한 과제라고 하겠다. 그렇지 않으면 선진제국 모양으로 이유기에 있는 아이들을 위해서 아이들이 즐겨 먹을 수 있는 이유식을 크게 발전시켜서 이유기의 아이들에게 저렴하게 공급할 수 있는 생산공장과 제도의 마련이 긴급하다고 하겠다. 우리 민족의 체위를 향상 시키는데 영양학자와 영양사들에게 기대 하는 바가 크다. 육아하는 어머니의 교육정도와경제적인 면이 아기 체위에 주는 영향에 대한 연구에서는 교육정도가 높고, 경제적으로 좋은 위치에 있는 엄마가, 교육정도가 낮고 경제적으로 가난한 위치에 있는 어머니보다 아이들 체위에 훨씬 좋게 기를 수 있다는 것을 알았다. 특히 이유기에 들어간 6개월 이후에 체위 격차가 심한 것을 볼 때 보충해 주는 음식물의 적절한 보급이 얼마나 필요한가를 말해 주는 것이며 이에는 어머니의 교양과 열의와 경제적 뒷받침이 얼마나 필요하다는 것을 말해주는 것이다. 지역별로 서울에서 부유층 가정과 학교 아동, 농촌 지역 가정과 학교아동, 강원도 산간지역 가정과 학교 아등으로 나누어서 자라나는 아동들의 체위와 이학적 소친을 연구 조사한 바로는 서울 부유층이 제일 좋고 그 다음이 서울 빈한층, 강원도 산간지역 아동의 순으로 좋았으며 농촌지역 아종은 체위가 가장 떨어졌다. 구각증, 구내염등은 강원도 산간지역 아동에 제일 많고, 다음이 농촌지역, 서울 판자촌지역의 순으로 많으며 서울부유충지역이 가장 적어서 이는 산간일수록 또 는 빈한할수록 등물성단백질이 부족되는 것을 말해 주는 것이다. 지역별 혈색소치는 109gm/100ml 이하인 경우가 서울 빈한층가정 아동에 제일 많아서 51.7%나 되며 다음이 산간지역가정, 농촌지역가정의 순으로 많으며 서울부유층가정 아동은 2.2%에 지나지 않는다. 한국아등의 체위와 일본아동의 체위를 비교해 본 바로는 출생 후 약 12개월까지는 별차가 없지만 그후로는 점차로 그 격차가 심해져서 $12{\sim}15$세 사이에 평균체중면에서 5kg정도, 신장면에서 5cm정도의 큰 격차를 나타냈다. 그러나 그후로 성인이 되어감에 따라서 그 격차는 좁아졌다. 이는 일본국이 경제적으로 우리보다 우위에 있음에 따라서 아이들 성장에 필요한 영양분을 적기에 적당하게 공급해 주었기 때문이며 우리는 많은아이들이 가만하기 때문에 그 나이에 맞는 영양분 보급을 적당히 하지 못한 결과로 생각할 수 밖에 없다. 한국 아동의 발육표준치를 1965년초에 측정한 것과 1975년도에 측정한 것을 비교해 본 결과 1975년 치는 1965년도치에 비해 체중과 신장 면에서 상당히 증가하였다. 이는 우리라라 경제상태가 좋아지면서 굶는 아이들이 적어지거나 없어졌을 뿐만 아니라 식품 내용이 개선된 때문으로 해석된다. 따라서 민족의 체위가 개선되고 향상되려면 제일 먼저 해결되어야 할 문제는 국가의 경제력이 향상될뿐만 아니라 빈부의 격차가 적어져서 우리나라에 생을 받은 사람은 누구나 굶는 자가 없이 균형 있는 영양분을 충분히 섭취 할 수 있는기회를 갖도록 되어야 하겠다. 영양학자와 식품관리자들은 우러나라 아이들이 타고난 체위의 잠재성을 충분히 키우기 위해서 어떠한 음식물이 얼마나 필요한지 계산하여 이를 작물로 충분히 충당할 수 있도륵 계획해서 농수산물을 생산하도록 해야겠다. 영양학자들은 우리 민족의 음식물을 개선해서 아기들이 즐겨 먹을 수 있는 어른들의 음식물, 영양식을 발전시켜 이유기에 받는 우리 어린아기들의 수난을 조속히 극복하는 것이 바람직하다. 또한 영양에 대한 교육을 국민학교, 중학교 교과과정에 많이 넣어서 교육하고 영양에 대한 교육과 보급을 조직적으로, 신문, 라디오, 텔레비젼등을 통해서 성인교육을 강화해서 모든 국민들이 적은 돈을 가지고도 보다 나은 영양물을 구해서 섭취할 수 있는 지혜를 가지도록 해야겠다. 국민학교 재학중 및 졸업시기를 전후딘서 체위가 많이 떨어지며 그 영향이 일생동안 간다는 것을 감안할 때 국민학교에서 점심 한끼라도 영양식을 보급해서 우리 국민체위 향상을 위해서 나라에서 직접적으로 공헌하는 바가 있었으면 한다.

• Journal of Internet Computing and Services
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• v.16 no.1
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• pp.57-65
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• 2015

As information technology fusion is accelerated, the researches to improve the quality and productivity of crops inside a plant factory actively progress. Advanced growth environment management technology that can provide thermal environment and air flow suited to the growth of crops and considering the characteristics inside a facility is necessary to maximize productivity inside a plant factory. Currently running plant factories are designed to rely on experience or personal judgment; hence, design and operation technology specific to plant factories are not established, inherently producing problems such as uneven crop production due to the deviation of temperature and air flow and additional increases in energy consumption after prolonged cultivation. The optimization process has to be set up in advance for the arrangement of air flow devices and operation technology using computational fluid dynamics (CFD) during the design stage of a facility for plant factories to resolve the problems. In this study, the optimum arrangement and air flow of air circulation fans were investigated to save energy while minimizing temperature deviation at each point inside a plant factory using CFD. The condition for simulation was categorized into a total of 12 types according to installation location, quantity, and air flow changes in air circulation fans. Also, the variables of boundary conditions for simulation were set in the same level. The analysis results for each case showed that an average temperature of 296.33K matching with a set temperature and average air flow velocity of 0.51m/s suiting plant growth were well-maintained under Case 4 condition wherein two sets of air circulation fans were installed at the upper part of plant cultivation beds. Further, control of air circulation fan set under Case D yielded the most excellent results from Case D-3 conditions wherein air velocity at the outlet was adjusted to 2.9m/s.

• Journal of Soil and Groundwater Environment
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• v.12 no.5
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• pp.39-53
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• 2007

Generally, fractured medium can be described with some key parameters, such as hydraulic conductivities or random field of hydraulic conductivities (continuum model), spatial and statistical distribution of permeable fractures (discrete fracture network model). Investigating the practical applicability of the well-known conceptual models for the description of groundwater flow in fractured media, various types of hydraulic tests were applied to studies on the highly fractured media in Geumsan, Korea. Results from single-hole packer test show that the horizontal hydraulic conductivities in the permeable media are between $7.67{\times}10^{-10}{\sim}3.16{\times}10^{-6}$ m/sec, with $7.70{\times}10^{-7}$ m/sec arithmetic mean and $2.16{\times}10^{-7}$ m/sec geometric mean. Total number of test interval is 110 at 8 holes. The number of completely impermeable interval is 9, and the low permeable interval - below $1.0{\times}10^{-8}$ m/sec is 14. In other words, most of test intervals are permeable. The vertical distribution of hydraulic conductivities shows apparently the good correlation with the results of flowmeter test. But the results from the cross-hole test show some different features. The results from the cross-hole test are highly related to the connectivity and/or the binary properties of fractured media; permeable and impermeable. From the viewpoint of the connection, the application of the general stochastic approach with a single continuum model may not be appropriate even in the moderately or highly permeable fractured medium. Then, further studies on the investigation method and the analysis procedures should be required for the reasonable and practical design of the conceptual model, with which the binary properties, including permeable/impermeable features, can be described.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.19 no.2
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• pp.131-146
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• 2014

High-resolution seismic profiles coupled with sediment sampling were analyzed to investigate the acoustic characters and distribution patterns of the late Holocene sediments in Gamak Bay of the South Sea, Korea. The mean grain size of surficial sediment lies around $6.3{\sim}9.7{\Phi}$. Sediments in the bay consist of silt and clay with progressive decrease toward the inner bay. The seismic sedimentary sequence overlying the acoustic basement can be divided into two sedimentary units (GB I and II) by a prominent mid-reflector (Maximum Flooding Surface; MFS). The acoustic basement occurs at the depth between 20 m and 40 m below the sea-level and deepens gradually southward. The GB I, mostly occupying the channel-fill, is characterized by reflection-free seismic facies. It can be formed as late Transgressive System Tract (TST), interpreted tidal environment deposits. MFS appears at the depth of about 15~28 m below the sea-level and is well defined by even and continuous reflectors on the seismic profile. The GB II overlying MFS is composed of acoustically transparent to semitransparent and parallel internal reflectors. GB II is interpreted as the Highstand System Tract (HST) probably deposited during the last 6,000 yrs when the sea level was close to the present level. Especially, it is though that the GB II was subdivided into two layers (GB II-a and II-b) by a HST-reflector and this was classified by wind, sea water flux, and tidal current.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.4
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• pp.286-294
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• 2014

The purpose of this study is to investigate the effects of applying density current generator (hereafter referred to as DCG to large lakes on the operating conditions of DCG, de-stratification, water quality improvement and inhibition of algae occurrence. As a result of a survey conducted to derive the optimum operating parameters of DCG in a condition to minimize eco-toxicity, the following conclusions were obtained. During the survey period, a marked stratification appeared in September to October 2011 and May 2012. At this time, the average depth of water to form thermocline was found to be $5{\pm}2$ m, so the location of discharge port for the operation of DCG was determined to be about 5 m below from the surface. To minimize the adverse effects of benthos and obtain the effect of water mixture at the time of water circulation, the mixing ratio of surface water and deep water was designed to be 3:1 by means of ecotoxicological assessment on the DCG operating characteristics. To select the appropriate operating hours for DCG, DCG was operated by 12 hr, 24 hr, 36 hr and 48 hr. As its result, the formation of thermocline did not occur during the operation of 36 hr. Also, It was effected that start reoperating from 3rd day after stop 2days under the condition of operated during 36 hr with calculated power consumption. Under the above conditions, the results of DO and water temperature analysis during the operation of DCG showed that the stratification, which was distinct previously, appeared to be weak, and relatively lower levels than those before operation were found as a result of water quality analysis on COD and chlorophyll-a, which leads to the conclusion that the water body is maintained at a stable condition due to the circulation of water by the occurrence of density current resulting from the operation of DCG.