• 대한기계학회논문집
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• 제11권2호
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• pp.304-313
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• 1987

본 논문에서는 하부가열식 실험용 태양연못을 제작하여 열유속과 초기의 소금 농도구배를 변화시켜 가면서 실험을 수행하였다.실험을 통하여 측정한 각 층안의 온도와 소금농도구배 및 하부혼합층의 성장율 등을 바탕으로 지배방정식과 가정을 세 운뒤 이들 방정식을 풀어 실험테이터와 비교하였다.

• Structural Engineering and Mechanics
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• 제78권5호
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• pp.585-597
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• 2021

This paper presents a comparative study of analytical method, finite element method (FEM) and Multilayer Perceptron (MLP) for analysis of a contact problem. The problem consists of a functionally graded (FG) layer resting on a half plane and pressed with distributed load from the top. Firstly, analytical solution of the problem is obtained by using theory of elasticity and integral transform techniques. The problem is reduced a system of integral equation in which the contact pressure are unknown functions. The numerical solution of the integral equation was carried out with Gauss-Jacobi integration formulation. Secondly, finite element model of the problem is constituted using ANSYS software and the two-dimensional analysis of the problem is carried out. The results show that contact areas and the contact stresses obtained from FEM provide boundary conditions of the problem as well as analytical results. Thirdly, the contact problem has been extended based on the MLP. The MLP with three-layer was used to calculate the contact distances. Material properties and loading states were created by giving examples of different values were used at the training and test stages of MLP. Program code was rewritten in C++. As a result, average deviation values such as 0.375 and 1.465 was obtained for FEM and MLP respectively. The contact areas and contact stresses obtained from FEM and MLP are very close to results obtained from analytical method. Finally, this study provides evidence that there is a good agreement between three methods and the stiffness parameters has an important effect on the contact stresses and contact areas.

• 설비공학논문집
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• 제11권4호
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• pp.448-456
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• 1999

Variations of thickness and effective thermal conductivity of frost forming on the horizontal] cylinder with respect to time were measured under cross flow. The local heat flux around the cylinder was determined by measuring the radial temperature distribution in the cylinder having small holes drilled axially in which T-type thermocouples were inserted, then by using one dimensional cylindrical heat conduction equation. The thickness and the surface temperature of the frost layer around the cylinder were measured periodically while developing the frost. Each experiment was peformed by varying the Reynolds number, the temperature, and the humidity condition. Specially the dew point temperature of the most cases was below the freezing point. Experimental data showed that the frost layers on the front and the rear surface were thicker than those on the top and the bottom one which was near the separation point. The thickness and effective thermal conductivity of the frost layer were affected by inlet air velocity, temperature, and humidity. Moreover, the effective thermal conductivity and the effective thermal resistance increase with respect to time.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2001년도 학술대회 논문집
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• pp.92-94
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• 2001

We investigated quench recovery characteristics of Au/YBCO thin film meander lines. YB$a_{2}$$Cu_{3}$ $O_{7}$films were coated in-situ with a gold layer and patterned into 2 mm wide meander lines by photolithography. The limiters were tested with simulated fault currents at various source voltages. Resistance decreased first slowly and then rapidly to zero. Resistance vs. time curves for different source voltages fell on top of each other when translated horizontally. The slowly varying portion of data fell on straight lines of a slope on a semi-log scale at all source voltages. A heat balance equation reflecting heat loss from meander lines to surroundings explains these results quantitatively.

• 한국토양비료학회지
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• 제44권1호
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• pp.15-21
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• 2011

Transport of heavy metals such as Cd is affected by several rate-limiting processes including adsorption and desorption by exchange reactions in soils. In this study, column transport and batch kinetic experiments were performed to assess Cd mobility in a double-layered soil with a reclaimed saline and sodic soil (SSS) as top soil and macroporous granule (MPG) as a bottom layer. For individual soil layer having different physical and chemical properties, Cd was considered to be nonlinear reactivity with the soil matrix in layered soils. The dispersive equation for reactive solutes was solved with three types of boundary conditions for the interface between soil layers. The adsorption of Cd with respect to the saline-sodic sandy loam and the MPG indicated that the nature of the sites or the mechanisms involved in the sorption process of Cd was different and the amounts of Cd for both of samples increases with increasing amounts of equilibrium concentration whereas the amount of Cd adsorbed in saline-sodic sandy loam soil was higher than that in MPG. The results of breakthrough curve indicating relative Cd retardation accompanied by layer material and sequence during leaching showed that the number of pore volumes to reach the maximum relative concentration of 1 increased in the order of MPG, SSS, and double layer of SSS-MPG. Breakthrough curves (BTCs) from column experiments were well predicted with our double-layered model where independently derived solute physical and retention parameters were implemented.

• 한국환경농학회지
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• 제12권3호
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• pp.209-218
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• 1993

토양(土壤)중에 있어서 살충제(殺蟲劑) ethoprophos의 행동특성(行動特性)을 조사(調査)한 결과(結果)를 요약(要約)하면 다음과 같다. 실내조건(室內條件)중의 토양(土壤)중 ethoprophos분해(分解)는 일차반응식(一次反應式)에 따랐으며, 반감기(半減期)는 10, 18, $25^{\circ}C$ 에서 각각 12.4, 5.5, 2.5일이었고, Arrhenius activation energy는 73.8 KJ/mol이었다. 수분함량(水分含量)이 7, 14, 19%인 토양(土壤)에서 ethoprophos의 반감기(半減期)는 각각 46.4, 17.6, 6.9일이었으며 Empirical방정식에서 수분의존도(水分依存度)(B)값은 1.67이었다. Ethoprophos의 토양(土壤)중 흡착등온선(吸着等溫線)은 Freundlich식(式)에 따랐으며 흡착분배계수(吸着分配係數)(Kd)값은 0.27이었다. Mini-lysimeter를 이용한 실외조건(室外條件)하의 이동실험(移動實驗)에서 ethoprophos는 대부분이 $0{\sim}2cm$층위(層位)에 분포(分布)되었으며 6cm층위(層位)까지 이동(移動)되었다. 실외포장(室外圃場)에서 ethoprophos의 분해(分解)는 기상변화(氣象變化)와 밀접한 관계를 보였으며, 3월과 10월의 처리에서 반감기(半減期)는 각각 17일과 5일 정도이었고, 처리 후 약 37일에는 90%까지 분해(分解) 소실(消失)되었다. 토양(土壤)중 농약(農藥)의 행동(行動) 예측(豫測) computer model에 의한 ethoprophos의 이동성(移動性)과 잔유성(殘留性)의 예측치(豫測値)는 분석치(分析値)와 유사(類似)하였다.

• Wind and Structures
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• 제23권5호
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• pp.465-483
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• 2016

This study aims to enhance the understanding of the surface pressure distribution around rectangular bodies, by considering aspects such as the suction pressure at the leading edge on the top and side faces when the body aspect ratio and wind direction are changed. We carried out wind tunnel measurements and numerical simulations of flow around a series of rectangular bodies (a cube and two rectangular bodies) that were placed in a deep turbulent boundary layer. Based on a modern numerical platform, the Navier-Stokes equations with the typical two-equation model (i.e., the standard $k-{\varepsilon}$ model) were solved, and the results were compared with the wind tunnel measurement data. Regarding the turbulence model, the results of the $k-{\varepsilon}$ model are in overall agreement with the experimental results, including the existing data. However, because of the blockage effects in the computational domain, the pressure recovery region is underpredicted compared to the experimental data. In addition, the $k-{\varepsilon}$ model sometimes will fail to capture the exact flow features. The primary emphasis in this study is on the flow characteristics around rectangular bodies with various aspect ratios and approaching wind directions. The aspect ratio and wind direction influence the type of wake that is generated and ultimately the structural loading and pressure, and in particular, the structural excitation. The results show that the surface pressure variation is highly dependent upon the approaching wind direction, especially on the top and side faces of the cube. In addition, the transverse width has a substantial effect on the variations in surface pressure around the bodies, while the longitudinal length has less influence compared to the transverse width.

• 물과 미래
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• 제25권4호
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• pp.51-59
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• 1992

구름 물리학을 응용한 강수모형이 Geogakakos와 Bras(1984)에 의하여 개발된 바 있다. 본 연구는 그들이 제시한 강수모형을 호우모형으로 수정한 것이다. 수정의 근간은 수운적 크기분포(HSD)가 강우 생성류에 미치는 영향과 강우강도에 종속이다는 점을 반영한 것이다. 이 HSD식을 운정과 운저의 유출 수분질량 및 지상에 내린 강우량, 구름층내의 저류량식에 적용하였다. 전주 측후소의 실측 기상자료를 입력자료로 하여 본 수정모형의 매개변수를 조정하였다. 그 결과 매시간 계산 강우량이 기존모형은 큰 편차를 보였으나 본 연구를 통해 제시한 수정모형은 실측 호우에 잘 부합되었다.

• 지구물리와물리탐사
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• 제14권3호
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• pp.234-241
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• 2011

오일샌드는 고유가로 인하여 최근 활발하게 탐사 및 개발이 진행되고 있다. 오일샌드는 일반적으로 박층으로 존재하기 때문에 이의 탐지를 위해서는 지표 탄성파탐사보다는 시추공 주변의 고해상도 영상화가 장점인 다성분 VSP 탐사가 효과적이다. 또한 중합전 위상막 구조보정의 경우, 단방향 파동방정식을 이용하기 때문에 다성분 자료를 이용한 영상화에 효과적이다. 이 연구에서는 박층 오일샌드의 영상화를 위하여, 다성분 역VSP 탐사자료를 이용한 중합전 위상막 구조보정의 적용성을 고찰하였다. 중합전 위상막 구조보정에 사용할 다성분 역VSP 탐사자료의 전처리 과정으로 입사각과 회전변환을 이용한 파 분리 방법을 제안하고, 이를 합성탄성파탐사자료를 통하여 검증한 결과 파 분리가 효과적으로 되는 것을 확인하였다. 또한 분리된 P파와 PS파 자료를 이용하여 구조보정을 실시하였을 시, PS파 구조보정 결과가 P파 구조보정 결과보다 넓은 반사면의 영상화가 가능하고 고해상도의 영상을 획득하였다. 그리고 캐나다 오일샌드 매장지역을 모사한 합성탄성파탐사자료를 생성하고 이를 영상화 한 결과, P파 구조보정 결과보다 PS파를 이용한 구조보정 결과가 박층 오일샌드의 상 하부 경계면을 정확하게 영상화하였다.

• 대한기계학회논문집B
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• 제34권10호
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• pp.925-931
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• 2010

본 논문은 공동 주위 난류유동특성을 LES 기법으로 수치해석을 수행하여 알아보았다. 본 연구에 적용된 레이놀즈수는 공동 깊이만큼의 높이 h 에서의 유속을 기준으로 $1.0{\times}10^5$ 이며 3 차원 공동에서의 유동특성을 알아보았다. 적절한 비압축성 Filtered Navier-Stokes 방정식을 적용하기 위해, 계산격자를 공동 표면 근처에는 조밀하게 멀어질수록 성기게 생성하였으며, 이는 계산시간을 단축시키며 빠른 수렴을 도와준다. 또한, Boussinesq 가설을 subgrid-scale 난류모델에 적용하였고, Subgrid-scale 난류점성을 얻기 위해 smagorinsky-Lilly SGS 모델을 적용하였으며, 그 때의 CFL 수는 1.0 이다. 또한, 본 논문은 서로 다른 4 가지 형상의 공동의 및 입구조건의 변화에 따른 유동 특성도 함께 연구되었다.