• 한국공간구조학회논문집
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• 제13권2호
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• pp.67-73
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• 2013

This paper attempted to bridge this gap by identifying the number of flat-plate solar collectors. The characteristics of wind pressure coefficients acting on flat-plate solar collectors which are most widely used were investigated for various wind direction. Findings from this study found that the location where the maximum wind pressure coefficient occurred in the solar collector was the edge of the collector. Regarding the characteristics according to the number of collectors, the paper found that downward wind pressure coefficient of the lower edge of the collector was higher than the upward wind pressure coefficient of the upper edge of the collector in the basic module (1 piece). However, as the number of collectors increases, the upward wind pressure coefficient of the upper edge become higher than the downward wind pressure coefficient of the lower edge. Finally yet important, it was found that the location of the maximum wind pressure coefficient was changed according to the number of solar collectors.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2008년도 정기총회 및 학술발표대회
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• pp.101-104
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• 2008

In this study, rainfall adjust and forecasting using artificial neural network(ANN) which includes a correlation coefficient is application in Seoul region. It analyzed one-hour rainfall data which has been reported in 25 region in seoul during from 2000 to 2006 at rainfall observatory by AWS. The ANN learning algorithm apply for input data that each region using cross-correlation will use the highest correlation coefficient region. In addition, rainfall adjust analyzed the minimum error based on correlation coefficient and determination coefficient related to the input region. ANN model used back-propagation algorithm for learning algorithm. In case of the back-propagation algorithm, many attempts and efforts are required to find the optimum neural network structure as applied model. This is calculated similar to the observed rainfall that the correlation coefficient was 0.98 in missing rainfall adjust at 10 region. As a result, ANN model has been for suitable for rainfall adjust. It is considered that the result will be more accurate when it includes climate data affecting rainfall.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1079-1088
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• 2018

A line overload emergency control strategy based on the source-load synergy coefficient is proposed in this paper. First, the definition of the source-load synergy coefficient is introduced. When line overload is detected, the source-load branch synergy coefficient and source-load distribution synergy coefficient are calculated according to the real-time operation mode of the system. Second, the generator tripping and load shedding control node set is determined according to the source-load branch synergy coefficient. And then, according to the line overload condition, the control quantity of each control node is determined using the Double Fitness Particle Swarm Optimization (DFPSO), with minimum system economic loss as the objective function. Thus load shedding for the overloaded line could be realized. On this basis, in order to guarantee continuous and reliable power supply, on the condition that no new line overload is caused, some of the untripped generators are selected according to the source-load distribution synergy coefficient to increase power output. Thus power supply could be restored to some of the shedded loads, and the economic loss caused by emergency control could be minimized. Simulation tests on the IEEE 10-machine 39-bus system verify the effectiveness and feasibility of the proposed strategy.

• Tribology and Lubricants
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• 제36권6호
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• pp.324-331
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• 2020

Wedging in a frictional elastic system is defined if the state of stick exists after the external loading on the system is removed. This paper presents a method to determine the critical coefficient of wedging for an elastic frictional system by considering the separation state. Wedging is always possible if the coefficient of friction exceeds a critical value known as the critical wedging coefficient. This method requires two concepts: a necessary and sufficient condition for wedging, which can be interpreted as positive spanning sets of constraint vectors existing in the wedged system, and the minimal positive basis that enables a minimum wedging coefficient. The algorithm based on the positive spanning concept is repeatedly executed after eliminating nodes from the contact stiffness matrix, for which the separation states are impending. The simulation results show that once a node enters the separation state, it never returns to the contact state again and the critical wedging coefficient reduces during repeated algorithm execution. The benefit of this method is that the computation time permits handling models with large numbers of contact nodes. The algorithm can also numerically find the critical wedging coefficient, thereby contributing to fastening and assembly performance improvements in mechanical systems.

• 한국농공학회지
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• 제12권3호
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• pp.2003-2012
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• 1970

In order to the influence of grain size distribution on compressive strength and coefficient of permeability, unconfined compression test and permeability test were performed for seventy samples that have various grain-size distributions. Its results are as follows: 1. Maximum unconfined compressive strength appears at the dry side of optimum moisture content. 2. Unconfined compressive strength is proportional to the increase of percent passing of No. 200 sieve. 3. Precent of deformation in failure increases in proportion to the increase of percent passing of No. 200 sieve, and modulus of No. 200 sieve, and modulus of deformation also increases in proportion to percent passing of No. 200 sieve. 4. Unconfined compressive strength increases in proportion to uniformity coefficient, liquid limit and plastic index, but it decreases gradually according to the increase of coefficient of grading and classification area. 5. Maximum dry density decreases according to the increase of void ratio. 6. Coefficient of permeability decreases according to the increase of percent passing of No. 200 sieve, and when percent of No. 200 sieve, and when percent passing of No. 200 enlarged more than 40%, it becomes less than $10^{-6}cm/sec$ which is the limit of coefficient of permeability of core material for earth dam proposed by Lee. 7. Coefficient of permeability increases according to the increase of coefficient of grading, classification area and index of Talbot formula r, but it was rather decrease by the increase of uniformity coefficient. 8. Coefficient of permeability seems to depend on the size and the shape of the flow path which is a series of void to be concerned by the size and the proprton of soil grain, even though void ratios are same.

• 한국해안·해양공학회논문집
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• 제21권3호
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• pp.216-223
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• 2009

수면보다 높은 사각기둥 저항체가 등간격으로 배치되어 있는 경우의 상당저항계수 식의 횡방향에 따른 항력상호작용계수를 연구하여 제안하였다. 저항체의 횡방향 이격거리에 따른 에너지 손실이 오리피스의 공극률에 따른 에너지 손실과 동일하다고 가정하고 오리피스의 에너지 손실계수를 차용하여 횡방향 항력상호작용계수를 제안하였다. 이 항력상호작용계수를 사용하는 상당저항계수 식을 김 등(2008)에 의해 사용된 수리조건에 대해 그 해석능력이 검증된 FLOW-3D를 이용하여 수치실험한 결과와 비교하였다. 그 결과가 잘 일치하였고 이로부터 바닥마찰뿐만 아니라 수면보다 높은 정방형 다열기둥의 종방향 및 횡방향 이격거리에 따라 변화되는 저항정도를 고려할 수 있는 제안된 상당저항계수 식의 타당성을 검증하였다.

• 멤브레인
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• 제12권2호
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• pp.90-96
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• 2002

멤브레인 여과 실험에서 얻어진 데이터 처리에 간단한 수치해석을 적용하여 삼투압(osmotic pressure) 과 구배확산계수(gradient diffusion coefficient)를 도출하는 새로운 방법론을 제시하였다. 삼투압과 구배확산계수는 이론 및 실험적으로 쉽게 구할 수 없는 물리적 특성치로서 멤브레인 여과의 특성 규명에 중요하다. 모델 라텍스 콜로이드의 여과시간에 따른 투과플럭스(permeate flux) 값과 이에 대한 수치적분과 수치미분 데이터로부터 분산된 입자농도의 함수인 삼투압 관계식을 구했다. 이로부터 계산된 열역학적 계수(thermodynamic coefficient)는 입자농도가 증가할수록 감소하는 거동을 보였고, 여기에 기존에 제시되어 있는 수력학적 계수(hydrodynamic coefficient)를 도입하여 구배확산계수를 산출하였다. 아울러, 본 연구에서 계산된 입자농도에 따른 구배확산계수의 결과와 동일한 멤브레인과 라텍스 콜로이드의 여과에 대해서 기존에 통계역학적 시뮬레이션으로 예측한 결과를 비교하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.1053-1056
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• 2008

콘크리트의 투수계수는 콘크리트 구조물의 내구성능 및 미세구조의 밀실성을 판단하는 핵심적인 재료 매개변수이다. 투수계수를 산정하기 위한 많은 연구들이 있었으나, 시멘트 페이스트 및 골재 각각이 콘크리트의 투수성능에 미치는 영향을 다룬 연구는 드물다. 더우기, 탄산화가 염소이온의 확산계수에 큰 영향을 미칠 수 있음에도 불구하고, 탄산화된 콘크리트에 대한 확산계수를 다룬 연구는 더욱 드문 실정이다. 본 연구의 목적은 탄산화 및 비탄산화된 콘크리트의 투수계수를 추정할 수 있는 기초적 접근방법을 개발하는 것이다. 본 연구에서는 미세구조 모델 및 시멘트의 경화특성을 기초로 투수계수를 산정할 수 있는 해석적 기법이 개발되었다. 본 연구에서는 시간단계별로 변화하는 투수계수의 해석과 중성화된 콘크리트의 투수계수이다. 탄산화된 콘크리트에서 감소된 공극량이 계산되었으며 이는 투수계수의 산정에 이용되었다. 본 연구결과는 실험적 결과를 얻어서 상호 비교하여 검증하였다.

• 한국수자원학회논문집
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• 제54권12호
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• pp.1223-1232
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• 2021

본 연구에서는 연중 일유량의 불균등 정도를 파악하기 위해 "유량 지니계수"라는 새로운 개념의 분석방법을 제시한다. 유량 지니계수는 오름차순한 연중 일유량 발생일자의 누계백분율과 일최빈유량의 오름차순 누계백분율과의 면적관계를 이용하여 산정한다. 유량 지니계수는 0~1 사이의 값으로 표현되며, 불균등의 정도는 5단계로 구분할 수 있다. 유량 지니계수를 이용하면 상류 지점에 대한 하류 지점의 유량 안정도를 산정할 수 있다. 또한, 유황분석 기준유량별로 불균등에 미치는 영향의 정도를 수치적으로 파악할 수 있다. 4대강 본류 상·하류 8개 지점의 장기간 일유량 자료를 이용하여 유량 지니계수의 적용성을 검토하였다. 유량지니계수는 상류 댐에 의한 하류에서의 유량조절 효과를 분석하는 데에도 활용될 수 있을 것이다.

• Transactions on Electrical and Electronic Materials
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• 제13권4호
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• pp.196-199
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• 2012

CdS thin film was prepared on glass substrate by chemical bath deposition in an alkaline solution. The optical properties of CdS thin film were investigated using spectroscopic ellipsometry. The real (${\varepsilon}_1$) and imaginary (${\varepsilon}_2$) parts of the complex dielectric function ${\varepsilon}(E)={\varepsilon}_1(E)+i{\varepsilon}_2(E)$, the refractive index n(E), and the extinction coefficient k(E) of CdS thin film were obtained from spectroscopic ellipsometry. The normal-incidence reflectivity R(E) and absorption coefficient ${\alpha}(E)$ of CdS thin film were obtained using the refractive index and extinction coefficient. The critical points $E_0$ and $E_1$ of CdS thin film were shown in spectra of the dielectric function and optical constants of refractive index, extinction coefficient, normal-incidence reflectivity, and absorption coefficient. The dispersion of refractive index was analyzed by the Wemple-DiDomenico single-oscillator model.