• Wind and Structures
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• 제20권6호
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• pp.763-791
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• 2015

"Wind and Ports" is a European project that has been carried out since 2009 to handle wind forecast in port areas through an integrated system made up of an extensive in-situ wind monitoring network, the numerical simulation of wind fields, the statistical analysis of wind climate, and algorithms for medium-term (1-3 days) and short term (0.5-2 hours) wind forecasting. The in-situ wind monitoring network, currently made up of 22 ultrasonic anemometers, provides a unique opportunity for detecting high resolution thunderstorm records and studying their dominant characteristics relevant to wind engineering with special concern for wind actions on structures. In such a framework, the wind velocity of thunderstorms is firstly decomposed into the sum of a slowly-varying mean part plus a residual fluctuation dealt with as a non-stationary random process. The fluctuation, in turn, is expressed as the product of its slowly-varying standard deviation by a reduced turbulence component dealt with as a rapidly-varying stationary Gaussian random process with zero mean and unit standard deviation. The extraction of the mean part of the wind velocity is carried out through a moving average filter, and the effect of the moving average period on the statistical properties of the decomposed signals is evaluated. Among other aspects, special attention is given to the thunderstorm duration, the turbulence intensity, the power spectral density and the integral length scale. Some noteworthy wind velocity ratios that play a crucial role in the thunderstorm loading and response of structures are also analyzed.

• Journal of the Korean Data and Information Science Society
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• 제22권6호
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• pp.1089-1096
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• 2011

본 논문에서는 댐으로 물이 복합 포아송 과정을 따라 유입되고, 댐 수위가 적정수준 ${\lambda}$를 넘어서게 되면 방출률 M으로 물을 방출하는 무한 댐 모형이 고려된다. 한번 내리는 비의 양이 지수분포를 따르는 경우, 정상상태에서 댐 수위의 확률적 성질들을 구한다. 댐 운영과 관리에 관련된 여러 비용을 고려한 후, 장시간에 걸친 단위시간당 평균 비용을 구하고, 이를 최소화하는 방출률 M과 적정수준${\lambda}$가 유일하게 존재함을 보인다. MATLAB을 이용하여 수치적인 결과도 함께 보인다.

• 한국기계가공학회지
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• 제15권3호
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• pp.28-35
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• 2016

Forging operations are non-stationary processes occurring because of indirect pressure, generally, under conditions of three-dimensional stress and deformation. Furthermore, due to friction and the constraints of die geometry, deformation is not homogeneous. Material flow and deformation are largely determined by the shape of the tools. It is well known that net-shape forging can improve the mechanical strength of the final product as well as reduce material waste. Oxygen-free copper that is used for electrical and electronic components has excellent electrical and thermal conductivity. Oxygen-free copper parts have a low productivity in cutting process. Thus, the forging process is performed in order to improve the low productivity in cutting process. The forging of oxygen-free copper for electrode body parts was modeled using finite element simulation and forging experiments that were conducted for producing electrode body parts at room temperature. In order to reduce the cost of cutting products, the forging was performed in a closed cavity to obtain near-net or net-shape parts.

• 한국조리학회지
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• 제20권6호
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• pp.254-261
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• 2014

레토르트 김치찌개의 최적 가열 살균 조건 설정을 위해 정치식 및 회전식 레토르트 방식을 이용하여 최적화 연구를 수행하였다. 연구 고찰 결과 가열 특성은 레토르트 살균 방식에 의해 영향을 많이 받아 회전식에서는 $120.7^{\circ}C$, 13분, 정치식에서는 $120.7^{\circ}C$, 20분의 가열 살균이 최적 공정 조건으로 나타났다. 두 가지 레토르트 방식에서 김치찌개 파우치 내 냉점의 $F_0$ 값은 동일한 결과를 보여 회전식이 정치식 보다 승온이 더 빠르며, 또한 빠른 온도 상승으로 시료 위치별 온도 편차도 적게 발생하였다. 이러한 전열 특성으로 냉점에서 동일 $F_0$ 값 도달에 있어 회전식 레토르트 방식이 정치식에 비해 가열 살균시간이 35~45%의 단축되는 큰 장점이 있어 전반맛, 향, 색상과 조직감이 유의차 (p<0.05) 있게 향상되었다. 이러한 장점으로 육, 해물, 야채 등의 고형물이 포함되어 있는 다양한 메뉴의 레토르트 파우치 식품의 관능품질이 크게 향상될 것으로 기대된다.

• 한국세라믹학회지
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• 제53권3호
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• pp.295-300
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• 2016

To investigate the thermal conductivity and the structural properties of naturally cooled excimer-laser annealed Si, molecular-dynamics (MD) simulations have been performed. The thermal conductivity of crystalline Si (c-Si) was measured by direct method at 1000 K. Steady-state heat flow was measured using a stationary temperature profile; significant deviations from Fourier's law were not observed. Reliable processes for measuring the thermal conductivity of c-Si were presented. A natural cooling process to admit heat flow from molten Si (l-Si) to c-Si was performed using an MD cell with a size of $48.9{\times}48.9{\times}97.8{\AA}^3$. During the cooling process, the temperature of the bottom $10{\AA}$ of the MD cell was controlled at 300 K. The results suggest that the natural cooling system described the static structural property of amorphous Si (a-Si) well.

• 한국기계가공학회지
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• 제5권1호
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• pp.7-12
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• 2006

Recently, the fractal interpolation methods have been widely introduced and used to estimate and analyze various theoretical and experimental data. Because of the chaotic behaviors of dynamic cutting force data, some method for end-milling force analysis must be used. The fractal analysis used in this paper is fractal linear interpolation and fractal dimension. Also, several methods for computing fractal dimensions have been used in which the fractal dimension of the typical dynamic end-milling force was calculated according to number of data points that are generally lower than 200 data points sampled. This fractal analysis shows a possible prediction of end-milling force that has some dynamic chatter property or stationary property in endmilling operation.

• 대한산업공학회지
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• 제42권1호
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• pp.30-37
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• 2016

A multi-server queueing system with an infinite buffer and impatient customers is analyzed. The system operates in the finite state Markovian random environment. The number of available servers, the parameters of the batch Markovian arrival process, the rate of customers' service, and the impatience intensity depend on the current state of the random environment and immediately change their values at the moments of jumps of the random environment. Dynamics of the system is described by the multi-dimensional asymptotically quasi-Toeplitz Markov chain. The ergodicity condition is derived. The main performance measures of the system are calculated. Numerical results are presented.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.450-455
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• 2001

An analytical study is made of transient adjustment process of an initially stationary, stably-stratified fluid in a square. The boundary walls are highly-conducting. The overall Rayleigh number $R_a$ is large. Considerations are given to both opposing (${\delta}w/{\delta}T>0$) and cooperating (${\delta}w/{\delta}T<0$) configurations. The flow character in opposing configuration can be classified into (a) a forced-convection dominaut mode (${\delta}w/{\delta}T>1/\sqrt{2}$), (b) a buoyancy-convection dominant mode ($0<{\delta}w/{\delta}T<1/\sqrt{2}$), and (c) a static mode (${\delta}w/{\delta}T{\cong}1/\sqrt{2}$). Global evolutionary processes are depicted. and physical rationalizations are provided.

• 지질공학
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• 제2권2호
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• pp.147-154
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• 1992

난수 발생 방법을 이용하여 시간과 규모의 영역에서 일련의 지진 발생에 대해 가상 수치 계산을 수행 했다. 가상 수치 계산의 이론은 지진 발생에 관련된 두 종류의 통계적 모델에 기초 하였다. 이들 모델들은 각기 독립적으로 발생하는 지진에 관련된 고정 포아송 처리와 여진에 관련된 분기 마르코프 처리등이다. 계산된 일련의 지진 발생들은 실제 발생한 지지의 목록과 유사함을 보여 주었다.

• 한국경영과학회지
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• 제30권2호
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• pp.73-80
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• 2005

In this paper, we consider characteristics of waiting times in s1n91e-server 3-node tandem queues with finite buffers, a Poisson arrival process and deterministic service times at all nodes. There are three buffers : one at the first node is infinite and the others are finite. We obtain the fact that sojourn time or departure process is independent of the capacities of the finite buffers and does not depend on the order of service times, which are the same results in the literature. Moreover, the explicit expressions of stationary waiting times in all areas of the systems can be derived as functions of the finite buffer capacities. We also disclose a relationship of waiting times in subareas of the systems between two blocking policies communication and manufacturing. Some numerical examples are also provided.