• 한국대기환경학회지
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• 제19권4호
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• pp.397-414
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• 2003

The performance of one-particle stochastic Lagrangian models for passive tracer dispersion are evaluated against measurements in horizontally-homogeneous neutrally-stratified atmospheric surface layer. State-of-the-technology models as well as classical Langevin models, all in class of well mixed models are numerically implemented for inter-model comparison study. Model results (far-downstream asymptotic behavior and vertical profiles of the time averaged concentrations, concentration fluxes, and concentration fluctuations) are compared with the reported measurements. The results are: 1) the far-downstream asymptotic trends of all models except Reynolds model agree well with Garger and Zhukov's measurements. 2) profiles of the average concentrations and vertical concentration fluxes by all models except Reynolds model show good agreement with Raupach and Legg's experimental data. Reynolds model produces horizontal concentration flux profiles most close to measurements, yet all other models fail severely. 3) With temporally correlated emissions, one-particle models seems to simulate fairly the concentration fluctuations induced by plume meandering, when the statistical random noises are removed from the calculated concentration fluctuations. Analytical expression for the statistical random noise of one-particle model is presented. This study finds no indication that recent models of most delicate theoretical background are superior to the simple Langevin model in accuracy and numerical performance at well.

• 화약ㆍ발파
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• 제34권4호
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• pp.10-18
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• 2016

화약 발파는 물질이 연소할 때 발생하는 에너지를 파괴 동력으로 이용한다. 화약은 흑색화약으로부터 강력한 위력을 가진 다이너마이트에 이어 취급의 안정성도 향상시킨 에멀션 폭약의 개발에까지 이르고 있으며, 또한 뇌관과 같은 화공품도 공업뇌관과 도화선으로부터 전기 뇌관, 비전기 뇌관에 이어 초정밀 시차를 제어할 수 있는 전자뇌관의 개발에까지 발전되어 왔다. 그러나 아무리 성능이 우수한 화약과 뇌관을 사용한다고 하더라도 좋은 발파 결과를 얻을 수 있는 것은 아니다. 실제 현장의 다양한 조건을 어떻게 고려하여 설계 및 시공에 활용할 것인가는 전적으로 발파기술자의 손에 달려 있다. 암반을 대상으로 하는 발파는 많은 미지의 영향 변수들 때문에 실제 현장에서의 경험에 기초한 접근 방법이 매우 중요하다. 또한 현장에서의 관찰 결과를 분석하고 실험을 통해 정량화된 경험적 모델을 도출하거나, 이론적 근거를 정립하여 이론적 모델로 발전시키는 것은 발파 설계에의 활용뿐만 아니라 새로운 기술개발에 대한 아이디어를 제공한다는 측면에서도 필요하다. 본 논문에서는 발파 분야에서 개발된 몇 가지 경험적 모델과 이론적 모델들을 통해 활용 시 주의해야 할 사항들이 고찰되었다.

• Journal of Mechanical Science and Technology
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• 제17권9호
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• pp.1349-1357
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• 2003

This paper deals with verification of the theoretical model for dynamic behavior of Pipeline Inspection Gauge (PIG) traveling through high pressure natural gas pipeline. The dynamic behavior of the PIG depends on the differential pressure across its body. This differential pressure is generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. To analyze the dynamic behavior characteristics such as gas flow in pipeline, and the PIG position and velocity, not only the mathematical models are derived, but also the theoretical models must be certified by actual pigging experiment. But there is not any found results of research on the experimental certification for dynamic behavior of the PIG. The reason is why the fabrication of the PIG as well as, a field application are very difficult. In this research, the effectiveness of the introduced solution using the method of characteristics (MOC) was certified through field application. In-line inspection tool, 30" geometry PIG, was fabricated and actual pigging was carried out at the pipeline segment in Korea Gas Corporation (KOGAS) high pressure system, Incheon LT (LNG Terminal) -Namdong GS (Governor Station) line. Pigging is fulfilled successfully. Comparison of simulation results with experimental results show that the derived mathematical models and the proposed computational schemes are effective for predicting the position and velocity of the PIG with a given operational conditions of pipeline.

• Korean Membrane Journal
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• 제7권1호
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• pp.1-18
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• 2005

The permeate flux decline due to membrane fouling can be addressed using a variety of theoretical stand-points. Judicious selection of an appropriate theory is a key toward successful prediction of the permeate flux. The essential criterion f3r such a decision appears to be a detailed characterization of the feed solution and membrane properties. Modem theories are capable of accurately predicting several properties of colloidal systems that are important in membrane separation processes from fundamental information pertaining to the particle size, charge, and solution ionic strength. Based on such information, it is relatively straight-forward to determine the properties of the concentrated colloidal dispersion in a polarized layer or the cake layer properties. Incorporation of such information in the framework of the standard theories of membrane filtration, namely, the convective diffusion equation coupled with an appropriate permeate transport model, can lead to reasonably accurate prediction of the permeate flux due to colloidal fouling. The schematic of the essential approach has been delineated in Figure 5. The modern approaches based on appropriate cell models appear to predict the permeate flux behavior in crossflow membrane filtration processes quite accurately without invoking novel theoretical descriptions of particle back transport mechanisms or depending on adjust-able parameters. Such agreements have been observed for a wide range of particle size ranging from small proteins like BSA (diameter ${\~}$6 nm) to latex suspensions (diameter ${\~}1\;{\mu}m$). There we, however, several areas that need further exploration. Some of these include: 1) A clear mechanistic description of the cake formation mechanisms that clearly identifies the disorder to order transition point in different colloidal systems. 2) Determining the structure of a cake layer based on the interparticle and hydrodynamic interactions instead of assuming a fixed geometrical structure on the basis of cell models. 3) Performing well controlled experiments where the cake deposition mechanism can be observed for small colloidal particles (< $1\;{\mu}m$). 4) A clear mechanistic description of the critical operating conditions (for instance, critical pressure) which can minimize the propensity of colloidal membrane fluting. 5) Developing theoretical approaches to account for polydisperse systems that can render the models capable of handing realistic feed solutions typically encountered in diverse applications of membrane filtration.

• 한국도서관정보학회지
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• 제32권2호
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• pp.121-144
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• 2001

정보경제학의 탄생과 개념정의 및 연구분야를 간략히 살펴본 후, 정보경제학의 논의와 이해를 위해 반드시 검토되어야 하는 주요개념인 정보경제, 자원, 불확실성과 정보의 가치를 비교적 상세히 고찰하였다. 아울러 모델의 간략한 역사와 모델을 에워싸고 있는 문제점을 검토해 보고, 특히 문헌정보학의 실제와 이론연구의 진단과 실험도구로서 대단한 잠재력을 갖고 있는 사회과학에 관련된 약간의 모델적용을 규명해 보았다.

• Wind and Structures
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• 제12권2호
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• pp.89-101
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• 2009

The Monte Carlo procedure was used to simulate wind load effects on a light-frame low-rise structure of irregular shape and a main wind force resisting system. Two analytical models were studied: rigid-beam and rigid-plate models. The models assumed that roof diaphragms were rigid beam or rigid plate and shear walls controlled system behavior and failure. The parameters defining wall stiffness, including imperfections, were random and included wall stiffness, wall capacity and yield displacements. The effect of openings was included in the simulation via a set of discrete multipliers with uniform distribution. One and two-story buildings were analyzed and the models can be expanded into multiple-floor structures provided that the assumptions made in this paper are not violated.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2004년도 학술발표회
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• pp.1290-1294
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• 2004

In this study, new stochastic point rainfall models which can consider the correlation structure between rainfall intensity and duration are developed. In order to consider the negative and positive correlation simultaneously, the Gumbels type-II bivariate distribution is applied, and for the cluster structure of rainfall events, the Neyman-Scott cluster point process is selected. In the theoretical point of view, it is shown that the models considering the dependent structure between rainfall intensity and duration have slightly heavier tail autocorrelation functions than the corresponding independent mode]s. Results from generating long time rainfall events show that the dependent models better reproduce historical rainfall time series than the corresponding independent models in the sense of autocorrelation structures, zero rainfall probabilities and extreme rainfall events.

• 한국시스템다이내믹스연구
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• 제1권1호
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• pp.103-131
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• 2000

If a system such as a port has a large boundary and complexity, and the system's substance is considered as a black box, forecast accuracy will be very low. Futhermore various components in a port exert significant influence on each other. To copy with these problem the form of structure models were introduced by using SD method. The Competitive Ports Model had several sub-systems consisting of each Unit Port models, and each Unit Port model was made by quantitative, qualitative factors and their feedback loops. The fact that all components of one port have influence on the components of the other ports should be taken into account to construct Competitive Port Models. However, with the current approach that is impossible, and in this paper therefore, models were simplified by HFP adapted to integrate level variables of unit port models. Although many studies on modelling of port competitive situation have been conducted, both theoretical frame and methodology are still very weak. In this study, a new algorithm called ESD(Extensional System Dynamics) for the evaluation of port competition was presented, and applied to simulate port systems in northeast asia.

• 태양에너지
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• 제18권3호
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• pp.205-215
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• 1998

Entrainment in thermosyphons and heat pipes was characterized in view of the interfacial stability associated with the critical Weber number and the entrainment limit at the onset of liquid entrainment from the liquid or wicked interface. Both literature review and theoretical analysis on the entrainment models were peformed in order to evaluate accuracy of the predicted value. For this purpose, the models were categorized in two groups according to their entrainment mechanism and interfacial configurations, i.e., the wave-induced entrainment and the shear-induced entrainment, respectively. Thus, the twelve models(five models for the wave-induced entrainment and seven for the shear induced entrainment) were examined to obtain individual trends and their discrepancies from the general tendency of the overall models. As a result, the critical Weber numbers and entrainment limits were calculated and represented as a function of vapor temperature for the chosen characteristic dimensions of the interface.

• 천문학회보
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• 제41권1호
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• pp.42.2-42.2
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• 2016

It is well known that theoretical models of Wolf-Rayet stars are not consistent with observational data in terms of temperature and stellar radius. Recent study in analytical and numerical simulations show the importance of density inhomogeneity in stellar envelope. Using 1-dimensional numerical simulations, we study how such clumpiness arisen over convective surface of Wolf-Rayet stars affect their evolutionary path. Starting from pure helium star models, we constructed 21 different initial conditions by varying stellar mass, metallicity, and the clumpiness of the sub-surface convection zone. We run the simulations until the oxygen-burning is reached and find that the influence of the clumpiness is sensitive to the initial metallicity. Our models with high metallicity including the effect of the density inhomogeneity can roughly explain the observed properties of Wolf-Rayet stars such as stellar radius and temperature. By contrast, despite a considerable amount of density inhomogeneity is given, low metallicity models could not fully explain observations. To understand the inconsistency in low metallicity models, detailed study with improved model is required, taking account of the error range of the observations.