• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.109-120
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• 2013

This paper presents the results of a laboratory investigation into a study on undrained characteristics of a geogrid-encased stone column (GESC) installed in soft clay under cyclic load. In order to analyze behavior of settlement, pore water pressure, stress concentration ratio and strain of the GESC compared to a stone column, a series of reduced-scale laboratory tests were performed. The model tests show that GESC provides a simple and effective method of deformation resistance and settlement restraint when a short-term cyclic load is applied. The maximum strain of geogrid occurred at 1.2D and 1.5D from the top of the column. This paper highlights the importance of considering overlay effect and replacement ratio on cyclic load supporting GESC.

• Journal of the Korea Society of Computer and Information
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• v.13 no.4
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• pp.31-37
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• 2008

In this paper, we propose a dynamic job relocation strategy that considering application's characteristics in multiple grid sites. This scheme classifies application to execute in multiple grid sites by their characteristics : computing intensive application, network intensive application. Also, it eliminates the communication between sites by allocating the network intensive application in single site, thus reducing the total job execution time. But if a number of free nodes to execute the network intensive application aren't found in single site, the proposed scheme the first allocates the network intensive application in multiple sites to minimize network latency. Then if the network intensive application being executed in multiple sites suitable free nodes are found in single site. the proposed scheme relocates the application being executed in multiple sites to another single site. This results in reducing the total job execution time. Through simulation, we show that the proposed dynamic job reallocation strategy improves the performance of Data Grid environment compared with previous strategies.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.1
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• pp.1-9
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• 2007

At present various methods relating resource access control in grid environment are being studied. Most of the access authorization to grid resource is designed fit to the attributes and the role of user. But resource access control is to be made in the respect of business model to activate grid. Therefore this study suggests a model that can operate resource access control driven by grid accounting information. On the base of collection of accounting information about grid job, processing cost is yielded. If the user's available fund is less than processing cost, it gets to control grid job by the resource access control policy. Finally when grid job is completed, user is assigned to pay the charges for using resource of supplier. Then resource provider gets to supply stable resource in grid by participating it voluntarily to use idle resource. This study is esteemed to realize utility computing environment correspondent to economic principle by ensuring resource access policy of organizations which participate in grid.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.247-247
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• 2022

제트류는 복잡한 흐름 중 하나로 다양한 크기의 에디가 다양한 운동량을 가지고 있다. 이러한 제트류를 구현하기 위해서는 난류 운동 에너지 등 제트류의 특성을 잘 반영하여야 한다. 제트를 구현하기 위해서는 수리학적 모델, 현장 실험 등 많은 방법이 있으며, 본 연구에서는 상대적으로 공간, 시간적 비용이 적게 드는 수치해석 방법을 사용하여 연구를 진행하였다. 대표적인 수치해석방법에는 DNS(Direct Numerical Simulation), LES(Large Eddy Simulation), RANS(Reynolds Averaged Navier Stokes) 등이 있다. RANS는 시간 평균 흐름 특성만 산출하며 제트의 복잡성을 재현하는 데 한계가 있어, 본 연구는 DNS와 LES 모델을 이용하여 제트류를 구현하는 것에 초점을 맞추었다. DNS는 해당 격자에서 발생하는 모든 에디를 직접 해석 때문에 난류 모델링이 필요하지 않지만, 많은 수의 그리드가 필요하여 수치해석 시 소요시간이 긴 편이다. LES는 대규모 에디는 직접 해석하지만 일정 크기 이하의 소용돌이를 해석하기 위해서 모델이 필요하다. 따라서 서브 그리드 모델에 따라 약간 다른 결과를 보인다. 이러한 문제점을 해결하기 위해 본 연구에서는 LES의 기존 서브 그리드 모델을 사용하지 않고 신경망 모델로 학습한 DNS 결과를 활용하는 방법을 제안한다. 우선 DNS와 LES 모델을 사용하여 에너지 스펙트럼을 비교하여 서브 그리드 모델이 시작하는 파수를 찾는다. 이후 특정 파수 아래의 작은 에디를 모사할 적절한 신경망 모델을 결정하여 DNS의 작은 에디를 신경망 알고리즘이 모사할 수 있도록 학습시킨다. 이후 기존 서브 그리드 모델을 사용하지 않고 학습된 신경망 알고리즘을 사용한 LES 모델이 모사한 제트류와 실제 DNS 모델을 사용한 제트류를 비교 및 평가한다.

• Journal of the Korean GEO-environmental Society
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• v.15 no.11
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• pp.43-51
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• 2014

In this study, a series of pullout experiments were conducted on geogrid with attached passive reinforcement with respect to silt containments. Experiments were performed on man-made sand ground containing different silt of 0 %, 17 %, 35 % under various normal stresses 30 kPa, 60 kPa, 120 kPa respectively. The pullout test results showed that passive reinforcement increased the pullout strength over all silt contained condition and showed up to 20 % increases for same soil condition. The test results converted to the coefficient of interaction of pullout test to investigate the effect of reinforcement and the case of passive reinforcement showed 0.7~1.6 distribution depend on a silt contents. Therefore it is concluded that the overall length of geogrid can be reduced under the low vertical stress conditions.

• Journal of Korea Water Resources Association
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• v.34 no.2
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• pp.131-140
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• 2001

The present study is focused on improving the methodology for the determination of parameters involved in USLE(Universal Soil Loss Equation) based on distributed system concept and investigation of sediment delivery ratio. Generally the distributed system concept consists of grid networks throughout the watershed and sediment can be traced from grid to rid in the direction of the steepest descent. The sediment yield data together with physical data of 10 small irrigation reservoirs in Kyounggi-Do are collected. After the sediment delivery ratio of a grid is defined to be related tothe fraction of forested or covered with delivery proofing area of the grid, the preportionality coefficient(C$_1$) is introduced. The distributed system model is calibrated using the available data for 8 reservoirs and is verified with the data for the ramaining 2 reservoirs, and regression analysis is made to express the proportionality coefficient $C_1$ in terms of watershed physical characteristics. By applying this results the verification of the distributed system model for 2 reservoirs showed a fair result, which justifies the applicability of the proposed method in the present study.

• Journal of the Korean Geotechnical Society
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• v.25 no.11
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• pp.75-86
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• 2009

This paper presents the results of a numerical investigation on load carrying capacity of geogrid-encased stone columns to use as load carrying column(s) supporting a foundation load. A validated 3D stress-pore pressure coupled model that can effectively show rapid drainage capability of stone columns and encasement effect of geogrid was adopted and a parametric study was carried out on a number of influencing factors. It is shown that the geogrid encased stone columns can be effectively used as foundation load supporting columns in soft ground. The results of numerical investigation were presented so that the relationship between the load carrying capacity of geogrid-encased stone columns and the influencing factors can be identified. Practical implications of the findings are also discussed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.662-671
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• 2020

Recently, for the purposes of reducing carbon dioxide(CO₂) emissions in the island area, countermeasures to decrease the operation rate of diesel generator(DG) and to increase one of renewable energy sources(RES) is being studied. In particular, the demonstration and installation of stand-alone micro-grid(MG) system which is composed of DG, RES and energy storage system(ESS) has been implemented in some island areas such as Gapa-do, Gasa-do and Ulleung-do island. However, many power quality(PQ) problems may be occurred due to an intermittent output of RES including photovoltaic(PV) system and wind power(WP) system in a normal operating of constant voltage & constant frequency(CVCF) inverter-based MG system. Therefore, this paper presents a modeling of the 30kW scale MG system using PSCAD/EMTDC, and also implements a 30kW scale CVCF inverter-based MG system as test devices to analyze normal operating characteristics of MG system. From the simulation and test results, it is confirmed that the proposed methods are useful and practical tools to improve PQ problems such as under-voltage, over-voltage and unbalanced load in CVCF inverter-based MG system.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.410-411
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• 2011

본 논문에서는 태양광 전원, 배터리, 마이크로터빈, 스마트 홈 등 다양한 목적과 특성을 가진 요소로 구성된 마이크로그리드를 효율적으로 제어, 관리하기 위한 분산 지능형 제어원리를 제안한다. 기존의 중앙집중식 제어원리는 중앙에서 전체 시스템에 대한 정보를 취득하여 운영에 대한 의사결정을 독점하는 구조였다면 제안하는 원리는 마이크로그리드의 구성요소가 각각 지능형 에이전트를 기반으로 스스로 데이터를 취득하고 이웃 에이전트와의 대화와 협조를 통해 분산제어를 수행하는 방식이다. 각 에이전트 사이는 근거리 무선통신 방식인 Zigbee를 이용하였고 마이크로그리드를 실시간으로 해석하기 위하여 MATLAB 기반의 실시간 시뮬레이터를 이용하였다. 실시간 마이크로그리드 시뮬레이션 모델과 에이전트 역할을 하는 마이크로 컨트롤러를 연계하여 Hardware-in-the-loop 기반의 데모시스템을 구축하였고 제안하는 원리에 대해 검증하였다.

• Review of KIISC
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• v.22 no.5
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• pp.73-78
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• 2012

스마트그리드는 기존 전력망에 IT 기술을 융합한 차세대 전력망이다. 전력망에 IT 기술을 도입함으로써 운영효율이 증가하고 다양한 부가서비스가 창출되지만 반대로 사이버 보안위협은 증가하게 된다. 사이버 보안위협의 기술적 증가요인으로는 신재생에너지의 보급으로 인한 전력망 연결 접점 증가와 실시간 양방향 통신으로 인한 스마트그리드 기기 공격, 양방향 통신 프로토콜 공격 가능성 존재 등이 있다. 또한, 환경적 증가요인으로는 스마트그리드는 전력망 특성상 사고 발생시 피해 규모가 크므로, 상대국 및 테러집단에 의한 주요 공격대상이 되고 있다는 점이다. 본 논문에서는 이러한 스마트 그리드 사이버 보안위협을 사전에 차단하기 위해, 스마트그리드의 핵심 기술이라 할 수 있는 AMI의 보안 취약점을 발견할 수 있는 현실적인 취약점 점검 항목을 제시한다.