• Computers and Concrete
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• 제13권5호
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• pp.587-601
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• 2014

A sophisticated finite element modeling approach is proposed to simulate unbonded post-tensioned concrete slabs. Particularly, finite element contact formulation was employed to simulate the sliding behavior of unbonded tendons. The contact formulation along with other discretizing schemes was selected to assemble the post-tensioned concrete system. Three previously tested unbonded post-tensioned two-way and one-way slabs with different reinforcement configurations and boundary conditions were modeled. Numerical results were compared against experimental data in terms of global pressure-deflection relationship, stiffness degradation, cracking pattern, and stress variation in unbonded tendons. All comparisons indicate a very good agreement between the simulations and experiments. The exercise of model validation showcased the robustness and reliability of the proposed modeling approach applied to numerical simulation of post-tensioned concrete slabs.

• 대한전자공학회논문지TC
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• 제43권2호
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• pp.39-43
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• 2006

본 논문은 잡음이 존재하는 미지 시스템 출력 신호의 3차 통계치인 cumulant를 이용한 AR 식별에 관한 것이다. 미지 시스템 식별을 위한 알고리즘에서는 Parametric Modeling 기법중에서 Global Convergence 보장 및 시스템의 진폭과 위상 정보를 모두 표현할 수 있는 Cumulant를 이용한 AR (Auto Regressive) 식별 방법을 적용하였다. 식별 과정에서 미지 시스템을 하나의 AR 시스템으로 간주하였고 입력 신호를 발생하여 이를 통과시킨 후 잡음이 부가된 출력 신호를 얻어 이를 이용하였다. 신호대 잡음비의 변화에따른 AR 시스템의 식별을 수행한 결과 원래의 시스템 출력치와 유사한 양호한 식별 결과를 얻을 수 있었고 극점이 z 변환의 단위원내에 존재함을 확인하였다.

• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1479-1489
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• 2004

The effect of fluctuation of Equivalence Ratio (ER) in a turbulent reactive field has been studied in order to check the global combustion characteristics induced by the local fluctuation. When the flow is premixed on a large scale, closer examination on a small scale reveals that local fluctuations of ER exist in an imperfectly premixed mixture, and that these fluctuations must be considered to correctly estimate the mean reaction rate. The fluctuation effect is analyzed with DNS by considering the joint PDF of reactive scalar and ER, followed by modeling study where an extension of stochastic mixing models accounting for the ER fluctuation is reviewed and tested. It was found that models prediction capability as well as its potential is in favor to this case accounting the local ER fluctuation. However, the effect of local fluctuation did not show any notable changes on the mean global characteristics of combustion when statistical independence between the reactive scalar and ER field is imposed, though it greatly influenced the joint PDF distribution. The importance of taking into account the statistical dependency between ER and combustible at the initial phase is demonstrated by testing the modeled reaction rate.

• 한국소음진동공학회논문집
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• 제21권8호
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• pp.761-767
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• 2011

Free and forced vibration analysis of the global ship structure using the 3-dimensional finite element(FE) method requires not only the specialized knowledge such as ship structure interacted with fluid, damping and various excitations due to propulsion system but also time-consuming manual tasks in FE modeling, analysis and response evaluation. As a result, the quality of the vibration analysis highly depends on engineer's expertise and experience. In this study, a framework system to improve the efficiency of global ship vibration analysis is introduced. The system promising the utilization of MSC/Patran and MSC/Nastran consists of various modules to support data management, FE modeling of ship structure and loading, input deck generation for free and forced vibration analysis, data extraction and evaluation of analysis results, and databases for FE models of marine diesel engines and vibration criteria. The system may be useful for pursuing standardization of uncertain analysis factors as well as reducing time, cost and human dependency in ship vibration analysis.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.779-784
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• 2011

Free and forced vibration analysis of the global ship structure using the 3-dimensional finite element(FE) method requires not only the specialized knowledge such as ship structure interacted with fluid, damping and various excitations due to propulsion system but also time-consuming manual tasks in FE modeling, analysis and response evaluation. As a result, the quality of the vibration analysis highly depends on engineer's expertise and experience. In this study, a framework system to improve the efficiency of global ship vibration analysis is introduced. The system promising the utilization of MSC/Patran and MSC/Nastran consists of various modules to support data management, FE modeling of ship structure and loading, input deck generation for free and forced vibration analysis, data extraction and evaluation of analysis results, and databases for FE models of marine diesel engines and vibration criteria. The system may be useful for pursuing standardization of uncertain analysis factors as well as reducing time, cost and human dependency in ship vibration analysis.

• 한국지반환경공학회 논문집
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• 제16권5호
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• pp.13-25
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• 2015

This paper proposes an extended model evaluation method that considers not only the model performance but also the model structure and parameter uncertainties in hydrologic modeling. A simple reservoir model (SFM) and distributed kinematic wave models (KWMSS1 and KWMSS2 using topography from 250-m, 500-m, and 1-km digital elevation models) were developed and assessed by three evaluative criteria for model performance, model structural stability, and parameter identifiability. All the models provided acceptable performance in terms of a global response, but the simpler SFM and KWMSS1 could not accurately represent the local behaviors of hydrographs. Moreover, SFM and KWMSS1 were structurally unstable; their performance was sensitive to the applied objective functions. On the other hand, the most sophisticated model, KWMSS2, performed well, satisfying both global and local behaviors. KMSS2 also showed good structural stability, reproducing hydrographs regardless of the applied objective functions; however, superior parameter identifiability was not guaranteed. A number of parameter sets could result in indistinguishable hydrographs. This result indicates that while making hydrologic models complex increases its performance accuracy and reduces its structural uncertainty, the model is likely to suffer from parameter uncertainty.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2023년도 학술발표회
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• pp.69-69
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• 2023

격자 기반의 지면모형을 구동하기에 앞서 사용자의 목적에 따른 모델의 정확도와 모델의 구동 시간의 적절한 균형을 이루는 지면 모델의 격자 크기의 설정은 중요하다. 특히, 격자 크기에 따라 화재 모의 결과 영향이 매우 클 수 있지만, 이에 관한 연구들을 거의 이루어지지 않았다. 화재 모의는 탄소 순환뿐만 아니라 물 순환에도 직접적인 영향을 미치기 때문에 이를 위한 적절한 격자 크기 설정은 중요하다. 본 연구에서는 지면모형인 NCAR Community Land Model version 5(CLM 5)-biogeochemistry (BGC) 모형과 2000년부터 2019년의 The Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) 기상자료 이용하여서 지면 모델 격자 크기(1.9°×2.5°, 0.47°×0.63°, 0.25°×0.25°)에 따른 전 지구 규모의 화재 시뮬레이션 결과들을 분석하였다. 연평균 화재면적은 격자 크기가 제일 큰 1.9°×2.5° 격자의 시뮬레이션에서 연평균 450M ha로 가장 작게 나타났으며 격자의 크기가 작아질수록 화재의 크기는 증가하는 것으로 나타났다. 지면 모델의 격자가 작아짐에 따라 토양 입자의 분포가 세분화되고 이에 따라 투수 계수값이 증가하며 높은 토양수분의 분포들을 줄어들고 낮은 토양수분의 분포는 증가함을 확인하였다. 토양수분이 줄어듦에 따라 화재 연소성 정도를 나타내는 변수의 값이 증가하고 이에 따라 화재 발생빈도 및 화재 확산이 증가하여 지면 모델의 화재면적을 더 증가시키는 요인이 됨을 확인하였다. 이 연구를 바탕으로 하여 화재 모의의 불확실성 요소를 이해하고, 격자 크기에 따라 화재 모의 관련 매개변수의 수정이 필요할 것으로 판단된다.

• Earthquakes and Structures
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• 제24권6호
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• pp.393-404
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• 2023

This paper presents the application of hybrid-simulation-based adapter elements for the non-linear two-scale analysis of reinforced concrete frames with masonry infills under seismic-like demands. The approach provides communication and distribution of the computations carried out by two or more remote or locally distributed numerical models connected through the OpenFresco Framework. The modeling consists of a global analysis formed by macro-elements to represent frames and walls, and to reduce global degrees of freedom, portions of the structure that require advanced analysis are substituted by experimental elements and dimensional couplings acting as interfaces with their respective sub-assemblies. The local sub-assemblies are modeled by solid finite elements where the non-linear behavior of concrete matrix and masonry infill adopt a continuum damage representation and the reinforcement steel a discrete one, the conditions at interfaces between concrete and masonry are considered through a contact model. The methodology is illustrated through the analysis of a frame-wall system subjected to lateral loads comparing the results of using macro-elements, finite element model and experimental observations. Finally, to further assess and validate the methodology proposed, the paper presents the pushover analysis of two more complex structures applying both modeling scales to obtain their corresponding capacity curves.

• 한국환경과학회지
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• 제5권4호
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• pp.429-440
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• 1996

A global carbon cycle model (GCCM), that incorporates interaction among the terrestrial biosphere, ocean, and atmosphere, was developed to study the carbon cycling aid global carbon budget, especially due to anthropogenic $CO_2$ emission. The model that is based on C, 13C and 14C mass balance, was calibrated with the observed $CO_2$ concentration, $\delta$13C and $\Delta$14C in the atmosphere, Δ14C in the soil, and $\Delta$14C in the ocean. Also, GCCM was constrained by the literature values of oceanic carbon uptake and CO, emissions from deforestation. Inputs (forcing functions in the model) were the C, 13C and 14C as $CO_2$ emissions from fossil fuel use, and 14C injection into the stratosphere by bomb-tests. The simulated annual carbon budget of 1980s due to anthropoRenic $CO_2$ shows that the global sources were 5.43 Gt-C/yr from fossil fuel use and 0.91 Gt-C/yr from deforestation, and the sinks were 3.29 Gt-C/yr in the atmosphere, 0.90 Gt-C/yr in the terrestrial biosphere and 2.15 Gt-C/yr in the ocean. The terrestrial biosphere is currently at zero net exchange with the atmosphere, but carbon is lost cia organic carbon runoff to the ocean. The model could be utilized for a variety of studies in $CO_2$ policy and management, climate modeling, $CO_2$ impacts, and crop models.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2004년도 Proceedings of ISRS 2004
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• pp.162-165
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• 2004

The authors' previous study found an interannual covariability between actual evapotranspiration (ET) and the Normalized Difference Vegetation Index (NDVI) over northern Asia. This result suggested that vegetation controls interannual variation in ET. In this prior study, NDVI data from the Pathfinder AVHRR Land (PAL) dataset were analyzed. However, studies of NDVI interannual change are subject to uncertainty, because NDVI data often contain errors associated with sensor- and atmosphere-related effects. This study is aimed toward reducing this uncertainty by employing NDVI dataset, from the Global Inventory Monitoring and Modeling Studies (GIMMS) group, in addition to PAL. The analysis was carried out for the northern Asia region from 1982 to 2000. 19-year interannual change in PAL-NDVI and GIMMS-NDVI were both compared with interannual change in model-assimilated ET. Although the correlation coefficient between GIMMS-NDVI and ET is slightly less than for PAL-NDVI and ET, for both NDVI datasets the annual maximum correlation with ET occurs in June, which is near the central period of the growing season. A significant positive correlation between GIMMS-NDVI and ET was observed over most of the vegetated land area in June as well as PAL-NDVI and ET. These results reinforce the authors' prior research that indicates the control of interannual change in ET is dominated by interannual change in vegetation activity.