• Journal of the Korean Operations Research and Management Science Society
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• v.32 no.4
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• pp.19-35
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• 2007

This study is for detecting the Braess Paradox by stable dynamics in general transportation networks. Stable dynamics, suggested by Nesterov and de Palma[18], is a new model which describes and provides a stable state of congestion in urban transportation networks. In comparison with user equilibrium model based on link latency function in analyzing transportation networks, stable dynamics requires few parameters and is coincident with intuitions and observations on the congestion. Therefore it is expected to be an useful analysis tool for transportation planners. The phenomenon that increasing capacity of a network, for example creating new links, may decrease its performance is called Braess Paradox. It has been studied intensively under user equilibrium model with link latency function since Braess[5] demonstrated a paradoxical example. However it is an open problem to detect the Braess Paradox under stable dynamics. In this study, we suggest a method to detect the Paradox in general networks under stable dynamics. In our model, we decide whether Braess Paradox will occur in a given network. We also find Braess links or Braess crosses if a network permits the paradox. We also show an example how to apply it in a network.

• Journal of the Korean earth science society
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• v.38 no.7
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• pp.522-534
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• 2017

The purpose of this study is to verify urban flow and thermal environment by using the simulated Computational Fluid Dynamics (CFD) model in the area of Gangnam Seonjeongneung, and then to compare the CFD model simulation results with that of Seonjeongneung-monitoring networks observation data. The CFD model is developed through the collaborative research project between National Institute of Meteorological Sciences and Seoul National University (CFD_NIMR_SNU). The CFD_NIMR_SNU model is simulated using Korea Meteorological Administration (KMA) Local Data Assimilation Prediction System (LDAPS) wind and potential temperature as initial and boundary conditions from August 4-6, 2015, and that is improved to consider vegetation effect and surface temperature. It is noticed that the Root Mean Square Error (RMSE) of wind speed decreases from 1.06 to $0.62m\;s^{-1}$ by vegetation effect over the Seonjeongneung area. Although the wind speed is overestimated, RMSE of wind speed decreased in the CFD_NIMR_SNU than LDAPS. The temperature forecast tends to underestimate in the LDAPS, while it is improved by CFD_NIMR_SNU. This study shows that the CFD model can provide detailed and accurate thermal and urban area flow information over the complex urban region. It will contribute to analyze urban environment and planning.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.3
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• pp.63-74
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• 1984

The system dynamics is a systematic method supplemented by the decision making Process of management to the numerical and theoretical analyses in the field of the operation research or the industrial engineering. The system dyamics seems to be one of the most useful mathematical methods for forecasting the future social system or for evaluating the alternative plans. Land-use/transportation system dynamics model is constructed from the urban activity generation model based on the economic base hyphothesis using the DYNAMO simulation language. The model was applied to Daegu city and showed the validity.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.203-206
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• 2007

In urban flood model, the features like roads, buildings, and river's banks have great effect on flow dynamics and flood propagation and it must be accounted for model set-up. Two-dimensional hydraulic models in high-density building areas are at the forefront of current research into flood inundation mechanisms, but they are however constrained by inadequate parameters of topography and friction due to insufficient and inaccurate data. This paper describes the development of urban flooding with the extraction of building areas and estimates the its influence on flood inundation extent, and present initial results of flood simulation varying grid size.

• Journal of the Korean Society for Railway
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• v.9 no.6 s.37
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• pp.792-797
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• 2006

In general, the Maglev vehicle is ran over the elevated guideway consisted of steel or concrete structure. Since the running behaviour of the vehicle is affected by the flexibility of the guideway, the consideration of the flexibility of guideway is needed for evaluation of dynamics of both the vehicle and guideway. A new technique based on flexible multibody dynamics is proposed to model the Maglev vehicle, levitation controller, and guideway into a coupled model. To verify the technique, an urban Maglev vehicle is analyzed using the technique and discussions are carried out.

• Journal of the Korean Association of Geographic Information Studies
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• v.18 no.2
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• pp.92-104
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• 2015

In order to analyze the impacts of climate change, a time and space integrated model was developed in this study using system dynamics and GIS. The model built was used to carry out a simulation on the inundation impact on A-gu of Busan Metropolitan city resulting from the sea level rise scenario of IPCC and storm surge, which is the worst case. Through this, the flooded area and population until 2100 were predicted. Also, the result and significance of each alternative was reviewed improving the model by establishing alternative scenarios of protection, accommodation and retreat as plans of reaction to sea level rise. The combination of system dynamics and GIS has advantages of how the diverse variables change until the target year can be traced and, accordingly, not only the results but also the processes of spatial change can be examined by calculating the value of change process at each time step. The synergy of this model presumed to be a foothold for solving problems which are becoming difficult to predict due to increase in uncertainty and complexity such as the support for decision making for urban resilience to natural disasters.

• Korean Management Science Review
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• v.25 no.3
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• pp.27-43
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• 2008

This study analyzes the changes of Gyeongju local society because of setting up low and intermediate level radioactive waste disposal site by using urban dynamics model. Specifically, after examining 'Gyeongju Long-Term Development Plan' announced in 2007, I establish the number of industries, population, gross local product, residents' income, and the long term employment condition as essential change-causing factors in Gyeongju local society based on the Big3 government project, and forecast it by using 'Gyeongju long-Term Development Plan' and all sorts of statistical data. In this stage, I assume 3 scenarios(basic, optimistic, and pessimistic view) to estimate the changes of local society more exquisitely, and scenarios are composed through mediation about variables of a growth rate and an inflow or outflow rate. The result shows that Gyeonaju local society would have growing changes by 2020. The essential change-causing factors are as follows. The case of population is estimated that it starts going down at the level of approximately 270 thousand by 2009, starts going up continuously after 2009, the year of completion of low and intermediate level radioactive waste disposal site, and increases from the level of about 300 thousand as minimum to 340 thousand as maximum in 2020. The estimates of other cases are made that the number of Industries has about 10 thousand increases, gross local product has almost 6 trillion increases, nominal gross national income doubles, as well as residences have approximately 280 thousand increases, and also made that employment condition also improves continuously, and diffusion ratio of house starts going up but the amount of supplies is a little bit insufficient in the long view.

• Journal of Environmental Science International
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• v.1 no.1
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• pp.35-43
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• 1992

Handling the emergency problems such as Chemobyl accident require real time prediction of pollutants dispersion. One-point real time sounding at pollutant source and simple model including turbulent-radiation process are very important to predict dispersion at real time. The stability categories obtained by one-dimensional numerical model (including PBL dynamics and radiative process) are good agreement with observational data (Golder, 1972). Therefore, the meteorological parameters (thermal, moisture and momentum fluxes; sensible and latent heat; Monin-Obukhov length and bulk Richardson number; vertical diffusion coefficient and TKE; mixing height) calculated by this model will be useful to understand the structure of stable boundary layer and to handling the emergency problems such as dangerous gasses accident. Especially, this simple model has strong merit for practical dispersion models which require turbulence process but does not takes long time to real predictions. According to the results of this model, the urban area has stronger vertical dispersion and weaker horizontal dispersion than rural area during daytime in summer season. The maximum stability class of urban area and rural area are "A" and "B" at 14 LST, respectively. After 20 LST, both urban and rural area have weak vertical dispersion, but they have strong horizontal dispersion. Generally, the urban area have larger radius of horizontal dispersion than rural area. Considering the resolution and time consuming problems of three dimensional grid model, one-dimensional model with one-point real sounding have strong merit for practical dispersion model.al dispersion model.

• Atmosphere
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• v.21 no.1
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• pp.95-108
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• 2011

The effects of an apartment complex on flow and pollutant dispersion in an urban area are numerically investigated using a computational fluid dynamics (CFD) model. The CFD model is based on the Reynolds-averaged Navier-Stokes equations and includes the renormalization group k-${\varepsilon}$ turbulence model. The geographic information system (GIS) data is used as an input data of the CFD model. Eight numerical simulations are carried out for different inflow directions and, for each inflow direction, the effects of an apartment complex are investigated, comparing the characteristics of flow and dispersion before and after construction of the apartment complex in detail. The observation data of automatic weather system (AWS) is analyzed. The windrose analysis shows that the wind speed and direction after the construction of the complex are quite different from those before the construction. The construction of the apartment complex resulted in the decrease in wind speed at the downwind region. It is also shown that the wind speed increased partially inside the apartment complex due to the channeling effect to satisfy the mass continuity. On the whole, the wind speed decreased at the downwind region due to the drag effect by the apartment complex. As a result, the passive pollutant concentration increased (decreased) near the downwind region of (within) the apartment complex compared with that before the construction.

• Korean System Dynamics Review
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• v.8 no.2
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• pp.51-82
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• 2007

The purpose of this paper is exploring changes in land use pattern when considering environmental carrying capacity. A sustainable development requires a society to define sustainability constraints, environmental carrying capacity. Environmental carrying capacity can be defined as a level of human activity a region can sustain at a desired level of quality of environment. This concept of environmental carrying capacity can be applied to land use to explore sustainable land use pattern. Since land use pattern can affect environment in an important way, exploring sustainable land use pattern within the limit of environmental carrying capacity can suggest useful implications for a sustainable regional management and planning. For this purpose, this paper built the environmental carrying capacity land use model and applied it to the Metropolitan Area, Korea. System dynamics modeling methods was used to build the model. The model developed in this paper consisted of 6sectors; population, housing, industry, land, environment, and traffic sector. The model limits its main focus on the NO2 level as an indicator of quality of environment in Metropolitan Area. Box model was translated into system dynamics model and combined to urban dynamics model to estimate NO2 level, the maximum number of population, industry structure, housing and maximum amount of land use for industrial, housing, and green space that can sustain desirable NO2 level. Metropolitan area was divided into 16 areas and the model was applied to each area. Since NO2 is flowing in and out from each area, model was built to allow this transboundering nature of air pollutants. Based on the model estimation, several policy implications for a sustainable land use pattern was discussed.