• Korean System Dynamics Review
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• v.9 no.1
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• pp.73-92
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• 2008

Internet portal sites have served customers for more than a decade in Korea. There have been several such sites have survived, succeeded and led the internet industry. What is the source of their competitiveness? We assumed that the network effect, which can vary dynamically, is an important factor; so we tried to build and analyze a system dynamics model on portal sites that represent their advertising business model. This model includes not only the network effect, but also customer's' expectations of the quality of portal sites, which also varies dynamically. As a result of our research, we can state that the network effect is important to stabilize and increase portal sites' quality, market share, income and cash flow. And we know that investment at a level above that which is merely required is necessary to preserve and stabilize their business.

• Journal of the Korean Operations Research and Management Science Society
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• v.32 no.3
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• pp.63-80
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• 2007

This study is a generalization of 'stable dynamics' recently suggested by Nesterov and de Palma[29]. Stable dynamics is a new model which describes and provides a stable state of congestion in urban transportation networks. In comparison with user equilibrium model that is common 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. An equilibrium in stable dynamics needs only maximum flow in each arc and Wardrop[33] Principle. In this study, we generalize the stable dynamics into the model with multiple traffic classes. We classify the traffic into the types of vehicle such as cars, buses and trucks. Driving behaviors classified by age, sex and income-level can also be classes. We develop an equilibrium with multiple traffic classes. We can find the equilibrium by solving the well-known network problem, multicommodity minimum cost network flow problem.

• Journal of Korean Society of Transportation
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• v.19 no.3
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• pp.115-131
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• 2001

The Purpose of this study is to develop a simulation model for large-scale network with interrupted flow as well as uninterrupted flow. The Cell Transmission(CT) theory is used to simulate traffic flow. Flow transition rules have been newly developed to simulate traffic flows at merging and diverging sections, and signalized intersections. In the model, it is assumed that dynamic OD table is exogenously given. Simulation results for toy network shows that the model can explain queue dynamics not only in signalized intersections of urban arterials, but also in merging and diverging sections of freeway. In case study, the model successfully simulated traffic flows of 145,000 vehicles on CBD network of city of Seoul with 74 traffic zones, 133 signalized intersections among 395 nodes and 1110 links.

• Journal of Korean Society of Transportation
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• v.22 no.3 s.74
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• pp.179-201
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• 2004

Online traffic flow modeling is attracting more attention due to intelligent transport systems and technologies. The flow-density relation plays an important role in traffic flow modeling and provides a basic way to illustrate traffic flow behavior under different traffic flow and traffic density conditions. Until now the research effort has focused mainly on the shape of the relation. The time series of the relation has not been identified clearly, even though the time series of the relation reflects the upstream/downstream traffic conditions and should be considered in the traffic flow modeling. In this paper the flow-density relation is analyzed dynamically and interpreted as a states diagram. The dynamic flow-density relation is quantified by applying fuzzy logic. The quantified dynamic flow-density relation builds the basis for online application of a macroscopic traffic flow model. The new approach to online modeling of traffic flow applying the dynamic flow-density relation alleviates parameter calibration problems stemming from the static flow-density relation.

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2000.09a
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• pp.129-137
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• 2000

This paper presents groundwater flow characteristics in discontinuous rock mass using fracture network program(NAPSAC) by statistical approach. Equivalent permeability coefficients are estimated from borehole data around Mabuk test tunnel site and fracture map on the arch of the tunnel. The reliability of fracture network model is obtained from determination of input data for statistical fracture network analysis from the real data(data of fracture network, data of hydraulic tests). The variation of permeability and mean anisotropic permeability coefficients are calculated from the realized model by increasing the size. As a result of analysis, a strong anisotropy of permeability is observed according to the direction of the fracture sets around the test tunnel.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.378-386
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• 2000

This paper presents groundwater flow characteristics in discontinuous rock mass using fracture network program(NAPSAC) by statistical approach. Equivalent permeability coefficients are estimated from borehole data around Mabuk test tunnel site and fracture map on the arch of the tunnel. The reliability of fracture network model is obtained from determination of input data for statistical fracture network analysis from the real data(data of fracture network, data of hydraulic tests). The variation of permeability and mean anisotropic permeability coefficients are calculated from the realized model by increasing the size. As a result of analysis, a strong anisotropy of permeability is observed according to the direction of the fracture sets around the test tunnel.

• International Journal of Computer Science & Network Security
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• v.22 no.2
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• pp.413-423
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• 2022

The NHIS provides free or highly subsidized healthcare to all people by providing financial fortification. However, the financial sustainability of the scheme is threatened by numerous factors. Therefore, this work sought to provide a solution to process claims intelligently. The provided Petri net model demonstrated successful data flow among the various participant. For efficiency, scalability, and performance two main subsystems were modelled and integrated - data input and claims processing subsystems. We provided smart claims processing algorithm that has a simple and efficient error detection method. The complexity of the main algorithm is good but that of the error detection is excellent when compared to literature. Performance indicates that the model output is reachable from input and the token delivery rate is promising.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.36 no.3
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• pp.169-176
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• 2020

The authors developed a nodal network model that simulates the flow of moist air and the thermal behavior of a target area. The nodal network model was enhanced using a parameter estimation technique based on the measured temperature, humidity, and schedule data. However, the nodal model is not good enough for predicting humidity of the target space, having 55.6% of CVRMSE. It is because re-evaporation effect could not be modeled due to uncertain factors in the field measurement. Hence, a data-driven model was introduced using an artificial neural network (ANN). It was found that the data-driven model is suitable for predicting the condensation compared to the nodal model satisfying ASHRAE Guideline with 3.36% of CVRMSE for temprature, relative humidity, and surface temperature on average. The model will be embedded in automated devices for real-time predictive control, to minimize the risk of surface condensation at dressroom in an apartment housing.

• Journal of the Korean Society of Groundwater Environment
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• v.5 no.2
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• pp.80-87
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• 1998

Since groundwater flow paths have one of the major roles to transport the radioactive nuclides from the radioactive waste repository to the biosphere, the discrete fracture network model is used for the rock block scale flow instead of the porous continuum model. This study aims to construct a three dimensional discrete fracture network to interpret the groundwater flow system in the study site. The modeling work includes the determination of the probabilistic distribution function from the fracture geometric and hydraulic parameters, three dimensional fracture modeling and model calibration. The results of the constant pressure tests performed in a fixed interval length at boreholes indicate that the flow dimension around boreholes shows mainly radial to spherical flow pattern. The fracture transmissivity value calculated by Cubic law is 6.12${\times}$10$\^$-7/ ㎡/sec with lognormal distribution. The conductive fracture intensity estimated by FracMan code is 1.73. Based on this intensity, the total number of conductive fractures are obtained as 3,080 in the rock block of 100 m${\times}$100 m${\times}$100 m.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.2
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• pp.167-175
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• 2020

The Two-fluid Model, proposed by Herman and Prigogine in 1979, is a macroscopic model for describing network operability in urban networks. Since the Two-fluid Model parameters change according to the traffic flow characteristics, it is necessary to identify the cause of flow change when analyzing the operability using the parameters. This study compared the crash risk according to rainfall using the Two-fluid Model parameters, and explained that the driving behavior affects the operability of the urban network. The results of the parameters estimation showed poor network operation under rainfall condition. The factors of drivers' crash risk perception model were calculated, and driving behavior was analyzed due to crash risk according to rainfall. In both the morning and evening, drivers tended to slow down their speeds to reduce the crash risk, because the risk on rainy days could be high when the speed was the same as on a sunny days. However, the crash risk was still higher on rainy days than sunny. In the future, it is necessary to analyze the relationship between the network operation and the crash risk in various networks and to improve both.