• Korea-Australia Rheology Journal
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• v.16 no.4
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• pp.201-212
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• 2004

Properties of polymer based nanocomposites depend on dispersion state of embedded fillers. In order to examine the effect of dispersion state on rheological properties, a new bi-mode FENE dumbbell model was proposed. The FENE dumbbell model includes two separate ensemble sets of dumbbells with different fric­tion coefficients, which simulate behavior of well dispersed and aggregated carbon nanotubes (CNTs). A new parameter indicating dispersion state of the CNT was proposed to account for degree of dispersion quantitatively as well as qualitatively. Rheological material functions in elongational, steady shear, and oscillatory shear flows were obtained numerically. The CNT/epoxy nanocomposites with different dis­persion state were prepared depending on whether a solvent is used for the dispersion of CNTs or not. Dis­persion state of the CNT in the epoxy nanocomposites was morphologically characterized by the field emission scanning electronic microscope and the transmission electron microscope images. It was found that the numerical prediction was in a good agreement with experimental results especially for steady state shear flow.

• Water Engineering Research
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• v.4 no.1
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• pp.45-58
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• 2003

Two-dimensional depth-averaged advection-dispersion equation was simulated using FEM. In the straight rectangular channel, the advection-dispersion processes are simulated so that these results can be compared with analyti-cal solutions for the transverse line injection and the point injection. In the straight domain the standard Galerkin method with the linear basis function is found to be inadequate to the advection-dispersion analysis compared to the upwind finite element scheme. The experimental data in the S-curved channel were compared with the result by the numerical model using SUPG(Streamline upwind Petrov-Galerkin) method.

• Communications for Statistical Applications and Methods
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• v.29 no.4
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• pp.413-420
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• 2022

In this study we adapt discrete weibull regression model for clustered count data. Discrete weibull regression model has an attractive feature that it can handle both under and over dispersion data. We analyzed the eighth Korean National Health and Nutrition Examination Survey (KNHANES VIII) from 2019 to assess the factors influencing the 1 month outpatient stay in 17 different regions. We compared the results using clustered discrete Weibull regression model with those of Poisson, negative binomial, generalized Poisson and Conway-maxwell Poisson regression models, which are widely used in count data analyses. The results show that the clustered discrete Weibull regression model using random intercept model gives the best fit. Simulation study is also held to investigate the performance of the clustered discrete weibull model under various dispersion setting and zero inflated probabilities. In this paper it is shown that using a random effect with discrete Weibull regression can flexibly model count data with various dispersion without the risk of making wrong assumptions about the data dispersion.

• Coupled systems mechanics
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• v.4 no.1
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• pp.67-98
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• 2015

Numerical prediction of dynamic behavior of fully coupled saturated porous media is of great importance in many engineering problems. Specifically, static and dynamic response of soils - porous media with pores filled with fluid, such as air, water, etc. - can only be modeled properly using fully coupled approaches. Modeling and simulation of static and dynamic behavior of soils require significant Verification and Validation (V&V) procedures in order to build credibility and increase confidence in numerical results. By definition, Verification is essentially a mathematics issue and it provides evidence that the model is solved correctly, while Validation, being a physics issue, provides evidence that the right model is solved. This paper focuses on Verification procedure for fully coupled modeling and simulation of porous media. Therefore, a complete Solution Verification suite has been developed consisting of analytical solutions for both static and dynamic problems of porous media, in time domain. Verification for fully coupled modeling and simulation of porous media has been performed through comparison of the numerical solutions with the analytical ones. Modeling and simulation is based on the so called, u-p-U formulation. Of particular interest are numerical dispersion effects which determine the level of numerical accuracy. These effects are investigated in detail, in an effort to suggest a compromise between numerical error and computational cost.

• Journal of Environmental Impact Assessment
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• v.9 no.4
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• pp.323-338
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• 2000

A Korean air dispersion modeling software, AirMaster, was developed on a basis of dispersion theories adopted in U.S. EPA's ISC3 (Industrial Source Complex - version 3) model to assess the air quality impact from the stacks. Key characteristics of AirMaster are as follows: 1) The building downwash effect can be easily simulated; 2) The screen, long term, and short term models can be run independently; 3) The input data to run the model such as meteorological and terrain data are supplied automatically from the databases in AirMaster; and 4) The modeling procedure is easy and simple under the GUI window environment. In order to validate AirMaster, comparisons with ISC3 model and Indianapolis tracer experiment were carried out. It was shown that AirMaster was identical to ISCST3 and ISCLT3 models in predicting the 1 hr to annual concentrations from the stack under various stack emission and meteorological conditions. The 1 hr concentrations predicted by AirMaster also showed a good agreement with the Indianapolis tracer measurements.

• 한국가스학회:학술대회논문집
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• 1997.09a
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• pp.211-216
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• 1997

• Proceedings of the Korea Water Resources Association Conference
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• 1993.07a
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• pp.151-157
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• 1993

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.6
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• pp.745-753
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• 2019

Recently, with the development of long-range / high-altitude guided weapon system for defense against ballistic missile, test range and firing altitude for guided weapons are increasing. Due to the increase in the test range and the intercepting altitude, it is expected to increase the range of safety area required for the firing test. Comparing to the foreign countries which have many desert or non-residence, in the domestic circumstances where the population is concentrated and distributed, it is more important to predict the falling area and to set the safety area for safely carry out the long-range / high-altitude intercept test. In this paper, we consider the following three points. The first is the booster fall trajectory modeling, the second is the shroud fall trajectory modeling, and finally, the debris dispersion modeling for the missile intercept. Especially, the AUTODYN model was used to predict debris falling area which produced in the high-speed guided missile intercepting test.

• ETRI Journal
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• v.36 no.4
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• pp.654-661
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• 2014

We develop accurate finite-difference time-domain (FDTD) modeling of polymer bulk heterojunction solar cells containing Ag nanoparticles between the hole-transporting layer and the transparent conducting oxide-coated glass substrate in the wavelength range of 300 nm to 800 nm. The Drude dispersion modeling technique is used to model the frequency dispersion behavior of Ag nanoparticles, the hole-transporting layer, and indium tin oxide. The perfectly matched layer boundary condition is used for the top and bottom regions of the computational domain, and the periodic boundary condition is used for the lateral regions of the same domain. The developed FDTD modeling is employed to investigate the effect of geometrical parameters of Ag nanospheres on electromagnetic fields in devices. Although negative plasmonic effects are observed in the considered device, absorption enhancement can be achieved when favorable geometrical parameters are obtained.

• Journal of Environmental Impact Assessment
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• v.14 no.6
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• pp.427-441
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• 2005

In order to choose proper dispersion model and emission factors suitable in Korea in evaluating the effect of pollutants emitted by the vehicles in highway on nearby area, various road dispersion models and vehicle emission factors were reviewed. With theoretical inter-comparisons of the exiting models for line source, CALINE 3 and CALINE 4 models which were suggested by US EPA were selected as the road dispersion models for further evaluation with the measurement. The emission factors suggested by Korean Ministry of Environment was turned out to be appropriate since the classification of vehicle kinds was simple and easy to apply in Korea. The comparisons of predicted concentrations by CALINE 3 and 4 models with the measurements in flat, fill and bridge road types showed that CO and PM-10 were in good agreements with experiments and the differences between CALINE 3 and 4 models are negligible. The model concentrations of $NO_2$ by CALINE 4 were also in good agreement with the measurement but those by CALINE 3 were over-predicted. The discrepancies in CALINE 3 model were due to rapid decay reaction of $NO_2$ near the highway, which was not included in CALINE 3 model. For the road type with one & two side cutting grounds, the similar patterns as the flat & fill road type for CO, PM10, & $NO_2$ were observed but the number of data for comparison in these cases were not enough to draw the conclusion. These results lead to the conclusion that CALINE4 model is proper in road environmental impact assessment near the highway in flat, fill and bridge road types.