• Journal of the Korean Association of Geographic Information Studies
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• v.7 no.1
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• pp.28-38
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• 2004

The purpose of this study is to analyze the urban hydrologic state by the use of GIS, resolution and interpolation. The determination coefficient($R^2$) and Regression Formula were derived from the contour of digital map for the accuracy, and DEM data was made by using TIN interpolation by the size of the grid. By using the observed DEM data, topographical factors were extracted from the small basin, size, the width of a basin and the slope, and were applied in the urban runoff model. Through the model, we tried to find out the most suitable runoff model in a small basin of Yosu-Munsu area. As a result of applying models to the drainage considered, the runoff hydrograph estimated by SWMM model was closer to the observed one than that estimated by ILLUDAS model. The difference between the runoff hydrograph by SWMM and the observed one is maximum error of 19%, minimum error of 5% and average error of 13%. The influence of duration in contrast to pick time is insignificant in a urban small basin. As a conclusion of this study, SWMM model was more suitable and applicable for the urban runoff model than ILLUDAS model due to its accuracy and various abilities.

• Journal of Korea Water Resources Association
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• v.55 no.6
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• pp.447-459
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• 2022

This study estimated the grid-type precipitation quantile for the Korean Peninsula using PERSIANN-CCS-CDR (Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Cloud Classification System-Climate Data Record), a satellite based re-analysis precipitation data. The period considered is a total of 38 years from 1983 to 2020. The spatial resolution of the data is 0.04° and the temporal resolution is 3 hours. For the probability distribution, the Gumbel distribution which is generally used for frequency analysis was used, and the probability weighted moment method was applied to estimate parameters. The duration ranged from 3 hours to 144 hours, and the return period from 2 years to 500 years was considered. The results were compared and reviewed with the estimated precipitation quantile using precipitation data from the Automated Synoptic Observing System (ASOS) weather station. As a result, the parameter estimates of the Gumbel distribution from the PERSIANN-CCS-CDR showed a similar pattern to the results of the ASOS as the duration increased, and the estimates of precipitation quantiles showed a rather large difference when the duration was short. However, when the duration was 18 h or longer, the difference decreased to less than about 20%. In addition, the difference between results of the South and North Korea was examined, it was confirmed that the location parameters among parameters of the Gumbel distribution was markedly different. As the duration increased, the precipitation quantile in North Korea was relatively smaller than those in South Korea, and it was 84% of that of South Korea for a duration of 3 h, and 70-75% of that of South Korea for a duration of 144 h.

• Journal of Korea Water Resources Association
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• v.45 no.2
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• pp.179-189
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• 2012

To simulate the transport of pollutant, a numeric model for the advection-diffusion equation with the decay term is developed. This is finite-difference model using the implicit method (with the weight factor ${\alpha}$) and Gauss-Seidel SOR(successive over-relaxation). This model is compared to the analytical solutions (of simpler dimensional or boundary conditions), and in the condition of Peclet number < 5~20, the result shows stable condition, and Crank-Nicolson method (${\alpha}$=0.5) shows the more accurate results than fully-implicit method (${\alpha}$=1). The mass of advection, diffusion and decay is calculated and the error of mass balance is less than 3%. This model can evaluate the 3-D concentrations of the advection-diffusion and decay problems, but this model uses only the finite-difference method with the fixd grid system, so it can be effectively used in the problems with small Peclet numbers like the pollutant transport in groundwater.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.3
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• pp.232-242
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• 2015

For stealth performance consideration, many UAV designs are adopting tailless lambda-shaped configurations which are likely to have unsteady dynamic characteristics. In order to control such UAVs through automatic flight control system, more accurate estimation of dynamic stability derivatives becomes essential. In this paper, dynamic stability derivatives of a tailless lambda-shaped UAV are estimated through numerically simulated forced oscillation method incorporating dynamic mesh technique. First, the methodology is validated by benchmarking the CFD results against previously published experimental results of the Standard Dynamics Model(SDM). The dependency of initial angle of attack, oscillation frequency and oscillation magnitude on the dynamic stability derivatives of a tailless UAV configuration is then studied. The results show reasonable agreements with experimental reference data and prove the validity and efficiency of the concept of using CFD to estimate the dynamic derivatives.

• Journal of Korea Water Resources Association
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• v.45 no.4
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• pp.349-360
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• 2012

A horizontally curvilinear non-hydrostatic free surface model that was applicable to three-dimensional viscous flows was developed. The proposed model employed a top-layer equation to close kinematic free-surface boundary condition, and an isotropic k-${\varepsilon}$ model to close turbulence viscosity in the Reynolds averaged Navier-Stokes equation. The model solved the governing equations with a fractional step method, which solved intermediate velocities in the advection-diffusion step, and corrects these provisional velocities by accounting for source terms including pressure gradient and gravity acceleration. Numerical applications were implemented to the wind-driven currents in a two-dimensional closed basin, the flow in a steep-sided trench, and the flow in a strongly-curved channel accounting for secondary current by the centrifugal force. Through the numerical simulations, the model showed its capability that were in good agreement with experimental data with respect to free surface elevation, velocity, and turbulence characteristics.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.10
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• pp.961-969
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• 2013

In this study, the numerical analysis of a turbulent flow around both a staggered and an inline tube bundle was conducted using ANSYS CFX V.13, a commercial CFD software. The flow was assumed to be steady, incompressible, and isothermal. According to the CFD Best Practice Guideline, the sensitivity study for grid size, accuracy of the discretization scheme for convection term, and turbulence model was conducted, and its result was compared with the experimental data to estimate the applicability of the CFD Best Practice Guideline. It was concluded that the CFD Best Practice Guideline did not always guarantee an improvement in the prediction performance of the commercial CFD software in the field of tube bundle flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1555-1569
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• 2000

Numerical simulation of fluid flow with moving free surface has been carried out. For the free surface flow, a VOF(Volume of Fluid)-based algorithm utilizing a fixed grid system has been investigated. In order to reduce numerical smearing at the free surface represented on a fixed grid system, a new free surface tracking algorithm based on the donor-acceptor scheme has been presented. Novel features of the proposed algorithm are characterized as two numerical tools; the orientation vector to represent the free surface orientation in each cell and the baby-cell to determine the fluid volume flux at each cell boundary. The proposed algorithm can be easily implemented in any irregular non-uniform grid systems that are usual in finite element method (FEM). Moreover, the proposed algorithm can be extended and applied to the 3-D free surface flow problem without additional efforts. For computation of unsteady incompressible flow, a finite element approximation based on the explicit fractional step method has been adopted. In addition, the SUPG(streamline upwind/Petrov-Galerkin) method has been implemented to deal with convection dominated flows. Combination of the proposed free surface tracking scheme and explicit fractional step formulation resulted in an efficient solution algorithm. Validity of the present solution algorithm was demonstrated from its application to the broken dam and the solitary wave propagation problems.

• Journal of the Korean Magnetics Society
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• v.10 no.1
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• pp.16-21
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• 2000

Magnetic properties and crystallographic properties of $Cu_{0.95}Ge_{0.95}Fe_{0.1}O_3$ were studied by using x-ray diffraction, superconducting quantum interference device (SQUID) and Mossbauer spectroscopy. Our sample has orthorhombic structure and the lattice constants are a = 4.795 $\AA$, b = 8.472 $\AA$, c = 2.932 $\AA$. The spin-Peierls (SP) transition temperatures of our sample is 13 K. The Mossbauer spectra consisted with two Zeeman sextets and one doublet due to $Fe^{3+}$ions. The Zeeman sextets come from tetrahedral $Fe^{3+}$ions and the doublets come from octahedral $Fe^{3+}$ions. The jump up of magnetic hyperfine field of 2nd Zeeman sextet and the increasing of the values of quadrupole splitting and isomer shift of doublet below SP transition temperature could be interpreted related with the atomic displacements. The N el temperature is 715 K, the Debye temperature are 540 K for octahedral site and 380 K for tetrahedral site, respectively.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.8
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• pp.45-53
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• 1999

Electromagnetic scattering by finite number of conducting strips loaded on a grounded dielectric is considered for the TM polarization case from the viewpoints of transmitting(receiving) leaky wave antenna and grating coupler. An integro-differential equation whose unknowns are the induced currents over the strips is derived and solved by use of the method of moments. In order to construct the non-uniform leaky wave structures with specific source(current) distributions over the strips, distances between two adjacent strips and strip width are simultaneously varied along the structure. From some results for the current distributions over the strips and surface wave powers, it is observed that the maximum coupling efficiencies of the appropriately constructed non-uniform leaky wave structures from the viewpoints of both a receiving leaky wave antenna and a grating coupler amount upto 95%, which are about 15% improvements compared with those(80%) of the uniform structures.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.2
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• pp.151-160
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• 2002

A modeling system for three-dimensional flow (FEMOS) has been developed and applied to simulate the tidal currents of Asan Bay. The system can consider tidal flats changing with time and uses a finite element method that can adapt coastline change effectively. The simulation results for Asan Bay with large tidal flats, shallow water depth and high tidal range showed good agreements with the observed currents of long-term variations at the medium layer and short-term variations of vertical profiles. Based on the simulated tidal currents, the horizontal distributions of bottom shear stress were calculated and showed close relation with the change of bottom topography. The system can be used widely to study coastal circulation in the coastal region with complex geography.