• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.5 s.236
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• pp.568-576
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• 2005

A 3-D finite element model combined with a volume tracking method is presented in this work to simulate the mold filling for casting processes. Especially, the analysis involves an adaptive grid method that is created under a criterion of element categorization of filling states and locations in the total region at each time step. By using an adaptive grid wherein the elements, finer than those in internal and external regions, are distributed at the surface region through refinement and coarsening procedures, a more efficient analysis of transient fluid flow with free surface is achieved. Adaptive grid based on VOF method is developed in tetrahedral element system. Through a 3-D analysis of the benchmark test of the casting process, the efficiency of the proposed adaptive grid method is verified. Developed FE code is applied to a typical industrial part of the casting process such as aluminum road wheel.

• Journal of Energy Engineering
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• v.15 no.3 s.47
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• pp.188-193
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• 2006

This paper intends to present theoretical study and its application result of the way of the temperature distribution embodiment through the production of subdivided nod's temperature from the average, maximum and minimum temperature following acoustic speed measurement with a set of acoustic speed meters at the arbitrary section in the furnace. By measuring the acoustic speed between the speed meters, flue gas temperature field can be determined. Then Subdivided arbitrary grid's temperatures can be infered out of surrounding nod's temperature distribution, and finally the entire grid's temperature distribution will be found. In this article, theoretical background, related system setup. and real application result are examined and discussed.

• Journal of Korea Water Resources Association
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• v.44 no.7
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• pp.511-522
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• 2011

Two-dimensional shallow water model based on the cut cell and the adaptive mesh refinement techniques is presented in this paper. These two mesh generation methods are combined to facilitate modeling of complex geometries. By using dynamically adaptive mesh, the model can achieve high resolution efficiently at the interface where flow changes rapidly. The HLLC Reimann solver and the MUSCL method are employed to calculate advection fluxes with numerical stability and precision. The model was applied to simulate the extreme urban flooding experiments performed by the IMPACT (Investigation of Extreme Flood Processes and Uncertainty) project. Simulation results were in good agreement with observed data, and transient flows as well as the impact of building structures on flood waves were calculated with accuracy. The cut cell method eased the model sensitivity to refinement. It can be concluded that the model is applicable to the urban flood simulation in case the effects of sewer and stormwater drainage system on flooding are relatively small like the dam brake.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.3
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• pp.207-219
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• 1993

Tsunamis along the east coast of Korea accompanying the 1983 East Sea central region earthquake is hindcasted with numerical models for tsunami propagation and inundation. Both linear and nonlinear models were used to compute propagation and elevation of tsunami waves on the coastal area of Korea. For the mesh refinement, grid system was divided into two sub-regions in Korean coastal area with final 10m grid resolution at interior area where serious inundation was observed. Calculated tsunami height distribution showed a general agreement with coastal observation. With interior detailed mesh system at mid-east coast region, the inundatin at the port of Imwon were qualitatively well reproduced by inundation and runup model.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.79-82
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• 2004

In this study, a new refinement technique for 3-dimensional hexahedral element mesh is proposed, which is aimed at the control of mesh density. With the proposed scheme the mesh is refined adaptively to the elemental error which is estimated by 'a posteriori' error estimator based on the energy norm. A desired accuracy of an analysis i.e. a limit of error defines the new desired mesh density map on the current mesh. To obtain the desired mesh density, the refinement procedure is repeated iteratively until no more elements to be refined exist. In the algorithm, at first the regions of mesh to be refined are defined and, then, the zero-thickness element layers are inserted into the interfaces between the regions. All the meshes in the regions, in which the zero-thickness layers are inserted, are to be regularized in order to improve the shape of the slender elements on the interfaces. This algorithm is tested on a simple shape of 2-d quadrilateral element mesh and 3-d hexahedral element mesh. A numerical example of elastic deformation of a plate with a hole shows the effectiveness of the proposed refinement scheme.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2002.02a
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• pp.486-493
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• 2002

본 연구에서는 정밀시비를 위한 전자지도 작성 시스템을 개발하고, 질소 시비량 지도를 작성하였다. 개발된 토양 유기물 함량 계측 센서는 0.07%~7.96%가지의 토양 유기물 함량을 $R^2$= 0.85, SEP=0.72, bias=-0.13으로 계측할 수 있었으며, 작성된 시비량 지도를 이용한 시비는 58.7%의 정확성을 보였다. 시비량 지도에 의한 정밀시비는 획일적인 시비의 정밀시비 30.5%에 비해 91%의 정확성 향상을 보였다. 그러나 개발된 센서의 오차로 인하여 유기물 함량 등급 분류 간격이나 격자 간격 면에서 세분화된 지도는 작성할 수 없었다. 좀 더 정확하고 세분화된 시비량 지도 작성을 위해서는 오차 범위가 작은 정밀한 센서의 개발이 요구된다. 또한 토양 유기물 센서뿐만 아니라 다른 토양 상태를 계측할 수 있는 센서들이 개발된다면 다양하고 정확한 시비량 지도를 작성할 수 있을 것으로 판단된다. 작성된 전자 지도는 농작업의 의사결정에 도움을 주며, 빠른 처방이 가능할 것이다.

• Journal of computational fluids engineering
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• v.19 no.1
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• pp.1-6
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• 2014

Since experiments on the actual operational status are said to be very impractical because of their economic and repeatability problems, it is difficult to understand the thermal profiles of aerospace or military equipments. Thus, the CFD codes with considering the radiation heat transfer are used to compensate the defect. In case, analyzing the radiation exchanges between the object surfaces are very important. Because the temperature and the IR signal distributions of the object surface are significantly affected by the radiative heat transfer. To achieve accurate thermal radiation exchange between surfaces, it is important to calculate the radiation view factor precisely. Finer subdivision of meshes can be used to increase the accuracy of radiation view factor, but if the mesh is subdivided infinitely, the time required for calculation increases significantly and thus decreasing the efficiency. If the subdivision is not sufficient, assurance of accuracy is not guaranteed. In this paper, optimal mesh subdivision method using the solid angle has been successfully tested and found to be useful in increasing the efficiency of calculating the shape factors.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.5
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• pp.335-347
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• 2013

In February 2008, high storm waves due to a developed atmospheric low pressure system propagating from the west off Hokkaido, Japan, to the south and southwest throughout the East Sea (ES) caused extensive damages along the central coast of Japan and along the east coast of Korea. This study consists of two parts. In the first part, we estimate extreme storm wave characteristics in the Toyama Bay where heavy coastal damages occurred, using a non-hydrostatic meteorological model and a spectral wave model by considering the extreme conditions for two factors for wind wave growth, such as wind intensity and duration. The estimated extreme significant wave height and corresponding wave period were 6.78 m and 18.28 sec, respectively, at the Fushiki Toyama. In the second part, we perform numerical experiments on wave-structure interaction in the Fushiki Port, Toyama Bay, where the long North-Breakwater was heavily damaged by the storm waves in February 2008. The experiments are conducted using a non-linear shallow-water equation model with adaptive mesh refinement (AMR) and wet-dry scheme. The estimated extreme storm waves of 6.78 m and 18.28 sec are used for incident wave profile. The results show that the Fushiki Port would be overtopped and flooded by extreme storm waves if the North-Breakwater does not function properly after being damaged. Also the storm waves would overtop seawalls and sidewalls of the Manyou Pier behind the North-Breakwater. The results also depict that refined meshes by AMR method with wet-dry scheme applied capture the coastline and coastal structure well while keeping the computational load efficiently.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.4
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• pp.243-258
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• 2005

A fully-nonlinear two-dimensional dynamically interfaced nested tidal model has been developed with improved efficiency, usability, relocatability and also adopting different time steps for economizing computational times, which is based on two-dimensional tidal model of Choi(1990) with resolution of $1/15^{\circ}$ inlatitude by $1/12^{\circ}$ in longitude covering the whole Yellow and East China Seas continental shelf. To illustrate the validity and applicability of the present model, numerical model experiment was carried out for tidal distribution in the Yellow Sea and the East China Sea emphasizing the Saemangeum area with enhanced grid system. The results from comparison with observed value showed that the present model gives reasonable agreement. The present modeling system is a relocatable tide forecasting system designed to predict tides at any location within the Yellow Sea and the East China Sea continental shelf sea.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.4
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• pp.345-351
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• 2010

The finite volume time domain (FVTD) method gives accurate results for the calculation of electromagnetic wave propagation but it requires large amount of computer memory. In this paper we propose a modified FVTD that employs a time subdivision. The time-subdivided FVTD (TS-FVTD) method is enough to divide the space domain grid with a large step size. This method can reduce computation time and memory resources. We check the effectiveness of the proposed method in order to apply to the analysis of electromagnetic field from rough surface with dielectric waveguide.