• The Korean Journal of Rheology
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• v.6 no.2
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• pp.129-138
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• 1994

공압출되는 sheet die에서 고분자 물질의 비등온 유동유동을 수치모사하였다. 유변학 적 식으로 power-law model을 사용하였고, 격자생성법을 이용한 유한차분법을 사용하였다. 수치계산을 통해 수축채널에서의 온도 분포를 구해보고 점도가 채널에서의 온도 분포를 구 해 보고 점도가 채널에서의 압력강하 및 신장속도에 미치는 영향을 알아보았다. 압력강하는 외부 유체의 점도 및 heat dissipation의 영향을 크게 받았다. 신장속도는 외부 유체의 점도 가 증가함에 따라 커진 반면 내부 유체의 점도가 증가함에 따라 커진반면, 내부 유체의 점 도증가에 따라 감소하였고, heat dissipation에 의해 증가하였다.

• Korean Journal of Remote Sensing
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• v.24 no.2
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• pp.179-188
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• 2008

This study aims for generating a city spatial model required for the creation of a 3D noise map. In this study, we propose an efficient method to generate 3D models of the terrain and buildings using only a digital map and draft maps previously established without using any sensory data. The terrain model is generated by interpolating into a grid the elevation values derived from both the contour lines and the elevation point of the digital map. Building model is generated by combining the 2D building boundaries and the building elevations extracted from the digital map and the draft map, respectively. This method has been then applied to a digital map and three sets of draft maps created in the different times. covering the entire area of Yeongdeungpo-gu. The generated city spatial model has been successfully utilized for the noise analysis and the 3D visualization of the analysis results.

• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.643-648
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• 2003

The phase-shifting diffraction-grating interferometer proposed in the investigation uses a diffraction grating that performs manifold functions of beam splitting, beam recombination, and phase shifting. The reference and measurement waves generated by means of diffraction have different amplitudes depending on their orders of diffraction, so the interference fringe pattern resulting from the two waves tends to yield poor visibility. To cope with this problem, we select a phase grating of reflection type and attempt to improve the interference visibility with optimization of the groove shape of the grating through electromagnetic analysis.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.1
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• pp.231-236
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• 2017

The space harmonics generated by a plane-wave incident upon a multi-layered dielectric grating can undergo strong resonance scattering variations known as GMR(guided-mode resonance). To clarify these effects, we examine the field propagation and dispersion curve inside the grating region by using a rigorous equivalent transmission-line theory(RETT). The results show that, at the peak of a scattering resonance, the reflected mode is almost identical to a leaky wave that can be supported by the grating structure. Thus, we confirm and generalize previous research that has occurred GMR effect associated with the free-resonant character of leaky waves at multi-layered dielectric gratings. Quantitative simulation results illustrating the behavior of typical gratings are given, and the special case of normal incidence is discussed for TM mode.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1353-1357
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• 2007

국내에서 홍수 범람과 농지침수 분석에 이용되는 FLUMEN 모형은 원형섬 주변 처오름 현상과 급변류 해석만이 검증되어 소개되었다. 따라서 FLUMEN 모형의 만곡부나 합류부 등 개수로에서 적용가능성을 파악하기 위해서 하상경사 급변화, 원형 교각 주변 흐름변화, $180^{\circ}$ 만곡부 및 $90^{\circ}$ 합류부 실험 결과와 비교 검토를 수행하였다. FLUMEN 모형은 유한 체적법을 이용한 수치 계산으로 천이구간에서 발생하는 불연속점에서도 수치 모의가 잘 이루어지며, 만곡 수로와 합류 수로에서 전체적인 수심 분포가 최대 6%미만의 오차를 보이고 있어 매우 양호한 수치 모의를 할 수 있다. 또한 임의의 기하학적 형상을 원하는 위치에 반영한 지형 격자망 생성이 가능하다. 따라서 FLUMEN은 교각 주변, 만곡부 및 합류부 흐름 특성을 비교적 정확한 모의가 가능하며, 실제 하천에 적용하기에 충분한 수치 모의 능력을 지닌 모형이라 판단된다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.11-21
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• 2005

A three-dimensional parallel Euler flow solver has been developed for the simulation of unsteady rotor-fuselage interaction aerodynamics on unstructured meshes. In order to handle the relative motion between the rotor and the fuselage, the flow field was divided into two zones, a moving zone rotating with the blades and a stationary zone containing the fuselage. A sliding mesh algorithm was developed for the convection of the flow variables across the cutting boundary between the two zones. A quasi-unsteady mesh adaptation technique was adopted to enhance the spatial accuracy of the solution and to better resolve the wake. A low Mach number pre-conditioning method was implemented to relieve the numerical difficulty associated with the low-speed forward flight. Validations were made by simulating the flows around the Georgia Tech configuration and the ROBIN fuselage. It was shown that the present method is efficient and robust for the prediction of complicated unsteady rotor-fuselage aerodynamic interaction phenomena.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.2
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• pp.97-104
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• 2005

A simple but efficient grid generation technique by using the modified compressible form of stream function has been formulated. Transformation of a physical plane to a streamline plane, the Von Mises Transformation, has been widely used to solve the differential equations governing flow phenomena, however, limitation arises in low velocity region of boundary layer, mixing layer and wake region where the relatively large grid spacing is inevitable. Modified Von Mises Transformation with simple mathematical adjustment for the stream function is suggested and applied to solve the confined coaxial turbulent jet mixing with simple $\kappa-\epsilon$ turbulence model. Comparison with several experimental data of axial mean velocity, turbulent kinetic energy, and Reynolds shear stress distribution shows quite good agreement in the mixing layer except in the centerline where the turbulent kinetic energy distributions were somewhat under estimated. This formulation is strongly suggested to be utilized specially for free turbulent mixing layers in axisymmetric flow conditions such as the investigation of mixing behavior, jet noise production and reduction for Turbofan engines.

• Journal of Environmental Science International
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• v.16 no.4
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• pp.523-532
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• 2007

This study utilized the 1/25,000 topographic map of the upper area from the Geum-ho watermark located at the middle of Geum-ho river from the National Geographic Information Institute. For the analysis, first, the influence of the size of critical area to the hydro topographic factors was examined changing grid size to $10m{\times}10m,\;30m{\times}30m\;and\;50m{\times}50m$, and the critical area for the formation of a river to $0.01km^2{\sim}0.50km^2$. It is known from the examination result of watershed morphology according to the grid size that the smaller grid size, the better resolution and accuracy. And it is found, from the analysis result of the degree of the river according to the minimum critical area for each grid size, that the grid size does not affect on the degree of the river, and the number of rivers with 2nd and higher degree does not show remarkable difference while there is big difference in the number of 1st degree rivers. From the results above, it is thought that the critical area of $0.15km^2{\sim}0.20km^2$ is appropriate for formation of a river being irrelevant to the grid size in extraction of hydro topographic parameters that are used in the runoff analysis model using topographic maps. Therefore, the GIUH model applied analysis results by use of the river level difference law proposed in this study for the explanation on the outflow response-changing characters according to the decision of a critical value of a minimum level difference river, showed that, since an ogival occurrence time and an ogival flow volume are very significant in a flood occurrence in case of not undertow facilities, the researcher could obtain a good result for the forecast of river outflow when considering a convenient application of the model and an easy acquisition of data, so it's judged that this model is proper as an algorism for the decision of a critical value of a river basin.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.1
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• pp.41-50
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• 2002

An attempt has been made to establish digital bathymetric and topographic database in the form of grid point value(GPV) with an interval of one-minute horizontal space fur a wide region of seas adjacent to Korean Peninsula and also with an interval of one-arcsecond for coastal seas of Korean Peninsula. Especially terrestrial and marine data fusion work using mean sea level as vertical datum plane has been performed for one-arcsecond GPV dataset. It is believed that the compiled bathymetric dataset are reliable comparing with existing dataset so for and can be utilized for ocean simulations of intermediate scale process and also detailed coastal inundation process.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.560-565
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• 2016

최근 대형 컨테이너선의 개발이 지속적으로 이루어짐에 따라 슬래밍에 의한 선수 및 선미의 구조안정성 문제가 대두되고 있지만 설계 단계에서 슬래밍에 대해 고려하기에는 현상의 복잡성으로 인해 어려움이 많았다. 이를 위해 KRISO에서 시행된 WILS JIP의 선수 단면 형상 및 선미 단면인 쐐기 형상으로 격자를 생성하여 EDISON CFD 다상유동 해석자를 통해 수치해석을 시도하였다. 기존 방식과 달리 계산 시간 절감을 위하여 격자 변형 기법을 적용하지 않고 모형 시험결과를 기반으로 한 유입류 조건을 설정하여 입수 충격 문제를 해석해보았다. 그 결과, 선미 형상의 경우 선행연구와 유사하게 실험 결과에 근접한 유체 충격력을 정량적으로 얻어낼 수 있었다. 선수 형상의 경우에서는 구상 선수로 인해 파생되는 센서 위치별 충격력의 변화를 확인할 수 있었으며, 실제 유동에 가까운 유동 형상과 슬래밍에 의한 충격력을 개략적으로 구할 수 있었다.