• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.396-399
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• 2007

풍력 블레이드용으로 설계된 에어포일에 대하여 풍동 시험을 수행하였다. 설계된 에어포일의 레이놀즈수 범위에 맞추고자 코드 길이 40cm의 모델에 대하여 유속 17m/s, 35m/s, 50m/s에 대하여 에어포일 표면에서의 압력과 에어포일 뒤쪽 레이크에서의 압력을 측정하였다. 이를 통하여 설계에 사용된 기법의 타당성과 설계된 에어포일에 대하여 설계 변수에 대한 실질적 만족도에 대하여 평가하였다. 이와 더불어 표면 거칠기에 대한 모사를 위하여 트립도트를 부착하여 시험을 수행하였다. 이를 통하여 레이놀즈수와 표면 거칠기에 따른 에어포일의 성능 및 유동 변화 특성에 대하여 파악 할 수 있었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.115.1-115.1
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• 2013

4세대 방사광 가속기에 설치되는 out-vacuum 언듈레이터 진공용기는 내경 5.2 mm, 길이 5 m인 매우 얇고 긴 형태로 제작된다. 좁은 간격의 언듈레이터 진공용기를 지나는 전자의 진행을 용이하게 하기 위해서는 높은 내부 진공도와 매끄러운 내부 표면이 요구된다. 현재 시제품으로 제작된 언듈레이터 진공용기의 요구 진공도는 Pave < $5{\times}10^{-7}$ mbar이며, 내부 표면 거칠기는 Ra < 150 nm 이하이다. 언듈레이터 진공용기는 알루미늄을 압출하여 제작한 후 초정밀 기계가공으로 제작하였다. 본 논문에서는 현재까지 수행한 공정 개발 결과를 정리하여 보고하고자 한다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.1
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• pp.91-97
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• 2013

The input parameters of scattering models for computing the backscattering coefficients of earth terrains are mainly soil moisture and surface roughness. The backscattering coefficients of soil surfaces are more sensitive to surface roughness than soil moisture. In this study, we propose a precise measurement method for roughness parameters and analyze measurement errors. We measured surface roughness using a pin-board profiler(1 m, 0.5 cm interval) and a laser profiler(1 m, 0.25 cm interval). The measurement differences between two profilers in an average sense are 0.097 cm for root-mean-square (RMS) height and 1.828 cm for correlation length. The analysis of the correlation functions and relative errors shows that the laser measurements are more stable than the pin-board measurements. The differences of the calculated backscattering coefficients using a surface scattering model between pin-board and laser profiler measurements are less than 1 dB.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.2
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• pp.289-296
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• 2019

Recently, the development of smartphone camera technology enables to shoot high quality video. In order to utilize these techniques in various ways, it is necessary to be able to transmit signals to an external device such as a external display. The transmission performance of the video signal is determined by the loss of the transmission line and the length of the wiring. In this paper, we propose the HDMI transmission line design criterion according to the wiring length changed according to the smartphone design and the surface roughness amplitude of the printed circuit board conductor wiring material. Also, we verified the proposed design criteria for the actual smartphone design. The proposed design criterion can be applied to various application fields including high-speed signal transmission line besides mobile application.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.6 s.97
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• pp.615-621
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• 2005

In this paper, a model for simulating synthetic aperture radar(SAR) images of earth surfaces. The earth surfaces include forest area, rice crop field, other agricultural fields, grass field, road, and water surface. At first, the backscattering models are developed for bare soil surfaces, water surfaces, short vegetation fields such as rice fields and grass field, other agriculture areas, and forest areas. Then, the SAR images are generated from the digital elevation model(DEM) and digital terrain map. The DTM includes ten parameters, such as soil moisture, surface roughness, canopy height, leaf width, leaf length, leaf density, branch length, branch density, trunk length, and trunk density, if applicable. The scattering models are verified with measurements, and applied to generate an SAR image for an area.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6C
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• pp.395-406
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• 2006

Drilled shafts are a common foundation solution for large concentrated loads. Such piles are generally constructed by drilling through softer soils into rock and the section of the shaft which is drilled through rock contributes most of the load bearing capacity. Drilled shafts derive their bearing capacity from both shaft and base resistance components. The length and diameter of the rock socket must be sufficient to carry the loads imposed on the pile safely without excessive settlements. The base resistance component can contribute significantly to the ultimate capacity of the pile. However, the shaft resistance is typically mobilized at considerably smaller pile movements than that of the base. In addition, the base response can be adversely affected by any debris that is left in the bottom of the socket. The reliability of base response therefore depends on the use of a construction and inspection technique which leaves the socket free of debris. This may be difficult and costly to achieve, particularly in deep sockets, which are often drilled under water or drilling slurry. As a consequence of these factors, shaft resistance generally dominates pile performance at working loads. The efforts to improve the prediction of drilled shaft performance are therefore primarily concerned with the complex mechanisms of shaft resistance development. The shaft resistance only is concerned in this study. The nature of the interface between the concrete pile shaft and the surrounding rock is critically important to the performance of the pile, and is heavily influenced by the construction practices. In this study, the influences of asperity characteristics such as the heights and angles, the strength characteristics and elastic constants of surrounding rock masses and the depth and length of rock socket, et. al. on the shaft resistance of drilled shafts are investigated from elasto-plastic analyses( FLAC). Through the parametric studies, among the parameters, the vertical stress on the top layer of socket, the height of asperity and cohesion and poison's ratio of rock masses are major influence factors on the unit peak shaft resistance.

• Korean Journal of Remote Sensing
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• v.36 no.5_1
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• pp.693-706
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• 2020

For ten meteorological observatories running an automated synoptic observing system (ASOS), we classified the observation environments into five classes based on the World Meteorological Organization (WMO) classification guidelines. Obstacles (such as topography and buildings) and land-cover types were the main factors in evaluating the observation environments for the sunshine duration, air-temperature, and surface wind. We used the digital maps of topography, buildings, and land-cover types. The observation environment of the sunshine duration was most affected by the surrounding buildings when the solar altitude angle was low around the sunrise and sunset. The air-temperature observation environment was determined based on not only the solar altitude angle but the distance between the heat/water source and ASOS. There was no water source around the ASOSs considered in this study. Heat sources located near some ASOSs were not large enough to affect the observation environment. We evaluated the surface wind observation environment based on the roughness length around the ASOS and the distance between surrounding buildings and the ASOS. Most ASOSs lay at a higher altitude than the surroundings and the roughness lengths around the ASOSs were small enough to satisfy the condition for the best level.

• Korean Journal of Agricultural and Forest Meteorology
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• v.19 no.4
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• pp.232-245
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• 2017

In this study, the high-resolution numerical simulation results considering landuse characteristics are analyzed by using single layer Urban Canopy Model (UCM) in Weather Research Forecast (WRF). For this, the impact of urban parameters such as roughness length and anthropogenic heat in UCM is analyzed. These values are adjusted to Seoul metropolitan area in Korea. The results of assessment are verified against observation from surface and flux tower. Forecast system equipped with UCM shows an overall improvement in the simulations of meteorological parameters, especially temperature at 2 m, surface sensible and latent heat flux. Major contribution of UCM is appreciably found in urban area rather than non-urban. The non-urban area is indirectly affected. In simulated latent heat flux, applying UCM is possible to simulate the change similarly with observations on urban area. Anthropogenic heat employed in UCM shows the most realistic results in terms of temperature and surface heat flux, indicating thermodynamic treatment of UCM could enhance the skills of high resolution forecast model in urban and non-urban area.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.1-12
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• 1992

Generally, laser machines with high generated power can be developed by means of enhancing their mean power, since the enhancement of mean power exerts an influence on peripheral parameters and machining performance. In this research, we evaluate the various machining properties by the use of two machines which bear different mean power each other, so that we may study various effects of the enhancement of mean power. As a result, when the mean power comes to be enhanced to 75%, we obtain the increase of output energy up to 69% and of peak power more than 95%, and also obtain almost twice of the cutting speed. Moreover we find the fact that if the test pieces have enough thickness in contrast with output energy, the pulse frequency moves toward the frequency bandwidth which takes proportion to the cutting speed mas well as to the amount of material removal per unit time. In addition it is finally obtained that the laser machine with high output power yields small taper degrees at kerf parts, while it has large cutting widiths and dross lengths.

• Journal of the Korean Association of Geographic Information Studies
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• v.1 no.1
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• pp.99-108
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• 1998

In order to represent the surface characteristics in local meteorological model, soil type, vegetation index, surface roughness length, surface albedo and leaf area index should be prescribed on the surface process parameterization. In this study, the $1^{\circ}/1^{\circ}leaf$ area index, surface roughness length, and snow free surface albedo and fine mesh NDVI with seasonal variation derived from the satellite observation were applied to the land surface process parameterization. From comparison between with and without satellite data in the interactions between biosphere and atmosphere, land and atmosphere, the sensitivity of the simulated heat, energy and water vapor fluxes, ground temperature, wind, canopy water content, specific humidity, and precipitation fields were investigated.