• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.230-235
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• 1997

Coupling loss variation as the shape of fiber ends and the fiber arrangement in a fiber Fabry-Perot cavity, formed with two optical fibers with dielectric mirror coatings on their ends, is analyzed. For the intended features it is assumed that one of two fibers is processed to have a concave mirror whose curvature is the same as that of the wavefront of the Gaussian beam from the first fiber. In this assumption, it was turned out that the coupling loss at the cavity length of 15 ${\mu}{\textrm}{m}$ is less than 0.5% even with tilt angle of 0.2$^{\circ}$, curvature error of 70 ${\mu}{\textrm}{m}$, cavity length error of 8 ${\mu}{\textrm}{m}$, and lateral alignment error of 0.5 ${\mu}{\textrm}{m}$. Thus, low loss and high-finesse fiber Fabry-Perot filters whose cavity length is greater than several ${\mu}{\textrm}{m}$ can be obtained easily if the receiving fiber end is properly formed.

• Journal of the Korean Institute of Landscape Architecture
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• v.37 no.3
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• pp.61-68
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• 2009

The objective of this study was to examine the possibility of utilizing the immersion stereoscopic image with a curved-screen-display as a tool for evaluating the landscape. The curved-screen-display ensures the continuity of the image and can be simultaneously evaluated by many people. Fifty-meter-wide Gangnamdaero Boulevard in Seoul was selected for this study, and the simulation was done using computer graphics. With the computer simulation, a questionnaire on landscape preferences was conducted according to different visual environments (immersion, non-immersion) and different projection types(stereoscopic or plane image). In the results of this study, the landscape preference was largely dependent on the immersion environment. Using the immersion-type simulation, the observer can easily evaluate the preference with higher judgment power. The stereoscope or plane projection type does not have any significant result in terms of its judgment power. This result implies that it is very important to strengthen the sense of immersion by expanding the screen into an angled view in which the observer can become immersed while making and projecting the simulation to evaluate the landscape. As a landscape evaluation tool for examining the efficiency and usefulness of immersion simulation, this study has limitations in that it controls many factors in street landscape that adversely affect judgment. Accordingly, a detailed comparison and verification of the stereoscopic image in various environments, including street width and building height ratio, must be conducted.

• Journal of Space Technology and Applications
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• v.1 no.3
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• pp.364-374
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• 2021

This research discusses the change in radio frequency (RF) characteristics according to the number of Gores on the deployable mesh antennas for potential micro-satellite applications. The deployable type of lightweight mesh antenna can be used for various space missions such as communication/SAR/ SIGINT. In order to implement an ideal curvature of antenna surface, sufficient number of antenna rib structures are required. However, the increase in antenna ribs affects various design factors of the antenna system, especially total system mass, complexity of deployable mechanism and reliability. In this paper, the proper number of ribs for the mesh antenna were derived by comparison of electro-magnetic (EM) simulation results of example of antenna model in accordance with the various number of ribs.

• Journal of the Korean Association of Geographic Information Studies
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• v.16 no.2
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• pp.129-140
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• 2013

This study reviewed different results according to the selection of viewpoints and considerations of the neighborhood in the analysis of view to regulate the height of buildings. To do this, 4 cases were set according to the analytical methodology and a GIS simulation was performed. Characteristics of each methodology were compared and analyzed by simulated values with ANOVA(analysis of variance) and post-hoc analysis. First, the method using moving viewpoints was found to be appropriate for the regulation of building height as it could reflect basic characteristics of landscape which was sequential and it did not show big difference in analysis result according to situational setting. Second, the method using grid viewpoints showed a problem that viewpoints at left and right sides viewed ridges of other mountains than the background mountains of the target land. Additionally, the simulation method that induces three-dimensional cross-sections between multiple sight-surface and virtual construction points created at viewpoints used in this study was found to be useful in the simulation review with various settings as it induced the marginal height of the spot quantitatively.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.2
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• pp.62-70
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• 2001

As the ship hull is a compound-curved structure, plate bending process is indispensible. The process includes press bending process for forming major 1st curvature and heating process for forming the rest curvature. Especially the heating process that is above 50 percents of entire bending work is carried out exclusively by skillful workers. Many researches have been made to automate the heating process but most of these are about line heating process and researches for triangle heating process are rare. This study is a fundamental study to develop a efficient analysis method for triangle heating and focused on clarifying the deformation characteristics of plate by triangle heating. In this paper, we carried out heating experiments and analysed the deformation characteristics of plate to explain the deformation characteristics of plates rationally by showing the phase transformed high temperature region. Also we investigated the heating effect on the hull material properties by mechanical tests.

• Fire Science and Engineering
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• v.30 no.2
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• pp.35-42
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• 2016

The membrane structure provides high satisfaction with lightweight, improved workability, reduced cost, and a free shape. Thus, its applications expanding. On the other hand, in an architectural membrane that is vulnerable to fire, the development of various architectural membranes with flame resistance is in demand. Therefore, this study applied basalt woven fabric safety for flame resistance, excellent heat insulation and thermal properties on an architectural membrane. The PTFE- coated basalt woven fabric membrane was compared with a PTFE coated glass fiber membrane by DSC/TGA, strength properties, flammability, and incombustibility properties. In addition, this study confirmed the membrane applicability of basalt woven fabric and basalt-glass hybrid woven fabric through a comparison with existing architectural membranes.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.55-59
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• 1992

최근 신 연삭 공구인 미세한 지립의 다이아몬드 휠을 이용함으로써 고경도와 취성을 지니는 엔지 니어링 세라믹스등의 신소재및 초경재 등 난삭재류를 대상으로 경면 가공을 추구하고자 노력이 진행중이다. 이는 래핑이나 폴리싱 등의 유리 지립에 의한 경면 창성법에 비하여 가공 능률이나 가공 정도가 높고 곡면이나 홈 등의 복잡 형상부의가공에도적용할 수 있다는 잇점이 있기 때문이다. 따라서 현재 이러한 신 연삭 가공법은 지금까지 연삭 가공후에 연마 가공 공정을 부가함으로써 초정 밀 효과를 지닐 수 있었던 각종 부품들에대한 단일 최종 마무리가공 공정으로의 응용에많은 기대를 걸고 있다. 본 연구는 높은 압축 강도치, 고온경도치와 내마모성, 강성 등을 지님으로써 외부 압력에 대한 변형률이 극히 적어 금형 칫수에가까운 제품을 생산할 수 있다는 특성으로 근래그 사용도가 급증 하고 있는 초경합금 금형재를 대상으로 해그 동안 난삭재에 대한 최적 가공 조건 설정이 정립되어 있지 못했던 관계로 인하여 기존의 숙련자 경험에만 주로 의존 할 수 밖에 없었던 단순한 다이아몬드 연삭 공구의 활용추세로부터 탈피하고 Diamond wheel 및 범용 연삭 공구를 최적으로 활용함으로써 연삭 가공의 초정밀화를 달성하며후 가공을 생략할 수 있는 가공 공정을 창출 해내기위하여, 상관 관계를 연삭 저항 및 가공 표면 품위등의 측면으로분석, 평가해봄으로써 초정밀 가공 차원에서의 최적 가공 조건 설정을 위한 지침을 명확하게 규명하기 위하여 실험적으로 수행하게 된 것이다.

• Journal of The Geomorphological Association of Korea
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• v.19 no.2
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• pp.81-98
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• 2012

This research aims 1) to analyse the spatial occurrence of red soils, in Korea 2) to predict their spatial distribution using terrain analyses, and 3) to interpret results from the perspective of pedogeomorphological processes. Red soils (often called red-yellow soils) in Korea are frequently found on welldrained plains and gently sloping areas. These soils are widely believed paleo-soils that were formed under hot and humid climatic conditions in the past. The spatial distribution of red soils was derived from the soil map of Korea, and a DEM based soil prediction was developed, based on a continuity equation to depict water and material flows over the landscape. About 64.5% of the red soil occurrence can be explained by the prediction. Close examinations between surveyed and predicted red soil maps show few distinctive spatial features. Granitic erosional plains at the inland of Korea show comparatively low occurrence of red soils, which might indicate active geomorphological processes within the basins. The occurrence of red soils at limestone areas is more abundant than that of the predicted, indicating the influence of parent materials on the formation of red soils. At and around lava plateau at Cheulwon and Youncheon, the occurrence of red soils is underestimated, which might partly be explained by the existence of loess-like surface deposits. There are also distinctive difference of prediction results between northern and southern parts of Korea (divided by a line between Seosan and Pohang). The results of this research calls for more detailed field-based investigations to understand forming processes of red soils, focusing on the spatial heterogeneity of pedological processes, the influence of parent materials, and difference in uplift patterns of the Korean peninsula.

• Korean Journal of Remote Sensing
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• v.28 no.5
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• pp.549-559
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• 2012

This paper presents a comparative analysis on the applicability of a priori statistic information about adjustment models when the surface shape parameters are estimated at an arbitrary point in an elevation data. Although the reliability of the estimates are known to be affected by surface condition and the adjustment models, there has been little research in a systematic and detail way. When the raw data have been taken from a real measurement, its true value cannot be known, however, thus this study used simulation data in order to analyze clearly the applicability of adjustment models. The generation of simulated data was performed by superimposing horizontal, slope, and curve surfaces and adding a certain amount of noise. Comparative analysis was performed by associating the a posteriori estimates with a priori statistics of each adjustment models. The experimental results show the estimation characteristics of adjustment models against varying surface conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.235-242
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• 2014

To investigate pressure distributions on the shaft surface of the air bearing, the commercial CFD software was employed to study three different nozzle geometries to improve the nozzle performance: general drill-shaped, matched cube-shaped and trimmed exit nozzles. Under the influence of stagnation point, the maximum pressure was observed at the center of shaft surface for all cases. Owing to the blocking effect of a fine gap between the shaft surface and the nozzle exit, the drill-shaped nozzle has the rapid local pressure increase near the nozzle exit corner, generating the ring vortex in the radial direction within pressure ratio of 6.92, and its pressure becomes negative in a certain range of downstream. In comparison, the contoured nozzle showed a local pressure increase in the measured range of pressure ratios, but a negative pressure appeared within the pressure ratio of about 10. The trimmed nozzle was seemed to extend the high pressure zone near the stagnation point in the radial direction substantially, and no negative pressure was appeared in the whole range. Based on these observations, it is found that trimming nozzle exit becomes more effective for improving the performance than modifying the nozzle inside contour.