• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.943-947
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• 2014

NMPB 2008을 포함한 일부 소음 예측식에서는 기상학적 요소를 고려할 수 있다. 특히 NMPB 2008을 이용하여 소음을 예측할 경우에는 기상학적인 요소의 고려는 필수적이다. 하지만, 우리나라의 실제 기상 상황을 반영할 수 있는 방법이 없는 것이 현실이다. 본 연구에서는 기상학적 요소를 적용하기 위해서 하향 굴절 발생 빈도를 적용하여 소음도를 비교하였다. 기상학적 요소의 하향 굴절 발생 빈도의 증가에 따라 소음도가 증가하는 것을 확인하였고, 1kHz 이상의 주파수에서 거리에 따른 소음도의 차이에 상대적으로 큰 영향을 미치는 것을 확인하였다. 기상학적 요소의 적용은 예측 소음도의 정확도를 향상시킬 것으로 기대된다.

• Journal of KSNVE
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• v.11 no.2
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• pp.329-335
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• 2001

The analytical model of the ground wave can be used for the prediction of the noise level from a source above a plain and homogeneous ground surface with no obstacles nearby. Sound propagation along the surface of the ground can be affected by the roughness of the ground surface and the direction of the wind. The effects of the ground surface and the wind can be formulated in terms of the ground coefficient and the noise source parameter. Upward and downward conditions can also be addressed by considering the direction of the wind. The ground coefficient and the noise source parameter are estimated using the measured noise levels of two points under particular environmental condition, and the noise levels of arbitrary points under the same environmental condition can be estimated. The proposed method can be utilized to estimate the noise level of specific noise environment and its validity was confirmed with the results of actual field measurement.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1802-1806
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• 2009

최근 들어 국내외에서는 하천환경 및 생태서식처 기능을 갖는 자연형 하천으로의 복원에 대한 연구가 활발히 진행되고 있다. 이러한 하천복원의 범주에서 하천 내 설치되는 수공구조물에 대한 중요성이 많이 언급 되고 있는데 그 중 대표적인 것으로 수제를 들 수 있다. 하천 내 설치하는 수제(groyne)는 제방보호 및 유로변경의 목적으로 하천내에 시공되는 구조물 중의 하나로서 하천복원과정에 있어 필수불가결한 구조물 중의 하나로 인식되고 있다. 근래에 들어 경제성 및 환경성을 갖는 수제에 대한 연구로 변형수제에 대한 연구들이 진행 되고 있는데 변형수제의 대표적인 형상으로는 L형, T형 수제 및 굴절, 열쇠형 수제 등이 있다. 각각의 수제들은 그 형상에 따라 수제주변에서 국부적인 흐름구조가 다르게 발생하게 된다. 이러한 수제들은 수제 고유의 형태에 대한 흐름특성 연구들이 주로 이루어지고 있는 반면에 수제의 투영길이에 대한비교는 수행되지 않았다. 즉 동일한 수제길이를 갖더라도 설치각이나 형태에 따라 투영면적에 대한 유수단면적의 변화가 발생하게 된다. 본 연구에서는 그림과 같이 상향 또는 하향굴절수제를 대상으로 팔길이(AL)의 변화를 주었으며, 팔길이 변화로 인해 발생되는 투영길이(L')와 동일한 길이를 갖는 연직수제를 제작하여 흐름특성을 관측하고 비교하여 보았다. 수제는 군집 형태로 건설되는 것이 일반적이나 여러 가지 형태의 조합으로 건설되기도 하는데 이러한 투영길이에 대한 비교는 수제설계 시 기초자료로 활용될 수 있을 것이다.

• Journal of Bio-Environment Control
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• v.11 no.1
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• pp.5-11
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• 2002

In this study, new development of natural ventilation window was accomplished to control environment of greenhouse with no use of farced ventilation during hot season. The ventilation effect of developed ventilation window was investigated in experimental greenhouse which was designed using side wall panel and folding type panel fur natural ventilation. Folding panel type ventilation window was designed to open upper part of the side wall and top of the roof using two hinges which are located bottom of the side wall and the roof panel to grab one side of each panels and guide the other side along with the guidance rail. Developed ventilation window has top ventilation part with maximum moving distance X=ι (1-cos$\theta$)=848.5 mm and side ventilation part with maximum moving distance Y=ι/2 $\times$sin$\theta$=1,184.4 mm at 45$^{\circ}$ of theoretical opening angle. It took 4.5 minutes to open roof vent fully and temperature at 1.2 and 0.8 m height decreased after 1 minute from starting opening and became equilibrium state maintaining 3-4$^{\circ}C$ difference after 2 minutes from complete opening. Air exchange rate was 15.2~39.3 h$^{-1}$ which was more than 10~15 h$^{-1}$ of continuous type and Venlo type greenhouse. The descent effect of temperature by ventilation windows was two times higher than Venlo type greenhouse.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.3
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• pp.47-52
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• 2011

Directional couplers based on plasmonic waveguides with nano-scale three channels are designed by utilizing mode coupling effect as well as rib-guiding structure. Longitudinal modal transmission-line theory(L-MTLT) is used for simulating the light propagation and optimizing the design parameters. The designed plasmonic coupler operating as power splitter has nano-scale size of about 200~250 nm width. In order to achieve the desired power splitting ratio, the refractive index of guiding modes is evaluated along the width variation of center channel. Finally, a power splitter based on triple rib directional coupler, which ensures maximum power transfer from one outermost guide to the other outermost guide, is designed.

• Journal of Space Technology and Applications
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• v.4 no.1
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• pp.48-61
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• 2024

In this paper, we introduce the concept of the cube satellite Chungnam National University Laser Unity Bus (CLUB), which can provide an integrated infrastructure for various ground-space laser applications. With the advent of the new space era, the rapid expansion of space utilization has begun to reveal the limitations of conventional radio frequencies. As space missions diversify, lasers are garnering attention as a viable alternative. Between ground and space, lasers are applied in various fields including satellite laser ranging (SLR), laser weapons, and laser communication. However, laser used between the ground and space are significantly influenced by the Earth's atmosphere. Consequently, understanding the atmospheric effects on laser propagation is crucial. In particular, atmospheric turbulence, which refracts and distorts laser beams, intensifies closer to the Earth's surface, exerting a greater impact on the uplink than on the downlink. While downlink verification is facilitated by ground detection, verifying the uplink poses challenges due to the necessity of space-based detection. In response to these challenges, we propose the idea of cube satellite as a means to enhance understanding and verification of laser propagation in the uplink. Additionally, we present the results of conceptual design by analyzing requirements, focusing on mission design of the CLUB cube satellite, following the stages of systems engineering for systematic cube satellite development.

• The Journal of the Acoustical Society of Korea
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• v.34 no.2
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• pp.98-107
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• 2015

It is investigated that there exists the possibility of the false target signals induced by reverberation in an active sonar system due to the internal waves in shallow water. The rays down-refracted from the internal waves may generate strong bottom-reverberation signals, which can result in false target signals. Sound waves emitted from a source propagate 3-dimensionally. Therefore, the study of internal waves on the reverberation should be studied for azimuthal direction as well as 2-dimensional (r-z) plane. Internal-wave modelling was conducted, based on solitons which were predicted with the various conditions such as, the range of source-soliton, horizontal widths of soliton. Variable depth sonar (VDS) was assumed as a source, of which the depth was located in the minimum sound speed layer in a simulation environment. Finally, the simulation on the reverberation level with time was made based on ray-based reverberation model, and the results implied that several false-target signals could be displayed on the PPI(Plan Position Indicator) scope simultaneously with range from source to soliton, and the horizontal width of soliton.