• Journal of the Korea Convergence Society
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• v.9 no.2
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• pp.1-6
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• 2018

In this study, the investigation results of conducted and radiated emission for DC/DC converter circuit applied in electric vehicles are presented. A frequency spreading circuit was used to improve the EMI characteristics of a power converter designed by using MPQ4433 chip. The frequency spreading circuit using a TLV3201 chip was designed and applied to the power converter. A PCB was fabricated based on the EMI minimization procedures and simulated and measured results were presented for the far-field and near-field conducted and radiated emissions using the fabricated circuit. The measurement were done as CISPR 25 standardized test procedures. It is clearly showed that the EMI characteristics were improved 20% in case frequency spreading was applied. The EMI reduction technique using the frequency spreading proposed in this study was first applied to the design of power converter module for automobile. It is expected that the method presented here can be effectively used for EMI improvement in the future.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.6
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• pp.375-382
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• 2020

Owing to the rapid development of infrared guided weapon systems, the threat to aircraft survivability is constantly increasing, and research on infrared stealth technologies are being conducted to ensure aircraft survival. In this study, we analyze the minimum infrared signature of an aircraft according to its flight altitude by considering the characteristics of infrared guided missiles, which detect the contrast signature between the aircraft and background. We conducted computational fluid dynamics simulations for the convective coefficient, and heat transfer simulations were performed considering convection, conduction, and radiation for flight conditions. Thus, we obtained the surface temperature distribution of the aircraft and analyzed the aircraft infrared signature based on the flow characteristics around it. Furthermore, the optimum emissivity for the minimum infrared signature was derived, and the effect of the infrared signature was analyzed when this optimum emissivity was applied to the fuselage surface for each flight condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.9
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• pp.737-744
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• 2012

The finite volume method for radiation is applied for the analysis of radiative base heating by SE and PE of the aircraft exhaust plume. The exhaust plume is considered as an absorbing, emitting, and scattering medium, while the base plane is assumed to be cold and black. The radiative properties of non-gray gases are obtained through the WSGGM, and the particle is modelled as spheres. The present method is validated by comparing the results with those of the backward Monte-Carlo method and then the radiative base heating characteristics are analyzed by changing such various parameters as particle concentration, temperature, and scattering phase function. The results show that the radiative heat flux coming into the base plane decreases with altitude and distance, but it increases as the particle temperature increases. The forward scattering of particles increases PE while it decreases SE.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.4
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• pp.309-318
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• 2019

The thermal design of the Lunar Terrain Imager (LUTI) on the Korean Pathfinder Lunar Orbiter (KPLO) was performed and the soundness of the thermal design was verified by thermal analysis. The thermal environment of the lunar mission orbit should be reflected in the thermal design because the IR radiation of the lunar surface is important, unlike the earth orbit. The components or modules exposed to the outside of the satellite are insulated with MLI as much as possible, but the camera tube and the radiator are functionally exposed, so the thermal shield using the concept of radiation shape factor is mounted on the front to mitigate IR radiation. The IR emissivity is important in the front side of the radiator that receives little solar radiation, and components that are susceptible to thermal deformation such as the tube use a radiation heater to minimize the temperature gradient. Through the investigation of computational results, it was confirmed that the thermal design of LUTI is stable in various situations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.8
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• pp.640-647
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• 2014

Infrared signature of aircraft exhaust plume is the critical factor for aircraft survivability. To improve the military aircraft survivability, the accurate prediction of infrared signature for the propulsion system is needed. The numerical analysis of thermal fluid field for nozzle inflow, free stream flow, and plume region is conducted by using the in-house code. Weighted Sum of Gray Gases Model based on Narrow Band with regrouping is adopted to calculate the spectral infrared signature emitted from aircraft exhaust plume. The accuracy and reliability of the developed code are validated in the one-dimensional band model. It is found that the infrared radiant intensity is relatively more strong in the plume through the analysis, the results show the different characteristic of the spectral infrared signature along the temperature, the partial pressure, and the species distribution. The continuous spectral radiant intensity is shown near the nozzle exit due to the emission from the nozzle wall.

• Korean Journal of Remote Sensing
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• v.29 no.4
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• pp.399-406
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• 2013

The quality of satellite imagery should be improved and stabilized to satisfy numerous users. The radiometric characteristics of an optical sensor can be a measure of data quality. In this study, a band aggregation technique and spectral response function of hyperspectral images are used to simulate multispectral images. EO-1 Hyperion and Landsat-8 OLI images acquired with about 30 minutes difference in overpass time were exploited to evaluate radiometric coefficients of OLI. Radiance values of the OLI and the simulated OLI were compared over three subsets covered by different land types. As a result, the index of agreement shows over 0.99 for all VNIR bands although there are errors caused by space/time and sensors.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.4
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• pp.385-390
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• 2012

A radial heat sink, adopted to LED(light emitting diode) downlight, was optimized. Discrete transfer radiation model (DTRM) was used to calculate radiation heat transfer, and numerical model was verified with experimental results. The effects of number of fin, long fin length and middle fin length on overall thermal resistance and radiation heat transfer were analyzed. As the emissivity increased, thermal resistance decreased due to the increment of radiation heat transfer. The radial heat sink was optimized and optimum number of long fins is 19~28, optimum length of long fin is about half of radius of heat fink and optimum fin ratio is 0.4~0.7.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.10a
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• pp.57-58
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• 2017

In this paper, we have studied electromagnetic susceptibility tests of the battery protection circuit module of a lithium ion battery. Electromagnetic susceptibility tests can be divided into conducted susceptibility for electromagnetic waves flowing through power lines, input / output lines, antenna ports, and radiated susceptibility for spatially radiated electromagnetic waves. A lithium ion battery of S company was used as an experimental sample, and conducted susceptibility tests were conducted on Surge (IEC 61000-4-5), Ring wave (IEC 61000-4-12), and Damped oscillatory wave(IEC 61000-4-18). Radiated susceptibility tests were performed according to IEC 61000-4-3.

• Journal of Environmental Impact Assessment
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• v.23 no.6
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• pp.477-491
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• 2014

The purpose of this study is to develop urban planning for mitigating thermal comfort by analyzing the relationship between various physical environmental factors and radiation fluxes focused on urban areas of Changwon city, Gyeongsangnam-do. Physical environmental factors were analyzed by sky view factor (SVF), land cover and land use types using GIS program. Radiation fluxes were measured upward and downward in solar and terrestrial radiation by mobile measurement during 3 days (2 daytime and 1 nighttime) in summer season. SVF is high in urban park less around buildings. High dense building sites were low. Downward solar radiation fluxes were the highest about $700W/m^2$ at daytime, and decreased in spatial type arranged dense buildings. Upward solar and terrestrial radiations was affected by land cover types that have thermal features such as reflectivity, emissivity, and heat capacity. Therefore, urban space needs appropriate planning with building arrangement, green walls and land cover replacement for mitigating thermal comfort in urban area.

• Defense and Technology
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• no.1 s.131
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• pp.54-65
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• 1990

미래의 전자전 체계들은 성능과 작전가용도가 증가되도록 요구될 것이며, 더욱 복잡해져 가고 있는 위협환경에 대응할수 있는 전자전 체계라야 할 것이다. 그러기 위해서는 유효복사 출력(ERP)을 높이고, ECM 에너지의 질을 더욱 개선하며, 방사에너지의 제어를 한층 잘해야 할 것이다. 이와함께 아주 높은 수준의 작전 가용도가 요구될 것인데, 이는 새로 개발되는 항공기들의 매우 높은 출격율을 유지하기 위한 것이다. 지원비용을 막대히 증가시키지 않고 이런 고도 수준의 가용도를 달성하려면 역시 신뢰성과 정비유지성을 상당히 개선해야만 한다