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통계적 방법을 이용한 적외선 신호 대비값 계산 방법 연구
한국일(K.I. Han),최준혁(J.H. Choi),하남구(N.K. Ha),장현성(H.S. Jang),이승하(S.H. Lee),김동건(D.G. Kim),김태국(T.K. Kim) 한국전산유체공학회 2017 한국전산유체공학회지 Vol.22 No.1
Infrared signals are frequently used to detect objects exposed to wide variety of environmental conditions. Detection by infrared signature is accomplished by distinguishing objects by using the IR radiant contrast between objects and the background. There are several methods of estimating the IR radiant contrast. The inverse distance weighting method, which is one of the IR radiant contrast estimation method using the effect of distance from objects, is known to be an effective way to analyze radiant contrast for complex backgrounds. However this method has a disadvantage of requiring a long calculation time. In this study we propose a statistical method of estimating the IR radiant contrast by using randomly selected pixels of arbitrary number among background pixels to reduce calculation time. Some measured IR images in MWIR and LWIR regions are used to test the applicability of the method proposed and we found that the proposed method is very effective in determining the IR radiant contrast showing very rapid estimation with minar accuracy loss.
비균일 대기상태를 고려한 함정의 적외선 신호 특성 분석
최준혁(J.H. Choi),김도휘(D.H. Kim),한국일(K.I. Han),하남구(N.K. Ha),장현성(H.S. Jang),이승하(S.H. Lee),김동건(D.G. Kim),김태국(T.K. Kim) 한국전산유체공학회 2017 한국전산유체공학회지 Vol.22 No.1
The IR signal entering into a sensor is composed of the following components: the self-emitted component directly from the object surface, the reflected components of the solar and sky irradiance at the object surface, and the scattered component by the atmosphere without reference to any object surfaces. The self-emitted and reflected components from the object can be lowered by the atmospheric layer between the object and the IR sensor. The principle factors influencing the atmospheric transmittance are the air temperature, the relative humidity and the observation distance. Previous studies on IR signal transmission through the atmosphere are focused on uniform atmospheric conditions and the non-uniform nature of the atmosphere was not properly treated in modeling. In this study, we use the local atmospheric transmittance to simulate the non-uniform atmosphere in analyzing the IR signal from the object surface. The results show that the nonuniform analysis of the atmosphere becomes more important as the wavelength of IR signal increases.
방사성(放射性) 폐액(廢液)의 자연증발(自然蒸發)에 관한 연구(硏究)
강일식,김태국,유성연,Kang, I.S.,Kim, T.K.,Yoo, S.Y. 대한설비공학회 1993 설비공학 논문집 Vol.5 No.1
The performance of the evaporation facility of low radioactive liquid waste is studied experimentally. The evaporation facility comprises storage pools, feeding pumps, evaporation units with 1,040 sheets of cloth and air handling units. As the results of this study, it is found that the evaporation rate increases as the waste feed rate increases, the relative humidity of induced air decreases, and the air velocity increases. The modified Dalton's evaporation equation derived from experimental data is $E_h=(0.0168+0.0141V){\Delta}H$. The optimum operating conditions of the evaporation facility are waste feed rate of $4.5./hr.m^2$ and air velocity of 1.47m/sec.
모델 단순화에 의한 CFRP 복합 구조물의 유효 열전도율 추출 방법 연구
김동건(D.G. Kim),한국일(K.I. Han),최준혁(J.H. Choi),이장준(J.J. Lee),김태국(T.K. Kim) 한국전산유체공학회 2015 한국전산유체공학회지 Vol.20 No.4
The thermal balance test in vacuum chamber for satellite structures is an essential step in the process of satellite development. However, it is technically and economically difficult to fully replicate the space environment by using the vacuum chamber. To overcome these limitations, the thermal analysis through a computer simulation technique has been conducted. The CFRP composite material has attracted attention as satellite structures since it has advantages of excellent mechanical properties and light weight. However, the nonuniform nature of the thermal conductivity of the CFRP structure should be noted at the step of thermal analysis of the satellite. Two different approaches are studied for the thermal analyses; a detailed numerical modeling and a simplified model expressed by an effective thermal conductivity. In this paper, the effective thermal conductivities of the CFRP composite structures are extracted from the detailed numerical results to provide a practical thermal design data for the satellite fabricated with the CFRP composite structure. Calculation results of the surface temperature and the thermal conductivities along x, y, z directions show fairly good agreements between the detailed modeling and the simplified model for all the cases studied here.
격자 세분화 방법을 고려한 복사열전달 형상계수 계산 기법 연구
김동건(D.G. Kim),한국일(K.I. Han),최준혁(J.H. Choi),이장준(J.J. Lee),김태국(T.K. Kim) 한국전산유체공학회 2014 한국전산유체공학회지 Vol.19 No.1
Since experiments on the actual operational status are said to be very impractical because of their economic and repeatability problems, it is difficult to understand the thermal profiles of aerospace or military equipments. Thus, the CFD codes with considering the radiation heat transfer are used to compensate the defect. In case, analyzing the radiation exchanges between the object surfaces are very important. Because the temperature and the IR signal distributions of the object surface are significantly affected by the radiative heat transfer. To achieve accurate thermal radiation exchange between surfaces, it is important to calculate the radiation view factor precisely. Finer subdivision of meshes can be used to increase the accuracy of radiation view factor, but if the mesh is subdivided infinitely, the time required for calculation increases significantly and thus decreasing the efficiency. If the subdivision is not sufficient, assurance of accuracy is not guaranteed. In this paper, optimal mesh subdivision method using the solid angle has been successfully tested and found to be useful in increasing the efficiency of calculating the shape factors.