• 에너지공학
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• 제15권4호
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• pp.250-255
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• 2006

원자력 분야에서 중성자 수송계산을 위해 개발되어 널리 사용되는 방향차분법을 시간 종속 복사 열전달식의 해를 구하는데 적용하였다. 광자의 방향별 밀도를 자체수반형 2계 편미분방정식으로 나타내어 해의 안정성을 높였고 매질의 온도방정식의 비선형성은 다단계 선형화법을 사용하여 근사하였다. 본 연구에서 개발된 해법을 전형적인 Marshak wave 문제에 적용하였고 계산 결과를 기존의 Monte Carlo의 계산결과와 비교하여 그 우월성을 보였다.

• 천문학회지
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• 제54권6호
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• pp.183-190
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• 2021

We have revisited Monte Carlo radiative transfer calculations for clumpy molecular clouds. Instead of introducing a three-dimensional geometry to implement clumpy structure, we have made use of its stochastic properties in a one-dimensional geometry. Taking into account the reduction of spontaneous emission and optical depth due to clumpiness, we have derived the excitation conditions of clumpy clouds and compared them with those of three-dimensional calculations. We found that the proposed approach reproduces the excitation conditions in a way compatible to those from three-dimensional models, and reveals the dependencies of the excitation conditions on the size of clumps. When bulk motions are involved, the applicability of the approach is rather vague, but the one-dimensional approach can be an excellent proxy for more rigorous three-dimensional calculations.

• 천문학회보
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• 제46권2호
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• pp.81.2-81.2
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• 2021

Emission features formed through Raman scattering with atomic hydrogen provide unique and crucial information to probe the distribution and kinematics of a thick neutral region illuminated by a strong far-ultraviolet radiation source. We introduce a new 3-dimensional Monte-Carlo code to describe the radiative transfer of line photons subject to Raman and Rayleigh scattering with atomic hydrogen. In our Sejong Radiative Transfer through Raman and Rayleigh Scattering (STaRS) code, the position, direction, wavelength, and polarization of each photon is traced until escape. The thick neutral scattering region is divided into multiple cells. Each cell is characterized by its velocity and density, which ensures flexibility of the code in analyzing Raman-scattered features formed in a neutral region with complicated kinematics and density distribution. We are continuously developing STaRS to adopt the absorption and scattering effect by dust. This presentation introduces STaRS and its current state and study.

• 한국의류학회지
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• 제20권4호
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• pp.647-654
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• 1996

The purpose of this study was to analyze the effect of fiber type, compressional resilience and moisture transport properties of wool and polyester fiber on the heat transfer of insulation nonwovens. The results obtained were as follows: 1) Overall heat transfer of wool nonwoven was slightly higher than that of polyester nonwovens. Warmability of wool nonwoven was lower than that of polyester nonwovens. The radiative heat transfer was in the range of 11~18% of overall heat transfer in polyester nonwovens and 25% in wool nonwoven. 2) As wool nonwoven compressed, overall heat transfer was increased by increasing radiative heat transfer and wamability was decreased due to the poor compressional resilience. 3) Increasing rate of heat transfer by moisture absorption in wool nonwoven was lower than that of polyester nonwovens. Thickness and compressional resilience of wool nonwoven were reduced extremely by moisture absorption.

• 대한기계학회논문집
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• 제16권10호
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• pp.1955-1962
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• 1992

본 연구에서는 무한 원형관 안의 복사에 참여하는 참여가스에 면을 도입시키 면, 참여가스로부터 원형관 벽면으로의 복사 열유속(radiatve heat flux)이 증진 또는 감소되는 현상을 연구하는 데 있다. 참여가스는 흡수, 방사 특성이 온도와 파장에 변하지 않는 회체가스(gray gas)이거나, 화석 연료 연소시 연소가스의 성분이며, 복사 에 참여하는, 수증기와 이산화탄소의 혼합물이다. 편의상, 이 가스를 실제가스(real gas)라 부르기로 한다.도입면은 동축 무한 원형관(coaxial Infinite cylinder)이다. 참여가스의 성분, 계의 직경, 동축 무한 원형관 사이의 직경비, 면의 방사율, 면과 가 스의 온도가 열전달 증진에 미치는 영향을 연구하고자 한다.

• 대한조선학회논문집
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• 제39권1호
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• pp.61-72
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• 2002

본 연구는 부유식 해양구조물(FPSO) 소각탑 구조물에 발생하는 온도 분포 및 열응력 해석 기법을 개발하는 것을 목표로 한다. 이를 위하여 소각열에 의하여 소각탑에 발생하는 온도분포를 구하는 과정을 이론화하고 온도분포 해석을 위한 과정을 제시하였다. 그리고 온도 분포가 발생시키는 열응력 해석을 위한 기본 과정을 제시하고 예를 보였다. 온도 분포 해석을 위하여 소각열에 의한 복사열전달 현상에 의한 열전달량, 설계 환경에 의한 대류 열전달량 해석 과정을 정립하였다. 정립된 과정을 근거로 온도 해석을 위한 해석 기법을 개발하였다. 또한 열응력 해석을 위한 해석 과정을 정립하고 그 과정을 근거로 열응력 해석 기법을 개발하였다. 본 연구의 결과는 부유식 해양구조물의 소각탑 열응력 해석 및 설계 과정에 활용될 수 있을 것이다.

• 대한기계학회논문집B
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• 제20권8호
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• pp.2681-2692
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• 1996

The finite-volume method for radiation in a three-dimensional non-orthogonal gas turbine combustion chamber with absorbing, emitting and anisotropically scattering medium is presented. The governing radiative transfer equation and its discretization equation using the step scheme are examined, while geometric relations which transform the Cartesian coordinate to a general body-fitted coordinate are provided to close the finite-volume formulation. The scattering phase function is modeled by a Legendre polynomial series. After a benchmark solution for three-dimensional rectangular combustor is obtained to validate the present formulation, a problem in three-dimensional non-orthogonal gas turbine combustor is investigated by changing such parameters as scattering albedo, scattering phase function and optical thickness. Heat flux in case of isotropic scattering is the same as that of non-scattering with specified heat generation in the medium. Forward scattering is found to produce higher radiative heat flux at hot and cold wall than backward scattering and optical thickness is also shown to play an important role in the problem. Results show that finite-volume method for radiation works well in orthogonal and non-orthogonal systems.

• 한국전산유체공학회지
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• 제16권1호
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• pp.22-29
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• 2011

In this study, the glass fiber drawing from a silica preform in the furnace for the optical fiber manufacturing process is numerically simulated by considering the radiative heating of cylindrically shaped preform. The one-dimensional governing equations of the mass, momentum, and energy conservation for the heated and softened preform are solved as a set of the boundary value problems along with the radiative transfer approximation between the muffle tube and the deformed preform shape, while the furnace heating is modeled by prescribing the temperature distribution of muffle tube. The temperature-dependent viscosity of silica plays an important role in formation of preform neck-down profile when the glass fiber is drawn at high speed. The calculated neck-down profile of preform and the draw tension are found to be reasonable and comparable to the actual results observed in the optical fiber industry. This paper also presents the effects of key operating parameters such as the muffle tube temperature distribution and the fiber drawing speed on the preform neck-down profile and the draw tension. Draw tension varies drastically even with the small change of furnace heating conditions such as maximum heating temperature and heating width, and the fine adjustment of furnace heating is required in order to maintain the appropriate draw tension of 100~200 g.

• 대한기계학회논문집B
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• 제21권10호
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• pp.1363-1370
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• 1997

Single liquid droplet combustion processes including heating, evaporation, droplet burning and flame radiation were theoretically investigated by adopting nongray gas radiation model for the radiative transfer equation (RTE). n-Heptane was chosen as a fuel and the numerical results were compared with the experimental data available in the literature. The discrete ordinate method (DOM) was employed to solve the radiative transfer equation and the weighted sum of gray gases model (WSGGM) was applied to account for nongray effect by CO$_{2}$, and H$_{2}$0. Therefore, detailed effects by nongray gas and its comparison with the gray gas model could be figured out in the results. It is found that the radiative heat flux is higher when the nongray model is used, thereby reducing the maximum gas temperature and the flame thickness, but the total burning time increases due to the deceased conductive heat flux in nongray model. Consequently, a better agreement with experimental data could be obtained by using nongray model.

• 천문학회보
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• 제44권2호
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• pp.44.3-44.3
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• 2019

Since the detection of 3.3-micron PAH (polycyclic aromatic hydrocarbon) and 3.4-micron aliphatic hydrocarbon features in the spectra of Titan (Bellucci et al. 2009; Kim et al. 2011) and Saturn (Kim et al. 2012), respectively, the 3.3-micron feature of gaseous CH4 has been thought to be still the important spectral feature in the 3-micron absorption structures of Titan and Saturn. However, the analyses of the 3.3-and 3.4-micron emission structures of Saturn revealed that the influence of the gaseous CH4 on the structures is rather minimal (Kim et al. 2019). We present synthetic spectra of gaseous CH4, and the PAH and aliphatic haze particles in order to show the degree of influence of their spectra on the 3.3-and 3.4-micron emission structures of Saturn, and we compare these synthetic spectra with currently available observations. We constructed these synthetic spectra using newly developed radiative transfer equations. These equations are able to address detailed radiative processes in the atmospheres containing various gases and haze particles. We expect these radiative transfer equations can also be widely applied to the investigation of radiative transfer processes and the analyses of the spectra of celestial objects such as the Earth, the Moon, planets, and interstellar nebulae.