• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.257-261
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• 2004

Computational fluid dynamics analysis was carried out for thermo-chemical flow field in Arcjet thruster with mono-propellant Hydrazine ($N_2$H$_4$) as a working fluid. The theoretical formulation is based on the Reynolds Averaged Navier-Stokes equations for compressible flows with thermal radiation. The electric potential field governed by Maxwell equation is loosely coupled with the fluid dynamics equations through the Ohm heating and Lorentz force. Chemical reactions were assumed being infinitely fast due to the high temperature field inside the arcjet thruster. An equilibrium chemistry module for nitrogen-hydrogen mixture and a thermal radiation module for optically thin media were incorporated with the fluid dynamics code. Thermo-physical process inside the arcjet thruster was understood from the flow field results and the performance prediction shows that the thrust force is increased by amount of 3 times with 0.6KW arc heating.

• 천문학회보
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• 제44권1호
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• pp.64.1-64.1
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• 2019

Thermal fracture and cracking near the perihelion are found to be a possible mechanism to produce the dust trail of the near-Earth asteroid, (3200) Phaethon (Jewitt and Li, 2013, ApJ 771, L36). It is, however, not well understood how the debris particles were escalated from the regolith against the asteroid's gravity. Thus, the scenario that these debris particles are responsible for the detected activities (Li and Jewitt, 2013, ApJ, 145, 154), is not complete yet. Here, we hypothesize that the thermal radiation pressure around the perihelion passage would exert substantial force outwards from the regolith on dust grains, and they can be lifted up and contributes the dust tail formation with further help of solar radiation pressure. Our modeling indicates that particles with sizes of roughly ~1-10 micron can be ejected from Phaethon by the mechanism, while a detailed model of gravitational field is required for accurate estimation of the particle size range. Our idea is not necessarily limited to Phaethon case, but is applicable to any atmosphereless bodies.

• Journal of Astronomy and Space Sciences
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• 제31권1호
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• pp.33-39
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• 2014

This paper describes an experimental approach to evaluate the effective doses of space radiations at high-altitude by combining the measured data from the Liulin-6K spectrometer loaded onto the air-borne RC-800 cockpit and the calculated data from CARI-6M code developed by FAA. In this paper, 15 exposed dose experiments for the flight missions at a high-altitude above 10 km and 3 experiments at a normal altitude below 4 km were executed over the Korean Peninsula in 2012. The results from the high-altitude flight measurements show a dramatic change in the exposed doses as the altitude increases. The effective dose levels (an average of $15.27{\mu}Sv$) of aircrew at the high-altitude are an order of magnitude larger than those (an average of $0.30{\mu}Sv$) of the normal altitude flight. The comparison was made between the measure dose levels and the calculated dose levels and those were similar each other. It indicates that the annual dose levels of the aircrew boarding RC-800 could be above 1 mSv. These results suggest that a proper procedure to manage the exposed dose of aircrew is required for ROK Air Force.

• 한국음향학회지
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• 제6권3호
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• pp.5-16
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• 1987

본 논문에서는 충격으로 인한 점탄성층을 가진 경계가 고정된 원형 평판으로부터의 음압복사에 대해 이론적, 실험적으로 연구한다. 층을 가진 평판의 운동을 모우드 해석법과 회전 관성효과와 전단력에 의한 변형을 고려한 Mindlin 의 평판이론으로부터 구한 고유치를 이용하여 구한다. 탄성구와 평판사이의 접촉력은 Hertz 이론으로 구하고 평판의 진동으로부터 복사되는 음압은 Rayleigh integral에 의해 구한다. 또한 층을 가진 평판으로부터 복사되는 음의 파형과 발생되는 음을 감소시키는 방법을 예측한다.

• 한국축산식품학회지
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• 제29권3호
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• pp.302-309
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• 2009

This study investigated the effects of infrared (IR) radiation combined with air blast thawing on the physical properties of pork. Regardless of air velocity, increasing IR dosage produced an exponential increase in the thawing rate of pork. This rate increased further when air blast velocity was increased. IR treatments showed significantly lower thawing loss than that of 0 Watt treatment, while increasing air velocity significantly increased thawing loss of pork (p<0.05). Increasing both IR power and air velocity tended to decrease the cooking loss of pork. Moreover, increased IR power tended to decrease the water holding capacity and shear force of pork. The shear force changes were not significant (p>0.05). Shear force also increased with increasing air velocity. In addition, the higher the air velocity the higher the shear force of pork. In Commission Internationale de l'Eclairage (CIE) colour determination, control of temperature prevented discolouration from overheating of sample surface. The results suggest that IR dosage combined with air blast has potential in thawed meat quality aspects, and that humidity control could prevent surface drying.

• 한국소음진동공학회논문집
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• 제25권1호
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• pp.33-39
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• 2015

This paper investigates the underwater acoustic radiation from a periodically stiffened cylindrical shell excited resiliently mounted machinery. Underwater acoustic radiation is important to a submarine. Generally, submarine structure can be modeled as stiffened cylindrical shell immersed in water. Analytical model is derived for the far-field acoustic radiation from machinery installed inside cylindrical shell. The analytical model includes the effect of fluid loading and interactions between periodic ring stiffeners. Transmitted force from machine to a shell through isolator can be different by the impedance of shell. In this paper the effect of a shell impedance for acoustic radiation is investigated. Impedance of a shell should be considered if thickness of a shell is thin.

• 한국음향학회지
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• 제27권7호
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• pp.357-364
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• 2008

정상파와 초고주파 집속 빔을 이용한 초음파 음향집게의 개발 가능성을 타진하는 것을 목적으로, 수중에 놓인 미세입자의 위치를 제어할 수 있는 시스템을 구축하였다. 그 시스템은 입자를 평면 정상파의 방사력에 의해 1차적으로 포획하여 집속 빔의 초점 부근으로 이동시킨 다음, 초고주파 집속 빔의 방사력을 이용하여 2차적으로 포획하는 것이다. 구축된 시스템에 의해 구형 미세 입자의 위치제어 실험을 행한 결과, 정상파 음장에서는 음압의 마디에 입자가 잘 포획되었으며, 주파수의 조정에 의해 그 입자를 임의 위치로 이등조작이 가능하였다. 그리고 단일의 초고주파 집속 빔에 의해서는 음원으로부터 멀어지는 방향으로만 구동력이 작용하나, 2개의 대항하는 집속 빔을 사용할 경우 그 중심 부근에 포획됨을 알았다.

• 한국방사선학회논문지
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• 제8권7호
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• pp.371-376
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• 2014

CdTe 멀티에너지 X선 영상센서와 ROIC를 패키징 하기 위한 flip chip bump bonding, Au wire bonding 및 encapsulation 공정조건을 개발하였으며 성공적으로 모듈화 하였다. 최적 flip chip bonding 공정 조건은 접합온도 CdTe 센서 $150^{\circ}C$, ROIC $270^{\circ}C$, 접합압력 24.5N, 접합시간 30s일 때이다. ROIC에 형성된 SnAg bump의 bonding이 용이하도록 CdTe 센서에 비하여 상대적으로 높은 접합온도를 설정하였으며, CdTe센서가 실리콘 센서에 비하여 쉽게 파손되는 것을 고려하여 접합압력을 최소화하였다. 패키징 완료된 CdTe 멀티에너지 X선 모듈의 각각 픽셀들은 단락이나 합선 등의 전기적인 문제점이 없는 것을 X선 3D computed tomography를 통해 확인할 수 있었다. 또한 Flip chip bump bonding후 전단력은 $2.45kgf/mm^2$ 로 측정되었으며, 이는 기준치인 $2kgf/mm^2$ 이상으로 충분한 접합강도를 가짐을 확인하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.743-747
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• 2003

In recent years, several studies of the practical application of active sound and vibration control have been developed to plate to plate response with various boundary conditions. This study considers vibration and sound radiation for the clamped rectangular plate. The radiation of a sound from rectangular plate can be calculated that the velocity of a vibrating plate is analyzed. The vibration formulation is based on a variation method for the vibration of the plate, and assumes no damping, no fluid loading of the structure. And the plate is exited by harmonic point force. The radiation of sound from plate is analyzed in the far field, and is calculated from the Rayleigh integral. The prediction results of vibration and sound level have proved with FEM or BEM.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.194-198
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• 2006

In this study, numerical modeling was performed to analyze air flow including radiation heat transfer inside a small chamber. Characteristics of heat transfer between source plate and target through glass are investigated for various surface temperature of heat source plate with buoyancy effect due to gravity force. Conduction heat transfer through the glass is considered and heat source plate is assumed to be a black body. Target surface temperature is largely affected by the radiation heat transfer. It can also be seen that as the source temperature increases target surface is dominated by radiation rather than convective heat transfer by air.