• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.4
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• pp.359-370
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• 2015

The present study aims to numerically investigate the behavior of liquid droplet driven by capillarity force imbalance on horizontal surfaces ranging from hydrophilic to hydrophobic, under various conditions. The droplet behavior has been simulated using an in-house solution code(PowerCFD), which employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with interface capturing method(CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The detailed droplet behavior was obtained under various conditions for droplets with different initial shapes, contact angles and surface tension forces(or Bond number). The mechanism of droplet transport was examined using the numerical results on the droplet shapes.

• 한국생물공학회:학술대회논문집
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• 2003.10a
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• pp.384-387
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• 2003

We measured the inlet concentration of odorous gases from the food-waste composting facility for 90 days. In consequence of this survey, we ascertained that the gaseous concentration was detected $10{\sim}100ppm$ in operating time, but $0{\sim}10ppm$ in a shutdown of the facility. The initial removal efficiency of this biofilter was roughly represented 80%, however, 90% before and after twenty days. We have thought that this biofilter accomplished the treatment of those odorous gases effectively, because the pressure-drop was not exceeded a value of $20mmH_2O$ after 90 days.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.235-244
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• 2001

Liquefaction may be caused by sudden decrease in the soil strength under undrained conditions. This loss of soil strength is related to the development of excess pore pressures. During this study, fines content affects the maximum and minimum void ratios are investigated. The results of static and cyclic triaxial test on silty saturated sands are presented. These tests are performed to evaluate liquefaction strength and static and cyclic behavior characteristics. The samples are obtained from Saemangeum and drying on air. The main results are summarized as follows : 1) The maximum and minimum void ratio lines follow similar trends. 2) Maximum and minimum void ratios are established at 20~30% fines content. 3) As confining pressures and overconsolidation ratio are increased, the resistance to liquefaction are increased. 4) Instability friction angles are increased with increasing initial relative density. 5) The resistance to liquefaction are decreased with increasing effective stress ratio.

• Fire Science and Engineering
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• v.18 no.4
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• pp.35-41
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• 2004

The water spray characteristics of the sprinkler heads is a very important factor affecting the fire suppression performance, and it is largely dependent on the shape of the head nozzle. This study investigated shape factors and spray distribution performances for the sprinkler heads of four domestic companies with big market shares. The experimental results revealed that all flow constants exceeded the required regulation limits, however showed big differences between head types although they have the same design limit. They were however relatively consistent regardless of the pressure increases. The spray distribution of some head samples showed severe directional eccentricity, which suggests more study for the improvement.

• Proceedings of the KIPE Conference
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• 2009.11a
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• pp.179-181
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• 2009

고압 방전 램프는 점등 후부터 정상상태에 이르기까지 방전관 내부의 온도 및 압력이 광범위하게 변화하는 복잡한 동작 특성으로 모델링이 어렵다. 이러한 특성은 램프를 구동하는 안정기의 설계에 어려움이 따른다. 램프의 구동에는 초기 점화 시 높은 점화용 전압 펄스를 필요로 한다. 점화 후에 정상상태에 다다르면 램프 전극의 소모를 줄이기 위해 교류로 구동되어야 한다. 하지만 램프를 교류로 구동하게 되면 음향 공진 현상이 발생할 수 있다. 음향 공진 현상은 램프 구동 전류의 맥동성분이 큰 경우에도 발생을 할 수 있으므로 구동 전류의 맥동 성분의 크기는 최소화 돼야 한다. 램프의 수명시간을 길게 하려면, 안정기는 램프를 정격전력으로 구동하여야 한다. 따라서 안정기에서는 정전력 제어가 필요하게 된다. 램프 전류의 극성이 변화할 때, 램프 전류는 spike전류와 중첩이 된다. 본 논문에서는 spike 전류를 저주파구형파 램프 전류의 포락범위 안에 유지하고, 고주파 스위칭시손실을 줄이기 위해 소프트 스위칭 기법을 이용한 회로 설계를 제안했다. 제안된 방법은 시뮬레이션 및 이론적 수식적 방법으로 검증 했다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.4
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• pp.34-42
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• 2004

In this paper, a double gimbal is used for roll/yaw attitude control of spacecraft and two feedback controllers are designed. One is a PD controller of no phase difference between roll and yaw control input. The other is a PD controller with a phase lag compensator about the yaw control input. The phase lag compensator is designed a first order system and a lag parameter is designed for the control of yaw angle. There are two case simulations for each of controllers; constant disturbance torques and initial errors of nutation. We obtain the results through simulations that a steady-state error and a rising time of yaw angle are developed by the compensator. In this paper, simulation parameters use the values of KOREASAT 1.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.303-306
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• 2011

An experimental study has been conducted to investigate the effects of an ultrasonic standing-wave field to the behavior of methane/air premixed flame. Visualization technique utilizing the schlieren method was employed for the observation of premixed flame behavior. The shape of flame front and local flame velocity were measured according to the variation of reactants pressure and chamber opening/closing condition. The flame front was distorted and severely deformed to a lotus-type flame by the interaction of ultrasonic standing-wave and the reflection wave coming from an end wall of reactor.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.548-553
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• 2011

The device for studying combustion characteristic of aluminum powder and water was developed. The device has ability to adjust temperature, pressure, and equivalent ratio to some specified value which effect on combustion characteristic of aluminum and water mixture. Methane combustor, water supply device, aluminum powder feeder, and linear combustor are assembled to aluminum combustion test device. Each device has the ability to supply matter to combustor on steady and quantitatively controlled manner and test sequence specified by user can be automatically controlled. The combustion of aluminum powder was observed when integrated device was operated normally.

• Journal of Powder Materials
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• v.22 no.3
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• pp.203-207
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• 2015

This study investigated the microstructure and wear resistance property of HPHT(high pressure high temperature) sintered PDC(polycrystalline diamond compact) in accordance with initial molding pressure. After quantifying an identical amount of diamond powder, the powder was inserted in top of WC-Co sintered material, and molded under four different pressure conditions (50, 100, 150, $200kgf/cm^2$). The obtained diamond compact underwent sintering in high pressure, high temperature conditions. In the case of the $50kgf/cm^2$ initial molding pressure condition, cracks were formed on the surface of PDC. On the other hand, PDCs obtained from $100{\sim}200kgf/cm^2$ initial molding pressure conditions showed a meticulous structure. As molding pressure increased, low Co composition within PDC was detected. A wear resistance test was performed on the PDC, and the $200kgf/cm^2$ condition PDC showed the highest wear resistance property.

• Elastomers and Composites
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• v.34 no.3
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• pp.239-246
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• 1999

Side wall samples from a used automotive tire were subjected to subcritical and supercritical decomposition and extraction with three solvents, water, 28% ammonia solution and ammonia. For 6mm cube samples the rate of supercritical extraction with water followed a first-order kinetics with an activation energy of 140 kJ/mol. Solvent power of 28% ammonia so lotion at supercritical condition was found to be higher than supercritical water at initial extraction as pressure decreased. These phenomena were considered to be an effect of ammonia involved in water.