• 한국세라믹학회지
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• 제49권6호
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• pp.620-624
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• 2012

The role of moisture remaining inside the deposition chamber during the formation of the cubic boron nitride (c-BN) phase in BN film was investigated. BN films were deposited by an unbalanced magnetron sputtering (UBM) method. Single-crystal (001) Si wafers were used as substrates. A hexagonal boron nitride (h-BN) target was used as a sputter target which was connected to a 13.56 MHz radiofrequency electric power source at 400 W. The substrate was biased at -60 V using a 200 kHz high-frequency power supply. The deposition pressure was 0.27 Pa with a flow of Ar 18 sccm - $N_2$ 2 sccm mixed gas. The inside of the deposition chamber was maintained at a moisture level of 65% during the initial stage. The effects of the evacuation time, duration time of heating the substrate holder at $250^{\circ}C$ as well as the plasma treatment on the inside chamber wall on the formation of c-BN were studied. The effects of heating as well as the plasma treatment very effectively eliminated the moisture adsorbed on the chamber wall. A pre-deposition condition for the stable and repeatable deposition of c-BN is suggested.

• Geomechanics and Engineering
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• 제16권3호
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• pp.309-320
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• 2018

In this paper, a numerical study using finite element method with considering soil-structure interaction was conducted to investigate the stress and deformation behavior of a sheet pile wall structure. In numerical model, one of the nonlinear elastic material constitutive models, Duncan-Chang E-v model, is used for describing soil behavior. The hard contact constitutive model is used for simulating the behavior of interface between the sheet pile wall and soil. The construction process of excavation and backfill is simulated by the way of step loading. We also compare the present numerical method with the in-situ test results for verifying the numerical methods. The numerical analysis showed that the soil excavation in the lock chamber has a huge effect on the wall deflection and stress, pile deflection, and anchor force. With the increase of distance between anchored bars, the maximum wall deflection and anchor force increase, while the maximum wall stress decreases. At a low elevation of anchored bar, the maximum wall bending moment decreases, but the maximum wall deflection, pile deflection, and anchor force both increase. The construction procedure with first excavation and then backfill is quite favorable for decreasing pile deflection, wall deflection and stress, and anchor forces.

• 한국분무공학회지
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• 제2권4호
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• pp.1-6
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• 1997

In the case of analyzing the combustion phenomena in a small high speed DI diesel engine, one demands the experimental results of the impinging spray on the wall as a basic characteristics. In the experiments presented here, diesel fuel oil was injected into a high pressure chamber in which compressed air at room temperature was charged. The single spray was impinged on a flat wall. The growth of the spray was photographed with transmitted light or scattered light. The effect of the spray axis angle to the wall on the impinging spray was revealed. Finally, the experimental results was presented, that is, the radius and height of the impinging spray was influenced by above mentioned variable.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제30회 춘계학술대회논문집
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• pp.149-152
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• 2008

30톤급 액체로켓엔진 실물형 연소기의 형상에 따른 연소특성속도에 대한 연구를 수행하였다. 본 연구에서 연소기의 형상은 연소기 헤드와 분리가 가능한 내열재 및 채널 냉각형 연소실(${\varepsilon}$=3.2), 그리고 일체형인 팽창비가 각각 3.5와 12인 재생냉각형 연소기이다. 연소압력은 약 53${\sim}$60 bar 그리고 추진제 유량은 약 89 kg/s이고, 적용된 분사기는 리세스수가 1.0인 동축 와류형이다. 설계점 연소시험에서 팽창비가 12인 일체형 재생냉각 방식의 연소기가 가장 큰 연소특성속도를 보였는데 이는 추진제인 케로신이 분무되기 전 챔버 냉각으로 인한 온도 상승에 따른 엔탈피의 증가 및 연소압력의 증가에 기인한 것이다.

• 한국자동차공학회논문집
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• 제7권7호
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• pp.54-65
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• 1999

In this study, the flow field, spray structure, and combustion process were investigated in a direct injection diesel engine having an offset bowl in a combustion chamber. The KIVA-3V code was used in this study. In order to obtain accurate results, a droplet atomization model, wall impingement model, and ignition delay concept were added to KIVA-3V code. The results showed that the offset bowl engine had a large vortex flow. The direction of this flow counteracted to the direction of fuel injection in one side of combustion chamber. It decreased local turbulent kinetic energy and eventually nonuniform combustion was resulted in an offset bowl engine. In comparison with a center bowl engine case, the peak cylinder pressure was decreased about 6%. Finally , the effect of swirl on combustion was investigated in an offset bowl engine . As the became stronger, the nouniform characteristics in combustion were increased.

• 한국자동차공학회논문집
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• 제9권4호
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• pp.18-26
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• 2001

OSKA engine was developed to remove the dense core of injection sprays. The engine uses impinging spray on a small pip, which spray after impinging is broken into smaller drops and disperses into fee space in chamber. In this paper the pip size is analyzed to give more dispersion of spray and fuel vapor. The gas phase is modelled by the Eulerian continuum conservation equations of mass, momentum, energy and fuel vapour fraction. The liquid phase is modelled following the discrete droplet model approach in Lagrangian form, and the droplet wall interaction is modelled as a function of the velocity normal to impaction lands. The droplet distributions, vapor fractions and gas flows are analyzed for various injection pressure cases. Numerical results indicate that the land diameter of 5.6mm has the best performance of spray dynamics and vaporization in the test sizes.

• 대한기계학회논문집A
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• 제32권2호
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• pp.135-142
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• 2008

Experimental studies on the aerodynamic coupling effect on natural frequencies, critical speed and flutter instability of rotating disks are investigated in this paper. The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and damping and stiffness components. The experiments performed using a vacuum chamber and ASMO/DVD disks rotating in vacuum, open and enclosure in several gaps with stationary wall give three main results. One is that the aerodynamic effect by the surrounding air reduces the natural frequencies and critical speeds of the vibration modes. The second is that natural frequency of disks rotating in open air is larger than that in enclosure. Finally, it is shown that the disk vibration is reduced as the gap between the disk and the rigid wall decreases.

• 한국의학물리학회지:의학물리
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• 제7권2호
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• pp.29-40
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• 1996

조사선량율 5mR/h 이상에서 동작하는 원통형 전리함을 설계ㆍ제작하고 상용의 전류계를 이용하여 전하수집 특성을 조사하였다. 전리함은 전체 길이 15.5cm, 직경 5.22cm인 원통형이고 활성체적은 190.4㎤이다. 전리함의 전극은 벽면, 중심축 및 보호전극으로 구성하고, 이들을 동심축상에 배치하여 바탕전류가 8.39$\times$$10^{-14}$ $\pm$1.5$\times$$10^{-15}$ A이 되게 하였다. 전리함에 인가된 전입이 400V일 때 Cs$^{137}$에 대하여 99.7%의 수집효율을 보였으며, 상용의 선량계와 비교한 결과 교정정수 4.531$\times$19$^{7}$ R/C를 구하였다. 에너지 응답특성은 Cs$^{137}$ 을 1로 하였을 때 Am$^{241}$과 Co$^{60}$ 는 각각 1.30, 1.05로 나타났다. 방사선이 전리함의 측면으로 입사할 경우 입사방향에 따른 응답특성의 차이는 무시할 수 있었다.

• 동력기계공학회지
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• 제10권1호
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• pp.90-95
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• 2006

Pneumatic control systems have been mainly used as a high speed operating system. Therefore, state change of air in a control volume was assumed to be adiabatic change and, pneumatic control systems have been analyzed by using this assumption. Especially, when absolute value of pressure change in the control volume is small, there is a tendency to neglect effect of temperature change on pneumatic control system because temperature change owing to pressure change is small. In this study, an effect of temperature change of air on the decompression control process was analyzed by considering change of mass flow rate, and heat transfer characteristics between air in the chamber and the chamber wall. As a result, this study could confirm that a slight temperature change of the air in the pneumatic pressure control system can influence on the dynamic characteristics of pressure response, and pressure control performance.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
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• pp.270-273
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• 2003

The characteristic of constant volume micro combustor was investigated experimentally. The shape of micro combustor was cylindrical and has row aspect ratio or has relatively large diameter compared with chamber height. Diameter and chamber height was varied to investigate the geometric effect of combustor on the flame propagation. Diameter of 15 mm and 7.5 mm was designed while chamber height was designed to be 1mm, 2mm, and 3mm. The effect of initial pressure was also investigated parametrically from 1bar to 3bar. The gas used in this study was stoichiometric mixture of methane and air. The maximum pressure achieved in down scaled combustors was lower than that of conventional combustor because heat loss to wall was dominant as expected. The maximum pressure responded favorably with the change of height of combustor and the initial pressure, the maximum pressure was also increased. The flame propagation was possible when the specific condition was satisfied. Although the quenching distance of stoichiometric mixture of CH4 and Air is 2.5 mm, the flame could propagate even under quenching distance as the initial pressure increased.