• Journal of the Korean Society of Propulsion Engineers
• /
• v.14 no.6
• /
• pp.38-44
• /
• 2010

The shock wave and boundary layer interaction patterns in an over-expanded rocket nozzle are associated with the production of undesirable side-forces during the start-up and shut-down processes of the engine. In the present work, a computational study is carried out to investigate the effect of the transient nozzle pressure ratio (NPR) on the flow fields inside the nozzle. The unsteady, compressible, axisymmetric, Navier-Stocks equations with SST k-${\omega}$ turbulence model are solved using a fully implicit finite volume scheme. NPR is varied from 2.0 to 10.0, in order to simulate the start-up and shut-down processes of the rocket engine. It is observed that the interaction patterns and the hysteresis phenomenon strongly depend on the time variation of NPR, leading to significantly different characteristics in the lateral forces.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.34 no.4
• /
• pp.53-62
• /
• 2006

Two-dimensional steady flowfields generated by transverse injection jets into a supersonic mainstream are numerically simulated. Fine-scale turbulence effects are represented by a k-${\omega}$ SST two-equation closure model which includes $y^+$ effects on the turbulence model. Solution convergence is evaluated by using Grid Convergence Index(GCI), a measure of uncertainty of the grid convergence. Comparison is made with experimental data and other turbulence models in term of surface static pressure distributions, the length of the upstream separation region, and the penetration height. Results indicate that the k-${\omega}$ SST model correctly predicts the mean surface pressure distribution and the upstream separation length for low static pressure ratios. However, the numerical predictions become less consistent with experimental results as the static pressure ratio increases. All these results are taken within 1% error band of grid convergence.

• Journal of Adhesion and Interface
• /
• v.19 no.3
• /
• pp.118-122
• /
• 2018

In this study, polyurethane hot melt adhesive containing ester groups was synthesized. Three kinds of chain extenders were used to find out the best chain extender. Results showed that adhesive containing 1,4-butanediol as a chain extender exhibited the highest peel strength among them. Also, it was found that there existed the optimum molecular weight of 1,4-butanediol containing adhesive for make the highest peel strength.. Moreover, hot melt adhesive containing 1,4-butanediol chain extender was applied to various kinds of textiles substrate such as cotton, polyester, and urethane coated polyester textiles to study the effects of different substrates on the peel strength and water resistance at $60^{\circ}C$. It was found that cotton substrate showed the highest peel strength and urethane coated polyester substrate showed the highest resistance on $60^{\circ}C$ water.

• Nuclear Engineering and Technology
• /
• v.26 no.4
• /
• pp.526-535
• /
• 1994

For the evaluation of the corrosion behavior of the aluminum cladding in the KMRR(Korea Multipurpose Research Reactor) fuel, a modified Griess correlation was derived by introducing a heat flux factor derived from the comparison of the measured in-reactor corrosion data with the prediction of the Griess correlation. As a design criterion on the corrosion to maintain the KMRR fuel integrity, prevention of the oxide spallation was conservatively selected, which is conservatively assumed to occur when the temperature difference across the oxide layer exceeds 114$^{\circ}C$. A bounding power history of the KMRR fuel was determined by examining all the power histories of the KMRR fuel from cycle 1 to equilibrium cycle, and used to predict the maximum possible corrosion. Results of the corrosion prediction of the KMRR fuel with the bounding power history showed that the maximum local thickness of the oxide layer would be below 50$\mu$m and the design criterion on the oxide spallation would be satisfied with a factor of two margin. Therefore, it can be said that corrosion of the cladding will not impair the integrity of the KMRR fuel. Nevertheless, the applicability of the modified Griess correlation to the KMRR needs to be further verified through the KMRR fuel corrosion surveillance.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.39 no.4
• /
• pp.523-530
• /
• 2019

Pavement distress and traffic accidents are caused by pot-hole. In addition, direct and indirect damages of road users are increasing, such as loss of life due to personal injury and damage to vehicles. Generally, the asphalt concrete pavements are continuously aging from the production process to the terminal performance period. Aging causes stripping due to cracks and moisture penetration and weakening the pavement structure to induce pot-hole. In this study, adhesion performance and moisture sensitivity were evaluated according to aging degree in order to investigate the effect of aging on asphalt pavement. As a result of the study, the viscosity of the asphalt binder was increased with aging and the bond strength of the aged was increased 2~3 times than that of the unaged. The results of accelerated aging test showed an increases in indirect tensile strength and the increase in the TSR (Tensile Strength Ratio) by 4.2~8.9 %. As a result, it is noted that the anti-stripping and adhesion performances of the aged asphalt concrete are improved compared to the unaged one under the aging conditions of asphalt binder coated on aggregates.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.47 no.1
• /
• pp.17-25
• /
• 2019

An intake of Aircraft becomes S-shaped geometry due to spatial limitation or procuring survivability. But curvature of the S-shaped geometry makes secondary flow or flow separation which is the cause of non-uniform pressure distribution. In this study, boundary layer suction is applied to RAE M 2129 S-Duct by attaching sub duct. Design variable is suction location and angle. A mass flow rate drawn out by suction at the sub duct outlet is constant over every model. A grid dependency test was conducted to verify validity of computation. The comparison among the CFD (Computation Fluid Dynamics), ARA experimental result, and ARA computation result of non-dimensional pressure distribution on the Port side and Starboard Side confirmed the validity of CFD. In this study, Distortion Coefficient was used for evaluating aerodynamic performance of S-Duct. The analysis, which was about flow separation, vortex, mass flow rate distribution, and pressure distribution were also investigated. Maximum 26.14% reduction in Distortion Coefficient was verified.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.48 no.5
• /
• pp.6-11
• /
• 2011

We have developed dissolved ozone decompose system in the used ozonated water for the semiconductor and LCD fabrication processes, which will be base of obtaining core process technology in the high performance, low price semiconductor and LCD fabrications. Using this technology, it is possible for the semiconductor wafer and LCD planer to process more rapid and chip, and productivity will be improved.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.233.1-233.1
• /
• 2016

화학적 방법에 의한 NTE graphite의 박리 또는 전도도 개선을 위한 도핑공정을 수행할 경우, 결함 및 불순물 생성에 의해 재결정화 공정 및 순도 개선을 위한 별도의 공정을 필요로한다. 본 연구에서는 건식 방법으로써 10,000K 이상의 초고온 RF 열플라즈마를 이용하여 in-situ 방법으로 흑연의 박리, 결함 제거, 결정성 향상 및 도핑 공정을 수행하고, 도핑특성을 평가하였다. 질소 도핑을 위하여 암모니아 가스를 첨가하여 NTE graphite를 도핑 처리하였으며, 시뮬레이션을 통하여 반응기 내부의 온도분포를 파악하고, 도핑을 위한 암모니아가스가 분해되어 도핑공정이 수행될 수 있는 투입위치를 결정하였다. 질소 도핑율은 암모니아 가스의 주입위치에서의 온도 및 가스 주입 유량 등의 공정조건에 따라 변화됨을 확인하였고, XPS 분석결과 최대 14.87 atomic%의 도핑율의 결과를 얻었다.

• Journal of Periodontal and Implant Science
• /
• v.30 no.3
• /
• pp.631-639
• /
• 2000

Desquamative gingivitis is characterized by a diffuse erythema of the free and attached gingiva associated with areas of vesiculation, erosion, and desquamation. Desquamative gingivitis is not a distinct disease entity but represents a reaction pattern of the gingiva to various stimuli. Pemphigus vulgaris, cicatricial pemphigoid, and lichen planus may presents as desquamative gingivitis. We observed 3 patients whose disease was limited to the gingiva, and studied them by light and direct immunofluorescence microscope. We classified them according to clinical, histologic, and immunopathologic observations. Identification of the underlying causes of desquamative gingivitis is of utmost importance and is dependent upon clinical, histologic, and immunologic criteria.

• Korean Journal of Cleft Lip And Palate
• /
• v.5 no.1
• /
• pp.11-20
• /
• 2002

정상 연구개의 근육조직에 대한 여러가지 해부학적 연구가 있어 왔지만, 구개열의 근육조직에 대한 연구는 이보다 훨씬 적었다. 또한 정상 연구개 근육조직의 형태를 잘 이해하는 것이 연구개 기능회복에 절대 필요할 것으로 사료되며 이에, 우리는 2개의 사체에서 채취한 정상상악골 및 연구개를 포함한 조직에서 연구개부위의 박리를 시행하여 근부착에 대한 해부학적 관찰을 시행하였다. 구개열환자에 있어서 연구개 근육들은 전후방적인 방향성을 가지고 있으며, 경구개 뼈의 후방 가장자리에 직접 근부착을 한다는 점에서 정상과 달랐다. 구개열 수술에 있어서 이러한 비정상적인 근부착을 박리하여 횡적방향으로 재구성하여 정중부에서 봉합하는 것이 정상적 연구개 sphincter를 만들고 연구개를 후방으로 후퇴시켜 정상적 연구개 해부구조를 재구성할 수 있는 방법이다.