• Proceedings of the KSR Conference
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• 2006.05b
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• pp.1102-1107
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• 2006

• Korean Journal of Optics and Photonics
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• v.18 no.2
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• pp.142-148
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• 2007

A mechanically induced long-period fiber grating array was fabricated and its transmission characteristics were measured. The grating away consisted of a rubber cover and a 45 cm metal bar with 10 grating groups. Each grating group was composed of 60 gratings. The period of the grating of the grating groups was increased by $10{\mu}m$ increments from $690{\mu}m$ to $780{\mu}m$. The long period fiber grating was induced when the pressure was applied on the long period grating array and the resonant wavelength depended on the position of applied pressure. The experimental results shows that this long period fiber grating away can be used as a various band rejection filter or a fiber optic sensor.

• The Korean Journal of Rheology
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• v.6 no.2
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• pp.104-118
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• 1994

단섬유 보강 플래스틱 재료의 사출성형 충전공정에서 금형재의 유동장이 섬유 배향 상태를 형성하는데 중요한 역할을 할 뿐만 아니라 섬유의 배향상태가 역으로 유동장에 영향 을 미친다. 충전유동과 섬유 배향의 연계해석을 위하여 단섬유에 의한 추가적인 응력을 포 함하는 Dinh과 Armstrong의 이방성 구성방정식을 충전유동의 해석에 도입하였다. 평명방향 으로의 속도구배에 의한 응력을 고려하여 새롭게 유도된 압력 지배방정식과 에너지방정식을 유한요소법과 유한차분법을 이용하여 풀고 동시에 2차배향텐서의 변화방정식을 4차 Runge-kutta 방법을 이용하여 풀었다. 절점 게이트 주변의 확장유동영역과 라인게이트를 통한 수축유동영역에서 평면방향으로의 속도구배에 의한 응력이 유동장에 미치는 영향을 고 찰하였다. 확장유동영역에서는 평면방향으로의 속도구배에 의한 영향이 추가적인 유량으로 나타나면서 주어진 유량조건하에서 평면방향으로의 속도구배에 의한 응력을 고려하지 않은 경우보다 작은 압력구배를 나타냈다. 수축유동영역에서는 위와 반대의 결과를 보였다. 이러 한 경향은 섬유의 부피분율이증가하거나 모양비가 커짐에 따라 증가한다.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.2
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• pp.37-46
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• 2007

In this study, combustion fields of the end-burning hybrid combustor with tangential oxidizer injectors are examined. Momentum ratio of oxidizer is used as a main parameter to analyse the combustion efficiency with temperature, pressure, swirl velocity and mixture fraction field. It was found that as momentum ratio decreases the overall combustion efficiency is enhanced with the pressure field being insensitive to momentum ratio keeping quasi-uniform distribution. Irrespective to the momentum ratio, annular hot region commonly occurred in the upper combustion chamber where this phenomenon was left for a future improvement to be followed.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1986.11a
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• pp.47-51
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• 1986

로울러 베어링의 로울러는 길이방향으로 적당하게 Profiling하여 양단부에서 발생하는 응력집중을 줄이고 있다. 로울러와 레이스간의 접촉을 단순한 탄성접촉문제로 해석하는 경우에는 유막의 개념이 없어서 로울러와 레이스 사이의 압력분포와 유막형상을 정확하게 나타내기가 어려우므로 탄성변형과 압력에 따른 윤활유의 점도 변화를 고려한 탄성유체윤활(EHL)해석이 필요하다. 대부분의 해석은 무한장 로울러로 취급하는 것이 보통이며 실제의 로울러에 해당하는 유한한 길이의 선접촉 EHL 해석은 Mostofi & Gohar 및 Kuroda & Arai의 해석 정도이나 각각은 수렴하중이 작거나 로울러의 길이가 아주 짧은 경우에 해당한다. 본 연구에서는 FDM과 Newton-Raphson method를 이용하여 길이가 유한한 실제 크기의 Profiled 로울러에 대한 EHL상태에서의 압력분포와 유막형상을 보다 하중이 온 경우에 대해서 구하고자 한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.87-90
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• 2003

It has been well known that the major feature of compressible flow fields might be different depending on their formation processes. The objectives of the present study is to investigates the effect of jet development on the time history of supersonic jet flow field, accompanying nonequilibrium condensation. Especially, the behaviors of Mach disk diameter and location in a supersonic moist air jet are presented in terms of nozzle pressure ratio and initial relative humidity. The relative humidity of moist air is controlled at the nozzle supply, and the nozzle pressure ratio is varied to obtain the moderately underexpanded flows at the exit of the nozzle, installed in an indraft wind tunnel. It is found that at the same pressure ratio the Mach disk diameter increases with the initial relative humidity, while moves further upstream. Furthermore, the values of Mach disk diameter and location for increasing pressure ratio show larger than those for increasing.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.19-27
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• 2018

In this study, a numerical study was conducted to characterize the E-D nozzle which changes according to the nozzle pressure ratios. Three different numerical analysis models were designed by changing the pintle inflection angles. When the nozzle pressure ratio is low, the outside air flows into the E-D nozzle to form an open flow field. As the nozzle pressure ratio increases, the flow transition occurs to become the closed flow field where the recirculation region is isolated inside the nozzle. Also, the highest thrust coefficient was obtained in the analytical model with high pintle inflection angle at all nozzle pressure ratios.

• Journal of the Korean Vacuum Society
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• v.11 no.1
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• pp.68-75
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• 2002

It is observed the characteristic of the microwave air plasma in the wide range of the operating pressure, 1 mTorr ~ 760 Torr. The microwave air plasma was generated by an AC-type microwave source manufactured with a magnetron taken from a commertial microwave oven and the input power was fixed at 370 W. Characteristics of the plasmas were observed by an injection Langmuir probe and an OES(Optical Emission Spectroscopy). The breakdown electric field is drastically changed at 500 mTorr. For < 500 mTorr, the ratio of the breakdown electric field and the pressure decreased inversely to the pressure, $5.7\times10^4$V/m-Torr.However, the ratio increased linearly as 43 V/m-Torr for the operating pressure, > 500 mTorr. The minimum breakdown electric field was observed about 12. kV/m at 500 mTorr. It corresponds that the input frequency equals to the collision frequency. The effective collision cross section of the air at this pressure was calculated as $9.23\times10^{-l6}\textrm{cm}^2$.The results of the OES measurement revealed that the main ions were composed of the oxygen, argon, and nitrogen for > 500 mTorr. In contrast, only oxygen and argon ions were dominated for < 500 mTorr. ion temperature of oxygen (O(II)) in the air was decreased from about 1.2 eV to 0.5 eV as the pressure increased. Langmuir probe data shows that the plasma density for < 500 mTorr was higher that for > 500 mTorr.

• Journal of Navigation and Port Research
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• v.39 no.1
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• pp.77-82
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• 2015

Slamming means that the hull hits the waves and receives impact pressure. This slamming effect may cause harm to people and when you put the hull at risk. so it is very harmful for cargo safety. Therefor slamming impact pressure should be fully considered in ship designing. In this study the model of wedged type structure are produced aimed to simulate a free fall that the experiments were carried out on different weight and free fall height. The flow field has been obtained by 2-frame grey level cross correlation PIV(Particle Image Velocimetry) method and experiment was divided into water entry and water exit. The impact pressure of free fall structure by a pressure acquisition system apply to dewetron system. The angles between a model and the water surface are adapted $15^{\circ}$ respectively. The weight change of models was given as 1.5, 1.8 and 2.0kg. To study slamming phenomenon for free fall height the experiments were carried out by the free fall height of 100, 200 and 300mm. The experimental value of the impact pressure according to the changes in weight was increase impact pressure in proportion to the increase in weight and higher free falling height has also influenced the increase in impact pressures.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1826-1828
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• 2001

본 논문에서는 주기적으로 홈을 새긴 V자 홈과 평판 사이에 광섬유를 놓고 압력을 인가함으로써 유도되는 파장가변 가능한 장주기 광섬유격자의 제작 및 특성에 대해서 살펴 보았다. 이러한 방식으로 제작된 장주기 광섬유격자의 투과특성 및 모드결합 특성은 기존의 장주기 광섬유격자와 유사한 특성을 보이면서도 모드결합이 일어나는 중심파장을 거의 180nm 이상으로 가변할 수 있었다.