• 한국분무공학회지
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• 제22권4호
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• pp.169-174
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• 2017

The objective of this study was to verify the experimental and numerical results of spray evolution injected from different types of the nozzle-hole geometries. Spray visualization was taken by high speed camera under the different conditions. For the simulations of spray tip penetration, turbulence, evaporation and break-up model were applied K-zeta-f, Dukowicz and Wave model, respectively. Also, the prediction accuracy of spray tip penetration was increased by varying the spray cone angle. At the same time, the results of this work were compared in terms of spray tip penetration, and SMD characteristics. The numerical results of spray evolution process and spray tip penetration showed good agreement with experimental one.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2000년도 제18회 학술발표회 논문개요집
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• pp.154-154
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• 2000

FED(Field emission display)의 FEAs(Field emitter arrays)에 형성되어 있는 micro-tip 은 tip 표면의 오염이나 진공내부의 잔류가스에 대단히 민감하다. 특히, emitter 물질의 일함수 및 겉모양 같은 기하학적 요소에 민감한 전계방출 소자의 특성상 tip 선단이 oxidation 될 경우 일함수가 증가하여 전자방출에 필요한 구동전압이 증가하고 전자 방출의 불균일성이 커지는 문제점이 발생한다. 이에 고진공의 동작 환경 및 FEAs 제작과정이나 공기의 노출에 발생하는 tip 표면의 오염물질 제거가 요구된다. 따라서 본 연구에서는 40$\times$40mm2 FEAs에 laser power, scan speed을 달리하며 laser(cw Nd-YAG, 1064nm)을 조사하였다. laser cleaning 효과를 보기 위해 laser irradiation 전, 후에 진공도 5$\times$10-7torr irradiation 후에 emitter tip의 뚜렷한 기하학적 모양의 변화를 볼 수는 없었지만, I-V 특성이 향상 되는 것을 볼 수 있었다.

• Journal of Welding and Joining
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• 제19권1호
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• pp.33-39
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• 2001

The welding quality by Gas Tungsten Arc Welding shows very high level, but the welding speed is lower than that of gas metal arc welding. Also, the welding quality by automatic GTAW is variable as the arc characteristics is changed by the consumption of electrode tip. The purpose of this study is to investigate the relation between the properties of tungsten electrode tip and the various arc characteristics at high current region. In this study, the high welding current 200A was applied to the repeated arc start test and long term arcing test using the $\phi$3.2 tungsten electrodes with cone angle 30$^{\circ}$, 45$^{\circ}$, 60$^{\circ}$sharp tip, and 60$^{\circ}$surface polished (S.P.) sharp tip. It was confirmed that the maximum arc pressure by the initial electrode condition was highest in 45$^{\circ}$sharp tip, and the next in 60$^{\circ}$sharp tip, the last was in 30$^{\circ}$sharp tip and 60$^{\circ}$S.P.. But, the maximum arc pressure after the repeated arc start test and long term arcing test was decreased considerably. But, the maximum arc pressure was highest also in 45$^{\circ}$ sharp tip after the tests, the next was in 30$^{\circ}$sharp tip, and the last was in 60$^{\circ}$sharp tip and 60$^{\circ}$S.P.. The arc start characteristics was the most excellent in 60$^{\circ}$S.P., By long term arcing test, the lanthania included in tungsten electrode was extinguished at tip surface preferentially, therefore the arc characteristics of electrode tip got worse.

• 한국유체기계학회 논문집
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• 제15권3호
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• pp.5-11
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• 2012

This study is to develop a 1kW-class horizontal axis wind turbine(HAWT) rotor blade which will be applicable to relatively low wind speed regions in southwest islands in Korea. Shape design of 1kW-class small wind turbine rotor blade is carried out using a blade profile with relatively high lift to drag ratio by blade element momentum theory(BEMT). Aerodynamic analysis on the newly designed rotor blade is performed with the variation of tip speed ratio. Power coefficient and pressure coefficient of the designed rotor blade are investigated according to tip speed ratio.

• 한국기계가공학회지
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• 제12권3호
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• pp.41-47
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• 2013

This study was carried out to improve the design of fuel injection nozzle for marine medium speed diesel engine. For this purpose, fuel injection nozzle was modeled and simulated using CATIA V5R19 and FLUENT & MSC Nastran. Analyses of flow and heat transfer, respectively, were performed to find the optimal design of fuel injection nozzle. As the results, big pressure drop, which may lead to cavitation damage, was occurred at inlet of fuel injection hole with diameter 0.3mm. Furthermore, it was confirmed that the increase of mean temperature of fuel injection nozzle was almost a half in comparison with that of fuel injection nozzle tip.

• 한국정밀공학회지
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• 제20권4호
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• pp.84-91
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• 2003

The paper presents a power control algorithm for a full pitch-controlled wind power system. The design of a pitch controller, in general, is performed by linearizing the torque in the vicinity of a operating point assuming the tip speed ratio is constant. For power control, however, the tip speed ratio is no longer a constant. In this study, a reference pitch model is derived in terms of a wind speed, angular velocity, and pitch angle. The reference pitch model is used to design a controller without linearizing the non-linear torque model of the blade. The validity of the algorithm is demonstrated with the results produced through sets of simulation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.185-188
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• 2002

The objective of present paper is to apply a stereoscopic PIV(Particle Image Velocimetry) techiique for measuring the 3 dimensional flow structure of turbulent wake behind a marine propeller with 5 blades. It is essential to measure 3-components velocity fields for the investigation of complicated near-wake behind the propeller. The out-of-plane velocity component was measured using the particle images captured by two CCD cameras in the angular displacement configuration.400 instantaneous velocity fields were measured for each of few different blade phases of $0^{\circ},\;18^{\circ},\;36^{\circ}\;and\;54^{\circ}$. They were ensemble averaged to investigate the spatial evolution of the propeller wake in the region ranged from the trailing edge to the region of one propeller diameter(D) downstream. The phase-averaged velocity fields show the viscous wake formed by the boundary layers developed along the blade surfaces. Tip vortices were formed periodically and the slipstream contraction occurs in the near-wake region. The out-of-plane velocity component has large values at the tip and trailing votices. With going downstream, the axial turbulence intensity and the strength of tip vortices were decreased due to the visous dissipation, turbulence diffusion and blade-to-blade interaction. The blade wake traveling at higher speed with respect to the tip vortex overtakes and interacts with tip vortices formed from the previous blade. Tip vortices are separated from the wake and show oscillating trajectory

• 한국정밀공학회지
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• 제28권5호
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• pp.591-598
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• 2011

Tip position control of a flexible cantilever is difficult due to the non-minimum phase dynamics that result from the finite propagating speed of a mechanical wave along the cantilever. In this paper, we propose a method for the tip position control using a light and cheap accelerometer that does not bring any significant change to the dynamics of the cantilever system. The linear system identification model of the flexible cantilever is obtained with measurements by a laser displacement sensor. A Kalman estimator is designed with this model and calculates the estimated tip position with the acceleration data of the accelerometer that is attached on the tip of the cantilever. To verify reliability of the estimator, the estimated tip position is used to the feedback control system that uses a fuzzy logic controller. The control results are compared with those of the fuzzy control system where the real tip position is measured by a laser displacement sensor. Also, the performance of the estimator with the accelerometer is presented and discussed.

• 대한기계학회논문집B
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• 제30권5호
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• pp.446-456
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• 2006

The effect of relative position of the stationary turbine blade for the fixed vane has been investigated on blade tip and shroud heat transfer. The local mass transfer coefficients were measured on the tip and shroud fur the blade fixed at six different positions within a pitch. A low speed stationary annular cascade with a single turbine stage was used. The chord length of the tested blade is 150 mm and the mean tip clearance of the blade having flat tip is 2.5% of the blade chord. A naphthalene sublimation technique was used for the detailed mass transfer measurements on the tip and the shroud. The inlet flow Reynolds number based on chord length and incoming flow velocity is fixed to $1.5{\times}10^5$. The results show that the incoming flow condition and heat transfer characteristics significantly change when the relative position of the blade changes. On the tip, the size of high heat/mass transfer region along the pressure side varies in the axial direction and the difference of heat transfer coefficient is up to 40% in the upstream region of the tip because the position of flow reattachment changes. On shroud, the effect of tip leakage vortex on the shroud as well as tip gap entering flow changes as the blade position changes. Thus, significantly different heat transfer patterns are observed with various blade positions and the periodic variation of heat transfer is expected with the blade rotation.

• 한국해양환경ㆍ에너지학회지
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• 제14권4호
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• pp.230-238
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• 2011

100 kW 용량의 조류발전용 수평축 터빈(HAT)임펠러의 성능에 대한 연구를 위하여 단면 및 날개 끝 형상을 변형시킨 지름700 mm의 모형 임펠러를 설계하고 부산대학교 예인수조에서 모형 시험을 수행하였다. 축척효과를 확인하기 위하여 각각의 임펠러에 대하여 회전수를 바꾸어 레이놀즈수 변화에 따른 특성을 살펴보았으며 날개끝속도비(TSR)별로 비교 검토 하였다. 본 연구에서 제안된 레이크 임펠러의 성능이 기존 임펠러 보다 우수함을 확인 하였으며 추후 실험시설을 보완하여 보다 큰 레이놀즈수에서 실험을 수행하고 계산과 비교할 예정이다.