• 한국기계가공학회지
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• 제11권2호
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• pp.27-33
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• 2012

A marine propeller is designed for preventing cavitation priority. Cavitation is a phenomenon which is defined as the vibration or noise by dropping the pressure on the high-speed rotation of the propeller. There has to be a enough thrust on the low-speed rotation for preventing cavitation. Thus, it has to be considered in the increasing of the number of blade and the angle of wing to design the propeller. In addition, flow resistance will be increasing by narrowing the width between blades. So high quality surface roughness of the hub to minimize flow resistance is required. Interference problems with tool and neighboring surfaces often take place from this kind of characteristics of the propeller. During 5-Axis machining of these propellers, the excessive local interference avoidance, necessary to avoid interference, leads to inconsistency of cutter posture, low quality of machined surface. Therefore, in order to increase the surface quality, it is necessary to minimize the cutter posture changes and create a continuous tool path while avoiding interference. This study, by using a MC-space algorithm for interference avoidance and a MB-spline algorithm for continuous control, is intended to create a 5-Axis machining tool path with excellent surface quality. Also, an effectiveness is confirmed through a verification manufacturing.

• 한국항공우주학회지
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• 제43권8호
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• pp.722-730
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• 2015

궤도천이용 추력기 시스템에 활용되는 다축 핀틀 추력기 시스템의 구동장치 개수 감소에 대한 필요성으로부터 구동장치 연동 메커니즘을 고안하였다. 본 연구에서는 궤도천이용 추력기 시스템의 주요 임무인 압력제어와 추력분배가 가능한 시스템 설계를 위해 구동장치 개수 감소 가능성 확인 모델을 설계하였다. 가능성 확인 모델을 근거로 피스톤을 적용한 연동 메커니즘을 고안하였고, 수치적 근거와 더불어 AMESim을 활용한 시뮬레이션을 통해 3개의 구동장치로 4개의 핀틀 추력기가 구동 가능하다는 결과를 얻었다.

• 한국항공우주학회지
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• 제46권3호
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• pp.189-196
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• 2018

고고도 무인기용 프로펠러의 추력 및 토크를 측정하기 위한 시험장치를 고안하였으며, 직경 1 m급 2개의 모델에 대해 성능시험을 수행하였다. 기계적인 동력을 측정하기 위해 프로펠러 회전축에 토크센서를 설치하였으며, 작은 추력을 정밀하게 측정하기 위해 프로펠러 및 구동부 전체를 지지하는 가이드레일 시스템을 적용하였다. 반복성시험 분석 및 불확도 분석을 통해 프로펠러 성능시험에 영향을 미치는 인자들을 고찰하였다. 불확도 분석결과는 추력 로드셀의 정밀도와 시험부 풍속을 결정하는 측정인자의 정밀도가 유사한 정도로 프로펠러 성능시험에 영향을 주고 있음을 나타내고 있다. 특정 RPM 조건에서 풍속을 변경시켜가며 프로펠러의 성능을 측정한 후, 5개의 서로 다른 RPM 조건에 대한 측정결과를 프로펠러 성능계수로 나타내었다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 춘계학술대회
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• pp.409-413
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• 2007

To assure the structural integrity for the hub and low speed shaft (LSS) of the drive train, it is necessary to obtain the ultimate aerodynamic loads acting on the wind turbine blade. The aim of this study is to predict the time histories of 3 forces and 3 moments at the hub and the LSS based on the design load case of the IEC 61400-1. From the calculated results most of the load components have rotor revolution frequency whereas thrust and torque of the LSS show blade passage frequency. It turns out that the EWM wind condition involves the maximum ultimate loads at both hub and LSS of the horizontal axis wind turbine.

• 지구물리
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• 제9권3호
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• pp.249-262
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• 2006

The 29 May 2004 offshore Uljin, Korea earthquake was predominantly thrust-faulting at a depth of approximately 12 (±2) km. The mainshock attained the seismic moment of M0 =5.41 (±1.87)  1016 N m (Mw = 5.1). The focal mechanism indicates a subhorizontal P-axis trending 264° and plunging 2°. The orientation of P- and T-axis is consistent with the direction of absolute plate motion generally observed within the plates, hence the cause of the May 29 shock is the broad-scale stress pattern from the forces acting on the downgoing slab along the Japan trench and inhibiting forces balancing it. The 29 May 2004 earthquake occurred along a deep seated (~12 km), pre-existing feature that is expressed on the surface as the basement escarpment along the western and southern slopes of the Ulleung basin. The concentrated seismicity along this basement escarpment suggests that this feature may qualify as a seismic zone - the Ulleung basement escarpment seismic zone (UBESZ).

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권1호
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• pp.73-82
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• 2016

In order to extend the operational life of Underwater Moored Platforms (UMPs), a horizontal axis water turbine is designed to supply energy for the UMPs. The turbine, equipped with controllable blades, can be opened to generate power and charge the UMPs in moored state. Three-dimensional Computational Fluid Dynamics (CFD) simulations are performed to study the characteristics of power, thrust and the wake of the turbine. Particularly, the effect of the installation position of the turbine is considered. Simulations are based on the Reynolds Averaged Navier-Stokes (RANS) equations and the shear stress transport ${\kappa}-{\omega}$ turbulent model is utilized. The numerical method is validated using existing experimental data. The simulation results show that this turbine has a maximum power coefficient of 0.327 when the turbine is installed near the tail of the UMP. The flow structure near the blade and in the wake are also discussed.

• 제어로봇시스템학회논문지
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• 제14권4호
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• pp.385-391
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• 2008

To effectively cope with a complexity of kinematic metrology due to workspace enlargement of the planar stage, the linear induction motor is suggested as its new driving source. Especially, the linear induction motor under uniform plate type of secondary doesn't inherently have a periodical force ripple which is generally shown in the brushless DC motor. But, it presents a poor transient characteristic at zero or low speed zone owing to time delay of flux settling, resulting in slow response. To improve the servo property of linear induction motor and apply successfully it to the precision stage, this paper discusses a modified vector control methodology. The controller has a novel input form, fixed d-axis current, q-axis current and forward-fed DC current, to control thrust force and normal force of the linear induction motor independently. Influence of the newly introduced input and the feasibility of controller are validated experimentally.

• 한국항공우주학회지
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• 제47권5호
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• pp.335-343
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• 2019

한국형발사체 3단의 무추력 비행구간에서는 추력기 자세제어시스템에 의해 롤, 피치, 요 축에 대한 3축을 제어하고, 추력 비행구간에서는 롤 축에 대한 제어를 추력기 자세제어시스템에 의해 수행한다. 발사체 자세제어시스템으로 사용되는 추력기의 추진제는 하이드라진과 같은 전통적인 독성 추진제가 주로 사용되어 왔으나 최근에는 친환경적인 ADN 및 HAN 등과 같은 무독성(청정) 추진제가 많이 연구되고 있다. 특히, 과산화수소 추진제는 독성이 없고 제작 및 시험평가에 있어서 상대적으로 저렴해서 독성 추진제의 대안 중 하나로 떠오르고 있다. 본 논문에서는 한국형발사체 3단의 자세제어를 위해 개발 중인 50N 급 과산화수소 단일추진제 추력기 자세제어시스템의 설계내용 및 시제품 제작, 시험결과를 기술하였다.

• Wind and Structures
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• 제32권5호
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• pp.471-485
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• 2021

Onshore wind turbines may experience substantially different wind loads depending on their working conditions, i.e. rotation velocity of rotor blades, incoming freestream wind velocity, pitch angle of rotor blades, and yaw angle of the wind-turbine tower. In the present study, aerodynamic loads acting on a horizontal axis wind turbine were accordingly quantified for the high tip speed ratio (TSR) at high yaw angles because these conditions have previously not been adequately addressed. This was analyzed experimentally on a small-scale wind-turbine model in a boundary layer wind tunnel. The wind-tunnel simulation of the neutrally stratified atmospheric boundary layer (ABL) developing above a flat terrain was generated using the Counihan approach. The ABL was simulated to achieve the conditions of a wind-turbine model operating in similar inflow conditions to those of a prototype wind turbine situated in the lower atmosphere, which is another important aspect of the present work. The ABL and wind-turbine simulation length scale factors were the same (S=300) in order to satisfy the Jensen similarity criterion. Aerodynamic loads experienced by the wind-turbine model subjected to the ABL simulation were studied based on the high frequency force balance (HFFB) measurements. Emphasis was put on the thrust force and the bending moment because these two load components have previously proven to be dominant compared to other load components. The results indicate several important findings. The loads were substantially higher for TSR=10 compared to TSR=5.6. In these conditions, a considerable load reduction was achieved by pitching the rotor blades. For the blade pitch angle at 90°, the loads were ten times lower than the loads of the rotating wind-turbine model. For the blade pitch angle at 12°, the loads were at 50% of the rotating wind-turbine model. The loads were reduced by up to 40% through the yawing of the wind-turbine model, which was observed both for the rotating and the parked wind-turbine model.

• Tribology and Lubricants
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• 제30권3호
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• pp.131-138
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• 2014

This study investigates the effects of the slopes of the rotational axis and bearing preloads on the natural frequencies and onset speeds of the instability of a rotor supported on gas foil bearings (GFBs). The predictive model for the rotating system consists of a rigid rotor supported on two gas foil journal bearings (GFJBs) and a pair of gas foil thrust bearings (GFTBs). Each GFJB supports approximately half the rotor weight. As the slope of the rotational axis increases from $0^{\circ}$(horizontal rotor operation) to $90^{\circ}$(vertical rotor operation), the applied load on the GFJB owing to the rotor weight decreases. The predictions show that the natural frequency and onset speed of instability decrease significantly with an increase in the slope of the rotational axis. In a parametric study, the nominal radial clearance and preload for the GFJB were changed. In general, a decrease in the nominal radial clearance lead to an increase in the natural frequency and onset speed of instability. For constant assembly clearance, the decrease in the preload changed the natural frequency and onset speed of instability with insignificant improvements in the rotordynamic stability. The present predictions can be used as design guidelines for GFBs for oil-free high-speed rotating machinery with improved rotordynamic performance.