• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1566-1569
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• 2008

The flow visualization is conducted in order to investigate an unsteady flight characteristic of a model dragonfly. The flapping wings are analyzed using smoke-wire and high speed camera. The results of this experiment show that three mechanisms and high incidence angle of the wings are responsible for the lift. The leading edge vortex, which is induced by the rapid acceleration of the wing at the beginning of a stroke, causes the lift enhancement. The delayed stall during the stroke and the fast supination and pronation of the wing near the end of each stroke are also responsible for the lift generation.

• Journal of computational fluids engineering
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• v.10 no.2
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• pp.60-68
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• 2005

For study on the unsteady wall interference effect, flows around a forced oscillating airfoil in closed test-section wind tunnels have been numerically investigated by solving compressible Navier-Stokes equations. The numerical scheme is based on a node-based finite-volume method with the Roe's flux-difference splitting and an implicit time-integration method coupled with dual time-step sub-iteration. The Spalart-Allmaras one-equation model is employed for the turbulence effect. The computed results of the oscillating airfoil having a thin wake showed that the lift curve slope is increased and the magnitude of hysteresis loop is reduced by the interference effects. Since the vortex around the airfoil is generated and convected downstream faster than the free-air condition, the phase of lift, drag and pitching moment coefficients was shifted. The pressure on the test section wall shows harmonic terms having the oscillating frequency contained in the wail effect.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.879-885
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• 2000

This study is carried out to make clear the reason of occurrence of sudden acceleration incident of AT vehicle. The stepping motor is used to control the engine speed at idle by compensating the volume of air. By the way it's valve is contaminated by blow-by gas, deposit and back fire etc. This contamination could occur the load of motor at low temperature. This plays an important role in damaging the motor's coil with the motor's performance interfered. If it's coil is damaged the ISC could malfunction. If these phenomena occur, the speed of engine may increase or the engine may stall with hunting.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.845-850
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• 2003

Unsteady nature of a tip leakage vortex in an axial flow fan operating at a design and off-design operating conditions has been investigated by measuring the velocity fluctuation in a blade passage with a rotating hotwire probe sensor. Two hot-wire probe sensors rotating with the fan rotor were also introduced to obtain the cross-correlation coefficient between the two sensors located in the vortical flow as well as the fluctuating velocity. The results show that the vortical flow structure near the rotor tip can be clearly observed at the quasi-orthogonal planes to a tip leakage vortex. The leakage vortex is enlarged as the flow rate is decreased, thus resulting in the high blockage to main flow. The spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region at higher flow rates than the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition.

• Proceeding of EDISON Challenge
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• 2012.04a
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• pp.17-20
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• 2012

본 연구는 전산유체해석 프로그램인 EDISON_CFD를 이용하여 NACA63-425 에어포일과 이 에어포일을 기반으로 만든 뒷전 두께가 2% 4%인 NACA63-425G02, NACA63-425G04에 대하여 두께 변화에 따른 공력 특성 변화를 수치해석을 수행 하였다. 난류점성내의 압축성 조건에서 받음각에 따른 양력계수, 항력계수, 양항비 등을 비교하여 Flatback 에어포일의 장단점에 대하여 결과를 분석해 보았다.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.409-417
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• 2009

An investigation of surge inception in a centrifugal compressor was done with measurements of steady and unsteady static pressure. Vaneless diffuser and vaned diffuser were tested. Analyses of the static pressure and the pressure fluctuation showed that stall at the impeller leading edge occurred at first, and then it extended to downstream. In case of the vaneless diffuser, deterioration of the pressure rise in the impeller triggered instability. For the vande diffuser, instability that was generated in the impeller propagated into the vaned diffuser, however the pressure recovery by the vaned diffuser made the operation of the compressor stable at low flow rate.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.10
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• pp.161-167
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• 2001

This paper presents an approach to nonlinear engine idle controller and intake manifold absolute pressure(MAP) observer based on mean torque production model. A stable engine idle speed is important in that the unstable engine Idle mode can make engine to drooping or stall state. A sliding fuzzy controller has been designed to control engine idle speed under load disturbance. A sliding observer is also developed to estimate the intake manifold absolute pressure and compared with the actual MAP sensor value. The sliding mode observer has shown good robustness and good tracking performance. The inputs of sliding fuzzy controller are the errors of rpm and MAP. The output is a duty cycle(DC) for driving a idle speed control valve(ISCV).

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1996.06c
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• pp.728-736
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• 1996

Solid/Liquid(S/L) separation is crucial for biological treatment of animal wastewater. Liquid portion from S/L separation has less BOD-load and proper post-strip treatment can be obtained . Screen or declined sieve was normally used to separate the solid parts. For better separating efficiency a vibration and a cylindrical separator were constructed and tested. The results are summarized as follows : Solids removal efficiency and moisture content of separated solid were 15-26% and 85-88%, respectively for the vibration separator. For the cylindrical separator, solid removal efficiency and moisture content of solid were 16-39% and 86-89% , respectively. The greatest amount of drymatter was obtained when operating vibration separator with 10。 inclination and 100% vibrating power. For the cylindrical separator maximum efficiency was obtained with 40rpm and 19 inclination . The vibration and the cylindrical separator have shown 21% and 26% in BOD removal, respectively. These two types of separator were proved to be applicable methods for animal wastewater separation.

• Journal of Korean Society of Transportation
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• v.12 no.2
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• pp.31-45
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• 1994

One of the significant problems in urban areas is lack of parking spaces. Therefore, maximizing the number of cars that can be parked in a given area becomes increasingly important as land costs increase. This paper presents a methodology of optimal parking lot design in relatively small areas. The discussion is limited to self-parking surface rectangular lots. The selection of stall dimensions and aisle widths is based on the regulations of parking lot design standards of Korea. A personal computer software, OPALD, was developed and implemented to design optimal parking lots. OPALD iterates angles of parking stalls from 45 to 90 degree, generates the combination of paring angles, and selects the best angles to fit the given area. A drawing data file is also generated to draw layouts of parking lots in the CAD pakage (AutoCAD). Application of OPALD shows good results to design parking lots in relatively small areas. By-products of this research represents the parking modules of various angles.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.15 no.3
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• pp.33-45
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• 2007

The collision avoidance maneuver flight simulation for tilt rotor unmanned aerial vehicle was performed by time-accurate numerical integration method based on wind tunnel test data. Five representative collision avoidance maneuvers were simulated under constraints of aerodynamic stall, propulsion power, structural load, and control actuator capability. The collision avoidance performances of the maneuvers were compared by the computed collision avoidance times. The sensitivities of initial flight speed and collision zone shape on the collision avoidance time were investigated. From these results, it was found that the moderate pull-up turn maneuver defined using moderate pitch and maximum roll controls within simulation constraints is the most robust and efficient collision avoidance maneuver under the various flight speeds and collision object shapes in the tilt rotor UAV applications.