• International Journal of Aeronautical and Space Sciences
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• 제16권3호
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• pp.339-346
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• 2015

Aerodynamic flow control phenomena were investigated with a low-current DC surface discharge plasma actuator. The plasma actuator was found to operate in three different discharge modes with similar discharge currents of about 1 mA or less. Stable continuous DC discharge without audible noise was obtained at higher ballast resistances and lower discharge currents. However, even with continuous DC power input, a low-frequency self-pulsed discharge was obtained at lower ballast resistances, and a high-frequency self-pulsed discharge was obtained at higher set-point currents and higher ballast resistances, both with audible noise. The Schlieren image reveals that the low-frequency self-pulsed mode produces a synthetic jet-like flow implying that a gas heating effect plays a role, even though the discharge current is small. The high-frequency self-pulsed mode produces pulsed jets in a tangent direction, and the continuous DC mode produces a steady straight pressure wave. Particle image velocimetry (PIV) images reveal that the induced flow field by the low-frequency self-pulsed mode has flow propagating in the radial direction and centered between the electrodes. The high-frequency self-pulsed mode and continuous DC mode produce flow from the anode to the cathode. The perturbed region downstream of the cathode is larger in the high-frequency self-pulsed mode with similar maximum speeds.

• Journal of international Conference on Electrical Machines and Systems
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• 제1권3호
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• pp.282-288
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• 2012

A special pulsed electromagnetic actuator is presented whose plunger consists of two parts made of carbon steel and permanent magnet, respectively. The actuator exhibits a high holding force and small consumption of energy. The movement of the plunger is controlled by short current pulses. The static characteristics and other operation properties of the device are modeled numerically.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 춘계학술대회 논문집
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• pp.351-352
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• 2009

On-demand ejection of ultra-fine droplets that uses both electrohydrodynamic (EHD) force and mechanical actuation is presented. The liquid meniscus was controlled by a piezoelectric actuator and droplets were ejected by EHD force. Through these effects, it was possible to obtain a high operational jetting frequency of 5kHz with a short delay-time (about 50 us) when compared with existing on-demand EHD jetting methods, such as the pulsating jet mode (3-10 msec) and the pulsed-voltage cone-jet mode(3.6 msec). Also, we obtained ultra-fine droplets at a volume that was at the femto-liter level simultaneously. The jetting characteristics were examined for both hydrophobicity and hydrophilicity of the surface of a capillary.

• 한국항공우주학회지
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• 제45권11호
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• pp.907-913
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• 2017

아크 플라즈마에 의해 구동되는 스파크 제트의 다양한 에너지 공급 방법에 따른 효율적 운전 성능 특성에 대한 실험적 연구를 수행하였다. 펄스 당 37 mJ의 주입 에너지에 의한 급속한 기체의 가열에 의해 약 330 m/s의 고속 제트가 발생함을 확인하였다. 제트의 최대 속도와 침투 거리는 각각 주입된 전력량과 펄스 당 주입된 에너지에 비례하였다. 낮은 에너지에서는 오리피스 직경이 작을수록 더 높은 속도의 제트가 발생하였다. 공급 에너지가 같다면 전류를 높인 펄스가 펄스 폭을 높인 펄스보다 높은 속도의 제트를 발생시켰다. 펄스 폭이 약 $10{\mu}s$이고 펄스 당 에너지가 약 10 mJ인 경우가 효율적인 운전에 보다 더 적합한 것으로 확인되었다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제53권1호
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• pp.15-19
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• 2004

In this paper, we present the fabrication and characteristic analysis of Sagnac interferometric optical fiber senior(OFS) system for detecting pulsed ultrasonic signal in underwater. The hollow cylindrical mandrel wound round by single mode optical fiber is used as sensing component. The ultrasonic signal source is simulated by the PZT actuator operated by an function generator. The distance dependency of the OFS's sensitivity was measured. The sensitivity has been shown to be inversely propotional to the square-root of distance between ultrasonic source and sensing component. It has also been shown that the OFS could detect the signals less affected by ultrasonic path comparing to conventional acousto-electric sensor. and accurate location of ultrasonic signal could be carried out using two OFSs.

• 한국전산유체공학회지
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• 제17권2호
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• pp.71-77
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• 2012

Numerical simulations are carried out for flow over a circular cylinder controlled by the momentum forcing which is generated by a pair of plasma actuators symmetrically mounted on the cylinder surface. A popular and empirical plasma model is used for the spatial distribution of momentum forcing. In this study, we consider two different types of actuation, i.e., steady and unsteady (or pulsed) actuation. In the unsteady actuation, the actuation is turned on and off periodically, its frequency being a control parameter. The objective of this study is to investigate the effects of actuator location and actuation frequency on the flow structures and the forces on the cylinder. Results show that the cylinder wake can be effectively controlled by proper actuator location. For example, when the actuators are located at $120^{\circ}$ from the stagnation point, vortex shedding is completely suppressed with the boundary layer almost fully attached to the surface, resulting in drag reduction and lift elimination.

• 한국정밀공학회지
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• 제16권3호통권96호
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• pp.72-77
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• 1999

This paper presents 2-dimensional vibration cutting increases dynamic stiffness of tool support and improves the quality of machined surface in micro-machining. 2-dimensional vibration cutting is generated by two piezo actuators arranged orthogonally. A sine-type voltage is input to one actuator and a phase-shifted sine-type voltage is input the other. Then the vibration device actuates the tool in a 2-D elliptical motion with pulsed cutting force. It is a characteristic of 2-D vibration cutting that some negative thrust force occurs as the direction of friction on a tool rake surface is reversed. It helps not only chip flow smoothly and continuously but also cutting force be reduced. The quality of machined surface by 2-D vibration cutting depends on such parameters as vibration amplitude, frequency, cutting speed, depth of cut, etc. Compared to conventional cutting through tool path simulation and experiments under several conditions, the 2-D vibration cutting is verified to bring forth a great decrease of cutting forces, much better surface roughness and moreover much less burr.

• 한국항공우주학회지
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• 제33권9호
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• pp.1-8
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• 2005

이차원 타원형 날개꼴에서 펄스제트 브로잉에 의한 박리 제어 효과에 대하여 연구하였다. 박리 유동의 능동제어기술 개발을 위하여 압축공기를 사용하는 연속제트/간헐제트 엑츄에이터를 설계제작하여 타원형 날개 풍동 실험 모델에 장착하였다. 아음속 유동에서 날개 주위 유동장의 PIV 측정과 유동의 가시화을 통하여 간헐제트 브로잉의 타원형 날개의 실속제어 효과와 실용성에 대해 실험연구를 수행하였다. PIV 실험 결과 제트 브로잉에 의해 난류 후류 영역과 박리 버블의 크기를 현저하게 감소시킴으로써 박리제어가 가능함을 보였다. 간헐제트는 연속제트보다 박리제어에 보다 효과적이었다. 간헐제트의 주파수를 증가시키면 보다 높은 받음각에 이르기까지 난류 박리 후류를 효과적으로 억제할 수 있었다.