• Advances in aircraft and spacecraft science
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• 제1권1호
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• pp.69-91
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• 2014

Numerical investigations are presented, which show that a back-flow flap can improve the dynamic stall characteristics of oscillating airfoils. The flap was able to weaken the stall vortex and therefore to reduce the peak in the pitching moment. This paper gives a brief insight into the method of function of a back-flow flap. Initial wind tunnel experiments were performed to define the structural requirements for a detailed experimental wind tunnel characterization. A structural integration concept and two different actuation mechanisms of a back-flow flap for a helicopter rotor blade are presented. First a piezoelectric actuation system was investigated, but the analytical model to estimate the performance showed that the displacement generated is too low to enable reliable operation. The seond actuation mechanism is based on magnetic forces to generate an impulse that initiates the opening of the flap. A concept based on two permanent magnets is further detailed and characterized, and this mechanism is shown to generate sufficient impulse for reliable operation in the wind tunnel.

• 한국항공우주학회지
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• 제35권9호
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• pp.761-770
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• 2007

본 연구에서는 압력 왜곡과 유동각 왜곡을 모사하기 위하여 삼각날개를 이용한 와류 발생장치를 설계하였다. 삼각날개는 목표한 와류코어 위치와 압력왜곡율(DC90), 와류각을 만족하기 위해 후퇴각 $65^{\circ}$를 사용하였으며, 와류의 분포 영역을 넓히기 위해 삼각날개 전단면에 $45^{\circ}$ 와동 플랩을 적용하였다. 제작된 와류 발생장치는 시뮬레이션 덕트를 적용한 유동 왜곡 시험에서 전압력 왜곡율의 설계 요구조건을 만족하였으며, 시험 결과로부터 검증된 전산유체해석 결과를 이용하여 와류코어 위치와 와류각의 목표 성능을 확인하였다.

• 대한의용생체공학회:의공학회지
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• 제42권1호
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• pp.25-30
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• 2021

Objective: The aim of this study is to consider the effect of skin tissue necrosis by improving blood flow in animal skin models for low frequency pulsed electromagnetic fields (LF_PEMF) stimulation. Methods: Twenty rats (Wistar EPM-1 male, 280-320 g) were randomly divided into control groups (n=10) and the PEMF groups (n=10). To induce necrosis of the skin tissue, skin flap was treated in the back of the rat, followed by isolation film and skin flap suturing. Subsequently, the degree of necrosis of the skin tissue was observed for 7 days. The control group did not perform any stimulation after the procedure. For the PEMF group, LF_PEMF (1 Hz, 10 mT) was stimulated in the skin flap area, for 30 minutes a day and 7 days. Cross-polarization images were acquired at the site and skin tissue necrosis patterns were analyzed. Results: In the control group, skin tissue necrosis progressed rapidly over time. In the PEMF group, skin tissue necrosis was slower than the control group. In particular, no further skin tissue necrosis progress on the day 6. Over time, a statistically significant difference from the continuous necrosis progression pattern in the control group was identified (p<0.05). Conclusions: It was confirmed that low frequency pulsed electromagnetic fields (LF_PEMF) stimulation can induce relaxation of skin tissue necrosis.

• 한국자동차공학회논문집
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• 제18권5호
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• pp.136-144
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• 2010

Exhaust gas recirculation (EGR) is an emission control technology allowing significant NOx emission reduction from light-and heavy duty diesel engines. The future EGR type, dual loop EGR, combining features of high pressure loop EGR and low pressure loop EGR, was developed and optimized by using a commercial engine simulation program, GT-POWER. Some variables were selected to control dual loop EGR system such as VGT (Variable Geometry Turbocharger)performance, especially turbo speed, flap valve opening diameter at the exhaust tail pipe, and EGR valve opening diameter. Applying the dual loop EGR system in the light-duty diesel engine might cause some problems, such as decrease of engine performance and increase of brake specific fuel consumption (BSFC). So proper EGR rate (or mass flow) control would be needed because there are trade-offs of two types of the EGR (HPL and LPL) features. In this study, a diesel engine under dual loop EGR system was optimized by using design of experiment (DoE). Some dominant variables were determined which had effects on torque, BSFC, NOx, and EGR rate. As a result, optimization was performed to compensate the torque and BSFC by controlling start of injection (SOI), injection mass and EGR valves, etc.