• 제목/요약/키워드: Lift Off

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공기윤활 범프 저어널 베어링의 부상 특성에 관한 연구 (A Study on the Lift-off Characteristics of an Air-lubricated Bump Foil Journal Bearing)

  • 이남수;이용복;최동훈;김창호
    • 한국윤활학회:학술대회논문집
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    • 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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    • pp.236-242
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    • 2001
  • In this paper the effect of bump compliance, load, and the number of pad on the lift-off speed is studied. When the load is greater and bump compliance lower, the shaft is lifted off at higher rotating speed. And when the load is applied near the center of pad, lift-off speed is lower. When the number of pad increases, the lift-off speed is higher. The lift-off characteristics can be used to lengthen the life time of the coating and design the rotating machinery supported by bump bearings.

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다양한 센서 측정 거리로부터 획득한 자기적 와전류 신호의 불변 변환 처리 기법 (Lift-Off Invariance Transformations for Electromagnetic Eddy Current Nondestructive Evaluation Signals)

  • 김대원
    • 한국자기학회지
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    • 제14권6호
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    • pp.207-212
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    • 2004
  • 전자기학의 분야에서 와전류를 이용한 응용 분야는 매우 다양하다. 예를 들면, 핵을 이용한 원자력 발전소의 증기 발생 튜브 또는 비행기의 엔진이나 날개 부분의 결함 등을 자기적 특성을 이용하여 비파괴 검사를 하는 등의 일이다. 와전류의 특성을 결정짓는 가장 중요한 인자 중 하나가 바로 센서 측정 거리 (lift-off)인데 이것은 와전류를 측정한 센서와 피검사 물체간의 물리적인 공간거리를 뜻한다. 이 인자는 와전류 신호의 특성을 정확하게 분석해내는데 매우 중요함에도 불구하고 실제 필드에서는 모든 경우마다 그 정확한 값을 측정해내기가 힘들 뿐더러 일정한 거리를 상시 유지 하기도 어렵다. 따라서 자기적 신호의 하나인 와전류로 하여금 다양한 상황에서의 lift-off로 변화에도 영향을 받지 않고 일정한 특성을 유지하게끔 해주는 기술이 필요하다. 이 논문은 다양한 lift-off로부터 얻어진 와전류를 보상하여 일정한 성질을 유지하도록 하는 기법을 설명하고 있다. 다양한 lift-off로 부터 얻어진 와전류들은 신호 획득 거리가 0인 이상적 상태의 신호들로 보상 변환 되어 다음 단계인 피검사 시료상의 결함 또는 흠집의 물성이나 특성 파악에 계속해서 쓰이게 된다.

공기윤활 범프 저어널 베어링의 부상 특성에 관한 연구 (A Study on the Lift-off Characteristics of an Air-lubricated Bump Foil Journal Rearing)

  • 이용복;김창호;이남수;최동훈
    • Tribology and Lubricants
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    • 제17권6호
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    • pp.441-446
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    • 2001
  • In this paper the effect of bump compliance, load, and the number of pad on the lift-off speed is studied. When the load is greater and bump compliance lower, the shaft is lifted off at higher rotating speed. And when the load is applied near the center of pad, lift-off speed is lower. When the number of pad increases, the lift-off speed is higher. The lift-off characteristics can be used to lengthen the lift time of the coating and design the rotating machinery supported by bump bearings.

단면 확대 덕트 내에 형성된 삼지화염의 부상특성에 관한 실험적 연구 (An Experimental Study on the Lift-off Characteristics of the Triple Flame within a Diverging Duct)

  • 서정일;김남일;오광철;신현동
    • 한국연소학회:학술대회논문집
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    • 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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    • pp.85-91
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    • 2003
  • The lift-off characteristics of the triple flame within a diverging duct have been studied experimentally using a multi-slot burner, which can control the concentration gradient and the mean velocity independently. In this experiment the triple flame was stabilized successfully in lift-off condition and flame stabilization with a duct or without a duct, lift-off heights, and some other characteristics were examined for propane flame. It was examined that the effects with various concentration gradient and mean velocity on the triple flame. It was found that minimum value of the lift-off heights exist at a certain concentration gradient for constant mean velocity and flame with a duct is more stable than that without. Moreover the propagation velocity of the flame becomes maximum at a certain concentration gradient regardless of mean velocity.

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The Effects of Lift-Off from Wall Thinning Signal in Pulsed Eddy Current Testing

  • Park, Duck-Gun;Angani, C.S.;Kishore, M.B.;Kim, C.G.;Lee, D.H.
    • Journal of Magnetics
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    • 제17권4호
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    • pp.298-301
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    • 2012
  • In order to know the effect of surface irregularity in the detection of local wall thinning of pipeline using pulsed eddy current (PEC), the lift-off effects on PEC signal have been investigated. Three kinds of parameters in the PEC signal, which is "peak amplitude", "time to peak amplitude" and "time to zero crossing" are analyzed to separate the lift-off effects in the PEC signal. The distance from sensor to the bottom of sample which is the total thickness of combined insulator and sample is kept constant. The magnitude of the differential peak amplitude is increased with increasing sample thickness, the time to peak amplitude is increased with increasing the sample thickness. To determine the effect of lift-off, a number of balanced transient responses combining wall thinning locations and lift-off distances were plotted.

동축 확산 부상화염의 Blow-off와 연소 특성 (Blow-off and Combustion Characteristics of a Lifted Coaxial Diffusion Flame)

  • 곽지현;전충환;장영준
    • 대한기계학회논문집B
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    • 제27권8호
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    • pp.1089-1096
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    • 2003
  • An experiment was performed to investigate lift-off, blow-off and combustion characteristics of a lifted coaxial diffusion flame according to fuel jet and air velocity. A jet diffusion flame which is attached on the nozzle rim begins to be lifted with increase of air velocity, and finally becomes blow-off at higher air velocity. In experiment, blow-off limit increased with increase of fuel jet velocity, however lift-off occurred at lower air velocity. Flame structure and combustion characteristics were examined by schlieren photos, temperature distributions and emission concentration distributions. Flame temperature became higher at midstream and its RMS became larger at up and downstream with increase of air velocity. Local NO concentration decreased but $CO_2$concentration increased with increase of air velocity, which shows combustion reaction becomes close to be stoichiometric at higher air velocity in spite of lift-off.

발사체 이륙 시 음향 하중 예측 정확도 향상 (Improved Prediction of Lift-off Acoustic Loads for a Launch Vehicle)

  • 최상현;이정권;이익진
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2014년도 춘계학술대회 논문집
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    • pp.207-210
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    • 2014
  • This paper is concerned with the prediction of lift-off acoustic loads for a launch vehicle. Intense acoustic load is generated when a launch vehicle is lifted off, and it can induce vibrations of a launch vehicle which cause damage or malfunction of a launch vehicle and a satellite. Lift-off acoustic loads of NARO are predicted by the modified Eldred's second method and the result is compared with the measured data in flight test. The prediction shows similar peak and shape of spectrum to the test data, but some discrepancy can be observed due to the predicted margin. In order to reduce such discrepancy, the sound pressure levels with four source distribution assumptions are calculated. Also, the surface diffraction effects are considered in the predict ion of lift-off acoustic loads, and the predicted result is more similar to the test data.

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농도구배가 삼지화염의 부상특성에 미치는 영향에 관한 실험적 연구 (An Experimental Study on the Lift-off Characteristics of the Triple Flame with Concentration Gradient)

  • 서정일;김남일;오광철;신현동
    • 한국연소학회:학술대회논문집
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    • 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
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    • pp.7-14
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    • 2004
  • The lift-off characteristics of the triple flame have been studied experimentally with various mean velocities and concentration gradients using a multi-slot burner, which can control the concentration gradient and the mean velocity independently, Lift-off height, axial maximum velocity, flame temperature, and some other characteristics were examined for methane and propane flame, It was found that minimum values of the lift-off heights exist at a certain concentration gradient for constant mean velocity, and this result implies that the propagation velocity has a maximum value at this condition, OH radical distribution was measured with LIF method and velocity variation along streamline was measured with PlV system. In addition maximum temperature along streamline was measured with CARS system. The intensity of the diffusion flame affects on the propagation velocity of triple flame in the region of very weak concentration gradient.

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산소부화공기가 동축 비예혼합 제트의 연소특성에 미치는 영향 (I) - 화염의 부상과 안정성 (Effect of Oxygen Enriched Air on the Combustion Characteristics in a Coaxial Non-Premixed Jet ( I ) - Lift-off and Flame Stability -)

  • 곽지현;전충환;장영준
    • 대한기계학회논문집B
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    • 제28권2호
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    • pp.160-166
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    • 2004
  • Combustion using oxygen enriched air is known as a technology which can increase flame stability as well as thermal efficiency due to improving the burning rate. Lift-off, blowout limit and flame length were examined as a function of jet velocity, coflow velocity and OEC(Oxygen Enriched Concentration). Blowout limit of the flame below OEC 25% decreased with increase of coflow velocity, but the limit above OEC 25% increased inversely. Lift-off height decreased with increase of OEC. In particular, lift-off hardly occurred in the condition above OEC 40%. Flame length of the flames above OEC 40% was increased until the blowout occurred. Great flame stability was obtained since lift-off and blowout limit significantly increased with increase of OEC.

교류전류를 이용한 결함탐상에 관한 연구 - 주파수와 Lift-off 효과 - (A Study on the Detection of Defects Using AC Current -The Effect of Frequency and Lift-off-)

  • 김훈;김정엽;문봉호
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집A
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    • pp.529-533
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    • 2001
  • NDI technique system using AC current is newly developed for inspection of defects. This technique is non-contact measurement system and can be applied for locating and sizing of surface defects in components. In this paper, the technique was applied for evaluating the location and size for 2-dimensional surface cracks and we had investigated the influence of frequency and lift-off. The results show that defects are able to detect with the variety of voltage, and the measuring voltage for the depth of defects are under the influence of the measuring frequency and the lift-off.

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