• Title, Summary, Keyword: oscillation

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An Assessment on the Formation of Oscillation Mark of the Continuously Casted Steel Slabs (연속주조된 강재 슬래브 표면의 Oscillation Mark 형성에 관한 평가)

  • Park, Tae-Ho;Kim, Ji-Hun;Choi, Joo;Ye, Byung-Joon
    • Journal of Korea Foundry Society
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    • v.23 no.5
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    • pp.257-267
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    • 2003
  • In early solidification during the continuous casting of steel slabs, the formation of oscillation marks on the surface of slabs was mainly affected by carbon contents and casting conditions. The control of oscillation mark is required for the HCR(Hot Charged Rolling) process because the deep oscillation marks seriously deteriorate the surface qualities of steel slabs. The metallographic study has revealed that the oscillation mark can be classified principally according to the presence or absence of a small 'subsurface hook' and the depth of the oscillation marks in the subsurface structure at the basis of individual oscillation marks. The subsurface hook of oscillation marks was either straight or curved. When the amount of overflow was small and the subsurface hook was formed in the top of oscillation marks, the subsurface hook was straight and the oscillation mark was shallow. The oscillation marks without subsurface hook have small early solidification shell and were formed wide. The actual negative strip time$(t_N)$ was changed by the effect of meniscus level fluctuation Therefore irregular early solidification shell and oscillation mark were formed.

Experimental Studies on Self-Oscillation of a Swirl Coaxial Injector

  • Kim, Dongjun;Wonho Jeong;Jihyuk Im;Youngbin Yoon
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • pp.228-233
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    • 2004
  • The spray and acoustic characteristics by the self-oscillation of a swirl coaxial injector were experimentally studied. The self-oscillation of a swirl coaxial injector is defined as pressure and flowrate oscillations by a time-delayed feedback between liquid and gas phase and has strong influences on atomization and mixing processes. Hence the occurrence and effect of the self-oscillation are measured using shadow photography technique, acoustic test and PDPA. The occurrence of self-oscillation largely depends on the injection conditions, such as pressure drop of liquid phase and relative momentum ratio. From the experimental results, self-oscillation occurs when the momentum of gas phase is enough large and the smaller the pressure drop of liquid phase is, the better self-oscillation occurs at the same momentum ratio. The self-oscillation is also affected by injector geometries, increasing the recess length results in the expansion of self-oscillation region and the increase of sound pressure level. The self-oscillation of a swirl coaxial injector accompanies a high intensity scream and this scream may provide harmful disturbances to combustion processes. Self-oscillation leads to strong changes in the drop size distribution and smoothly varies the slope of radial SMD distribution.

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Effects of Surface Depression on Pool Convection and Oscillation in GTAW (GTA 용접에서 용융풀의 표면 변형이 유동과 진동에 미치는 영향)

  • 고성훈;최상균;유중돈
    • Journal of Welding and Joining
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    • v.17 no.6
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    • pp.70-77
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    • 1999
  • Surface depression in the arc welding is calculated numerically to analyze its influence on pool convection and oscillation. The magnitude of surface depression due to arc pressure on the stationary GTA pool surface is relatively small, and fluctuations of the surface and velocity are caused mainly by arc pressure. The inward flow on the surface due to the electromagnetic force and positive surface tension gradient acts to decrease surface depression. Surface depression appears to have minor effects on average flow velocity and thus pool geometry. Pool oscillation occurs due to surface vibration, and oscillation frequencies are affected mainly by the surface tension and pool width. The input parameters such as arc pressure and current have negligible effects on the oscillation frequency, and the surface tension gradient has limited effects. Since the oscillation frequency varies slightly according to penetration, pool oscillation for the partial penetration weld pool is applicable to monitor the pool width.

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An experimental study on instability and control of co-flow diffusion flames (동축류 확산화염의 불안정성과 제어에 관한 실험적 연구)

  • Lee, Hyeon-Ho;Hwang, Jun-Yeong;Jeong, Seok-Ho;Lee, Won-Nam
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.1
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    • pp.153-164
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    • 1997
  • Flame oscillation phenomena in a co-flow diffusion flame was experimentally studied with periodic fuel supply using a solenoid valve. The degree of excitation was controlled by changing the volume flux of fuel passing through the valve. Flame oscillation frequencies were measured utilizing a photodiode, a spectrum analyzer, video and high speed movies. Laser planar visualization was employed to study the correlation between the flame oscillation and the toroidal vortices. Observed are three regimes of flame oscillation, where the oscillation frequencies are for the multiples of excitation, the excitation itself and the flame natural oscillation. Both periods of natural oscillation and of excitation induced oscillation exist over one cycle of the excitation in the frequency multiplied regime. It is considered as an effect of balancing the influence of buoyancy driven vortex with that of excitation induced vortex near the excitation rate of 0.2. Flame shapes are become monotonous as increasing the excitation frequency to the range of over two fold of the natural oscillation. The flame oscillation can be modulated to the frequency of either multiples of excitation or excitation itself under certain conditions. This implies that the flame oscillation could be modulated to avoid the resonance frequency of the combustor, and shows the possibility of active control of the flame oscillation.

Dynamic Behaviors of Oscillating Edge-Flame in Low Strain Rate Counterflow Diffusion Flames (저신장율 대향류확산화염에서 진동불안정성을 갖는 에지화염의 동적거동)

  • Park, June-Sung;Kim, Hyun-Pyo;Park, Jeong;Kim, Jeong-Soo;Keel, Sang-In
    • 한국연소학회:학술대회논문집
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    • pp.65-72
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    • 2006
  • Experiments in methane-air low strain rate counterflow diffusion flames diluted with nitrogen have been conducted to study the behavior of flame extinction and edge flame oscillation in which flame length is less than the burner diameter and thus lateral conduction heat loss in addition to radiative heat loss could be remarkable at low global strain rates. Critical mole fraction at flame extinction is examined with velocity ratio and global strain rate. Onset conditions of edge flame oscillation and flame oscillation modes are also provided with global strain rate and added nitrogen mole fraction to fuel stream (fuel Lewis number). It is seen that flame length is closely relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation considerably. Edge flame oscillations in low strain rate flames are experimentally described well and are categorized into three: a growing oscillation mode, a decaying oscillation mode, and a harmonic oscillation mode. The regime of flame oscillation is also provided at low strain rate flames. Important contribution of lateral heat loss even to edge flame oscillation is clarified.

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Machining of Repetitive Micro Patterns using Oscillation Micro Milling (진동 마이크로 밀링을 이용한 미세 반복 패턴 가공 기술 연구)

  • Ro, Seung-Kook;Khim, Gyungho;Park, Jong-Kweon
    • Journal of the Korean Society for Precision Engineering
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    • v.31 no.5
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    • pp.381-387
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    • 2014
  • This paper introduces a system to machine micro-sized patterns effectively on surface based on micro-milling process using tools with simultaneous rotation and oscillation, oscillation micro milling. To review the effectiveness of proposed concept, we integrated a micro-spindle supported by active magnetic bearings with a precision 3-axis air bearing stage using double-wedge mechanism, and tested this oscillation milling. Two types of oscillation milling were tested, which are linear oscillation milling with a flat end mill and elliptical oscillation milling with a ball end mill with 0.3 mm of diameter. The spindle was rotating 110 krpm and workpiece was moving constant speed of 2~8 mm/sec during the oscillation milling. As the results, multiple oval shape dimples were generated in regular spacing, and the variation of elliptical motion made different shapes of patterns. The results showed that proposed oscillation milling can be successfully used for machining repeated micro-patterns.

Phase Model Analysis of Yeast Glycolytic Oscillation

  • Kim, Won-Sup;Han, Seung-Kee
    • Proceedings of the Korean Biophysical Society Conference
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    • pp.78-78
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    • 2003
  • The glycolysis is one of the most important metabolic reactions through which the glucose is broken and the released energy is stored in the form of ATP. Rhythmic oscillation of the intracellular ATP is observed as the amount of the influx glucose is small in the yeast. The oscillation is also observed in the population of the yeast cells, which implies that the glycolytic oscillation of the yeasts is synchronous. It is not clear how the synchronous oscillation could be organized among the yeast cells. Although detailed mathematical models are available that show synchronization of the glycolytic oscillation, the stability of the synchronous oscillation is not clear. We introduce a phase model analysis that reduces a higher dimensional mathematical model to a much simpler one dimensional phase model. Then, the stability of the synchronous oscillation is easily determined by the stability of the corresponding fixed solution in the phase model. The effect of perturbation on the oscillatory rhythm is also easily analyzed in the reduced phase model.

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Combustion Control and Symptom Detection on Self-excited Combustion Oscillation (자려 연소진동에 관한 연소제어와 징후의 검출)

  • Yang Young-Joon
    • Journal of the Korean Society of Marine Engineering
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    • v.28 no.7
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    • pp.1111-1122
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    • 2004
  • An idea to suppress the self-excited combustion oscillation was applied to the flames. The characteristics of unsteady combustion were examined and the unsteady combustion was driven by forced pulsating mixture supply that can modulate its amplitude and frequency. The self-excited combustion oscillation having weaker flow velocity fluctuation intensity than that of the forced pulsating supply can be suppressed by this method. The effects of the forced pulsation amplitude and frequency on controlling self-excited combustion oscillations were also investigated comparing with the steady mixture supply. The unsteady combustion used in this experiment plays an important role in controlling self-excited combustion oscillation. Symptoms of self-excited combustion oscillation were also studied in order to predict the onset of combustion oscillation before it proceeded to a catastrophic failure For the purpose, the unique measures to observe the onset of self-excited combustion oscillations based on the careful statistics of fluctuating properties in flames, such as pressure or emission of OH radicals, have been proposed.

Effects of geometric parameters of fluidic flow meter on flow rate (Fluidic 유량계의 기하학적 변수가 유동률에 미치는 영향)

  • Park, Gyeong-Am;Yun, Gi-Yeong;Yu, Seong-Yeon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.12
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    • pp.1608-1614
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    • 1997
  • The fluidic flow meter detects the gas flow rate based on the principle of fluidic oscillation instead of the conventional displacement method. It has many merits: wide rangeability, no moving mechanical parts and calibration insensitive to physical properties of fluids. The width of nozzle, size of oscillation chamber, size of target, width of outlet are tested to obtain the effects of jet oscillation on the fluidic flow meter. As the width of nozzle is too wide compared with the size of target, jet oscillation is unstable. The oscillation frequency decreases as the distance between the nozzle and target increases and also as the distance between target and outlet contraction increases. Two different vortexes exist in the front and the rear regions of the target, and they affect the oscillation frequency. The outlet contraction is very important, because the feedback flow is generated by the blocking of the flow. As the width of outlet increases, the jet oscillation frequency decreases. The linearity of this tested flow meter is quite good.

Observation and Analysis of the Oscillation of 4-Bundled Conductor System (4도체 송전선로의 진동현상 조사.분석(I))

  • Sohn, H.K.;Lee, H.K.;Lee, D.I.;Chu, J.H.;Yu, C.H.
    • Proceedings of the KIEE Conference
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    • pp.368-370
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    • 2001
  • The oscillation is very dangerous in bundled transmission lines. But we have no data for oscillation phenomena in real transmission lines. In order to develop the control method of the osculation, we need to know the amplitude and relations between winds and other conditions. So we observed and analyzed the oscillation in some 4 bundled lines, which have high failure rate. We try to suggest the oscillation phenomena of the 4 bundled lines. In the future we will try to observe and analyze the oscillation for developing protection methods of transmission lines from the oscillation.

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