• 소음진동
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• 제10권6호
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• pp.991-997
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• 2000

The objective of this study is to examine the onset condition and the frequency characteristics of the low-frequency combustion oscillation in a surface burner. For this purpose, extensive parametric studies have been performed experimentally and the effects of size of each section, the equivalence ratio, and the entrance velocity on oscillatory behavior explored. The experimental results were discussed in comparison with the other combustors associated tilth the low-frequency combustion oscillation. The combustion mode is driven at high combustion rate by the lift of unstable flame near the lower limit of the combustible equivalence ratio. The oscillation frequency is dependent not on the burner geometry but on the equivalence ratio and the combustion load. Low-frequency combustion mode was formed to be divided into two different modes, named C1 and C2 respectively. Two modes occurred individually, simultaneously or transitionally according to the equivalence ratio and combustion load. The characteristics of low-frequency oscillation is different from each other depending on the type of combustors. The surface burner has also its own characteristics of low -frequency oscillation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 추계학술대회 논문집 전력기술부문
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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.

• Design & Manufacturing
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• 제15권2호
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• pp.56-62
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• 2021

In this study, design technology of a non-mechanical flow meter using fluidic oscillation generated during the fluid flow in the chamber was investigated. To with respect to design a splitter, which is the most important factor in fluid oscillation, a transient flow simulation analysis was performed for three types of shapes and changes in inlet flow velocity. The oscillation characteristics with respect to the time in each case were compared, and it was confirmed that the SM03 model was the best among the presented models. In addition, the FFT analysis of the fluid oscillation results for the SM03 model was used to obtain a linear correlation between the flow velocity change and the maximum frequency, and a frequency of 20.957 (Hz/m/s) per unit flow velocity was obtained. Finally, injection molding simulation and molding experiment of the chamber with the designed splitter were performed.

• 소음진동
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• 제7권5호
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• pp.729-736
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• 1997

The subspan oscillation is the most important in bundled transmission lines, which can cause conductor damage and transmission line hardware failures. So it is necessary to analyze the subspan oscillation in details for transmission lines. This paper suggests the basic concept and theoretical analysis method of subspan oscillation for 6 bundle conductor transmission line, which considers wind speed, subspan length and conductor tension. Especially this paper uses a spacer damper model with clamp-arm flexibility and damping characteristics. Theoretical analysis results are proposed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 A
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• pp.522-524
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• 2003

This paper presents a stability estimation method for subspan oscillation on overhead transmission line. It has been used method by conductor's fatigue limit or subspan oscillation amplitude. But it is not proper to estimation of subspan oscillation. We suggest to instability index for estimation method of subspan oscillation. And we tried to 4 bundled conductor system. This result will use to establish of the subspan location rules.

• Journal of applied mathematics & informatics
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• 제13권1_2호
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• pp.223-232
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• 2003

In this paper we investigate the oscillation of nonlinear differdntial equation with damping term. Some new oscillation criteria for the equation are obtained.

• 한국주조공학회지
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• 제24권1호
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• pp.26-33
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• 2004

The pressure of the mold flux acting on the meniscus shell was investigated through the coupling analysis of heat transfer in the mold and fluid flow in the flux caused by the mold oscillation. Finite element method was employed to solve the conservation equation associated with appropriate boundary conditions. As reported by previous workers, the axial pressure is positive on the negative strip time and negative on the positive strip time. A maximum pressure is predicted toward the top of the meniscus shell which has the thin shell arid a maximum value is in proportion to the relative mold oscillation velocity. The relative mold oscillation velocity was changed by the effect of meniscus level fluctuation. Therefore the pressure of the mold flux acting on the meniscus shell was different each cycle of the mold oscillation due to the irregularity of relative mold oscillation velocity.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1533-1542
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• 2003

In the present study, the characteristics of pressure oscillation and heat transfer performance in an oscillating capillary tube heat pipe were experimentally investigated with respect to the heat flux, the charging ratio of working fluid, and the inclination angle to the horizontal orientation. The experimental results showed that the frequency of pressure oscillation was between 0.1 Hz and 1.5 Hz at the charging ratio of 40 vol.%. The saturation pressure of working fluid in the oscillating capillary tube heat pipe increased as the heat flux was increased. Also, as the charging ratio of working fluid was increased, the amplitude of pressure oscillation increased. When the pressure waves were symmetric sinusoidal waves at the charging ratios of 40 vol.% and 60 vol.%, the heat transfer performance was improved. At the charging ratios of 20 vol.% and 80 vol.%, the waveforms of pressure oscillation were more complicated, and the heat transfer performance reduced. At the charging ratio of 40. vol.%, the heat transfer performance of the OCHP was at the best when the inclination angle was 90$^{\circ}$ the pressure wave was a sinusoidal waveform, the pressure difference was at the least, the oscillation amplitude was at the least, and the frequency of pressure oscillation was the highest.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1518-1526
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• 2015

For now, there are some low frequency oscillations in the power system which feature low frequency oscillation with positive damping and cannot be explained by traditional low frequency oscillation mechanisms. Concerning this issue, the dynamic damping effect is put forward on the basis of the power-angle curve and the study of damping torque in this article. That is, in the process of oscillation, damping will dynamically change and will be less than that of the stable operating point especially when the angle of the stable operating point and the oscillation amplitude are large. In a situation with weak damping, the damping may turn negative when the oscillation amplitude increases to a certain extent, which may result in an amplitude-increasing oscillation. Finally, the simulation of the two-machine two-area system verifies the arguments in this paper which may provide new ideas for the analysis and control of some unclear low frequency phenomena.

• 전기학회논문지
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• 제62권2호
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• pp.228-231
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• 2013

This paper proposes a new method that reduces RCS(rader cross section) of the aluminum plate using a oscillation system composed of a VGA(variable gain amplifier) and a phase shifter. Once the oscillation system receives the external-RF signal through a probe on aluminum plate, it makes an amplified signal with a specific phase to cancel the signal reflected from the aluminum plate. The signal transmitted from the oscillation system has the same amplitude and out of phase with the reflected signal. And it can be controlled by the VGA and the phase shifter in the oscillation system. In order to validate the performance of the proposed oscillation system, FEM simulator was used and we measured how much an amplitude of the signal reflected from the aluminum plate rotated in phi direction is reduced in an anechoic chamber.