• 대한기계학회논문집B
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• 제26권9호
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• pp.1234-1240
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• 2002

A new feedback control law is proposed and tested for suppressing the vortex shedding from a circular cylinder in a uniform flow. The lift coefficient ( $C_{L}$) is employed as a feedback control signal and the control forcing is given by a rotational oscillation of the cylinder. The influence of the feedback transfer function on the $C_{L}$ reduction is examined. The main rationale of the feedback control is that a feedback control forcing is imposed at a phase which is located outside the range of lock-on. By applying the feedback control law, $C_{L}$ is reduced significantly. Furthermore, the reduction mechanism of $C_{L}$ is analyzed by showing the vortex formation modes with respect to the forcing phase.e.ase.e.

• 한국연소학회지
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• 제6권2호
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• pp.8-14
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• 2001

The effects of unsteady combustion are experimentally studied using forced pulsating mixture supply. It was shown that unsteady combustion used in this experiment plays an important role in controlling self-excited combustion oscillations. It may also have desirable performances, from a practical point of view, such as high combustion load, augmented heat transfer, reduced pollutant emissions and so on. We examined the characteristics of unsteady combustion driven by forced pulsating mixture supply in a small duct-combustor with a rearward-facing step. Further, we found its influence on the onset of self-excited combustion oscillations, the possibility of suppressing self-excited combustion oscillations and the reason why the self-excited combustion oscillation was suppressed using the forced pulsating mixture supply, comparing with the steady mixture supply.

• International Journal of Control, Automation, and Systems
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• 제5권1호
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• pp.35-42
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• 2007

This paper presents an INS(Inertial Navigation System) grade, surface micro-machined differential resonant accelerometer(DRXL) manufactured by an epitaxially grown thick poly silicon process. The proposed DRXL system generates a differential digital output upon an applied acceleration, in which frequency transition is measured due to gap dependent electrical stiffness change. To facilitate the resonance dynamics of the electromechanical system, the micromachined DRXL device is packaged by using the wafer level vacuum sealing process. To test the DRXL performance, a nonlinear self-oscillation loop is designed based on the extended describing function technique. The oscillation loop is implemented using discrete electronic elements including precision charge amplifier and hard feedback nonlinearity. The performance test of the DRXL system shows that the sensitivity of the accelerometer is 24 Hz/g and its long term bias stability is about 2 mg($1{\sigma}$) with dynamic range of ${\sigma}70g$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1995년도 추계학술대회 논문집 학회본부
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• pp.120-124
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• 1995

TCSC can not only increase power flow but also damp low frequency oscillation by controlling firing angles of thyristors. But, a model considering voltage, current firing angles is not derived. This paper used a small signal model considirng these variables which was derived in paper [1]. TCSC model is combined with swing equation. Being related to rotor angles and firing angles of thyristors, current and synchronizing torque coefficient is reformulated. Because firing angles of thyristors can be controlled only twice within one period, swing equation is transformed to discrete time model. It is shown that low frequency oscillation can be damped by controlling firing angles in one machine infinite bus power system.

• ETRI Journal
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• 제31권6호
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• pp.755-764
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• 2009

This paper presents a switched self-biasing and a tail current-shaping technique to suppress the 1/f noise from a tail current source in differential cross-coupled inductance-capacitance (LC) voltage-controlled oscillators (VCOs). The proposed LC VCO has an amplitude control characteristic due to the creation of negative feedback for the oscillation waveform amplitude. It is fabricated using a 0.13 ${\mu}m$ CMOS process. The measured phase noise is -117 dBc/Hz at a 1 MHz offset from a 4.85 GHz carrier frequency, while it draws 6.5 mA from a 0.6 V supply voltage. For frequency tuning, process variation, and temperature change, the amplitude change rate of the oscillation waveform in the proposed VCO is 2.1 to 3.2 times smaller than that of an existing VCO with a fixed bias. The measured amplitude change rate of the oscillation waveform for frequency tuning from 4.55 GHz to 5.04 GHz is 131 pV/Hz.

• 대한기계학회논문집B
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• 제26권7호
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• pp.951-958
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• 2002

Rapid expansion of a moist air or a stream through a supersonic nozzle often leads to non-equilibrium condensation shock wave, causing a considerable energy loss in flow field. Depending on amount of latent heat released due to non-equilibrium condensation, the flow is highly unstable or a periodical oscillation accompanying the condensation shock wave in the nozzle. The unsteadiness of the condensation shock wave is always associated with several kinds of instabilities as well as noise and vibration of flow devices. In the current study, a passive control technique using a porous wall with a plenum cavity underneath is applied for the purpose of alleviation of the condensation shock oscillations in a transonic nozzle. A droplet growth equation is coupled with two-dimensional Navier-Stokes equation system. Computations are carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. An experiment using an indraft wind tunnel is made to validate the present computational results. The results show that the oscillations of the condensation shock wave are completely suppressed by the current passive control method.

• 전기학회논문지P
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• 제58권3호
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• pp.323-327
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• 2009

The oscillation is very dangerous in bundled transmission lines, besides 4 bundle transmission lines are very weak for subspan oscillations. In some cases, subspan oscillations are continuously occurred in the same subspan. In order to develop the control method of the above subspan oscillation, this paper suggests a method of applying twin spacers to the subspans. We have carried out some tests to analyze the oscillation phenomena after installing twin spacers on 4 bundle overhead lines, and we got a good effect for controling subspan oscillations by installing twin spacers.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 춘계학술대회 논문집 전기설비전문위원
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• pp.200-202
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• 2008

The oscillation is very dangerous in bundled transmission lines, especially 345kV 4 bundle transmission lines are very weak for subspan oscillations. In some cases, subspan oscillations are continuously occurred in the same subspan. In order to develop the control method of the above subspan oscillation, this paper suggests a method of applying twin spacers to the subspans. We have carried out some tests to analyze the oscillation phenomena after installing twin spacers on 34sky real lines, and we got a good effect for controling subspan oscillations.

• 대한수학회논문집
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• 제26권3호
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• pp.499-513
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• 2011

By using the Riccati transformation technique, we study the oscillation and asymptotic behavior for the third-order nonlinear delay dynamic equations $(c(t)(p(t)x^{\Delta}(t))^{\Delta})^{\Delta}+q(t)f(x({\tau}(t)))=0$ on a time scale T, where c(t), p(t) and q(t) are real-valued positive rd-continuous functions defined on $\mathbb{T}$. We establish some new sufficient conditions which ensure that every solution oscillates or converges to zero. Our oscillation results are essentially new. Some examples are considered to illustrate the main results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.679-680
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• 2007

The oscillation is very dangerous in bundled transmission lines, especially 345kV 4 bundle transmission lines are very weak for subspan oscillations. In some cases, subspan oscillations are continuously occurred in the same subspan. In order to develop the control method of the above subspan oscillation, this paper suggests a method of applying spacers for 2 bundled conductors to the subspans. In the future we will try to observe and analyze the oscillation after installing the spacers for 2 bundled conductors, and suggest the effective method for controling subspan oscillations.