• Kyungpook Mathematical Journal
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• v.56 no.1
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• pp.29-40
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• 2016

In this paper, we consider the nonlinear hyperbolic equations with forcing term. Some suffcient conditions for the oscillation are derived by using integral averaging method and a generalized Riccati technique.

• Korean Journal of Mathematics
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• v.28 no.4
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• pp.865-875
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• 2020

We provide detailed proofs for local gradient estimates for weak solutions to elliptic equations in divergence form with partial Dini mean oscillation coefficients subject to conormal derivative boundary conditions.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3009-3014
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• 2007

The effectiveness of passive control techniques for alleviating the pressure oscillation generated in a supersonic cavity flow was investigated numerically and experimentally, respectively. The control device includes a sub-cavity installed near the leading edge of a rectangular cavity. Time-dependent supersonic cavity flow characteristics with turbulent features were examined by using the three-dimensional, mass-averaged Navier-Stokes computation based on a finite volume scheme and large eddy simulation. The results show that the pressure oscillation near the trailing edge dominates overall time-dependent cavity pressure variations. Such an oscillation can be attenuated more significantly in the presence of the sub-cavity compared with the cavity without sub-cavity, and a larger sub-cavity leads to better control performance.

• Journal of Electrical Engineering and Technology
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• v.11 no.6
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• pp.1693-1699
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• 2016

The oscillation character of permanent magnetic motor is highly related to its slot-pole match. By calculating air-gap magnet field and radial electromagnetic force of 6-phase fractional-slot concentrated-winding permanent magnetic motor with slot-pole match of 48/44, 48/46, 48/50 and 48/52 under no load and load status, oscillation character of permanent magnetic motor is analyzed. A 20kW prototype with 48 slots and 44 poles is designed. With many sensors attaching to the corresponding parts, oscillatory acceleration is measured, and spectrum of oscillation frequency is recorded as well. The experiment results give proof to the analysis method for permanent magnetic motor oscillation in this paper.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.441-444
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• 2007

Surge tank generally are used near the downstream end of tunnels of penstocks to reduce change in pressure caused by waterhammer resulting from load changes on the turbines. In this paper, the surge tank with chamber is selected to analyze water surface oscillation. the governing equation are derived using the law of conservation of mass and momentum. the water surface oscillation in the surge tank are computed using governing equation. In the case of upsurging, water surface oscillation is damped gradually and in the case of downsurging, it is damped rapidly.

• Journal of applied mathematics & informatics
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• v.29 no.5_6
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• pp.1557-1569
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• 2011

In this paper, we consider the oscillation of the following certain second order nonlinear differential equations $(r(t)(x^{\prime}(t))^{\alpha})^{\prime}+q(t)x^{\beta}(t)=0$>, where ${\alpha}$ and ${\beta}$ are ratios of positive odd integers. New oscillation theorems are established, which are based on a class of new functions ${\Phi}={\Phi}(t,s,l)$ defined in the sequel. Also, we establish some interval oscillation criteria for this equation.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1682-1685
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• 2004

Gas Turbine combustors for power plant can be reduced NOx emissions using lean premixed combustion technology. But the combustors are likely to occur combustion oscillations which damage operation reliability and mechanical life of the gas turbines. In this paper, characterizations of oscillation in a gas turbine combustor for power plant are presented. Combustion dynamics occur $1{\sim}1.5$ psi in amplitude with low frequency less than 140Hz during normal operation. An abnormal high level dynamics, 2.0 psi amplitude occur at 125 Hz frequency. Abnormal combustion oscillation is reduced by modulation of fuel supply valve control schedule.

• Journal of KSNVE
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• v.7 no.6
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• pp.985-991
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• 1997

Combustion instability is a common phenomenon in a ducted flame burner and is known as accompanying low frequency oscillation. This is due to the interaction between unsteady heat release rate and sound pressure field, that is, thermoacoustic feedback. In Rayleigh criterion, combustion instability is triggered when the heat addition is in phase with acoustic oscillation. A Rijke type burner with a pre-mixed flame is built for investigating the effect of Reynolds number and equivalence ratio on thermoacoustic oscillation. The results suggest that the frequency of max, oscillation is dependent on Reynolds number and equivalence ratio whereas its magnitude is not a strong function of these two parameters.

• Journal of Navigation and Port Research
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• v.32 no.7
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• pp.537-542
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• 2008

A lot of cargo accidents occurred due to insufficient securing in the case of marine transportation. If the residual tension of securing rope can be predicted, it will be very useful in the handling of cargo securing work of operators. It was confirmed in the previous study that the fluctuation tension cf securing rope by oscillation could be predicted. In this paper, in order to the prediction of residual tension of securing rope, the experiments were carried out to measure the residual tension of securing rope under the oscillation and cyclic loadings. The residual tensions of two tests were in good agreement with each other. It can be predicted through the cyclic loading test in the estimated fluctuation tension without oscillation test by ship motion simulator.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1820-1831
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• 2003

Characteristics of self-excited combustion oscillation are experimentally studied using confined premixed flames stabilized by a rearward-facing step. A new idea to suppress combustion oscillation was applied to the flames. The characteristics of unsteady combustion were examined, which is 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 the 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 oscillations, and it also exhibits desirable performances, from a practical point of view, such as high combustion load and reduced pollutant emissions of nitric oxide.