• 대한전자공학회논문지
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• 제27권8호
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• pp.1289-1293
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• 1990

In this paper, the oscillation condition for the linear phase-conjugate oscillator which consists of one photorefractive crystal, two conventional mirrors, and two pump waves applied externally has been analyzed. In the result, it has been shown that the oscillation condition of this oscillator can be easily controlled by adjusting the various parameters such as the intensity ratio, polarization states, and light path difference of two pump waves, etc.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.324-333
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• 2009

This paper presents a numerical simulation study of the transient behavior of a $2{\times}340MW$ pump-turbine power plant, where the results show an unstable behavior at runaway. First, the modeling of hydraulic components based on equivalent schemes is presented. Then, the 2 pump-turbine test case is presented. The transient behavior of the power plant is simulated for a case of emergency shutdown with servomotor failure on Unit 1. Unstable operation at runaway with a period of 15 seconds is properly simulated using a 1-dimensional approach. The simulation results points out a switch after 200 seconds of the unstable behavior between a period of oscillations initially of 15 seconds to a period of oscillation of 2.16 seconds corresponding to the hydraulic circuit first natural period. The pressure fluctuations related to both the rigid and elastic water column mode are presented for oscillation mode characterization. This phenomenon is described as a switch between a rigid and an elastic water column oscillation mode. The influence of the rotating inertia on the switch phenomenon is investigated through a parametric study.

• 한국유체기계학회 논문집
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• 제10권1호
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• pp.34-40
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• 2007

In this study, the characteristic of a vane pump of automotive power steering system is numerically analyzed. The vane pump changes the energy level of operation fluid by converting mechanical input power to hydraulic output. To simulate this mechanism, moving mesh technique is adopted. As a result, the flow rate and pressure are obtained by numerical analysis. The flow rate agrees well with the experimental data. Moreover, the variation and oscillation of the pressure around the rotating vane are observed. As a result of flow characteristics, The difference of pressure between both side of vane tip causes the back flow into the rotor. As the rotational velocity increases, the flow rate at the outlet and the pressure in the vane tip rises with higher amplitude of oscillation. In order to reducing the oscillation, the design of devices for decreasing the cross-area of the outlet part and returning the flow from the outlet to the inlet is required.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1999년도 추계 학술발표회 논문집
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• pp.149-154
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• 1999

This paper describes a passive safety injection system with free piston Stirling pump working withabundant decay heat in the nuclear reactor during the hypothetical accident. The water column in the tube assembly connected from the hot chamber to the cold chamber in the pump oscillates periodically due to thermal volume changes of non-condensable gas in each chamber. The oscillating pressure in the water column is converted into the pumping power with a suction-and-bleed type valve assembly. In this paper a dynamic model describing the frequency of oscillation and pumping pressure is developed. It was found that the pumping pressure is a function of the temperature difference between the chambers. Also, the frequency oscillation depends on the length of the tube with water column.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.1144-1147
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• 2017

발사체 엔진 시동 및 정지시 발생하는 압력 섭동 및 압력 강하에 대한 검토를 수행하였다. 특히 PSD(Pogo Suppression Device)이 존재하는 경우 엔진 시동 혹은 정지시 이에 대한 영향을 검토하기 위해 연구를 수행하였다. 해석을 수행하기 위해 상용 1D 해석 프로그램인 Flowmaster를 사용하여 추진제 탱크 및 PSD, 엔진을 모델링하였다. 해석 결과 PSD가 설치되어 있어도 엔진 시동 및 정지시 터보펌프 입구에서의 압력 강하 및 상승에 변화가 없음을 확인하였다. 단, PSD의 본래 목적에 맞게 배관에서의 높은 주파수 대역의 압력 섭동을 낮추는 효과를 확인하였다.

• International Journal of Fluid Machinery and Systems
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• 제4권1호
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• pp.76-83
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• 2011

This study highlights especially the mechanism of vortex cavitation occurrence from the end of the suction duct in a double-suction volute pump and pump oscillation which causes cavitation noise from the pump. In this study, full 3D numerical simulations have been performed using a commercial code inside the pump from the inlet of suction duct to the outlet of delivery duct. The numerical model is based on a combination of multiphase flow equations with the truncated version of the Rayleigh-Plesset model predicting the complicated growth and collapse process of cavity bubbles. The experimental investigations have also been performed on the cavitating flow with flow visualization to evaluate the numerical results.

• International Journal of Fluid Machinery and Systems
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• 제7권3호
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• pp.94-100
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• 2014

In double-suction centrifugal pumps, it was found that cavitation instabilities occur with vibration and a periodic chugging noise. The present study attempts to identify cavitation instabilities in the double-suction centrifugal pump by the experiment and Computational Fluid Dynamics (CFD). Cavitation instabilities in the tested pump were classified into three types of instabilities. The first one, in a range of cavitation number higher than breakdown cavitation number, is cavitation surge with a violent pressure oscillation. The second one, in a range of cavitation number higher than the cavitation number of cavitation surge, is considered to be rotating cavitation and causes the pressure oscillation due to the interaction of rotating cavitation with the impeller. Last one, in a range of cavitation number higher than the cavitation number of rotating cavitation, is considered to be a surge type instability.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1996년도 제24회 추계학술대회
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• pp.168-175
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• 1996

This paper reports on theoretical study of the pressure overshoot in the delivery ports and pressure rising within balanced type vane pump. Pressure overshoot occur due to the accelerated fluid through the notch, so, result in pressure ripple, flow ripple, and noise. For calculating the pressure rising and fluctuations of pressure, we have modeled mathematically used continuity equation based on compressibility and momentum equation considered fluid inertia in the notch, and analyzed simultaneously. As a results of analysis, we have found oscillation of pressure and compression chamber pressure depend on the rotational speeds, bulk modulus of working fluid, notches, number of vane and camring. Using the model, notches have been shown to be important design factor in relaxing the rapid pressure rising and reducing the amplitudes of pressure overshoot.

• International Journal of Fluid Machinery and Systems
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• 제3권1호
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• pp.50-57
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• 2010

The attachment of inducer in front of main impeller is a powerful method to improve cavitation performance. Cavitation surge oscillation, however, often occurs at partial flow rate and extremely low suction pressure. As the cavitation surge oscillation with low frequency of about 10 Hz occurs in a close relation between the inlet backflow cavitation and the growth of blade cavity into the throat section of blade passage, one method of installing an axi-asymmetrical plate upstream of inducer has been proposed to suppress the oscillation. The inlet flow distortion due to the axi-asymmetrical plate makes different elongations of cavities on all blades, which prevent the flow from becoming simultaneously unstable at all throat sections. In the present study, changes of the suppression effects with the axial distance between the inducer inlet and the plate and the changes with the blockage ratios of plate area to the cross-sectional area of inducer inlet are investigated for helical inducers with tip blade angles of $8^{\circ}$ and $14^{\circ}$. Then a conceivable application will be proposed to suppress the cavitation surge oscillation by installing axi-asymmetrical inlet plate.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.748-753
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• 2004

The performance of a valveless micropump driven by chamber wall oscillation was numerically investigated for various frequency and amplitude of the oscillation. The numerical study was performed in the range of oscillation frequency from 200Hz to 1000Hz and amplitude from $1{\mu}m$ to $15{\mu}m$. And optimal values for the parameters are found. At the oscillation frequency 600Hz, the net flow rate of micropump shows a maximum value. Also the results show good agreement with the experimental results. The total flow rate was increased with the oscillation amplitude. However, the net flow rate was found to be decreased over $7{\mu}m$.