• International Journal of Fluid Machinery and Systems
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• v.9 no.3
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• pp.237-244
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• 2016

An unsteady three-dimensional simulation based on Reynolds time-averaged governing equation and RNG $k-{\varepsilon}$ turbulence model, was presented for pump-as-turbine, the pressure fluctuation characteristic of hydraulic turbine with guide vane was obtained. The results show that the time domains of pressure fluctuation in volute change periodically and have identical cycles. In volute tongue and inlet pressure fluctuations are light, while in dynamic and static coupling interface pressure fluctuations are serious; In impeller blade region the pressure fluctuation of pressure surface are lighter than that of suction surface. The dominant frequencies of pressure fluctuation concentrate in low frequency region, and concentrate within 2 times of the blade passing frequency.

• Proceedings of the KIEE Conference
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• 1989.11a
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• pp.313-316
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• 1989

A steady state analysis of a load commutated current source inverter which is widely used in high voltage - high power induction motor drive systems at present is presented and its related results are discussed. This analysis proposes a method by which we can determine the output capacitor playing a dominant role on the performance of the system. It is shown that the capacitance of output capacitors is mainly dependent on the range of frequencies that the inverter is operated in the load commutated state.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.10
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• pp.1666-1673
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• 1997

In order to investigate the characteristics of sound-structure interaction plate having a cut-out, we modeled a rectangular cavity and the flexible plate of the cavity. Because the particle velocity of air is the same as that of plate on the plate, we could easily redefine vibration equation using the velocity potential. We calculated the natural frequencies of plate using orthogonal polynomial functions which satisfy the boundary conditions in the Rayleigh-Ritz method. For the change of vibration characteristics, the effect of sound-structure interaction is more dominant than that of cut-out size.

• Journal of KSNVE
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• v.6 no.6
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• pp.709-715
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• 1996

In recent years, the piping vibration in many Power Plants is being increased by the aged generating facilities due to a long time use. Generally, the pressure fluctuations associated with the flow-induced excitations in this case are broadband in nature. Mainly, the dominant sources of vibration are a vortex-shedding, plane waves and boundary layer turbulence. The peak level of the spectrum is proportional to the dynamic head. A severe disturbance in pipeline results in the generation of intense broadband internal sound waves which can propagate through the piping system. The characteristic frequencies of operating loads of 20%, 57%, 70%, 100% are 4 - 6 Hz and coincide with the results from impact hammering test and FEM analysis. We chose the wire energy absorbing rope restraint as a vibration reduction method after reviewing the various conditions such as site, installing space and economic cost etc. After installation, the vibration level was reduced about 54% in velocity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.339.1-339
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• 2002

Noise of the VVVF inverter and DC/DC converter, which are the most dominant noise sources of maglev train at low speed, is studied. The coils inside inverter and converter are excited by the electro-magnetic forces, which results in core vibration and generations of the noise. It is found that the spectra of the noise show many harmonics, where there exist several different fundamental frequencies. (omitted)

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.9
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• pp.98-105
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• 1995

Recent microwave IC's reach to the extent of high operating frequencies at which bonding wires limit their performance as dominant parasitic components. Double bonding wires separated by an internal angle have been firstly characterized using the Method of Moments with the incorporation of the ohmic resistance calculated by the phenomenological loss equivalence method. For a 30$^{\circ}$ internal angle, the calculated total reactance is 45% less than that of a single bonding wire due to the negative mutual coupling effect. The radiation effect has been observed decreasing the mutual inductance, whereas for parallel bonding wires it greatly increases the mutual inductance. This calculation results can be widely used for designing and packaging of high frequency and high density MMIC's and OEIC's.

• Journal of Plant Biology
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• v.19 no.4
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• pp.111-118
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• 1976

The marine algal vegetation of spring season in the intertidal belt of Jeju Island, Korea, was carried out by the quadrat method at 4 transects; Moseulpo, Kangjeong, Whabug, and Hado in 1976. The transects were divided into 5 stations by exposed frequencies of the substratum from water, such as more than 50%, 46-49%, 28-45%, 7-27%, and less than 6%. As a result, the algal vegetations were separated into three groups, high, middle and low algal communities. The representative dominant species of each group are aas follows. High algal community: Porphyra suborbiculata, Bangia fusco-purpurea, Gloiopeltis furcata. Middle algal community: Ishige okamurai, Hizikia fusiforme, Corallina pilulifera, Sargassum thunbergii. Low algal community: Sargassum ringgoldianum, Sarg. confusum. The coverage of these groups is 43.5, 57.6%, and 77.3%, respectively.

• The Plant Pathology Journal
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• v.23 no.3
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• pp.219-222
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• 2007

A total of the 261 Phytophthora infestans isolates collected from 2003 to 2005 in Korea were investigated for their physiological race composition. Among the isolates, we detected 18 physiological races and the dominant races were R0.1.3.5.6.10.11 and R0.1.3.5.6.7.10.11 with frequencies of 18.4% and 11.4%, respectively. All of the P. infestans races carried multiple virulence genes and showed virulence to the potato resistance genes R1, R3, R5, R6, R7, R10 and R11, but not to R8 and R9. Therefore, it is likely that the physiological races of P. infestans were diverse in Korea.

• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.169-170
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• 2015

This paper describes a result for extraction of dynamic parameters from synchrophasor measurements collected on the KEPCO system. Dominant modes of the system are estimated by oscillation detecting program. The critical wide-area modes of KEPCO system have frequencies in the 0.68 Hz and 0.92Hz. This results can serve as a reference in the future for reliable system operation in KEPCO system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.98-103
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• 2003

This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a HRSG. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At this tube bank, dominant frequencies of vibration in this system were 43.5, 67.5㎐. The 3$\^$rd/ acoustic natural frequency calculated was 68.5㎐. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}$20%, acoustic resonance could occur. In this system, in order to prevent acoustic resonance, acoustic baffle was installed in the tube bank before operating. But acoustic resonance occurred. So, we evaluate the effect of acoustic mode due to baffle extension length. After investigating, we did revise acoustic baffle to eliminate acoustic resonance effectively.