• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.13-19
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• 2011

Lift off acoustic loads of KSLV-I were predicted by the modified NASA SP-8072 source distribution method (method 2) and the result was compared with those of measurements in the flight test of KSLV-I. In the second flight test, lift off acoustic loads were measured by outer microphones attached on the cable mast. The onboard data measuring outer acoustic pressure at the interstage of KSLV-I also can be obtained. The predicted result showed very similar peak and the shape of spectrum when compared with the measured spectrum and a margin about +7 dB.

• Korean Journal of Optics and Photonics
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• v.3 no.4
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• pp.239-243
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• 1992

We have investigeted the interference phenomena of the second harmonic waves of Nd:YAG laser generated at KDP single crystals and the nitrogen CARS signals. To get the phase difference between the successively generated nonlinear optical signals, a phase shifting unit made of BK-7 glass and a high pressure gas cell are used. Coherence lengths of several samples for the nonlinear signals are measured. Adjusting the thickness of the phase shifting unit where the CARS signals make destructive interference completely, the CARS spectrum of nitrogen suppressed over wide wavelength range is obtained. Also, we have observed the change in degree of suppression of the spectrum for the variation of the thickeness of the phase shifting unit.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.339-339
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• 2011

진공 플라즈마와 달리 개방된 공간에서 방전되는 대기압 플라즈마는 진공상태에서 수행되는 에칭, 증착 등의 복잡한 플라즈마 공정을 경제적이고 신속하게 수행할 수 있어, 최근 들어 연구가 활발히 진행 중이다. 이와 관련하여 He, Ar, $N_2$, $O_2$, Air 등의 여러 종류의 기체를 50 kHz 고전압에서 방전하여 대기 중에서 저온 플라즈마 공정이 가능한 아크젯 타입의 플라즈마 소스를 개발하였다. 개발된 플라즈마 소스에서는 입력전압, 기체유량, 노즐의 구조와 크기 등의 여러 운전변수에 따라 플라즈마의 방전특성이 변화되었다. 특히 본 연구에서는 아크젯의 플라즈마 발생부의 물질성분(SUS, Aluminum, Cupper)에 따른 플라즈마의 기체온도 및 전자여기 온도의 변화를 광방출분광법(OES)를 이용한 Synthetic spectrum method와 Boltzmann plot method을 통해 살펴보았다. 전압-전류 특성곡선, 시간분해 이미지 촬영법, 기체온도 측정법 등을 이용하여 발생된 플라즈마의 물리적인 특성을 분석하였다. 특히 물질의 성분에 따라 발생되는 플라즈마의 기체 및 전자여기 온도가 이차 전자 방출계수 및 물질의 전도도와의 상관관계가 있는지 연구가 진행 중이다.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1659-1660
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• 2006

After end of the 20th environmental problem was became issue. So about mercury free lighting sources are being studied very much. In this paper, a mercury and electrode free bulb was designed. in this bulb was injected mixed of Xe, Ne and Kr Gases. and then the bulb was discharged by 13.56MHz RF Power after spectrum, color coordinates and brightness were measured by spectrum meter CS-1000. Measured results were compared and analyzed, also analysis was able to do a characteristic of a gas defensive fight in proportion to a mixing ratio. Therefore the most of high brightness which was 4500cd/m2 was gained in 1:1 ratio of Xe:Ne at 60W input power.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1156-1161
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• 2001

Acoustic intensity is usually estimated by the cross-spectrum of acoustic pressure at two adjacent microphones. The cross-spectrum calculated by digital Fourier transform technique will unavoidally have leakage error since the period of signal will not be usually coincident with record length. Therefore, the acoustic intensity estimated by the conventional FFT analyzer will show distorted value. In this paper, the expression of the Fourier transformed date of a harmonic signal with a single frequency is formated when there is leakage error. The method to elimate the effect of leakage error from the contaminated data is also proposed. Some numerical examples show the validation of the proposed method.

• Bulletin of the Korean Chemical Society
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• v.19 no.9
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• pp.942-947
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• 1998

The >$^13C$ NMR spectrum of >$^13CO$ adsorbed on Pd particles varies dramatically depending on dispersion. The spectrum of highly dispersed Pd particles supported on silica is a powder pattern ∼800 ppm wide with a first moment of 410 ppm. A low dispersion sample has a motionally narrowed line centered at 750±30 ppm and only ∼85 ppm full width at half height (FWHH). Over several years, high dispersion samples show an increase in the intensity near 750 ppm. These observations are interpreted as an increase of mobile bridging CO on high dispersion Pd surfaces of particles which resulted from smoothing of the metal particle surfaces in the presence of CO.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.5
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• pp.261-269
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• 2018

This study examines earthquake-induced sloshing effects on liquid storage tanks using computation fluid dynamics. To achieve this goal, this study selects an existing square steel tank tested by Seismic Simulation Test Center at Pusan National University as a case study. The model validation was firstly performed through the comparison of shaking table test data and simulated results for the water tank subjected to a harmonic excitation. For a realistic estimation of the wall pressure response of the water tank, three recorded earthquakes with similar peak ground acceleration are applied:1940 El Centro earthquake, 2016 Gyeongju earthquake, and 2017 Pohang earthquake. Wall pressures monitored during the dynamic analyses are examined and compared for different earthquake motions and monitoring points, using power spectrum density. Finally, the maximum dynamic pressure for three earthquakes is compared with the design pressure calculated from a seismic design code. Results indicated that the maximum pressure from the El Centro earthquake exceeds the design pressure although its peak ground acceleration is less than 0.4 g, which is the design acceleration. On the other hand, the maximum pressure due to two Korean earthquakes does not reach the design pressure. Thus, engineers should not consider only the peak ground acceleration when determining the design pressure of water tanks.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.131-137
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• 2024

Aerodynamic noise generated by the surrounding flow of a train traveling at high speed affects both outdoor and indoor noise. This study's goal is to develop a test method to measure and quantitatively evaluate aerodynamic noise through pressure perturbation data on the train surface. To accurately evaluate aerodynamic noise, it is important to separate and evaluate the compressive and incompressible pressure fluctuations mixed in the acquired surface pressure fluctuation data. This is because the noise transmission characteristics of the two pressure fluctuations are different. First, the installation length and interval of the microphone were determined to acquire surface pressure fluctuation data, and wavenumber-frequency analysis was performed to separate incompressible pressure fluctuation and compressible pressure fluctuation to obtain a sound pressure level spectrum. Finally, as a result of comparing the test results measured in the train head and trail, It was confirmed that the pressure fluctuation on the train head surface was greater than that on the tail.

• Journal of KSNVE
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• v.7 no.1
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• pp.71-79
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• 1997

The objective of this study is to investigate experimentally the effect of surface conditions of the plate on the impinging jet noise. The experimental results about the spectrum, the sound pressure level and the directivity are pressented and discussed in relation with the surface conditions. Regardless of the surface conditions, the pure tones of high level are generated at the same frequency band and the overall sound power level of impinging jets is much higher than that of the free jet. However, the velocity dependence of the sound pressure level and the directivity are different between smooth surfaces and rough surfaces. The dependence of sound pressure level on the jet velocity shows that the smooth surface generates quadrupole-type sound like free jets. However, the perforated or the rough surface radiates sound power exactly proportional to the sixth power of the jet velocity, indicating that the source is fixed dipole type. The directivities of 1/3 octave band sound pressure level for both the free and impinging jet show the peak directivity at 115$^\circ$ upstream, probably due to the refraction associated with velocity gradient.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.7
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• pp.626-633
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• 2012

In this paper, sound pressure sensitivity of the fiber optic acoustic sensor according to sensor direction and mandrel material were investigated experimentally. Three different directions were selected as stand, lay, and hole. Hollow cylinder type mandrel dimension is 30 mm in outer diameter, 45 mm in length, and 2 mm in thickness, and about 50 m optical fibers were wounded on the surface of the mandrel. Non-directional sound speaker was used as a sound source. Sagnac interferometer and single mode fiber, a laser with 1,550 nm in wavelength, $2{\times}2$ coupler were used. Based on the experimental results, lay direction's sensitivity is the highest in the frequency range of 2 kHz~4 kHz. 'PTFE+carbon' material is more sensitive than PTFE in the frequency range of 5 kHz~20 kHz. Sound pressure detection sensitivity depends on the mandrel direction and material under certain frequency.