• 제목/요약/키워드: low frequency

검색결과 11,436건 처리시간 0.039초

공명기 배열을 이용한 중속 디젤엔진 배기 소음기의 저주파수 대역 성능 개선 연구 (A Study on the Performance Improvement of Medium Speed Diesel Engine Exhaust Silencer in the Low-frequency Range Using Array Resonators)

  • 김영현;주원호;배종국
    • 한국소음진동공학회논문집
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    • 제19권7호
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    • pp.693-698
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    • 2009
  • Various acoustic tests were carried out to investigate the acoustic performance of diesel engine exhaust silencers. In order to consider flow effects, the test facility was set up composed of fan, duct and silencer. Using the test facility, insertion loss tests were carried out to improve the acoustic performance in the low-frequency ranges. Through a series of tests, it was found out that the array resonators having multi-perforated holes inside the exhaust silencer, might be very effective in the low frequency range. Consequently, the hybrid-type silencer which is the combination of reflective silencer with array resonators and conventional absorptive silencer, was proposed and its high performance in the low-frequency range was also verified.

공명기 배열을 이용한 디젤엔진 소음기의 저주파수 대역 성능 개선 연구 (A Study on the Improvement of Acoustic Performance of Diesel Engine Exhaust Silencer in the Low-Frequency Range using Array Resonators)

  • 이태경;김영현;주원호;배종국
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2007년도 춘계학술대회논문집
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    • pp.30-35
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    • 2007
  • Various acoustic tests were carried out to investigate the acoustic performance of diesel engine exhaust silencers. In order to consider flow effects, test equipment composed of fan, duct and silencer was set up. Using the test equipment, insertion loss tests were carried out to improve the performance in the low-frequency ranges. Through a series of tests, the fact that array resonators may be effective in the low-frequency noise has been verified. Consequently, the hybrid-type silencer which is the combination of reflective silencer with array resonators and conventional absorptive silencer were proposed and its high acoustic performance in the low-frequency range has also been verified.

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Phase inversion of seismic data

  • Kim, Won-Sik;Shin, Chang-Soo;Park, Kun-Pil
    • 한국지구물리탐사학회:학술대회논문집
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    • 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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    • pp.459-463
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    • 2003
  • Waveform inversion requires extracting a reliable low frequency content of seismic data for estimating of the low wave number velocity model. The low frequency content of the seismic data is usually discarded or neglected because of the band-limited response of the source and the receivers. In this study, however small the spectral of the low frequency seismic data is, we assume that it is possible to extract a reliable phase information of the low frequency from the seismic data and use it in waveform inversion. To this end, we exploit the frequency domain finite element modeling and source-receiver reciprocity to calculate the $Frech\`{e}t$ derivative of the phase of the seismic data with respect to the earth model parameter such as velocity, and then apply a damped least squares method to invert the phase of the seismic data. Through numerical example, we will attempt to demonstrate the feasibility of our method in estimating the correct velocity model for prestack depth migration.

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동적변화에 강인한 연료전지 발전시스템의 저주파 리플전류 제거 알고리즘 개발 (Development of Robust Algorithm to Eliminate Low Frequency Current Ripples in Fuel Cell Generation System)

  • 김종수;강현수;최규영;이병국
    • 전기학회논문지
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    • 제58권9호
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    • pp.1720-1727
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    • 2009
  • This paper presents that generation and propagation mechanism of low frequency current ripples generated by a rectification effect of an inverter in fuel cell generation system is analyzed. The ripple reduction methode using hardware components such as capacitors and inductors is examined to reduce low frequency current ripples. A new fast and robust low frequency current ripple elimination algorithm is then proposed to incorporate a single loop current controller, which directly controls fuel cell current, without any extra hardware. The proposed algorithm can completely eliminate this current ripple as well as an overshoot or undershoot is significantly reduced. And the de link voltage and output current are well regulated by inverter controller. The validity of proposed algorithm is verified both computer simulation using PSIM 6.0 and experiment with a 1kW laboratory prototype.

고주파용 소형 저 위상잡음 주파수 합성기 설계에 관한 연구 (A Study on Low Phase Noise Frequency Synthesizer Design with Compact Size for High Frequency Band)

  • 김태영
    • 한국군사과학기술학회지
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    • 제15권4호
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    • pp.450-457
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    • 2012
  • In this paper, we designed low phase noise frequency synthesizer with compact size for High frequency band (Ku-band). The paper addresses merits and demerits of single loop and dual loop frequency synthesizer. The phase noise characteristics of the phase-locked loop frequency synthesizer were predicted based on the analysis for phase noise contribution of noise sources. The proposed model in this paper more accurately predicts the low phase noise frequency synthesizer with compact size for high frequency band.

광릉과 제주도에 서식하는 박새 Song의 변이 (Song Variations of Great Tits inhabiting Kwangnung and Chejudo)

  • Hahm, Kyu-Hwang;Peak, Woon-Kee
    • The Korean Journal of Ecology
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    • 제17권3호
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    • pp.379-385
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    • 1994
  • Sonograms of songs recorded in Kwangnung and Chejudo were analyzed to investigate the features and variances in the songs of Great tit, Parus major variety. Songs of Great tits were identified, most of which were repetitions of phrases compoed of high-frequency note and low-frequency note. Variances between the songs of the two areas in the minimum and maximum of low-frequency were significat. The CV range of the Great tit group in Chejudo was wider than that in Kwangnung. Interregional variance level was significant in the minimum (P<0.04) and maximum (P<0.0001) of low-frequency.

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저주파수 흡음을 위한 헬름홀쯔 공명기 배열형 패널 (A Helmholtz Resonator Array Panel for Low Frequency Sound Absorption)

  • 김상렬;김양한
    • 한국소음진동공학회논문집
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    • 제15권8호
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    • pp.924-930
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    • 2005
  • Sound absorptive materials have good performance in high frequency range, not at low frequencies. Therefore it has been great challenge to develop a sound absorbing structure that is good at low frequency. We propose to use a Helmholtz resonator array panel for this purpose. A Helmholtz resonator is one of noise control elements widely used in many practical applications. The resonator is a simple structure composed of a rigid-walled cavity with a neck, but it has very high performance at resonance frequency. This paper discusses the sound absorption of Helmholtz resonator array panels at normal and random incidence. First, various experimental results are introduced and studied. Secondly, we theoretically predict the absorptive characteristics of the resonator away panel. The theoretical approach is based on the Fourier analysis for a periodic absorber. We believe that this method can be used to design a panel for low frequency noise control.

고압전동기 고정자 권선에서 부분방전 펄스의 전송 (Propagation of Partial Discharge Pulse in High Voltage Motor Stator Windings)

  • 김희동
    • 대한전기학회논문지:전기물성ㆍ응용부문C
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    • 제52권11호
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    • pp.512-515
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    • 2003
  • This paper is to investigate how partial discharge pulse signal can flow in 6.6㎸ motor stator windings. Pulse propagation is experimentally analyzed in stator windings using a variety of frequency-domain techniques. The experiments were performed on two stator windings in the laboratory. Spectrum analyzer(9KHz to 3㎓) with tracking generator(100kHz to 3㎓) was used. Sweep time of the tracking generator was looms. The frequency spectrum of the response signal was detected by active FET probe(1㎓). The active FET probe has a flat amplitude response up to 1㎓ without high frequency attenuation. The stator winding acts as a low-pass filter below 600KHz, the high-frequency components being highly declined. The resonance peaks show about 1.1MHz and 2MHz in low frequency of No. 1 and No. 2 stator windings, respectively. This low-frequency range indicates that attenuation is low. The peaks of partial discharge magnitude show about 900MHz, 1.6MHz in No. 1 stator winding and about 800KHz, 1.4MHz in No. 2 stator winding.

인터넷 쇼핑몰의 고객관리 방안에 관한 연구 - 온라인 구매빈도와 쇼핑몰 로열티에 의한 고객세분화를 중심으로 - (A CRM Strategy of Internet Shopping Mall: Focused on a Classification of Online Consumer Group by Buying Frequency and Mall Loyalty)

  • 박철;전종근
    • Journal of Information Technology Applications and Management
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    • 제9권4호
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    • pp.127-149
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    • 2002
  • Online consumers were classified four groups by online buying frequency and shopping mall loyalty in this study; high frequency-high loyalty, high frequency-low loyalty, low frequency-high loyalty, and low frequency-low loyalty groups. Four groups were compared by Internet usage, flow experience, innovativeness, perceived risks of Internet shopping, Internet shopping behaviors, and demographics. Through an online survey of 396 Internet shoppers, there found significant differences of those variables among four groups. The implications for customer relationship management of Internet shopping mall are discussed and further researches are suggested.

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좌골신경손상 백서의 통증과 기능회복에 저주파 전기자극과 수중운동이 미치는 효과 (Effects of Pain and Functional Recovery when Low Frequency Electrical Stimulation and Aqua-exercise Applied to Sciatic Nerve Injured Rats)

  • 김용억
    • 대한임상전기생리학회지
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    • 제6권1호
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    • pp.17-30
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    • 2008
  • This study was investigated the effects of pain and functional recovery when low frequency electrical stimulation and aquatic exercise applied to sciatic nerve injured rats. The rats were assigned into four groups; Group I(n=20, control group), Group II(n=20, low frequency electrical stimulation group), Group III(n=20, aquatic exercise group), Group (n=20, applied low frequency electrical stimulation and aquaatic exercise group). Each IV group measured hot plate examination, sciatic nerve functional index(SFI), c-fos.. In hot plate examination, group II, IV showed effect than group Iat 14 days after injured(p<0.01) and group III, Ⅳ showed effect than group I at 21, 28 days after in-jured(p<0.01, p<0.001). In SFI, group II, III, IV showed effect II, III, IV than group I and group IV showed effect than group II at 14, 21 days after injured(p<0.001). group II, III, IV showed effect than group I at 28 days after injured(II = p<0.01, III and IV = p<0.001). Effects of pain and function recovery when low frequency electrical stimulation and aqua-exercise applied to sciatic nerve injured rats, group Ⅳ were most effected to sciatic nerve injured rats. As well as group II and III were effected to sciatic nerve injured rats.

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