• Title/Summary/Keyword: Reduced Frequency

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Active Vibration Control of Clamped Beams Using Filtered Velocity Feedback Controllers (Filtered Velocity Feedback 제어기를 이용한 양단지지보의 능동진동제어)

  • Shin, Chang-Joo;Hong, Chin-Suk;Jeong, Weui-Bong
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.21 no.5
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    • pp.447-454
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    • 2011
  • This paper reports a filtered velocity feedback(FVF) controller, which is an alternative to direct velocity feedback(DVFB) controller. The instability problems due to high frequency response under DVFB can be alleviated by the suggested FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The FVF controller and the dynamics of clamped beams under forces and moments are first formulated. The effects of the design parameters(cut-off frequency, gain, and damping ratio) on the stability and the performance are then investigated. The cut-off frequency should be selected not to affect the system stability. The magnitude of the open loop transfer function(OLTF) at the cut-off frequency should be small. As increasing the gain of the FVF controller, the magnitude of the OLTF is increased, so that the closed loop response can be reduced more. The enhancement of the OLTF at the cut-off frequency is reduced but the phase behavior around the cut-off frequency is distorted, as the damping ratio is increased. The control performance is finally estimated for the clamped beam. More than 10 dB reductions in velocity response can be achieved at the modal frequencies from the first to eighth modes.

Active Vibration Control of Clamped Beams using Filtered Velocity Feedback Controllers (Filtered Velocity Feedback 제어기를 이용한 양단지지보의 능동진동제어)

  • Shin, Chang-Joo;Hong, Chin-Suk;Jeong, Weui-Bong
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2011.04a
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    • pp.264-270
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    • 2011
  • This paper reports a filtered velocity feedback (FVF) controller, which is an alternative to direct velocity feedback (DVFB) controller. The instability problems due to high frequency response under DVFB can be alleviated by the suggested FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The FVF controller and the dynamics of clamped beams under forces and moments are first formulated The effects of the design parameters (cut-off frequency, gain, and damping ratio) on the stability and the performance are then investigated. The cut-off frequency should be selected not to affect the system stability. The magnitude of the open loop transfer function (OLTF) at the cut-off frequency should be small. As increasing the gain of the FVF controller, the magnitude of the OLTF is increased, so that the closed loop response can be reduced more. The enhancement of the OLTF at the cut-off frequency is reduced but the phase behavior around the cut-off frequency is distorted, as the damping ratio is increased The control performance is finally estimated for the clamped beam. More than 10dB reductions in velocity response can be achieved at the modal frequencies from the first to eighth modes.

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Analytical Surge Behaviors in Systems of a Single-stage Axial Flow Compressor and Flow-paths

  • Yamaguchi, Nobuyuki
    • International Journal of Fluid Machinery and Systems
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    • v.9 no.1
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    • pp.1-16
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    • 2016
  • Behaviors of surges appearing near the stall stagnation boundaries in various fashions in systems of a single-stage compressor and flow-path systems were studied analytically and were tried to put to order. Deep surges, which enclose the stall point in the pressure-mass flow plane, tend to have either near-resonant surge frequencies or subharmonic ones. The subharmonic surge is a multiple-loop one containing, for example, in a (1/2) subharmonic one, a deep surge loop and a mild surge loop, the latter of which does not enclose the stall point, staying only within the stalled zone. Both loops have nearly equal time periods, respectively, resulting in a (1/2) subharmonic surge frequency as a whole. The subharmonic surges are found to appear in a narrow zone neighboring the stall stagnation boundary. In other words, they tend to appear in the final stage of the stall stagnation process. It should be emphasized further that the stall stagnation initiates fundamentally at the situation where a volume-modified reduced resonant-surge frequency becomes coincident with that for the stagnation boundary conditions, where the reduced frequency is defined by the acoustical resonance frequency in the flow-path system, the delivery flow-path length and the compressor tip speed, modified by the sectional area ratio and the effect of the stalling pressure ratio. The real surge frequency turns from the resonant frequency to either near-resonant one or subharmonic one, and finally to stagnation condition, for the large-amplitude conditions, caused by the non-linear self-excitation mechanism of the surge.

Study on the Dynamic Analysis Based on the Reduced System (축소모델 기반 구조물의 동적해석 연구)

  • Kim, Hyung-Gi;Cho, Maeng-Hyo
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.21 no.5
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    • pp.439-450
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    • 2008
  • In this study, the reduced system for the dynamic analysis is proposed and the selection criterion of the primary degrees of freedom is presented considering the relation between natural frequency and external loading frequency. A well-constructed reduced system can assure the accurate representation of the dynamic behavior under arbitrary dynamic loads. For selecting the primary degrees of freedom of the reduced system, we employ the robust two-level condensation scheme of which the reliability has been proven through previous study. In the numerical examples, the reliability of the dynamic analysis based on the reduced system is demonstrated through comparing with those of global system.

An Optimization of Speech Database in Corpus-based speech synthesis sytstem (코퍼스기반 음성합성기의 데이터베이스 최적화 방안)

  • Jang Kyung-Ae;Chung Min-Hwa
    • Proceedings of the KSPS conference
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    • 2002.11a
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    • pp.209-213
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    • 2002
  • This paper describes the reduction of DB without degradation of speech quality in Corpus-based Speech synthesizer of Korean language. In this paper, it is proposed that the frequency of every unit in reduced DB should reflect the frequency of units in Korean language. So, the target population of every unit is set to be proportional to their frequency in Korean large corpus(780K sentences, 45Mega phonemes). Second, the frequent instances during synthesis should be also maintained in reduced DB. To the last, it is proposed that frequency of every instance should be reflected in clustering criterion and used as criterion for selection of representative instances. The evaluation result with proposed methods reveals better quality than using conventional methods.

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A Reduction of Speech Database in Corpus-based Speech Synthesis System (코퍼스기반 음성합성기의 데이터베이스 감축방안)

  • Jang Kyung-Ae;Chung Min-Hwa;Kim Jae-In;Koo Myoung-Wan
    • MALSORI
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    • no.44
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    • pp.145-156
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    • 2002
  • This paper describes the reduction of DB without degradation of speech quality in Corpus-based Speech synthesizer of the Korean language. In this paper, it is proposed that the frequency of every unit in reduced DB reflect the frequency of units in the Korean language. So, the target population of every unit is set to be proportional to its frequency in Korean large corpus (780k sentences, 45Mega phones). Secondly, the frequent instances during synthesis should be also maintained in reduced DB. To the last, it is proposed that frequency of every instance be reflected in clustering criteria and used as another important criterion for selection of representative instances. The evaluation result with proposed methods reveals better quality than that using conventional methods.

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A Novel Ripple-Reduced DC-DC Converter

  • Tao, Yu;Park, Sung-Jun
    • Journal of Power Electronics
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    • v.9 no.3
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    • pp.396-402
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    • 2009
  • A DC/DC converter generally needs to work under high switching frequency when used as an adjustable power supply to reduce the size of magnetic elements such as inductors, transformers and capacitors, but with the rising of the switch frequency, the switch losses will increase and the efficiency will reduce. Recently, to solve these problems, research is actively being done on a soft switching method that can be applied under high frequency and on a PWM converter that can be applied under low frequency such as a multi-level topology. In this paper a novel DC-DC conversion method for reducing the ripple of output voltage is proposed. In the proposed converter, buck converters are connected in series to generate the output voltage. By using this method, the ripple of output voltage can be reduced compared to a conventional buck converter. Particularly when output voltage is low, the number of acting switching elements is less and the result of ripple reduction is more obvious. It is expected that the converter proposed in this paper could be very useful in the case of wide-range output voltage.

Stuttering Reduction Rate during Sentence Reading: Choral Speech and Altered Auditory Feedback (문장읽기에서의 말더듬 감소율: 합독과 변조청각피드백)

  • Park, Jin;Park, Heeyoung
    • Phonetics and Speech Sciences
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    • v.4 no.4
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    • pp.109-115
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    • 2012
  • This paper mainly aims to investigate how differently choral speech and altered auditory feedback (i.e., delayed auditory feedback, frequency-altered feedback) enhance speech fluency during sentence reading. To do this, a stuttering reduction rate was used and measured how much stuttering in frequency was reduced during each of the fluency enhancing conditions (i.e, typical choral reading, DAF, FAF) relative to typical solo reading. The results showed that stuttering frequency was reduced in the three fluency enhancing conditions and the highest mean value in stuttering reduction rate was observed during typical choral reading. Some discussion was provided in relation to the stuttering reduction rate observed during typical choral reading and its further speculation.

Vibration Analysis of a Cable Supported Wind Turbine Tower Model (케이블 지지된 풍력발전기 타워 구조 모델의 진동해석)

  • Kim, Seock-Hyun;Park, Mu-Yeol;Cui, C.X.
    • Journal of Industrial Technology
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    • v.27 no.A
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    • pp.47-53
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    • 2007
  • A theoretical model based on Rayleigh-Ritz method is proposed to predict the resonance frequency of a W/T(Wind Turbine) tower structure supported by guy cables. In order to verify the validity of the theoretical model, a reduced W/T tower system is manufactured and tested. Frequency response and mode data are determined by modal testing and finite element analysis is performed to calculate the natural frequency of the tower model. Numerical and experimental results are compared with those by the theoretical analysis. Parametric study by the theoretical model shows how the cable tension and cable elasticity influence the resonance frequency of the W/T tower structure. Finally, vibration response under various rotating speed is investigated to examine the possibility of severe resonance.

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Frequency Modulation Method of ZVT Interleaved DC/DC Converter Using Auxiliary Coupled-Inductor (보조 커플드-인덕터를 이용한 ZVT 인터리브드 DC/DC 컨버터의 주파수 변조 기법)

  • Lee, Jong-Young;Lee, Soon-Ryung;Lee, Kang-Hyun;Won, Chung-Yuen;Yi, Je-Hyun;Cho, Bo-Hyung
    • Proceedings of the KIPE Conference
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    • 2016.11a
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    • pp.1-2
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    • 2016
  • This paper presents frequency modulation method of zero-voltage-transition interleaved DC/DC converter using auxiliary coupled-inductor. In conventional ZVT interlaved converter without semi-conductor devices in auxiliary circuit, the peak-to-peak value of coupled-inductor current has fixed value despite the change of load current. Then, as the load is reduced, the efficiency is reduced because of the conduction loss. The proposed frequency modulation method can reduce the conduction loss by controlling the current of coupled-inductor as the load condition using frequency modulation. The proposed method is verified by experimental results.

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