• Title, Summary, Keyword: Resonance

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A Study on the Subsynchronous Resonance by Flexible Frequency Operation (주파수 유연화 운영에 따른 발전기 축 비틀림에 관한 연구)

  • Cho, Yoon-Sung
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.29 no.4
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    • pp.62-68
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    • 2015
  • Subsynchronous Resonance is a condition where the electrical power systems composed of generator and transmission line exchange energy with mechanical turbine-generator system at the frequency of the combined below the subsynchronous frequency. Therefore, the frequency of power systems should be associated with the subsynchronous resonance. This paper describes subsynchronous resonance by flexible frequency operation. It focuses on the characteristics and behavior of subsynchronous resonance. The subsynchronous resonance is being conducted by real-time digital simulator and the IEEE benchmark model for subsynchronous resonance have been utilized for the test systems.

Analysis on the cascade high power piezoelectric ultrasonic transducers

  • Lin, Shuyu;Xu, Jie
    • Smart Structures and Systems
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    • v.21 no.2
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    • pp.151-161
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    • 2018
  • A new type of cascade sandwiched piezoelectric ultrasonic transducer is presented and studied. The cascade transducer is composed of two traditional longitudinally sandwiched piezoelectric transducers, which are connected together in series mechanically and in parallel electrically. Based on the analytical method, the electromechanical equivalent circuit of the cascade transducer is derived and the resonance/anti-resonance frequency equations are obtained. The impedance characteristics and the vibrational modes of the transducer are analyzed. By means of numerical method, the dependency of the resonance/anti-resonance frequency and the effective electromechanical coupling coefficient on the geometrical dimensions of the cascade transducer are studied and some interesting conclusions are obtained. Two prototypes of the cascade transducers are designed and made; the resonance/anti-resonance frequency is measured. It is shown that the analytical resonance/anti-resonance frequencies are in good agreement with the experimental results. It is expected that this kind of cascade transducer can be used in large power and high intensity ultrasonic applications, such as ultrasonic liquid processing, ultrasonic metal machining and ultrasonic welding and soldering.

Resonance Condition of the Resonance Cavity and Air Gap in the Sacred Bell of the Great King Seongdeok (성덕대왕신종의 명동과 간극의 공명조건)

  • Kim, Seock-Hyun;Jeong, Won-Tae;Kang, Yun-June
    • The Journal of the Acoustical Society of Korea
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    • v.30 no.4
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    • pp.223-230
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    • 2011
  • Korean bell is hung with some air gap between the bell bottom and the ground. In addition, it has a peculiar acoustic element, so called resonance cavity below the bell. A proper design of the air gap and cavity size dramatically amplifies the bell sound by resonance effect. Bell interior cavity, air gap and resonance cavity consist of an acoustic cavity system. When the acoustic cavity frequency coincides with the natural frequency of the bell body, the frequency component is significantly amplified. On the Sacred Bell of the Great King Seongdeok, this study proposes a resonance condition of the cavity system considering air gap effect for the first time. With the exact dimension of the bell, boundary element analysis is performed using SYSNOISE. Finally, this study reveals how the temperature in season influences the resonance condition and proposes a concept of variable type resonance cavity. By using the variable type resonance cavity, the cavity size is controlled on site and exact resonance is available regardless of temperature difference in season.

Comparison Analysis of Donor Liver Volumes Estimated with 3D Magnetic Resonance and 3D Computed Tomography Image Data

  • Kim, Myeong-Seong;Park, Kyeong-Seok;Cho, Jae-Hwan
    • Journal of Magnetics
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    • v.19 no.3
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    • pp.261-265
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    • 2014
  • Three-dimensional computed tomography is an effective tool to estimate the liver volume of living donors for the live liver transplantation. When additional operation is required, magnetic resonance imaging is conducted to determine the safety of the donor. This study compared the accuracy of magnetic resonance imaging and computed tomography in estimating 3D liver volume of 23 male and 7 female donors who underwent both magnetic resonance imaging and computed tomography tests before the transplantation. The analysis was conducted to see whether the liver's estimated total volumes and the left lobe volumes obtained from 3D-magnetic resonance imaging and 3D-computed tomography were identical. Volumes of the right lobe estimated with 3D-magnetic resonance imaging and 3D-computed tomography were compared with the actual volume of the right lobe harvested in the operating room because the volume of the right lobe is an important determinant in the safety of the donor. The total volume of the liver estimated from 3D-magnetic resonance imaging and 3D-computed tomography differed (1238.1904 units and 1402.364 units respectively). The left lobe volume of the liver estimated with 3D-magnetic resonance imaging and 3D-computed tomography also differed (450.530 units and 554.490 units, respectively). The right lobe volume of the liver estimated with 3D-magnetic resonance imaging and 3D-computed tomography were 787.660 units and 847.545 units, respectively, while the actual average right lobe volume of the harvested liver was 678.636 units. 3D-computed tomography has been widely used to estimate the right lobe volume of the donors' liver. However, 3D-magnetic resonance imaging was also very effective in estimating the volume of the liver. Thus, 3D-magnetic resonance imaging is also expected to become an important tool in determining the safety of the donors before transplantation.

A Case Study on the vibration and noise by acoustic resonance in the tube bank of a boiler of 75MW power plant (75MW 급 발전용 보일러 관군에서의 음향공진에 의한 진동/소음 사례연구)

  • Kim, Cheol-Hong;Bang, Kyung-Bo;Ju, Young-Ho;Byun, Hyung-Hyun
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.150-155
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    • 2000
  • This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a power plant. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At the resonance, the value of vibration in this system was 595 ${\mu}m$, p-p and the sound pressure level was maximum 103 dBA. And the resonance frequency was found to be 35 Hz. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}20%$, acoustic resonance is possible. In this system, the difference of these frequencies was 1.8%. We can evaluate the possibility of acoustic resonance by using damping parameter. We did eliminate acoustic resonance by installing baffle in tube bank. After installing baffle, the level of vibration and noise was reduced dramatically.

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Relationship Between the Resonance Frequency and QTS for Microspeaker (마이크로스피커에서 공명진동수와 QTS 사이의 연관성)

  • Oh, Sei-Jin
    • Korean Journal of Materials Research
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    • v.21 no.7
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    • pp.403-409
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    • 2011
  • Micro speakers are used to reproduce sound in small electric and information and communications devices, such as cellular phones, PMPs, and MP3 players. The acoustical properties and sound quality, which are changed due to the decreased size of the speaker, are often adjusted varying the type and thickness of the diaphragm. The most widely used diaphragm material is thin polymer. It was previously reported by the author of this paper that the resonance frequency of a micro speaker is changed by the type and thickness of a polymer diaphragm. In this paper, the frequency response near the resonance frequency of a micro speaker was studied as functions of the type and thickness of the polymer diaphragm. While $R_{max}$ and $R_{DC}$ were affected by the type and thickness, an analysis of the electrical impedance curve revealed that $R_o(= R_{max}/R_{DC})$ and ${\Delta}f$ were not changed. Thus, $Q_{TS}$ which was function of $R_o$, ${\Delta}f$, and the resonance frequency, is only related to the resonance frequency. The increase of the resonance frequency led to a proportional rise of $Q_{TS}$. The change of the frequency response near the resonance frequency was not dependent on the type or thickness of the polymer diaphragm, but was affected by the resonance frequency.

Draw resonance in polymer processing: a short chronology and a new approach

  • Hyun, Jae-Chun
    • Korea-Australia Rheology Journal
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    • v.11 no.4
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    • pp.279-285
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    • 1999
  • Draw resonance is both an important and interesting instability encountered in various extensional-deformation-dominated polymer processing operations. It is important because of its paramount relevance to the productivity and quality issue in the related industry: and it is interesting because of as yet unanswered questions as to what its cause and origin are in terms of physics involved. Specifically, a short chronological account of the draw resonance research is presented in this paper bringing several previous results together and focusing on the derivation of a new criterion for draw resonance based on the interaction of the traveling times of some kinematic waves propagating along the spinline from the die exit to the take-up position. The new explanation of draw resonance put forward here based on the physics of the system is seen to have wide implications on both theoretical and practical aspects of draw resonance instability. The importance of the role played by spinline tension in determining draw resonance is an example of the former whereas interpretation of the mechanism of the draw resonance eliminator is an example of the latter. Finally, an approximate yet a very fast and convenient method for determining draw resonance is also derived based on the above findings and found to agree well with the exact stability results.

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Research of Synthetic Resonance Characteristics for Electrohydraulic Thrust Vector Control Actuation System (전기-유압식 추력벡터제어 구동장치시스템의 합성공진 특성 연구)

  • Min, Byeong-Joo;Choi, Hyung-Don;Kang, E-Sok
    • Aerospace Engineering and Technology
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    • v.7 no.1
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    • pp.151-160
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    • 2008
  • In this paper, the analysis results of synthetic resonance characteristics are described for the electrohydraulic thrust vector control actuation system. The synthetic resonance is induced by integration of position servo actuation system on the flexible launch vehicle mounting structure. The new resonance mode is synthesized due to composition of hydraulic resonance for electrohydraulic position servo system with inertia load condition and structural resonance for flexible mounting structure. This synthetic resonance can make stability of control system worse by feedback and amplification of control system. The exact nonlinear analysis model of this phenomenon is developed to predict and design a control algorithm for improvement characteristics. The DPF (Dynamic Pressure Feedback) control algorithm has been designed and has excellent resonance suppression capability.

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