• Title, Summary, Keyword: Resonance

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A Study on the Pressure Resonance with Combustion Chamber Geometry for a Spark Ignition Engine (스파크 점화기관의 연소실 형상에 따른 공진현상 해석에 관한 연구)

  • Park, Gyeong-Seok;Jang, Seok-Hyeong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.12
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    • pp.1905-1910
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    • 2001
  • Pressure resonance frequency that is caused in the combustion chamber can be interpreted by acoustic analysis. Until now the pressure resonance has been assumed and calculated to a disc type combustion chamber that neglected the combustion chamber height because the knock occurs near the TDC(top dead center). In this research FEM(finite element method) has been used to calculate the pressure resonance frequency inside the experimental engine combustion. The error of the resonance frequency obtained by FEM has decreased about 50% compared to the calculation of Draper's equation. Due to the asymmetry in the shape of the combustion chamber that was neglected in Draper's equation we could find out that a new resonance frequency could be generated. To match the experimental results, the speed of sound that satisfies Draper's equation is selected 13% higher than the value for pent-roof type combustion chamber.

Ferromagnetic resonance of Hensler $Ni_2$MnGa thin films

  • M. D. Huang;Lee, N. N.;Lee, Y. P.;J. Y. Rhee;J. Dubowik
    • Journal of the Korean Vacuum Society
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    • v.12 no.S1
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    • pp.116-119
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    • 2003
  • $Ni_2$MnGa films, deposited on mica and glass substrates, were studied by ferromagnetic resonance (FMR) technology. The temperature-dependent resonance field was measured and a martensitic phase transformation (MT) was found between 310 and 340 K, exhibiting an abnormality on the curve. The easy axis is found to be in the film plane. The line width increases as a whole with decreasing temperature, which is discussed in terms of the motional narrowing mechanism. The resonance field was also measured as a function of orientation and the results were fitted, exhibiting a good consistence.

Impedance Matching Based Control for the Resonance Damping of Microgrids with Multiple Grid Connected Converters

  • Tan, Shulong;Geng, Hua;Yang, Geng
    • Journal of Power Electronics
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    • v.16 no.6
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    • pp.2338-2349
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    • 2016
  • This paper presents an impedance-matching-based control scheme for the harmonic resonance damping of multiple grid-connected-converters (GCCs) with LCL filters. As indicated in this paper, harmonic resonance occurs if a GCC possesses an output impedance that is not matched with the rest of the network in some specific frequency bands. It is also revealed that the resonance frequency is associated with the number of GCCs, the grid impedance and even the capacitive loads. By controlling the grid-side current instead of the converter-side current, the critical LCL filter is restricted as an internal component. Thus, the closed-loop output impedance of the GCC within the filter can be configured. The proposed scheme actively regulates the output impedance of the GCC to match the impedance of the external network, based on the detected resonance frequency. As a result, the resonance risk of multiple GCCs can be avoided, which is beneficial for the plug-and-play property of the GCCs in microgrids. Simulation and experimental results validate the effectiveness of the proposed method.

Efficiency evaluation and characteristics of receiver coil under different inserted resonance coils in wireless power charging system for MAGLEV

  • Chung, Yoon Do;Jeon, Haeryong
    • Progress in Superconductivity and Cryogenics
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    • v.20 no.1
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    • pp.23-27
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    • 2018
  • As the wireless power transfer (WPT) technology based on strongly resonance coupled method realizes large power charging without any wires through the air, there are advantages compared with the wired counterparts, such as convenient, safety and fearless transmission of power. From this reason, the WPT systems have started to be applied to the wireless charging for various power applications such as train, underwater ship, electric vehicle. This study aims for the effect and characteristics of different inserted resonance coil between Tx and Rx coils for charging system of superconducting magnetic levitation (MAGLEV) train. The transfer efficiency and effect are evaluated with helix type, rectangular type copper resonance coil, and HTS resonance coil under bulb and HTS magnet load, respectively. The input power is adapted with radio frequency (RF) power of 370 kHz below 500 W.

Analysis of Magnetic Resonance Characteristics and Images of Korean Red Ginseng (홍삼의 자기공명 특성과 영상 분석)

  • 김성민;임종국
    • Journal of Biosystems Engineering
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    • v.28 no.3
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    • pp.253-260
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    • 2003
  • In this study, the feasibility of magnetic resonance techniques for nondestructive internal quality evaluation of Korean red ginseng was examined. Relaxation time constants were measured using various grades of red ginsengs. Solid state magnetic resonance imaging technique was applied to image dried red ginsengs which have low moisture contents (about 13%). A 7 tesla magnetic resonance imaging system operating at a proton resonant frequency of 300 ㎒ was used for acquiring MR images of dried Korean red ginseng. The comparison test of cross cut digital images and magnetic resonance images of heaven grade, good grade with cavity inside, and good grade with white part inside red ginseng suggested the feasibility of the internal quality evaluation of Korean red ginsengs using MRI techniques. A good grade red ginseng included abnormal tissues such as cavities or white parts inside was observed by the signal intensity of MR image based on magnetic resonance properties of proton nucleus. Analysis on an one dimensional profile of acquired MR image of Korean red ginseng showed easy discrimination of normal and abnormal tissues. MR techniques suggested ways to detect internal defects of red ginsengs effectively.

Analysis of the Efficiency According to Resonant Repeater Application in Magnetic Resonant Wireless Power Transfer System (자기공진방식의 무선전력전송 시스템에서 공진 중계기 적용 여부에 따른 전력전송 효율 분석)

  • Baek, Seung-Myung;Kim, Dong-Eun;Shon, Jin-Geun
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.67 no.4
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    • pp.221-226
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    • 2018
  • In this paper, the power transfer efficiency analysis based on the resonant repeater in a magnetic resonance wireless power transfer system is proposed. The efficiency of the magnetic resonance method was verified by comparing the general frequency with the resonance frequency. The resonance repeater was arranged to increase the efficiency and increase the transfer distance. When using resonant repeaters, the maximum efficiency increase is about 36.23[%] and the transfer distance was extended to more than 20[cm]. Through this study, confirmed the effect of using resonance repeaters in wireless power transfer system. As a result, it can be expected that the overall technology related to wireless power transfer system will be more valuable for energy-IT technology.

Magnetic Resonance Imaging with Intermolecular Double Quantum Coherences

  • Ahn, Sang-Doo
    • Journal of the Korean Magnetic Resonance Society
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    • v.8 no.2
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    • pp.108-114
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    • 2004
  • Recently a new method for magnetic resonance imaging based on the detection of relatively strong signal from intermolecular multiple quantum coherences (iMQCs) is reported. Such a signal would not be observable in the conventional framework of magnetic resonance; it originates in long-range dipolar couplings that are traditionally ignored. In this paper, we present the results of experimental studies to assess the feasibility of intermolecular double quantum coherences (iDQCs) imaging in humans. We show that the iDQC images are readily observable at 4T and that they do indeed provide different contrast than appears in conventional images.

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