• Title, Summary, Keyword: Resonance

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Breast Magnetic Resonance Image (MRI) Guideline: Breast Imaging Study Group of Korean Society of Magnetic Resonance in Medicine Recommendations

  • Choi, Seon Hyeong;Kang, Bong Joo;Jung, Seung Eun
    • Investigative Magnetic Resonance Imaging
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    • v.22 no.4
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    • pp.205-208
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    • 2018
  • The purpose of this study is to establish an appropriate protocol for breast magnetic resonance imaging (MRI) in the discipline of image quality standards. The intention of the protocol is to increase effectiveness of medical image information exchange involved in construction, activation, and exchange of clinical information for healthcare.

Acoustic resonance by length of acoustic baffle at Finned Tube bank (핀-튜브군에서 배플 길이에 따른 음향공진)

  • 방경보;류제욱
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.98-103
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    • 2003
  • This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a HRSG. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At this tube bank, dominant frequencies of vibration in this system were 43.5, 67.5㎐. The 3$\^$rd/ acoustic natural frequency calculated was 68.5㎐. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}$20%, acoustic resonance could occur. In this system, in order to prevent acoustic resonance, acoustic baffle was installed in the tube bank before operating. But acoustic resonance occurred. So, we evaluate the effect of acoustic mode due to baffle extension length. After investigating, we did revise acoustic baffle to eliminate acoustic resonance effectively.

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$^{19}F$ MR Imaging of 5-FU Metabolism in Mice

  • Chaejoon Cheong;Lee, Seung-C.;Jae-G. Seo;Kim, Sung W.;Lee, Chulhyun;Kim, Chul S.;Taegyun Yang
    • Journal of the Korean Magnetic Resonance Society
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    • v.5 no.2
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    • pp.110-117
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    • 2001
  • $^{19}$ F imaging of mice was carried out. For $^{19}$ F imaging, 5-flouro-uracil (5-FU) was injected into a mouse and in vivo detection of the catabolism of 5-FU to a-fluoro-P-alanine (FBAL) was carried out. The chemical shift selective (CHESS) imaging technique was employed. The 19F spectra and images give temporal and spatial information of the metabolism for 5-FU in mice.

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FEM acoustic modal analysis due to location of acoustic baffles to avoid acoustic resonance in the tube bank of boiler for power plant (보일러 튜브군의 음향공진 회피를 위한 음향배플의 위치에 따른 FEM 음향모드해석)

  • Ahn, Sung-Jong;Ju, Young-Ho;Kim, Cheol-Hong
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.150-154
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    • 2012
  • A flow induced mechanical vibration and acoustic resonance should be considered at design stage because they are mainly occurred in the tube bank of boiler. Acoustic resonance is occurred when the vortex shedding frequency of tube bank coincides with the acoustic natural frequency of the cavity. Effective solution to avoid acoustic resonance is installing acoustic baffles in the tube banks parallelly inside of the flow cavity. Thus, location and number of acoustic baffles should be exactly calculated to eliminate the acoustic resonance. This paper presents case study of acoustic resonance due to inappropriate number and location of acoustic baffles. Measured frequency and mode in the study is verified by FEM acoustic modal analysis. The number and location of acoustic baffles to avoid acoustic resonance are calculated by using FEM acoustic modal analysis.

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Experimental study on moonpool resonance of offshore floating structure

  • Yang, Seung-Ho;Kwon, Sun-Hong
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.5 no.2
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    • pp.313-323
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    • 2013
  • Offshore floating structures have so-called moonpool in the centre area for the purpose of drilling, installation of subsea structures, recovery of Remotely-Operated Vehicle (ROV) and divers. However, this vertical opening has an effect on the operating performance of floating offshore structure in the vicinity of moonpool resonance frequency; piston mode and sloshing mode. Experimental study based on model test was carried out. Moonpool resonance of floating offshore structure on fixed condition and motion free condition were investigated. And, the effect of cofferdam which is representative inner structure inside moonpool was examined. Model test results showed that Molin's theoretical formula can predict moonpool resonance on fixed condition quite accurately. However, motion free condition has higher resonance frequency when it is compared with that of motion fixed. The installation of cofferdam moves resonance frequency to higher region and also generates secondary resonance at lower frequency. Furthermore, it was found that cofferdam was the cause of generating waves in the longitudinal direction when the vessel was in beam sea.

Resonance Phenomenon and Its Effects of Laser Texture Disk

  • Choa, Sung-Hoon;Wang, Geng
    • Journal of Mechanical Science and Technology
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    • v.14 no.7
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    • pp.744-751
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    • 2000
  • To achieve lower flying height for high areal recording density, the laser zone texturing of the disk needs to be designed to reduce glide height. One problem of the laser bump design is that the regular laser bump pattern often produces glide resonance phenomenon, which leads to failure of the glide height test. However, it was found in this study that glide resonance is an intrinsic problem of the glide head used and resonance phenomenon depends on the type of the head slider, that is, the natural frequency of the slider body. Therefore, higher glide height or glide failure caused by glide resonance does not lead to head/media interface problem in the real drive operating conditions in which the data head is used. Pseudo-random bump pattern greatly reduces the glide resonance. Smaller bump pitch will also help to reduce the glide resonance. However, as bump spacing becomes smaller, glide height will be increased due to increased air pressure developed around the bumps. Lowering bump height is the most effect way to reduce glide avalanche.

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A Study on the Analysis of Damping Loads to Prevent Harmonic Resonance (고조파 공진 억제를 위한 완충부하 투입량 분석에 관한 연구)

  • Lim, Chan-Ho;Lee, Kyeong-Seob;Yu, Won-Kun;Lee, Heung-Jae
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.59 no.2
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    • pp.262-266
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    • 2010
  • During the restoration process of primary restorative transmission system, the over voltage may happen due to nonlinear interaction between the unloaded transformer and the transmission system. This over voltage is caused by harmonic resonance and can be prevented by damping loads that are connected before restoration process of primary restorative transmission system. But it is very difficult to predict the occurrence possibility of the harmonic resonance previously. This paper analyzes the relationship between the harmonic resonance and the amount of damping loads to prevent the harmonic resonance. This paper calculates the minimum amount of damping loads to prevent harmonic resonance while changing the length of primary restorative transmission line. And this paper confirmed that the amount of damping loads is not proportional to length of transmission line. The result of this paper will be used as important experiment data to predict the occurrence possibility of harmonic resonance previously.

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.