• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.157-158
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• 2016

LCL 필터는 스위칭 고조파를 저감하는 저역통과필터로써 L 필터에 비해 경제적이며 효과적인 스위칭고조파 감쇄능력을 갖는다. 하지만 LCL 필터는 L 필터에서 존재하지 않은 공진문제를 야기한다. 이러한 LCL 필터의 공진현상은 계통주입전류의 품질을 저하시키고 LCL 필터의 고조파 억제성능을 저하시킬 수 있는 잠재적 요소이다. 최근에는 스위칭 고조파 및 LCL 필터 공진성분 뿐만 아니라 기본파 주파수 부근의 저차 고조파 성분도 계통주입전류를 왜곡시키는 원인의 하나로 밝혀져다. 그러므로 LCL 필터를 설계하기 위해서는 주요 주파수 영역에서의 정확한 필터동작해석이 요구된다. 본 논문은 기본파 주파수, 공진주파수, 스위칭주파수에 대한 L 필터와 LCL 필터의 주파수응답을 통해 필터의 동작을 해석하며, 시뮬레이션을 통해 계통주입전류의 스위칭 고조파 및 저차 고조파를 저감하기 위한 최적의 필터인덕터 비율을 제안한다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.295-299
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• 2004

본 논문에서는 주기 비안정 연속계의 해석을 위한 주파수 방법이 제안된다. 비안정시스템의 안정화를 위한 기존의 주파수 해석법을 일부 수정하여 연속계를 포함한 비안정 시스템에 적합하도록 수정하였으며, 직류모터와 동기발전기로 구성되어 있는 전기-기계 시스템에 적용하여 유용성을 보였다. 복잡한 비안정 연속계의 문제를 각 요소별 주파수 응답을 분리하고 조합하는 작업들을 통하여 쉽게 풀 수 있음을 보였다. 모터-발전기로 구성되어있는 전기-기계 시스템에서 발전기의 상호유도인덕턴스의 시간에 따른 주기적 변화와 장선(long electrical line)의 부하가 시스템의 불안정성을 야기함을 보였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.101-106
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• 2011

In the present paper, the phenomena of abnormal noise and vibration due to acoustic resonance of CFBC(Circulating Fluidized Bed Combustion) boiler was presented. The acoustic resonance which occurred in the gas path of CFBC boiler system was caused by coincidence of vortex shedding frequency of tube bank and acoustic natural frequency of duct and hopper. And, the phenomena of beating arose from the interference of two closed resonant waves at 66.4Hz and 70.8Hz. There are two control methods for acoustic resonance in this system. The first method is to change the vortex shedding frequency from the structural alterations on the tube bank. And the second method is to change the acoustic natural frequency of the gas path with the installation of anti-noise baffles. The second one which is relatively easy to apply, was adapted in this study. As a result, the noise and vibration level have been decreased by 41dB and 94% at 66.4Hz, respectively. And the improvement of noise and vibration at 70.8Hz was identified by sensory evaluation.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.6
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• pp.861-866
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• 2011

This paper described the hybrid power generation using ocean wave that consists of linear power generation system and vibrational power generation system. The linear power generation system is made up of the winding coil, the permanent magnet and it is performed stable generation regardless of the wave frequency using directly the ocean wave velocity. And the vibration power generation system consists of the winding coil, the permanent magnet and spring. When the vibration system natural frequency in the vibrational power generation system is tuned to the ocean wave frequency, the relative velocity of between the winding coil and the permanent magnet is faster than the velocity of ocean wave up and down motion, then we can obtain more the electric power. Therefore, in this paper, the proposed hybrid power generation using ocean wave have merits that obtaining the more electric energy in resonance frequency and carrying out stable generation even over the range of resonance frequency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.323-324
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• 2011

• The Journal of the Acoustical Society of Korea
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• v.21 no.2
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• pp.150-159
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• 2002

The possibility of a broadband noise reduction of piezoelectric smart panels is experimentally studied. Piezoelectric smart panel is basically a plate structure on which piezoelectric patch with shunt circuits is mounted and sound absorbing material is bonded on the surface of the structure. Sound absorbing materials can absorb the sound transmitted at mid frequency region effectively while the use of piezoelectric shunt damping can reduce the transmission at resonance frequencies of the panel structure. To be able to tune the piezoelectric shunt circuit, the measured electrical impedance model is adopted. Resonant shunt circuit composed of register and inductor in stories is considered and the circuit parameters are determined based on maximizing the dissipated energy through the circuit. The transmitted noise reduction performance of smart panels is investigated using an acoustic tunnel. The tunnel is a square crosses sectional tunnel and a loud speaker is mounted at one side of the tunnel as a sound source. Panels are mounted in the middle of the tunnel and the transmitted sound pressure across the panels is measured. Noise reduction performance of a double smart panel possessing absorbing material and air gap shows a good result at mid frequency region except the first resonance frequency. By enabling the piezoelectric shunt damping, noise reduction is achieved at the resonance frequency as well. Piezoelectric smart panels incorporating passive method and piezoelectric shunt damping are a promising technology for noise reduction in a broadband frequency.

• The Journal of the Acoustical Society of Korea
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• v.38 no.3
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• pp.340-343
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• 2019

In this paper, a problem of mechanical resonance between traction motor's rigid body mode and traction motor's excitation force is introduced, and a bogie design variable affecting the control of resonance response is reviewed numerically. To solve the resonance problem in rotating machinery with variable rotational speeds, resonance frequency should be out of rotational machine's operation range or dynamic stiffness of structures should be increased for resonance response enough to be low. In general, operation range of a traction motor is from 0 r/min to 4800 r/min. It is not possible that all bogie modes are more than 80 Hz. Therefore, it is very important to find design factor affecting resonance response of traction motor's rigid body modes. It is found that key design variable is the gab between transom pipes from finite element analysis. The larger gab is, the higher resonance response when resonance between traction motor's excitation force and traction motor's rigid body mode is happened.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.625-632
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• 2010

The moduli of concrete has been determined by various testing methods. The impact resonance (IR) method has been shown to be truly a simple nondestructive testing method which produces consistent results. It is possible to determine not only the modulus but also damping ratio from the IR test. However, the values of elastic modulus and damping ratio of concrete from the test is known to be affected by various test conditions including, specimen support condition, impact steel ball size and sampling rate. In this study, the optimum IR test conditions are suggested and validated experimentally. The test results showed that the recommended test conditions yielded a variation of resonant frequency within ${\pm}0.3%$ and damping ratio ${\pm}10.0%$. In addition, the modulus from the IR test was comparable to that from a static test when the effect of strain amplitude was properly taken into account.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.2
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• pp.28-33
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• 2003

The piezoelectric transformer converters electrical energy into mechanical energy, It is high efficiency and small size transformer for high output voltage. The piezoelectric transformer operates the resonance frequency and the output voltage waveform is close to sine wave. Therefore, it is suitable for driving the LCD backlight in the notebook computer. In this paper, we discussed about the inverter which os driving piezoelectric transformer by generating sine wave through LC resonance after converting input DC voltage to the gate signal of FET. As the result of experiments, it was showed that the resonance frequency and voltage gain of the piezoelectric transformer was proportional to the load variation, and voltage gain was independent of the input voltage variation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.2
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• pp.118-124
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• 2004

The objective of the paper is to demonstrate the noise reduction characteristics of an air-gap resonator, which is composed of an air gap and a partition sheet. By means of installing the air-gap resonator in an enclosed cavity, acoustic resonance can be effectively suppressed using a small space. In particular, it is revealed from a simple, one-dimensional model that the air-gap resonator serves as the Helmholtz resonator that generally absorbs acoustic resonance energy at its resonance frequency. As a result, the air-8ap resonator also has a resonance frequency, which can be predicted with a simple frequency equation derived in the paper. Finally, verification experiments show that the air-gap resonator can be effectively designed by predicting a reasonable gap thickness using the simple frequency-equation.