• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.1
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• pp.20-26
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• 2012

The objective of this study is to assess plastic deformation in aluminium alloy by acoustic nonlinearity of laser-generated surface waves. A line-arrayed laser beam made by high-power pulsed laser and mask slits is utilized to generate the narrowband surface wave and the frequency characteristics of laser-generated surface waves are controlled by varying the slit opening width and slit interval of mask slits. Various degrees of tensile deformation were induced by interrupting the tensile tests so as to obtain aluminum specimens with different degrees of plastic deformation. The experimental results show that the acoustic nonlinear parameter of a laser-generated surface wave increased with the level of tensile deformation and it has a good correlation with the results of micro-Vickers hardness test and electron backscatter diffraction (EBSD) test. Consequently, acoustic nonlinearity of laser-generated surface wave could be potential to characterize plastic deformation of aluminum alloy.

• Proceedings of the KIPE Conference
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• 2012.11a
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• pp.119-120
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• 2012

본 논문에서는 수중음향 센서를 위한 전력증폭기용 전원회로로 멀티레벨 가변전압출력 AC-DC 컨버터를 제안한다. 제안하는 가변전압출력 AC-DC 컨버터는 입력단측의 입출력측 절연 및 멀티전원전압을 얻기 위한 고효율 위상제어 풀 브리지 DC-DC컨버터와 출력단측의 응답특성이 빠른 멀티레벨 가변출력전압을 얻기 위한 2개 Flying capacitor 3-level converter와 1개의 다이오드 브리지로 구성되어 있다. 본 논문에서 제안하는 멀티레벨 컨버터는 수중음향 센서를 위한 전력증폭기용 전원회로로서 유용하게 사용될 것으로 예상한다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.2
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• pp.126-130
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• 2009

The present study describes an investigation into the characteristics of combustion oscillation and its suppression instability of a silo type gas turbine combustor in commercial power plant. Combustion oscillation is occurred the combustor in near full load during operation. As a result of FFT analysis of the combustion dynamics, the frequency of the oscillation is analyzed as the 1'st longitudinal mode of acoustic resonance of the combustor. For suppress of the instability, combustion tuning with adjust of fuel valve schedule is carried out, which changes equivalent ratio of each burners. As the result, the oscillation is successfully reduced with meeting the level of NOx emission regulation.

• Proceedings of the KIPE Conference
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• 2015.11a
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• pp.161-162
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• 2015

본 논문은 수중음향센서용 전력증폭기를 위한 멀티레벨 가변 출력전압 AC/DC 컨버터를 제안한다. 제안하는 AC/DC 컨버터는 멀티레벨 가변출력전압을 얻기 위해 2개의 flying-capacitor 3-level converters와 하나의 다이오드 브리지 회로로 구성되어 있다. 또한 본 논문에서는 제안하는 AC/DC 컨버터의 상세 회로도와 설계 가이드라인을 제시하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10B
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• pp.1200-1209
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• 2011

In this paper, we propose a novel energy efficient MAC protocol which is based on orthogonal frequency division multiple access (OFDMA) and exploits the physical characteristic that propagation loss of acoustic wave depends on the distance. In the proposed scheme, sensor nodes are grouped according to the distance to sink node. Then, each group uses a different frequency band. The proposed scheme not only enables all sensor nodes to maintain the signal-to-noise ratio above a certain required level (Accepted Minimum SNR, AMS), but also reduces overall transmission power consumption. In addition, the dynamic sub-channel allocation is employed in order to improve data transmission rate. Simulations show that proposed MAC protocol has better performance in a delay-tolerant underwater acoustic sensor networks.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.4
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• pp.328-334
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• 2012

Power flow finite element method(PFFEM) combining power flow analysis(PFA) with finite element method is efficient for vibration analysis of a built-up structure, and power flow boundary element method(PFBEM) combining PFA with boundary element method is useful for predicting the noise level of a vibrating complex structure. In this paper, the coupled PFFE/PFBE method is used to investigate the vibration and radiated noise of the unmanned underwater vehicle(UUV) in water. PFFEM is employed to analyze the vibrational responses of the UUV, and PFBEM is applied to analyze the underwater radiation noise. The vibrational energy of the structure is treated as an acoustic intensity boundary condition of PFBEM to calculate underwater radiation noise. Numerical simulations are presented for the UUV in water, and reliable results have been obtained.

• Fire Science and Engineering
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• v.23 no.5
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• pp.153-160
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• 2009

This study aims to review the propagation characteristics of fire alarm sound in building through computer simulation. In order to achieve this goal, the sound power level of existing three different emergency alarms were measured in an anechoic chamber. Sound power level of alarm bell was 98.6dB and electronic-siren speaker was 95.7dB, and electronic-siren phon was 101.8dB at the voltage of DC 24V in the condition of anechoic chamber. As the results of acoustic simulation, it was shown that sound levels at the corridor of the building were relatively high and even. But, there were large difference in sound level at all the frequency bands between corridor and lecture rooms. This mean that alarm sound couldn't be recognized sometimes in lecture rooms. Through the computer simulation, the propagation characteristics of fire alarm sound could be forecasted and compared due to plans of buildings.

• Proceedings of the KIPE Conference
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• 2004.07b
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• pp.887-890
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• 2004

This paper presents a microprocessor controlled electronic ballast for HID lamps, which gives automatic switching between MH and HPS lamps. Lamp identification is carried out by checking variation of lamp impedance at warm-up phase. Direct spread spectrum is done by applying 1 kHz triangular wave for removing acoustic resonance. This frequency modulation of 1 kHz gives also low EMI level. The microprocessor controls the voltage of DC-bus, the voltage of ignition pulses, the power of output. A 250W electronic ballast is implemented with ATmega16 CPU.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.399-400
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• 2013

본 논문에서는 수중음향 센서를 위한 전력증폭기용 전원회로로 멀티레벨 가변전압출력 AC-DC 컨버터의 제어 알고리즘을 제안한다. 제안하는 제어 알고리즘은 최종 출력으로 5-레벨 가변전압을 얻기 위한 2대의 Flying capacitor 3-level converter의 전력 균등분담 제어를 위해 사용되며, 플라잉 커패시터의 전압 밸런싱 제어를 위해 사용된다. 본 논문에서 제안하는 제어 알고리즘은 수중음향 센서를 위한 전력증폭기용 전원회로에서 유용하게 사용될 것으로 예상한다.

• Journal of KSNVE
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• v.8 no.2
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• pp.289-296
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• 1998

To predict the noise propagation from an elevated railway, sound radiation characteristics of elevated structure are measured by using the sound intensity method. In the base of the results, we propose the source model of elevated structure noise and the calculation model for elevated railway noise. Acoustic model of the former is modeled a row of single sources with directivity cos .theta. positioned in the center of a bogie and arranged in the lower side of slabs. Also prediction model is presented with rolling noise and elevated structure noise calculated by considering the power level of a source for one-third octave band, ground absorption and barrier deflection. Noise level unit patterns of a passing train is calculated based on this model and the results are compared with available field data.