• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.604-605
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• 2008

Modal participation factor (MPF) is a widely used in a mode-coupling squeal noise problem for finding the most sensitive component over a complex brake system in a vehicle using eigenvectors of sub-components. This methodology requires the problematic total response of system by the unstable squeal noise at a specific frequency as well as eigenvectors of each component belonging to brake system. In this paper, a unit-force response analysis is performed for intact total system to obtain eigenvectors of each component and then such data is directly used for the contribution analysis of a squeal noise problem. Since the eigenvectors of each component induced from virtual unit-excitation is most reliable owing to the intact boundary condition, it can be expected that the corresponding contribution analysis with MPF also provides a trustworthy result.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.1096-1101
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• 2000

In machine tools, often a gearbox is installed to control the rotating speed of spindle, which sometimes generates problems of noise and vibration due to errors in tooth-meshing. In this study, the characteristics of, noise and vibration of given gearbox for a machine tool are analyzed experimentally. From the measurement, it was observed that the tooth-meshing component of the sound pressure level from the gearbox took its maximum at a specific operational speed. Therefore, the main content of this study is to investigate the reason why the above mentioned characteristics are observed. By investigating the natural frequencies of the components in gearbox, it was found that the natural frequencies of the rotating gear-shaft and gearbox for twisting mode were closely related to the first and second peak of sound pressure levels respectively. Thereform, in this study, those relations were identified by the impact test of rotating gear-shaft and-gearbox. In addition, we inserted the rubber between housing and bed, and analyze the effect of the rubber insertion on noise reduction by Operational Deflection Shapes.

• 센서학회지
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• 제31권2호
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• pp.120-124
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• 2022

With advancements in underwater stealth technology for naval vessels, new sensor configurations for detecting targets have been attracting increased attention. Latest underwater mines adopt multiple sensor configurations that include electric field sensors to detect targets and to help acquire accurate ignition time. An underwater electric field sensor consists of a pair of electrodes, signal processing unit, and preamplifier. For detecting underwater electric fields, the preamplifier requires low-noise amplification at ultra-low frequency bands. In this paper, the specific requirements for low-noise preamplifiers are discussed along with the experimental results of various setups of matched transistors and chopper stabilized operational amplifiers. The results showed that noise characteristics at ultra-low frequency bands were affected significantly by the voltage noise density of the chopper amplifier and the number of matched transistors used for differential amplification. The fabricated preamplifier was operated within normal design parameters, which was verified by testing its gain, phase, and linearity.

• 한국철도학회논문집
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• 제16권1호
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• pp.14-19
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• 2013

고속철도차량의 실내소음은 승객에서 불쾌감, 피로감 및 스트레스를 유발하는 요인으로 이에 대한 지속적인 연구가 필요하다. 특히, 고속철도 차량이 개활지와 터널 등 다양한 주행환경에서 운행되고 있는 우리나라 현실에서는 이러한 환경에서의 실내소음 변화에 대한 구체적인 연구가 필요하다. 따라서, 본 연구에서는 현재 우리나라에 운영되고 있는 고속철도 차량에 대한 실내 소음의 특성을 분석하는 연구를 수행하였다. KTX와 KTX-산천 차량의 실내에 마이크로폰을 설치하여 주행 시 발생하는 실내소음을 분석하였으며, 축상, 대차 및 차체 가속도 센서를 설치하여 구조기인의 원인이 되는 진동을 검토하였다. 본 연구를 통해서 고속철도 차량의 속도에 따른 실내소음의 특성이 도출되었으며, 주행 환경이 실내소음에 미치는 영향을 개활지와 터널주행 시 발생하는 실내소음의 차이를 통해서 검토하였다. 또한, 차체진동과 실내소음에 대한 전달함수분석을 통해서 차체진동이 실내소음에 미치는 영향을 검토하였다.

• 한국도로학회논문집
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• 제7권4호
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• pp.125-140
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• 2005

본 연구에서는 콘크리트 포장에서 발생하는 소음을 저감시키기 위한 최적의 임의간격 횡방향 타이닝 설계 간격을 제안하였다. 기존 문헌조사를 바탕으로 소음 발생에 대한 원인을 규명하였고, LCG(linear congruential generators) 알고리즘 이론을 이용하여 특정 주파수에 집중되는 에너지를 효과적으로 분산시킬 수 있는 타이닝의 간격을 설계하였다. 실내 시뮬레이션 결과를 대구-포항 고속국도 현장에 적용하였고 기존 국내외에 적용된 임의간격 횡방향 타이닝 시공도 병행하여 실내 외 소음 및 교통소음을 비교하였다. 실내 외 소음 측정 결과, 피치 소음으로 인한 소음을 감소시킴으로써 임의간격 횡방향 타이닝 구간이 일반구간 보다 낮은 소음도를 보였으나, 그 효과가 크지 않았다. 교통 소음 측정에서도 전체적으로 일반 타이닝 구간에 비해 임의 간격 횡방향 타이닝 구간에서 더 큰 소음저감 효과를 확인할 수 있었으나, pass-by 소음 측정과는 다소 차이를 보였다.

• 한국소음진동공학회논문집
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• 제22권3호
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• pp.264-274
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• 2012

Evaluation on the environmental noise is carried out by surveying subjective response of residents with physical measurement of noise during long period in field. Particularly field survey is used to make regulations from the analysis on how many people are annoyed for specific noise level, and laboratory test used to analyze the relationship between physical parameters of noise and subjective responses. In the laboratory controlling the variables is easy but the results could be biased because the condition in room would be different with field. Most of all noise exposure time is considered to be different with real situation, and this study aimed to evaluate the subjective response by exposure time of transportation noise, by applying three kinds of variable how much they give effects on the annoyance as the exposure time is operating condition, windows type and sound level. As a result there was somewhat difference between operating type and annoyance, which is caused by the sound characteristics operated in different condition. However the window type didn't give much effect to the annoyance as much as sound type. This means that the subjective response could give similar result by exposure time even for different window types. Most of all, the main factor affecting subjective response is considered to be the sound level and the exposure time.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.185-192
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• 2004

The aeroacoustic characteristics of a centrifugal fan for a vacuum cleaner and its noise reduction method are studied in this paper. The major noise source of a vacuum cleaner is the centrifugal fan. The impeller of the fan rotates at over 30000 rpm, and generates very high-level noise. It was revealed that the dominant noise source is the aerodynamic interaction between the rotating impeller and stationary diffuser. The directivity of acoustic pressure showed that most of the noise propagates backward direction of the fan-motor assembly. In order to reduce the high tonal sound generated from the aerodynamic interaction, unevenly pitched impeller and diffuser, and tapered impeller designs were proposed and experiments were performed. Uneven pitch design of the impeller changes the sound quality while the overall sound power level (SPL) and the performance remains similar. The effect of the tapered design of impeller was evaluated. The trailing edge of the tapered fan is inclined. This reduces the flow interaction between the rotating impeller and the stationary diffuser because of some phase shifts. The static efficiency of the new impeller design is slightly lower than the previous design. However, the overall SPL is reduced by about 4 dB(A). The SPL of the fundamental blade passing frequency (BPF) is reduced by about 6 dB (A) and the 2$\^$nd/ BPF is reduced about 20 dB (A). The vacuum cleaner with the tapered impeller design produces lower noise level than the previous one, and the strong tonal sound was dramatically reduced.

• 한국전자통신학회논문지
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• 제13권5호
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• pp.949-958
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• 2018

음성 인식 제어 시스템은 사용자의 음성을 인식하여 주변 장치를 제어하는 시스템이다. 최근 음성 인식 제어 시스템은 스마트기기 뿐만 아니라, IoT(: Internet of Things), 로봇, 차량에 이르기까지 다양한 환경에 적용되고 있다. 이러한 음성 인식 제어 시스템은 사용자의 음성 외에 주변 잡음에 의한 인식률 저하가 발생한다. 이에 본 논문은 사용자의 음성 외에 주변 잡음을 제거하기 위하여 MEMS(: Microelectromechanical Systems) 마이크로폰용 이중 채널 음성 빔포밍 하드웨어 구조를 제안하였으며, 제안한 하드웨어 구조를 TowerJazz $0.18{\mu}m$ CMOS(: Complementary Metal-Oxide Semiconductor) 공정을 이용하여 ASIC(: Application-Specific Integrated Circuit)을 설계하였다. 설계한 이중 채널 음성 빔포밍 ASIC은 $48mm^2$의 Die size를 가지며, 사용자의 음성에 대한 지향성 특성을 측정한 결과 4.233㏈의 특성을 보였다.

• 한국정밀공학회지
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• 제10권1호
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• pp.77-88
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• 1993

In this paper, we propose a stereo vision system to solve correspondence problem with large disparity and sudden change in environment which result from small distance between camera and working objects. First of all, a specific feature is divided by predfined elementary feature. And then these are combined to obtain coded data for solving correspondence problem. We use Neural Network to extract elementary features from specific feature and to have adaptability to noise and some change of the shape. Fourier transformation and Log-polar mapping are used for obtaining appropriate Neural Network input data which has a shift, scale, and rotation invariability. Finally, we use associative memory to obtain coded data of the specific feature from the combination of elementary features. In spite of specific feature with some variation in shapes, we could obtain satisfactory 3-dimensional data from corresponded codes.

• International Journal of Internet, Broadcasting and Communication
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• 제12권2호
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• pp.37-44
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• 2020

The fifth generation (5G) mobile communication has been commercialized and the 5G applications, such as the artificial intelligence (AI) and the internet of things (IoT), are deployed all over the world. The 5G new radio (NR) wireless networks are characterized by 100 times more traffic, 1000 times higher system capacity, and 1 ms latency. One of the promising 5G technologies is non-orthogonal multiple access (NOMA). In order for the NOMA performance to be improved, sometimes the additive signal-dependent Gaussian noise (ASDGN) channel model is required. However, the channel capacity calculation of such channels is so difficult, that only lower and upper bounds on the capacity of ASDGN channels have been presented. Such difficulties are due to the specific constraints on the dependency. Herein, we provide the capacity of ASDGN channels, by removing the constraints except the dependency. Then we obtain the ASDGN channel capacity, not lower and upper bounds, so that the clear impact of ASDGN can be clarified, compared to additive white Gaussian noise (AWGN). It is shown that the ASDGN channel capacity is greater than the AWGN channel capacity, for the high signal-to-noise ratio (SNR). We also apply the analytical results to the NOMA scheme to verify the superiority of ASDGN channels.