• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.144-149
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• 2006

최근 저소음형 fan 의 도입과 컴퓨터 케이스의 설계 변경 등으로 컴퓨터 소음이 저감되어, HDD 나 CD/DVD-ROM 등에서 발생하는 협대역 소음들이 문제가 되기도 한다. 특히 HDD 의 소음은 회전 속도의 증가와 휴대용 컴퓨터나 외장 HDD와 같이 사용자에 근접한 환경에서 사용되는 빈도가 높아짐에 따라 소음제어에 대한 관심이 증가되고 있다. 본 연구에서는 HDD 소음 분석 및 제어에 적합한 방법론 정립을 위한 음향/진동 분석이 수행되였다. 먼저 음압과 음향 파워, 진동속도를 측정하여 각 면의 기여도와 문제가 되는 주파수 대역을 선정하여 그 원인이 무엇인지를 실험적으로 찾아내고, 소음저감을 발안을 제시하였다. 이러한 개선 방안들은 실험적인 방법으로 검증되었으며, 음향 진동 분석을 통한 소음원 파악 및 적절한 개선 방향의 설정은 향후 HDD 설계시 유용한 정보로 활용될 수 있을 것이다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.11
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• pp.1093-1101
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• 2007

This study presents the design improvement process for door module. Its objective evades the resonance generated at module plate due to the operation of window regulator motor. For this study, the design improvement process is composed of experimental methods having three steps. First step is modal analysis at door assembly status for acquisition of dynamic characteristics which are modal frequency and damping. Second step is a vibration experiment to get the test mode considered an efficiency of window regulator motor. Last step is a vibration measurement by the form of $6{\times}6$ array on module plate. A vibration measurement of $6{\times}6$ array form can be got to three analysis results which are a transfer path of vibration using cross correlation function, a vibration map using OA level and a contribution by frequency band using coherent output power spectrum on module plate. These results are applied to SDM(structural dynamic modification) for design improvement to get around the resonance on module plate by the excitation of window regulator motor.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.291-296
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• 2007

This study presents the evaluation process for door module. Its objective evades the resonance generated at module plate due to the operation of window regulator motor. For this study, the design improvement process is composed of experimental methods having three steps. First step is modal analysis at door assembly status for acquisition of dynamic characteristics which are modal frequency and damping. Second step is a vibration experiment to get the test mode considered an efficiency of window regulator motor. Last step is a vibration measurement by the form of $6{\times}6$ array on module plate. A vibration measurement of 6x6 array form can be got to three analysis results which are a transfer path of vibration using cross correlation function, a vibration map using OA level and a contribution by frequency band using coherent output power spectrum on module plate. These results are applied to SDM(structural dynamic modification) for design improvement to get around the resonance on module plate by the excitation of window regulator motor.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.4
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• pp.18-26
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• 1996

Based on experimental analysis, the characteristics of pulsating pressure wave propagation is clarified by testing of 4-stroke gasoline engine. The pulsating pressure wave in exhaust system is generated by pulsating gas flow due to working of exhaust valve. The pulsating pressure wave is closely concerned to the loss of engine power according to back pressure and exhaust noise. It is difficult to exactly calculate pulsating pressure wave propagation in exhaust system because of nonlinear effect. Therefore, in the first step for solving these problems, this paper contains experimental model and analysis method which are applied two-port network analysis. Also, it shows coherence function, frequency response function, back pressure, and gradient of temperature in exhaust system.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1996.03a
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• pp.72-78
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• 1996

Based on experimental analysis, the characteristics of pulsating pressure wave propagation is clarified by testing of 4-stroke gasoline engine. The pulsating pressure wave in exhaust system is generated gyulsating gas flow due the working of exhaust valve. The pulsating pressure wave is closely concerned to the loss of engine power according to back pressure and exhaust noise. It is difficult to exactly calculate pulsating pressure wave nonlinear effect. Therefore, in the first step for solving these problems, this paper contains experimental model and analysis method which are applied two-port network analysis. Also, it shows coherence function, frequency response function. back pressure, and gradient of temperature in exhaust system.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.122-130
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• 2024

Vibration of compressor in the air-conditioner outdoor unit have known to be main noise source radiated from outdoor unit. However, as the operating speed of compressor increase, the relative contribution of flow induced vibration and noise is also increase. In this paper, the numerical method was established to predict fluid-borne noise from compressor discharging pipe of air-conditioner outdoor unit. In this step, numerical result was compared to experimental one to verify numerical method. Additionally, the effects of pressure pulsation of compressor and compressor vibration into radiated noise were investigated in frequency domain. It was confirmed that the compressor vibration contributed to the low frequency band, while the pressure pulsation dose to the high frequency band.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.3
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• pp.379-388
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• 2020

The contents and scope of this study are to analyze the problems of the current radio service and radio station classification system, and to investigate the radio wave management cases in the United States to provide a reasonable and efficient radio wave management method. The results of this study can be used as basic data when revising the legal system regarding radio wave enforcement regulations, radio service and radio station classification standards. It is expected that in the future, a detailed commentary on the definition and classification system of new radio / radio stations will be prepared to increase policy compliance in practice, while contributing to enhancing the consistency and efficiency of radio station licensing and inspection.

• The Journal of the Acoustical Society of Korea
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• v.41 no.3
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• pp.326-334
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• 2022

In this paper, we propose speech enhancement algorithm as a pre-processing for robust speech recognition in noisy environments. Auxiliary-function-based Independent Vector Analysis (AuxIVA) is performed with weighted covariance matrix using time-varying variances with scaling factor from target masks representing time-frequency contributions of target speech. The mask estimates can be obtained using Neural Network (NN) pre-trained for speech extraction or diffuseness using Coherence-to-Diffuse power Ratio (CDR) to find the direct sounds component of a target speech. In addition, outputs for omni-directional noise are closely chained by sharing the time-varying variances similarly to independent subspace analysis or IVA. The speech extraction method based on AuxIVA is also performed in Independent Low-Rank Matrix Analysis (ILRMA) framework by extending the Non-negative Matrix Factorization (NMF) for noise outputs to Non-negative Tensor Factorization (NTF) to maintain the inter-channel dependency in noise output channels. Experimental results on the CHiME-4 datasets demonstrate the effectiveness of the presented algorithms.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.40-47
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• 1989

Alternator noises are composed of magnetic noise, mechanical noise, and ventilation noise. These noises depend on the design of magnetic parts and fans, the machining accuracy of each element, and assembled conditions. In running alternator there are various exciting forces which can generate noises and vibrations. In order to identify the noise sources of the alternator, the characteristics of noises and vibrations are analyzed as rotating speed is increased. And the experiment for structural vibration is carried out. From results of experimental study, the noise sources are identified and their contributions to the overall noise level are investigated. Their results can lead the instruction to the noise reduction on the alternator.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.2
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• pp.140-144
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• 2004

The selectable dual band LNA usually uses common source transistor pair each input of which is selectively driven at a different frequency in a series resonant form. This paper analyzes the degradation in noise figures of the MOSFET common source pair with series resonance when it is driven concurrently at both inputs with different frequencies as a concurrent dual band LNA. Results of analysis will be compared with the measured noise figures of CMOS LNA with double inputs fabricated in 0.18 $\mu\textrm{m}$ CMOS process. Additionally, analyzing the contributions of FET channel noise and source noise from the LNA operating in the other band, this paper proposes optimum matching topology which minimizes the added noises for concurrent operation.