• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.1
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• pp.62-68
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• 2014

Recently, MRI(magnetic resonance imager) scanner is continually used for medical diagnosis and many biomedical researches. When it operates, however, intense noise is generated. The SPL(sound pressure level) of the noise approaches 130 dB especially in 3 T(Tesla) MRI. Meanwhile, more than 3 T MRI scanners have been developed to get higher-resolution images, so louder noise is expected in the future. The intense noise makes patients feel nervous and uncomfortable. Moreover, it could possibly cause hearing loss to patient in extreme cases. For this reason, some active noise control systems have been researched. One of them used feedback Filtered-X LMS(FXLMS) algorithm which is able to control only narrowband noises and possible to diverge in severe case. In this paper, we determine the property of MRI noise. Using the property, we applied a method of open-loop and adaptive control for reducing MRI noise at target point inside bore. We verified performance of the method with computer simulation and preliminary experiment. The results demonstrate that the method can effectively reduce MRI noise at target point.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1419-1424
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• 2007

Centrifugal turbo blower is requested highly efficiency and low noise in FCEV, but the noise generated by this machine causes of the most serious problems in the NVH performance. In general, centrifugal turbo blower is dominated by mechanical noise and aerodynamic noise. Mechanical noise is generated by rotation of the bearing, misalignment and unbalance. And aerodynamic noise is generated by the strong intersection between the flow discharged from the impeller and the cut-off in the casing. The first object of this study is to comprehend a noise property of the blower through the noise test. And, second object is to bring up the method that can reduce blower noise.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.5
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• pp.516-523
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• 2008

Centrifugal turbo blower is requested highly efficiency and low noise in FCEV, but the noise generated by this machine causes of the most serious problems in the NVH performance. In general, centrifugal turbo blower is dominated by mechanical noise and aerodynamic noise. Mechanical noise is generated by rotation of the bearing, misalignment and unbalance. And aerodynamic noise is generated by the strong intersection between the flow discharged from the impeller and the cut-off in the casing. The first object of this study is to comprehend a noise property of the blower through the noise test. And, second object is to bring up the method that can reduce blower noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.546-552
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• 2012

This paper is a study on squeal noise simulation under the consideration of temperature and pressure dependent material properties of friction material. For this, data of pressure and temperature dependent material properties of lining is achieved by using lining data base and exponential curve fit. Complex eigenvalue analysis is performed for predicting squeal noise frequency and instability and chassis dynamo test is performed for achieving squeal noise frequency, sound pressure level, occurrence temperature & pressure. Initial multi models are composed for considering complex interface conditions such as pad ear-clip, piston-housing and guide pin-torque member. The simulation result of base models is compared with the test result. Squeal noise simulation under the consideration of temperature and pressure dependent material properties of friction material is performed and analyzed using multi models. And additional condition is disc material property variation. Entire simulation conditions are combined and analyzed. Finally, this paper proposes direction of the warm squeal noise model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.690-693
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• 2006

As the silence of vehicle is more important, noise reduction of tire is more required. Noise of tire is divided into structure home noise and air borne noise. Tire tread has the property such as Hardness. Pattern Noise is caused by changing of tread hardness. This property has influence on the mechanisms which are Block Impact & Stick-slip sound. In the study, we found that the effect of Hardness is related to more Stick-Slip than Impact.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.6
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• pp.1120-1125
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• 2010

In the speech system, for example hearing aid as well as speech communication, speech quality is degraded by environmental noise. In this study, to enhance the speech quality which is degraded by environmental speech, we proposed an algorithm to reduce the noise and reinforce the speech. The minima controlled recursive averaging (MCRA) algorithm is used to estimate the noise spectrum and spectral weighting factor is used to reduce the noise. And partial masking effect which is one of the human hearing properties is introduced to reinforce the speech. Then we compared the waveform, spectrogram, Perceptual Evaluation of Speech Quality (PESQ) and segmental Signal to Noise Ratio (segSNR) between original speech, noisy speech, noise reduced speech and enhanced speech by proposed method. As a result, enhanced speech by proposed method is reinforced in high frequency which is degraded by noise, and PESQ, segSNR is enhanced. It means that the speech quality is enhanced.

• The Journal of the Acoustical Society of Korea
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• v.20 no.7
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• pp.69-75
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• 2001

Intra-speaker variation, noise environments, and mismatch between training and test conditions are the major reasons for the speaker verification system unable to use it practically. In this study, we propose robust end-point detection algorithm, noise cancelling with the microphone property compensation technique, and inter-speaker discriminate technique by weighting cepstrum for robust speaker verification system. Simulation results show that the average speaker verification rate is improved in the rate of 17.65% with proposed end-point detection algorithm using LPC residue and is improved in the rate of 36.93% with proposed noise cancelling and microphone property compensation algorithm. The proposed weighting function for discriminating inter-speaker variations also improves the average speaker verification rate in the rate of 6.515%.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.5
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• pp.462-467
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• 2009

Reduction of the structure-borne noise of the naval vessel is very important in order to reduce the underwater radiated noise of it. One of the important factors to reduce the structure-borne noise of the installed machine in a ship is the design of the foundation having sufficiently high mechanical impedance. In this paper, the mechanical impedance of the foundation for the fan-coil unit in a naval vessel is evaluated numerically according to variation of the thickness of the foundation. And also, the forced vibration analysis is conducted considering the dynamic property of the anti-vibration mount. Through the analysis results, it can be known that the dynamic property of the anti-vibration mount should be considered when the minimum level of the mechanical impedance of the foundation is set.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.676-681
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• 2001

We usually divide the noise of exhaust system into pulsation noise and flow noise. Pulsation noise is the shock wave to occur when the burning gas of low pressure emits and include harmonic having basic frequency as the exhaust cycle of engine. Flow noise is the noise that is produced when gas flow emits into the atmosphere through the pipe and has the character of frequency like pink noise which has the high level of high frequency component. A muffler is divided into reflective type and absorptive type. We usually use the muffler compounding the property of them. In this study, it is the case of transfer matrix method that a muffler is compounded to analyze the elements of each section according to sound wave's proceed direction. But we use simple model. So, we use finite element method that takes short time to analyze. Acoustic analysis gives us transfer matrix to use FEA of SYSNOISE and we use STAR-CD for fluid analysis. We made database that is based on analytical results about the muffler of expansion type, extended type, offset type, reverse type, and perforated type and developed the muffler design system to perform work efficiently.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.717-719
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• 2013