• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.7 s.112
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• pp.677-682
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• 2006

In the case of aeroacoustic test in windtunnel, measurement accuracy is reduced by not only Doppler effects but also by the microphone self noise due to airflow and high turbulence in the wall boundary layer. Microphone array measurements can be easily utilized for the solutions of these problems. In this paper, geometrical optics approach and diagonal term elimination of cross spectral matrix was introduced to the de-dopplerization and self noise reduction methods for the microphone array measurement. For the validation, beamforming tests for sinusoidal point source were performed in the closed type test section of windtunnel, and their performances of beam width and sidelobe rejection were significantly improved.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.822-825
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• 2005

In the case of aeroacoustic test in windtunnel, measurement accuracy is reduced by not only Doppler effects but also by the microphone self noise due to airflow and high turbulence in the wall boundary layer. Microphone array measurements can be easily utilized for the solutions of these problems. In this paper, geometrical optics approach and diagonal term elimination of cross spectral matrix was introduced to the de-dopplerization and self noise reduction methods for the microphone array measurement. For the validation, beamforming tests for sinusoidal point source were performed in the closed type test section of windtunnel, and their performances of beam width and sidelobe rejection were significantly improved.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.5
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• pp.1089-1095
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• 2005

This paper presents a new low-cost Built-In Self-Test (BIST) circuit for 50Hz low noise amplifier (LNA). The BIST circuit is designed for system-on-chip (SoC) transceiver environment. The proposed BIST circuit measures the LNA specifications such as input impedance, voltage gaih, noise figure, and input return loss all in a single SoC environment.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.26-31
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• 2000

There are various noises generated by friction. Among the rest, eliminating squeal noise generated during braking is an important task for the improvement of vehicle passengers' comfort. The parameters affecting brake squeal noise are the material properties of the braking pad, the dynamic properties of the brake parts and the dimensions of the brake assembly etc. Also, the squeal noise changes its inherent form with the normal load and sliding speed. In this study, the characteristics of brake squeal noise generated by friction is analyzed experimentally. The experiment focused on the analysis of friction self-excited vibration and squeal noise level. Friction self-excited vibration is caused by the dry friction between pads and rotor, and occurs as a function of their relative sliding speeds. And Friction self-excited vibration is raised the brake squeal noise.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.4
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• pp.169-174
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• 2002

This paper presents a high-resolution capactive microaccelerometer using branched finger electrodes with high-amplitude sense voltage. From the fabricated microacceleromcter, the total noise is obtained as 9 $\mu\textrm{g}$/√Hz at the sense voltage of 16.5V, while the conventional microaccelerometers have shown the noire level of 25~800 $\mu\textrm{g}$/√Hz. We reduce the mechanical noise level of the microaccelerometer by increasing the proof-class based on deep RIE process of an SOI wafer. We reduce the electrical noise level by increasing the amplitude of AC sense voltage. The nonlinearity problem caused by the high-amplitude sense volage has been solved by a new electrode design of branched finger type, resulting in self force-balancing effects for the enhanced linearity and bandwidth. The fabricated microaccelerometer shows the electrical noise of 2.4 $\mu\textrm{g}$/√Hz at the sense voltage of 16.5V, which is an order of magnitude reduction of the electrical noise of 24.3 $\mu\textrm{g}$/√Hz measured at 0.9V. For the sense voltage higher than 2V, the electrical noise of the microaccelerometer is lower than the voltage-independent mechanical noise of 11 $\mu\textrm{g}$/√Hz. Total noise, composed of the electrical noise and the mechanical noire, has been measured as 9 $\mu\textrm{g}$/√Hz at the sense voltage of 16.5V, which is 31% of the total noise of 28.6 $\mu\textrm{g}$/√Hz at the sense voltage 0.9V. The self force-balancing effect in the blanched finger electrodes increases the stiffness of the microaccelerometer from 1.1N/m to 1.61N/m as the sense voltage increases from 0V to 17.8V, thereby generating additional stiffness at the rate of 0.0016$\pm$0.0008 N/m/V$^2$.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.336-337
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• 2010

In the underwater veicle self-noise from the propeller reduces the sensor sensitivity. To increase the sensor sensitivity SNORE ring(Self-noise reduction ring) has been used. In this paper to calculate the effectiveness of the SNORE ring and de-coupeler numerical simulation is conducted. Based on the simulation results CRP(Carbon reinforced plastic)and SNORE ring reduced noise and vibration.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.72-73
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• 2010

In this paper, the main noise sources and its radiated noise levels of upwind horizontal-axis wind turbines are experimentally and theoretically investigated. Theoretical predictions for indentifying the dominant source locations are made by using the empirical noise prediction model of Brooks et al. (1989) for the airfoil self noise. Through the comparison of theoretical results with the experimental results, turbulence-boundary-layer-trailing-edge (TBL-TE) noise is revealed to be the dominant source over all frequency range and separation and stall (S-S) noise is possibly important in the relative lower frequency range compared with TBL-TE noise.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.76-82
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• 2015

Active matter는 스스로 에너지를 가지고 움직이는 개체들이 서로 상호작용을 하여 집단적인 움직임을 보이는 물질이다. Rotational noise model은 반발 상호작용과 rotational noise를 가지고 있는 self-propelled particle로 active matter를 설명한다. 이 연구에서는 rotational noise model에서의 상 도표와 클러스터 형성을 알아보고 입자들의 집단적인 운동을 도와주거나 방해할 수 있는 leader 입자와 seed가 클러스터의 운동에 어떠한 영향을 주는지 알아본다.

• Journal of the Chungcheong Mathematical Society
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• v.26 no.2
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• pp.411-420
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• 2013

We consider fractional Gussian noise and FARIMA sequence with Gaussian innovations and show that the suitably scaled distributions of the FARIMA sequences converge to fractional Gaussian noise in the sense of finite dimensional distributions. Finally, we figure out ACF function and estimate the self-similarity parameter H of FARIMA(0, $d$, 0) by using R/S method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.611-616
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• 2002

Bearing diagnostics is difficult in a gearbox because bearing signals are masked by the strong gear signals. Self adaptive noise cancellation(SANC) is useful technique to seperate bearing signals from gear signals. While gear signals are correlated with a long correlation length, bearing signals are not correlated with a short length. SANC seperates two components on the basis of correlation length. Then we can find defect frequency component in the envelope spectrum of the bearing signals.