• Journal of computational fluids engineering
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• v.17 no.1
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• pp.16-22
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• 2012

Acoustic pressure field around the centrifugal fan is predicted by a aero-acoustic splitting method. Unsteady flow field is obtained by solving the incompressible Navier-Stokes equations using commercial code, while the acoustic waves generated inside the centrifugal fan and shroud are predicted by solving the far field acoustics analysis. Computational results show that the acoustic waves of BPF tone are generated by interactions of the blades with the shroud. Acoustic results is validated by experimental results This paper describes the influence of geometric parameters on the noise generation from the section of blades and shroud. One of the effective ways to reduce BPF noise is optimization method using Genetic Algorithm, which effectively minimize eccentricity, is suggested. New improving design was developed by optimization method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.5 s.98
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• pp.558-563
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• 2005

This research aims to derive the general emotion and preference of the 25 sounds by using the questionnaire method to provide the contents for the soundscape design fit to the characteristics of the given situation. The results can be summarized as follows : Nature sounds except dog barking and locust crying showed highest preference, and the traffic sounds, baby crying and footstep of upper floor showed the lowest. Hereby, the sound recognition can be different each other according to quality of tone and situation even they are the same sounds. The most impressive, wanted to be conserved and retrospective sound was the nature sound, and the most wanted to be removed sound was the machinery sound. And the social sound was shown as the most korean and fit to the art theme street.

• Transactions of the Society of Information Storage Systems
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• v.3 no.2
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• pp.54-58
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• 2007

Using metal/Si materials as a recording layer, we have achieved good results for a SR disc (super resolution disc). Mainly by controlling metal composition and the ratio of metal to Si of recording layer, signal qualities were greatly enhanced. At the mark length of 75nm, the best CNR (Carrier to Noise Ratio) was about 45dB. Write power was reduced down to about 6.5mW. LFN (Low Frequency Noise) could also be reduced down to 14dB. Single tone pattern jitters for every mark whose length is from 2T through 8T were achieved to be below 10%. The readout signal was stable sustaining CNR>40dB during about 15,000 times reading. The so-called "3T-problem" could be avoided.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.144-151
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• 2006

Sound generated from a moving vehicle often carries information on the condition of vehicle, for example, whether it has faults or not, where the fault exists. The latter is possible especially by MFAH(moving frame acoustic holography) and beamforming method. MFAH is applicable to the sound source of pure tone or narrow band noise. For the beamforming method, we have to know what kind of wave the sound source radiates, for example, plane wave or spherical wave. That is, whether the above methods are applicable depends on the characteristics of sound source. To apply these methods to the fault detection, we have to know the characteristics of wave from faults. In this research, a machine diagnosis technique based on the above holographic approaches is introduced to find the position of faults. The signal due to faults is modeled based on the fact that the faults radiate impulsive noise, and analyzed in time and frequency domain. The way how MFAH and beamforming method can be used is introduced to find the position of source.

• Journal of Communications and Networks
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• v.7 no.1
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• pp.13-20
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• 2005

In this paper, a new multi carrier, direct sequence code division multiple access (MC-DS-CDMA) system is proposed. Our new signal construction is based on convolutional encoding of the transmitted data, serial-to-parallel (S/P) conversion of the encoded data, Walsh-Hadamard-transformation (WHT), a second S/P conversion of the WHT outputs, spread spectrum (SS) modulation with a common pseudo-noise (PN) sequence, and then multicarrier transmission. The system bit error rate (BER) performance in frequency selective fading channel in the presence of additive white Gaussian noise (AWGN) and a jamming tone is analyzed and simulated. The numerical results are compared with those from an orthogonal MC-DS-CDMA system of Sourour and Nakagawa [7]. It is shown that the two systems have almost the same BER performance, but the proposed scheme has better anti-jamming ability.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.2070-2071
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• 2007

본 연구에서는 변압기의 주 소음원인이 되는 120[Hz]와 240[Hz]및 360[Hz] 주파수에 대한 다중음/단일채널 적응 능동제어기법을 이용한 능동 제어시스템을 구성하였다. 이 능동 제어시스템을 이용하여 변압기에서 발생되어 나오는 소음을 저감시켰고 모의실험을 통해 소음이 감쇄되는 것을 확인하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.806-809
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• 2004

This research aims to derive the general emotion and preference of the 25 sounds by using the questionnaire method to provide the contents for the soundscape design fit to the characteristics of the given situation. The results can be summarized as follows; Nature sounds except dog barking and locust crying showed highest preference, and the traffic sounds, baby crying and footstep of upper floor showed the lowest. Hereby, the sound recognition can be different each other according to quality of tone and situation even they are the same sounds. The most impressive, wanted to be conserved and retrospective sound was the nature sound, and the most wanted to be removed sound was the machinery sound. And the social sound was shown as the most korean and fit to the art theme street.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.256-262
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• 1997

The characteristics of the unstable impinging circular jet were investigated based on the frequency characteristics and the sound field of the impinging-tones. Two symmetric modes Si and S2, associated with low frequency and high frequency respectively, and one helical mode H have been observed by measuring frequency and phase-distribution around the jet. Radiation characteristics of impinging-tone were studied by measuring axial directivity. It was founded that the radiation patterns of symmetric and helical mode are different and it is toward the plate as the impinging distance increased. By estimating the convection velocity of the unstable jet, it was founded that the convection speed decreases with the frequency and its decreasing pattern varies with unstable modes S1, S2 and H, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.9C
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• pp.829-835
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• 2002

DSL(digital subscriber line) transceiver designers have concerned the impulsive noise as well as NEXT(near-end crosstalk) and FEXT(far-end crosstalk) immunities Down as the strongest sources that limit the DSL channel capacity. In these noise environment the analysis on the performance of DSL should be needed. Therefore, in this paper we have estimated and simulated the SNR(signal-to-noise ratio) margin of DMT(discrete multi-tone) signal in Gauss, NEXT, FEXT and impulse noise environment by modeling an Middleton's Class A impulse signal with the test Cook pulses. As a result, it is known that the transmission rate of uplink is limited by noise characteristics rather than by loop length, but that of downlink limited complexly by both of noise characteristics and loop length. In conclusion, these results will be utilized as the threshold of ADSL performance in the complex noise environment including impulse noise.

• Journal of Power System Engineering
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• v.3 no.3
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• pp.60-69
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• 1999

The noise and vibration sources of rotary compressor for room air-conditioner are pressure pulsation of compression process, cavity resonance of inner space, structural radiation noise of shell and impact noise of discharge valve. Among them, pressure pulsation is very important noise and vibration source. Because it transferred various kinds of noise and vibration like as mentioned above. In this reason, muffler and resonator are used in order to absorb and remove these noises. But an analytical prediction using acoustic analysis does not coincident with the experimental result. The difference between analysis and actual state is due to the assumption of analysis. This paper covered with new concept of muffler design based on the turbulence kinetic energy of flow by using CFD. From this analysis, it is possible to decide the best position of discharge port of muffler. Therefore $2{\sim}3dB$ noise reduction effect is acquired in rotary compressor of 5000 BTU grade. Also new approach of resonator design is suggested. From this study, the characteristics of resonator and surge hole (a kind of resonator without pipe length) are identified. The former is useful for pure tone noise (narrow frequency band), and the latter is effective for broad frequency band. This paper shows that it is very available to use 3 dimensional analysis of resonator in order to predict more exact tuning frequency. The result is proved by a lot of experiments. From combination of fluid analysis and acoustic analysis, up stream position is effective location of resonator concerning turbulence motion of fluid.