• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.12
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• pp.969-976
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• 2014

Nowadays, it is required for naval ships to estimate 3D underwater radiated noise pattern in all direction at peak frequencies of hull vibration for the reduction of being detected and doing the effective operation. For this purpose, the numerical method has to be developed to calculate 3D underwater radiated noise pattern with experimental data. It is very difficult to obtain the experimental data for the real ship. Alternative to get the experimental results is to use NAH(near-field acoustic holography) in acoustic tank with experimental model. Application of NAH in acoustic tank for the experimental model needs some investigation of reflection wave from the wall of the acoustic tank and unmeasured zone of the experimental model due to the supporting structure for it. In this study, the effect of reflection wave in the acoustic tank and unmeasured area of the experimental model when using the NAH was investigated with experiment and numerical model. From these, it is known for the error due to reflection wave can be reduced when the distance between the measurement plane and source is being shorten. Also, unmeasured area of the experimental model gives rise to some error in the estimation of the far-field acoustic pressure.

• Journal of the Institute of Convergence Signal Processing
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• v.11 no.2
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• pp.151-156
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• 2010

This paper is a study on image noise reduction of modified sigma filter by image decomposition using directivity. Conventional sigma filter has been shown to be a good solution both in terms of filtering accuracy and computational complexity. However, the sigma filter does not preserve well small edges especially for high level of additive noise. In this paper, we propose here a new method using a modified sigma filter. In our proposed method the input image is first decomposed in two components that have features of horizontal, vertical and diagonal direction. Then, two components are applied HPF and LPF. By applying a conventional sigma filter separately on each of them, the output image is reconstructed from the filtered components. Added noise is removed and our proposed method preserves the edges from the image. Comparative results from experiments show that the proposed algorithm achieves higher gains, on average, 2.6 dB PSNR than the sigma filter and 0.5 dB PSNR than the modified sigma filter. When relatively high levels of noise added, the proposed algorithm shows better performance than two conventional filters.

• Journal of the Korean Institute of Intelligent Systems
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• v.17 no.7
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• pp.945-951
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• 2007

Noise cancellation is essential for the devices which use speech as an interface. In real environments, speech quality and recognition rates are degraded by the auditive noises coming near the microphone. In this paper, we propose a noise cancellation algorithm using stereo microphones basically. The advantage of the use of multiple microphones is that the direction information of the target source could be applied. The proposed noise canceller is based on the Wiener filter. To estimate the filter, noise and target speech frequency responses should be known and they are estimated by the spectral classification in the frequency domain. The performance of the proposed algorithm is compared with that of the well-known Frost algorithm and the generalized sidelobe canceller (GSC) with an adaptation mode controller (AMC). As performance measures, the perceptual evaluation of speech quality (PESQ), which is the most widely used among various objective speech quality methods, and speech recognition rates are adopted.

• Journal of Environmental Science International
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• v.18 no.4
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• pp.389-400
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• 2009

In this research, we measured the number of lanes, distance, disposition of apartment that are affecting the road traffic noise to evaluate the current condition of G city's road traffic noise. We decide on a basis regarding an apartment price formation factor, and the apartment current price and the results that compared. To have a point scale, we set the maximum road traffic noise at a 8 lane road for 5 points, give 4 points for a 6 lane road, which has a $2.1{\sim}2.5\;dB(A)$ difference compared to a 8 lane road, give 3 points for a 4 lane road, which has a $5.2{\sim}5.5\;dB(A)$ difference compared to a 8 lane road, and set 2 points for a 2 lane road and lower. If we set the standard floor plan as horizontal and a living room facing the roadside, the horizontal and living room facing the opposite side of the road is 1 point because it differs by 14.1 dB(A), and the vertical is 3 points since the difference is 5.3 dB(A). If we make grades by the distance, making standard the fifth floor with little soundproof effect from apartment to road, we observe a measurement below 2.9 dB(A) at a distance of less than 10 m and 5 dB(A), decreased at a distance of 20 m. Therefore, 4 points were given for less than 10m, 3 points for $10{\sim}20\;m$, 2 points for more than 20 m as we can apply the effect of a decay distance of line sound source and the decrease in noise effects of more than 6 dB(A), 1 point for more than 40m, and 0 points for more that 80 m since it is negligible. 28 apartments got 0 points because there is no effect of road traffic noise from other apartments, and 50 apartments where only the road at one side effect them got $5{\sim}10$ points. 4 apartments (17-2, 6-3, 10-4, 3-3) received over 20 points. 15 cases showed a difference between developer price and resale price, and 11 cases (73%) among them showed the same trend (price increases with a low road traffic noise restriction factor point) with the point of road traffic noise restriction factor. 4 cases demonstrated the opposite trend, showing price increases with a high restriction factor point. Among the 4 cases, case numbers 2,6 and 9 appear to be more affected by the location factor (business district) than the road traffic noise restriction factor, and case number 1 appears to be affected by the building factor (openness and direction).

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.250-261
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• 2023

In this study, the noise contributions by the duct, stator and rotor, which are the propulsor components, are evaluated to identify the flow noise source in cavitation and non-cavitation conditions on pumpjet propulsion and the noise levels in both conditions are compared. The unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equation based on the homogeneous mixture assumption is applied on the suboff submarine hull and pumpjet propeller in the cavitation tunnel, and the Volume of Fluid (VOF) method and Schnerr-Sauer cavitation model are used to describe the two-phase flow. Based on the flow simulation results, the acoustic analogy formulated by Ffowcs Williams and Hawkings (FW-H) equation is applied to predict the underwater radiated noise. The noise contributions are evaluated by using the three types of impermeable integral surface on the duct, stator and rotor, and the two types of permeable integral surface surrounding the propulsor. As a result of noise prediction, the contribution by the stator is insignificant, but it affects the generation of flow noise source due to flow separation in the duct and rotor, and the noise is predominantly radiated into the upward and right where the flow separations are. Also, the noise is radiated into the thrust direction due to pressure fluctuation between suction and pressure sides on the rotor blades, and the it can be seen that the cavitation effect into the noise can be considered through the permeable integral surface.

• Phonetics and Speech Sciences
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• v.4 no.3
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• pp.103-110
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• 2012

In this paper, a target signal detection method using multiple signal classification (MUSIC) algorithm is proposed. The MUSIC algorithm is a subspace-based direction of arrival (DOA) estimation method. Using the inverse of the eigenvalue-weighted eigen spectra, the algorithm detects the DOAs of multiple sources. To apply the algorithm in target signal detection for GSC-based beamforming, we utilize its spectral response for the DOA of the target source in noisy conditions. The performance of the proposed target signal detection method is compared with those of the normalized cross-correlation (NCC), the fixed beamforming, and the power ratio method. Experimental results show that the proposed algorithm significantly outperforms the conventional ones in receiver operating characteristics (ROC) curves.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.301-304
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• 2004

In this paper, we propose a method to find the optimal direction of the multi beam between each station on the point-to-point link by genetic algorithm. In the proposed method, maximum value in optimal direction on each station is used as a fitness function. The beam of millimeter wave generates a lot of multi-peak because of much influence of noise. About each gene, we simulated this method using 16bit, 32bit, and 32bit split algorithm. 32bit split uses 16bit gene information. Each antenna makes 32bit gene information by adding gene information of two antennas having 16bit gene. Through the proposed method, we could have gotten a good output without 32bit gene information.

• The Journal of the Acoustical Society of Korea
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• v.14 no.1E
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• pp.88-97
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• 1995

The main purpose of this paper is to show the realizaability of the proposed highly effective direction finiding method which performs extremely well under the circumstances like low signal-to-noise ratio (S/N), very closely located signal sources, and so on. In order to achieve the purpose, the degree to which the proposed method is superior to the MUSIC(multiple signal classification) with respect to the S/N is discussed, and the result is analyzed in terms of the S/N and the number of sample data.

• Journal of Korea Society of Digital Industry and Information Management
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• v.5 no.1
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• pp.83-88
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• 2009

This paper consider the problem of direction of arrival(DOA) estimation in the presence of multipath propagation. The sensor elements are assumed to be linear and uniformly spaced. Numerous authors have advocated the use of a beamforming preprocessor to facilitate application of high resolution direction finding algorithms The benefits cited include reduced computation, improved performance in environments that include spatially colored noise, and enhanced resolution. Performance benefits typically have been demonstrated via specific example. The purpose of this paper is to provide an analysis of a beamspace version of the MUSIC algorithm applicable to two closely spaced emitters in diverse scenarios. Specifically, the analysis is applicable to uncorrelated far field emitters of any relative power level, confined to a known plane, and observed by an arbitrary array of directional antenna. In this paper, we researched about optimize beam forming to smart antenna system. The covariance matrix obtained using fourth order cumulant function. Simulations illustrate the performance of the techniques.

• Journal of KSNVE
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• v.8 no.2
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• pp.346-352
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• 1998

This paper presents actuating characteristics of an asymmetric high-speed optical pick-up fine actuator that can be installed in a small area such as a notebook personal computer. In the asymmetric actuator four points (mass center, actuation center, supporting point of wire suspension on a bobbin, and optical axis) are not coincident so that the proposed actuator suspension reveals undesirable suspension resonance in the pitch and yaw direction. Lumped parameter dynamic model in each direction is used to investigate the driving characteristics with respect to relative location of the four points. Some of desired design directions toward reducing resonance peaks are suggested by using sensitivity information. In order to avoid undesirable resonance, at least supporting point on the obbin must be located in the middle of the mass and actuation center of the asymmetric pick-up actuator.