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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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The Journal of the Acoustical Society of Korea
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Journal DOI :
The Acoustical Society of Korea
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Volume & Issues
Volume 33, Issue 6 - Nov 2014
Volume 33, Issue 5 - Sep 2014
Volume 33, Issue 4 - Jul 2014
Volume 33, Issue 3 - May 2014
Volume 33, Issue 2 - Mar 2014
Volume 33, Issue 1 - Jan 2014
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Numerical Investigation on the Flow Noise Characteristics of the Hybrid Vertical-axis Wind Turbine
Kim, Sanghyeon ; Cheong, Cheolung ;
The Journal of the Acoustical Society of Korea, volume 33, issue 6, 2014, Pages 351~357
DOI : 10.7776/ASK.2014.33.6.351
In this paper, flow noise characteristics of the hybrid vertical-axis wind turbine is investigated. Hybrid vertical-axis wind turbines consisting of two types of vertical-axis wind turbines, Savonius and Darrieus, are devised to maximize merits of one turbine and thus minimize demerits of the other turbine. In order to predict flow noise radiating from hybrid vertical-axis wind turbines, hybrid computatioinal aero acoustic techniques are used. First, unsteady flow fields around the turbine are predicted using computational fluid dynamics method. Then, the flow noise radiations from the turbines are predicted by applying acoustic analogy to the predicted flow fields. Based on numerical results, noise characteristics of a hybrid vertical-axis wind turbine is investigated and is compared with those of Savonius and Darrieus wind turbines.
Comparative Study on Viscous and Inviscid Analysis of Partial Cavitating Flow for Low Noise Propeller Design
Kim, Ji-Hye ; Ahn, Byoung-Kwon ; Park, Cheol-Soo ; Kim, Gun-Do ;
The Journal of the Acoustical Society of Korea, volume 33, issue 6, 2014, Pages 358~365
DOI : 10.7776/ASK.2014.33.6.358
When a ship propeller having wing type sections rotates at high speed underwater, local pressure on the blade decreases and various types of the cavitation inevitably occur where the local pressure falls below the vapor pressure. Fundamentally characteristics of the cavitation are determined by the shapes of the blade section and their operating conditions. Underwater noise radiated from a ship propeller is directly connected to the occurrence of the cavitation. In order to design low noise propeller, it is preferentially demanded to figure out key features: how the cavity is generated, developed and collapsed and how the effect of viscosity works in the process. In this study, we first perform inviscid analysis of the partial cavity generated on two dimensional hydrofoil. Secondly, viscous analysis using FLUENT with different turbulence and cavitation models are presented. Results from both approaches are also compared and estimated.
Low-Frequency Active Echo Reduction Using a Tile Projector
Lee, Jae-Wan ; Woo, Sangbeom ; Jang, Hada ; Lee, Keunsang ; Kim, Wan-Gu ; Kang, Hwi-Suk ; Ohm, Won-Suk ; Park, Youngcheol ; Yoon, Suk Wang ; Seo, Youngsoo ;
The Journal of the Acoustical Society of Korea, volume 33, issue 6, 2014, Pages 366~374
DOI : 10.7776/ASK.2014.33.6.366
With the advent of submarine detection technology using low-frequency active sonar there is a call for a new submarine stealth device that can replace the existing passive anechoic tiles. Proposed in this study is a low-frequency echo reduction technique based on active impedance matching, which employs a tile projector designed to cover a wide area such as the surface of a ship. To judge the feasibility of the active impedance matching technique finite-element simulations of low-frequency echo reduction are performed. Based on the analysis, a tile projector is designed, fabricated, and tested in an acoustic tank for its low-frequency echo reduction performance.
A New Parallel Method for Narrowband Active Noise Control
Kim, Seong-Woo ; Park, Young-Cheol ; Seo, Young-Soo ; Youn, Dae Hee ;
The Journal of the Acoustical Society of Korea, volume 33, issue 6, 2014, Pages 375~382
DOI : 10.7776/ASK.2014.33.6.375
In many practical active noise control applications, the primary noise contains multiple closely-spaced harmonics. A narrowband ANC system consists of adaptive filters excited by a composite reference signal, which is the set or sum of sinusoids. This paper analyzes and shows that the convergence speeds of the direct form, parallel form, and simplified parallel form narrowband ANC systems are affected by the fundamental frequency and frequency separation between two adjacent sinusoids in the reference signal. This paper also proposes the new simplified parallel form narrowband ANC system whose convergence speed is independent on the frequency of the reference signal. Computer simulations are conducted to verify the analysis presented in the paper and to compare the proposed narrowband ANC system with the conventional narrowband ANC system.
Adaptive Beamforming Method for Turning Towed Line Array SONAR
Lee, Seokjin ; Park, Kyung-Min ; Chung, Suk-Moon ;
The Journal of the Acoustical Society of Korea, volume 33, issue 6, 2014, Pages 383~391
DOI : 10.7776/ASK.2014.33.6.383
In order to detect underwater acoustic signals, various SONAR array types have been developed, including towed line array SONAR system (TASS). However, the TASS suffers from performance degradation which is caused by aperture deformation during a turn, because the TASS have a long-aperture array. A parabolic array model for turning TASS have been developed to solve the degradation problem occurred during a turn. In this paper, adaptive beamforming system is developed using the parabolic TASS model to cancel interference signals. The developed beamforming system is based on generalized sidelobe canceller (GSC) structure and self-tuning adaptive algorithm.
Algorithm and Experimental Verification of Underwater Acoustic Communication Based on Passive Time-Reversal Mirror
Eom, Min-Jeong ; Kim, J.S. ; Cho, Jung-Hong ; Kim, Hoeyong ; Sung, Il ;
The Journal of the Acoustical Society of Korea, volume 33, issue 6, 2014, Pages 392~399
DOI : 10.7776/ASK.2014.33.6.392
The underwater acoustic communication is characterized by doubly spread channels, which are the delay spread due to multiple paths and the doppler spread due to environmental fluctuations or a moving platform. An equalizer is used to remove the inter-symbol interferences that the delay spread causes, but an equalizer doesn't use an acoustic environment such as a multipath. However, a passive time-reversal mirror is simpler than an equalizer because a matched filter is implemented numerically at the receiver structure along with one-way propagation. In this paper, a passive time-reversal mirror is applied to remove interferences due to a multipath in sea-going experimental data in East Sea in Oct. 2010 and improved communication performance is confirmed. The performance is verified by comparing the signal-to-interference plus noise ratio before/after passive time-reversal mirror. It is also performed independently of the passive time-reversal mirror and adaptive equalizer and the bit error rate is compared to verify the performance of underwater acoustic communication.
Development of Audio Watermark Decoding Model Using Support Vector Machine
Seo, Yejin ; Cho, Sangjin ;
The Journal of the Acoustical Society of Korea, volume 33, issue 6, 2014, Pages 400~406
DOI : 10.7776/ASK.2014.33.6.400
This paper describes a robust watermark decoding model using a SVM(Support Vector Machine). First, the embedding process is performed inversely for a watermarked signal. And then the watermark is extracted using the proposed model. For SVM training of the proposed model, data are generated that are watermarks extracted from sounds containing watermarks by four different embedding schemes. BER(Bit Error Rate) values of the data are utilized to determine a threshold value employed to create training set. To evaluate the robustness, 14 attacks selected in StirMark, SMDI and STEP2000 benchmarking are applied. Consequently, the proposed model outperformed previous method in PSNR(Peak Signal to Noise Ratio) and BER. It is noticeable that the proposed method achieves BER 1% below in the case of PSNR greater than 10 dB.
Underwater Acoustic Communication of FH-MFSK Method with Multiple Orthogonal Properties
Lee, Hyeung-Woo ; Kim, Ki-Man ; Son, Yun-Joon ; Kim, Woo-Sik ; Chun, Seung-Yong ; Lee, Sang-Kook ;
The Journal of the Acoustical Society of Korea, volume 33, issue 6, 2014, Pages 407~412
DOI : 10.7776/ASK.2014.33.6.407
In this paper, we propose an underwater acoustic communication of FH-MFSK(Frequency-Hopped Multiple Frequency Shift Keying) system with multiple orthogonal property. Generally, the processing of FSK(Frequency Shift Keying) method is simple, but it is vulnerable to ISI (Inter-Symbol Interference) caused by multipath transmission. In this paper, the orthogonal codes are generated with the same number of transmitting symbols, and these codes are corresponding to multiple frequencies. We used m-sequence to generate multiple orthogonal codes. We compared the performance of proposed method with conventional MFSK method via the experiment. As a result, we confirmed that the proposed method shows 6~10 % lower error rate at 100 bps than conventional method.
Influence of Underwater Channel Time-Variability on Communication Throughput Efficiency
Hwang, Chan-Ho ; Kim, Ki-Man ; Lee, Dong-Won ; Park, Tae-Doo ;
The Journal of the Acoustical Society of Korea, volume 33, issue 6, 2014, Pages 413~419
DOI : 10.7776/ASK.2014.33.6.413
Underwater acoustic channel has time-variability. Time varying channel which disturbs the continuous transmission of information data reduces the underwater acoustic communication performance. In this paper, we show the temporal coherence as time-variability of channel and indicate throughput efficiency in accordance with transmission time of information data. Then we analyzed influence of underwater channel time-variability on communication throughput efficiency. We confirmed that the throughput efficiency reduced when the time-variability of the channel increased via lake trial.
An Enhanced Affine Projection Sign Algorithm in Impulsive Noise Environment
Lee, Eun Jong ; Chung, Ik Joo ;
The Journal of the Acoustical Society of Korea, volume 33, issue 6, 2014, Pages 420~426
DOI : 10.7776/ASK.2014.33.6.420
In this paper, we propose a new affine projection sign algorithm (APSA) to improve the convergence speed of the conventional APSA which has been proposed to enable the affine projection algorithm (APA) to operate robustly in impulsive noise environment. The conventional APSA has two advantages; it operates robustly against impulsive noise and does not need calculation for the inverse matrix. The proposed algorithm also has the conventional algorithm's advantages and furthermore, better convergence speed than the conventional algorithm. In the conventional algorithm, each input signal is normalized by
-norm of all input signals, but the proposed algorithm uses input signals normalized by their corresponding
-norm. We carried out a performance comparison of the proposed algorithm with the conventional algorithm using a system identification model. It is shown that the proposed algorithm has the faster convergence speed than the conventional algorithm.