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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 34, Issue 6 - Nov 2015
Volume 34, Issue 5 - Sep 2015
Volume 34, Issue 4 - Jul 2015
Volume 34, Issue 3 - May 2015
Volume 34, Issue 2 - Mar 2015
Volume 34, Issue 1 - Jan 2015
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Analysis of Surface Sound Channel by Low Salinity Water and Its Mid-frequency Acoustic Characteristics in the East China Sea and the Gulf of Guinea
Kim, Hansoo ; Kim, Juho ; Paeng, Dong-Guk ;
The Journal of the Acoustical Society of Korea, volume 34, issue 1, 2015, Pages 1~11
DOI : 10.7776/ASK.2015.34.1.001
Salinity affects sound speed in the low salinity environment, in the seas where freshwater from large rivers and flows into the marginal sea area near the Yangtze River and the Niger River. In this paper, SSC (Surface Sound Channel) formed by low salinity water was investigated in the East China Sea and the Gulf of Guinea of rainy season. The data from KODC (Korea Oceanographic Data Center) in the East China Sea and from ARGO (Array for Real-time Geostrophic Oceanography) in the Gulf of Guinea of the tropical area were used for analysis. SSC haline channel was formed 14 times among 32 SSC occurrences when the 90 data from 9 points were analyzed during a decade (2000 ~ 2009) in the East China Sea. In the Gulf of Guinea, haline channel was formed 18 times among 20 SSC occurrences during 3 years (2006 ~ 2009). When the sound speed gradient was analyzed from temperature-salinity gradient diagram, the gradients of both salinity and temperature affect SSC formation in the East China Sea. In contrast, the salinity gradient mostly affects SSC formation due to the least change of temperature in the well-developed mixed layer in the Gulf of Guinea. Their acoustic characteristics show that channel depth is 6.5 m, critical angle is
and difference of transmission loss between surface and thermocline is 11.5 dB in the East China Sea, while channel depth is 18 ~ 24 m, critical angle is
and difference of transmission loss is 21.5 ~ 27.9 dB in the Gulf of Guinea. These results are expected to be used as a basic understanding of the acoustic transmission changes due to low salinity water at the estuaries and the ocean with heavy precipitation.
Simulation of Temporal Variation of Acoustic Transmission Loss by Internal Tide in the Southern Sea of Jeju Island in Summer
Kim, Juho ; Kim, Hansoo ; Paeng, Dong-Guk ; Pang, Ig-Chan ;
The Journal of the Acoustical Society of Korea, volume 34, issue 1, 2015, Pages 12~19
DOI : 10.7776/ASK.2015.34.1.012
In this paper, temporal variations of acoustic transmission loss (TL) affected by internal tide are studied by computer simulation using oceanic data measured in the southern sea of Jeju Island in summer. Temperature was measured with depth (bottom depth are nearly 80 m) in two sites near Seogwipo coast every one hour for 25 hours during July 27 and 28, 2009. The periodic fluctuation of temperature due to the internal tide was observed and its vertical displacement was more than 10 m. In order to investigate temporal variation of TL by internal tide, acoustic propagation between two measurement sites (3.8 km distance) was simulated with a source depth of 10 m. TL variation for 1/3 octave band of 100 Hz center frequency highly coincided with tidal period but more complex variation with indistinct tidal period was observed for 1 kHz. Maximun standard deviation of TL variation was 4.2 dB for 100 Hz at 2.8 km distance from a source and it was 3.7 dB for 1 kHz. The tidal variation was also shown in detection range and its maximum variance was less than 1 km. These results imply that temporal variation of TL should be considered for acoustic researches at the southern sea of Jeju Island.
A Study on the Characteristics of Underwater Sound Transmission by Short-term Variation of Sound Speed Profiles in Shallow-Water Channel with Thermocline
Jeong, Dong-Yeong ; Kim, Sea-Moon ; Byun, Sung-Hoon ; Lim, Yong-Kon ;
The Journal of the Acoustical Society of Korea, volume 34, issue 1, 2015, Pages 20~35
DOI : 10.7776/ASK.2015.34.1.020
Underwater acoustic channel impulse responses (CIR) are influenced by sound speed profile (SSP), and the variation of CIR has significant effects on the performance of underwater acoustic communication systems. A significant change of SSP can occur within a short period, which must be considered during the design of underwater acoustic modems. This paper statistically analyzes the effect of the variation of SSP on the long-range acoustic signal propagation in shallow-water with thermocline using numerical modeling based on the data acquired from JACE13 experiment near Jeju island. The analysis result shows that CIR changes variously according to the SSP and the depth of the transmitter and receiver. We also found that when the transmitter and receiver are deeper, the variation of sound wave propagation pattern is smaller and signal level becomes higher. All CIR obtained in this study show that a series of bottom reflections due to downward refraction and small bottom loss in the shallow water with thermocline can be very important factor for long-range signal transmission and the performance of underwater acoustic communication system in time varying ocean environment can be very sensitive to the variation of SSP even for a short period of time.
Efficient Prediction of Broadband Noise of a Centrifugal Fan Using U-FRPM Technique
Heo, Seung ; Cheong, Chulung ;
The Journal of the Acoustical Society of Korea, volume 34, issue 1, 2015, Pages 36~45
DOI : 10.7776/ASK.2015.34.1.036
Recently, a lot of studies have been made about the methods used to generate turbulent velocity fields stochastically in order to effectively predict broadband flow noise. Among them, the FRPM (Fast Random Particle Mesh) method which generates turbulence with specific statistical properties using turbulence kinetic energy and dissipation obtained from the steady solution of the RANS (Reynolds Averaged Navier-Stokes) equations has been successfully applied. However, the FRPM method cannot be applied to the flow noise problems involving intrinsic unsteady characteristics such as centrifugal fan. In this paper, to effectively predict the broadband noise generated by centrifugal fan, U-FRPM (unsteady FRPM) method is developed by extending the FRPM method to be combined with the unsteady numerical solutions of the unsteady RANS equations to generate the turbulence considered as broadband noise sources. Firstly, an unsteady flow field is obtained from the unsteady RANS equations through CFD (Computational Fluid Dynamics). Then, noise sources are generated using the U-FRPM method combined with acoustic analogy. Finally, the linear propagation model which is realized through BEM (Boundary Element Method) is combined with the generated sources to predict broadband noise at the listeners' position. The proposed technique is validated to compare its prediction result with the measured data.
Enhanced Multi-Channel Adaptive Noise Control Compensating Nonlinear Distortions
Kwon, Oh Sang ;
The Journal of the Acoustical Society of Korea, volume 34, issue 1, 2015, Pages 46~51
DOI : 10.7776/ASK.2015.34.1.046
In fields of controlling acoustical noises, the overall adaptive control system is nonlinear due to the loudspeaker, amplifiers, converters, and microphones, etc. and the performance of noise control is decreased by the extent of nonlinearities, so an adaptive control system compensating nonlinear distortions is needed. In this paper, a new multi-channel adaptive noise controller was proposed, which was combined with the adaptive compensator to effectively linearize nonlinear distortions in the overall adaptive control system. Through computer simulations, the proposed adaptive compensator could linearize the nonlinear distortions and the proposed noise controller had better capability of controlling the noises than the conventional LMS controller.
Prediction of the Environmental Noise Level of Railway Cars Crossing a Concrete Bridge
Jang, Seungho ;
The Journal of the Acoustical Society of Korea, volume 34, issue 1, 2015, Pages 52~59
DOI : 10.7776/ASK.2015.34.1.052
In the conventional model for the prediction of the railway environmental noise, one used an empirical formula of the total noise level at specific distances. Only a function of the distance to the source was also used to calculate the noise level near the railway bridges. However, the noise varies depending on the position of the receiver as well as the distance from the source especially at concrete bridges. In this paper, a noise propagation model in the railway concrete bridge was derived by considering the diffraction at the bridge deck and the ground effect and applying the ISO 9613-2 noise propagation model. We compared the predicted and measured values of environmental noise at a high-speed railway bridge, and it was confirmed that this prediction model gives relatively small errors.
Improvement of Muzzle Localization Using Linear Microphone Array
Jung, Seong-Woo ; Kim, Yang-Hann ;
The Journal of the Acoustical Society of Korea, volume 34, issue 1, 2015, Pages 60~65
DOI : 10.7776/ASK.2015.34.1.060
In this paper, we used the sound of gunshots recorded by multiple microphones to increase the accuracy of the calculation of the distance between sniper and the microphone array. This method is crucial for achieving military objectives. Gunshots are comprised of the explosion of driving gas from the muzzle and the supersonic shock wave from the flying bullet. The original distance calculation method compares the time difference of arrival and angle of incidence to estimate the sniper's location. The disadvantage of this method is that when the angles of incidence coincide the margin of error increases, to solve this problem we suggest a new method using the characteristic changes of the shock wave with the increase of perpendicular distance between the microphone and the trajectory of the bullet. This theory is verified by experiments.
Direction-of-Arrival Estimation for the Ring-Type Multimode Vector Hydrophone based on the Pressure Gradient-Acceleration Relationship
Kim, Wan-Jin ; Kim, Woo Shik ; Bae, Ho Seuk ; Joh, Cheeyoung ; Seo, Hee-Seon ; Choi, Sang Moon ;
The Journal of the Acoustical Society of Korea, volume 34, issue 1, 2015, Pages 66~74
DOI : 10.7776/ASK.2015.34.1.066
Conventional hydrophones can only measure acoustic pressure. To measure both acoustic pressure and incident direction, various types of vector hydrophones have been researched. In this paper, we deal with a ring-type multimode vector hydrophone divided into 4 elements and present a direction-of-arrival (DoA) estimation method based on the pressure gradient-acceleration relationship. The performance of the presented method is analyzed by the simulation based on the sensor modeling and is verified by the water tank experiment. The proposed method could work under the multi-frequency condition and may be utilized in many applications due to its low computation complexity.
Single Ping Clutter Reduction Algorithm Using Statistical Features of Peak Signal to Improve Detection in Active Sonar System
Seo, Iksu ; Kim, Seongweon ;
The Journal of the Acoustical Society of Korea, volume 34, issue 1, 2015, Pages 75~81
DOI : 10.7776/ASK.2015.34.1.075
In active sonar system, clutters degrade performance of target detection/tracking and overwhelm sonar operators in ASW (Antisubmarine Warfare). Conventional clutter reduction algorithms using consistency of local peaks are studied in multi-ping data and tracking filter research for active sonar was conducted. However these algorithms cannot classify target and clutters in single ping data. This paper suggests a single ping clutter reduction approach to reduce clutters in mid-frequency active sonar system using echo shape features. The algorithm performance test is conducted using real sea-trial data in heavy clutter density environment. It is confirmed that the number of clutters was reduced by about 80 % over the conventional algorithm while retaining the detection of target.
Codebook Design Method Based on Minimax Optimization for Data Transmission over WCDMA Voice Channel
Lee, Junho ; Son, Jongmok ; Lee, Dong Wook ; Park, Yongseok ;
The Journal of the Acoustical Society of Korea, volume 34, issue 1, 2015, Pages 82~91
DOI : 10.7776/ASK.2015.34.1.082
In this paper, a novel codebook design method for data modem over voice channel is presented. Proposed method searches the symbols which have the maximum probability distribution overlap in the symbol space and minimizes the overlap to improve the symbol error rate via minimax optimization. We present numerical simulations and an example implementation. We also give the results of the experiment tests.