• The Journal of the Acoustical Society of Korea
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• 제38권2호
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• pp.177-183
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• 2019

In this paper, we proposed an application method of ICA (Independent Component Analysis) to passive line array sonar to separate interferences from target signals in low frequency band and compared performance of three conventional ICA algorithms. Since the low frequency signals are received through larger bearing angles than other frequency bands, neighboring beam signals can be used to perform ICA as measurement signals of the ICA. We use three ICA algorithms such as Fast ICA, NNMF (Non-negative Matrix Factorization) and JADE (Joint Approximation Diagonalization of Eigen-matrices). Through experiments on real data obtained from passive line array sonar, it is verified that the interference can be separable from target signals by the suggested method and the JADE algorithm shows the best separation performance among the three algorithms.

• The Journal of the Acoustical Society of Korea
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• 제38권4호
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• pp.443-449
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• 2019

To protect the patient's internal organs when a patient with cardiovascular disease occurs, it is important to reduce the elapsed time by providing emergency medical services. Decisions for conducting cardiopulmonary resuscitation are mainly made using the carotid palpation method, which directs the pulse of the carotid artery, which can diagnose the patient's condition according to one's own subject and cause cerebral blood flow to be blocked by excessive pressure in the carotid due to the weaken cardiopulmonary function. In this study, we developed a multimodal patch-type probe based on multi-channel ultrasound Doppler pairs and oxygen saturation measurement modules which can monitor cardiopulmonary functions. From the in-vivo experiments, the developed probe can be utilized as a novel tool that can increase the survival rate of cardiovascular disease patients by objectively monitoring the cardiopulmonary function of the patient quantitatively and promptly in an emergency situation.

• The Journal of the Acoustical Society of Korea
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• 제38권3호
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• pp.334-339
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• 2019

In this study, the vibration test method to nondestructively evaluate the possibility of vehicle BSR (Buzz, Squeak, Rattle) noise generation in spot-welded structures was proposed. The weld quality was predicted by analyzing the local vibration transmission characteristics for the beam-shaped structure attached to testing spots. The bending stiffness was evaluated from the identified vibration properties. From the change in the stiffness, the weld quality was evaluated. For verification of the proposed method, the welded specimens were fabricated with partial changes in welding parameters. The local vibration transfers were measured. The frequency bands affected by the weld quality was identified. The capability of evaluating the welding parameters including defect position and quality variations was investigated. The proposed method enables fast quality evaluation to minimize the possibility of BSR noise generation in the manufactured vehicle.

• The Journal of the Acoustical Society of Korea
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• 제38권3호
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• pp.266-274
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• 2019

As can be seen in the statistics on domestic performance facilities, small or large scale of acoustic renovations seem to be unavoidable in many of those facilities due to its senility. However it is hard to find case studies which can be referred to for its acoustic renovation process. This study tried to provide a case study example of acoustic renovation for a high school auditorium which has many restrictions as a cultural heritage building. Requirements from the client and acoustic problems found through a field measurement of existing space motivated acoustic design solutions and alternatives which can improve the acoustics of the space. The whole process from the initial stage of diagnosing acoustic problems to the final stage of a post acoustic evaluation after the completion of construction was described. The result from the post acoustic evaluation suggested that reverberation characteristics of the space as well as definition and clarity have been greatly improved by applying acoustic design solutions and alternatives. However, loudness of sounds in the space didn't reach the aimed level, which is due to the limited capability of slat ceiling structure for providing strong early reflections.

• The Journal of the Acoustical Society of Korea
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• 제38권3호
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• pp.302-307
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• 2019

In modern Anti-Submarine Warfare, there are various ways to locate a submarine in a two-dimensional space. For more effective tracking and attack against a submarine the depth of the target is a critical factor. However, it has been difficult to find out the depth of a submarine until now. In this paper a possible solution to the depth estimation of submarines is proposed utilizing DIFAR (Directional Frequency Analysis and Recording) sonobuoy information such as contact bearings at or prior to CPA (Closest Point of Approach) and the target's Doppler signals. The relative depth of the target is determined by applying the Pythagorean theorem to the slant range and horizontal range between the target and the hydrophone of a DIFAR sonobuoy. The slant range is calculated using the Doppler shift and the target's velocity. the horizontal range can be obtained by applying a simple trigonometric function for two consecutive contact bearings and the travel distance of the target. The simulation results show that the algorithm is subject to an elevation angle, which is determined by the relative depth and horizontal distance between the sonobuoy and target, and that a precise measurement of the Doppler shift is crucial.

• The Journal of the Acoustical Society of Korea
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• 제40권1호
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• pp.1-9
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• 2021

High-frequency bistatic sea surface scattering channels according to sea state were measured at an experimental site of Geoje bay in April 2020, and compared with predictions based on scattering theory. A linear frequency-modulated signal with a center frequency of 128 kHz and a bandwidth of 32 kHz was used for the acoustic measurements. Sea surface wavenumber spectrum was calculated from surface roughness data measured by a wave buoy, and bistatic scattering cross-section of Small Slope Approximation (SSA) based on the wavenumber spectrum was estimated. In addition, scattering from near-surface bubbles using wind speed measured during experiments was considered. Surface scattering channel intensity impulse responses were simulated using the scattering cross-section and the simulation results were compared and analyzed with the field data.

• The Journal of the Acoustical Society of Korea
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• 제40권1호
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• pp.92-98
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• 2021

The noise management in the interior of the power plant is difficult because the interior is large and the noise level varies greatly from location to location. Therefore, a noise visualization system capable of analyzing the noise distribution is required in order to effectively manage the interior noise. A noise mapping system was developed that can model the inside of the turbine room and create a noise map by measuring the noise level at selected points. And in order to increase the reliability of the model, the model was modified through a method of comparing the noise map and the actual noise measurement results. Facility abnormalities can be determined through regular analysis of noise maps, and a method of effectively managing the interior noise is presented by comparing and analyzing the frequencies and levels of the current and previous noise at a specific point. By using the mapping system, it is possible to establish noise countermeasures that can improve the working environment, check the machine for abnormalities, and increase the reliability of the facility through preventive maintenance.

• The Journal of the Acoustical Society of Korea
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• 제41권1호
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• pp.1-8
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• 2022

This paper identifies the cause of the high frequency calibration limit of the acoustic chamber type calibrator for microphone calibration and presents a method to improve it. By using a commercial finite element analysis software, we analyzed the calibration frequency limit of the acoustic chamber type calibrator through eigen-frequency and frequency domain analysis. Based on this, we designed and fabricated an acoustic chamber type calibrator that can precisely calibrate within 1 dB from about 2 Hz to 6.4 kHz and verified its performance through experiments. The acoustic chamber type calibrator fabricated through this study has the advantage of being able to calibrate multiple microphones simultaneously in a wide frequency range, so it can be usefully used for simple calibration for multiple microphones.

• The Journal of the Acoustical Society of Korea
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• 제41권3호
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• pp.255-267
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• 2022

In this paper, noise characteristics of bubbles created by an orifice-type bubble generator are studied. In order to understand the overall bubble noise characteristics, the bubble noise spectra proposed by Strasberg and Blake, respectively, are examined, and an air injection experiment was performed in the large cavitation tunnel of KRISO to measure the bubble noise. The experiments were performed under a quiescent condition and flow conditions using 5 types of air bubble generator. From the measurement results, the characteristics of the bubble noise spectrum according to the experimental conditions are observed, and the effect of each parameter on bubble noise is analyzed by regression analysis. Finally, empirical models based on the regression analysis for bubble noise are presented, and it is confirmed that the estimated bubble noise is in good agreement with the measured results.

• The Journal of the Acoustical Society of Korea
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• 제42권1호
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• pp.1-6
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• 2023

Sound radiated from a structure in vibration is an important physical characteristic to evaluate vibro-acoustic problem. Although sound radiation power can be typically obtained by intensity measurement, long measuring time and strict measuring condition remain difficult. As an alternative method, simulation-based estimation can be taken into account and its accuracy is known to be acceptable. However, difficulty still lies in that specialized softwares may be necessary to obtain sound radiation power and radiation efficiency. In this context, this study suggests two methods using an ordinary FE method to calculate sound radiation power. They are well-known reciprocity technique and p-p method, which are basically test methods. It is shown that either method can practically estimate sound radiation in the frame of conventional Finite Element Method (FEM). The methods and their corresponding limit are discussed with some results.