• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.178-185
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• 2011

The micro-perforated panel absorber (MPPA) is one of promising noise control elements because of its applicability to extreme environments where general porous materials cannot be used. Since the MPPA is inherently non-porous sound absorber, it can be a good candidate of acoustic protection system of a space launcher. The overall sound pressure level inside payload fairings of commercial launch vehicles is so high (around 140 dB OASPL) that the conventional linear impedance model cannot be directly applied to the design of the acoustic protection systems. In this paper an acoustic impedance models of a micro-perforated panel absorber at high sound pressure environment were reviewed and the use of the impedance on the practical design of MPPAs was addressed. The variation of absorption characteristics of MPPA was discussed according to the design parameters, e.g., perforation ratio, the minute hole diameter, the thickness of MPP and the incident sound pressure level.

• Phonetics and Speech Sciences
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• v.4 no.2
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• pp.95-104
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• 2012

Thyroidectomy patients may have vocal paralysis or paresis, resulting in a breathy voice. The aim of this study was to investigate the aerodynamic and acoustic characteristics of a breathy voice in thyroidectomy patients. Thirty-five subjects who have vocal paralysis after thyroidectomy participated in this study. According to perceptual judgements by three speech pathologists and one phonetic scholar, subjects were divided into two groups: breathy voice group (n = 21) and non-breathy voice group (n = 14). Aerodynamic analysis was conducted by three tasks (Voicing Efficiency, Maximum Sustained Phonation, Vital Capacity) and acoustic analysis was measured during Maximum Sustained Phonation task. The breathy voice group had significantly higher subglottal pressure and more pathological voice characteristics than the non breathy voice group. Showing 94.1% classification accuracy in result logistic regression of aerodynamic analysis, the predictor parameters for breathiness were maximum sound pressure level, sound pressure level range, phonation time of Maximum Sustained Phonation task and Pitch range, peak air pressure, and mean peak air pressure of Voicing Efficiency task. Classification accuracy of acoustic logistic regression was 88.6%, and five frequency perturbation parameters were shown as predictors. Vocal paralysis creates air turbulence at the glottis. It fluctuates frequency-related parameters and increases aspiration in high frequency areas. These changes determine perceptual breathiness.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.1
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• pp.137-146
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• 2019

The ultrasonic phased arrays are used for treating tumors in the human body by the focus control of the acoustic pressure at the desired position. The magnitude and phase of the surface acoustic pressure in each ultrasonic transducer is controlled by the magnitude and phase of the applied voltage to it. In this paper, the relationship between the applied voltage and the surface acoustic pressure of the ultrasound transducer is modelled, and the desired voltage is realized by PWM technique. The validity of the proposed method is verified by computer simulation of the focus control of a ultrasonic phased array composed of 61 ultrasonic transducers.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.1
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• pp.1-8
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• 2012

Acoustic-pressure response of diluted hydrogen-air diffusion flames is investigated numerically by adopting a fully unsteady analysis of flame structures in low and high pressure regimes. As acoustic frequency increases, finite-rate chemistry is enhanced through a nonlinear accumulation of heat release rate for any pressure regime, leading to a high amplification index. Same numerical results are analyzed with application of a pressure-sensitive time lag model, and thereby, interaction index and time lag are calculated for each pressure regime. The interaction index has the largest value in each pressure regime at an acoustic frequency near 1000 Hz. In a high-pressure regime, flames are more unstable than in a low-pressure regime. The interaction index shows a good agreement with the amplification index.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.3
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• pp.190-198
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• 2013

In order to predict acoustic pressure distributions by exterior incident wave at Cylindrical Hydrophone Array (CHA) sensor's positions, acoustic pressure analysis is performed by using beam tracing method. Beam tracing method is well-known of reliable pressure analysis methods at high-frequency range. When an acoustic noise source is located at the center of rectangular room, acoustic pressure analysis is performed by using both beam tracing method and Power Flow Boundary Element Method (PFBEM). By comparing with results of beam tracing method and those of PFBEM, the accuracy of beam tracing method is verified. We develop the CHA pressure analysis program by verified beam tracing method. The developed software is composed of model input, sensor array creator, analysis option, solver and post-processor. We can choose a model option of 2D or 3D. The sensor array generator is connected to a sonar which is composed of center position, bottom, top and angle between sensors. We also can choose an analysis option such as analysis frequency, beam number, reflect number, etc. The solver module calculates the ray paths, acoustic pressure and result of generating beams. We apply the program to 2D and 3D CHA models, and their results are reliable.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06c
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• pp.477-481
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• 1998

This paper describes the application of a coupled finite element-boundary element method to obtain the steady-state response of a hydrophone. The particular structure considered is a flooded piezoelectric spherical shell. The hydrophone is three-dimensionally simulated to transduce an incident plane acoustic pressure onto the outer surface of the sonar spherical shell to electrical potentials on inner and outer surfaces of the shell. The acoustic field formed from the scattered sound pressure is also simulated. And the displacement of the shell caused by the externally incident acoustic pressure is shown in temporal motion. The coupled FE-BE method is described in detail.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.1
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• pp.25-39
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• 2018

In this paper, an integrated analysis model for evaluating the underwater acoustic performance of the multilayered acoustic coatings containing visco-elastic composite layers with hollow glass microspheres is described. The model uses the effective medium theory considering the acoustic scattering and resonance effects of the inclusions. Also, the model incorporates the compressive deformation mechanism associated with hydrostatic pressure. The technique developed in this work was used as the acoustic layer design and performance analysis tools for the practical hull coatings and acoustic baffles in Korean next generation submarines.

• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1738-1746
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• 2004

When there are low signal to noise relationships or low coherences between measured pressure and a reference sensor, a pressure field measured and estimated by NAH (Nearfield Acoustic Holography) becomes noisy on the hologram and source planes. This paper proposes a method to obtain the high coherent de-noised pressure signals from low coherent noisy ones by combining a wavelet algorithm with NAH. The proposed method obtains the de-noised field from acoustic fields on a noise source plane reconstructed through backward propagation of NAH. Thus this method does not need high coherent pressure signals on the hologram surface while the conventional nearfield acoustic holography requires high-coherent signals. The proposed method was verified by numerical simulation using noisy signals, composed of original signals and imposed noises distributed on the hologram surface.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.280-284
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• 2003

The field application of acoustic emission(AE) testing for brand-new metal pressure vessel were performed. We will introduce the test procedure for acoustic emission test such as instrument check distance between sensors, sensor location, whole system calibration, pressurization sequence, noise reduction and evaluation. The data of acoustic emission test contain many noise signal, these noise can be reduced by time filtering which based on the description of observation during AE test.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.97-104
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• 1998

The objective of this study is to understand the generation mechanism of sound and to develop a prediction method for the unsteady flow field and the acoustic pressure field of a centrifugal fan. Lowson's method is used to predict the acoustic pressure in a free field. A DVM(discrete vortex method) is used to model the centrifugal fan and to calculate the flow field. In order to compare the experimental data, a centrifugal fan and wedge introduced by Weidemann are used in the numerical calculation and the results are compared with the experimental data.