• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.2
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• pp.119-127
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• 2014

An epoxy coating applied to the concrete surface of a containment building deteriorates in hazardous environments such as those containing radiation, heat, and moisture. Unlike metals, the epoxy coating on a concrete liner absorbs and discharges moisture during the degradations process, so it has a different density and volume during service. In this study, acoustic impedance was adopted for characterizing the degradation of a glass-reinforced epoxy coating using the acoustic reflection coefficient (reflectance) on a rough epoxy coating. For estimating the acoustic reflectance on a wavy epoxy coating surface, a probabilistic model was developed to represent the multiple irregular reflections of the acoustic wave from the wavy surface on the basis of the simulated annealing technique. A number of epoxy-coated concrete specimens were prepared and exposed to accelerated aging conditions to induce an artificial aging degradation in them. The acoustic impedance of the degraded epoxy coating was estimated successfully by minimizing the error between a waveform calculated from the mathematical model and a waveform measured from the surface of the rough coating.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.471-473
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• 2009

In this paper, we propose a double talk and noise robust acoustic echo canceler for hands-free telephony applications. The proposed system includes a double-talk detection method that detects the double-talk durations, which uses covariance between microphone input signa and estimated microphone input signal. And proposed adaptive algorithm for estimating acoustic echo path, uses normalized auto-covariance matrix of input signal with multiplication of residual error power and projection order of AP(affine projeciton) algorithm. It is confirmed that the proposed algorithm shows better performance from acoustic interference cancellation (AIC) viewpoint in double talk and noisy environments.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.10 s.175
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• pp.90-98
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• 2005

A monitoring system is necessary to make the polishing process more reliable in order to ensure the high quality and performance of the final products. Generally, AE (Acoustic Emission) is known to be closely related to the material removal rate (MRR). As the surface becomes rougher, the MRR and AE increase. Therefore, the surface roughness can be indirectly estimated using the AE signal measured during the polishing. In this study, an AE sensor-based monitoring system was fabricated to detect the very small AE signal resulting from the friction between a tool and a workpiece during polishing. The performance of this monitoring system was estimated according to polishing conditions, the relation between the level of the AE RMS and the surface roughness during the polishing was investigated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.71-79
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• 2008

A helmholtz resonator has been widely used for the purpose of suppressing the low frequency noises propagated from various heat and fluid machineries. However, the conventional resonator has demerits that the effective absorption bandwidth is narrow and the absorption performance is not so outstanding in the only limited configurations of neck and cavity as well. In order to overcome these problems, in this paper, a resonator with perforated neck is proposed. The absorption performances of the resonator are measured by two-microphone method and estimated by transfer matrix method. The measured values of normal absorption coefficients agree well with the estimated values. By introducing the perforated plates at the neck of a resonator, it is shown that the absorption performance have been significantly improved.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.48 no.4
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• pp.487-494
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• 2012

Acoustical backscattering characteristics of Japanese anchovy can be estimated by Kirchhoffray mode model (KRM model) due to estimate exact body and swim-bladder shape of the fish, the samples were rapidly frozen by dry-ice and alcohol. X-ray photos for ventral and lateral direction for 6 samples were taken and the 3D coordinates of the body swim-bladder were estimated by digitizing from the photos. The angles between the axis of body and swim-bladder were about $9^{\circ}$ at 38kHz and $7^{\circ}$ at 120kHz, 200kHz. General formula of TS and BL estimated were < $TS_{38kHz}$ >=20logBL-67.3, < $TS_{120kHz}$ >=20logBL-66.6, < $TS_{200kHz}$ >=20logBL-67.0. As a result, we confirmed KRM model is very useful to estimate TS (Target Strength) for design of experiment and it also can be applied to estimate the abundance of Japanese anchovy distributed by 2 frequency difference method in the survey area.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.2
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• pp.176-184
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• 2013

Quantification of road noise is a challenging issue in the development of tire noise since its transfer paths are complicated. In this paper, a simplified model to estimate the road noise is developed. Transfer path of the model is from wheel to interior. The method uses the wheel excitation force estimated throughout inverse method. In inversion procedure, the Tikhonov regularization method is used to reduce the inversion error. To estimate the wheel excitation force, the vibration of knuckle is measured and transfer function between knuckle and wheel center is also measured. The wheel excitation force is estimated by using the measured knuckle vibration and the inversed transfer function. Finally interior noise due to wheel force is estimated by multiplying wheel excitation force in the vibro-acoustic transfer function. This vibro-acoustic transfer function is obtained throughout measurement. The proposed method is validated by using cleat excitation method. Finally, it is applied to the estimation of interior noise of the vehicle with different types of tires during driving test.

• The Journal of the Acoustical Society of Korea
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• v.37 no.1
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• pp.1-11
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• 2018

Sound propagation in shallow water changes from spherical spreading to cylindrical spreading, depending on boundary conditions, and this point is defined as a transition point of the sound propagation condition. Theoretically, the transition point can be estimated using the transmission loss as a function of source-receiver range. In this paper, the transmission loss curve in a Pekeris waveguide is predicted using a parabolic-equation based acoustic propagation model and using this transmission loss curve, the range from the source of the transition point is estimated, which is compared to the critical distance calculated using the sound speed ratio of water to sediment. In addition, the effects of the sound speed profile and source depth change on the transition point are investigated. Finally, the transition point is estimated using the transmission loss data measured during the period of the SAVEX15 (Shallow Water Acoustic Variability EXperiment 2015) conducted 65 km southwest of Jeju Island in May 2015, and it is compared to the ocean environmental parameters to understand the properties of sound propagation in the experimental area.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.24 no.3
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• pp.271-279
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• 2006

Acoustic Emission (AE) technology is an effective nondestructive testing for continuous monitoring of defect formation and failures in structural materials. This paper presents a source location model using Acoustic Emission (AE) sensors in a Pre-Stressed Concrete (PSC) beam and the evaluation of the model was performed through lab experiments. 54 AE events were made on the surface of the 5m-PSC beam using a Schmidt Hammer and arrival times were measured with 7AE sensors. The source location f3r each event was estimated using least squares. The results were compared with actual positions and the RMSE (Root Mean Square Errors) was about 2cm.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.2
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• pp.139-147
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• 2017

Acoustic performance of splitter silencers was investigated by using 3-dimensional commercial software and experiments. Flow resistivity of sound absorbing material was indirectly estimated by using an impedance tube setup and a curve fitting method. In addition the acoustic impedance of perforated plate was determined by an empirical formulation. Such properties have been used as input parameters in the commercial software. The prediction for a splitter silencer with 1000 mm length was compared with the experimental result. The numerical method is then applied to identify the effects of number of splitters, length of splitters, absorptive material density, and porosity of a perforated plate on the performance of the splitter silencers. As the number and length of splitter increases, the acoustic performance significantly increases. Although the increase of density of absorptive material also increase the acoustic performance, a change in the density over a certain level hardly affect it. The increase of porosity will enhance the performance especially at higher frequencies.

• Journal of the Korean Society of Visualization
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• v.3 no.2
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• pp.51-56
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• 2005

Acoustic excitations were imposed to coaxial air jet of non-premixed jet flame with hydrogen gaseous injected axially in the center of the flow. The frequencies of excitation were three dominant resonant frequencies at 1L, 2L, 3L. modes including specially 514 Hz (2L-mode) which was estimated theoretically as longitudinal mode of combustor characteristics. The mixing enhancement by acoustic forcing has been investigated quantitatively using PLIF and PIV. The effect of acoustic excitation on combustion process was significant to enhance mixing rate that coincides with specific resonant frequencies. And the behavior of vortex-interaction on flame structure was a good evidence to investigate the phenomenon of shear/mixing layer of fuel-air jet structure. The results obtained in this study concludes that generated streamwise vortex by acoustic excitation has a potential to enhance the mixing rate and abating NOx emissions.