• The Transactions of the Korean Institute of Electrical Engineers D
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• v.52 no.5
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• pp.219-219
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• 2003

This paper described about the acoustic wave measurement method to diagnose GIS for particles. We measured and analyzed the signals of acoustic waves with two type acoustic sensors having 125kHz and 50kHz resonant frequency respectively when the particles were bounced on the inside surfaces of GIS tanks by the electrostatic force. To use two sensors for the diagnosis of GIS, we set up the calibration method for this measurement method. We showed the output characteristics of two sensors according to the sizes and materials of particles in the experiment. As the results, the inception voltages bouncing particles depended on the materials and the extinction voltages bouncing them depended on the sizes and materials. We found out that the relationship between sizes of particles and output voltages of sensors didn′t have linearity but the ratios of between peak values of two sensors depended on the materials of GIS enclosures and the sizes of particles.

• International Journal of Advanced Culture Technology
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• v.10 no.3
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• pp.339-345
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• 2022

In this paper, the effect of porosity on the acoustic phase velocity of the 3D printed Kelvin closed-cell structure was investigated using the spectral phase analysis. Since Kelvin cells bring about the large amount of scattering, acoustic pulses in ultrasonic measurements undergoes a distortion of waveforms due to the dispersion effect. In order to take account on the dispersion, mathematical expressions for calculating the phase velocity of longitudinal waves propagating normal to the plane of the Kelvin structure are suggested by introducing a complex wave number based on Fourier transform. 3D Kelvin structure composed of identical unit-cells, a polyhedron of 14 faces with 6 quadrilateral and 8 hexagonal faces, was developed and fabricated by 3D CAD and 3D printer to represent the micro-structure of porous materials such as aluminum foam and cancellous bone. Total nine samples of 3D Kelvin structure with different porosity were made by changing the thickness of polyhedron. Ultrasonic pulse of 1MHz center frequency was applied to the Kelvin structures for the measurement of the phase velocity of ultrasound using the TOF(time-of-flight) and the phase spectral method. From the experimental results, it was found that the acoustic phase velocity decreased linearly with the porosity.

• Nuclear Engineering and Technology
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• v.56 no.2
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• pp.688-706
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• 2024

Austenitic stainless steels (ASS) are extensively employed in various sectors such as nuclear, power, petrochemical, oil and gas because of their excellent structural strength and resistance to corrosion. SS304 and SS316 are the predominant choices for piping, pressure vessels, heat exchangers, nuclear reactor core components and support structures, but they are susceptible to stress corrosion cracking (SCC) in chloride-rich environments. Over the course of several decades, extensive research efforts have been directed towards evaluating SCC using diverse methodologies and models, albeit some uncertainties persist regarding the precise progression of cracks. This review paper focuses on the application of Acoustic Emission Technique (AET) for assessing SCC damage mechanism by monitoring the dynamic acoustic emissions or inelastic stress waves generated during the initiation and propagation of cracks. AET serves as a valuable non-destructive technique (NDT) for in-service evaluation of the structural integrity within operational conditions and early detection of critical flaws. By leveraging the time domain and time-frequency domain techniques, various Acoustic Emission (AE) parameters can be characterized and correlated with the multi-stage crack damage phenomena. Further theories of the SCC mechanisms are elucidated, with a focus on both the dissolution-based and cleavage-based damage models. Through the comprehensive insights provided here, this review stands to contribute to an enhanced understanding of SCC damage in stainless steels and the potential AET application in nuclear industry.

• Proceedings of the Optical Society of Korea Conference
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• 2007.02a
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• pp.239-240
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• 2007

• Bulletin of the Korean Space Science Society
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• 2007.10a
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• pp.41-41
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• 2007

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.33-36
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• 2007

Acoustic holography exhibits the spatial distribution of sound pressure in time or frequency domain. The obtained picture often contains far more than what we need in practice. For example, when we need to know only the locations and overall propagation pattern of sound sources, a method to show only what we need has to be introduced. One way of obtaining the necessary information is to use envelope in space. The spatial envelope is a spatially slowly-varying amplitude of acoustic waves which contains the information of sources' location. A spatial modulation method has been theoretically developed to get a spatial envelope. By applying the spatial envelope, not only the necessary information is obtained but also computation time is reduced during the process of holography. The spatial envelope is verified as an effective visualization scheme in time domain by being applied to complicated sound fields.

• Journal of Ocean Engineering and Technology
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• v.34 no.3
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• pp.227-236
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• 2020

Underwater acoustics, which is the domain that addresses phenomena related to the generation, propagation, and reception of sound waves in water, has been applied mainly in the research on the use of sound navigation and ranging (SONAR) systems for underwater communication, target detection, investigation of marine resources and environment mapping, and measurement and analysis of sound sources in water. The main objective of remote sensing based on underwater acoustics is to indirectly acquire information on underwater targets of interest using acoustic data. Meanwhile, highly advanced data-driven machine-learning techniques are being used in various ways in the processes of acquiring information from acoustic data. The related theoretical background is introduced in the first part of this paper (Yang et al., 2020). This paper reviews machine-learning applications in passive SONAR signal-processing tasks including target detection/identification and localization.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.504-509
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• 1998

A new method is proposed for the isolation of resonances from scattered waves for acoustic wave resonance scattering problems. The resonance scattering function consisting purely of resonance information is defined. Acoustic wave scattering from a variety of submerged bodies is numerically analyzed. The classical resonance scattering theory (RST) and the new method compute identical magnitude of the resonance from each scattered partial wave, however, the phases are significantly different. The exact .pi.-radians phase shifts through the resonance and anti-resonance show that the proposed method properly extracts the vibrational resonance information of the scatterer. Due to the difference in the phase of each, partial wave, the new method and RST generate different total resonance spectra.

• Journal of the Korean Institute of Navigation
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• v.17 no.1
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• pp.99-105
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• 1993

Underwater acoustic positioning systems have been extensively used not only in surface position fixing but also in underwater position fixing. Recently, these systems have been applied in the field of installation and underwater inspection offshore platforms etc. But in these systems are included the fixing errors as results of a signal with noise and irregular motion of vessel by ocean waves. In this paper to improve the accuracy of the position fixing a Kalman filter is applied to the short baseline(SBL) acoustic positioning system. The optimal position obtained by the Kalman filter is compared with the raw position and it is confirmed that the former is more accurate than the latter.

• Smart Structures and Systems
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• v.13 no.1
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• pp.155-171
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• 2014

Various monitoring techniques are now available for structural health monitoring and Acoustic Emission (AE) is one of them. One of the major advantages of the AE technique is its capability to locate active cracks in structural members. AE crack locating approaches are affected by the signal attenuation and dispersion of elastic waves due to inhomogeneity and geometry of reinforced concrete (RC) members. In this paper, a novel technique is described based on signal processing and sensor arrangement to process multisensory AE data generated by the onset and propagation of cracks and is validated with experimental results from an in-situ load test. Considering the sources of uncertainty in the AE crack location process, a methodology is proposed to capture and locate events generated by cracks. In particular, the relationship between AE events and load is analyzed, and the feasibility of using the AE technique to evaluate the cracking behavior of two RC slab strips during loading to failure is studied.