• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.2
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• pp.165-173
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• 2011

The acoustic emission(AE) technique is a well established method to carry out structural health monitoring(SHM) of large structures. However, the real-time monitoring of the crack growth in the roller coaster support structures is not easy since the vehicle operation produces very large noise as well as crack growth. In this investigation, we present the waveform parameter filtering method to classify acoustic sources in real-time. This method filtrates only the AE hits by the target acoustic source as passing hits in a specific parameter band. According to various acoustic sources, the waveform parameters were measured and analyzed to verify the present filtering method. Also, the AE system employing the waveform parameter filter was manufactured and applied to the roller coaster support structure in an actual amusement park.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.374.1-374
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• 2002

The eventual purpose of this research is to make optimum standards for acoustic-environment by using not only physical characteristics but also subjective appraisals. First, basic Physical data were measured which were necessary to establish standards for acoustic environment in campus buildings, TSP has used to measure sound levels, reverberation times, clearness indexes, and speech-transmission-index. (omitted)

• Journal of the Korean Institute of Educational Facilities
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• v.28 no.3
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• pp.3-14
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• 2021

Speech information of teachers is transmitted to students in classrooms so that appropriate aural environment should be provided for academic purposes. Many researches have been undertaken for classroom acoustics, and acoustic standards of domestic classrooms were suggested based on the reverberation time and background noise level. However, these standards are suitable for middle and high schools and so not consider the auditory ability by ages. As a precedent research, the present study was begun to suggest an acoustic standard for lower grade elementary school classrooms with children under age 9 who have not normal auditory ability. In order to do this, acoustic performances of the lower grade classrooms were measured and compared with the general classrooms. Also, change of acoustic parameters depending on the desk layout was measured and analyzed. The measured acoustic parameters were background noise, signal to noise ratio, RT, STI, D₅₀, and IACC. As a result, it was found that background noise is exceed the standard of 35dB(A) at the schools along the road sides. Also, it was shown that most of acoustic parameters are higher in the classrooms built recently rather than the old classrooms. Generally, there are not much difference of acoustic parameters among the various desk layouts but, better acoustic performances are acquired at the center line and the seats near sound source. Also, Higher IACC was measured at the seats on the center line facing the source squarely.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.10
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• pp.1843-1850
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• 2000

Sound absorption coefficient for the absorptive panels comprized of a perforated plate. an absorbent material and an air gap was measured and compared with theoretical value. The absorptive panels are composed of three basic combinations (a perforated plate + an air gap + an absorbent material. a perforated plate + an absorbent material, a perforated plate + an absorbent material + an air gap). As a result. it is found that the sound absorption for low frequency range is strongly affected by the resonance produced by perforated plate and air gap. And the sound absorption for high frequency depends on the porosity of perforated plate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.406-410
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• 2005

The wind turbine, Europe and the United States are different with the standards process each other when the manufacturing company which in order to demand the standards process to a construction in the multi country with interested parties of the corresponding nation to, always the re-agreement is difficult. Korean wind turbine also detail there is not a standard, when it produces and establishes of wind turbine, the problem point occurs. It is like that investigation of international standards system it leads and when it prepares the Acoustic noise measurement of the Wind Turbine Systems of Korea, it prepares the base for industrial development wind turbine of Korea.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.6_spc
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• pp.687-696
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• 2016

A series of process to design an acoustic lens for underwater imaging is reviewed and the method to evaluate characteristics of the lens is investigated. If the target specification of lens is given, the design process consists of the material selection, evaluation of its properties, lens geometry design, prediction of lens characteristics, manufacturing, and evaluation by measurement. In this study, an actual acoustical lens is made by cutting polymethylpentene block. The characteristics of lens are predicted by the hybrid method, combination of ray tracing and Rayleigh integral. For the direct comparison between the prediction and measurement results, a simulation method based on the equivalent source method is suggested to reflect the actual radiation pattern of transducer used for measurements. Finally, the measurement is conducted in a small water tank to observe the actual characteristics of the manufactured lens.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.5
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• pp.465-475
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• 2004

This paper is the first part of the study on the development of a smart active layer (SAL) sensor, which consists of two parts. In this first part, the theory and concept of the SAL sensor is investigated, which is designed for the detection of elastic waves caused by internal cracks and damages in structures. For the development SAL sensor, (i) the basic theory of elastic waves was studied, (ii) the feasible study of the SAL as an elastic waves detection sensor using the finite element analysis (FEA) with respect to a piezoceramic disc was performed. (iii) the comparison of performances between some piezoceramic sensors and a commercial acoustic emission (AE) sensor was accomplished to ensure the applicability by the experimental means, such as a pencil lead break test. Also, the conceptional study for the SAL sensor, which can be utilized for the effective detection and locating of defects by the arrangement of regularly distributed sensors, was discussed.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.360-367
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• 2009

The acoustic emission(AE) behavior of reinforced concrete slab under flexural loading was investigated to assess the integrity. This study was aimed at identifying the characteristics of AE response associated with damage development. By applying cyclic loading in various load steps, it was able to differentiate each AE source such as distributed micro crack initiation, friction, flexural crack and localized diagonal tension crack. The secondary peak and the change of AE hit rate gave valuable criteria fur assessment. From the analysis of the felicity ratio, furthermore, it was shown that this values can be used for evaluating the degree of concrete damage. Based on the experimental results, this approach for practical AE application may provide a promising method for estimating the level of damage and distress in concrete structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.1
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• pp.1-5
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• 2010

Acoustic emission(AE) has emerged as a powerful nondestructive tool to detect or monitor preexisting defects and leaks in the vessel structures. A Bragg grating based acoustic emission sensor system is developed. Various type of fiber Bragg grating sensor including the variable length of sensing part was fabricated and prototype sensor system was tested by using PZT pulser and pencil lead break sources. Two types of sensor attachment were used. First, the fiber Bragg grating sensor was attached fully to the surface using bonding agent. Second one is that one part of fiber was attached to the surface partly by bonding and the other part of fiber will be act as a cantilever. That is, the resonant frequency of the fiber Bragg grating sensor will depend on the length of sensing part. The final goal of the sensor system is to provide on-line monitoring of cracks or leaks in reactor vessel head penetration of nuclear power plants.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.392-396
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• 2001

Revision of KS, Korean Standards, is currently actively discussed. It is just the time for a new world class standards under the new system with WTO, World Trade Organization. This paper is a part of “Researchs on the Standards in the Building Acoustic Field”, as one of KS revision projects. The aim of this study is to define the requirements for measuring the reverberation time and other major room acoustical parameters.