• Smart Structures and Systems
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• v.29 no.6
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• pp.777-783
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• 2022

Even though several deep learning-based methods have been applied in the field of acoustic source localization, the previous works have only been conducted using the two-dimensional representation of the beamforming maps, particularly with the planar array system. While the acoustic sources are more required to be localized in a spherical microphone array system considering that we live and hear in the 3D world, the conventional 2D equirectangular map of the spherical beamforming map is highly vulnerable to the distortion that occurs when the 3D map is projected to the 2D space. In this study, a 3D deep learning approach is proposed to fulfill accurate source localization via distortion-free 3D representation. A target function is first proposed to obtain 3D source distribution maps that can represent multiple sources' positional and strength information. While the proposed target map expands the source localization task into a point-wise prediction task, a PointNet-based deep neural network is developed to precisely estimate the multiple sources' positions and strength information. While the proposed model's localization performance is evaluated, it is shown that the proposed method can achieve improved localization results from both quantitative and qualitative perspectives.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.227-236
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• 2003

Leaks in underground pipelines can cause social, environmental and economical problems. One of relevant countermeasures against leaks is to find and repair of leak points of the pipes. Leak noise is a good source to identify the location of leak points of the pipelines. Although there have been several methods to detect the leak location with leak noise, such as listening rods, hydrophones or ground microphones, they have not been so efficient tools. In this paper, acoustic emission (AE) sensors and accelermeters are used to detect leak locations which could provide all easier and move efficient method. Filtering, signal processing and algorithm of raw input data from sensors for the detection of leak location are described. A 120m-long pipeline system for experiment is installed and the results with the system show that the algorithm with the AE sensors and accelerometers offers accurate pinpointing of leaks. Theoretical analysis of sound wave propagation speed of water in underground pipes, which is critically important in leak locating, is also described.

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.4
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• pp.278-284
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• 1997

EMAT는 비접촉으로 초음파를 송수신 할 수 있는 탐촉자로서 시험체와 탐촉자간의 접촉을 위한 매개 물질이 필요치 않으므로, 움직이고 있는 물체에 초음파탐상법을 적용하고자 하는 분야와 초음파의 속도를 정밀하게 측정하고자 하는 분야에 주로 응용된다. 구체적으로는 길이가 긴 튜브류의 결함 탐상, 용접중인 재료의 용접상태 감시, 기차바퀴 및 레일의 결함 탐상, 고온상태인 재료의 결함 탐상 등이 비접촉 특성을 이용하여 적용될 수 있는 분야이며, 재료의 집합조직 및 소성이방성의 측정, 재료의 미세조직 및 기계적 강도의 예측, 그리고 잔류응력의 측정 등이 정밀한 초음파속도 및 감쇠의 측정으로부터 적용될 수 있는 분야이다. EMAT가 일반적인 접촉식초음파탐상법에 비하여 특별한 분야에의 응용에 큰 장점을 가지고 있지만, 낮은 에너지 전환효율, 넓은 불감영역, 그리고 사용주파수의 한계 등의 문제를 가지고 있기 때문에 기존의 접촉식 방법의 적용이 용이한 분야에의 적용은 필요하지 않다. 그러나 특별한 목적과 용도에의 적용 필요성이 생길 경우에는 적절한 연구를 통하여 알맞은 탐촉자를 제작하고 탐상 방법을 개발함으로서 본래의 목적에 알맞은 탐상이 수행될 수 있다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.230-233
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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 "Researches 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 of rooms with reference to other acoustical parameters. In the former KS, there is no items matched with this purpose. Therefore measuring reverberation time and other room acoustical parameters with confidential test procedure was impossible. On these basis, a new part of KS is proposed, and some problems remained and further discussions in the proposed draft are described in this study.

• Proceeding of Spring/Autumn Annual Conference of KHA
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• 2003.11a
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• pp.83-87
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• 2003

In recent days, IAQ(Indoor Air Quality) is regarded as one of the most important environmental factors as well as thermal and acoustic comfort. Various architectural materials are applied and air-tightness of the building is more strengthening to save energy consumption. This is why the air quality of the newly built houses became worse. In this study, contaminants(CO, CO$_2$, Radon, TVOCs, HCHO) density was measured in a newly built house and evaluation was carried out by ASHRAE and EPA Standards. As a result, CO, CO$_2$, TSP and Radon density of the newly built house was in a range of ASHRAE and EPA Standards, but it turned out TVOCs and HCHO density exceeds almost 3${\sim}$5 times in comparison with that of ASHRAE and EPA Standards.

• Korean Journal of Materials Research
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• v.5 no.3
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• pp.268-274
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• 1995

세라믹재료의 동탄성계수 측정을 위한 공진주파수 측정장치를 구성하였다. 구조용 세라믹 재료로 이용되는 $Al_{2}$O_{3}$, SiC, $Si_{3}$N_{4}$의 온도를 120$0^{\circ}C$까지 5$0^{\circ}C$의 온도간격으로 올리면서 torsional resonant frequency와 flexural resonant frequency를 측정하고, 측정된 공진주파수로부터 각 재료의 탄성계수를 구하였다. SiC의 경우는 120$0^{\circ}C$의 온도까지 탄성계수가 선형적으로 감소하였으나, $Al_{2}$O_{3}$와 $Si_{3}$N_{4}$의 경우에는 각각 100$0^{\circ}C$와 80$0^{\circ}C$까지는 선형적으로 감소하나, 그 이상의 온도에서는 탄성게수의 감소폭이 증가하는 현상을 보였다. 이러한 현상은 다결정재료에서의 grain boundary sliding에 의한 것으로 알려져 있다. 상온에서 공진법으로 측정된 동탄성계수의 측정결과는 초음파법으로 측정한 결과와 비교하였는데, 4% 내에서 서로 일치하는 결과를 보였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.336-339
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• 2000

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 of laboratory test facilities with suppressed flanking transmission. In the former KS, there is no items matched with this purpose. Therefore comparing several results with different measuring conditions of a laboratory and results between different laboratories was impossible. On these basis, a new part of KS is proposed, and some problems remained and further discussions in the proposed draft are described in this study.

• Journal of the Korean Society for Nondestructive Testing
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• v.14 no.1
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• pp.16-22
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• 1994

In contrast to the machineries using rolling element bearings, systems with journal bearings generally operate in large scale and under severe loading condition such as steam generator turbines and internal combustion engines. Failure of the bearings in these machineries can result in the system breakdown. To avoid the time consuming repair and considerable economic loss, the detection of incipient failure in journal bearings becomes very important. In this experimental approach, acoustic emission monitoring is applied to the detection of incipient failure caused by several types of abnormal operating condition most probable in the journal bearing systems. It has been known that the intervention of foreign materials, insufficient lubrication and misassembly etc. are principal factors to cause bearing failure and distress. The experiment was conducted under such designed conditions as hard particles in the lubrication layer, insufficient lubrication, and metallic contact in the simulated journal bearing system. The results showed that acoustic emission could be an effective tool to detect the incipient failure in journal bearings.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.1
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• pp.68-76
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• 2011

Acoustic emission(AE) has emerged as a powerful nondestructive tool to detect any further growth or expansion of preexisting defects or to characterize failure mechanisms. Recently, this kind of technique, that is an in-situ monitoring of inside damages of materials or structures, becomes increasingly popular for monitoring the integrity of large structures like a huge wind turbine blade. Therefore, it is required to find a symptom of damage propagation before catastrophic failure through a continuous monitoring. In this study, a new damage location method has been proposed by using signal mapping algorithm, and an experimental verification is conducted by using small wind turbine blade specimen; a part of 750 kW real blade. The results show that this new signal mapping method has high advantages such as a flexibility for sensor location, improved accuracy, high detectability. The newly proposed method was compared with traditional AE source location method based on arrival time difference.

• The Journal of the Acoustical Society of Korea
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• v.22 no.6
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• pp.463-471
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• 2003

The results of the APMP (Asia Pacific Metrology Programme) regional intercomparison of acoustic calibrators were reviewed and analyzed. The artefacts used in intercomparison are a sound level calibrator and a pistonphone. The microphones used to measure the output pressure level are 1" and 1/2" standard microphones (LS1P, LS2P) as well as 1" and 1/2" reference microphones (WS1P/F, WS2P/F). The results obtained using standard microphones are satisfactory, but those obtained by the reference microphones, even though E/sub n/ values are within ±1.0, showed great deviations. Such results had come from the inaccurate calibration of reference microphones. By using the correct calibration results which were obtained by the recently established international standards, the new results were very similar to those of the foreign standard institutes.