• Journal of the Korean Society of Manufacturing Process Engineers
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• v.3 no.3
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• pp.11-16
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• 2004

In this study, the characteristics of signals such as acoustic emission, vibration amplitude and noise level which are derived from the abnormal condition of compressor are investigated. The normal condition, vane stick sound and roller defect condition are chosen to analyze the signal in each cases. From the feature extraction of each signals, the dominant parameters of each signals which can identify the abnormal condition are suggested.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.883-887
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• 2002

We should maintain the maximum operation capacity for production facilities and find properly out the fault of each equipment rapidly in order to decrease a loss caused by its failure. The acoustic and vibration signals of a machine always carry the dynamic information of the machine. These signals are very useful fur the feature extraction and fault diagnosis. We performed a fundamental study which develops a system of fault diagnosis for a pump. We experimented vibrations by acceleration sensors and noises by microphones, compared and analysed for normal products, artificially deformed products. We tried to search a change of the dynamic signals according to machine malfunctions and analyse the type of deformation or failure. The results showed that acoustic signals as well as vibration signals can be used as a simple method lot a detection of machine malfunction or fault diagnosis.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.5
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• pp.27-36
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• 2013

Linear stability analysis for combustion instability within a cylindrical port of solid rocket motor has been conducted. The analysis of acoustic energy has been performed by a commercial COMSOL code to obtain the mode function associated to each acoustic mode prior to the calculation of stability alpha. An instability diagnosis based on the linear stability analysis of Culick is performed where special interests have been focused on 5 stability factors(alpha) such as pressure coupling, nozzle damping, particle damping and additionally, flow turning effect and viscous damping to take into account the flow and viscosity effect near the fuel surface. The instability decay characteristics depending on the particle size is also analyzed.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.573-584
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• 2012

Breast and prostate tumors or cancers tend to be stiffer than the surrounding normal tissue. However, the difference in echogenicity between cancerous and normal tissues is not clearly distinguishable in ultrasound B-mode imaging. Thus, imaging the stiffness contrast between the two different tissue types helps to diagnose lesions quantitatively, and such a method of imaging the elasticity of human tissue is termed ultrasound elasticity imaging. Recently, elasticity imaging has become an effective complementary diagnostic modality along with ultrasound B-mode imaging. This paper presents various elasticity imaging methods that have been reported up to now and describes their characteristics and principles of operation.

• Magazine of the Korea Institute for Structural Maintenance and Inspection
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• v.17 no.1
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• pp.48-59
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• 2013

응력파의 기반한 비파괴 검사법은 비교적 실험 절차 및 실험에 필요한 장비가 단순하고, 인체에 해가 없으며, 비용이 저렴한 특성을 갖고있다. 따라서 건축/토목 구조물의 비파괴 검사에 매우 효과적인 방법으로 알려져 있다. 하지만 기존의 가속도계, 변위계, 지오폰과 같은 부착 센서를 사용할 경우 표면 처리, 센서의 부착 및 이동에 따른 추가적인 시간이 소요되고, 센서와 구조물의 불완전한 커플링으로 인한 측정 결과의 신뢰성 및 일관성을 유지하지 어렵다는 문제를 발생시킨다. 최근 이러한 문제의 해결책으로 Air-coupled sensor (ACS)의 사용이 각광받고 있으며, 여러 연구자들에 의해 ACS의 가능성 및 실용성이 증명되고 있다. 기존의 접촉센서와 비교하여 ACS를 사용했을 때 얻을 수 있는 가장 큰 장점은 센서의 커플링 문제를 근본적으로 해결하여 신뢰도가 높고 일관적인 측정이 가능하고, 대형 건축/토목 구조물의 표면을 음향스캔하여 결과를 신속하게 처리하여 실시간으로 시각화 할 수 있다는 점이다. 이론적으로 ACS를 이용하여 측정하는 물리값은 콘크리트 내부에서 발생된 응력파의 일부가 공기중으로 전파된 누설파 (Leaky wave)이다. 콘크리트 비파괴 검사에 주로 사용하는 100 kHz이하의 저주파를 측정할 경우 일반적으로 콘텐서마이크가 ACS로 사용될 수 있다. 기존 연구자들은 실험 및 이론적 연구를 통하여 응력파에 기반한 비파괴 방법에서 ACS가 기존의 접촉 센서를 대체할 수 있다는 점을 보여주고 있다. 현재 미국에서는 연방 도로청 (FHWA) 및 국가표준기술연구소 (NIST)의 연구비 지원으로 ACS의 실용성을 높이기 위하여 최적화된 음향반사판의 설계를 통한 ACS 의 민감도를 높이기 위한 연구, 다채널 센서 배열 및 데이터 통합을 위한 새로운 알로리즘 개발, 자동화 및 로봇 기술과 융합과 같은 연구가 활발히 진행되고 있다. 멀지 않은 미래에는 ACS를 장착한 무인 로봇이 다양한 종류의 건축/토목 구조물의 건전도를 평가하기 위하여 종횡무진 활약하는 모습을 현실 속에서 볼 수 있을 것이라 기대한다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.425-430
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• 2008

To verify the system performance of portable AE leak diagnosis system which can measure with moving conditions, AE activities such as RMS voltage level, AE signal trend, leak rate degree according to AE database, FFT spectrum were measured during operation on total 11 valves of the secondary system in nuclear power plant. AE activities were recorded and analyzed from various operating conditions including different temperature, type of valve, pressure difference, valve size and fluid. The results of this field study are utilized to select the type of sensors, the frequency band for filtering and thereby to improve the signal-to-noise ratio for diagnosis for diagnosis or monitoring of valves in operation. As the final result of application study above, portable type leak diagnosis system by AE was developed. The outcome of the study can be definitely applied as a means of the diagnosis or monitoring system for energy saving and prevention of accident for power plant valve. The purpose of this study is to verify availability of the acoustic emission in-situ monitoring method to the internal leak and operating conditions of the major valves at nuclear power plants. In this study, acoustic emission tests are performed when the pressurized temperature water and steam flowed through glove valve(main steam dump valve) and check valve(main steam outlet pump check valve) on the normal size of 12 and 18 ". The valve internal leak monitoring system for practical field was designed. The acoustic emission method was applied to the valves at the site, and the background noise was measured for the abnormal plant condition. To improve the reliability, a judgment of leak on the system was used various factors which are AE parameters, trend analysis, frequency analysis, voltage analysis and amplitude analysis of acoustic signal emitted from the valve operating condition internal leak.

• The Journal of the Acoustical Society of Korea
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• v.38 no.5
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• pp.568-573
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• 2019

In the diagnosis of pulmonary diseases, auscultation technique is simpler than the other methods, and lung sounds can be used for predicting the types of pulmonary diseases as well as identifying patients with pulmonary diseases. Therefore, in this paper, we identify patients with pulmonary diseases and classify lung sounds according to their sound characteristics using various convolutional neural networks, and compare the classification performance of each neural network method. First, lung sounds over affected areas of the chest with pulmonary diseases are collected by using a single-channel lung sound recording device, and spectral features are extracted from the collected sounds in time domain and applied to each neural network. As classification methods, we use general, parallel, and residual convolutional neural network, and compare lung sound classification performance of each neural network through experiments.

• The Journal of the Acoustical Society of Korea
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• v.25 no.3
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• pp.144-150
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• 2006

Clinicians usually use stethoscopic auscultation for the diagnosis of heart diseases. However, the heart sound signal has varying characteristics due to the noise and/or the conditions of the patients. Also, it is not easy for junior clinicians to find the acoustical differences between different kinds or heart sound signals. which may result in errors in the diagnosis. Thus it will be quite useful for the clinicians to make use of an automatic classification system using signal processing techniques. In this paper, we propose to use hidden Markov models in stead of artificial neural networks which have been conventionally used for the automatic classification of heart sounds. In the experiments classifying heart sound signals. we could see that the proposed methods were quite successful in the classification accuracy.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.6
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• pp.87-94
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• 2007

Reuse of recycled aggregate from demolished concrete structure is beneficial and necessary from the viewpoint of environmental preservation and effective utilization of resources. The most important mechanical properties of recycled aggregate concrete (RAC) are the compressive strength, the tensile and the flexural strengths, the bond strength and the elastic modulus of such concrete. In particular, the stress-strain relation and fracture process of RAC in compression is especially important in theoretical and numerical analysis as well as engineering design of RAC structures. In this paper, to clarify the characteristics of fracture process in RAC, acoustic emission(AE) method is applied to detect micro-cracking in concrete under compression. From AE parameters, it is found that cracking and fracture behaviors in recycled aggregate concrete fairly differ from that of normal and recycled sand concrete.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.429-440
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• 2023

This study explores recent research trends and potential applications of ultrasound optical imaging-based multimodal technology. Ultrasound imaging has been widely utilized in medical diagnostics due to its real-time capability and relative safety. However, the drawback of low resolution in ultrasound imaging has prompted active research on multimodal imaging techniques that combine ultrasound with other imaging modalities to enhance diagnostic accuracy. In particular, ultrasound optical imaging-based multimodal technology enables the utilization of each modality's advantages while compensating for their limitations, offering a means to improve the accuracy of the diagnosis. Various forms of multimodal imaging techniques have been proposed, including the fusion of optical coherence tomography, photoacoustic, fluorescence, fluorescence lifetime, and spectral technology with ultrasound. This study investigates recent research trends in ultrasound optical imaging-based multimodal technology, and its potential applications are demonstrated in the biomedical field. The ultrasound optical imaging-based multimodal technology provides insights into the progress of integrating ultrasound and optical technologies, laying the foundation for novel approaches to enhance diagnostic accuracy in the biomedical domain.