• 소음진동
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• 제7권2호
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• pp.215-222
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• 1997

The flow and acoustic fields due to a vortex ring interaction with a rigid sphere are simulated numerically. The flow field is regarded as three-dimensional inviscid and incompressible. The vorticity is assumed to be concentrated inside the finite core of vortex filament. The vortex filament curve, described by parabolic blending curve function, is used to effectively solve the modified Biot-Savart equation. The interaction between a vortex ring and a rigid sphere using the parabolic blending curve is calculated. The trajectory of the vortex ring is obtained with several different initial positions between the ring and the sphere. The force variations acting on the sphere are calculated by using the boundary integral method. Finally, we can also obtain the acoustic signals at the far field observation positions from the force variations acting on the rigid surface. We can find that the dipole axis of the directivity patterns are rotated during the interacting phenomena.

• 대한의용생체공학회:의공학회지
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• 제7권1호
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• pp.3-10
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• 1986

In this paper, a scanconverter which displays the biological signals of low frequency on CRT for the purpose of easy read-out is attempted to design for using the CRTC, and it stows some good effectivenesses The results obtained in this experiment are as follows : (1) Using only one chip, CRT controller, it can display both waveforms and characters simultaneously. (2) The flexibility of CPU program can be obtained using the sub-microproce ssor function of CRTC chip. (3) The trend of digital data is possible through the graphic function (4) The vibration of displayed waveform can be prevented using the chip simplification and the trigger signal of one chip. (5) Operation with microprocessor malies the expansion and interface easy.

• 음성과학
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• 제4권2호
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• pp.41-54
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• 1998

Speech signals are, depending on the characteristics of waveform, classified as voiced sound, unvoiced sound, and silence. Voiced sound, produced by an air flow generated by the vibration of the vocal cords, is quasi-periodic, while unvoiced sound, produced by a turbulent air flow passed through some constriction in the vocal tract, is noise-like. Silence represents the ambient noise signal during the absence of speech. The need for deciding whether a given segment of a speech waveform should be classified as voiced, unvoiced, or silence has arisen in many speech analysis systems. In this paper, a voiced/unvoiced/silence classification algorithm using spectral change in the wavelet transformed signal is proposed and then, experimental results are demonstrated with our discussions.

• Smart Structures and Systems
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• 제9권5호
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• pp.441-459
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• 2012

Identification of vibration parameters from the analysis of the dynamic response of a structure plays a key role in current health monitoring systems. This study evaluates the capabilities of the recently developed Synchrosqueezed Wavelet Transform (SWT) to extract instant frequencies and damping values from the simulated noise-contaminated response of a structure. Two approaches to estimate the modal damping ratio from the results of the SWT are presented. The results obtained are compared to other signal processing methods based on Continuous Wavelet (CWT) and Hilbert-Huang (HHT) transforms. It was found that the time-frequency representation obtained via SWT is sharped than the obtained using just the CWT and it allows a more robust extraction of the individual modal responses than using the HHT. However, the identification of damping ratios is more stable when the CWT coefficients are employed.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.643-646
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• 2005

The paper discusses the main problems in induction motor diagnosis by motor current and vibration signals, possible faults and effects produced by these faults in the signal spectrums. Decision Tree is introduced as a tool to diagnose the motor status, this expert system is implemented to detect the incipient defects, supervise and predict them, and plan the maintenance of the motor.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 추계학술대회 논문집
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• pp.174-179
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• 2002

In metal cutting, Chatter is an unstable cutting phenomenon which is due to the interaction of the dynamics of the chip removal process and the structural dynamics of machine tool. when vibration and chatter occurs, it reduces tool life, results in poor surface roughness and low productivity of the machining process. In this study, the experiments were conducted in CNC lathe without cutting fluid to investigated phenomenon of the chatter, In the experiments, accelerometers were set up at the tail stock and tool holder and the signals were picked up. In order to observe the effect of chatter on the surface roughness profiles, in this paper, surface roughness profiles will be generated under the ideal condition and the occurrence of the chatter based on the surface simulation model.

• 콘크리트학회지
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• 제3권3호
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• pp.121-128
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• 1991

시험체의 공지모드를 분석하여 대형 기계용 기초 콘크리트의 두께를 측정하였다. 시험체에 강철구 자유낙하에 의한 기계적인 충격을 가하여 진동을 발생시키고, 이 진동신호를 광대역 원추형 압전 탑촉자로 수신하였다. 수신된 진동신호를 FFT를 사용하여 주파수로부터 시험체의 두께를 결정하였다. 여러 층으로 이루어진 콘크리트 블록의 경우, 이 방법으로 결정된 값은 실제의 두께와 잘 일치하였다. 또한 이 방법은 두께 측정 뿐만 아니라 경계면의 접합 상태 파악에 활용될 수 있다.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 1998년도 추계학술대회 학술발표 논문집
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• pp.597-608
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• 1998

A diagnosis system that provides early warnings regarding machine malfunction is very important for rolling mill so as to avoid great losses resulting from unexpected shutdown of the production line. But it is very difficult to provide early warnings in rolling mill. Because dynamics of rolling mill is non-linear. This paper proposes a new method for diagnosis of rolling mill using wavelet to solve this problem. Proposed method that measures the vibration signals of rolling mill on-line and analyze it using wavelet to acquire pattern datas. And we design a nero-fuzzy model that diagnose a rolling mill using this data. Validity of the new method is asserted by numerical simulation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 D
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• pp.2067-2069
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• 2003

본 연구는 진동 신호의 전력 스펙트럼 밀도(PSD)해석을 이용하여 베어링 초기 고장을 검출할 수 있는 기법을 제시하였다. 외륜, 내륜, 볼에 대하여 각각 폭 0.3 mm의 미소한 흠을 낸 베어링을 이용하여 고장 특성 주파수 패턴 및 부하변동에 따른 영향을 분석하고 고장검출이 용이한 고장 주파수 대역을 설정하였다. 실험결과로부터 제시된 검출기법이 유도전동기 베어링 초기 고장에 적용 가능함을 입증하였다.

• 조명전기설비학회논문지
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• 제28권5호
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• pp.23-30
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• 2014

This paper presents an on-line diagnosis system for identifying health and faulted conditions in squirrel-cage induction motors using stator current, temperature, and partial discharge signals. The proposed diagnosis system can diagnose induction motor faults such as broken rotor bars, air-gap eccentricities, stator winding insulations, and bearing faults. Experimental results obtained from induction motors show that the proposed system is capable of detecting induction motor faults.