• Journal of the Korean Society for Nondestructive Testing
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• v.11 no.1
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• pp.31-37
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• 1991

Acoustic emission(AE) signals detected during metal cutting were applied as the experimental test to sensing tool wear and chipping on the NC vertical milling machine. The in-process detection of cutting tool wear including chipping, cracking and fracture has been investigated by means of AE in spite of vibration or noise through intermittent metal cutting, then the following results were obtained 1) When the tool wear is increased suddenly, or the amplitude of AE signals changes largely, it indicates chipping or breaking of the insert tip. 2) It was confirmed that AE signal is highly sensitive to the cutting speed and tool wear. 3) At the early period of cutting, the wear were large and RMS value increased highly by the influence of minute chipping and cracking, etc. Therefore, the above situations should be considered for the time when the tool would be changed.

• Nuclear Engineering and Technology
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• v.35 no.1
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• pp.25-34
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• 2003

The research on the development of the fault monitoring system for the thermal reduction reactor has been performed preliminarily in order to support the successful operation of the thermal reduction reactor. The final task of the development of the fault monitoring system is to assure the integrity of the thermal$_3$ reduction reactor by the acoustic emission (AE) method. The objectives of this paper are to identify and characterize the fault-induced signals for the discrimination of the various AE signals acquired during the reactor operation. The AE data acquisition and analysis system was constructed and applied to the fault monitoring of the small- scale reduction reactor, Through the series of experiments, the various signals such as background noise, operating signals, and fault-induced signals were measured and their characteristics were identified, which will be used in the signal discrimination for further application to full-scale thermal reduction reactor.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.04a
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• pp.139-142
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• 2004

As fiber reinforced composite materials are widely used in aircraft, space structures and robot arms, the study on the non-destructive testing methods of the composite materials has become an important research area for improving their reliability and safety. In this paper, the AE signal analyzer with the resonance circuit to extract the specified frequency of the acoustic emission signal were designed and fabricated. The noise levels of the fabricated AE signal analyzer by the disturbance such as impact or mechanical vibration had a very small value comparable to those of the conventional AE signal analyzer. Also, the crack detection capabilities of the fabricated AE signal analyzer under the static and dynamic tensile test were evaluated and compared with the conventional AE signal analyzer.

• Korean Journal of Optics and Photonics
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• v.29 no.1
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• pp.32-39
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• 2018

The impact of the amplified spontaneous emission (ASE) on the gain recovery time of a bulk semiconductor optical amplifier (SOA) is investigated. The gain-recovery time is obtained by determining the time evolution of the gain, carrier density, and ASE in an SOA, after the propagation of a short pump pulse and continuous-wave (CW) probe of gain dynamics. In the simulation, a wide-band-semiconductor model, which can be characterized by the material gain coefficient over a wide wavelength range, is used, because the gain bandwidth of a practical SOA is very wide. The pump pulse and counterpropagating CW probe field are considered in the simulation, with the ASE noise spectrum equally divided.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.271-277
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• 2003

Recently as the environmental noise getting influential social problem, it is the fact that the demand on noise reduction increases with the advance of the standard of living. Therefore increasing the interest on the noise in common, it is eagerly demanded that the endeavour for reducing the noise of the rotating machinery, especially the machinery related a flowing including the household electric products, which is pointed out the primary noise source in environment. As proceeding study for fan noise, theory of fan noise property is arranged and this control method is shown. Blade passage noise of total noise spectrum. Thus in the aspect of noise reduction, noise source and identification of noise radiation characteristics of axial flow fan are demanded in detail. The sound source is analyzed by using sound pressure and sound intensity. In that time, synchronization of axial flow fan using optical sensor is executed, and to identify the location of exact noise source in the fan profile determination of recording time is proposed. In the rotating of tan, it is explained that the location of noise source exists in and by the directivity, the noise radiation pattern of axial flow fan is determined and the flow of sound is visualized in the figure of contour mapping.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.5
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• pp.502-509
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• 2010

A test facility which can simultaneously measure turbocharger operating condition variables and vibro-acoustic emission in the situations that are quite similar to real internal combustion engine operating conditions has been introduced. Using this facility, a new method sweeping from full open throttle to deep surge region along constant speed curves can be utilized instead of the stationary method that has been traditionally used to obtain turbocharger compressor maps. Data covering an extensive range of the compressor performance map have been collected and analyzed. An experimental study is performed to define a noise diagram that correlates vibro-acoustic measurements to aerothermodynamic operating conditions. An instrumentation set in the facility allows the automatic definition of the operating point on the turbine and compressor map of the turbocharger. Also, radiated sound pressure and casing vibration data corresponding to the point are obtained by a microphone in the vicinity of the compressor casing and an accelerometer on the casing. The major source(s) of noise at specific operating point on the map can be easily identified with these maps. Also, acoustic characteristics of a given turbocharger at the vicinity of the surge as well as in the surge are also defined. Finally, the possibility to define mild surge region of a turbocharger using vibro-acoustic measurements is studied.

• Journal of Mechanical Science and Technology
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• v.18 no.6
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• pp.1019-1025
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• 2004

Pressure variation is one of the major sources on noise emission in the axial type oil piston pumps. Therefore, it is necessary that the pressure variation characteristics of the oil hydraulic piston pumps be clarified to reduce the pump noise. Pressure variations in a cylinder at the discharge region and the pump noise were simultaneously measured with discharge pressures and rotational speeds during the pump working. To investigate the effects of the pre-compression and the V-notch in the valve plate, we used the three types of valve plates. In this research, it is clear that the pressure variation characteristics of axial type oil piston pumps is deeply related to the pre-compression and to the V-notch design in valve plate. Therefore, we could reduce the pump noise by using the appropriate pre-compression angle and the notch design that are between the suction port and the discharge port in valve plate.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.3
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• pp.178-185
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• 2006

This paper investigates the steady-state combustion characteristics of the Homogeneous charge compression ignition(HCCI) engine with variable valve timing(VVT) and dimethyl ether(DME) direct injection, to find out its benefits in exhaust gas emissions. HCCI combustion is an attractive way to lower carbon dioxide($CO_2$), nitrogen oxides(NOx) emission and to allow higher fuel conversion efficiency. However, HCCI engine has inherent problem of narrow operating range at high load due to high in-cylinder peak pressure and consequent noise. To overcome this problem, the control of combustion start and heat release rate is required. It is difficult to control the start of combustion because HCCI combustion phase is closely linked to chemical reaction during a compression stroke. The combination of VVT and DME direct injection was chosen as the most promising strategy to control the HCCI combustion phase in this study. Regular gasoline was injected at intake port as main fuel, while small amount of DME was also injected directly into the cylinder as an ignition promoter for the control of ignition timing. Different intake valve timings were tested for combustion phase control. Regular gasoline was tested for HCCI operation and emission characteristics with various engine conditions. With HCCI operation, ignition delay and rapid burning angle were successfully controlled by the amount of internal EGR that was determined with VVT. For best IMEP and low HC emission, DME should be injected during early compression stroke. IMEP was mainly affected by the DME injection timing, and quantities of fuel DME and gasoline. HC emission was mainly affected by both the amount of gasoline and the DME injection timing. NOx emission was lower than conventional SI engine at gasoline lean region. However, NOx emission was similar to that in the conventional SI engine at gasoline rich region. CO emission was affected by the amount of gasoline and DME.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3383-3388
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• 2007

To compare the sensor performance of AE leak diagnosis system which can measure valve leak conditions, AE activities such as RMS voltage level, AE signal trend, leak rate degree according to AE database, FFT spectrum were measured on valve of the simulated test system for power plant. AE activities were recorded and analyzed from various operating conditions including different temperature, pressure difference, valve size and fluid using both piezoelectric acoustic emission sensor and Pb-Free acoustic emission sensor. The results of this 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 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.

• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.173-181
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• 2007

Radiated emission / susceptibility performance of the KSLV-I 2nd stage which are controlled from the unit level to the system level should be examined and managed all over the frequency ranges in order to ensure the normal operation of the SC, the 1st stage of the KSLV-I, ground support equipments which are installed at the space center, and other wireless communication networks. Not only unintentional electric field emissions from the KSLV-I system and its subsystems should be restricted to the levels less than the limits specified in the EMC requirements, but also proper test and evaluation method should be established, respectively. In this paper, radiated emission/susceptibility test limits, method, and test results of the KSLV-I 2nd stage engineering model are presented.