• The Journal of the Acoustical Society of Korea
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• v.24 no.2
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• pp.87-96
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• 2005

In matched field processing (MEP), the observed acoustic field data is basically correlated with the replica produced by the modeling. therefore the results of source localization and correlation is limited by the mismatch of the environment and sensor location. In this paper. the effects of mismatch in environment and system on the bias in estimating the source location are investigated in the context of source localization. In the Pekeris waveguide, the simulation shows that the mismatches in environment and system, can cause a significant biases in the source localization and a degradation in MFP correlation. Mismatch caused by uncertainties in array tilt and depth, bottom depth, bottom sound speed, etc. causes degradation in source localization performance.

• The Journal of the Acoustical Society of Korea
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• v.23 no.2
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• pp.134-145
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• 2004

The study aims to develop the underwater wireless telephone system. The system is designed based on the underwater acoustic communication channel parameters such as ambient noise, multipath effect and diver breathing noise. The system adopts SSB modem and its carrier frequency is about 33 kHz in which ambient noise level is low and therefore a high S/N ratio is easily obtained. The source level of the transmitter is designed as 131 dB re 1μPa. Its intelligibility index of sentence shows as 80% or mure in the range of less than 300m in the sea trial.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.27 no.2
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• pp.84-94
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• 2013

In case when the existing TRIAC phase controlled dimmer is drove for the LED lighting equipments, there are many problems such as the LED flicker in low phase-angles, the acoustic noise and elements damage by increase of the peak voltage in the input filter capacitor, mulfunction by insufficiency of the TRIAC holding current, and the abnormal oscillation by LC resonant. In this paper, we proposes the single-stage quasi-resonant PSR(Primary Side Regulation) PWM converter, and the design, the simulation and experiment are performed. As a result, it could confirm that the proposed PWM converter is the lighting equipments for LED drive which can alternate the existing 60W class incandescent bulbs and it has the high drive performance of the efficiency 80% and over, the power factor 0.95 and over under the normal voltage 220V. Finally, total harmonic distortion(THD) is gratified with a standard[1] of the lighting equipments and the durability is evaluated as the high reliablilty of 150,000 hours and over.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.252-257
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• 1988

This paper discribes an improved technique for locating partial discharge sites within operating transformers by ultrasonic method which utilizes the different travel times of the electrical and ultrasonic signals produced by partial discharges to determine the location of the sources. The technique was to develope the measurement system based on the enhancement of the acoustic emission signals using signal square, circuit to improve the detectable sensitivity and reliability. Also an ultrasonic pulse generator was designed and made to transmit periodically pulses equivalent to pratial discharges and to check the good performance of the system, echo effects and self-diagnosis. Through the laboratory work, it was confirmed that the system and the generator can be used satisfactorily for diagnosing power transformers and for studying echo effects and self-diagnosis of the system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.888-891
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• 2000

Drilling is one of the most important operations in machining industry and usually the most efficient and economical method of cutting a hole in metal. From automobile parts to aircraft components, almost every manufactured product requires that holes are to be drilled for the purpose of assembly, creation of fluid passages, and so on. It is therefore desirable to monitor drill wear and hole quality changes during the hole drilling process. One important aspect in controlling the drilling process is drill wear status monitoring. With the monitoring, we may decide on optimal timing for tool change. The necessity of the detection of tool wear, fracture and the abnormal tool state has been emphasized in the machining process. Accordingly, this paper deals with the cutting characteristics of the hot-rolled high strength steels using common HSS drill. The performance variables include drill wear data obtained from drilling experiments conducted on the workpiece. The results are obtained from monitoring of the cutting force and Acoustic Emission (AE) signals, and from the detection of the abnormal tool state with the computer vision system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.6B
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• pp.1106-1113
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• 2000

In this, paper, a DFT based polyphase filter bank for the fractional ratio oversampling is proposed. Proper fractional oversampling ratio gives lower aliasing than the critical sampling and, at the same time, lower computational load than the integer ratio oversampling. In addition, filter bank design becomes easier by the reduced aliasing effect of fractional ratio oversampling. Proposed fractional ratio oaversampling polyphase structure is applied to a subband adaptive filter for acoustic echo cancellation where long adaptive filter are ofter required. Echo cancellation results show that fractional ratio oversampling gives comparable performance to the integer ratio oversampling with less computational load.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.3
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• pp.239-246
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• 2003

Brushless D.C. Motor is widely used for industrial application because of high efficiency and high power density. Especially, in home appliance, BLDCM is very useful due to high control performance and low acoustic noise. In this paper, BLDCM and its controller are designed and developed for tread mill application. With the restricted stator structure, permanent magnet rotor is designed for manufacturing and cost effectiveness using CAD and FEM analysis. A ferrite magnetic material is used as a rotor magnet for the cost and temperature advantages. For a stable operation of tread mill, over current and temperature can be detected and protected. The designed BLDCM and its controller was verified by the experimental results.

• Electrical & Electronic Materials
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• v.9 no.6
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• pp.564-571
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• 1996

We calculated the drift-velocities of electrons and holes of I $n_{0.53}$(A $l_{x}$G $a_{1-x}$ )$_{0.47}$As, which is used for semiconductor materials of high performance HBTs, along with the various doping concentrations and Al mole fractions as well as the electric fields by Monte Carlo experiment. Especially, for the valence bands the accuracy of hole-drift-velocity was improved in the consideration of intervalley scattering due to the inelastic scattering of acoustic phonon. From the results the empirical formulas of the low- and high field mobility of electrons and holes were extracted by using nonlinear least square fitting method. The accuracy of the formulas was proved by comparing the formula of low-field electron mobility as well as drift-velocity of I $n_{0.53}$ G $a_{0.47}$As and of low-field hole mobility of GaAs with the measured values, where the error was below 10%. For the high-field mobilities of electron and hole the results calculated by the formulas were very well matched with the MC experimental results except at the narrow field range where the electrons produced the velocity overshoot and the corresponding error was about 30%.0%. 30%.0%.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.49-52
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• 2006

should be in English, A make out an economical, reliable and easy to adoptable instrument in turbine discharge measurement was restricted from lots of it's foundational condition. Not with standing the brilliant progress in new technology of these day, useful instrument for flow measurement in turbine is still ongoing. Nowaday, the increasing importance of renewable energy makes it more important that the measuring turbine efficiency as a decision making index of old turbines' replacement. In Turbine performance diagnosis, Kwater(Korea Water Corporation) got an enough ability and decent reputation for who has invested lots of time and effort for buildup and development. In Korea as a public corporation who should take a crucial roll in Turbine business, Kwater has introduced some developed new technology for other domestic concerned one. With this writing, I'd like to introduce ASFM system as a newly developed instrument that can cope with lots restriction in discharge measurement in turbine. Kwater adopted the system in 2005, and performed 2 times of trial test. The test result was good enough to use the system as a reference test method.

• Journal of Mechanical Science and Technology
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• v.18 no.2
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• pp.272-285
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• 2004

The losses at off-design points from a compressor cascade occur due to the deviation from a design incidence angle at the inlet of the cascade. The self-noise from the blade cascade at off-design points comes from a separated boundary layer and vortex sheddings. If the incidence angle to the cascade increases, stalling in blades may occur and the noise level increases significantly. This study applied Large-Eddy Simulations (LES) using deductive and deductive dynamic SGS models to low Mach-number, turbulent flow with each incidence angle to the cascade ranging from -40$^{\circ}$ to +20$^{\circ}$ and compared numerical predictions with measured data. It was observed that the oscillating separation bubbles attached to the suction surface do not modify wake flows dynamically for cases of negative incidence angles. However, an incidence angle greater than 8$^{\circ}$ caused a separated vortex near the leading edge to be shed downstream and created stalling. The computed performance parameters such as drag coefficient and total pressure loss coefficient showed good agreement with experimental results. Noise from the cascade of the compressor is summarized as sound generated by a structure interacting with unsteady, turbulent flows. The hybrid method using acoustic analogy was observed to closely predict the measured overall sound powers and directivity patterns at design and off-design points of blade cascade.