• Proceedings of the KIEE Conference
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• 1990.11a
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• pp.10-14
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• 1990

Variable Structure System(VSS) la being extended to a new control system of ac servo machines for its merits of simple mechanism and robustness. This paper has studied about applying VSS to position control for brushless servo motor. But VSS has the chattering problem of control input. This chattering phenomenon cause acoustic noises, torque ripple and increase harmonics of the current. One of the useful way to eliminate this defect of VSS, linearlizing the switching function is discussed here. Though the conventional method of linearizing the switching function diminishes the chattering, it may degrade the robustness of the system. In this paper, new linearized switching function which shows robust performance to the parametric variation and reduces chattering simultaneously is introduced and assured by simulation.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.4 no.2
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• pp.31-37
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• 1995

This study is focused on the prediction of appropriate tool life by clarifying the correlation between progressive tool wear and AE signal. when rcutting SM45C by End mill in machining center. First of all, end mill have a problem that position of sensor sticking because it is revolution tool, but I think that it can be bained specific character according to sticking Sensor in the Vise. Consequently, the following results have been obtained; 1. Each cutting speed of feed rate over 0.1mm had a tendency to increase linearly according to the RMSAE 2. The level of AE signal at the same cutting area was more sensitive to depth of cut tharn the variation of feed rate 3. In the range of cutting duringqr about 75minqr atqr cutting speed 27m/min flankqr wear turns up aboutqr 0.21mm, aboutqr 0.29mm in the caseqr of about 65minqr at 33/min, qr hereby RMSAE increased rapidly at 0.2mm flank wear, also AE-HIT and CUM-CNTS.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.5 no.1
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• pp.38-43
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• 1994

Though normal vocal cords show regular vibration, pathologic vocal cords show irregularity between peaks. Jitter means fluctuation in the time interval between peaks, and Shimmer means cycle to cycle variation in the amplitude of the peaks. We investigated the vocal vibration of Korean normal persons objectively. The fundamental frequency, Jitter, Shimmer and SNR(signal to noise ratio) of normal persons were compared with that of vocal Polyp Patients with CSpeech Program for the possibility of distinguishing the pathologic vocal vibration from normal. The results were as follows ; Comparing the fundamental frequency of vocal Polyp Patients with normal persons, great change was noted only in female cases. But the Jitter and Shimmer of vocal polyp patients were greater than normal significantly in both male and female cases. SNR was lower than normal in vocal polyp patients. In the conclusion, fundamental frequency, Jitter, Shimmer and SNR might be meaningful parameters distinguisuing pathologic vibration from normal.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.516-519
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• 2005

The pilot tidal current power plant is to be constructed at the Uldolmok between Chindo and Haenam, during next year. and extensive coastal engineering research works have been carried out. In this paper we describes some observation results of the tide and tidal current. as well as modeling work in order to investigate the tide and tidal current regime change in relation to the tidal current power plant (TCPP) construction. The special modeling skill in order to consider the turbine operation in the TCPP is developed and applied to the estimation for the flow regime change by the simple layout of the tidal current power plant.

• MALSORI
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• v.68
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• pp.1-15
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• 2008

This study investigated the vowel effect on laryngeal DDK (L-DDK) in terms of rate, regularity, and range. Thirteen normal speakers participated in this experiment. Speakers were asked to repeat the vowels /a, e, i, o, u/ for vocal fold adduction DDK, and /ha, he, hi, ho, hul for vocal fold abduction DDK. Acoustic data was analyzed via Motor Speech Profile. There were 6 parameters: DDKavp and DDKavr for rate of L-DDK, DDKcvp and DDKjit for regulariry of L-DDK, and DDKavi and DDKcvi for range of L-DDK. Results of MANOVA and Fredman analysis showed no significant vowel effect on rate and regularity of L-DDK. MANOVA revealed significant effects of vowels and vocal fold ab/adduction on range of L-DDK. DDK peak intensity (DDKavi) in vowel /i/ production was lower than in vowels /a, e, o, u/. Variation of DDK peak intensity (DDKcvi) was significantly greater for /ha/ than for /a/ production. The implication of these findings on voice and speech pathology is discussed.

• 유체기계공업학회:학술대회논문집
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• 1998.12a
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• pp.115-120
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• 1998

Aerodynamic noise generated by automobile cooling fan is investigated. Automobile cooling fans radiate both discrete frequency noise as well as broadband noise. In the present work, the former is considered through free-wake panel method coupled with acoustic analogy fully considering the retarded time variation on the blade surface, while the latter is taken into account by three well-established broadband noise components. Experiments were performed to supplement necessary inputs as well as to provide the final comparison with the predicted noise spectrum. The predicted noise levels at blade passing frequencies agree well with the experimental data for the first few harmonics. Although the predicted broadband noise levels at higher frequencies fall below the experimental data due to the fundamental shortcomings of the utilized formulations, the analysis offers a detailed physical understanding of the fan noise generation processes.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.12
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• pp.156-163
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• 2010

The brushless motor is getting widely applied to the automotive component with the advantage of the high efficiency, high reliability and etc.. Most of the motor applications require the low vibration and acoustic noise. The cogging torque is the one of the main cause of the noise and vibration. The step-skewed rotor is used to reduce the cogging torque. We analyze the characteristics of the step-skewed rotor and non skewed rotor with the same stator by using 2-dimensional FEM. And then we analyze the characteristics variation according to the rotor eccentricity. The prototype is made and tested. As the results, the step-skewed rotor structure reduce the cogging torque and local radial force but it is more sensitive to rotor eccentricity.

• Ocean Science Journal
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• v.41 no.3
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• pp.175-179
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• 2006

The Ieodo Ocean Research Station(IORS) is an integrated meteorological and oceanographic observation base which was constructed on the Ieodo underwater rock located at a distance of about 150 km to the south-west of the Mara-do, the southernmost island in Korea. The underwater ambient noise level observed at the IORS was similar to the results of the shallow water surrounding the Korean Peninsula (Choi et al. 2003) and was higher than that of deep ocean (Wenz 1962). The wind dependence of ambient noise was dominant at frequencies of a few kHz. The surface current dependence of ambient noise showed good correlation with the ambient noise in the frequency of 10 kHz. Especially, the shrimp sound was estimated through investigations of waveform and spectrum and its main acoustic energy was about 40 dB larger than ambient noise level at 5 kHz.

• New & Renewable Energy
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• v.1 no.2 s.2
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• pp.73-78
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• 2005

The pilot tidal current power plant is to be constructed at the Uldolmok between Chindo and Haenam, during next year, and extensive coastal engineering research works have been carried out. In this paper we describes some observation results of the tide and tidal current, as well as modeling work in order to investigate the tide and tidal current regime change In relation to the tidal current power plant [TCPP] construction. The special modeling skill in order to consider the turbine operation in the TCPP is developed and applied to the estimation for the flow regime change by the simple layout of the tidal current power plant.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2003.07a
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• pp.232-237
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• 2003

Sound has been rated negatively in many industrial areas as the noise to be removed. In the agricultural process such as rice milling based on grinding the surface of the rice, however, it may be anticipated that the sound can contain the some information on the process. In this research, on the assumption that variation of the shape of the rice kernel during milling may bring the change in frequency characteristic of sound signal, we tried to investigate the relationship between the milling degree in the grinding test mill and the resonance and anti-resonance frequencies (the frequencies at which the sound power has the extreme values). (omitted)