• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.3
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• pp.125-132
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• 2007

The purpose of present paper is to investigate a fracture characteristics of the finite-width single-edge-notch(SEN) carbon fiber/epoxy reinforced plastics(CFRP) plates by using an acoustic emission(AE). Uni-directionally oriented 10 plies CFRPs specimen which had different notch length were prepared for monotonic tensile test. Matrix cracking appeared over whole testing process and fiber breaking appeared later on mainly Load distribution factor of the matrix confirmed that increased according as increases of plate width ratio. The amplitude distribution of AE signal from a specimens is an aid to the determination of the different fracture mechanism such as matrix cracking, disbonding, interfacial delamination, fiber pull-out, fiber breaking, and etc. In the result of AE amplitude distribution analysis, matrix cracking, fiber disbonding or interfacial delamination, and fiber pull-out or fiber breaking signal correspond to <65dB, <75dB, and <90dB respectively, Also, changes of the slope of cumulative AE energy represented crazing phenomena or degradation of materials.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.1
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• pp.106-113
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• 2011

In this paper, the non-resonant SWG(Slotted Waveguide) antenna with double slots in narrow wall of rectangular waveguide is designed. Because energy radiated from each slot depends upon inclination angle of slot of the designed antenna, inclination angle of each slot is controlled to satisfy the amplitude distribution for required sidelobe level. Instead of the conventional extraction method of slot conductance, this amplitude distribution is made by the proposed method, which employs far-field radiation pattern calculated by Fourier transform of aperture field distribution on slot. The non-resonant double SWG antenna is designed by the proposed method and is manufactured. The antenna performances are measured and compared with the simulated results.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.2
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• pp.105-111
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• 2016

Ultrasonic metal welding, unlike the conventional welding techniques, does not require an external heat source, welding rod, or filler metal. Therefore, ultrasonic metal welding is not only economical but also environment-friendly, and hence, it has been receiving much attention. In ultrasonic welding, heat is generated because of the plastic deformation and the friction between both surfaces of the welded materials. It is important to identify the heat-affected zone by measuring the temperature generated at the weld. In this study, the effects of the welding pressure, welding time, and vibration amplitude on the temperature distribution in the weld were evaluated by performing a transient thermal analysis of the heat generated during ultrasonic metal welding. The experimental results indicated that the temperature of the weld tends to increase with the welding time and vibration amplitude. However, an increase in the pressure does not affect the temperature of the weld largely.

• Journal of Korean Ophthalmic Optics Society
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• v.7 no.2
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• pp.55-60
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• 2002

In this paper, we investigate the MTF in image plane using the shifted magnitude, the shifted direction, and the astigmatism as the real amplitude distribution of incident beam in an optical system is shifted. The shifted magnitudes of incident beam are 0.0, 0.25, 0.5 and 0.75 and the shifted directions of incident beam are 0 and ${\pi}/2$. We also consider the optical system having the astigmatism which are $0.0{\lambda}$, $0.25{\lambda}$, $0.5{\lambda}$, and $0.75{\lambda}$. As the shifted magnitude of the real amplitude distribution of incident beam increases, the MTFs of sagittal and tangential direction in an optical system having an aberration free decrease, but that in an optical system having the astigmatism which is $0.75{\lambda}$ and the shifted direction of incident beam which is ${\pi}/2$ increases. We know from these results that the shift of the real amplitude distribution of the incident beam in an optical system compensates the effect of astigmatism as the shifted direction of that in an optical system is ${\pi}/2$, and Stiles-Crawford effect having the shifted real amplitude distribution of incident beam in pupil area is minimized the effect of astigmatism for eye.

• MALSORI
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• no.66
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• pp.1-20
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• 2008

The purpose of this study was to investigate the characteristics of fundamental frequency(F0) and amplitude distributions in persons with cerebral palsy(CP) in the reading task. Participants were divided into three groups: 6 persons with spastic CP, 6 persons with athetoid CP and 6 normal persons who are around 15-20 years old. On the results of this study, firstly, in F0 distributions, most of the spastic CPs tended to appear narrow distributions on the basis of mode, but most of the athetoid CPs were opposite, and both of the CP groups tended to distribute highly on lower and higher frequencies than mean and mode. On the other hand, normal persons had a tendency to appear narrow distributions on the basis of mode. Finally, in amplitude distributions, the spastic CPs showed a tendency that there are little differences between the distribution of mode and the others, and most of the athetoid CPs showed a tendency that the distributions of mode were higher than the others. In addition to, the normal persons had a tendency that the distributions of mode were remarkably higher than both of the CP groups.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.32 no.4
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• pp.402-410
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• 1996

Recently carbon fiber reinforced plastic(CFRP) has been used structural materials in corrosive environment such as for water, chemical tank and chemical pipes. However, mechanical properties of such materials may change when CFRP are exposed to corrosive environment for long periods of time. Therefore, it is important to understand the effect of moisture absorption on mechanical properties of the CFRP. In this study, degradation behavior of immersed carbon fiber/epoxy resin composite material was investigated using acoustic emission(AE) technique. Fracture toughness test are performed on the compact tension(CT) test specimens that are pilled by two types of laminates $[0^{\circ}_2$/$90^{\circ}_2]_3s$ and $[0^{\circ}_2$/$90^{\circ}_2]_6s$During the fracture toughness test, AE test was carried out to monitor the damage of CFRP by moisture absorption. In spite of the change of moisture absorption rate, the fracture toughness of CFRP was not change. As immersion time increased, AE event count numbers decreased in low amplitude range of AE for amplitude distribution histogram. The event in low amplitude range was known to be generated by debonding of matrix-fiber interface. Therefore, decrease of AE event count numbers in low amplitude range represents that debonding of matrix-fiber interface which was probably generated by moisture absorption.

• Journal of Electrical Engineering and Technology
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• v.13 no.5
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• pp.2050-2058
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• 2018

Impulse characteristic of transmission tower grounding grid is needed for lightning protection of transmission line. This paper describes an outdoor experimental test facility established for large-scale grounding grid of transmission tower, made up of four impulse current generators and a circle current return electrode. The amplitude of impulse current is up to 100 kA. The results of the CDEGS simulation and GPR measurement reveal the uniform current distribution in the test arrangement. An impulse test for a square electrode with extended conductors is carried out in condition of three current waveforms with different amplitude. Based on the electrical network model and iterative algorithm method, a calculation model is proposed to simulate the impulse characteristic of large-scale grounding grid considering soil ionization. The curve of impulse resistance against the current amplitude shows the soil ionization both from the simulation and test. Deviation between the simulation and test result is less than 15%.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.7 no.4
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• pp.26-33
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• 1993

The acoustic emission automatic detection system is developed to observe tree deterioration phenomena. Applying an alternating voltage of 15(kVnns) toXLPE tree specimens, many pulses of small amplitude are detected when the bush type tree developes branch type and a few pulses of high amplitude prcxluced as branch type propagated to bush type tree. Therefore, it is known that pulses having small amplitude operates as a destructive factor. It is observed that the skewness of the amplitude and the number of average pulses as distribution tendency of three dimension are characteristic quantity of AE pulses. As the trajectory of skewness is farther from the origin on the S-plane, it is more likely to breakdown.

• Wind and Structures
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• v.18 no.6
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• pp.693-715
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• 2014

Stochastic processes are used to represent phenomena in many diverse fields. Numerical simulation method is widely applied for the solution to stochastic problems of complex structures when alternative analytical methods are not applicable. In some practical applications the stochastic processes show non-Gaussian properties. When the stochastic processes deviate significantly from Gaussian, techniques for their accurate simulation must be available. The various existing simulation methods of non-Gaussian stochastic processes generally can only simulate super-Gaussian stochastic processes with the high-peak characteristics. And these methodologies are usually complicated and time consuming, not sufficiently intuitive. By revealing the inherent coupling effect of the phase and amplitude part of discrete Fourier representation of random time series on the non-Gaussian features (such as skewness and kurtosis) through theoretical analysis and simulation experiments, this paper presents a novel approach for the simulation of non-Gaussian stochastic processes with the prescribed amplitude probability density function (PDF) and power spectral density (PSD) by amplitude modulation and phase reconstruction. As compared to previous spectral representation method using phase modulation to obtain a non-Gaussian amplitude distribution, this non-Gaussian phase reconstruction strategy is more straightforward and efficient, capable of simulating both super-Gaussian and sub-Gaussian stochastic processes. Another attractive feature of the method is that the whole process can be implemented efficiently using the Fast Fourier Transform. Cases studies demonstrate the efficiency and accuracy of the proposed algorithm.

• The Journal of the Acoustical Society of Korea
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• v.19 no.2
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• pp.46-53
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• 2000

In coastal bay waters, bubbles are generated by relatively heavy ship-traffic, breaking waves due to man-made structures and biological activities. Therefore, the bubble-generating mechanism as well as the bubble density distribution in the bay are quite different from the open ocean where breaking waves are major contributor for bubble density distribution. High frequency surface-backscattered signals were obtained in the coastal bay waters and they were analyzed to compare with those from the open waters in terms of the sea-surface backscattering strength at various grazing angles, the reverberation characteristics in the sub-surface layer and spectral spreading of the scattered signals. The results show that, the surface scattered signals have an irregular distribution of amplitude in time and the width of the spectral spreading is wider than that of the open sea with rough surface. Furthermore, the amplitude distribution of the reverberation signals is not following the Rayleigh distribution, that is eon to be a typical pattern for the open ocean. The results of our analysis imply that the bubble size and the bubble density in the bay are quite different from those observed in the open waters.