• Journal of Advanced Marine Engineering and Technology
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• v.38 no.1
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• pp.70-77
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• 2014

In this work, we studied basic characteristics of transmission lines employing various PSS (periodic strip structure) on silicon substrate for application to a miniaturization of RF components. According to the results, the transmission lines employing various PSS showed wavelength shorter than conventional coplanar waveguide due to their strong wave characteristics. Especially, with-contact structure was most effective for a miniaturization of RF component. Concretely, the size of the transmission line employing with-contact was only 4.39 % of the conventional coplanar waveguide, According to the bandwidth extraction result, the bandwidth of the transmission lines employing various PSS structures were wider than 384 GHz. Above results indicate that the transmission lines employing various PSS can be effectively used for application to a broadband and miniature RF component, and especially, with-contact is most effective for a miniaturization of RF components.

• Smart Structures and Systems
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• v.15 no.2
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• pp.283-297
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• 2015

Jacket-type offshore structures are always exposed to severe environmental conditions such as salt, high speed of current, wave, and wind compared with other onshore structures. In spite of the importance of maintaining the structural integrity for an offshore structure, there are few cases to apply a structural health monitoring (SHM) system in practice. The impedance-based SHM is a kind of local SHM techniques and to date, numerous techniques and algorithms have been proposed for local SHM of real-scale structures. However, it still requires a significant challenge for practical applications to compensate unknown environmental effects and to extract only damage features from impedance signals. In this study, the impedance-based SHM was carried out on a 1/20-scaled model of an Uldolmok current power plant structure in Korea under changes in temperature and transverse loadings. Principal component analysis (PCA)-based approach was applied with a conventional damage index to eliminate environmental changes by removing principal components sensitive to them. Experimental results showed that the proposed approach is an effective tool for long-term SHM under significant environmental changes.

• Journal of Biomedical Engineering Research
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• v.25 no.3
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• pp.227-233
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• 2004

In this paper, it is proposed that the four channel electrode arrangement at a frontal lobe and the noise reduction method using a JADE for the EEG biofeedback system. The proposed electrode arrangement is based on the retina-cornea dipole model. Using JADE and signals which are acquired by the proposed arrangement, four independent components are separated. To estimate a pure EEG component among four components, it is measured that a ratio of alpha wave to the whole signal and then the component that has a maximum value is considered as a pure EEG which the noise is eliminated. As a result of experiments, the proposed methods are effective in reduction of noises during acquisition of the EEG.

• The KSFM Journal of Fluid Machinery
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• v.19 no.6
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• pp.43-49
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• 2016

A performance analysis of a gasoline engine with a 2-stage turbocharger system for unmanned aerial vehicle(UAV) was conducted. One dimensional system analysis was conducted for the requirements of turbochargers and adequate turbochargers were selected from commercially available models for automobiles. Modeling and simulation were performed by Ricardo WAVE. Gasoline engine modeling was based on a 2.4 L 4-cylinder engine specification. The selected turbochargers and intercoolers were added to the engine model and simulated at 40,000 ft altitude condition. The results of the engine model and 2-stage turbocharger system model simulation showed break power 93 kW which is appropriate power required for the engine operation at the ambient conditions of 40,000 ft altitude.

• Journal of Korea Multimedia Society
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• v.20 no.10
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• pp.1662-1670
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• 2017

A-Scan NDT equipment is widely used in the industrial field because it is inexpensive and easy to carry but it is necessary to have a skilled inspection specialist who is trained to analyze the waveform of ultrasonic signal. Since the welding quality is judged subjectively by the specialist, there is a problem in the reliability of the quality. In the C-Scan NDT which overcomes the shortcomings of the A-Scan, welding part can be represented in the form of two dimensional image by combining one dimensional ultrasonic waveform so that the quality of welding can be grasped without the help of specialist. In order to develop C-Scan NDT, it is necessary to develop an array type two dimensional transducer and an algorithm to composing image by combining ultrasonic signals generated from a two dimensional transducer. In addition, the noise component must be minimized in the ultrasonic signal in order to display the quality of welding in the form of images. Therefore we propose a method to remove noise component from the ultrasonic wave and construct a two dimensional ultrasonic image.

• Journal of the Korean Institute of Telematics and Electronics
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• v.9 no.2
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• pp.17-23
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• 1972

In this paper, the radiation characteristics of a large circular loop antenna with sinusoidal current distribution is studded in a moving media with a constant velocity much less than the speed of light. The diameter of the circular loop antenna is comparable with or larger than wave length. In studing the radiation characteristics, vector potential for the antenna is derived and relative field pattern is plotted from the vector potentials. Finally the field patterns are compared with those of stationary media. It is found that maximum directivities are shifted to the direction of the velocity of the media, and the field intensities are decreased in that direction and increased in opposite direction by the velocity component paralell to the loop plane. It is also found that the deviations for the pattern are proportional to the velocity of the media, the frequency of the distributed current, the diameter of the loop antenna, and the daviation depends only upon the parallel component of the velocity to the loop plane.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.8
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• pp.1599-1605
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• 2012

We introduced an approach of modeling of a sound absorbing medium that had different absorbing coefficient according to frequency. To obtain the time domain result of the frequency characteristics of a sound absorbing medium, transmission line matrix modeling was used. To input sound absorbing effect in TLM modeling, we added a FIR filter at a node instead of absorbing component using resistance component. There were simulated the characteristics of time-shift, low pass filter, high pass filter using the FIR filter with 7-tap coefficients, then compared with theoretical results. From various simulation results, we could find that added FIR filter coefficient in TLM modeling was an useful way to model a sound absorbing medium.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.2
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• pp.92-104
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• 1993

In the present study, the velocity profiles and entrance length of developing transitional pulsating flows are investigated both analytically and experimentally in the entrance region of a square duct. The systems of conservation equations for transitional pulsating flows in a square duct are solved analytically by linearizing the non-linear convective terms. Analytical solutions are obtained in the form of infinite series for velocity pofiles. The experimental study for the air flow in a square duct(40mm*40mm*4000mm) is carried out to measure velocity profiles and other parameters by using a hot-wire anemometer with a data acquisition and processing system. The distribution of velocity profiles( $u_{ps}$ / $u_{m,ta}$) in the decelerating period is higher than in the accelerating period. The distribution of the axial component of the axial component of velocity in the transitional flow is nearly uniform in the central region of the duct, and decrease rapidly near the wall. The entrance length correlation of the transitional pulsating flows in a square duct is obtained to be $L_{e}$/ $D_{h}$=0.83 $A_{1}$R $e_{ta}$ /(.omega. sup+1)$^{2}$TEX>

• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.209-214
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• 1999

A field experiment generating shear waves by trench method was conducted at two places in Taejun area. We were able to separate the P- and S-waves by summing and subtracting the vertical and horizontal component of the data recorded at a three component downhole geophone in the borehole. The analysis of the records revealed that the shear waves were polarized to NS and EW directions. The faster shear waves were polarized to NS direction. The NS direction generally agrees with the dominant joints direction observed from the cores collected from the borehole.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.228-240
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• 1991

Many experimental data of fatigue crack propagation show that the fatigue crack propagation process is stochastic. Therefore, the study on the crack propagation must be based on the probabilistic approach. In the present paper, fatigue crack propagation process is assumed to be a discrete Markov process and the method is developed, which can evaluate the reliability of the structural component by using Markov chain model(Unit step B-model) suggested by Bogdanoff. In this method, leak failure, plastic collapse and brittle fracture of the critical component are taken as failure modes, and the effects of initial crack distribution, periodic and non-periodic inspection on the probability of failure are considered. In this method, an equivalent load value for random loading such as wave load is used to facilitate the analysis. Finally some calculations are carried out in order to show the usefulness and the applicability of this method. And then some remarks on this method are mentioned.