• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.4 s.109
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• pp.319-328
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• 2006

This paper presents a method for analysis of the mechanical behavior of a crankshaft in a four-cylinder internal combustion engine. The purpose of the analysis was to study the characteristics of the shaft in which the pin and arm parts were assumed to have a uniform section in order to simplify the modal analysis. The results of natural frequency transfer function and mode shape were compared with those obtained by experimental work. The results obtained from the comparison showed a good agreement with each other and consequently verified the analysis model. Furthermore, a prediction of crankshaft characteristics under the firing condition, by using the model, was performed. This study describes a new method for analyzing the dynamic behavior of crankshaft vibrations in the frequency domain based on the initial firing stages. The new method used RMS values to calculate the energy at each bearing journal and counter weight shape modification under the operating conditions.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.2
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• pp.45-53
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• 2002

This paper presents an algorithm for the appropriate parameter selection of a power system stabilizer and power converters in two-area power systems with a series HVDC links. The method for PSS is one of the classical techniques by allocating properly poly-zero positions to fit as closely as desired the ideal phase lead and by changing the gain to produce a necessary damping torque. Proper parameter of power converters are obtained in order to have sufficient speed and stability margin to cope with changing reference values and disturbances based on the Root-locus technique. The small signal and transient stability studies using the PSS and power converters parameters obtained from these methods show that a natural oscillation frequency of the study case system is adequately damped. The simulation used in the paper was performed by the Power System Toolbox software program based on MATLAB.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.1
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• pp.10-17
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• 2010

The interaction of oblique incident waves with a porous dual semi-cylindrical structure is investigated under the assumption of linear potential theory. The porous dual semi-cylindrical structure consists of two concentric bottom-mounted cylindrical structures that are porous in front half and transparent in back half. By changing porosity, gap, and wave characteristics(wave frequencies, incidence angle), the wave blocking performance as well as the wave loads and the wave run-up are obtained. As a convenient measure of overall wave blocking performance, the root mean square(R.M.S.) of the wave elevation in a sheltered region is used. It is found that the porous semi-cylindrical structure may significantly reduce the wave response in a sheltered region and the wave forces decrease largely compared to the impermeable structure. The dual structure is more effective in reducing the wave response in a sheltered region than the mono type in the region of high frequencies.

• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.59-73
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• 2017

Numerical analysis using 3D finite element program (PLAXIS 3D) evaluated the interaction of soil - pile structure under dynamic surface loading. The dynamic p-y curve of the 1-g shaking table experiment by numerical analysis was calculated, and the parametric studies were presented by considering the pile-soil condition, the pile tip condition, and the loading condition. The frequency of 1.4 Hz is almost equal to the natural frequency of the pile - soil system. The p and y values of resonance phenomenon are significantly different from the results of other frequencies. The results can be summarized by a third order polynomial function representing the trend line in the p-y curve. In the case of a single pile, the shape of the dominant curve was found to be an ellipse by mathematical proof. The elliptic equation can be used for the dynamic design or analysis of soil-pile system.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.9-14
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• 2008

In this paper, a new type of Yagi-Uda antenna that operates in the terahertz frequencies is designed. The proposed Yagi-Uda antenna can obtain high input resistance of approximately $2000{\Omega}$ at the resonance frequency by using a full-wavelength dipole instead of a half-wavelength dipole as the driver element. The current leakage into the bias line was minimized by applying the photonic bandgap structure to the bias line. By designing the antenna on a thin substrate, the impedance lowering of an antenna caused by the relative dielectric constant of the substrate was prevented and the end-fire radiation pattern which is the original radiation characteristic of the Yagi-Uda antenna could be obtained. We expect that the proposed Yagi-Uda antenna can achieve increased terahertz output power by improving the impedance mismatching problem with the photomixer.

• The Journal of the Acoustical Society of Korea
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• v.15 no.1
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• pp.46-53
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• 1996

Adaptive LMS algorithm has been used in many application areas due to its low complexity. In this paper input signal is transformed into the subbands with arbitrary bandwidth. In each subbands the dynamic range can be reduced, so that the independent filtering in each subbands has faster convergence rate than the full band system. The DCT transform domain LMS adaptive filtering has the whitening effect of input signal at each bands. This leads the convergence rate to very high speed owing to the decrease of eigen value spread Finally, the filtered signals in each subbands are synthesized for the output signal to have full frequency components. In this procedure wavelet filter bank guarantees the perfect reconstruction of signal without any interspectra interference. In simulation for the case of speech signal added additive white gaussian noise, the suggested algorithm shows better performance than that of conventional NLMS algorithm at high SNR.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.4
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• pp.389-403
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• 2004

This study presents the structural model modification based on the modal data such as natural frequencies and mode shapes. Preliminary structural model can be obtained using design drawings and field measurement, and therefore the deteriorated stiffness of a structure and the effect of the boundary conditions are difficult to be evaluated in preliminary analysis model, and the preliminary model can be modified using structural response data including static and/or dynamic characteristics. In this study, the structural model is modified based on the structural modal data using genetic algorithm. Modal testing were carried out for Imjin River Bridge and Hangjoo Bridge, the modal properties were estimated using modal identification techniques, and finally the structural models were updated using genetic algorithm. The modified structural model could give us more reliable structural analysis results and therefore those can be used for structural performance evaluation such as load carrying capacity and seismic capacity.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.5
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• pp.543-548
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• 2006

This paper is to be researched into ozone generation character of Bi-Ti-Si type high dielectric ceramic catalyst discharge tube. And conditions of basic experiment are the outside diameter of discharge tube : 52 mm, the length of discharge tube : 350 mm, the frequence : 900 Hz, the temperature of cooling water : $25^{\circ}C$, quantity of flow : 5, 10, 20 L/min, pressure : 1.2, 1.4, 1.6 atm, and distance of discharge gap : 0.4, 0.6, 0.8 mm. Ozone generation characteristics were measured to consumption power. At quantity of flow : 20 L/min, discharge gap : 0.6 mm, pressure : 1.6, and consumption power : 150 W, Maximum ozone generation efficiency of 175 g/kWh was obtained. And a range of maximum ozone generation efficiency was measured below the flow quantity of 20 L/min at below pressure of 1.6 atm. However, Maximum ozone generation efficiency was measured over the flow quantity of 20 L/min at over pressure of 1.6 atm.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.2
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• pp.1-7
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• 2003

Mode superposition method(MSM) is the most commonly used for solving linear response problems of structural dynamics. The major advantage of MSM is that usually a small number of lower mode is sufficient to analysis the response. However, the convergence is slow and many modes would be needed to give an accurate MSM in large structure with many degrees of freedom. The inaccuracies of MSM are caused by mode truncation in the solution. These demerits can be overcome by use of the mode acceleration method(MAM). Example analyses are carried out in simple beam subjected to harmonic loadings and compared the convergence of the joint displacements by the two methods. For relatively low frequency loadings, a good results was obtained by the lowest one mode in MAM, so the method is more economic in numerical analysis on an accurate solution.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.8
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• pp.1-8
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• 2000

We have achieved a high aspect ratio track-following microactuator (TFMA) which is capable of driving 0.3 ${\mu}m$ magnetic head for hard disk drive (HDD). it was fabricated on silicon on insulator (SOI) wafer with 20 ${\mu}m$ trick active silicon and 2 ${\mu}m$ thick thermally grown oxide and piggyback electrostatic principle was used for driving TFMA. The first vibration mode frequency of TFMA was 18.5 kHz which is enough for a recording density of higher than 10 Gb/in$^2$. Its displacement was 1.4 ${\mu}m$ when 15 V dc bias plus 15 V ac sinusoidal driving input was applied and its electrostatic force was 50 N. The fabricated actuator shows 7.51 dB of gain margin and 50.98$^{\circ}$ of phase margin for 2.21 kHz servo-bandwidth.