• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1416-1417
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• 2007

The high frequency pulsed power system is widely available for use in high frequency generator applications. We designed and fabricated our own high frequency pulsed power system to obtain very sort pulse width and high peak value and investigated microbe removal characteristics using it. This paper introduces a simple high voltage high frequency pulsed power system for removing various bacteria caused by dirty water. This system include power supply circuit, switching MOSFET, and flyback converter. We can also control the switching using a PIC one chip microprocessor. As a result, we can obtain good removing characteristics of various bacteria by adjusting the charging voltage, the pulse repetition rate and the electrical field inducing time.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.957-959
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• 2005

A noise reduction equipment in power systems was device combined in a passive element such as the form of L, R and C. A analysis of frequency characteristics for the transformer models shall be considered the additional capacitance between the windings($C_{ps}$), terminals($C_s$), and winding-ground($C_g$). A noise in transformer is modeled by take account into the different frequency. In case of the high frequency, transformer windings with stray capacitance have lower impedance. Therefore a noise is transferred from primary winding to secondary winding. Noise Cut Transformer(NCT) was the noise reduction device and was normally single phase two-winding type transformer. We analyzed frequency characteristics using the nodal network analysis with the equivalent circuit and the simulation of the MATLAB.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.682-685
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• 2005

In this research, how the evaluation of the spacial image influenced by the environmental friendly elements included in the visual information, and how the selection of the sound changed depending on the characteristics of spatial image by the 40 subjects were carried out. Vast tracts of green land and the waterfront were highly preferred and impressive than the other spaces. The green music, signal with water sound and bird chirping sound were highly scored. In the frequency characteristics of the factors, the first factor was artificial sound(high at the low frequency band), the second was natural sound(uniform at all frequency band) and the third was water sound(high at the middle and high frequency band over 500Hz). This shows that the proposal of the sound which has the frequency characteristics fit to the spacial image should be selected for the soundscape of the target space.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.256-262
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• 1997

The characteristics of the unstable impinging circular jet were investigated based on the frequency characteristics and the sound field of the impinging-tones. Two symmetric modes Si and S2, associated with low frequency and high frequency respectively, and one helical mode H have been observed by measuring frequency and phase-distribution around the jet. Radiation characteristics of impinging-tone were studied by measuring axial directivity. It was founded that the radiation patterns of symmetric and helical mode are different and it is toward the plate as the impinging distance increased. By estimating the convection velocity of the unstable jet, it was founded that the convection speed decreases with the frequency and its decreasing pattern varies with unstable modes S1, S2 and H, respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.402-407
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• 1997

For cylindrical shells, the closed-form solutions are limited only to the cases with special boundary and/or loading conditions. Though the finite element method is certainly a powerful solution approach for the general structural dynamics problems, it is known to provide reliable solutions only in the low frequency region due to the inherent high sensitivities of structural and numerical modeling errors. Instead, the spectral element method has been proved to provide extremely accurate dynamic responses even in the high frequency region. Since the wave characteristics of a cylindrical shell becomes identical to that of a flat plate as the frequency increases, an equivalent plate model (EPM) representing the high-frequency dynamic characteristics of a cylindrical shell is introduced herein. The EPM-based spectral element analysis solutions are compared with the known analytical solutions for the corresponding cylindrical shell to confirm the validity of the present modeling approach.

• Journal of the Korean Society of Industry Convergence
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• v.22 no.6
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• pp.739-748
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• 2019

In this study, cyclic triaxial tests were performed for liquefaction characteristics according to earthquake loading frequency. The test period was tested for 0.1Hz, 0.2Hz, 0.5Hz 1.0Hz, 1.5Hz. It was analyzed that the number of earthquake loading increases as the test result frequendy increases. Therefore, additional study of the liquefaction evaluation method was needed considering the local characteristics of the high frequency earthquakes in Korea and the cyclic triaxial test frequency(0.1Hz), which is mainly used in the design.

• Current Optics and Photonics
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• v.7 no.1
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• pp.28-32
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• 2023

Frequency characteristics of gain-saturated erbium-doped fiber amplifier (EDFA) are experimentally evaluated to mitigate the optical signal fluctuation induced by atmospheric turbulence in terrestrial freespace optical communication systems. Here, an acousto-optic modulator (AOM) is used to emulate optical signal fluctuations induced by atmospheric turbulence. The waveform which is generated in proportion to the refractive-index structural parameters is used to drive the AOM at various periodic frequencies. Thus, the dependence of the signal fluctuation suppression on the frequency is evaluated. The experiment is conducted using a periodic frequency sweep of the AOM driving voltage waveform and signal input power variation of the amplifier. It is observed that a low periodic frequency and high input signal power effectively suppress the optical signal fluctuation. This study evaluates the experimental results from the high-pass filter and gain-saturation characteristics of the EDFA.

• Journal of Mechanical Science and Technology
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• v.20 no.12
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• pp.2209-2217
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• 2006

Dynamic flow characteristics of a counter-flow vortex tube is investigated using hot-wire and piezoelectric transducer (PZT) measurements. The experimental study is conducted over a range of cold air outlet ratios (Y=0.3, 0.5, 0.7, and 1.0) and inlet pressure 0.15 MPa. Temperatures are measured at the cold air outlet and along the vortex tube wall. Hot-wire is located at cold outlet and PZT is installed at inner vortex tube by mounting at throttle valve. The cold outlet temperature results show that the swirl flow of vortex tube is not axisymmetric. The hot-wire and PZT results show that there exist two distinct kinds of frequency, low frequency periodic fluctuations and high frequency periodic fluctuations. It is found that the low frequency fluctuation is consistent with the Helmholtz frequency and the high frequency fluctuation is strongly related with precession oscillation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1901-1906
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• 1995

The frequency response functions of systems incorporating a non-linear cubic stiffness subject to sinusoidal excitation are derived using the Volterra series and the convergence characteristics investigated. It is shown that the series representation of the frequency response functions converges only when the sinewave input amplitude is within a certain range. Within the range of convergence the frequency response function based on the Volterra series approaches the analytical one as more higher order frequency response function terms are included. Proposed is a criterion for the studies systems to predict approximately the range of sinewave input amplitude for which the series representation of the frequency response functions converges.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.641-647
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• 2004

Characteristics of the high frequency pulsatile flow have been investigated experimentally to understand the flow phenomena in the hydraulic system. The accumulator in high frequency hydraulic system but that is not effective all frequency zone. Therefore, a hydraulic damper used with accumulator is suggested to reduce the high frequency pulsatile where the accumulator is not effective. The pulsating pressure obtained by Pressure measurement system are analyzed to power spectral density distribution. According to the variations of pump input pressure and actuator acceleration frequency, the pressure is measured with or without an accumulator or pulsatile damper The amplitude of pressure with damper is very lower than those without accumulator or damper due to absorbing function of damper. As the frequency of actuator acceleration is increased, the effect of damper becomes very important to decrease the amplitude of pulsatile Pressure waveform with high frequencies.