• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.556-560
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• 2001

In this paper, a soft-switching discontinuous mode (DCM) power factor corrected (PFC) converter is analyzed by applying the double Fourier series expansion. It is found that the fundamental component and higher-order harmonics included in the input current waveform are obtained by the Fourier series expansion of the mean value of the inductor current. From the theoretical analysis, a new method removing the distortion of the input current waveform is proposed. In spite of an open loop system, the proposed method makes a great improvement of the total harmonic distortion even if the ratio of output voltage to input voltage is very low.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.396-403
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• 1991

A solution is presented for the computation of the elastic-creep stresses in a hollow cylinder subjected to nonaxisymmetric temperature distribution. The creep problem is treated by the Maxwell creep model. Laplace transformation is used for reformation of the governing equation of elastic problem and Hooke's law in a function of .gamma. , .theta. , and creep constant. The governing equation is set up using the Airy stress function which leads to the biharmonic equation. The solution is obtained by using Fourer series method and Laplace inverse method used to obtain the stress components which include the variation of time. This solution shows excellent agreement with Lamkin's and Boley & Weiner's solution. The viscoelastic stresses are also obtained for the fuel rob tube subjecting nonaxisymmetric thermal load.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.5
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• pp.171-179
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• 2003

An Amplitude Proportional Friction Damper (APFD) is considered in order to improve the characteristics of Coulomb friction damper. The frictional force is proportional to the amplitude in APFD system and the system is non-linear as is Coulomb damper system. A free vibration analysis on the 1-DOF system has made to demonstrate the characteristics of the APFD system. The results show that APFD system has similar damping characteristics to the viscous damper. Also, the solution for the response of a base-excited system with APFD is developed through the application of a Fourier series to represent the frictional force of APFD. It is assumed that no stick-slips occur during any portion of the steady-state oscillation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.908-913
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• 2002

An analytical study is presented on the hydroelastic vibration of two rectangular identical plates coupled with a bounded fluid by using the finite Fourier series expansion method. It is observed that the two contrastive modes, the so called the out-of-phase and in-phase modes appear. The proposed analytical method is verified by observing a good agreement to three dimensional finite element analysis results. All natural frequency of the in-phase modes can be predicted well by the combination of the dry beam modes. The theoretical prediction for the out-of-phase mode can be improved by using the polynomial functions satisfying the plate boundary conditions and fluid volume conservation instead of using dry beam modes.

• Tribology and Lubricants
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• v.18 no.6
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• pp.411-417
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• 2002

Two dimensional slow viscous flow between a rotating cylinder and a translating plate is investigated using Stokes' approximation. An exact formal expression of the stream function is obtained by using the bipolar cylinder coordinates and Fourier series expansion. From the stream function obtained, the streamline patterns are shown and the pressure distribution in the flow field is determined. By integrating the stress distributions on the cylinder, the farce and the moment exerted on the cylinder are calculated. The flow rate through the gap between the cylinder and the plate is also determined as a function of the distance between the cylinder and the plate. Special attention is directed to the case of very small distance between the cylinder and the plate concerned with the lubrication theory and the minimum pressure is calculated to explain a possible cavitation.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.394-398
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• 1988

In this paper, the time-averaged behavior of the three-phase Inductor-Converter Bridge (ICB) circuit has been analyzed by using the state-space averaging method. The results are in closed form far from the results obtained by using the Fourier series. Therefore, the computational difficulties of the infinite Fourier series can be avoided and the results derived in this paper are available especially in real time control. Unlike the SFC, $S^{4}LCL$, DFC and other circuits which have time varying switching intervals for a constant time-averaged value of coil voltage, the ICB circuits operate with a clock-driven sequence of gate pulses which have constant switching intervals.

• Structural Engineering and Mechanics
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• v.21 no.2
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• pp.169-184
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• 2005

This study deals with the free vibration of a circular plate in contact with a fluid; submerged in fluid, beneath fluid or on fluid. An analytical method based on the finite Fourier-Bessel series expansion and Rayleigh-Ritz method is suggested. The proposed method is verified by the finite element analysis using commercial program with a good accuracy. The normalized natural frequencies are obtained in order to estimate the relative added mass effect of fluid on each vibration mode of the plate. Also, the location of plate coupled with fluid and the cases of free and bounded fluid surface are studied for the effect on the vibration characteristics.

• Journal of Mechanical Science and Technology
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• v.17 no.9
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• pp.1297-1315
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• 2003

This study deals with the free vibration of two identical circular plates coupled with a bounded or unbounded fluid. An analytical method based on the finite Fourier-Bessel series expansion and Rayleigh-Ritz method is suggested. The proposed method is verified by the finite element analysis using commercial program with a good accuracy The case of bounded or unbounded fluid is studied for the effect on the vibration characteristics of two circular plates. Also, the effect of gap between the plates on the fluid-coupled natural frequencies is investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.389.1-389
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• 2002

An analytical study is presented on the hydroelastic vibration of two rectangular identical plates coupled with a bounded fluid by using the finite Fourier series expansion method. It is observed that the two contrastive modes, the so called the out-of-phase and in-phase modes. All natural frequency of the in-phase modes can be predicted well by the combination of the beam modes in the air, but the natural frequency of the out-of-phase mode cannot be estimated precisely. (omitted)

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.10a
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• pp.143-149
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• 1995

A simple kinematically admissible velocity field is proposed to drtermine the final-stage extrusion load and the average extruded length in the square-die forward extrusion of non-axisymmetric bars from circular billets. The proposed velocity field is applied to the square-die extrusion of trochoidal gear-shaped bars and rectangular-shaped bars, the profile function of a rectangular being approximated by using a Fourier series. Experiments have been carried out with hard solder billets at room temperature. The theoretical predictions of the extrusion load are in good agreements with the experimental results and there is generally reasonable agreements in average extruded length between theory and experiment.