• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.1A
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• pp.11-15
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• 2006

A pre-amplified semiconductor optical amplifier-Mach-Zehnder interferometer(SOA-MZI) wavelength converter (WC) using a continuous wave-holding beam(CW-HB) is proposed and experimentally demonstrated at 10Gb/s. The proposed scheme achieves not only enhancement of input power dynamic range(IPDR) to over 20dB but also higher Q parameter of about 2 to 3 by no output signal distortion and higher extinction ratio(ER) of about 2dB to 5dB by low noise figure (NF), compared with the bias current control method.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.10a
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• pp.450-455
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• 1995

A three-dimensional numerical tool is developed to calculate the potential distribution, electric field, and conductance for any types of conductance probes immersed in the wavy liquid film with various shapes of its free surface. The tool is validated against various analytical solutions. It is applied to find out the characteristics of the wire-wire probe, the flush-wire probe and the flush-flush probe in terms of resolution, linearity, and sensitivity. The wire-wire probe shows high resolution and excellent linearity for various film thickness, but comparably low sensitivity for low film thickness fixed. The flush-wire probe shows good linearity and high sensitivity for varying film thickness, but resolution degrading with an increase in film thickness. In order to check the applicability of the three types of probes in the real situation, the Korteweg-de Vries(KdV) two-dimensional solitary wave is simulated. The wire-wire probe is strongly affected by the installation direction of the two wires; when the wires are installed perpendicularly to the flow direction, the wire-wire probe shows large distortion of the solitary wave. In order to measure the transverse profile of waves, the wire-wire probes and the flush-wire probes are required to be separately installed 2mm and 2mm, respectively.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.114-121
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• 2004

Frictional heating in brakes causes thermoelastic distortion of the contacting bodies and hence affects the contact pressure distribution. The resulting thermo-mechanical coupling can cause thermoelastic instability (TEI) if the sliding speed is sufficiently high, leading to non-uniform heating called hot spots and low frequency vibration known as hot judder. The vibration of brakes to the known phenomenon of frictionally-excited thermoelastic instability is estimated studying the interface temperature and pressure evolution with time. A simple model has been considered where a layer with half-thickness$\alpha$slides with speed V between two half-planes which are rigid and non-conducting. The advantage of this properlysimple model permits us to deduce analytically the critical conditions for the onset of instability, which is the relation between the critical speed and the growth rate of the interface temperature and pressure. Symmetrical component of pressure and temperature distribution at the layer interfaces can be more unstable than antisymmetrical component. As the thickness $\alpha$ reduces, the system becomes more apt to thermoelastic instability. For perturbations with wave number smaller than the critical$m_{cr}$ the temperature increases with m vice versa for perturbations with wave number larges than $m_{cr}$ , the temperature decreases with m.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.8
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• pp.1589-1595
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• 2007

Recently many communication systems ate adapting the OFDM(Orthogonal Frequency Division Multiplexing) for multimedia data services. However, OFDM has some problems that PAPR is increased when sub-carries are summed up with same phases. This problem causes severe signal distortions while the signal is passing through non-linear system such as power amplifier resulting in performance degradation of transmission system. In this paper, we use IF-Clipping method to solve PAPR problem and the signal distortion caused by clipping is limited by use of SAW (Surface Acoustic Wave) filter and power amplifier(TWTA). And we derive the optimal parameter(PAPR, Backoff) values to meet the spectrum mask of WiBro system.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.3
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• pp.163-171
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• 2024

Structural health monitoring for ships and offshore structures is important in various aspects. Ships and offshore structures are continuously exposed to various environmental conditions, such as waves, wind, and currents. In the event of an accident, immense economic losses, environmental pollution, and safety problems can occur, so it is necessary to detect structural damage or defects early. In this study, structural response data of multi-linked floating offshore structures under various wave load conditions was calculated by performing fluid-structure coupled analysis. Furthermore, the order reduction method with distortion base mode was applied to the structures for predicting the structural response by using the results of numerical analysis. The distortion base mode order reduction method can predict the structural response of a desired area with high accuracy, but prediction performance is affected by sensor arrangement. Optimization based on a genetic algorithm was performed to search for optimal sensor arrangement and improve the prediction performance of the distortion base mode-based reduced-order model. Consequently, a sensor arrangement that predicted the structural response with an error of about 84.0% less than the initial sensor arrangement was derived based on the root mean squared error, which is a prediction performance evaluation index. The computational cost was reduced by about 8 times compared to evaluating the prediction performance of reduced-order models for a total of 43,758 sensor arrangement combinations. and the expected performance was overturned to approximately 84.0% based on sensor placement, including the largest square root error.

• Journal of Welding and Joining
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• v.34 no.6
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• pp.62-68
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• 2016

Laser welding has superior characteristic such as low distortion, high welding speed, easy automation and real time control. But it is easy to occur weld defects such as porosity, crater, humping bead in the area of welding start and end. These weld defects can be suppressed by applying the wave shape control. In this study CW fiber laser was used for welding of $0.5mm^t$ pure titanium. Penetration properties were evaluated with the time of slope up and down. After then the bead shape was observed, and the maximum depth and the area of crater were measured. The bead shape of welding start area changed to be sharp with increase of slope up time and non-weld area of welding start increased. The crater and humping bead were suppressed with slope down time. The cooling rate of crater area was understood through measure of the hardness. Also, The distribution tendency of alloying elements was observed by EPMA and EDS. When wave shape control didn't applied to weld, the hardness of end weld increased due to rapid cooling rate and the hardness of rear part in the crater was higher than that of fore part. On the other hand, when the wave shape control was used for end weld, the increase of hardness in the end weld couldn't be found due to gradual cooling rate.

• Journal of the Korean Geotechnical Society
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• v.24 no.4
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• pp.115-123
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• 2008

The dispersive phase velocity of a wave propagating through multilayered systems such as a soil site is an important parameter and carries valuable information in non-destructive site characterization tests. The dispersive phase velocity of a wave can be determined using the phase spectrum, which is easily evaluated through the cross power spectrum. However, the phase spectrum determined using the cross power spectrum is easily distorted by background noise which always exists in the field. This causes distortion of measured signal and difficulties in the determination of the dispersive phase velocities. In this paper, a new method to evaluate the phase spectrum using the harmonic wavelet transform is proposed and the phase spectrum by the proposed method is applied to the determination of dispersion curve. The proposed method can successfully remove background noise effects. To evaluate the validity of the proposed method, numerical simulations of multi-layered systems were performed. Phase spectrums and dispersion curves determined by the proposed method were found to be in good agreement with the actual phase spectrums and dispersion curves biased by heavy background noise. The comparison manifests the proposed method to be a very useful tool to overcome noise effects.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.9
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• pp.1319-1324
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• 2002

A theoretical model on shock-vortex interaction is investigated using a numerical technique to solve Navier-Stokes equations. The shock-vortex interaction generated by this model based on the classical Rankin vortex is precisely investigated for a benchmark problem: Dosanjh and Weeks experiment. In terms of shock dynamics, the interaction is categorized to three stages: shock distortion, shock split, and shock-shock interaction. The quadrupolar structure of the sound source produced by the interaction is far supported with the present model, and the difference between experiment and theoretical model is also discussed in this paper.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.277-280
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• 2005

In this paper, we propose a frequency synthesizer for dualband repeater. The dual-band RF technology for applications to the wireless repeater for CDMA and WCDMA mobile communications has been developed in this paper. The dualband PLL module consisted of dual-band VCO and one PLL IC has been developed. The main technological efforts for the dual-band PLL module is to suppress the intermodulation distortion by applying the miniature ceramic filter using the slow wave characteristics. The dual-band miniature RF module including dual-band PLL module and one MCU controller is very attractive for applications to the miniature dual-band RF mobile repeaters.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.305-310
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• 2001

This paper presents the computational method for analyzing the compressible flow fields in a high voltage gas circuit breaker. There are many difficult problems in analyzing the gas flow in GCB due to complex geometry, moving boundary, shock wave and so on. In particular, the distortion problem of the grid due to the movement of moving parts can be worked out by the fixed grid technique. Numerical simulations are based on a fully implicit finite volume method of the compressible Reynolds-averaged Navier-Stokes equations to obtain the pressure, density, and velocity through the entire interruption process. The presented method is applied to the real circuit breaker model and the pressure in front of the piston is good agreement with the experimental one.