• Proceedings of the KSME Conference
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• 2001.06e
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• pp.430-435
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• 2001

This paper introduces a pressure correction method for microflow computation. Conventional CFD methods with no slip boundary condition fail to predict the rarefaction effect of the wall when simulating gas microflows in the slip-flow regime. Pressure correction method with an appropriate slip boundary condition is an efficient tool in analyzing microscale flows. The present unstructured SIMPLE algorithm adopts both the classical Maxwell boundary condition and Langmuir boundary condition proposed by Myong. The simulation results of microchannel flows show that the proposed method has an effective predictive capability for microscale flows.

• Journal of computational fluids engineering
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• v.16 no.2
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• pp.88-93
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• 2011

A numerical study of subcooled onset of nucleate boiling (ONB) in a micro-channel under pulsed heating using volume of fluids (VOF) model was conducted. The VOF simulation adopting the existing experimental condition is compared to the experimental data. The time to ONB was determined when the void fraction at the microheater surface first appeared. The theoretical superheat for homogeneous nucleation relatively predicts the transient ONB results of convective flow of water well based on local temperature distribution. It was found that once heat load increases at the heater, transient flow boiling starts to occur faster.

• Proceedings of the IEEK Conference
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• 2001.06d
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• pp.13-16
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• 2001

In the Dedicated Short Range Communication (DSRC) system channel, a large number of bit errors occur because of Additive White Gaussian Noise (AWGN) and fading. When an image data is transmitted under the condition, reconstructed image quality is significantly degraded. In this paper, as an alternative to the error correcting code and/or automatic repeat request scheme, we propose an error recovery scheme for image data transmission. We first analyze how transmission errors in the DSRC system channel degrade image quality. Then, in order to improve image quality, we propose error resilient and concealment schemes for still image transmission using DCT-based fixed length coding, hamming code, cyclic redundancy check, and interleaver. Finally, we show its performance by an experiment.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.244-247
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• 2000

This paper deals with methods for partial response maximum-likelihood (PRML) detection and crosstalk cancellation. In accrodance with the demand for increased recording density, 20 gigabyte (Gbyte) digital versatile disk (DVD) ROM channel is considered. Channel is modelled to be close to real optical channel using DIFFRACT$\^$TM/. After comparing the spectral characteristics of various PR polynomials, P(D)=1＋D＋D$^2$＋D$^3$is proposed as a target PR. The performance of the system is illustrated under the condition that the readout signal is degraded by crosstalk, radial tilt and nonlinear distortions in optics. The experimental results show that crosstalk and nonlinear distortions degrade performance by about 2dB, respectively. We also show that when radial tilt is added to the crosstalk, the performance degradation assumes quite significant proprotions.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1996.06a
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• pp.55-59
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• 1996

In this paper, we first analyze the influence of interference due to the time variation and delay spread of the mobile channel on an orthogonal frequency division multiplexing (OFDM) system. With the result, we obtain the bit error rate performance of the 16-QAM OFDM system. Second, we investigate the performance of the Reed-Solomon (RS) coded 16-QAM OFDM system when the number of subcarriers varies. In the investigation, we assume that the information transmission rate and the total bandwidth expansion due to coding, guard interval, and the number of subcarriers are fixed. Under this condition, it is observed that there are optimum numbers of subcarriers that minimize the post decoding symbol error probability of RS code for various channel states.

• The KSFM Journal of Fluid Machinery
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• v.3 no.2 s.7
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• pp.57-65
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• 2000

The aim of this paper is to understand the unsteady flow phenomena in a high speed centrifugal compressor channel diffuser. Instantaneous pressures aye measured at six locations in the diffuser using fast-response pressure transducers. Instantaneous pressure ratio decomposition was applied to analyze the pressure signal. In vaneless space where impeller-vaned diffuser interaction is strong, aperiodic unsteadiness is high and periodic pressure waveforms by blade passing are not clear at low flow rates, especially near vane suction side. High aperiodic unsteadiness decreases downstream of diffuser. The blade-to-blade pressure wave does not disappear in surge flow condition. In surge there exist not only large scale periodic surge wave but also blade-to-blade pressure wave.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1864-1876
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• 2015

In this paper, we propose a singular perturbation-like approach to EDFA gain controller design and analysis. Considering a three-level model of EDFA, a gain controller containing a state observer and a channel add/drop estimator is designed based on a singular perturbation - like concept. The proposed design methodology is shown to be effective and advantageous not only in theoretically verifying the asymptotic stability of systems with multi-time scales such as EDFA but also in designing an asymptotic estimator for channel add/drops which does not satisfy the matching condition.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.4
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• pp.11-18
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• 2006

Compound flow by confluence of two parallel flows through a convergent channel and its choking phenomenon are calculated by one-dimensional isentropic model and completely mixing model. Optical observations and pressure measurements for subsonic/subsonic compound flows are carried out and compared with the results of one-dimensional calculations. As a result, it is found that inlet conditions of one flow influence the behavior of the other flow as well as the choking condition and present experimental data agree well with the results of one-dimensional calculations.

• Electrical & Electronic Materials
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• v.9 no.3
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• pp.259-264
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• 1996

In this study, we performed a modeling for $K^{+}$ ion-exchanged diffused channel waveguide and waveguide-type optical coupler by Wentzel-Kramer-Brillouin(WKB) dispersion equation, normalized field distribution equation for mode and coupled mode theory, and examined the optical-power-dividing of the optical coupler fabricated by using the modeling condition. The optical-power-dividing was observed at the waveguide-type optical coupler with 3[.mu.m] line-width, 6[.mu.m] space between channel waveguides, and 3[mm] interaction length.h.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.487-490
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• 2002

The real chip and similarity model were used to investigate the thermal behavior and velocity distribution of air from the heat source with the location and the amount of heat experimentally and numerically, and compared. The heat generated in the block is not cooled by convection and show the high temperature by the stagnation of heat flow. After maintaining the high temperature of block by the natural convection, the sudden drop of temperature with the air flow was shown in the channel but the decreasing rate was small with the time. The inward block was effected by infinitesimal air flow generated between block and channel and outward block was effected by the entry condition.