• Proceedings of the KSME Conference
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.18.1-18.1
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• 2005

• Journal of the Korean Society for Marine Environment & Energy
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• 제20권1호
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• pp.37-44
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• 2017

Complexity of multiphase flows due to existence of more than two interface including free-surface in one system, cannot be simulated easily. Since more than two fluids affect to flows and disturb interface, non-linearities such as instabilities can be appeared. Among several instabilities on multiphase flows, one of representative is Rayleigh-taylor instability. In order to examine in importance of density disparity, several cases with numerous Atwood number are set. Moreover, investigation of influence on initial disturbance were also considered. Moving particle simulation (MPS) method, which was employed in this paper, was not widely used for multiphase problem. In this study, by adding new particle interaction models such as self-buoyance correction, surface tension, and boundary condition at interface models, MPS were developed having more strength of physics and robust. By applying newly developed multiphase MPS, considered cases are performed and compared each other. Additionally, though existence of disagreement of magnitude of rising velocity between theoretical values from linear potential theory and that of numerical simulation, agreement of tendency can be proved of similarity of result. the discordance of magnitude can be explained due to non-linear effects on numerical simulation which was not considered in theoretical result.

• Journal of the Institute of Electronics Engineers of Korea TC
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• 제38권12호
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• pp.20-28
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• 2001

In this paper, a extended blocking probability formula for reverse link of a DS/CDMA cellular system supporting voice and data service is derived in Rayleigh fading channel. Also, voice and data Erlang capacity considering shadowing are analyzed and compared with those considering both shadowing and multipath fading, respectively. Assuming that the blocking probability set 1% in the Rayleigh fading channel, they are observed that voice Erlang capacity of 13.38 Erlangs and data Erlang capacity of 8.92 Erlangs are supported at the data rate $R_b$=9.6 kbps, and voice Erlang capacity of 7.47 Erlangs and data Erlang capacity of 4.98 Erlangs are supported at the data rate $R_b$=14.4 kbps, respectively, and then are less 21.4% for $R_b$=9.6 kbps, 24.9% for $R_b$=14.4 kbps than Erlang capacity considering shadowing only, respectively. It is shown that the effect of multipath fading must not be ignored. Also, it is presented that accurate voice and data Erlang capacity which could be supported by the DS/CDMA cellular system.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제25권5B호
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• pp.931-941
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• 2000

We propose a serial acquisition scheme using antenna arrays for initial acquisition of direct sequence spread spectrum (DS-SS) signals, which can lower substantially the range of detectable signal-to-noise ratio (SNR). The proposed scheme uses the sum of the independent decision samples form psedo-noise (PN) co-phased noncoherent I-Q matched filters (MFs) associated with antenna arrays as a decision variable in order to enhance SNR of the resulting signal. We analyze its mean acquisition time performance under an additive white Gaussian noise (AWGN) channel and a flat Rayleigh fading channel by deriving the expressions for the probabilities of detection and false alarm. From mumerical results, we see that the acquisition performance of the proposal scheme becomes improved continually as the number of antennas increses.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제7권4호
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• pp.667-672
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• 2003

Smart antennas will be used mon widely for the higher data rate and the larger number of users as the demand of wireless multimedia service is increased. Therefore, the BER performance is analyzed in this paper for DS-CDMA and MC-CDMA systems using smart antennas. A reverse link channel is simulated assuming the frequency selective Rayleigh fading. The simulation results are presented based on the characteristics of DS-CDMA and MC-CDMA systems according to the signal spectrum bandwidth and the method of adaptive beamforming. The BER performances of both systems are improved as the beam width of smart antennas is decreased. Also, it is shown that the performance of MC-CDMA system is much better than that of DS-CDMA system as the number of users is increased.

• Journal of Energy Engineering
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• 제24권3호
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• pp.135-141
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• 2015

The core melts stratifies into lower mixture layer and upper metal layer by density in a severe accident condition. The decay heat generated from the mixture layer threatens the integrity of the reactor vessel. This study simulated the natural convection heat transfer of the mixture layer with volumetric heat source using the mass transfer system. $H_2SO_4-CuSO_4$ electroplating system was used as the mass transfer system. With the modified Rayleigh number of $3{\times}10^{14}$, the Nusselt number showed minimum at the bottom and increased along curvature to the top of the experimental apparatus.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제7권3호
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• pp.201-210
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• 1996

In this paper, we analyzed performance of a symbol timing recovery scheme for 16QAM Radio system. As a symbol timing recovery scheme, both maximum amplitude method(MAM) and wave difference method(WDM) are analyzed employing a pulse shaping filter, such as raised cosine filter(RCF) and nonlinear filter(NLF). Simulation result shows that the jitter performance of MAM or WDM using NLF is better than that using square root RCF. In order to estimate and compensate for the Rayleigh fading PSAM(Pilot Symbol Assisted Modulation) and space diversity are also employed. Consequently, BER performance of about $10^{-4}$ is obtained for $E_b/N_o$= 20 dB.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제4권2호
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• pp.417-426
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• 2000

In this paper, CE-CPSK(Constant Envelope Continuous Phase Shift Keying) modulated DS/SS(Direct Sequence Spread Spectrum) transceiver with 908 MHz carrier frequency and 1.5 MHz PN clock rate is proposed. To overcome the effect of nun-linear power amplifier, CE-CPSK modulation method which has the constant envelope and continuous phase characteristics is proposed. To analyze the DS/SS receiver performance with respect to code tracking loop, multipath fading channel is characterized as a two-ray Rayleigh fading channel. To compensate the demerit of analog delay locked loop, digital delay locked loop is employed for code tracking loop. Simulation and experimental examination has been carried out in AWGN(Additive White Gaussian Noise) and Rayleigh fading channel environment in order to prove validity of the proposed method.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 한국정보통신학회 2015년도 춘계학술대회
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• pp.677-680
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• 2015

In this paper, we propsed scheme to mitigate conflict and loss of message in vehicle communication. And vehicles that exist in the moving direction, were grouping to the cluster form. Through, to select best relay vehicle, transmit a message to the destination. In addition, we applied the double rayleigh fading environment so that can applied in real-environments. Therefore, vehicle communication network applied proposed scheme, can be problem of mitigate conflict and loss of message. Thus, Increase the reliability of the received signal.

• Proceedings of the KIEE Conference
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• 대한전기학회 2001년도 하계학술대회 논문집 C
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• pp.1844-1846
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• 2001

광섬유는 저손실, 광대역의 전송특성을 가지며 세경(細徑), 경량등 많은 장점을 가지고 있지만 동케이블과 같이 파단점, 불연속점등의 장해점 탐색에 대한 어려움이 있다. 이러한 문제점을 해결하기 위하여 OTDR(Optical Time Domain Reflectometer)은 고감도, 고정도의 광센싱 기술, 극초단 광펄스 레이다 기술, 광다중화 센서 네트웍기술, 실시간 광신호처리 기술 등 정밀 광계측 및 신호처리기술을 적용하여 설치된 광섬유의 손실 정도를 측정하는 시스템으로 광섬유에 입사된 광의 산란 가운데 Rayleigh 산란에 의해서 생기는 후방산란광을 관측하여 광파이버의 파단점 탐색 및 손실측정이 가능하다. 최근 대부분의 유선통신망은 광섬유를 이용한 광통신방식으로 이루어지고 있으며 이러한 광섬유의 고장점을 찾기 위한 방법은 OTDR방식이 유일하다고 할 수 있다. 본 논문은 Rayleigh 후방산란에 의한 광학적 특성을 규명하고 이러한 특성을 이용하여 이용한 광섬유 유지보수용 계측시스템을 설계, 제작하고 실험한 결과에 대하여 설명하고 고찰하였다. 측정거리를 40Km까지 측정하도록 하였으며, 모니터상에서의 거리 분해능은 5m정도를 가지며 1310nm의 파장을 사용하였다.