• 한국음향학회:학술대회논문집
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• 한국음향학회 1992년도 학술논문발표회 논문집 제11권 1호
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• pp.23-28
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• 1992

The purpose of this paper is to develop a new adaptive echo canceller improving convergence speed and near-end-talker detection performance of the conventional echo canceller. In a conventional adaptive echo canceller, an adaptive digital filter with TDL(Tapped-Delay Line) structure modelling the echo path uses the LMS(Least Mean Square) algorithm to cote the coefficients, and NET detector using energy comparison method prevents the adaptive digital filter to update the coefficients during the periods of the NET signal presence. The convergence speed of the LMS algorithm depends on the eigenvalue spread ratio of the reference signal and NET detector using the energy comparison method yields poor detection performance if the magnitude of the NET signal is small. This paper presents a new adaptive echo canceller which uses the pre-whitening filter to improve the convergence speed of the LMS algorithm. The pre-whitening filter is realized by using a low-order lattice predictor. Also, a new NET signal detection algorithm is presented, where the start point of the NET signal is detected by computing the cross-correlation coefficient between the primary input and the ADF(Adaptive Digital Filter) output while the end point is detected by using the energy comparison method. The simulation results show that the convergence speed of the proposed adaptive echo canceller is faster than that of the conventional echo canceller and the cross-correlation coefficient yield more accurate detection of the start point of the NET signal.

• Journal of Electrical Engineering and Technology
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• 제6권2호
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• pp.147-153
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• 2011

This paper proposes a methodology using a tool based on the branch-parameter continuation power flow (BCPF) in order to restore the power flow solvability in unsolvable contingencies. A specified contingency from a set of transmission line contingencies is modeled, considering the transient analysis and practice in the Korean power system. This tool traces a solution path that satisfies the power flow equations with respect to the variation of the branch parameter. At a critical point, in which the branch parameter can move on to a maximum value, a sensitivity analysis with a normal vector is performed to identify the most effective compensation. With the sensitivity information, the location of the reactive power compensation is determined and the effectiveness of the sensitivity information is verified to restore the solvability. In the simulation, the proposed framework is then applied to the Korean power system.

• 한국멀티미디어학회논문지
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• 제2권1호
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• pp.30-37
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• 1999

광대역 능동소음제거는 수 백개의 적응필터 텝 수를 갖는다. 탭 수가 긴 적응필터는 많은 계산량이 요구된다. 본 논문에서는 적응 계수벡터가 서브밴드로 계산되는 M-채널 QMF 펼터뱅크를 이용한 능동소음제거 시스템올 제안한다. 분해 필터뱅크와 합성 펼터뱅크는 cosine-modulated pseudo QMF 펼터를 사용한다. 오차경로의 전달특성을 온라인 인식하기 위한 기준신호는 적응필터의 출력신호와 저주파 대역의 서브 밴드 출력신호와의 차신호를 사용한다. 따라서 본 논문의 능동소음제거기는 계산량이 적고, 수렴속도가 빠른 견실한 시스템이 되도록 제안한다.

• 한국정보통신학회논문지
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• 제7권2호
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• pp.171-176
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• 2003

유성 버스트 통신은 NLOS 데이터 전송을 필요로 하는 1200km 이상의 장거리 VHF 통신로에서 효율적이며 경제적인 수단을 제공한다. 그러나, 유성 버스트 통신은 지금까지 버스트 주기의 감소로 인한 시스템의 총 도통율의 저하로 인하여 700Km 이하의 근거리통신에는 적합하지 않다고 알려져 있다. 이에 본 논문에서는 매우 짧은 근거리의 MB(Meteor Burst) 경로의 특성을 실험적으로 소개한다. 또한 경산시와 안동시간 50Km 간에서의 도통율과 평균 도통시간을 측정하여 산악지대 및 계곡에서의 근거리 유성버스트 통신로의 효용성을 실험을 통하여 나타낸다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 춘계학술대회 논문집 센서 박막재료연구회 및 광주 전남지부
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• pp.27-31
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• 2008

In this study, The new type of loop antenna which detects the partial discharge was designed based on microstrip line technology. In diagnosis of power cable, partial discharge signal generally occurred at the frequency range lower than 100MHz because high frequency PD signals could be lost along the propagation path in the cable. The new type of loop antenna sensor has been studied by using Simulation software named CST microwave studio version 5.0. In partial discharge measuring experiments, commercial HFCT sensor was used as a reference sensor. Several experiments were made over HFCT sensor and loop antenna sensor in detection partial discharge on MV XLPE cable of 22.9kV. In this study, we have shown our loop antenna sensor can apply as a commercial HFCT sensor.

• Journal of Advanced Marine Engineering and Technology
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• 제39권2호
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• pp.136-142
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• 2015

The shell and tube heat exchanger is an essential part of a power plant for recovering transfer heat between the feed water of a boiler and the wasted heat. The baffles are also an important element inside the heat exchanger. Internal materials influence the flow pattern in the bed. The influence of baffles in the velocity profiles was observed using a three-dimensional PIV (Particle Image Velocimetry) around baffles in a horizontal circular tube. The velocity of the particles was measured before the baffle and between them in the test tube. Results show that the velocity vectors near the front baffle flow along the vertical wall, and then concentrate on the upper opening of the front baffle. The velocity profiles circulate in the front and rear baffle. These profiles are related to the Reynolds number (Re) or the flow intensity. Velocity profiles at lower Re number showed complicated mixing to obtain the velocities and concentrate on the lower opening of the rear baffle as front wall. Numerical simulations were performed to investigate the effects of the baffle and obtain the velocity profiles between the two baffles. In this study, a commercial CFD package, Fluent 6.3.21 with the turbulent flow modeling, k-${\epsilon}$ are adopted. The path line and local axial velocities are calculated between two baffles using this program.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 춘계학술대회 논문집
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• pp.581-587
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• 2014

Intake silencers of high performance and with less pressure drop are developed for a household oxygen generator. First, the acoustic power of the target oxygen generator are experimentally evaluated according to ISO code. Then, the transmission loss of and the flow characteristics inside the existing intake silencer are predicted and analyzed. On a basis of these results, two intake silencers are proposed, which are designed to induce the swirling flow inside the intake silencer and thus to reduce the flow loss. The predicted TL and the pressure drop for these two new silencers are compared to the existing one, which shows that the proposed ones have higher TLs as well as less pressure drop. The reason for these improvements are explained by investigating the flow characteristics of the new silencers in detail.

• 대한산업공학회지
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• 제30권3호
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• pp.213-223
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• 2004

We consider the traffic grooming problem for the design of SONET/WDM(Synchronous Optical NETwork/Wavelength Division Multiplexing) ring networks. Given a physical network with ring topology and a set of traffic demands between pairs of nodes, we are to obtain a stack of rings with the objective of minimizing the number of ADMs installed at the nodes. This problem arises when a single ring capacity is not large enough to accommodate all the demands. As a solution method, an efficient algorithm based on the branch-and-price approach has been reported in the literature for the problem in which only unidirecional path switched ring (UPSR) was considered. In this study, we suggest integer programming models and the algorithms based on the same approach as the above one, considering two-fiber bidirectional line switched ring(BLSR/2), and BLSR/4 additionally. Using the results, we compare the number of required ADMs for all types of the ring architecture.

• Geomechanics and Engineering
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• 제12권1호
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• pp.127-138
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• 2017

A series of high-pressure isotropic compression tests were performed on four types of poorly graded silica sand that were artificially prepared based on representative grading curves and similar mineralogy composition of seabed sediment containing different fines contents existing in the Nankai Trough. The addition of fines steepens the initial compression path and increases the decrement of the void ratio after loading. The transitional behaviour of the poorly graded sand with a larger amount of fines content was identified. The slope of the normal compression line shows a slight decreasing tendency with the level of fines content. The bulk modulus of silica sand with fines was lower when compared with the published results of silica sand without fines. A small amount of particle crushing of the four types of poorly graded sand with variable fines content levels was noticed, and the results indicated that the degree of particle crushing tended to decrease as the fines content increased.

• 게임&엔터테인먼트 논문지
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• 제2권1호
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• pp.8-16
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• 2006

인터넷에서 게임 트래픽과 같은 대용량 데이터의 부하를 분산하고 안정적인 전송을 위해 멀티캐스트 라우팅 프로토콜을 사용한다. 다양한 멀티캐스트 알고리즘 중 최근 CBT(Core Based Tree) 방식이 널리 사용되고 있으나 코어 라우터로 트래픽 집중되는 병목현상과 코어라우터의 위치에 따라 푸어 코어(Poor core)현상이 발생한다. 본 논문에서는 코어 라우터의 병목현상을 초래하는 링크 레이트(Link Rate)에 따라 코어 라우터의 상태를 SS(Steady State), NS(Normal State), BS(Bottleneck State)로 구분하였으며, 코어 라우터의 과부하에 따라 멀티캐스트 라우팅 전략을 CBT에서 Anycast로 전환하는 방식을 제안하였다. 온라인 게임에서 교환되는 주요 패킷의 크기에 준하여 두 가지 라우팅 방식을 비교하고 트래픽의 증가에 따라 Anycast 라우팅 방식의 성능개선을 보였다.