• 한국유체기계학회 논문집
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• 제6권1호
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• pp.23-29
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• 2003

Three-dimensional flow through a tubular centrifugal fan with airfoil type blades is analyzed, and the effects of turbulence model and numerical scheme on the results are investigated. Standard $k-{\epsilon}$ model and k - w model are tested as turbulence closures. The numerical schemes for convection terms, i.e., Upwind Differencing Scheme (UDS), Mass Weighted Skewed upstream differencing scheme (MWS), Linear Profile Skewed upstream differencing scheme (LPS), and Modified Linear Profile Skewed upstream differencing scheme (MLPS) are also tested, and the performances of these schemes coupled with two turbulence models are evaluated. The static pressure distributions are compared with experimental data obtained in this work, which shows that the $k-{\epsilon}$ model gives better results than the k-w model.

• 대한수학회보
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• 제51권1호
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• pp.267-285
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• 2014

An upstream scheme based on the pseudostress-velocity mixed formulation is studied to solve convection-dominated Oseen equations. Lagrange multipliers are introduced to treat the trace-free constraint and the lowest order Raviart-Thomas finite element space on rectangular mesh is used. Error analysis for several quantities of interest is given. Particularly, first-order convergence in $L^2$ norm for the velocity is proved. Finally, numerical experiments for various cases are presented to show the efficiency of this method.

• 한국통신학회논문지
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• 제25권9A호
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• pp.1422-1430
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• 2000

S(Synchronous)-CDMA is a new cable modem technology applicable to the upstream channel for high speed multimedia communication using CATV networks. In this paper we analyze the transmitting and receiving process of S-CDMA scheme based on Terayon patent and derive bit error probability of S-CDMA and TDMA scheme in the $\varepsilon$-mixture impulse noise model which appropriately reflects impulse noise characteristics of upstream channel by using various parameters. This analysis results are a good match with the simulation results. We also compare Eb/No gain performance of S-CDMA with TDMA in 16, 32, 64, QAM.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.23-29
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• 2001

Three-dimensional flow through a tubular centrifugal fan with airfoil type blades are analyzed using CFX-TASCflow. Standard k - $\epsilon$ model and k - $\omega$ model are used as turbulence closures. The numerical schemes for convetion terms, i.e., Upwind Differencing Scheme(UDS), Mass Weighted Skewed Upstream Differencing Scheme(MWS), Linear Profile Skewed Upstream Differencing Scheme(LPS), and Modified Linear Profile Skewed Upstream Differencing Scheme(MLPS) are also tested. And, the performance of these schemes coupled with two turbulence models are evaluated. Computational static pressure distributions are compared with experimental data obtained in this work.

• 정보처리학회논문지C
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• 제13C권3호
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• pp.345-352
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• 2006

인터넷과 이동 네트워크로 구성된 유무선 통합 네트워크에서는 인터넷 상의 송신자와 이동 네트워크 상의 이동 호스트(MH, Mobile Host) 간 경로는 두 개 이상의 무선링크로 구성된다. 이와 같은 네트워크 이동 환경에서 TCP의 종단간 제어 특성을 유지하면서 무선링크에서의 패킷 전송 오류로 인한 TCP의 성능 저하를 극복하는 방안을 제안한다. 제안하는 방안에서는 수신된 패킷의 시퀀스 번호와 ACK 번호를 근거로 하여 무선링크 상에서의 전송 오류로 인한 패킷 손실 정보를 추출하고 이 정보를 상류의 라우터에게 전달함으로써 상류의 액세스 라우터나 이동 라우터에서 신속히 손실된 패킷을 재전송할 수 있도록 한다. 제안하는 방안은 상류 무선링크에서의 패킷전송 오류를 신속히 극복하는 특성을 가지며 모의실험을 통하여 제안한 방안의 TCP 전송률 성능을 평가하였다. TCP 종단간 제어 특성을 가지며 송신자나 수신자 측에 추가 기능이 요구되지 않는 snoop 방식과 비교할 때 제안하는 방안의 TCP 성능이 크게 개선됨을 모의실험을 통해 확인하였다.

• 대한기계학회논문집B
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• 제24권9호
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• pp.1148-1156
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• 2000

The QUICK scheme for convection terms is modified for unstructured finite volume method by using linear reconstruction technique and validated through the computation of two well defined laminar flows. It uses two upstream grid points and one downstream grid point in approximating the convection terms. The most upstream grid point is generated by considering both the direction of flow and local grid line. Its value is calculated from surrounding grid points by using a linear construction method. Numerical error by the modified QUICK scheme is shown to decrease about 2.5 times faster than first order upwind scheme as grid size decreases. Computations are also carried out to see effects of the skewness and irregularity of grid on numerical solution. All numerical solutions show that the modified QUICK scheme is insensitive to both the skewness and irregularity of grid in terms of the accuracy of solution.

• 한국전산유체공학회지
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• 제2권2호
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• pp.59-72
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• 1997

A numerical model is constructed to simulate the interactions of oblique shock wave / turbulent boundary layer on a strongly heated wall. The heated wall temperature is two times higher than the adiabatic wall temperature and the shock wave is strong enough to induce boundary layer separation. The numerical diffusion in the finite volume method is reduced by the use of a higher order convection scheme(UMIST scheme) which is a TVD version of QUICK scheme. The turbulence model is Chen-Kim two time scale model. The comparison of the wall pressure distribution with the experimental data ensures the validity of this numerical model. The effect of strong wall heating enlarges the separation region upstream and downstream. In order to eliminate the separation, wall suction is applied at the shock foot position. The bleeding slot width is about same as the upstream boundary layer thickness and suction mass flow is 10% of the flow rate in the upstream boundary layer. The final configuration of the shock reflection pattern and the wall pressure distribution approach to the non-viscous value when wall suction is applied.

• 자원ㆍ환경경제연구
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• 제9권4호
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• pp.621-639
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• 2000

High population and economic growth leads to ever increasing demand for water resources, prompting many regional conflicts for the water. With the observation, this paper examines the allocation problem of flowing water between upstream and downstream regions, We offer a two- region model in which the downstream region pays a portion of product to the upstream region in order to induce the upstream region to share the water. Our model shows that the "side-payment" does not always work, because the ex post income of the downstream region could be lower than the income without the side-payment This happens when the externality the upstream region imposes on the downstream region is small. The paper derives the condition under which the incentive mechanism like side-payment is likely to fail (or work). The model also shows that the higher the degree of externality is, the less amount of side-payment should be. The results of the paper suggest that the incentive scheme can help the regional conflicts be solved if the externality effect generated by the water use of upstream region is big enough, which is in fact the case where the conflict is severe.

• 대한토목학회논문집
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• 제7권4호
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• pp.147-157
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• 1987

대류 분산 모형의 유한 차분 방법으로 양해법, Bresler방법, 음해법, upstream차분법과 Chaudhari방법등을 선택하여 각 차분법들의 특성을 규명하고 수치실험을 통하여 이들의 효율적인 사용 방안을 제시하였다. 비교 분석 결과 Chaudhari방법은 수치 분산 현상에 가장 둔감한 반면 조건부 안정이고, Bresler방법은 overshooting에 민감한 반면 무조건 안정이라는 특성이 있다. 분산이 지배적인 흐름에서는 양해법이 가장 정확하고, 대류가 지배적인 흐름에서는 Chaudhari방법이 가장 정확하다. 계산 시간(CPU)은 양해법 또는 Chaudhari방법이 비슷하게 가장 작고 Bresler방법이 항상 가장 크다.

• 한국산학기술학회논문지
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• 제14권10호
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• pp.5156-5161
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• 2013

분산 공간 데이터 스트림 처리에서는 분산 노드의 활용도를 높이고 고장이 발생한 경우 신속하게 시스템을 복구하기 위해 하위 노드에서 처리된 튜플에 대해 상위 노드로 데이터를 백업한다. 그러나 데이터의 유입량이 증가하고 노드의 연산 결과를 다수의 하위 노드들과 공유할 때 튜플 처리가 지연되면 상위 노드의 삭제 지연으로 인해 백업 데이터의 손실을 야기할 수 있다. 본 논문에서는 노드들의 데이터 유입량과 하위 노드의 연산 처리율을 분석하고 적응적 업스트림 백업 방법을 적용하여 노드의 평균 부하율을 감소시키고, 노드 연산 결과의 공유에 따른 데이터 손실을 최소화하는 방법을 제안한다. 그리고 실험에서는 제안 기법을 통해 데이터 손실을 방지하고, 노드 모니터링에 소요되는 CPU 사용률을 평균 20% 감소시키는 결과를 나타낸다.