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비대칭 경로를 지원하는 개선된 DSR 라우팅에 관한 연구
이광배,김현욱,곽승욱,박용정 명지대학교 산업기술연구소 2001 産業技術硏究所論文集 Vol.20 No.-
This paper introduces a dynamic source routing protocol supporting asymmetric routes on mobile ad hoc network. For performance evaluation, average route discovery time, average data transfer time, average route recovery time and data reception rate were considered with several scenarios relating to connection pattern, moving scenario, usage of secondary route chche in intermediate nodes and periodic hello message interval. As the results, we found that the data reception rate increased as the node mobility went down and the number of maximum connections between nodes was reduced. In the case that secondary route cache was used in the intermediate nodes, the average data transfer time was decreased because the possibility of route discovery to destination node was increased. In addition, it was found that the hello message interval at 0.1 to 1 second was fairly good.
Computation of Water and Air Flow with Submerged Hydrofoil by Interface Capturing Method
Kwag, Seung-Hyun The Korean Society of Mechanical Engineers 2000 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.14 No.7
Free-surface flows with an arbitrary deformation, induced by a submerged hydrofoil, are simulated numerically, considering two-fluid flows of both water and air. The computation is performed by a finite volume method using unstructured meshes and an interface capturing scheme to determine the shape of the free surface. The method uses control volumes with an arbitrary number of faces and allows cell wise local mesh refinement. The integration in space is of second order, based on midpoint rule integration and linear interpolation. The method is fully implicit and uses quadratic interpolation in time through three time levels. The linear equations are solved by conjugate gradient type solvers, and the non-linearity of equations is accounted for through Picard iterations. The solution method is of pressure-correction type and solves sequentially the linearized momentum equations, the continuity equation, the conservation equation of one species, and the equations for two turbulence quantities. Finally, a comparison is quantitatively made at the same speed between the computation and experiment in which the grid sensitivity is numerically checked.
Lift/Drag Prediction of 3-Dimensional WIG Moving Above Free Surface
Kwag, Seung-Hyun The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.3
The aerodynamic effects of a 3-dimensional Wing in Ground Effect (WIG) which moves above the free surface has been numerically investigated via finite difference techniques. The air flow field around a WIG is analyzed by a Marker & Cell (MAC) based method, and the interactions between WIG and the free surface are studied by the pressure distributions on the free surface. Waves are generated by the surface pressure distribution, and a Navier-Stokes solver has been employed, to include the nonlinearities in the free surface conditions. The pressure values Cp and lift/drag ratio are reviewed by changing the height/chord ratio. In the present computations a NACA0012 airfoil with a span/chord ratio of 3.0 are treated. Through computational results, it is confirmed that the free surface can be treated as a rigid wavy wall.
Computation of Flows Around a High Speed Catamaran
Kwag, Seung-Hyun The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.4
A numerical study is carried out to clarify the characteristics of flow fields and breaking phenomena around a high speed catamaran hull advancing on calm water. Computations are carried out for Froude numbers between 0.2 and 1.0 and for ratios of the distance between hulls to the catamaran length varying between 0.2 and 0.5 for a mathematically defined Wigley hull. A Navier-Stokes solver which includes the nonlinearities of free surface conditions is employed. Computations are performed in a rectangular grid system based on the Marker & Cell method. For validation, present computation results are compared with existing experimental results. As an application, the results of the displacement catamaran are used for the breaking analysis.
Bow Wave Breaking and Viscous Interaction of Stern Wave
Kwag, Seung-Hyun The Korean Society of Mechanical Engineers 2000 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.14 No.4
The bow wave breaking and the viscous interaction of stern wave are studied by simulating the free-surface flows. The Navier-Stokes equation is solved by a finite difference method in which the body-fitted coordinate system, the wall function and the triple-grid system are invoked. After validation, the calculations are extended to turbulent flows. The wave elevation at the Reynolds number of $10^4$ is much less than that at $10^6$ although the Froude number is the same. The numerical appearance of the sub-breaking waves is qualitatively supported by experimental observation. They are also applied to study the stern flow of S-103 for which extensive experimental data are available. Although the interaction between separation and the stern wave generation are not yet clear, the effects of the bow wave on the development of the boundary layer flows are concluded to be significant.
Effect of Grid Size on the Computation of Free-Surface Waves
Seung-Hyun Kwag(곽승현) 한국해양공학회 1997 韓國海洋工學會誌 Vol.11 No.2
수치격자의 크기제한에 의한 자유표면 유동해석 문제를 효율적으로 다루기 위하여 자유표면의 모든 格子를 x 방향으로 4, 8, 12개로 等分割하고, y 방향으로는 4개로 잘게 잘라서 계산하였다. 이중격자 또는 삼중격자로 Navier-Stokes 방정식의 각항에 크기가 다른 격자를 사용해 효율을 향상시키는 계산방법의 연장으로, 본 논문에서는 자유표면 방정식에 보다 세분화된 격자를 적용해, Marker Particle 이동및 자유수면형성에 효율향상을 줄수 있는 수치방법을 도입하였다. 계산결과에 의하면 초기사용 격자가 coarse한 경우가 본방법의 효과가 커짐을 알수 있고 대상물체로는 층류유동에서 Wigley모형과 난류유동의 S103 모형이다.
Computation of Free Surface Flows and Detection of Sub - Breaking
Seung-Hyun Kwag(곽승현) 한국해양공학회 1999 韓國海洋工學會誌 Vol.13 No.3(Ⅰ)
준쇄파(쇄파발생전 리플형태의 불안정파)를 수치적으로 해석하고 예측하기 위하여 수중날개를 대상으로 점성유동장의 계산을 수행하였다. Navier-Stokes 방정식을 사용하여 자유수면을 계산하였고 정도향상을 위하여 Euler 형태의 자유표면조건에 고차의 유한차분법을 적용하였다. 이산화 과정에서 자유표면 격자에 3차 풍상미분항을 적용시켜 수치계산을 수행하였고, 계산결과를 사용하여 준쇄파의 생성조건을 규명하였다.