Browsing by Author "LEE, HY"

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AN ACCURATE COMPUTATION FOR RAPIDLY VARIED FLOW IN AN OPEN CHANNEL
(1992-02-15)
YANG, JC
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CHEN, KN
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LEE, HY
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土木工程學系
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Department of Civil Engineering
A new method combining the Preissmann four-point scheme and the Holly-Preissmann reach-back scheme is introduced to solve the rapidly varied flow problem in an open channel. The Preissmann four-point scheme is well known for the computation of one-dimensional unsteady flow. The Holly-Preissmann reach-back scheme integrates the Holly-Preissmann two-point scheme with the concept of reach-back characteristics, which allows the characteristics to project several time steps beyond the current time level. A spontaneous surge formation case is used to demonstrate and evaluate the applicability of the new method. It has been found that the results from this method are quite compatible with those of Preissmann four-point scheme. In addition, with the appropriate choice of the number of reach-back time steps, this new method can always avoid the numerical oscillation which usually exists when one uses the Preissmann four-point scheme for the condition of Courant number not close to unity.
INVESTIGATION OF USE OF REACH-BACK CHARACTERISTICS METHOD FOR 2D DISPERSION-EQUATION
(1991-10-01)
YANG, JC
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CHEN, KN
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LEE, HY
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土木工程學系
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Department of Civil Engineering
The use of the Holly-Preissmann two-point scheme has been very popular for the calculation of the dispersion equation. The key to this scheme is to use the characteristics method incorporating the Hermite cubic interpolation technique to approximate the trajectory foot of the characteristics. This method can avoid the excessive numerical damping and oscillation associated with most finite difference schemes for advection computation. On the basis of the fundamental idea of the Holly-Preissmann two-point scheme, a new technique is introduced herein for the computation of the two-dimensional dispersion equation. This new scheme allows the characteristics projecting back several time steps to fall on the spatial or temporal axis, while the characteristics foot is still solved by the Holly-Preissmann two-point method. The diffusion portion of the dispersion equation is solved by the commonly used Crank-Nicholson method. The calculation for these two processes consisting of advection and diffusion is carried out separately but consecutively in one time step, a method known as the split operator algorithm. A hypothetical model was constructed to demonstrate the applicability of this new technique for the calculation of the pure advection and dispersion equation in two dimensions.
THE W-MEDIAN OF A CONNECTED STRONGLY CHORDAL GRAPH
(1994-11-01)
LEE, HY
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CHANG, GJ
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交大名義發表
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應用數學系
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National Chiao Tung University
Suppose G = (V,E) is a graph in which every vertex x has a non-negative real number w(x) as its weight. The w-distance sum of a vertex y is D(G,W)(y) = SIGMA(xis-an-element-ofV) d(y,x)w(x). The w-median of G is the set of all vertices y with minimum w-distance sum D(G,W)(y). This paper shows that the w-median of a connected strongly chordal graph G is a clique when w(x) is positive for all vertices x in G. (C) 1994 John Wiley & Sons, Inc.