Browsing by Author "YANG, JC"

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AN ACCURATE COMPUTATION FOR RAPIDLY VARIED FLOW IN AN OPEN CHANNEL
(1992-02-15)
YANG, JC
;
CHEN, KN
;
LEE, HY
;
土木工程學系
;
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.
COUPLED SIMULATION OF TRANSIENT BED EVOLUTION IN ALLUVIAL CHANNELS
(1990-06-01)
YANG, JC
;
WANG, JY
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交大名義發表
;
土木工程學系
;
National Chiao Tung University
DETERMINATION OF UNIT HYDROGRAPHS BY MULTIPLE STORM ANALYSIS
(1994-12-01)
ZHAO, B
;
TUNG, YK
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YANG, JC
;
土木工程學系
;
Department of Civil Engineering
This paper discusses the derivation of a unit hydrograph by multiple storm analysis using least squares methods. Variations of least squares method was generalized using the framework of weighted ridge analysis. The paper also shows two theorems to support using multi-storm analysis to derive UH. In addition, an issue was addressed on the scaling effect in the conventional multi-storm analysis which could create potential bias toward large storms in deriving a multi-storm UH. For that, a simple scaling procedure was proposed to reduce such potential bias problem. Numerical investigations were conducted to examine the performance of the scaling procedure by comparing with the conventional multi-storm analysis (without scaling) and the HEC-1 weighing procedures. Based on various performance criteria using a total of 39 storms from three watersheds, the proposed scaling procedure was found to produce a quite desirable UH.
ESTIMATION OF UNIT-HYDROGRAPH BY RIDGE LEAST-SQUARES METHOD
(1995-05-01)
ZHAO, B
;
TUNG, YK
;
YANG, JC
;
土木工程學系
;
Department of Civil Engineering
Least squares (LS) methods are frequently used to determine an optimal unit hydrograph (UH) for a watershed. However, the conventionally used ordinary LS method could potentially produce a UH with unwanted fluctuation among hydrograph ordinates. When that occurs, the ridge LS method can be used to reduce noise fluctuation in a derived UH. In the framework of the ridge LS method, a UH can be obtained by minimizing the mean-squared error (MSE) of the estimated UH or direct runoff hydrograph (DRH). Therefore, the ridge LS method theoretically would enhance the predictability of the derived UH. This paper describes methodologies of obtaining the optimal ridge parameter for use in the ridge LS method to estimate a UH. Furthermore, the unit volume constraint is considered in the determination of the optimal ridge parameter. A statistical validation study is also conducted to show that a UH obtained by the ridge LS method has a better predictive capability than the one derived by the ordinary LS method.
INVESTIGATION OF USE OF REACH-BACK CHARACTERISTICS METHOD FOR 2D DISPERSION-EQUATION
(1991-10-01)
YANG, JC
;
CHEN, KN
;
LEE, HY
;
土木工程學系
;
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.
MONTE-CARLO SIMULATION FOR CORRELATED VARIABLES WITH MARGINAL DISTRIBUTIONS
(1994-03-01)
CHANG, CH
;
TUNG, YK
;
YANG, JC
;
土木工程學系
;
Department of Civil Engineering
As computation speed increases, Monte Carlo simulation is becoming a viable tool for engineering design and analysis. However, restrictions are often imposed on multivariate cases in which the involved stochastic parameters are correlated. In multivariate Monte Carlo simulation, a joint probability distribution is required that can only be derived for some limited cases. This paper proposes a practical multivariate Monte Carlo simulation that preserves the marginal distributions of random variables and their correlation structure without requiring the complete joint distribution. For illustration, the procedure is applied to the reliability analysis of a bridge pier against scouring.
MONTE-CARLO SIMULATION FOR CORRELATED VARIABLES WITH MARGINAL DISTRIBUTIONS - CLOSURE
(1995-07-01)
TUNG, YK
;
YANG, JC
;
土木工程學系
;
Department of Civil Engineering
NUMERICAL-SIMULATION OF DEGRADATION OF ALLUVIAL CHANNEL BEDS - DISCUSSION
(1989-05-01)
YANG, JC
;
交大名義發表
;
土木工程學系
;
National Chiao Tung University
;
Department of Civil Engineering
ON THE USE OF THE REACH-BACK CHARACTERISTICS METHOD FOR CALCULATION OF DISPERSION
(1991-02-05)
YANG, JC
;
HSU, EL
;
交大名義發表
;
土木工程學系
;
National Chiao Tung University
The Holly-Preissmann two-point finite difference scheme (HP method) has been popularly used for solving the advection equation. The key idea of this scheme is to solve the dependent variable (i.e. the concentration for the pollutant transport problem) by the method of characteristics with the use of cubic interpolation on the spatial axis. The interpolating polynomials of higher order are constructed by use of the dependent variable and its derivatives at two adjacent grid points. In this paper a new interpolating technique is introduced for incorporation with the Holly-Preissmann two-point method. The new method is denoted herein as the Holly-Preissmann reach-back method (HPRB) and allows the characteristics to project back several time steps beyond the present time level. Through stability analyses it has been observed that the increase of the reach-back time step numbers for the characteristics indeed reduces the numerical damping and dispersive phenomena. A schematic model has been constructed to demonstrate the merits of this new technique for the calculation of the pure advection and dispersion equations. Numerical experiments and comparisons with analytical solutions which support and demonstrate this new technique are presented.
OPTIMAL-DESIGN OF A PILOT OTEC POWER-PLANT IN TAIWAN
(1991-12-01)
TSENG, CH
;
KAO, KY
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YANG, JC
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交大名義發表
;
機械工程學系
In this paper, an optimal design concept has been utilized to find the best designs for a complex and large-scale ocean thermal energy conversion (OTEC) plant. The OTEC power plant under this study is divided into three major subsystems consisting of power subsystem, seawater pipe subsystem, and containment subsystem. The design optimization model for the entire OTEC plant is integrated from these subsystems under the considerations of their own various design criteria and constraints. The mathematical formulations of this optimization model for the entire OTEC plant are described. The design variables, objective function, and constraints for a pilot plant under the constraints of the feasible technologies at this stage in Taiwan have been carefully examined and selected. The numerical optimization method called Sequential Quadratic Programming SQP) is selected to obtain the optimum results. The main purpose of this paper is to demonstrate the design procedure with the optimization techniques for engineering and economics in the OTEC plant so that anyone else can build upon their models according to their needs.
SEDIMENT TRANSPORT MODELING BY COUPLING TECHNIQUE
(1994)
YANG, JC
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WU, CI
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土木工程學系
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Department of Civil Engineering
SENSITIVITY AND UNCERTAINTY ANALYSIS OF A SEDIMENT TRANSPORT MODEL - A GLOBAL APPROACH
(1993-12-01)
CHANG, CH
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YANG, JC
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TUNG, YK
;
土木工程學系
;
Department of Civil Engineering
Computerized sediment transport models are frequently employed to quantitatively simulate the movement of sediment materials in rivers. In spite of the deterministic nature of the models, the outputs are subject to uncertainty due to the inherent variability of many input parameters in time and in space, along with the lack of complete understanding of the involved processes. The commonly used first-order method for sensitivity and uncertainty analyses is to approximate a model by linear expansion at a selected point. Conclusions from the first-order method could be of limited use if the model responses drastically vary at different points in parameter space. To obtain the global sensitivity and uncertainty features of a sediment transport model over a larger input parameter space, the Latin hypercubic sampling technique along with regression procedures were employed. For the purpose of illustrating the methodologies, the computer model HEC2-SR was selected in this study. Through an example application, the results about the parameters sensitivity and uncertainty of water surface, bed elevation and sediment discharge were discussed.
STATISTICAL VALIDATION METHODS - APPLICATION TO UNIT HYDROGRAPHS
(1995-08-01)
ZHAO, B
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TUNG, YK
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YEH, KC
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YANG, JC
;
土木工程學系
In hydraulic and hydrologic studies, engineers develop new models or calibrate existing models by various techniques. One is often concerned with the model validity regarding its ability to predict future events. Five potentially useful statistical validation methods are presented. For illustration, they were applied to examine the predictability of unit hydrographs derived by various methods in the framework of the least squares and its variations. It was found that storm-stacking (conventional multistorm analysis) together with storm-scaling yields the most desirable UH, The general framework of these validation methods can also be applied to a validation study of other hydrologic and hydraulic models.
TIME-LINE INTERPOLATION FOR SOLUTION OF THE DISPERSION-EQUATION
(1990)
YANG, JC
;
HSU, EL
;
交大名義發表
;
土木工程學系
;
National Chiao Tung University
UNCERTAINTY ANALYSIS OF A COMPUTERIZED SEDIMENT TRANSPORT MODEL
(1992)
CHANG, JH
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TUNG, YK
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YANG, JC
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YEH, KC
;
土木工程學系
UNCERTAINTY AND RELIABILITY ANALYSES OF PIT MIGRATION MODEL
(1992)
YEH, KC
;
TUNG, YK
;
YANG, JC
;
土木工程學系
;
Department of Civil Engineering
USE OF CHARACTERISTICS METHOD WITH CUBIC INTERPOLATION FOR UNSTEADY-FLOW COMPUTATION
(1993-02-28)
YANG, JC
;
CHIU, KP
;
交大名義發表
;
土木工程學系
;
National Chiao Tung University
The specified-time-interval (STI) scheme has been used commonly in applying the method of characteristics (MOC) to unsteady open-channel flow problems. However, with the use of STI scheme, the numerical error for the simulation results can always be induced due to the interpolation used to approximate the characteristics trajectory. Hence, in order to remedy the numerical errors caused by the interpolation, one needs to seek some kind of interpolation technique with higher-order accuracy. Instead of the linear interpolation technique, which has been used very commonly and can induce serious numerical diffusion, the Holly-Preissmann two-point method, which is a cubic interpolation technique with fourth-order of accuracy, is proposed here to integrate with the method of characteristics for the computation of one-dimensional unsteady flow in open channel. The concept of reachback and reachout in space and time directions for the characteristics is also introduced to assure the model stability. The computed results from this new model are compared with those computed by using the Preissmann four-point scheme and the multimode method of characteristics with linear interpolation.