Browsing by Author "TUNG, YK"

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DETERMINATION OF UNIT HYDROGRAPHS BY MULTIPLE STORM ANALYSIS
(1994-12-01)
ZHAO, B
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TUNG, YK
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YANG, JC
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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
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TUNG, YK
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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.
EVALUATION OF SAFETY OF HYDRAULIC STRUCTURES AFFECTED BY MIGRATING PITS
(1993-06-01)
TUNG, YK
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YEH, KC
;
土木工程學系
;
Department of Civil Engineering
Because it can be carried by flowing water, a sand/gravel pit on the river bed could migrate downstream. Consequently, the presence of pits on river beds could pose a safety threat to in-stream hydraulic structures such as bridge piers. A pit migration model can be used to predict progressive changes of pit geometry as it migrates downstream. However, due to the existence of many uncertainties, the maximum pit depth cannot be predicted with certainty. This paper adopted a simple pit migration model and evaluated the uncertainty associated with the calculated maximum pit depth. Such information is essential for evaluating the probability that a migrating pit could pose a safety threat to a downstream hydraulic structure. Three reliability analysis techniques were applied and their performances were compared.
MONTE-CARLO SIMULATION FOR CORRELATED VARIABLES WITH MARGINAL DISTRIBUTIONS
(1994-03-01)
CHANG, CH
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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
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YANG, JC
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土木工程學系
;
Department of Civil Engineering
PROBABILITY-DISTRIBUTION FOR BENEFIT COST RATIO AND NET BENEFIT
(1992-03-01)
TUNG, YK
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交大名義發表
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土木工程學系
;
National Chiao Tung University
;
Department of Civil Engineering
Benefit/cost ratio and net benefit are the two most commonly used criteria for evaluating the economic merit of public development projects. Due to the existence of uncertainty in cost and benefit estimations, the benefit/cost ratio and net benefit cannot be quantified with absolute certainty. In most probabilistic benefit/cost analysis the probability distributions of the benefit/cost ratio are chosen arbitrarily. The intent of this paper is to present the results from a numerical experiment in attempting to identify the appropriateness of various commonly used probability distributions in describing the random behavior of the benefit/cost ratio and net benefit of an economic development project.
RELIABILITY-BASED PIER SCOUR ENGINEERING - DISCUSSION
(1994-02-01)
CHANG, CH
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TUNG, YK
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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
;
YANG, JC
;
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
;
YEH, KC
;
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.
UNCERTAINTY ANALYSIS OF A COMPUTERIZED SEDIMENT TRANSPORT MODEL
(1992)
CHANG, JH
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TUNG, YK
;
YANG, JC
;
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
UNCERTAINTY AND SENSITIVITY ANALYSES OF PIT-MIGRATION MODEL
(1993-02-01)
YEH, KC
;
TUNG, YK
;
土木工程學系
;
Department of Civil Engineering
Sand and gravel mining from a river bed results in irregular pits on the river bed. The migration of the pits might potentially threaten the safety of downstream bridge piers and other in-stream hydraulic structures. Models were developed to simulate the movement of pits for predicting the effect of migrating pits on in-stream structures. In view of random characteristics inherently residing in hydraulic and hydrologic processes, it is essential for an engineer to assess the overall uncertainty features of a hydraulic model output subjected to its stochastic input parameters. As an illustration, this paper analyzes the uncertainties of a pit migration model recently proposed by Lee et al. (1990) using three methods including the first-order variance estimation method, point estimation technique, and Latin hypercubic sampling. Comparisons of merits and limitations of these methods are also made.