Browsing by Author "Yeh, KC"

Now showing 1 - 14 of 14

Application of iterative explicit scheme to 1-D varied flows
(1996)
Hsu, CT
;
Yeh, KC
;
Wu, CM
;
土木工程學系
;
Department of Civil Engineering
Bend-flow simulation using 2D depth-averaged model
(1999-10-01)
Lien, HC
;
Hsieh, TY
;
Yang, JC
;
Yeh, KC
;
土木工程學系
The purpose of this paper is to present a 2D depth-averaged model for simulating and examining flow patterns in channel bends. In particular, this paper proposes a 2D depth-averaged model that takes into account the influence of the secondary flow phenomenon through the calculation of the dispersion stresses arisen from the integration of the products of the discrepancy between the mean and the true velocity distributions. The proposed model uses an orthogonal curvilinear coordinate system to efficiently and accurately simulate the flow field with irregular boundaries. As for the numerical solution procedure, the two-step split-operator approach consisting of the dispersion step and the propagation step with the staggered grid is used to numerically solve the flow governing equations. Two sets of experimental data from de Vriend and Koch and from Rozovskii were used to demonstrate the model's capabilities. The former data set was from a mildly curved channel, whereas the latter was from a sharply curved channel. The simulations considering the secondary flow effect agree well with the measured data. Furthermore, an examination of the dispersion stress terms shows that the dispersion stresses play a major role in the transverse convection of the momentum shifting from the inner bank to the outer bank for flows in both mild and sharp bends.
Depth-averaged two-dimensional curvilinear explicit finite analytic model for open-channel flows
(2000-05-30)
Hsu, CT
;
Yeh, KC
;
Yang, JC
;
土木工程學系
;
Department of Civil Engineering
A depth-averaged two-dimensional model has been developed in the curvilinear co-ordinate system for free-surface flow problems. The non-linear convective terms of the momentum equations are discretized based on the explicit-finite-analytic method with second-order accuracy in space and first-order accuracy in time. The other terms of the momentum equations, as well as the mass conservation equation, are discretized by the finite difference method. The discretized governing equations are solved in turn, and iteration in each time step is adopted to guarantee the numerical convergence. The new model has been applied to various flow situations, even for the cases with the presence of sub-critical and supercritical flows simultaneously or sequentially. Comparisons between the numerical results and the experimental data show that the proposed model is robust with satisfactory accuracy. Copyright (C) 2000 John Wiley & Sons, Ltd.
Iterative explicit simulation of 1D surges and dam-break flows
(2002-03-10)
Hsu, CT
;
Yeh, KC
;
土木工程學系
;
Department of Civil Engineering
The one-dimensional Saint Venant equations for shallow-water flows are used to simulate the flood wave resulting from the sudden opening (or Closure) of a gate or collapse of a dam. An iterative explicit characteristics-based finite-difference method, based on the explicit finite analytic method, is proposed to discretize the dynamic equation, and the conservative control volume method is used for the discretization of the continuity equation. Surge and dam-break, flows in a horizontal, rectangular and frictionless channel were first considered, under such conditions the analytic solutions exist. For the surge simulation, numerical results of the proposed scheme are nearly identical to those obtained from the Preissmann scheme. For the dam-break simulations addressing three ratios of tailwater depth to water depth in the reservoir, the proposed scheme, as compared with the analytic solutions, yields better results than those obtained by the MacCormack scheme, the Gabutti scheme, and Jha et al.'s flux splitting scheme (J. Hydraul. Res. 1996, 34(5):605-621). As the depth ratio approaches zero, the accuracy of the proposed scheme is still satisfactory, even with the dry-bed condition. Investigations then were made for more realistic dam-break flow waves propogating in a sloped and frictional channel. Lacking analytic solutions, the simulating results from the proposed scheme as well as those from Chen's scheme (J. Hydraul. Dir. 1980; 106(HY4):535-556) were compared with the laboratory data collected in 19601961 at the United States Army Engineer Waterways Experiments Station (WES). An assumed initial flow was required for the computer-simulated condition in Chen's model. However, this is riot the case in the proposed model, i.e., a real dry-bed condition was set as the initial condition in the downstream channel of the dam. The consistency between the two simulated results is obvious compared with the experimental data. Copyright (C) 2002 John Wiley Sons, L.td.
Method for performance evaluation of hydrologic and hydraulic models
(1996)
Yang, JC
;
Yeh, KC
;
Tung, YK
;
土木工程學系
;
Department of Civil Engineering
Modeling non-uniform-sediment fluvial process by characteristics method - Closure
(1996-04-01)
Yeh, KC
;
Li, SJ
;
Chen, WL
;
交大名義發表
;
土木工程學系
Numerical simulation of the pit migration
(1997)
Lien, HC
;
Yeh, KC
;
Yang, JC
;
土木工程學系
;
Department of Civil Engineering
The purpose of this paper is to simulate the migration of a pit in the channel bed. When water flows over a pit, the velocity at the upstream end of the pit slows down rapidly owing to the increment of the flow depth, and that at the downstream end of the pit speeds up because of the sudden contraction of the now area. Under such a flow condition, the equilibrium sediment transport formula is inadequate to simulate the local deposition and scouring around the pit. In addition, the critical bed-shear stress without considering the bed slope effect may increase the deposition rate near the upstream end and the scouring rate near the downstream end of the pit. This paper proposes a numerical model to simulate the migration of a pit by considering the nonequilibrium sediment transport behavior and the modified critical bed-shear stress for the movement of sediment on the large bed slope. The capability of the model was verified by comparing the simulated results with one of the experiments executed by Lee et at. (1993).
Regionalization of unit hydrograph parameters .1. Comparison of regression analysis techniques
(1997-04-01)
Tung, YK
;
Yeh, KC
;
Yang, JC
;
土木工程學系
;
Department of Civil Engineering
Hydrologic regionalization is a useful tool that allows for the transfer of hydrological information from gaged sites to ungaged sites. This study developed regional regression equations that relate the two parameters in Nash's IUH model to the basin characteristics for 42 major watersheds in Taiwan. In the process of developing the regional equations, different regression procedures including the conventional univariate regression, multivariate regression, and seemingly unrelated regression were used. Multivariate regression and seeming unrelated regression were applied because there exists a rather strong correlation between the Nash's IUH parameters. Furthermore, a validation study was conducted to examine the predictability of regional equations derived by different regression procedures. The study indicates that hydrologic regionalization involving several dependent variables should consider their correlations in the process of establishing the regional equations. The consideration of such correlation will enhance the predictability of resulting regional equations as compared with the ones from the conventional univariate regression procedure.
Regionalization of unit hydrograph parameters .2. Uncertainty analysis
(1997-04-01)
Yeh, KC
;
Yang, JC
;
Tung, YK
;
土木工程學系
;
Department of Civil Engineering
Hydrologic model parameters obtained from regional regression equations are subject to uncertainty. Consequently, hydrologic model outputs based on the stochastic parameters are random. This paper presents a systematic analysis of uncertainty associated with the two parameters, N and K, in Nash's IUH model from different regional regression equations. The uncertainty features associated with N and K are further incorporated to assess the uncertainty of the resulting IUH. Numerical results indicate that uncertainty of N and K from the regional regression equations are too significant to be ignored.
Reliability analysis of hydraulic structures considering unit hydrograph uncertainty
(1997-02-01)
Zhao, B
;
Tung, YK
;
Yeh, KC
;
Yang, JC
;
土木工程學系
Unit hydrographs (UHs), along with design rainfalls, are frequently used to determine the discharge hydrograph for design and evaluation of hydraulic structures. Due to the presence of various uncertainties in its derivation, the resulting UH is inevitably subject to uncertainty. Consequently, the performance of hydraulic structures under the design storm condition is uncertain. This paper integrates the linearly constrained Monte-Carlo simulation with the UH theory and routing techniques to evaluate the reliability of hydraulic structures. The linear constraint is considered because the water volume of each generated design direct runoff hydrograph should be equal to that of the design effective rainfall hyetograph or the water volume of each generated UH must be equal to one inch (or cm) over the watershed. For illustration, the proposed methodology is applied tb evaluate the overtopping risk of a hypothetical flood detention reservoir downstream of Tong-Tou watershed in Taiwan.
Simulation of bend flow by a depth-averaged two-dimensional model
(1996)
Lien, HC
;
Yang, JC
;
Yeh, KC
;
交大名義發表
;
土木工程學系
The purpose of this study is to develop a depth-averaged two-dimensional model to investigate the now pattern and the development of secondary-flow as flow passes through a bend. The depth-averaged model is developed on the basis of the orthogonal curvilinear coordinate system to account for the complex geometric boundary and the irregular channels. The influence of secondary-now is taken into account by adding a nearly triangular shape of velocity profile to the transverse mean velocity. The simulated results are compared with two sets of experimental data conducted by de Vriend & Koch (1977)(2) and Rozovskii (1961)(5) and the results from the moment model (Yeh & kennedy, 1993)(8) to show the capability of the newly-developed model. Simulation result shows that there is the consistent trend with the experimental data and the results from the Yeh's moment model.
Storm resampling for uncertainty analysis of a multiple-storm unit hydrograph
(1997-07-01)
Zhao, B
;
Tung, YK
;
Yeh, KC
;
Yang, JC
;
土木工程學系
Due to various types of uncertainties involved in the estimation of a unit hydrograph (UH), the UH derived by any method is subject to uncertainties. Based on the concept of the bootstrap resampling technique, a practical methodology called storm resampling is proposed to quantify the uncertainties of multiple-storm UH ordinates and any parameters involved in the estimation of the multiple-storm UH. The important UH ordinates and parameters may include UH peak discharge, UH time-to-peak, UH volume, condition number related to the effective rainfall matrix, mean square error of the UH, and ridge parameter. The proposed bootstrap-based storm resampling technique, along with the least squares and ridge least squares solution techniques, is applied to typhoon storm events over a watershed in Taiwan. The methodology can be applied to other UH solution techniques and other hydrological and hydraulic simulation/optimization models. (C) 1997 Elsevier Science B.V.
Storm resampling for uncertainty analysis of a multiple-storm unit hydrograph
(1997-07-01)
Zhao, B
;
Tung, YK
;
Yeh, KC
;
Yang, JC
;
土木工程學系
Due to various types of uncertainties involved in the estimation of a unit hydrograph (UH), the UH derived by any method is subject to uncertainties. Based on the concept of the bootstrap resampling technique, a practical methodology called storm resampling is proposed to quantify the uncertainties of multiple-storm UH ordinates and any parameters involved in the estimation of the multiple-storm UH. The important UH ordinates and parameters may include UH peak discharge, UH time-to-peak, UH volume, condition number related to the effective rainfall matrix, mean square error of the UH, and ridge parameter. The proposed bootstrap-based storm resampling technique, along with the least squares and ridge least squares solution techniques, is applied to typhoon storm events over a watershed in Taiwan. The methodology can be applied to other UH solution techniques and other hydrological and hydraulic simulation/optimization models. (C) 1997 Elsevier Science B.V.
Uncertainty analysis of sediment transport formulas
(1996)
Yeh, KC
;
Deng, SL
;
Wu, CM
;
土木工程學系
;
Department of Civil Engineering