Browsing by Author "YEH, KC"

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EVALUATION OF SAFETY OF HYDRAULIC STRUCTURES AFFECTED BY MIGRATING PITS
(1993-06-01)
TUNG, YK
;
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.
MODELING NON-UNIFORM-SEDIMENT FLUVIAL PROCESS BY CHARACTERISTICS METHOD
(1995-02-01)
YEH, KC
;
LI, SJ
;
CHEN, WL
;
土木工程學系
;
Department of Civil Engineering
This paper presents a numerical model based on a multimode characteristics method for fully coupled simulation of water and sediment movement in mobile-bed alluvial channels with nonuniform bed materials. Along with the characteristics, the temporal evolutions of flow depth and velocity, bed elevation, and bed-material composition of a well-defined river reach with proper boundary conditions can be simultaneously determined. From the results of the test runs, the proposed model provides useful information about the interactions among disturbance waves of different orders of magnitude and their influence on the formation of flow field, bed topography, and bed-material composition. Such information cannot be easily obtained from finite-difference methods.
MOMENT MODEL OF NONUNIFORM CHANNEL-BEND FLOW .1. FIXED-BEDS
(1993-07-01)
YEH, KC
;
KENNEDY, JF
;
交大名義發表
;
土木工程學系
;
National Chiao Tung University
A nonuniform, fixed-boundary, channel-bend flow is formulated as two coupled sets of equations, each comprising two simultaneous equations, derived from the cross-section-integrated equations (in circular cylindrical coordinates) of conservation of flux of moment of momentum, and the depth-integrated momentum and continuity equations. Boundary shear stresses are related to the primary-flow shear stress and the primary and secondary velocities. The equations are solved numerically and the results found to be in satisfactory agreement with experimental data. The moment formulation elucidates the interplay among the secondary and primary flows, notably the observed flattening of primary velocity profiles, over-shoot of the secondary flow, radial redistribution of the depth-averaged primary velocity, and the secondary translational velocity. The erodible-bed case is treated in the companion paper.
MOMENT MODEL OF NONUNIFORM CHANNEL-BEND FLOW .2. ERODIBLE BEDS
(1993-07-01)
YEH, KC
;
KENNEDY, JF
;
交大名義發表
;
土木工程學系
;
National Chiao Tung University
The hybrid integral-differential moment and momentum model of fixed-boundary channel-bend flows developed in the companion paper is extended to erodible-bed flows. The theta unit sediment discharge is formulated as a power of local depth-averaged theta velocity; and the r unit sediment discharge as proportional to the ratio of the excess of the r bed shear stress, over the radial component of the submerged weight of the sediment bed layer, to the theta bed shear stress. Bed topography is computed from two-dimensional (2D) sediment continuity. The resulting two coupled sets of simultaneous equations are solved numerically. The model yields accurate predictions of the velocities (primary and secondary), and 2D bed topography. The average radial bed slope, primary velocity-profile exponent, and secondary rotational and translational velocities exhibit much larger variations along the channel than in fixed-boundary bends. The increased variation and oscillatory behavior of these quantities are elucidated from moment-of-momentum conservation and interaction of bed topography and flow.
STATISTICAL VALIDATION METHODS - APPLICATION TO UNIT HYDROGRAPHS
(1995-08-01)
ZHAO, B
;
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
;
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.