Browsing by Author "Chiang, Shih-Wei"

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A Layer-Integrated Model of Solute Transport in Heterogeneous Media
(2014-12-01)
Chen, Hung-En
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Lee, Hui-Ping
;
Chiang, Shih-Wei
;
Tsai, Tung-Lin
;
Yang, Jinn-Chuang
This study presents a numerical solution to the three-dimensional solute transport in heterogeneous media by using a layer-integrated approach. Omitting vertical spatial variation of soil and hydraulic properties within each layer, a three-dimensional solute transport can be simplified as a quasi-three-dimensional solute transport which couples a horizontal two-dimensional simulation and a vertical one-dimensional computation. The finite analytic numerical method was used to discretize the derived two-dimensional governing equation. A quadratic function was used to approximate the vertical one-dimensional concentration distribution in the layer to ensure the continuity of concentration and flux at the interface between the adjacent layers. By integration over each layer, a set of system of equations can be generated for a single column of vertical cells and solved numerically to give the vertical solute concentration profile. The solute concentration field was then obtained by solving all columns of vertical cells to achieve convergence with the iterative solution procedure. The proposed model was verified through examples from the published literatures including four verifications in terms of analytical and experimental cases. Comparison of simulation results indicates that the proposed model satisfies the solute concentration profiles obtained from experiments in time and space.
ASSESSING VULNERABILITY OF RIVERBANK REVETMENTS IN A REGIONAL DRAINAGE SYSTEM DURING STORM OR TYPHOON EVENTS
(2015-01-01)
Lin, Ying-Tien
;
Yang, Jinn-Chuang
;
Hung, Sheng-Hsiang
;
Chiang, Shih-Wei
;
Chang, Yin-Lung
In this study, a quasi three-dimensional hydrodynamic model and field measurements were combined to assess the vulnerable segments of the De-Shang Creek drainage system during the 610 flood and Typhoon Kong-Ray. An automatic monitoring system was installed to record channel water levels, and the displacement and pore water pressure variations inside the riverbank revetments. The results show that the variations of water levels and pore water pressure were almost at the same pace, which indicates the drainage system inside the revetments work well. The flow-induced lateral shear stress and safety factor (S.F.) of river embankments from numerical simulations are the two indexes used to assess the vulnerability of the riverbank revetments. By using the 610 flood and Typhoon Kong-Ray as test cases, the combined hydrodynamic and revetment stability model is able to indicate if riverbank revetments are in danger during the storm or typhoon events. In the observational site, the damages of the revetments in the 610 flood may be due to the exceedance of the flow-induced shear stress over the critical resistance shear stress of the revetments. Overall, this study show the combined hydrodynamic and revetment stability model is a useful non-engineering method on assessing stability of riverbank revetments during storm or typhoon events.
Conjunction effect of stream water level and groundwater flow for riverbank stability analysis
(2011-02-01)
Chiang, Shih-Wei
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Tsai, Tung-Lin
;
Yang, Jinn-Chuang
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防災與水環境研究中心
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Disaster Prevention and Water Environment Research Center
Variations in pore-water pressure determined by the groundwater table within a riverbank have been investigated and recognized as an essential factor in determining riverbank stability with respect to mass failure. However, the effect of pore-water pressure is taken into account for most of the existing riverbank stability models under some simplified assumptions, and the limitations of predicting ability may arise. To avoid the unrealistic estimation of pore-water pressure distribution, the new approach proposed here is to couple riverbank stability with groundwater flow modeling, and apply this to tackle the conjunction effect between river stage and groundwater table. Moreover, riverbank material characteristics and the influence of infiltration can be taken into consideration via groundwater flow modeling. Two hypothetical examples, stage rising and stage falling, are used to investigate the capabilities of the present study and two representative methods. The simulated results show that riverbank failure is triggered particularly during the falling stage, which has been pointed out by other researchers as well. Furthermore, the riverbank material characteristics predominantly control the occurrence of failure and should be considered regarding assessment of riverbank stability. Additionally, the effects of parameters indicate that riverbanks with soil properties of low permeability or high specific yield with great infiltration intensity during the falling stage have a tendency to riverbank failure.
Examination of characteristics method with cubic interpolation for advection-diffusion equation
(2006-12-01)
Tsai, Tung-Lin
;
Chiang, Shih-Wei
;
Yang, Jinn-Chuang
;
土木工程學系
;
防災與水環境研究中心
In this study, the use of the characteristics method integrated with the Hermite cubic interpolation or the cubic-spline interpolation on the space line or the time line, i.e., the HCSL scheme, the CSSL scheme, the HCTL scheme, and the CSTL scheme, respectively, for solving the advection-diffusion equation is examined. The advection and diffusion of a Gaussian concentration distribution in a uniform flow with constant diffusion coefficient is used to conduct this investigation. The effects of parameters, such as Peclet number, Courant number, and the reachback number, on these four schemes used herein for solving the advection-diffusion equation are investigated. The simulated results show that the CSSL scheme is comparable to the HCSL scheme, and the two schemes seem insensitive to Courant number as compared with the HCTL scheme and the CSTL scheme. With large Peclet number, for small Courant number the HCTL scheme is more accurate than the HCSL scheme and the CSSL scheme. However, for large Courant number the HCTL scheme has worse computed results in comparison with the HCSL scheme and the CSSL scheme. With small Peclet number, the HCTL scheme, the HCSL scheme, and the CSSL scheme have close simulated results. Despite Peclet number, for small Courant number the CSTL scheme is comparable to the HCTL scheme, but for large Courant number the former scheme provides unacceptable simulated results in which very large numerical diffusion is induced due to the effect of the natural endpoint constraint. For large Peclet number the HCSL scheme and the CSSL scheme integrated with the reachback technique can improve simulated results, but for small Peclet number the HCSL scheme and the CSSL scheme seem not to be influenced by increasing the reachback number. (c) 2005 Elsevier Ltd. All rights reserved.