Browsing by Author "Hsieh, Te-Yung"

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A layer-integrated approach for shallow water free-surface flow computation
(2008-12-01)
Hung, Meng-Chi
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Hsieh, Te-Yung
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Tsai, Tung-Lin
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Yang, Jinn-Chuang
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土木工程學系
A novel semi-three-dimensional (semi-3D) layer-integrated approach was proposed in this study for the shallow water free-surface flow computation. A quadratic shape function proposed to approximate the velocity distribution in the layer ensures the continuity of velocities and shear stresses at interfaces. To discretize the governing equations, the finite volume formulation with staggered grid is used. As the two-dimensional (2D) sub-model for locating the free surface is not needed in this approach, the computational time consumption has been dramatically reduced. The model was verified through the wind-induced circulation in a closed basin by comparing the velocity profiles to the analytical solution. The formation of the velocity profiles due to change of viscosity distribution and the evolution process of water surface slope were also investigated. Further, the eddy viscosity is estimated by a function related to discharge, water depth, and Manning's n under the assumption of parabolic distribution of longitudinal velocity along the vertical direction for open channel flows. Two designed hypothetical cases were conducted to examine the proposed eddy viscosity relation and to demonstrate the capabilities of the proposed model. Copyright (C) 2007 John Wiley & Sons, Ltd.
Investigating effect of water level variation and surface tension crack on riverbank stability
(2017-06-01)
Chen, Chien-Hua
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Hsieh, Te-Yung
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Yang, Jinn-Chuang
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土木工程學系
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防災與水環境研究中心
During high flow season, the rise and fall of river water level could induce riverbank instability and threaten structural safety of flood-protection facilities on floodplains. Through a flume experiment, this paper investigates the influences of three factors (namely, drawdown rate of river stage, initial water elevation, and riverbank slope angle) on riverbank stability due to the fall of river water level. From the laboratory experiments it was observed that tension crack appeared in all riverbank failure cases and all failure patterns were of planar type. Moreover, this paper presents a riverbank stability analysis model that explicitly incorporates the integral effect of all forces acting upon the failure plane and tension crack. The prediction accuracy of the proposed model is examined by using experimental data obtained in this study and field data of the Hotophia Creek in the USA and the Sieve River in Italy. A comparison of model simulation results with and without considering tension crack clearly indicates the importance and necessity of including tension crack for achieving good accuracy in riverbank stability simulations. For practical application of the improved riverbank stability model, two empirical formulas for estimating tension crack location and failure plane angle were examined and modified to enhance their appropriateness in riverbank stability simulation. Finally, the improved model with the modified empirical formulas was verified to show its good prediction in riverbank stability analysis. (C) 2017 International Association for Hydro-environment Engineering and Research, Asia Pacific Division. Published by Elsevier B.V. All rights reserved.
Modelling of hyperconcentrated flow in steep-sloped channels
(2018-01-01)
Chen, Chien-Hua
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Lin, Ying-Tien
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Chung, Hau-Rong
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Hsieh, Te-Yung
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Yang, Jinn-Chuang
An unsteady two-dimensional depth-averaged numerical model for hyperconcentrated flows in steep-sloped alluvial channels is developed and applied to the Zhuoshui River in Central Taiwan. In this model, the suspended load and bed load are both included to reproduce actual sediment transport characteristics of steep-sloped channels in the chosen study river reaches. A rheological relationship for Bingham fluid and the formula for the sediment carrying capacity, established through laboratory experiments, are used to describe the hyperconcentrated flow behaviour in the model. At peak discharge during Typhoon Morakot, bed shear stress from the hyperconcentrated flow model can be 150% larger than that from the clear water model. According to the simulation for Tung-Pu-Rey Creek, an upstream tributary of Zhuoshui River, the temporal evolution of bed changes obtained from the model can be used to provide plausible explanations for the reasons behind levee failure during Typhoon Toraji.
Two dimensional shallow-water flow model with immersed boundary method
(2011-12-15)
Chung, Hau-Rong
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Hsieh, Te-Yung
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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
This study demonstrates an immersed boundary (IB) method which integrates a depth-averaged two dimensional flow model is proposed to tackle a typical fluid-solid phase problem in fluid dynamics field. The finite-difference scheme with curvilinear coordinate system is employed to discretize the shallow-water flow equations. Lagrangian markers and Eulerian grid are applied to portray the geometric contour of interior boundary and discretize the flow domain, respectively. The Dirac delta function is accordingly conducted to link both Lagrangian and Eulerian coordinate systems. The numerical simulations of single pier are performed and compared to examine the effect of marker's mesh width, grid size, and the various Dirac delta functions. Experimental data from literatures are compared with numerical results to justify the validity of the proposed IB model. To further demonstrate the model capability, the model is applied to the hypothetical cases of piers in parallel, and compared with theoretical results. (C) 2011 Elsevier Ltd. All rights reserved.
Two-Dimensional Numerical Investigation for Short- and Long-Term Effects of Spur Dikes on Weighted Usable Area of Rhinogobius candidianus (Goby)
(2013-12-01)
Chang, Yin-Lung
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Hsieh, Te-Yung
;
Chen, Chien-Hua
;
Yang, Jinn-Chuang
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土木工程學系
The weighted usable area (WUA) is one of the popular metrics to quantify the stream physical habitat and the effects of instream structures. However, most habitat studies only considered existing or proposed channel geometries in their WUA computations and not how the channel will evolve over time. This study reports a numerical investigation for the effects of spur dikes on WUA along the Juanchiao levee, Touchien River, Taiwan. Seven virtual dikes were placed along the outer bend in the study reach and the Rhinogobius candidianus was selected for target species. The horizontal two-dimensional (2D) flow fields at various flows and the corresponding WUAs for R. candidianus were computed under four channel bathymetry configurations, including: (1)existing; (2)immediately after dikes are implemented; (3)after 10-year channel migration without dikes; and (4)10years after dikes are implemented. The WUA obtained from the first two bathymetry configurations aimed to investigate the short-term spur dikes effect, whereas the last two examined the long-term effect. The channel geometry after 10years channel migration under the conditions of both with and without spur dikes were simulated through a 2D mobile bed model. The analyses of short-term effect showed the WUA of R. candidianus, shortly after the virtual dikes were placed, increases due to increased water depth near the dikes, especially in low-flow conditions. As for long-term effects, however, the WUA in the case with spur dikes are lower than the case without spur dikes, especially in relatively high-flow conditions. The adverse effects of spur dikes on WUA appeared in the long-term investigation and resulted from the ever-increasing water depth and flow velocity around the tip of spur dikes and the main channel. This study showed that the habitat quality and availability might be overestimated if the channel bed changes over time. When using the WUA approach to evaluate the effects of instream structure on physical habitat prior to actually placing them in the river, quantitative predictions of the long-term variation of channel geometry and the associated physical habitat conditions are important. (C) 2013 American Society of Civil Engineers.