Investigating the Influences of Channel Forcing Effect on Free Bars Using a 2D Finite-Element Morphodynamic Model
Date Issued
2009
Date
2009
Author(s)
Shao, Yun-Chuan
Abstract
In this study a two-dimensional finite-element (2D FE) morphodynamic model is developed to investigate the forcing effects of periodic width variation on free bars. Two features of the proposed model include: (1) The streamline curvature are used to correct the bed load direction effected by secondary flows. (2) The streamline upwind Petrov-Galerkin (SUPG) scheme is applied to solve the sediment continuity equation, which makes it possible to simulate the coexistence of free bars and forced bars (such as side bars and central bars). It is found that the coexistence of free and forced bars is a superposition of the two types of bedform. Thus the free-bar component can be extracted for our study. The results reveal that the bar height, wavelength and celerity of free bars affected by the effect of width variation lead to a periodic wavy pattern when the development of free bars reach the equilibrium state. The mean components of free bars in a cycle of channels with variable-width are inverse proportioned to the amplitude and wave number of width variation. We further derive a forcing factor by combining the amplitude with wave number of width variation and quantitatively prove that the free bars are suppressed by the forcing factor of channels with variable width.
Subjects
Morphodynamic model
finite-element method
streamline-upwind Patrov-Galerkin method
free bars
forcing effect
Type
thesis
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