Analytical Analysis of Linear Discretization Strategies in Unsteady Open Channel Flows

  • Mohamed S. Ghidaoui
  • Bryan W. Karney
  • Duncan A. McInnis
Conference paper


The equations governing unsteady flow in channels are ([8], [7], [1], [2])
$$\frac{{\partial v}}{{\partial t}} + v\frac{{\partial v}}{{\partial x}} + \frac{{\partial y}}{{\partial x}}+g\left({{S_1} - {S_0}} \right) + \frac{{vq}}{A} = 0$$
$$T\frac{{\partial y}}{{\partial t}} + vT\frac{{\partial y}}{{\partial x}} + A\frac{{\partial v}}{{\partial x}} - q = 0$$
in which t = time, x = distance along the channel, v(x, t) = the average velocity, y(x,t) = depth of the fluid, A(x,t) = the wetted cross sectional area of the channel, T(x,y) = the top width of A(x,t), S f = slope of the energy grade line, S 0 = slope of the bed of the channel, q = lateral inflow per unit length of the channel, and g = the acceleration of gravity. The first of these equations represents the momentum equation while the second is a statement of mass conservation or continuity. It is clear that these two equations are nonlinear hyperbolic partial differential equations (PDEs) which can seldom be solved analytically. As a result, numerical solutions are used to approximate the flow equations. Because of their hyperbolicity, these PDEs can be transformed into ordinary differential equations (ODEs). The result is
$$\frac{{dv}}{{dt}} \pm \frac{g}{c}\frac{{dy}}{{dt}} + g\left( {{S_1} - {S_0}} \right) + \frac{q}{A}\left( {v - c} \right) = 0$$
in which the positive (negative) sign refers to the so-called C + (C -) compatibility equation which is valid along the positive (negative) characteristic equation defined by \(\frac{{dx}} {{dt}} = v \pm c\)( with similar sign conventions).


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Copyright information

© Springer-Verlag Berlin Heidelberg 1995

Authors and Affiliations

  • Mohamed S. Ghidaoui
    • 1
  • Bryan W. Karney
    • 2
  • Duncan A. McInnis
    • 1
  1. 1.Department of Civil & Structural EngineeringThe Hong Kong University of Science & TechnologyKowloonHong Kong, China
  2. 2.Department of Civil EngineeringUniversity of TorontoTorontoCanada

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