Numerical Investigation of Two-Dimensional Backwater by the Finite Element Method

抄録

Investigation of two-dimensional backwater of obstacles, or of cross-sectional abrupt changes in a flow system including a large body of water, is often required in hydraulic engineering practice. The problem envisaged is modelled with the aid of the finite element Galerkin procedure, and the fully non-linear equations to be solved are adapted for the Newton-Raphson scheme. In view of the weak formulation of the continuity equation, the scheme can be operated from a cold start (zero initial guess) which produces acceptable linear solutions in the first iterative cycle. Convergence and accuracy explorations are made through model applications to a few channel-type basins, examining their sensitivities to four system parameters defined in advance. The model is also applied to the actual system of Kojima Lake: a man-made estuarine reservoir for irrigation water supply, aiming at investigating horizontal backwater establishment due to the flow expansion and contraction in the vicinity of an influent river mouth and outlet gate, and their implications. Reasonable agreement between computed and observed velocities shows the validity and applicability of the model.