ASSESSMENT OF MACCORMACK SCHEME IN UNSTEADY SEDIMENT LADEN FLOW COMPUTATION

MacCormack scheme as a numerical tool is assessed in solving de St. Venant equations as well as one dimensional advection dispersion equation for unsteady sediment laden flow. Method of characteristics is employed to obtain the next time values at upstream and downstream boundary points. Classical dam break problem, positive/negative surges with analytical solutions, and mass conservation of flow are used to verify the flow part of this numerical model. Sediment part of this model is only partially verified in an equilibrium condition. Although artificial viscosity is necessary in smoothing numerical oscillation inherited from this explicit, second order scheme, no effort is needed to track the hydraulic discontinuity in the case of sudden change from supercritical to subcritical flow. Cases of unsteady flows with different control are discussed in this article. Constrained by stability condition, the time step of MacCormack scheme is relatively small. Boundary conditions are troublesome in solving the advection dispersion equation by MacCormack scheme and it is recommended to be replaced by other scheme.