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            Net-Inflow Method | 
         
         
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              - Net-Inflow Method (8/94): 
                  
  Net-Inflow Method(NIM) is to simulate time-dependent incompressible 
                    viscous flow with moving free surface in any irregular domain. 
                    The position of the free surface is tracked by satisfying 
                    the Navior-Stokes equations and the free-surface boundary 
                    conditions simultaneously. No extra marker or free-surface 
                    kinetic equation is needed. As NIM allows one or more control 
                    volumes to be filled or unfilled in each time step, a large 
                    time step can be used to save computational effort. The CPU 
                    time can be further reduced by using the optional penalty-function 
                    method, which eliminates the pressure variables and replaces 
                    the continuity equation as a velocity constraint. When the 
                    Reynolds number is high (>> 1), the momentum convection in 
                    NIM is included in the equilibrium equation by using the Donor-Cell 
                    upwind method to avoid possible numerical instability. As 
                    the problem is highly non-linear due to the liquid inertia, 
                    unknown free-surface position and non-Newtonain viscosity, 
                    the governing equations have been solved iteratively with 
                    Newton-Raphson method and a fully-implicit time discretization. 
                    NIM has been implemented in a six-noded fixed-mesh triangular 
                    control-volume finite-element program to similate the free-surface 
                    flow in two-dimentional domain or the die-filling process 
                    in two-dimensional thin cavity. In its linear solver, only 
                    the non-zero entries of the sparse matrix are stored to reduce 
                    memory requirement and the linearized equations are solved 
                    iteratively by using the Generalized Minimum Residual Method 
                    (GMRES).
              
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