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Computational grid and time window

The computational grid must be defined by the user. The orientation (direction) can be chosen arbitrarily.


If the computational grid extends outside the input grid, the reader is referred to Section 2.5.3 to find the assumptions of SWASH on depth, current, water level, wind, bottom friction, porosity, grain size, structure height and vegetation density in the non-overlapping area.


The spatial resolution of the computational grid should be sufficient to resolve relevant details of the wave field. Usually a good choice is to take the resolution of the computational grid approximately equal to that of the bottom or current grid.


SWASH may not use the entire user-provided computational grid if the user defines exception values on the bottom grid (see command INPGRID BOTTOM) or on the curvilinear computational grid (see command CGRID). A computational grid point is either

It must be noted that for parallel runs using MPI the user must indicate an exception value when reading the bottom levels (by means of command INPGRID BOTTOM EXCEPTION), if appropriate, in order to obtain good load balancing.


The computational time window must be defined by the user. The computational window in time must start at a time that is early enough that the initial state of SWASH has propagated through the computational area before reliable output of SWASH is expected. Before this time the output may not be reliable since usually the initial state is not known.


The computational time step must be given by the user. Since, SWASH is based on explicit schemes, it is limited by a Courant stability criterion (which couples time and space steps). Moreover, the accuracy of the results of SWASH are obviously affected by the time step. Generally, the time step in SWASH should be small enough to resolve the time variations of computed wave field itself. Usually, it is enough to consider the time variations of the wave boundary conditions.


next up previous index
Next: Input grid(s) and time Up: Choice of grids and Previous: Introduction   Index
The SWASH team 2017-04-06