USER MANUAL SWAN Cycle III version 40.72A

which SWAN performs the computations.
General definitions and remarks 9
SWAN has the option to make computations that can be nested in (coarse) SWAN, WAM
or WAVEWATCH III. In such cases, the spectral grid need not be equal to the spectral
grid in the coarse SWAN, WAM or WAVEWATCH III run.
The spatial grids that need to be defined by the user are (if required):
• a computational spatial grid on which SWAN performs the computations,
• one (or more) spatial input grid(s) for the bottom, current field, water level, bottom
friction and wind (each input grid may differ from the others) and
• one (or more) spatial output grid(s) on which the user requires output of SWAN.
The wind and bottom friction do not require a grid if they are uniform over the area of
interest.
For one-dimensional situations, i.e. ∂/∂y ≡ 0, SWAN can be run in 1D mode.
If a uniform, rectangular computational spatial grid is chosen in SWAN, then all input and
output grids must be uniform and rectangular too, but they may all be different from each
other.
If a curvi-linear computational spatial grid is chosen in SWAN, then each input grid should
be either uniform, rectangular or identical to the used curvi-linear grid or staggered with
respect to the curvi-linear computational grid.
If an unstructured computational spatial grid is chosen in SWAN, then each input grid
should be either uniform, rectangular or identical to the used unstructured grid.
SWAN has the option to make computations that are nested in (coarse) SWAN, WAM or
WAVEWATCH III. In such runs, SWAN interpolates the spatial boundary of the SWAN,
WAM or WAVEWATCH III grid to the (user provided) grid of SWAN (that needs to
(nearly) coincide along the grid lines of WAM or WAVEWATCH III or the output nest
grid boundaries of SWAN). Since, the computational grids of WAM and WAVEWATCH
III are in spherical coordinates, it is recommended to use spherical coordinates in a nested
SWAN when nesting in WAM or WAVEWATCH III.
SWAN using an unstructured mesh may be nested in SWAN employing a regular grid and
vice versa. However, SWAN using an unstructured grid cannot be nested in WAM or
WAVEWATCH III.
Nesting from a 2D model to a 1D model is possible although is should not be done by
using the commands NGRID and NEST. Instead, define the boundary point of the 1D model
as an output point (using command POINTS) and write the spectra for that point using
the command SPECout. In the 1D model, this spectra is used as boundary condition using