USER MANUAL SWAN Cycle III version 40.72A

48 Chapter 4
With this optional command (not fully tested) a nested SWAN run can be carried out
with the boundary conditions obtained from a coarse grid WAM run (WAM Cycle 4.5,
source code as distributed by the Max Planck Institute in Hamburg). For this nested
SWAN run the user has to give the CGRID command to define the computational grid
before this BOUNDNEST2 command. The computational grid for SWAN in geographic space
is the area bounded by the WAM coarse run nest (WAM boundary points of the nest).
This implies that the boundaries of the WAM nest and the boundaries of the SWAN
computational area should be (nearly) identical (see below). The spectral frequencies and
directions of the coarse grid run do not have to coincide with the frequencies and directions
used in the nested SWAN run (as defined in the CGRID command); SWAN will interpolate
to these frequencies and directions in the nested run (see Section 2.6.3).
Note that SWAN will accept output of a WAM output location only if the SWAN grid
point on the nest boundary lies within a rectangle between two consecutive WAM output
locations with a width equal to 0.1 times the distance between these output locations on
either side of the line between these WAM output locations.
This BOUNDNEST command is not available for 1D computations.
Only boundary conditions generated by WAM Cycle 4.5 can be read properly by SWAN.
A nested SWAN run may use either Cartesian or spherical coordinates. A curvi-linear
grid may be used in the nested grid but the boundaries of this nest should conform to the
rectangular course grid nest boundaries.
WAM output files are unformatted (binary); this usually implies that WAM and SWAN
have to run on the same computer. For those cases where WAM and SWAN run on different
types of machines (binary files do not transfer properly), the option FREE is available in
this command. The distributed version of WAM does not support the required free format
nesting output; WAM users who modify WAM such that it can make formatted output,
must modify WAM such that the files made by WAM can be read in free format, i.e. with
at least a blank or comma between numbers.
Note that the format of time and date that can be accepted by SWAN is YYMMDDHHMMSS
(i.e. include seconds).
’fname’ a file name that contains all the names of WAM files containing the nested
boundary conditions in time-sequence (usually one file per day). For example,
the contents of ’fname’ can look like:
CBO9212010000
CBO9212020000
CBO9212030000
....
SWAN will read the boundary data from these WAM files one after the other.
UNFORMATTED the user indicates that the WAM files are binary.