USER MANUAL SWAN Cycle III version 40.72A
USER MANUAL SWAN Cycle III version 40.72A
USER MANUAL SWAN Cycle III version 40.72A
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56 Chapter 4<br />
[cfw]<br />
MADSEN<br />
[kn]<br />
Collins bottom friction coefficient.<br />
Default: [cfw] = 0.015.<br />
Note that [cfw] is allowed to vary over the computational region; in that<br />
case use the commands INPGRID FRICTION and READINP FRICTION to define<br />
and read the friction data. The command FRICTION is still required to define<br />
the type of friction expression. The value of [cfw] in this command is then<br />
not required (it will be ignored).<br />
indicates that the expression of Madsen et al. (1988) should be activated.<br />
equivalent roughness length scale of the bottom (in m).<br />
Default: [kn] = 0.05.<br />
Note that [kn] is allowed to vary over the computational region; in that case<br />
use the commands INPGRID FRICTION and READINP FRICTION to define and read<br />
the friction data. This command FRICTION is still required to define the type of<br />
friction expression. The value of [kn] in this command is then not required<br />
(it will be ignored).<br />
TRIad [trfac] [cutfr] [urcrit] [urslim]<br />
With this command the user can activate the triad wave-wave interactions using the LTA<br />
method in the <strong>SWAN</strong> model. If this command is not used, <strong>SWAN</strong> will not account for<br />
triads.<br />
[trfac] the value of the proportionality coefficient α EB .<br />
Default: [trfac] = 0.05.<br />
[cutfr] controls the maximum frequency that is considered in the triad computations. The<br />
value of [cutfr] is the ratio of this maximum frequency over the mean frequency.<br />
Default: [cutfr] = 2.5.<br />
[urcrit] the critical Ursell number appearing in the expression for the biphase.<br />
Default: [urcrit] = 0.2.<br />
[urslim] the lower threshold for Ursell number; if the actual Ursell number is below<br />
[urslim] triad interactions will not be computed.<br />
Default: [urslim] = 0.01.<br />
LIMiter [ursell] [qb]<br />
With this command the user can de-activate permanently the quadruplets when the actual<br />
Ursell number exceeds [ursell]. Moreover, as soon as the actual fraction of breaking<br />
waves exceeds [qb] then the limiter will not be used in case of decreasing action density.