GEN1 [cf10] [cf20] [cf30] [cf40] [edmlpm] [cdrag] [umin] [cfpm]
With this command the user indicates that SWAN should run in first-generation mode (see Scientific/Technical documentation).
[cf10] | controls the linear wave growth. | |
Default: [cf10] = 188. | ||
[cf20] | controls the exponential wave growth. | |
Default: [cf20] = 0.59 | ||
[cf30] | controls the exponential wave growth. | |
Default: [cf30] = 0.12 | ||
[cf40] | controls the dissipation rate, i.e., the time decay scale. | |
Default: [cf40] = 250. | ||
[edmlpm] | maximum non-dimensionless energy density of the wind sea part of the spectrum | |
according to Pierson Moskowitz. | ||
Default: [edmlpm] = 0.0036 | ||
[cdrag] | drag coefficient. | |
Default: [cdrag] = 0.0012 | ||
[umin] | minimum wind velocity (relative to current; all wind speeds are taken at 10 m | |
above sea level). | ||
Default: [umin] = 1. | ||
[cfpm] | coefficient which determines the Pierson Moskowitz frequency: | |
= 2 g [cfpm] /U_{10} | ||
Default: [cfpm] = 0.13 |
GEN2 [cf10] [cf20] [cf30] [cf40] [cf50] [cf60] [edmlpm] [cdrag] [umin] [cfpm]
With this command the user indicates that SWAN should run in second-generation mode (see Scientific/Technical documentation).
The variables are identical to those in the GEN1 command except that [cf50] and [cf60] are added.
[cf50] | controls the spectral energy scale of the limit spectrum. | |
Default: [cf50] = 0.0023 | ||
[cf60] | controls the spectral energy scale of the limit spectrum. | |
Default: [cf60] = -0.223 |
| JANSsen [cds1] [delta] | | | GEN3 < --> KOMen [cds2] [stpm] > (AGROW [a]) | | | WESTHuysen |
With this command the user indicates that SWAN should run in third-generation mode for wind input, quadruplet interactions and whitecapping.
Triads, bottom friction and depth-induced breaking are not activated by this command. See also the Scientific/Technical documentation for more information.
The option GEN3 KOMEN is default.
JANSSEN | linear growth | : Cavaleri and Malanotte-Rizzoli (1981), activated only |
if the keyword AGROW is present (see below) | ||
exponential growth | : Janssen (1989, 1991). | |
[cds1] | coefficient for determining the rate of whitecapping dissipation (= C_{ds}/). | |
Default: [cds1] = 4.5. | ||
[delta] | coefficient which determines the dependency of the whitecapping on wave number | |
(mix with Komen et al. formulation). | ||
Default: [delta] = 0.5. | ||
KOMEN | linear growth | : Cavaleri and Malanotte-Rizzoli (1981), activated only |
if the keyword AGROW is present (see below) | ||
exponential growth | : Komen et al. (1984). | |
[cds2] | coefficient for determining the rate of whitecapping dissipation (= C_{ds}). | |
Default: [cds2] = 2.36e-5. | ||
[stpm] | value of the wave steepness for a Pierson-Moskowitz spectrum (= ). | |
Default: [stpm] = 3.02e-3. | ||
WESTH | nonlinear saturation-based whitecapping combined with wind input of Yan (1987). | |
AGROW | if this keyword is used, the wave growth term of Cavaleri and Malanotte (1981) is | |
activated. | ||
if this keyword is NOT used, the wave growth term of Cavaleri and Malanotte (1981) | ||
is NOT activated. | ||
Note that in nonstationary runs SWAN start with INIT ZERO (see command INIT), | ||
wave energy remains zero unless wave energy penetrates over the boundary or AGROW | ||
is activated. In case of stationary runs, however, SWAN will start with a first guess. | ||
[a] | if the wave growth term of Cavaleri and Malanotte (1981) is activated, [a] is | |
the proportionality coefficient in that term. | ||
Default: [a] = 0.0015. |
WCAPping KOMen [cds2] [stpm] [powst] [delta] [powk]
With this command the user can influence whitecapping which is usually included in the computations. Can be de-activated with command OFF WCAP.
KOMEN | whitecapping according to Komen et al. (1984) is applied. | |
[cds2] | coefficient for determining the rate of whitecapping dissipation (= C_{ds}). | |
Default: [cds2] = 2.36e-5. | ||
[stpm] | value of the wave steepness for a Pierson-Moskowitz spectrum (= ). | |
Default: [stpm] = 3.02e-3. | ||
[powst] | power of steepness normalized with the wave steepness of a Pierson-Moskowitz | |
spectrum. | ||
Default: [powst] = 2. | ||
[delta] | coefficient which determines the dependency of the whitecapping on wave number. | |
Default: [delta] = 1. | ||
Note that this default has been changed since version 40.91A. The setting | ||
[delta] = 1 will improve the prediction of the wave energy at low frequencies, | ||
and hence the mean wave period. The original default was [delta] = 0, which | ||
corresponds to WAM Cycle 3. See the Scientific/Technical documentation for | ||
further details. | ||
[powk] | power of wave number normalized with the mean wave number. | |
Default: [powk] = 1. |
QUADrupl [iquad] [lambda] [Cnl4] [Csh1] [Csh2] [Csh3]
With this option the user can influence the computation of nonlinear quadruplet wave interactions. Default: the quadruplets are included
in the computations. Can be de-activated with command OFF QUAD.
Note that the DIA approximation of the quadruplet interactions
is a poor approximation for long-crested waves and frequency resolutions that are deviating much more than 10% (see command CGRID).
Note that DIA is usually updated per sweep, either semi-implicit ([iquad] = 1) or explicit ([iquad] = 2).
However, when ambient current is included, the bounds of the directional sector within a sweep may be different for each frequency bin
(particularly the higher frequencies are modified by the current). So there may be some overlap of frequency bins between the sweeps,
which is not energy conservative. To prevent this the user is advised to choose the integration of DIA per iteration instead of per sweep,
i.e. [iquad] = 3.
If you want to speed up your computation a bit more, than the choice [iquad] = 8 is a good one.
[iquad] | the quadruplets can be integrated by four different numerical procedures: | |
= 1 semi-implicit computation of the nonlinear transfer with DIA per sweep | ||
= 2 fully explicit computation of the nonlinear transfer with DIA per sweep | ||
= 3 fully explicit computation of the nonlinear transfer with DIA per iteration | ||
= 8 fully explicit computation of the nonlinear transfer with DIA per iteration, | ||
but neighbouring interactions are interpolated in piecewise constant manner. | ||
other techniques for the computation of quadruplets are | ||
= 4 Multiple DIA | ||
= 51 XNL (deep water transfer) | ||
= 52 XNL (deep water transfer with WAM depth scaling) | ||
= 53 XNL (finite depth transfer) | ||
Default: [iquad] = 2. | ||
[lambda] | coefficient for quadruplet configuration in case of DIA. | |
Default: [lambda]=0.25. | ||
[Cnl4] | proportionality coefficient for quadruplet interactions in case of DIA. | |
Default: [Cnl4]= 3 x 10^{7}. | ||
[Csh1] | coefficient for shallow water scaling in case of DIA. | |
Default: [Csh1]=5.5. | ||
[Csh2] | coefficient for shallow water scaling in case of DIA. | |
Default: [Csh2]=0.833333. | ||
[Csh3] | coefficient for shallow water scaling in case of DIA. | |
Default: [Csh3]=-1.25. |
| -> CONstant [alpha] [gamma] BREaking < | BKD [alpha] [gamma0] [a1] [a2] [a3]
With this command the user can influence depth-induced wave breaking in shallow water in the SWAN model.
If this command is not used, SWAN will account for wave breaking anyhow (with default options and
values). If the user wants to specifically ignore wave breaking, he should use the command: OFF BREAKING.
CONSTANT | indicates that a constant breaker index is to be used. | |
[alpha] | proportionality coefficient of the rate of dissipation. | |
Default: [alpha] = 1.0. | ||
[gamma] | the breaker index, i.e. the ratio of maximum individual | |
wave height over depth. | ||
Default: [gamma] = 0.73. | ||
BKD | indicates that the breaker index scales with both the | |
bottom slope (=) and the dimensionless depth (=kd) | ||
[alpha] | proportionality coefficient of the rate of dissipation. | |
Default: [alpha] = 1.0. | ||
[gamma0] | the reference for horizontal slopes. | |
Default: [gamma0] = 0.54. | ||
[a1] | first tunable coefficient for the breaker index. | |
Default: [a1] = 7.59. | ||
[a2] | second tunable coefficient for the breaker index. | |
Default: [a2] = -8.06. | ||
[a3] | third tunable coefficient for the breaker index. | |
Default: [a3] = 8.09. |
| -> JONswap CONstant [cfjon] | | COLLins [cfw] FRICtion < | MADsen [kn] | | RIPples [S] [D]
With this optional command the user can activate bottom friction. If this command is not used, SWAN will not account for bottom friction.
In SWAN four different formulations are available, i.e., that of Hasselmann et al. (1973, JONSWAP),
Collins (1972), Madsen et al. (1988) and Smith et al. (2011).
The default option is: JONSWAP with a constant friction coefficient. The recommended value for typical sandy bottoms is
0.038 m^{2}s^{-3}. Note that this value is to be applied for both wind sea and swell conditions.
(The use of the previous default value of 0.067 m^{2}s^{-3} is discouraged, even for wind sea conditions!)
For smoother seafloors, like the Gulf of Mexico, a lower value of 0.019 m^{2}s^{-3} is advised.
JONSWAP | indicates that the semi-empirical expression derived from the JONSWAP results | |
for bottom friction dissipation (Hasselmann et al., 1973, JONSWAP) should be | ||
activated. This option is default. | ||
CONSTANT | this default option indicates that the JONSWAP coefficient is constant. | |
[cfjon] | coefficient of the JONSWAP formulation. | |
Default: [cfjon] = 0.038. | ||
COLLINS | indicates that the expression of Collins (1972) should be activated. | |
[cfw] | Collins bottom friction coefficient. | |
Default: [cfw] = 0.015. | ||
Note that [cfw] is allowed to vary over the computational region; in that | ||
case use the commands INPGRID FRICTION and READINP FRICTION to define | ||
and read the friction data. The command FRICTION is still required to define | ||
the type of friction expression. The value of [cfw] in this command is then | ||
not required (it will be ignored). | ||
MADSEN | indicates that the expression of Madsen et al. (1988) should be activated. | |
[kn] | equivalent roughness length scale of the bottom (in m). | |
Default: [kn] = 0.05. | ||
Note that [kn] is allowed to vary over the computational region; in that case | ||
use the commands INPGRID FRICTION and READINP FRICTION to define and read | ||
the friction data. This command FRICTION is still required to define the type of | ||
friction expression. The value of [kn] in this command is then not required | ||
(it will be ignored). | ||
RIPPLES | indicates that the expression of Smith et al. (2011) should be activated. | |
Here friction depends on the formation of bottom ripples and sediment size. | ||
[S] | the specific gravity of the sediment. | |
Default: [S] = 2.65. | ||
[D] | the sediment diameter (in m). | |
Default: [D] = 0.0001. |
TRIad [itriad] [trfac] [cutfr] [a] [b] [urcrit] [urslim]
With this command the user can activate the triad wave-wave interactions using either the LTA method or the SPB method.
If this command is not used, SWAN will not account for triads.
[itriad] | indicates the approximation method for the triad computation: | |
= 1 the LTA method of Eldeberky (1996) | ||
= 2 the SPB method of Becq-Girard et al. (1999) | ||
Default: [itriad] = 1. | ||
[trfac] | proportionality coefficient. Its value is 0.8 in case of LTA, and 0.9 in | |
case of the SPB method. | ||
Default: [trfac] = 0.8. | ||
[cutfr] | controls the maximum frequency that is considered in the LTA computation. The | |
value of [cutfr] is the ratio of this maximum frequency over the mean frequency. | ||
Default: [cutfr] = 2.5. | ||
[a] | first calibration parameter for tuning K in Eq. (5.1) of Becq-Girard et al. (1999). | |
This parameter is associated with broadening of the resonance condition. | ||
The default value is 0.95 and is calibrated by means of laboratory experiments. | ||
Default: [a] = 0.95. | ||
[b] | second calibration parameter for tuning K in Eq. (5.1) of Becq-Girard et al. (1999). | |
This parameter is associated with broadening of the resonance condition. | ||
The default value is -0.75 and is calibrated by means of laboratory experiments. | ||
However, it may not be appropriate for true 2D field cases as it does not scale | ||
with the wave field characteristics. Hence, this parameter is set to zero. | ||
Default: [b] = 0.0. | ||
[urcrit] | the critical Ursell number appearing in the expression for the biphase. | |
Default: [urcrit] = 0.2. | ||
[urslim] | the lower threshold for Ursell number; if the actual Ursell number is below | |
[urslim] triad interactions will not be computed. | ||
Default: [urslim] = 0.01. |
VEGEtation < [height] [diamtr] [nstems] [drag] >
With this command the user can activate wave damping due to vegetation based on the Dalrymple's formula (1984). If this command is not
used, SWAN will not account for vegetation effects.
The vegetation (rigid plants) can be divided over a number of vertical segments and so, the
possibility to vary the vegetation vertically is included. Each vertical layer represents some characteristics of the plants. These
variables as indicated below can be repeated as many vertical layers to be chosen.
[height] | the plant height per layer (in m). | |
[diamtr] | the diameter of each plant stand per layer (in m). | |
[nstems] | the number of plant stands per square meter for each layer. | |
Note that [nstems] is allowed to vary over the computational region to | ||
account for the zonation of vegetation. In that case use the commands | ||
INPGRID NPLANTS and READINP NPLANTS to define and read the vegetation | ||
density. The (vertically varying) value of [nstems] in this command will | ||
be multiplied with this horizontally varying plant density. | ||
Default: [nstems] = 1. | ||
[drag] | the drag coefficient per layer. |
TURBulence [ctb] (CURrent [tbcur])
With this optional command the user can activate turbulent viscosity.
This physical effect is also activated by reading values of the turbulent viscosity
using the READGRID TURB command, but then with the default value of [ctb].
The command READGRID TURB is necessary if this command TURB is used since the
value of the viscosity is assumed to vary over space.
[ctb] | the value of the proportionality coefficient appearing in the energy | |
dissipation term. | ||
Default: [ctb] = 0.01. | ||
CURRENT | if this keyword is present the turbulent viscosity will be derived from the | |
product of the depth and the absolute value of the current velocity. If the | ||
command READGRID TURB is used, this option is ignored; the values read | ||
from file will prevail. | ||
[tbcur] | the factor with which depth x current velocity is multiplied in order to | |
get the turbulent viscosity. | ||
Default: [tbcur] = 0.004. |
MUD [layer] [rhom] [viscm]
With this command the user can activate wave damping due to mud based on Ng (2000). If this command or the commands
INPGRID MUDLAY and READINP MUDLAY are not used, SWAN will not account for muddy bottom effects.
[layer] | the thickness of the mud layer (in m). | |
Note that [layer] is allowed to vary over the computational region to | ||
account for the zonation of muddy bottom. In that case use the commands | ||
INPGRID MUDLAY and READINP MUDLAY to define and read the layer | ||
thickness of mud. The value of [layer] in this command is then not | ||
required (it will be ignored). | ||
[rhom] | the density of the mud layer (in kg/m^{3}). | |
Default: [rhom] = 1300. | ||
[viscm] | the kinematic viscosity of the mud layer (in m^{2}/s). | |
Default: [viscm] = 0.0076. |
LIMiter [ursell] [qb]
With this command the user can de-activate permanently the quadruplets when the actual Ursell number
exceeds [ursell]. Moreover, as soon as the actual fraction of breaking waves exceeds [qb] then the action limiter
will not be used in case of decreasing action density.
[ursell] | the upper threshold for Ursell number. | |
Default: [ursell] = 10.0. | ||
[qb] | the threshold for fraction of breaking waves. | |
Default: [qb] = 1.0. |
| -> TRANSm [trcoef] | | | | TRANS1D < [trcoef] > | | | OBSTacle < TRANS2D < [trcoef] > > & | | | | -> GODA [hgt] [alpha] [beta] | | DAM < | | DANGremond [hgt] [slope] [Bk] | | -> RSPEC | (REFL [reflc] < > ) LINe <[xp] [yp]> | RDIFF [pown] |
CANNOT BE USED IN 1D-MODE.
With this optional command the user provides the characteristics of a (line of) sub-grid obstacle(s)
through which waves are transmitted or against which waves are reflected (possibly both at the same
time). The obstacle is sub-grid in the sense that it is narrow
compared to the spatial meshes; its length should be at least one mesh length.
The location of the obstacle is defined by a sequence of corner points of a line. The obstacles interrupt
the propagation of the waves from one grid point to the next wherever this obstacle line is located between
two neighbouring grid points (of the computational grid; the resolution of the obstacle is therefore equal
to the computational grid spacing). This implies that an obstacle to be effective must be located such that
it crosses at least one grid line. This is always the case when an obstacle is larger than one mesh
length.
The computation of transmission and reflection is problematic if an obstacle runs exactly through one or
more grid points of the computational structured grid; SWAN will move the obstacle over a small
distance (1% of the mesh size) if this occurs. Note that this will not be done in case of unstructured
grids.
The reflection results are incorrect if more than one obstacle crosses the
same grid line between two neighbouring grid points. SWAN is not able to detect this, so the user must
check if his model fulfills this condition.
TRANSM | with this option the user indicates that the transmission coefficient is a constant. | |
[trcoef] | constant transmission coefficient, formulated in terms of wave height, i.e. ratio | |
of transmitted significant wave height over incoming significant wave height. | ||
Default: [trcoef]=0.0 (no transmission = complete blockage). | ||
TRANS1D | with this option the user indicates that the transmission coefficient is frequency | |
dependent. For each frequency the user can specify a transmission coefficient as | ||
indicated below. The number of these transmission values must be equal to the | ||
number of frequencies, i.e. [msc] + 1. | ||
[trcoef] | transmission coefficient per frequency, formulated in terms of wave height, i.e. | |
ratio of transmitted significant wave height over incoming significant wave height. | ||
TRANS2D | with this option the user indicates that the transmission coefficient is frequency | |
and direction dependent. For each direction the user can assign different trans- | ||
mission coefficients to frequencies. The number of these transmission values must | ||
be equal to the number of frequencies multiplied with the number of directions. | ||
[trcoef] | transmission coefficient per frequency for each direction, formulated in terms of | |
wave height, i.e. ratio of transmitted significant wave height over incoming | ||
significant wave height. It is advised to put the values assigned to all frequencies | ||
on a single line for each direction. So the number of lines equals the number of | ||
directions. Each line may be terminated with a continuation mark &. | ||
DAM | with this option the user indicates that the transmission coefficient depends on | |
the incident wave conditions at the obstacle and on the obstacle height (which | ||
may be submerged). | ||
GODA | with this option the user indicates to use the Goda/Seelig formula (1979) for | |
computing transmission coefficient. | ||
[hgt] | the elevation of the top of the obstacle above reference level (same reference | |
level as for bottom etc.); use a negative value if the top is below that reference | ||
level. If this command is used, this value is required. | ||
[alpha] | coefficient determining the transmission coefficient for Goda's transmission formula. | |
Default: [alpha]=2.6. | ||
[beta] | another coefficient determining the transmission coefficient for Goda's transmission | |
formula. | ||
Default: [beta]=0.15. | ||
DANGREMOND | with this option the user indicates to use the d'Angremond/Van der Meer formula | |
(1996) for computing the transmission coefficient. | ||
[hgt] | the elevation of the top of the obstacle above reference level (same reference | |
level as for bottom etc.); use a negative value if the top is below that reference | ||
level. If this command is used, this value is required. | ||
[slope] | the slope of the obstacle (in degrees). If this command is used, this value is required. | |
[Bk] | the crest width of the obstacle. If this command is used, this value is required. | |
REFL | if this keyword is present the obstacle will reflect wave energy (possibly in | |
combination with transmission). Reflections will be computed only if the spectral | ||
directions cover the full 360^{o}, i.e. if in the command CGRID the option CIRCLE | ||
is activated. | ||
[reflc] | constant reflection coefficient, formulated in terms of wave height, i.e. ratio | |
of reflected significant wave height over incoming significant wave height. | ||
Restriction: 0 [reflc] 1. | ||
Default: [reflc]=1, if the keyword REFL is present, otherwise [reflc]=0. | ||
Note: the program checks if the criterion [reflc]^{2} +[trcoef]^{2} 1 is | ||
fulfilled. | ||
RSPEC | indicates specular reflection which is the default. The angle of reflection | |
equals the angle of incidence. | ||
RDIFF | indicates diffuse reflection, i.e. specular reflection where incident waves | |
are scattered over reflected direction. | ||
[pown] | each incoming direction is scattered over reflected direction | |
according to cos^{}( - ). The parameter [pown] indicates the width | ||
of the redistribution function. | ||
Default: [pown] = 1. | ||
LINE | with this required keyword the user defines the location of the obstacle(s). | |
[xp], [yp] | coordinates of a corner point of the line that defines the location of the | |
obstacle(s) (in problem coordinates): | ||
if Cartesian coordinates are used in m or | ||
if spherical coordinates are used in degrees (see command COORD). | ||
At least two corner points must be provided. |
SETUP [supcor]
CANNOT BE USED IN CASE OF UNSTRUCTURED GRIDS.
If this optional command is given, the wave-induced set-up is computed and accounted for in the wave
computations (during the computation it is added to the depth that is obtained from the READ BOTTOM
and READ WLEVEL commands).
This approximation in SWAN can only be applied to open coast (unlimited supply of water from outside
the domain, e.g. nearshore coasts) in contrast to closed basin, e.g. lakes and estuaries, where this option
should not be used.
Note that set-up is not computed correctly with spherical coordinates.
Note that set-up is not supported in case of parallel runs using either MPI or OpenMP!
[supcor] | by default the wave-induced set-up is computed with a constant added such that the | |
set-up is zero in the deepest point in the computational grid. The user can modify | ||
this constant by the value of [supcor]. The user can thus impose a set-up in any | ||
one point (and only one) in the computational grid by first running SWAN, then | ||
reading the set-up in that point and adding or subtracting the required value of | ||
[supcor] (in m; positive if the set-up has to rise). | ||
Default: [supcor]=0. |
DIFFRACtion [idiffr] [smpar] [smnum] [cgmod]
If this optional command is given, the diffraction is included in the wave computation.
But the diffraction approximation in SWAN does not properly handle diffraction in harbours
or in front of reflecting obstacles (see Scientific/Technical documentation). Behind breakwaters with a
down-wave beach, the SWAN results seem reasonable. The spatial resolution near (the tip of)
the diffraction obstacle should be 1/5 to 1/10 of the dominant wave length.
Without extra measures, the diffraction computations with SWAN often converge poorly or not at all. Two
measures can be taken:
[idiffr] | indicates the use of diffraction. If [idiffr]=0 then no diffraction is taken | |
into account. | ||
Default: [idiffr]=1. | ||
[smpar] | smoothing parameter for the calculation of ^{ . }. During every | |
smoothing step all grid points exchange [smpar] times the energy with their | ||
neighbours. Note that [smpar] is parameter a in the above text. | ||
Default: [smpar] = 0. | ||
[smnum] | number of smoothing steps (n in the above text). For a = 0.2, it should be | |
approximately equal to . | ||
Default: [smnum] = 0. | ||
[cgmod] | adaption of propagation velocities in geographic space due to diffraction. | |
If [cgmod]=0 then no adaption. | ||
Default: [cgmod]=1. |
| WINDGrowth | | | | QUADrupl | | | | WCAPping | OFF < > | BREaking | | | | REFrac | | | | FSHift | | | | BNDCHK |
With this optional command the user can change the default inclusion of various physical processes (e.g.
for research purposes). This command is not recommended for operational use.
WINDGROWTH | switches off wind growth (in commands GEN1, GEN2 and GEN3). | |
QUADRUPL | switches off quadruplet wave-wave interactions (in command GEN3). | |
WCAPPING | switches off whitecapping (in command GEN3). | |
BREAKING | switches off depth-induced breaking dissipation. Caution: wave heights may | |
diverge in very shallow water. | ||
REFRAC | switches off refraction (action transport in -direction). | |
FSHIFT | switches off frequency shifting in frequency space (action transport in -space). | |
BNDCHK | switches off the checking of the difference between imposed and computed | |
significant wave height at the boundary of the computational grid (see also | ||
command SET). |