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GEN1 [cf10] [cf20] [cf30] [cf40] [edmlpm] [cdrag] [umin] [cfpm]

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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 10m above  
  sea level).  
  Default: [umin] = 1.  
[cfpm] coefficient which determines the Pierson Moskowitz frequency:  
  $ \sigma_{{PM}}^{}$ = 2$ \pi$ g  [cfpm] /U10  
  Default: [cfpm] = 0.13  


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GEN2 [cf10] [cf20] [cf30] [cf40] [cf50] [cf60] [edmlpm] [cdrag] [umin] [cfpm]

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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  


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         |    JANSsen [cds1] [delta] |
         |                           |
GEN3    < --> KOMen   [cds2] [stpm]   > (AGROW [a])
         |                           |
         |    WESTHuysen             |

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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 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 (= Cds/$ \tilde{{s}}^{4}_{{\rm PM}}$).  
  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 (= Cds).  
  Default: [cds2] = 2.36e-5.  
[stpm] value of the wave steepness for a Pierson-Moskowitz spectrum (= $ \tilde{{s}}^{2}_{{\rm PM}}$).  
  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.  


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WCAPping KOMen [cds2] [stpm] [powst] [delta] [powk]

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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 (= Cds).  
  Default: [cds2] = 2.36e-5.  
[stpm] value of the wave steepness for a Pierson-Moskowitz spectrum (= $ \tilde{{s}}^{2}_{{\rm PM}}$).  
  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.  


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QUADrupl [iquad] [lambda] [Cnl4] [Csh1] [Csh2] [Csh3]

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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 107.  
[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.  


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           | -> CONstant [alpha] [gamma]
BREaking  <
           |    BKD [alpha] [gamma0] [a1] [a2] [a3]

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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 (=$ \beta$) and the dimensionless depth (=kd)  
[alpha] proportionality coefficient of the rate of dissipation.  
  Default: [alpha] = 1.0.  
[gamma0] the reference $ \gamma$ 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.  


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           | -> JONswap CONstant [cfjon]
           |
           |    COLLins [cfw]
FRICtion  <
           |    MADsen  [kn]
           |
           |    RIPples [S] [D]

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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 m2s-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 m2s-3 is discouraged, even for wind sea conditions!) For smoother seafloors, like the Gulf of Mexico, a lower value of 0.019 m2s-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.  


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TRIad [itriad] [trfac] [cutfr] [a] [b] [urcrit] [urslim]

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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.  


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VEGEtation  < [height] [diamtr] [nstems] [drag] >

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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.  


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TURBulence  [ctb]  (CURrent [tbcur])

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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.  


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MUD  [layer]  [rhom]  [viscm]

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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/m3).  
  Default: [rhom] = 1300.  
[viscm] the kinematic viscosity of the mud layer (in m2/s).  
  Default: [viscm] = 0.0076.  


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LIMiter [ursell] [qb]

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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.  


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          | -> TRANSm [trcoef]                        |
          |                                           |
          |    TRANS1D < [trcoef] >                   |
          |                                           |
OBSTacle <     TRANS2D < [trcoef] >                    >                       &
          |                                           |
          |       | -> GODA [hgt] [alpha] [beta]      |
          |  DAM <                                    |
                  |    DANGremond [hgt] [slope] [Bk]  |

                         | -> RSPEC        |
          (REFL [reflc] <                   > ) LINe <[xp] [yp]>
                         |    RDIFF [pown] |

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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.

  1. If a straight line is defined with more than two points, then the sum of the reflection of the parts may differ from the situation when you define it with just two points. This is due to the way obstacles are handled numerically in SWAN. It defines from computational grid point to its neighbor whether there is a crossing with an obstacle. In defining which directions of the wave spectrum should be reflected, i.e which directions are pointed towards the obstacle, it uses the obstacle coordinates as defined by the user to define the angle of inclusion. This angle will be smaller if more points are defined, and so the reflected energy will be less for the computational grid point. This problem becomes smaller if the computational grid points are closer to the obstacle.

    So the advise is to define obstacles with the least amount of points possible.
  2. In case of sharp angles in the obstacles, it is very likely that there are more than one crossing between two computational grid points. In this case SWAN does not give correct reflection results.
  3. At the boundaries of the computational area, the reflected spectrum is not taken into account. This can only be resolved by a different treatment of the boundaries in the program. Until this time, it is recommended to place obstacles at the inner area of the computational grid, not at or through the boundaries.
  4. Obstacle lines are only effective when the obstacle line is bordered by wet points on both sides. In practice, this may give problems when a reflection line is also used to specify a boundary between wet and land points. This can be avoided by shifting the position of the reflection line or by creating wet points on the land side of the obstacle line.

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 360o, 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 $ \leq$ [reflc] $ \leq$ 1.  
  Default: [reflc]=1, if the keyword REFL is present, otherwise [reflc]=0.  
  Note: the program checks if the criterion [reflc]2 +[trcoef]2 $ \leq$ 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 $ \theta$ is scattered over reflected direction $ \theta_{{\rm refl}}^{}$  
  according to cos$\scriptstyle \tt [pown]$($ \theta$ - $ \theta_{{\rm refl}}^{}$). 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.  


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SETUP [supcor]

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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.  


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DIFFRACtion [idiffr] [smpar] [smnum] [cgmod]

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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:

  1. (RECOMMENDED) The user can request under-relaxation. See command NUMERIC parameter [alpha] and Scientific/Technical documentation (Eq. (3.31)). Very limited experience suggests [alpha] = 0.01.
  2. Alternatively, the user can request smoothing of the wave field for the computation of the diffraction parameter (the wave field remains intact for all other computations and output). This is done with a repeated convolution filtering. The mother filter is

    Eni, j = En-1i, j - a$\displaystyle \left[\vphantom{ E_{i-1,j} + E_{i,j-1} -4E_{i,j} + E_{i+1,j} + E_{i,j+1} }\right.$Ei-1, j + Ei, j-1 -4Ei, j + Ei+1, j + Ei, j+1$\displaystyle \left.\vphantom{ E_{i-1,j} + E_{i,j-1} -4E_{i,j} + E_{i+1,j} + E_{i,j+1} }\right]^{{n-1}}_{}$

    For a = 0.2 (recommended), the final width of the filter is $ \varepsilon_{x}^{}$ = $ {\frac{{1}}{{2}}}$$ \sqrt{{3n}}$$ \Delta$x (in x -direction and similarly in y -direction) and n is the number of repetitions (see Scientific/Technical documentation, Eq. (2.100)). Note that this smoothing option can not be applied in case of unstructured meshes.

[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 $ \nabla$ . $ \sqrt{{E_{\rm tot}}}$. 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 $ \lfloor$$ {\frac{{4\varepsilon_x^2}}{{3\Delta x^2}}}$$ \rfloor$.  
  Default: [smnum] = 0.  
[cgmod] adaption of propagation velocities in geographic space due to diffraction.  
  If [cgmod]=0 then no adaption.  
  Default: [cgmod]=1.  


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     |  WINDGrowth |
     |             |
     |  QUADrupl   |
     |             |
     |  WCAPping   |
OFF <               >
     |  BREaking   |
     |             |
     |  REFrac     |
     |             |
     |  FSHift     |
     |             |
     |  BNDCHK     |

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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 $ \theta$ -direction).  
FSHIFT switches off frequency shifting in frequency space (action transport in $ \sigma$ -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).  


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Next: Numerics Up: Model description Previous: Boundary and initial conditions   Index
The SWAN team 2017-03-23