| BSBT PROP < | Sec | | GSE [waveage] < MIn > | | HR | | | DAy |
Command to choose:
BSBT | the BSBT scheme will be used in the computations. | |
GSE | garden-sprinkler effect is to be counteracted in the S&L propagation scheme | |
(default for nonstationary regular grid computations) or in the propagation | ||
scheme for unstructured grids by adding a diffusion term to the basic equation. | ||
This may affect the numerical stability of SWAN (see Scientific/Technical | ||
documentation). | ||
[waveage] | the time interval used to determine the diffusion which counteracts the so-called | |
garden-sprinkler effect. The default value of [waveage] is zero, i.e. no added | ||
diffusion. The value of [waveage] should correspond to the travel time of | ||
the waves over the computational region. |
NUMeric ( STOPC [dabs] [drel] [curvat] [npnts] & | -> STAT [mxitst] [alfa] | < > [limiter] ) & | NONSTAT [mxitns] | ( DIRimpl [cdd] ) & ( SIGIMpl [css] [eps2] [outp] [niter] ) & ( CTheta [cfl] ) & ( CSigma [cfl] ) & ( SETUP [eps2] [outp] [niter] )
With this optional command the user can influence some of the numerical properties of SWAN.
STOPC | With this option the user can influence the criterion for terminating the | |
iterative procedure in the SWAN computations (both stationary and | ||
nonstationary). The criterion make use of the second derivative, or curvature, | ||
of the iteration curve of the significant wave height. As the solution of a | ||
simulation approaches full convergence, the curvature of the iteration curve will | ||
tend to zero. SWAN stops the process if the absolute change in H_{s} from one | ||
iteration to the next is less than [dabs] or the relative change in H_{s} from one | ||
iteration to the next is less than [drel] and the curvature of the iteration | ||
curve of H_{s} normalized with H_{s} is less than [curvat]. Both conditions need to | ||
be fulfilled in more than fraction [npnts]% of all wet grid points. | ||
[dabs] | Default: [dabs] = 0.005 [-] | |
[drel] | Default: [drel] = 0.01 [-] | |
[curvat] | Default: [curvat] = 0.005 [-] | |
[npnts] | Default: [npnts] = 99.5 [-] | |
STAT | indicates the use of parameters in a stationary computation. | |
[mxitst] | the maximum number of iterations for stationary computations. | |
The computation stops when this number is exceeded. | ||
Default: [mxitst] = 50. | ||
Note that [mxitst] can be set to 0 if one wants to check the input to the | ||
model without making computations. | ||
[alfa] | proportionality constant used in the frequency-dependent under-relaxation | |
technique. Based on experiences, a suggestion for this parameter is [alfa] = 0.01. | ||
In case of diffraction computations, the use of this parameter is recommended. | ||
Default: [alfa] = 0.00. | ||
NOT MEANINGFUL FOR NONSTATIONARY COMPUTATIONS. | ||
NONSTAT | indicates the use of parameters in a nonstationary computation. | |
[mxitns] | the maximum number of iterations per time step for nonstationary computations. | |
The computation moves to the next time step when this number is exceeded. | ||
Default: [mxitns] = 1. | ||
Note that [mxitns] can be set to 0 if one wants to check the input to the | ||
model without making computations. | ||
[limiter] | determines, in both stationary and nonstationary runs, the maximum change per | |
iteration of the energy density per spectral (,)-bin, given in | ||
terms of a fraction of the omni-directional Phillips level (see Scientific/ | ||
Technical documentation). | ||
Default: [limiter] = 0.1. | ||
DIRIMPL | this option is used to influence the numerical scheme for refraction. | |
[cdd] | A value of [cdd]=0 corresponds to a central scheme and has the largest | |
accuracy (diffusion 0) but the computation may more easily generate | ||
spurious fluctuations. A value of [cdd]=1. corresponds to a first order | ||
upwind scheme and it is more diffusive and therefore preferable if (strong) | ||
gradients in depth or current are present. | ||
Default: [cdd] = 0.5. | ||
SIGIMPL | controls the accuracy of computing the frequency shifting and the stopping criterion | |
and amount of output for the SIP solver (used in the computations in the presence | ||
of currents or time varying depth). | ||
CTHETA | this option prevents an excessive directional turning at a single grid point or vertex | |
due to a very coarse bathymetry or current locally. This option limits the directional | ||
turning rate c_{} based on the CFL restriction. (See Eq. 3.41 of Scientific/ | ||
Technical documentation). See also the final remark in Section 2.6.3. | ||
Note that if this command is not specified, then the limiter is not activated. | ||
[cfl] | upper limit for the CFL restriction for c_{}. A suggestion for this parameter is | |
[cfl] = 0.9. | ||
Default: [cfl] = 0.9 (when command CTHETA is activated). | ||
CSIGMA | this option prevents an excessive frequency shifting at a single grid point or vertex | |
due to a very coarse bathymetry or current locally. This option limits the frequency | ||
shifting rate c_{} based on the CFL restriction. See also the final remark in Section | ||
2.6.3. Note that if this command is not specified, then the limiter is not activated. | ||
[cfl] | upper limit for the CFL restriction for c_{}. A suggestion for this parameter is | |
[cfl] = 0.9. | ||
Default: [cfl] = 0.9 (when command CSIGMA is activated). | ||
SETUP | controls the stopping criterion and amount of output for the SOR solver in the | |
computation of the wave-induced set-up. | ||
[css] | A value of [css]=0 corresponds to a central scheme and has the largest | |
accuracy (diffusion 0) but the computation may more easily generate | ||
spurious fluctuations. A value of [css]=1. corresponds to a first order upwind | ||
scheme and it is more diffusive and therefore preferable if (strong) gradients in | ||
depth or current are present. | ||
Default: [css] = 0.5. | ||
[eps2] | Relative stopping criterion to terminate the linear solver (SIP or SOR). The | |
criterion for the SIP solver is based on | | A - |_{2} [eps2] ||_{2} | |
where A is a matrix, is the action density vector, is the right hand vector | ||
and k is the iteration number. | ||
The criterion for the SOR solver is based on | - |_{} [eps2] where | ||
is the set-up. | ||
Default: [eps2] = 1.e-4 in case of SIP and [eps2] = 1.e-6 in case of SOR. | ||
[outp] | output for the iterative solver: | |
0 = no output | ||
1 = additional information about the iteration process is written to the PRINT file | ||
2 = gives a maximal amount of output concerning the iteration process | ||
3 = summary of the iteration process | ||
Default: [outp] = 0. | ||
[niter] | maximum number of iterations for the linear solver. | |
Default: [niter] = 20 in case of SIP and [niter] = 1000 in case of SOR. |