There are four categories of output commands, the first two each with two classes:
  1. Locations
    1. commands defining sets of output locations at which the user requires output. Each set is indicated with a name ('sname' in this manual) which must be unique and not more than 8 characters long.
      Types of sets of output points:
      to define a set of output locations on a regular grid
      to define a set of output locations on a regular or curvi-linear grid
      to define a set of output locations along a curve
      to define a set of output locations along a depth or bottom contour line (with ISOLINE)
      to define a set of output locations along a depth- or bottom contour line (with RAY)
      to define a set of isolated output locations
      to define a set of output locations for a nested grid to be used in a subsequent SWAN run

      Commands FRAME, GROUP, RAY, ISOLINE and NGRID cannot be used in 1D-mode.

      If one gives one name for two sets of output locations, the first set is lost (first in the sequence in the command file). Three special names: BOTTGRID, COMPGRID and TESTPNTS are reserved for use by SWAN (see below). The user may not define sets with these names.
    2. commands defining additional geographical information to be used in plot output:
      defines a line to indicate e.g. coastlines or contours of a certain object (can be used in a plot generated with command PLOTGEOGR)
      plot (geographic) names (in a plot generated with command PLOTGEOGR)

      Commands LINE and SITES cannot BE USED IN 1D-MODE.
  2. Write / plot
    1. commands defining data file output (write) at the above defined set(s) of output locations:
      write spatial distributions (only for FRAMEs and GROUPs)
      write output for (set of) output location(s)
      write to data file the variance / energy (see command SET) density spectrum for (set of) output location(s)
      write to data file two-dimensional action density spectra (relative frequency) along the boundary of a nested grid (see command NGRID) to be used in a subsequent SWAN run.

      Commands BLOCK and NESTOUT cannot be used in 1D-mode.
    2. commands defining plot output at the above defined sets of output locations (and auxiliary plot output):
      a plot of a spatial distribution is required (contour line plot and / or vector plot)
      show the directional distribution of the action transport
      polar plot of a 2D variance / energy density spectrum, for (a set of) individual output location(s)

      Command PLOTGEOGR, PLOTSTAR and PLOTPP cannot be used in 1D-mode.
      It should be noted that the plot output of the model is not adapted to obstacles. For the plot, computational results may be interpolated from points at both sides of the obstacle; results for output points near an obstacle must therefore be interpreted with caution. The effect is for instance that the isolines of the wave height near the obstacle appear rather "ragged".
  3. Properties of output quantities (names, expected range of values etc.) can be set by means of the command QUANT
  4. The appearance of tables (number of decimals, number of data on a line of output) can be set by means of the command OUTFORMAT

Write or plot data

For definitions of output parameters: see the description of output quantities.

When integral parameters are computed by the user from the output spectrum of SWAN, differences with the SWAN-computed parameters may occur. The reasons are:

  1. SWAN accepts at the boundaries of the computational grid only the user-imposed incoming wave components and it replaces the user-imposed outgoing wave components with computed components (propagating to the boundary from the interior region).
  2. during the computation of the parameters, SWAN adds an analytical (diagnostic) high- frequency tail to the discrete spectrum.
  3. SWAN has an option to only compute within a pre-set directional sector (pre-set by the user). Wave components outside this sector are totally ignored by SWAN (no additions or replacements).

This is particularly relevant along the boundaries of SWAN where the user-imposed integral parameters (boundary conditions) may differ from the SWAN-computed parameters. The user is informed by means of a WARNING in the print file (the file with extension .prt) when the computed significant wave height differs more than 10%, say, from the user-imposed significant wave height (command BOUNDPAR2). The actual value of this difference can be set by the user (see the SET command).

Check locations and directions

When starting a project it is useful to check all input data, in particular locations of output points, nested grids, obstacles. Such objects are defined by means of point coordinates; errors are easily made when calculating coordinates.
Also the use of nautical directions (see command SET NAUTICAL) often gives rise to mistakes. Therefore it is good practice to make plots of wind fields, current velocity fields, and energy propation directions resulting from a computation.
These checks are performed by including the following commands in a control file, generating plots for the whole computational grid:

  • bottom together with location of output points, obstacles etc.:
    Plotgeo 'COMPGRID' file 'N1_bot.ps' color Depth &
    obstacles locations
  • bottom together with current velocities (if current is taken into account):
    Plotgeo 'COMPGRID' file 'N1_botcur.ps' color Depth vec vel
  • significant wave height together with star plot:
    Plotgeo 'COMPGRID' file 'N1_Hs.ps' color Hs star
  • average or peak period:
    Plotgeo 'COMPGRID' file 'N1_Per.ps' color Per
Also it is useful to check a curvilinear or an unstructured grid if one is using a non-regular grid. The PLOTGEO command has an option CMESH which results in the computational mesh being plotted together with e.g. bottom level. The command to generate this plot reads:
PLOT 'frame' FILE 'f02c.ps' title='Computational mesh' coord CMESH
It is also possible to plot an unstructured grid; here it is shown together with the bathymetry. See below:

© 2012: Nico Booij