do Instituto Hidrográfico

PRE-PROCESSING AND POST-PROCESSING OF MODEL WAVE DATA IN THE NEARSHORE 71
4. A Nowcast tool for the coastal
environment
After running the model, its outputs are transferred
into another computational environment where is
performed the phase of post-processing. For this
purpose was developed a MATLAB interface denoted by
‘TOTAL WAVE’ which makes available in real time, and
in an user friendly way, the main wave parameters both
in the nearshore and surf areas. A more detailed description
of this nowcast tool and its evolution in the last
year could be seen in [Soares et al (2000)] and [Rusu et
al (2001)]. From this reason it will be emphasized here
only the basic proprieties and some new features of
‘TOTAL WAVE’.
Any numerical model delivers the outputs requested
by the user from the ones that are available. In SWAN
these outputs could be divided into two categories: grid
variables, (which could be described by a scalar, or a
three-dimensional vector) and spectral variables (which
are described each one by a matrix). Besides the grid
point coordinates and the corresponding depth, the
main grid parameters computed were: the significant
wave height (Hs), the wave period (TM01), the wave
direction (u), the wavelength (Wl), the wave steepness
(Ste), the energy dissipation per unit time (Diss), the
normalized frequency width of the spectrum (Fspr) and
the directional width of the spectrum (Dspr). Once
being established the frequencies of the spectrum, the
1D spectrum in a point is a vector that gives the variance
densities (in m 2 /Hz) for the corresponding frequencies.
The 1D spectrum was computed along lines parallel
with the y-axis of the computational grid (i.e. quasi
parallel with the shoreline). Because the great amount
of data involved, the 1D spectrum couldn’t be computed
directly in the points of the computational grid and it
was reconstructed the grid in this way. A matrix having
the number of rows equal with the number of frequencies
and the number of columns equal with the number
of directions considered gives the 2D spectrum in a
point. The elements of this matrix will be the corresponding
values of the variance density (in m 2 /Hz.rad).
The 2D spectrum was computed only in points and from
these points it was built a line normal to the shore in the
middle of the domain.
‘TOTAL WAVE’ has in the top of its hierarchy the
site. The setting of the area is controlled by the same
global variables that are defined in the pre-processing
stage. These are: XCO*, YCO*, XLENC*, YLENC*,
MXC* and MYC*. The superscript * is 1 if was used the
first grid from ‘BARCO’ and 2 if was used the reshaped
grid (usually in the case of nested runs). All the bathymetric
data are loaded directly from the pre-processing
tool where was defined and configured the computational
grid of the model. Other global variables charac-
terizing the computational grid are: FLENC (the length
of the grid in frequency space), DLENC (the length of
the grid in directional space), MFC – the number of
meshes in frequency space and MDC – the number of
meshes in directional space. Once the site is set the next
option is to choose the case which is going to be
analyzed. MATLAB associates to each variable in its
workspace a matrix and if the grid variables are already
delivered by SWAN in a matrix form, the spectral files
describing the 1D or 2D spectrum are reconverted into
matrices by special subroutines.
After loading the case data it is displayed the main
desk of the selected site. The actions are controlled
through UI-menu commands. The functions of these
commands concern the starting of the simulations and
also some other options as: opening html-files, cumulative
or parallel analyze, changing the case or the site.
The simulations are generated by quasi-independent
modules which allow also a sequential analyze. They will
be briefly described as follows.
4.1 Global data evaluation
In this simulation could be made a field evaluation of
the wave conditions concerning the entire site, which
gives an overview of the wave variables distribution in the
area and allows an evaluation of the wave data accuracy.
As a result it is of important help in the process of correction
of the initial and (or) of the boundary conditions, as
well as in calibrating the optimal combination of the physical
processes activated of the wave model. On the other
hand this phase is a first step in identifying and analyzing
some relevant wave phenomena as shoaling, wave breaking,
refraction, infragravity motions, etc. In figure 15 can
be seen the command menu and the wave direction in the
field where the phenomenon of bottom induced refraction
is very well surprised. There are also available on the
command panel the field distribution of the wave height,
the period, the bathymetry, the wavelength and the steepness.
The points where are located the maximum values of
the variables are marked and the corresponding values are
displayed on the MATLAB command window.
4.2 Local data assessment
Using the map of the area in this phase can be
elected any point or line in the sea field to evaluate in
detail the values of the wave variables. The input in this
case are the point coordinates, or respectively the line
endpoints for the case of the line, and their location can
be selected directly from the map as a graphical input,
or alternatively, for imposed analytical values of the
respective points. In figure 16 are presented two arbitrary
locations (for a point and respectively a line) and
the values of the main wave variables (and respectively