do Instituto Hidrográfico

66 ANAIS DO INSTITUTO HIDROGRÁFICO N.º 15
1. Introduction
Areal time evaluation of the nearshore wave conditions
is of essential importance in ocean engineering
applications for the safe design and
exploitation of marine structures and installations as
well as for various military operations. For this reason
in the last years were developed almost all over the
world advanced wave prediction programs emphasizing
on the improvement of the wave data assessment in the
littoral regions and in the surf zones, where is dissipated
most of the wave energy. Developing of wave coastal
models and interacting of global and regional scale
models with high resolution wave models it is still one
of the greatest priorities of these programs. Such high
resolution models are likely to be run to surface areas
not more than 50km by 50km and the predictions may
be significantly improved by infusion of strategically
placed ‘in situ’ collected or remotely sensed data. In
shallow water, near the coast, the spectral phased averaged
models (as SWAN and HISWA appear also to offer
additional capabilities to the Navy especially for the
interpretation of the remote sensing data.
However, the general research in this area was
focussed up to now mainly in incorporating into the
models the effects of the large-scale global currents and
in improving the nonlinear source terms, for developing
more accurate algorithms. For this reason there is still
a strong need of new and more efficient computational
environments to perform an adequate processing of the
data, either before or after the model simulation. In this
perspective coupling the wave models with easy to use
pre and post processing tools should be considered as
subjects of prime interest in the field of the wave data
assimilation techniques.
2. The methodology proposed
As a reference point, for the methodology proposed
here, was used the SWAN spectral model. However the
new developed computational environment could be
useful and easily adapted to the most of the existent
wave models. SWAN is a high resolution numerical wave
model designed to obtain realistic estimates of wave
parameters in coastal areas, lakes and estuaries from
given wind, bottom, and current conditions. The model
is based on the action balance equation (or energy
balance in the absence of currents) with sources and
sinks. The SWAN model has been developed at the Delft
University of Technology, Department of Civil Engineering,
Delft, the Netherlands, [Ris et al (1998)]. It was
released in the public domain and can be downloaded
from the Internet. In SWAN the following wave propagation
processes are implemented: propagation through
geographic space, refraction due to bottom and current
variations, shoaling due to bottom and current variations,
blocking and reflections by opposing currents,
transmission through or blockage by obstacles. It also
accounts for the dissipation effects due to whitecapping,
bottom friction and wave breaking. The depth and
currents (if present) are input to SWAN. The first implementation
of the SWAN model in Portugal was made by
the ‘Instituto Hidrografico’ of the Portuguese Navy in
the context of the project PAMMELA. Initially were
performed simulations in the area Pinheiro da Cruz,
south of Lisbon and nearby Setubal, the implementation
of the model being extended now also to some other
areas from the Portuguese nearshore.
BARCO is the acronym of BAthymetry Reshape and
COnfigure and it is an original computation program
developed using the MATLAB environment. Its functions
are to assess bathymetries and isolines, to plot
maps and isomaps and to reshape grids. All these operations
can be made before, while or after the wave model
is run. As input this model uses exactly the same type of
files with the bathymetric data as the SWAN wave
model.
TOTAL WAVE is a post-processing interface that makes
available wave conditions in the nearshore and surf
zone, in a user-friendly way. The wave data propagation
and transform from the source to the end user can be
seen in figure 1, where is suggested also the main idea
which is behind the proposed treatment of the data.
That is some of the computational effort is taken from
the wave model by the pre-processing tool and is created
in this way a direct link between the stages of pre and
post-processing.
In order to point the advantages introduced by this
new interactive computational environment it is may be
better to enlarge the explanation of the procedure
proposed here (figure 1). First a general and easy to use
tool for assessing the bathymetric configuration developed
in the same environment (Matlab) as the postprocessing
tool, should be very useful before running
the model in the process of setting the most appropriate
area where the model is going to be run. Moreover in
the case of the nested runs its utility is even greater
because BARCO has the possibility of reshaping grids,
defining a sub-domain in the input area and working
simultaneously in different frames with both the initial
and the final area. Another reason is that the computational
time of the most of the wave models strongly
depends of the number of the output requests and
consequently all the computations that are made
outside the model have as a result a significant decreasing
of the computational time of the model itself. May
be it is also worth mentioning here that the programs
‘BARCO’ and TOTAL WAVE work in a real time and their