Abstract:
The use of numerical models to calculate the mean overtopping discharges is,
nowadays, more frequent in preliminary design of coastal structures, since they are
more flexible than both empirical/semi-empirical and physical models and, once
calibrated and validated, they can be applied reliably to a large range of alternative
structure geometries and wave conditions. There are different models that can be used
to calculate the mean overtopping discharges over a structure. The paper compares the
output from three numerical models used to predict the mean overtopping discharges:
AMAZON [1], based on solving the non-linear shallow-water equations; and two
models based on Reynolds averaged Navier-Stokes equations, COBRAS-UC [2], a
Eulerian model using the volume of fluid (VoF) method for surface capturing, and
SPHysics [3], a Lagrangian model based on Smoothed Particle Hydrodynamics (SPH).
The numerical results are also compared with experimental data obtained at the
National Civil Engineering Laboratory (LNEC), Portugal, in the framework of the
Composite Modelling of the Interactions between Beaches and Structures (CoMIBBs)
project, a joint research activity of the HYDRALAB III European project [4]. The
experimental work consists of wave propagation, with breaking, and wave overtopping
of an impermeable seawall, a common coastal defense structure employed at the
Portuguese coast.
Results of free-surface elevation along the computational domain and of mean
overtopping discharges are presented and discussed. Although the processes of wave
generation used in the laboratory and in the models were different, the agreement in the
free surface was reasonable: the wave period obtained with the models agreed very well
with the data and the shape of the wave presented some minor differences to the
physical model data, as well as the wave height. The results of mean overtopping
discharges obtained with the three models agreed very well with the physical model
results.
