The modelling of large individual waves for the computation of loads on ships and offshore structures in
extreme weather conditions is still a challenging problem. Since the early 50s the predictions of loads on
fixed offshore structures and motions of compliant or sailing structures due to surface waves are
commonly made by computations on the basis of the statistical/spectral description of the sea elevation
and of a linearized response model. Quadratic Transfer Functions or fully non-linear methods are used
only in specific cases. The linear approach is recognized to work reasonably well for the so-called
operational conditions, assuming that hydrodynamic and dynamic nonlinear effects can be neglected. On
the other hand, it is also recognized that the modelling of large amplitude motions and the modelling of
waves in the so-called survival conditions, i.e. extreme wave conditions, cannot recast a linear approach.
In these conditions the wave-wave interaction plays a fundamental role (energy transfer, down-shift, etc) in
the actual deterministic or spectral representation of the wave/flow field and thus in the related loads on
the structure.
In the present paper the nonlinear aspects related to the behavior of steep focusing breaking and non-
breaking waves are analyzed by means of numerical simulations and new experiments. The experiments
are carried out at the wave flume of the Laboratory of Maritime Engineering (LABIMA) of the Dept. of Civil
and Environmental Engineering of the University of Florence. The computations are carried out at
Hydrodynamic and MetOcean Laboratory (HyMOLab) of the Dept. of Engineering and Architecture of the
University of Trieste. The paper focuses the attention on the comparison between the results obtained with
a state-of-art viscous flow simulation and laboratory experiments, with particular emphasis on the spectral
energy exchange between component waves of a non-breaking and breaking focusing wave train. This
study is carried out as part of the research project “OpenViewSHIP Development of an integrated
computational ecosystem for the hydrodynamic design of the hull-propeller system”, co-financed by Friuli
Venezia Giulia Region in the field of industrial application of open-source CFD and High Performance
Computing.
