Stephan T. Grilli and Juan Horrillo
Associate Professor Graduate
student
Department of Ocean Eng.
niversity of Rhode Island
Narragansett, RI 02882, USA
Abstract :
A new method is proposed for the generation of permanent form
periodic waves, in a two-dimensional fully nonlinear potential flow model.
In this method, a constant volume is maintained in the computational domain
(``wave tank'') by simultaneously generating a mean current, equal and
opposite to the waves mean mass transport velocity. An absorbing beach
is modeled at the far end of the tank, with : (i) an external free surface
pressure, proportional to the normal particle velocity, to absorb energy
from high frequency incident waves; and (ii) a piston-like condition, at
the tank extremity, to absorb energy from low frequency waves. A new feedback
mechanism is proposed to adaptively calibrate the beach absorption coefficient,
as a function of time, for the beach to absorb the period-averaged energy
of waves entering the beach.
Wave generation and absorption are validated over constant depth, for tanks and beaches of various lengths, and optimal parameter values are identified for which reflection in the beach is reduced to less than a few percent. Using the new generation and absorption methods, shoaling of periodic waves is modeled over a 1:50 slope, up to very close to the breaking point. A quasi-steady state is thus reached in the tank for which (not previously calculated) characteristics of fully nonlinear shoaling waves are obtained.
Keywords :
Nonlinear wave modeling, streamfunction waves, wave generation, wave absorption, numerical wave tank, wave shoaling, Boundary Element Method