1Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2Present address: DITS, University of Rome ‘La Sapienza’, Italy.
Tóm tắt
For flood protection against storm tides, barriers of box-like
gates
hinged along a
bottom axis have been designed to span the three inlets of the Venice Lagoon.
While
on calm days the gates are ballasted to rest horizontally on the seabed,
in stormy
weather they are raised by buoyancy to act as a dam which is expected to
swing to
and fro in unison in response to the normally incident sea waves. Previous
laboratory
experiments with sinusoidal waves have revealed however that neighbouring
gates
oscillate out of phase, at one half the wave frequency, in a variety of
ways, and hence
would reduce the effectiveness of the barrier. Extending the linear theory
of trapped
waves by Mei et al. (1994), we present here a nonlinear
theory for subharmonic
resonance of mobile gates allowed to oscillate about a vertical plane of
symmetry.
In this part (1) the evolution equation of the Landau–Stuart type
is first derived for
the gate amplitude. The effects of gate geometries on the coefficients
in the equation
are examined. After accounting for dissipation effects semi-empirically
the theoretical
results on the equilibrium amplitude excited by uniform incident waves
are compared
with laboratory experiments.
