Numerical solution for trapped modes around inclined Venice gates

For protection against storm tides, four mobile barriers, each of which con sists of 20 gates hinged at the bottom axis, have been proposed to span the three inlets of the Venice lagoon. In stormy weather these gates are raise d from their housing to an inclination of 50 degrees from the horizon, so a s to act as a dam and to keep the water-level difference up to 2 m across t he barrier The gates were originally expected to swing in unison in respons e to the normally incident waves, but subsequent laboratory experiments rev ealed that the neighboring gates can oscillate out of phase in a variety of ways and affect the intended efficiency. In this paper we extend the linea r theory of Mel, Sammarco, Chan, and Procaccini for trapped waves around ve rtical rectangular gates and examine the inclined gates by using the hybrid finite-element method to account for the prototype geometry of the gates, the local bathymetry, and the intended sea-level differences. Finite elemen ts are employed only in the immediate neighborhood of the gate, while forma l analytical representations are used away from it. The factors affecting t he trapped wave period are studied, and the results are compared with exist ing laboratory experiments by Delft Hydraulics Laboratory.