Reflection and Transmission for a Porous Structure

Abstract

Effects of characteristics of incident waves and of the thickenss of structure on wave reflection by and transmission through a porous structure were studied. Use of an idealized porous structure which is a lattice composed of circular cylinders was made. The relative thickness of structure B/L was found to have appreciable effects on reflected and transmitted wave energies. The reflection coefficient Kr reaches to a maximum of it for B/L of about 0.2 to 0.25, then decreases as B/L increases, and remains approximately uniform for B/L larger than about 0.6. The transmission coefficient Kt, however, decreases nearly exponentially as B/L increases. Measurement of wave height within structure revealed a Dattern of standing waves having a loop at the front face and a node at the rear face of it. That relates to the trend of Kr. Analytical approaches to predict the transmitted wave height, and wave heights before and within porous structures are found to be useful.

Numerical Study of Solitary Wave Interaction with Porous Breakwaters

“…In these studies, the energy dissipation inside the structure has been taken into account through the linearized friction coefficient, which is evaluated by applying Lorentz's principle of equivalent work. Several theoretical expressions for reflection and transmission coefficients have been derived for linear waves ͑e.g., Sollitt and Cross 1972͒, linear long waves ͑e.g., Kondo and Toma 1972;Madsen 1974͒, and linear obliquely incident waves ͑e.g., Dalrymple et al 1991͒ interaction with rectangular porous breakwaters. Attempts have also been made to extend these models for breakwaters of trapezoidal shape ͑Madsen and White 1975͒ and arbitrary shape ͑Sulisz 1985͒.…”