Two-parameter wave reflection coefficient for an impermeable breakwater armored with Accropodes

Abstract

Coastal breakwaters serve a vital role in dissipating wave energy in severe ocean environments and mitigating disastrous impacts of global climate change. As one of the key metrics in evaluating performance of breakwaters, reflection coefficients are usually formulated empirically as a function of either the Iribarren number accounting for wave breaking or the relative water depth measuring wave dispersion. In this work, we conduct a scaled physical model experiment to investigate wave reflection from a horizontally composite breakwater with a steep impermeable slope armored by Accropodes. Tests with specifically designed regular wave conditions produce 400 plus measurements over a grid of Iribarren number and relative water depth to analyze their interplay in jointly determining the reflection coefficients. Empirical formulas in terms of either one or two parameters are proposed through regression analysis for performance evaluation. Error analysis indicates the two-parameter formulas outperform the one-parameter ones with significantly improved predictive skills for the studied breakwater. The two-parameter approach allows complementary influences from the Iribarren number and the relative water depth in fitting the observations and can have broad applications in studies of fluid-structure interactions involving wave reflection, overtopping, transmission, and armor stability, especially when the coastal structures are located outside the shallow-water zone.