Hydrodynamic Characteristics of Double-Caisson Composite Breakwater Under Regular Waves

Abstract

Abstract. A two-dimensional (2D) numerical wave flume is developed using the olaFlow solver based on the k–ω shear-stress transport turbulence model to investigate the hydrodynamic behavior of a double-caisson composite breakwater under regular waves. The study systematically analyzes wave pressure distribution, wave reflection, and transmission under varying rubble mound slopes (1:2, 1:1.75, and 1:1.5), rubble mound particle size distributions, and wave-wall structures. Model validation against experimental data demonstrates the reliability of the numerical approach. Results indicate that steeper rubble mound slopes enhance energy dissipation and reduce the reflection coefficient. A newly proposed coarse–fine–coarse vertical rubble grading scheme increases the reflection coefficient by up to 15% compared to uniform grading, while also minimizing wave transmission. The installation of an arc-shaped wave wall effectively decreases both reflection and transmission, but intensifies local pressure concentration near the junction of the rubble mound and caisson. During wave crests, significant pressure concentration is observed at the front caisson, whereas during wave troughs, the pressure concentration zone notably expands around the lower-right corner of the rear caisson. The findings shed light on how to improve breakwater designs and enhance coastal protection while balancing wave energy dissipation.