Experimental and numerical studies were carried out to investigate the process of wave-breakwater interaction.
A total of 825 experimental tests, involving 53 different rubblemound breakwater configurations, were conducted in a one metre wave flume. The test structures were subjected to monochromatic waves, ranging in height from 30mm to 200mm and in period from 0.8s to 2.0s. The armour units used were 50 mm stone, 50 mm steel spheres and 60 mm cubes. Three types of core and filter materials were used. These had D50 values of 16, 14 and 3.5mm.
The test structures were instrumented with pressure transducers placed along the outer face of the structure and at the core/filter interface. Specially designed capacitance gauges were installed throughout the core to monitor the motion of the phreatic surface. Observations were made of wave runup and rundown, wave breaking and air entrainment in the structure.
Wave energy dissipation across the armour layer was assessed as a function of armour unit type, core material type, thickness of the armour layer, breakwater slope and wave height and period.
An additional set of experimental tests was undertaken to investigate the mechanism by which naturally armouring breakwaters, that is breakwaters in which the initial profile is adjusted into a more stable profile as a result of wave action, gain their stability.
Numerical studies were undertaken to provide an assessment of the performance of an existing hybrid finite element-method of characteristics model for analysing the internal flow characteristics of a rubblemound breakwater.
From the results of tests undertaken using conventional structures it was found that the external pressure field was not influenced by core type, armour type or armour layer thickness. However, the internal pressure field was found to vary significantly with core and armour types.
A substantial reduction in the magnitude of the internal and external pressure fields was found for the natural profile structure compared with conventional structures.
Comparison of experimentally and numerically determined internal phreatic surface profiles showed mixed results. In general, a poor comparison between measured and predicted internal pressures was found.