In the present study, the influence of geometric scale, unit orientation (alternatively, flow direction), and the dimensionless Reynolds and Keulegan-Carpenter quantities on the hydrodynamic loading of Core-Loc armour units is explored through a series of physical modelling tests under unsteady and oscillatory flow conditions.

This study investigates the relationship between wave-induced hydrodynamics and the resulting loading on Core-Loc concrete armour units below the still water level in a breakwater structure. Physical modelling experiments were performed at the National Research Council in Ottawa in which a 3D-printed 12 cm Core-Loc armour unit was instrumented and fixed in place within a rubble mound structure. Testing featured simultaneous measurement of force on this instrumented unit, pressure head at the base of the unit, and flow velocities below the SWL. Two main scenarios were tested, the isolated unit and fully armoured scenarios, under a range of regular waves and irregular sea states. Analysis of force development on the instrumented unit indicates that maximum slope-normal forces (both into and away from the structure) are associated with extremes in pressure head above the instrumented unit, while slope-parallel force extremes (both upslope and downslope) occur at times of the fastest change in water level. These loadings are consistent with Morison’s equation and imply drag dominance in the slope-parallel direction and inertia dominance in the slope-normal direction. Significant differences in forces were observed between isolated (no neighbouring units) and embedded (with neighbouring units) armour unit test cases. The presence of the armour layer significantly increased the normal force exerted on the unit and reduced the parallel force. Irregular sea state testing shows force peaks following normal distribution. Analysis of flow above the armour layer showed that force, flow velocity and flow acceleration are symmetrical in the slope-parallel direction, but largely asymmetrical in the slope-normal direction, with the flow velocity and force on the unit in particular experiencing large asymmetries. Wave height analysis indicated that each wave height follows a similar force development pattern with a magnitude proportional to wave height. Wave period analysis showed the formation of small secondary waves as the period increases. Wave steepness affected the peak force loading of the instrumented unit in a mostly linear fashion up to the critical Iribarren number.