Experimental and numerical investigations of solitary wave-induced non-equilibrium scour around structure of square cross-section on sandy berm Coastal Engineering

A series of laboratory experiments and high-fidelity numerical simulations were carried out to investigate the scour induced by a solitary wave around a non-slender, vertical structure of a square cross-section on a sandy berm. Various wave and water level combinations, structure layouts, and dimensions were studied. The flow separation at the sharp edges resulted in counterclockwise rotating out-of-plane vortices that extended from the free surface to the sandy berm. These energetic vortices were found to be the primary driving mechanism of the scouring through entraining, and entrapping the sand particles into their cores, keeping them in suspension, carrying them, and releasing them as the vortices propagate along a spiral trajectory. The analyses also showed that the flow blockage by the structure could result in flow field modulation and exacerbate the scour processes. The structure dimension appeared to be the most influential factor in the scouring process, drastically altering the characteristics of the non-equilibrium scour holes. Irrespective of the structure dimension or layout, the scour depth was greater around the seaside edge of the structure while the scour width was larger on the leeside edge. The uncertainties associated with the maximum non-equilibrium scour depth were quantified via Monte Carlo simulations which showed that the impact of the structure dimension on the maximum scour depth was almost twice more significant than that of the layout.