Effect of wave motion on the scouring caused by a marine propeller jet: An experimental and numerical study

Bathymetry changes induced by marine propeller jets on movable beds are a crucial issue in harbors, especially in the maneuvering zone. The knowledge of the scour hole and deposition mound dimensions, due to propeller jets, is important in the context of sediment management. Although the presence of waves is well known in harbor environments, propeller jet scours are usually investigated under still water conditions neglecting the effect of wave interaction. Moreover, the interaction between waves and propeller jets can also occur in mooring out of harbors. For these cases, the interaction of wave induced hydrodynamics and propeller jets is a crucial issue that is still an open and challenging problem. This paper aims to address, for the first time, the knowledge gap by investigating the influence of waves on propeller jets in unconfined conditions, which in turn can lead to alterations in scour and deposition patterns. The study relies on a specific experimental investigation. The selection of the parameters of the experimental tests is based on the results of prior analyses aimed to investigate the propeller jets induced scour and deposition in still water conditions and in the presence of a current. Hence, regular waves with different parameters (i.e. wave height and wave period) have been then reproduced in a wave flume where a propeller jet has been installed. The experimental tests aimed to get insight on the scour profiles as well as scour hole bathymetry induced by propeller jets under the influence of regular wave propagation. Numerical simulations have been also performed to investigate the effects of the wave-induced velocity acting on the propeller jets hydrodynamics. Spectral analysis has been then applied to characterize the complex scoured form and bedforms on the bathymetry configuration induced by the tested propeller jet and waves.