Experimental study of tsunami-induced scour around a monopile foundation

This paper presents an experimental study of the tsunami-induced scour process around a monopile foundation, representative of those commonly used for offshore wind farms. The scour process is studied by subjecting the monopile to a time varying current, which enables a properly down-scaled experiment from the boundary layer and scour perspective. It is shown how the scaled experiments corresponds to real life idealized tsunami cases with periods ranging from 10 to 40 min. It is then shown that the boundary layers of the model tsunami are well described by recently developed empirical relations for tsunami boundary layers. By subjecting the monopile to several successive tsunami waves the scour process is shown to occur in a stepwise cumulative fashion, with the final equilibrium scour depth tending to the depth limited steady current limit. It is shown that the entire scour development can reasonably be predicted by a recently developed simple engineering model. Finally, the experimental results are compared to a fully coupled hydrodynamic and morphologic CFD model and a good correspondence is obtained.