Horizontal Planar Scale Test of Local Scour at Submerged Monopile.

Determination of the horizontal planar scale of local scour (HSLS) at a submerged monopile in water flow conditions is necessary for site selection and the intuitive effectiveness-evaluation of upstream protection projects. A simplified experimental method for the prediction of HSLS is proposed and validated with a set of indoor experiments. High efficiency was obtained by modelling the erodible bed in a thin layer at the millimeter scale, which is much smaller than the centimeter or meter scale for the prediction of scour depth. The experiment was conducted under steady, uni-directional flow in non-cohesive sand-bed conditions. A 15 cm diameter cylindrical monopile submerged 0.2 cm was rigidly fixed on a flume bed. The complete 5-minute process the HSLS undergoes to reach its equilibrium shape and size was observed. A comparison of the HSLS with other research show good agreement. Compared with the conventional method for the observation of the complete scour-hole process, which includes reaching maximum scour depth which may take days, the proposed method significantly improves the model-test efficiency. The fundamental mechanism of this high-efficiency in the HSLS' development process to reach its equilibrium state is that the HSLS is mainly influenced by the wake vortices, which are dependent on the cylinder-diameter Reynolds number instead of scour depth. [ABSTRACT FROM AUTHOR]