Experimental study of Bed Pattern around the Cylindrical Pile under Broken Waves

Cylindrical piles are often used in most of coastal and offshore structures such as bridges, wharfs, offshore wind turbine foundations and Oil platforms. Most of these structures are installed in shallow water and exposed to strong currents, waves and broken waves. These phenomena can cause scour around them which can damage their structural integrity and stability. In literature, scour process around the cylindrical piles under currents and waves have been studies frequently. However, there are very little knowledge about the bed forms due to the broken waves. In this paper, the effect of broken waves on the characteristics of bed forms around a cylindrical pile has been studied experimentally in a large wave flume. The three-dimensional bed topography was measured by Close Range Photogrammetry. Vortex ripples and truncated cone scour with vortex ripples were the main observed scour pattern. Shields parameter as well as Keulegan-Carpenter (KC) number were used as the non-dimensional parameters for bed form classification. It is noticed that the ripple height and ripple steepness for broken regular waves is less than non-breaking regular waves. However, the relative equilibrium scour depth for broken waves is larger than non-breaking waves.