Scour Protection around Offshore Wind Turbines: Monopiles

Abstract

The flow processes in a scour protection around a mono-pile in steady current is described in relation to transport of sediment in the scour protection based on physical model tests. Transport of sediment in the scour protection may cause sinking of the scour protection. This may reduce the stability of the mono-pile and change for instance the natural frequency of the dynamic response of an offshore wind turbine in an unfavorable manner. The most important flow process with regard to transport of sediment and sinking of the scour protection is found to be the horseshoe vortex. It is found that a larger pile diameter relative to the size of the protection stones will cause a larger sinking and that two layers of stones will decrease the sinking relative to one layer of stones with the same size.