Local scour around a monopile in reciprocating tidal current considering the effect of water depth

Abstract

Despite most of sea-crossing bridges and offshore wind farms being located in areas dominated by tides, researches about the effects of tidal current on the scour process around these buildings are still limited to this date. A three-dimensional sediment transport numerical model was established to investigate the local scour around a monopile under reciprocating tidal flow. The standard turbulence equation RNG (Renormalization-group) κ – ε was adopted to close the N-S equation and the finite difference method was applied to discretize the governing equation in the numerical model. Tidal currents were adapted by bidirectionally reversing sinusoidal currents. It showed in the results the scour pits grew periodically in the process of repeated scour and deposition with the change of the flow velocity and direction. Besides, it implied that tidal scour depth around the monopile deepened with the water depth, but the impact of water depth diminished gradually. The change of the maximum scour depth was less than 5% if water depth is more than 4 times pile diameter. It indicated that the scour depth around the pile will be almost no longer influenced by water depth if water depth is more than 4 times pile diameter. Therefore, the research results emphasize the significance of selecting suitable water depth conditions for the design process of offshore structures.