FORM DRAG AND EQUIVALENT SAND-GRAIN ROUGHNESS FOR WAVE-GENERATED SAND RIPPLES
AbstractModerate shoaling waves usually generate some small-scale bottom bedforms, i.e. sand ripples, which are 1-10cm tall and 10-100cm long. Wave-induced boundary layer flows over sand ripples are characterized by coherent vortices, which are alternatively generated on both sizes of ripples under the oscillatory free-stream motion. This process leads to a form drag, which significantly increases the local flow resistance. A large equivalent sand-grain roughness scaled with ripple dimension is therefore adopted in coastal models to account for ripple presences. Very few quantitative experimental results on this topic are available in the literature, so this study is aimed at filling this gap.
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