FORM DRAG AND EQUIVALENT SAND-GRAIN ROUGHNESS FOR WAVE-GENERATED SAND RIPPLES

  • Jing Yuan
  • Dongxu Wang

Abstract

Moderate 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.

References

Yuan, J. and Madsen, O.S. (2014), Experimental study of turbulent oscillatory boundary layers in an oscillating water tunnel. Coastal Engineering, 89: 63-84.

Madsen, O. S. (2002), Sediment transport outside the surf zone, Coastal Engineering Manual, vol. III. U.S. Army Corps of Engineers, Washington DC. Chapter 6.

Published
2018-12-30
How to Cite
Yuan, J., & Wang, D. (2018). FORM DRAG AND EQUIVALENT SAND-GRAIN ROUGHNESS FOR WAVE-GENERATED SAND RIPPLES. Coastal Engineering Proceedings, 1(36), sediment.85. https://doi.org/10.9753/icce.v36.sediment.85