Ole Secher Madsen, Arlendenovega Satria Negara, Kian Yew Lim, Hin Fatt Cheong


Experimental results for near-bottom current velocity profiles for flows over artificial, definitely 2D ripples made of 1.5 cm high aluminum angle-profile spaced at 10 cm intervals are obtained for the following cases: (i) current alone perpendicular to ripples; (ii) current alone parallel to ripples; (iii) combined orthogonal wave-current flows for current parallel to ripples; and (iv) current alone at an angle of 30° to the ripple axis. The velocity profiles are analyzed by the log-profile method, and show the roughness experienced by the current to increase as the angle between ripple and current direction increases, i.e. demonstrating convincingly the reality of the concept of a direction-dependent roughness for flows over a 2D rippled bottom. Roughness experienced by the velocity component perpendicular to the ripples is, however, found to be independent of the direction of the mainstream flow relative to that of the ripples, and the different roughness experienced by the perpendicular and parallel velocity components gives rise to a turning of the current velocity vector to become increasingly aligned with the ripple crests as the bottom is approached from above. Implications of this feature, in terms of net sediment transport direction in combined wave-current flows in inner-shelf coastal waters, is discussed.


flow over ripples; bottom roughness; wave-current interaction; boundary layer flows over 2D roughness elements

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Barrantes, A.I., O.S. Madsen. 2000. Near-bottom flow and flow resistance for currents obliquely incident to two-dimensional roughness elements. Journal of Geophysical Research 105(C11), 26, 253-264.

Madsen, O.S. 1994. Spectral wave-current bottom boundary layer flows. Proceedings 24th International Conference on Coastal Engineering, ASCE, Kobe 1, 384-398.

Madsen, O.S., S. Kularatne, H.F. Cheong. 2008. Experiments on bottom roughness experienced by currents perpendicular to waves. Proceedings 31 st International Conference on Coastal Engineering, ASCE, Hamburg, September 2008, 1, 845-853.

Mathisen, P.P., O.S. Madsen. 1996. Waves and currents over a fixed rippled bed: II. Bottom and apparent roughness experienced by currents. J. Geophysical Research 101(C7),16, 543-550.

Negara, A.S. 2009. Experimental study of turbulent current over fixed 2D and 3D bottom roughness. Thesis submitted for the degree of Master of Engineering, Department of Civil Engineering, National University of Singapore.

Schlichting, H. 1960. Boundary Layer Theory, fourth edition. McGraw Hill, New York.