PHASE DEPENDENT ROUGHNESS CONTROL OF SAND MOVEMENT

Douglas L. Inman, Edward B. Tunstall

Abstract


Experiments with wave motion over asymmetrical "ripple-like" forms show that the difference between a net sand transport in a down-wave versus an up-wave direction is related to a subtle phase dependent mechanism associated with the intensity of vortex formation in the lee of the form. Artificial roughness modules have been developed, consisting of arrays of asymmetrical forms resembling natural ripples. The asymmetry of the forms causes an intense vortex to form in the lee of the steep face. This vortex traps and suspends sediment, which when the orbital motion reverses its phase, is lifted above the roughness element and carried in the new direction. Thus, the direction of the net sand transport is dependent upon the relation between the steep face of the roughness element and the phase of the orbital velocity; the net transport being in the direction of the orbital velocity that is out-of-phase with the maximum vortex formation.

Keywords


roughness; sediment transport; phase dependent roughness

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