FLOW VISUALISATION AROUND A SOLID SPHERE ON A ROUGH BED UNDER REGULAR WAVES

Hela Vidura Vithana, Richard Robert Simons, Martin Hyde

Abstract


Flow visualization using Volumetric Three-component Velocimetry (V3V) was carried out during laboratory tests to determine threshold shear stress and forces on idealized spherical stones. Incipient motion tests consisted of light weight spherical particles of specific gravity=1.19-2.65 and diameter=9.6mm-31.8mm. In-line and uplift forces on a 50mm sphere sitting on a rough bed of similar spheres were measured using pressure transducers linked to tappings on the sphere surface. It was found that the Shields critical shear stress and stone protrusion has an exponential relationship. At an exposure of 0.2d and less, bed protection is remarkably stable. Incipient motion data for currents are applicable for waves when the flow is fully developed.

Keywords


Shear stress; incipient motion; flow visualization

References


Chin, C.O., and Y.M.Chiew. 1993. Effect of bed surface structure on spherical particle stability. Journal of Waterway, Port, Coastal and Ocean Engineering, 113(3), 231-242.http://dx.doi.org/10.1061/(ASCE)0733-950X(1993)119:3(231)

Kajiura, K. 1968. A model of the bottom boundary layer in water waves. Bulletin Earthquake Res. Inst., 46, 75-123.

Sleath, J.F.A. 1987. Turbulent oscillatory flow over rough beds. Journal of Fluid Mechanics, 82, 360-409.


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