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 Resources: Dredging and Offshore Engineering Lecture Notes



Home / Hopper Sedimentation /

    04-An analytical method to determine scour. (784)

The loading process of TSHD’s (Trailing Suction Hopper Dredgers) is often terminated because of the occurrence of scour/erosion of the just settled sand. If the flow velocity above the sediment is to high, scour will occur and the sand particles will not settle anymore. But when does this occur?, and what is the relation between the scour velocity and the sedimentation process? In the 30’s Shields discovered a relation between the particle Reynolds number and the shear stress, the well know Shields curve. Hjulstrøm also discovered a similar relation, but directly between the flow velocity and the particle diameter.
In the paper a relation is derived between the relevant grain parameters and the operational parameters, resulting in curves that can be plotted both in the Shields and the Hjulstrøm approach. Based on the geometry of the grain with respect to the sediment, different curves can be constructed for different cases of scour, from a single grain being eroded to the entire top layer being eroded. The “new” theory is added to the existing Camp, Miedema & Vlasblom model for Hopper Sedimentation, however it can also be used in any morphological problem.

Reference:

Miedema, S.A., "An Analytical Method To Determine Scour".  WEDA XXVIII & Texas A&M 39. St. Louis, USA, June  8-11, 2008.



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