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 Resources: Dredging and Offshore Engineering Lecture Notes

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 01-Lecture Notes Dredging Processes Hopper Sedimentation (1731)

Publication Dredging WEDA/TAMU 96

The sedimentation process in the hopper of a Trailing Suction Hopper Dredge (TSHD) is very complex. However it is debatable whether for estimation purposes it is necessary to model the processes involved in detail. For estimation purposes a black box approach may suffice. Based on the turbulent diffusion theory of Camp (1936, 1946) and Dobbins (1944) for sedimentation tanks, a method has been developed describing the sedimentation and thus the overflow losses in hoppers. The Camp theory considers particles of one diameter, but here the grain distribution is considered, which is the basis for calculating the overflow losses. In the time domain, a homogeneous flow above the sand bed is assumed. Using Camp as a first criterion, it is possible to determine which percentage of particles of a specified diameter will settle and which particles will have too small a settling velocity to settle. A second criterion is the scour velocity. If the velocity above the bed is greater than the scour velocity of a particle of a specified diameter, that particle will be re suspended. Both criteria will result in overflow losses. Given a specified mixture flow into the hopper, once the overflow losses are known, the loading curve can be determined. Since non-linearities are involved, the calculations are carried out in the time domain. The model is implemented in a computer program, which also calculates the stratification of the grain distribution in the hopper and the grain distribution of the material leaving the hopper through the overflow as a function of time. This paper is a follow-up of the paper of Vlasblom and Miedema (1995) at WODCON XIV. Some of the equations have been modified resulting in different loading curves. The implementation of scour has changed and a discussion about two-dimensional turbulent diffusion models has been added.

Reference:

Miedema, S.A. & Vlasblom, W.J., "Theory for Hopper Sedimentation". 29th Annual Texas A&M Dredging Seminar. New Orleans, June 1996.

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