Title
On the Influence of Fines on the Sedimentation Velocity in Hopper Dredgers
Author
Bleeker, N.
Contributor
Van Giffen, I. (mentor)
Van der Hout, R. (mentor)
Faculty
Mechanical, Maritime and Materials Engineering
Department
Offshore & Dredging Engineering
Programme
Dredging & Deep Sea Mining
Date
2015-08-26
Abstract
Clay particles, known for their adhesive properties, are commonly encountered in underwater soils. When producing large quantities of sand by means of dredging, fines are a byproduct and cause important viscosity changing effects altering the sand settling behavior. Much is already known in this field but knowledge lacks in the area where sand particles are affected by cohesive carrier fluids in environments similar to hopper settling areas during loading. By taking a closer look at the involved processes, knowledge is acquired in shear- and turbulent-flow sand-clay environments and another step is taken towards quantifying the effect of fines on the sedimentation velocity in hoppers. A versatile experimental setup is built allowing for separate shear flow and turbulence induced configurations. Shear affected sand settling velocities and turbulence induced concentration profiles are measured and analyzed. The shear flow settling effect shows contradicting results and leads to an interesting theory worthy of further investigation. The turbulence effect yields characteristic concentration profiles that are later used to determine key diffusion coefficients. Finally, clay characterizing factors are found using the theory proposed by Wang (1995). A 1DV model is developed using an advection-diffusion equation where the discretization techniques are based on an explicit method, a finite volume and an upwind scheme allowing settling of multi-sized particles. The simulation is used to determine diffusion coefficients for each of the conducted experiments. These diffusion coefficients yield interesting correlations with the input parameters finally resulting in an approximation of the diffusion coefficient as a function of the turbulent energy intensity allowing for a wider range of application.
Subject
Dredging
fines
clay
shear rate
diffusion
hindered settling
fall velocity
viscosity
shear settling
sedimentation
settling production
gelling
sedimentation velocity
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Embargo date
2025-08-26
Part of collection
Student theses
Document type
master thesis
Rights
(c) 2015 Bleeker, N.