Transporting large amounts of sand is mostly done hydraulically in dredging and mining. This method of sand transport is efficient and is used in land reclamation projects or extraction of oil from tar sands. Large pieces of equipment, such as pumps and pipe line systems, dredging vessels etc., are used enabling the sand water mixtures to be transported hydraulically. Therefore, a good understanding of the hydrodynamical behavior of sand water mixtures is eminent in order to further improve these kind of systems. In this thesis a numerical model has been developed which describe the hydraulic behavior of sediment fluid mixtures. In the model the volume concentration of solids varies from 0.0 to 0.6. Moreover, the model is able to describe mixtures consisting of multiple sized sand particles.@en

In recent years deep sea mining attracted a considerable amount of attention. The presence of valuable raw materials in the deep sea is interesting, securing the supply of these materials in the long term. These materials can be found, typically at depths of 2000-5000 meters, in the form of manganese nodules, massive sulfides and cobalt rich crusts. The deposits contain several metallic materials such as manganese, iron, copper, nickel and cobalt. Furthermore, massive deposits also contain elements such as germanium, selenium, tellurium and indium, which are in high demand in many industries. In order to process the manganese nodules the materials need to be transported from the deep sea to the surface. Typically this is done using a vertical hydraulic transport system or VTS in short. One of the challenges is to assure the flow, i.e. prevent possible clogging of the system. Particle sizes of manganese nodules range from 1/10 to 1/3 of the VTS pipe diameter. The objective of this paper is to numerically simulate the settling of one particle. Experimental data are used for validation. The equations of motion of a fluid flow are governed by the Navier-Stokes equations. These are discretized with the Finite Volume Method on a collocated grid and numerically solved using the fractional step method. Solids or particles are modeled using the Immersed Boundary Method (IBM). In this paper a free settling particle in a confined domain, in two dimensions, is simulated. The particle size with respect to the domain size is varied in the calculation. The settling velocity is lower in comparison with a free settling particle in an infinite domain. This is due to the so-called wall effect. The settling velocity from the numerical calculation is compared with the corrected settling velocity known from experimental data. The results from the calculation are in agreement with the experiments. @en

Sediment profiles in open channels are usually predicted by advection-diffusion models. Most basic forms consider the terminal settling velocity of a single particle in still clear water. Alternative forms account for hindered settling at higher concentrations. It is not known, however, how these modifications relate to mass and momentum conservation of each phase. For dilute flow, it is known that the original form can be derived from a two-phase analysis, assuming a dilute suspension, neglect of inertial effects in the momentum balance and using a linear drag force formulation. Here we study how and if it is possible to understand the hindered-settling modifications for the non-dilute case, and formulate a relation between advection-diffusion models and parameters involved in the turbulent drag force. This note verifies that the transient two-phase flow solutions converge to steady state, and compares the results to experimental data.

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Breaching has been an important mechanism for sand suction dredging for a long time. A special kind of breaching, unstable breaching, has recently been identified as a possible failure mechanism for sandy submerged slopes. This has increased the interest into the breaching process. At the Delft University of Technology we have started a research project on the subject of unstable breaching. In this paper we discuss the results obtained so far. First, we discuss a concept for laboratory experiments into the phenomena. Second, we propose a new numerical model, designed to investigate unstable breaching.@en

To model submarine flows of granular materials we propose an extension of the drift-flux approach. The extended model is able to represent dilute suspensions as well as dense granular flows. The dense granwular flow is modelled as a Herschel–Bulkley fluid, with a yield stress that depends on the dispersed phase pressure. Qualitative numerical experiments show that the model is able to correctly reproduce the stability of submerged sand heaps with different internal angles of friction and initial slopes. When initially starting with heaps with an angle smaller than the internal angle of friction, the heaps are stable. When starting with heaps with angles larger than the internal angle of friction, a flow of solid material is initiated. The flow later stops when the bed is at an angle smaller than the internal angle of friction.@en

In this paper, the concentration and velocity profiles of sediment water mixtures for open-channel flows are modelled numerically and validated with experimental results. A continuum approach, the drift flux model, is used. The mixture consists of volume fractions with different particle sizes. Hindered settling is taken into account with the closure relation of Richardson and Zaki. Transport equations are used for sediment transport. Turbulence is modelled with the LES (large eddy simulation) WALE model. The discretization of the transport and Navier-Stokes equations is done with the finite volume method. The Navier-Stokes equations are solved using a fractional step method. The numerical results are compared with experimental results concerning open-channel flows.@en