Drift-flux modeling of hyper-concentrated solid-liquid flows in dredging applications

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.Offshore and Dredging Engineerin

Advection-diffusion sediment models in a two-phase flow perspective

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.Offshore and Dredging Engineerin

An extension of the drift-flux model for submarine granular flows

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.Offshore and Dredging Engineerin