Dredging is the process of excavation of sediment, usually carried out underwater, with the purpose of the collection of the excavated sediment, such as sand, and subsequently its disposition at another location. In order to be able to predict the performance of dredging equipment, such as dredging pumps and hoppers, a two-phase numerical flow simulation method has been developed for conditions for which the volume fraction of the solid volume fraction (sand) is high. The method is based on the equations for the two-fluid model. The flow field is described by the conservation equations of mass and momentum for the solid phase (sand) and for the fluid phase (water), in combination with constitutive relations that describe the behaviour of the sand-water mixture, implemented in the commercial CFD-code Ansys CFX 14.0. The viscosity of suspensions has been analysed experimentally, utilizing a concentric cylinder rheometer. In the experimental work, carried out with neutrally buoyant particles, parameters that determine the behaviour of the suspension have been varied, using the same particulate and liquid material for all experiments. The solid volume fraction, particle diameter, liquid viscosity, and shear rate, have been varied systematically. An investigation has been carried out into a model for the particle pressure, required to model the formation of a particle bed when the volume fraction of the particles reaches its maximum obtainable value. Dredging is often carried out by ships, storing the sediment in a large hold called a hopper. A sand-water mixture is taken from the bottom of the dredging site and pumped into the hopper. As an example of the application of the developed simulation method, the flow in a hopper during the filling process is considered. A parameter study has been carried out by varying the flow conditions at the inlet of the hopper: velocity at the inlet, solid volume fraction at the inlet and particle diameter of the incoming suspension. The results show how these parameters affect the filling curve of the hopper, defined as the total mass of sand present inside the hopper as function of time.
|Award date||31 Aug 2016|
|Place of Publication||Enschede|
|Publication status||Published - 31 Aug 2016|