Cees van Rhee

Turbulent Interaction of a Buoyant Jet with Cross-Flow

AbstractThis paper presents large eddy simulations (LES) and experimental results of buoyant jets in cross-flow (JICF). Mixing behavior of buoyant JICF is governed by the velocity ratio (γ) and the jet Richardson number (Ri). Four buoyant JICF cases are studied with 0.68<γ<1.28 and 0.31<Ri<1.83. In this range, both initial buoyancy and initial momentum are important; the release of overflow dredging plumes is a practical example within this range. The shape, size, and vertical location of simulated jet concentration cross sections compare well to measured ones. The LES results are also compared with semiempirical formulas for buoyant JICF. Those formulas use an added mass coefficient (kn) and a spreading rate (β) as calibration parameters. In the present study, it is found that path, dilution, and spreading can be well predicted by applying kn=0 and β=0.7; those values result in better predictions than when using the advised values—namely, kn=1, 0.34<β<0.62. Cross contours for concentration (C/Cmax) and f...

Test Set-Up for Irregular Vertical Hydraulic Transport in Deep Ocean Mining

The mining of scarce minerals from the sea-floor at the depths of several kilometers and bringing them to a processing plant at the ocean surface requires new techniques. Seafloor Massive Sulphide (SMS) deposits are known to have an extremely rich mineral content, and are considered technically-economically-environmentally feasible to explore. Vertical hydraulic transport is the link between the sea-floor mining and the maritime vessel where the first processing stage will take place. Clogging of any part of the vertical transport system is an absolute disaster. Fine particles are conveyed faster than coarse particles. High concentrations of fines cannot bypass high concentrations of coarse particles, hence these particle fractions accumulate, potentially blocking the pipe. Fundamental research into yet unexplored physics is necessary. Besides numerical flow simulations, it is necessary to conducted experiments on the transport over large vertical distances. Such tests aim to investigate the dynamic development of density waves consisting of different particle diameters and clogging phenomenon thereof. Different particle size fractions have to be followed in real time as they overtake each other, and change their shape, merge and segregate. It is however impossible to back-scale the prototype riser to a one-pass laboratory test set-up, but the process can be simulated by repeated flow through an asymmetric vertical pipe loop, where slurry flow in the upward leg represent vertical hoist conditions and the slurry is returned quickly via the downward leg. The particle accumulation process is allowed to take place in the upward leg whereas in the downward leg the restoring process is nearly neutralized. The development of accumulations in time (= distance traveled to the ocean surface) can be followed upon multiple passes of the solids batches through the upward leg. The novelty of the described testing method is that the essentials of fundamental processes occurring in long vertical stretches are quantified in a specially designed laboratory setup. Via subsequent implementation of the results in a numerical flow simulation, reliable transport scenarios can be delineated.Copyright

Influence of Particle Geometry on the Simulation of Sand Cutting Process

Appropriate simulations of the sand cutting process are needed for dredging purposes. Software packages based on discrete element modeling (DEM) have offered useful tools to conduct the simulation and visualize the result. However, before moving to water saturated environment, simulations of the sand cutting process in atmospheric environment should first be treated. As known in reality the sand particles are not perfectly spherical, and their behavior is determined by their natural shape and material properties. Hence one of the key questions emerges to us, what particle geometry design is appropriate for a practical simulation.To answer that question, a group of simulations with various particle geometry designs are set up to imitate the natural behavior of the sand particles in cutting process. The simulations are conducted in 3D by the software package EDEM™. The outcome shows that the macro behavior of the sand specimen could be different when different types of particles are used. And the cutting force records registered on the cutting blade are influenced by the particles’ ability to rotate, which is determined by the geometry of the particles, too. Besides, there is a risk that some of the particle shapes may create orderly placement in the sand pile.Another topic discussed in this paper is the algorithm to calculate the porosity in the sand pile, which is useful for developing the simulation into water saturated environment. A numerical method based on a 3D grid system will be introduced in this part.This paper will show the detailed methodology and results of the simulation and analysis.© 2013 ASME

A New Approach to Model Hyperbaric Rock Cutting Processes

In deep sea mining processes, rock is being cut in a hyperbaric pressure environment. The effect of such a high pressure environment is of major influence on the cutting process. Due to deformation of the rock matrix, local fluid pressure differences will occur. This can result in a higher apparent strength of the rock, but also in a higher (loading) rate dependency.Our new modeling approach aims at combining both rock mechanics and fluid dynamics to model the high deformation (rate) behavior experienced in seabed excavations. This new approach is based on the Discrete Element Method to simulate the rock mechanics, combined with the use of Smoothed Particle Methods to model the influence of the fluid (pressure) on and in the rock. In this paper, emphasis is put on estimating the local (volumetric) deformation rate with the new approach. Eventually, the new technique will be validated with experiments and data available in literature. The new approach will give more insight in the physical processes that occur during cutting.Copyright

Numerical Methods for Modeling the Rock Cutting Process in Deep Sea Mining

The increasing demand on precious metals has motivated the development of a promising industry, deep sea mining. Currently major technical challenges exist in the development of this new industry, such as the vertical transportation, the seabed excavation process and the stability of the riser system. This paper will focus on the excavation process on the seabed.Considering the fact that the deep sea mining excavation process may occur at 3000∼6000 meters water depth, the hyperbaric pressure applied by the sea water will greatly influence the cutting process. Especially when the cutting speed of the cutter is very high, the so called “dilatancy hardening effect” (Brace and Martin, 1968) may make the seabed rock very difficult to excavate. These factors will make the rock excavation in deep sea much different from shallow water, which is the case in a normal dredging project. In this paper, the physics of the hyperbaric excavation process will first be described into detail.Because the hyperbaric rock cutting experiments are expensive, it is more feasible to make a numerical model to simulate the process, which eventually can replace the experiments. The main difficulties are to model the failure of rock and the interaction between the rock and the pore water. Considering the scale of the problem and the characteristics of the material, it is concluded that the discrete element method (DEM) will be the best tool to simulate the rock behavior. On the other hand, to describe the influence from the hyperbaric pressure which is induced by the sea water, governing equations for the fluid phase are derived and the finite volume method (FVM) is chosen to solve the equations. This paper will give a detailed description about the numerical methods and their interactions regarding this specific problem and show some preliminary tests on clay-like material cutting process.Copyright

Numerical calculations of environmental impacts for deep sea mining activities

With the expected dramatic increase of mineral resources consumption, deep sea mining (DSM) was proposed as a method supplying the running of world economy by cooperating with or compensating for the terrestrial mining industry. However, its industrialization process is hindered by various reasons including the technological feasibility, economic profitability, and the DSM environmental impacts. The objective of this paper is to calculate the DSM environmental impacts based on a DSM environmental impact framework, which was selected through a systematic literature review in earlier work. The numerical calculations focus on the initial DSM disturbances and plume source, species disturbance, sediment plume and tailings. More importantly, the interconnection between the sediment plume and the species disturbances is also analysed particularly in this paper. The research quantifies the environmental impacts into a systematic framework, which could be helpful to assess the comprehensive environmental performances of a DSM activity and to promote the DSM industrialization process in the future.

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.