Oleg Vinogradov

Simulation of grinding in a shaker ball mill

Little information currently exists on designing highly efficient ball mills for producing mechanically alloyed material. This work is an attempt at understanding the mechanisms of alloying in order to design better equipments. The problem of efficiency of mechanical alloying is investigated numerically by simulating the dynamics of a shaker ball mill. The model consists of two major parts: shaker ball mill dynamics simulation and the grinding model. The dynamics simulation is used to find out how the number of collisions, the total kinetic energy, and the rate of energy dissipation in the system depend on both the frequency and amplitude of vibrations and on the number of balls. The model of an ideal gas is used to validate the dynamics model. Two models are developed to simulate the distribution of radii of particles during the grinding process: a statistical model and a deterministic one, representing an average-case behavior of the statistical model. Both models compare favorably against each other as well as against experimental results.

A METHOD FOR QUASI-STATIC ANALYSIS OF TOPOLOGICALLY VARIABLE LATTICE STRUCTURES

The proposed time-independent quasi-static approach for simulations of lattice structures with imperfections is based on integration of the Inverse Broydens Method suitable for finding the equilibrium state for a large system of atoms interacting through strongly nonlinear potentials and the Recursive Inverse Matrix Algorithm (RIMA) capable of updating the inverse matrix when topological changes (broken or new bonds between the atoms) take place. In this approach, the crystal structure is treated as a truss system while the forces between the atoms situated at the nodes are defined by the inter-atomic potentials. Since both the Broydens and the RIMA algorithms deal with the inverse matrices of the structure their coupling makes the procedure computationally efficient. In addition, the method allows analysis of lattices subjected to mixed boundary conditions. The developed code was verified by the comparison with an alternative numerical procedure based on energy minimization technique. The model and the code developed were applied to the case of a 2D hexagonal lattice with the mode I crack embedded into the structure. For the cases considered, it was observed that the crack nucleation and growth were accompanied by the dislocation emission.

A molecular dynamics approach in simulations of fluid-solid particles flow

Abstract In the paper a discrete system of particles carried by fluid is considered in a planar motion. The volumetric density of particles is assumed to be small enough such that they can be treated within the framework of a molecular dynamics model. The fluid is then considered as a carrier of particles. The Landau-Lifshitz concept of turbulence is used to describe the fluctuating part of fluid velocity. This approach is applied to simulate different regimes (laminar and turbulent) and various states of particle motion (moving bed, heterogeneous flow, and homogeneous flow) using only two parameters, which have to be determined experimentally. These two parameters, found for a particular pipe and for a particular velocity from a simple experiment, then can be used for other pipe diameters and different velocities. The computer simulations performed for the flow of particles in pipes at different flow velocities and different pipe diameters agree favorably with experimental observations of the type of flow and critical velocities identifying transitions from one type to another.

Investigation of Cavitating Jet Effect on Bitumen Separation from Oil Sands

Abstract The effect of a submerged cavitating jet on as-mined oil sands is investigated in order to assess the potential of this new technological approach to bitumen extraction at low temperatures. A series of laboratory experiments have been performed using a custom-made experimental apparatus that allowed ablation measurements of oil sands samples and provided information regarding the volume of the extracted bitumen, the remaining volume of cleaned sand, the effects of the water temperature, and the time of exposure of the sample to a cavitating jet. A comparison of the results for cavitating and noncavitating jets is provided.

The effect of probability of coalescence on the evolution of bubble sizes in a turbulent pipeline flow: A numerical study

A population balance method in which continuum and discrete phases are integrated is developed to simulate the evolution of polydisperse population of bubbles in a turbulent pipeline flow. The investigation is focused on the effect of the coalescence efficiency on this evolution. A dilute system of bubbles under microgravity conditions is considered. It is found that if the initial coalescence efficiency is low, a slight increase produces a significant effect on the bubble coalescence rate, and thus on the evolution of the population. If, however, the initial coalescence efficiency is high, its increase results in a marginal effect on the way the population evolves. The results of simulations are validated against experimental data on the population mean.

Theoretical estimates of air bubble behavior in dense pipeline slurry flows

In the paper an approach to simulation of air bubbles behavior in dense slurry flowing in a pipeline is explored. It is based on establishing a relationship between the flow dissipation energy rate and the collisional dynamics of solid particles. This problem is important in hydrotransport technology of bitumen extraction from the oil sands. The dynamics of air bubbles distributed in slurry is investigated based on two models: a model of turbulence and a model describing particles collisional motion. The rate of air bubbles break-up as well as that of coalescence are estimated. The main parameters governing the bubbles break-up and coalescence are discussed.

Optimization Techniques in an Event-Driven Simulation of a Shaker Ball Mill

The paper addresses issue of efficiency of an event-driven simulation of a granular materials system. Performance of a number of techniques for collision detection optimization is analyzed in the framework of a shaker ball mill model. Dynamic computational geometry data structures are employed for this purpose. The results of the study provide insights on how the parameters of the system, such as the number of particles, the distribution of their radii and the density of packing, influence simulation efficiency.

Modeling of hydrogen-assisted cracking in iron crystal using a quasi-Newton method

A Quasi-Newton method was applied in the context of a molecular statics approach to simulate the phenomenon of hydrogen embrittlement of an iron lattice. The atomic system is treated as a truss-type structure. The interatomic forces between the hydrogen–iron and the iron–iron atoms are defined by Morse and modified Morse potential functions, respectively. Two-dimensional hexagonal and 3D bcc crystal structures were subjected to tensile numerical tests. It was shown that the Inverse Broyden’s Algorithm—a quasi-Newton method—provides a computationally efficient technique for modeling of the hydrogen-assisted cracking in iron crystal. Simulation results demonstrate that atoms of hydrogen placed near the crack tip produce a strong deformation and crack propagation effect in iron lattice, leading to a decrease in the residual strength of numerically tested samples.

A model of oil sand lump digestion

The process of digestion of an oil sand lump moving in the heated water flow is considered. A lump is modelled as a heated sphere subjected to shear stresses and ambient temperature and melting when the combined effect of these two factors exceeds some critical value. This critical value is introduced in the form of a critical temperature and it is associated with the minimum adhesive strength of bitumen. This temperature is a model constant that can be determined from an experiment. The complicated heat transfer conditions of a lump are taken into account by averaging the Nusselt number (the second experimental constant of the model). A numerical analysis of the dependence of digestion rates on water and lump temperatures, and on lump sizes is performed to illustrate the applicability of the model.

APPLICATION OF INVERSE BROYDEN'S METHOD FOR COMPUTATIONAL ANALYSIS OF HYDROGEN CONTRIBUTION TO THE NEAR-NEUTRAL PH STRESS CORROSION CRACKING

An Inverse Broydens Method was applied in the context of a molecular statics approach for the analysis of the contribution of hydrogen to the near-neutral pH stress corrosion cracking. A 3D crystal structure was tested numerically. It is shown that the Inverse Broydens Method provides a computationally efficient technique to evaluate the effect of hydrogen on the material degradation. Simulation results demonstrated that atoms of hydrogen placed near the crack tip produced a strong effect on deformation and crack propagation in bcc iron leading to a 15–20% loss in a residual strength of numerically tested samples.