Localized fluidization in granular materials: Theoretical and numerical study

We present analytical and numerical results on localized fluidization within a granular layer subjected to a local injection of fluid. As the injection rate increases the three different regimes previously reported in the literature are recovered: homogeneous expansion of the bed, fluidized cavity in which fluidization starts developing above the injection area, and finally the chimney of fluidized grains when the fluidization zone reaches the free surface. The analytical approach is at the continuum scale, based on Darcy's law and Therzaghi's effective stress principle. It provides a good description of the phenomenon as long as the porosity of the granular assembly remains relatively homogeneous, i.e. for small injection rates. The numerical approach is at the particle scale based on the coupled DEM-PFV method. It tackles the more heterogeneous situations which occur at larger injection rates. The results from both methods are in qualitative agreement with data published independently. A more quantitative agreement is achieved by the numerical model. A direct link is evidenced between the occurrence of the different regimes of fluidization and the injection aperture. While narrow apertures let the three different regimes be distinguished clearly, larger apertures tend to produce a single homogeneous fluidization regime. In the former case, it is found that the transition between the cavity regime and the chimney regime for an increasing injection rate coincides with a peak in the evolution of inlet pressure. Finally, the occurrence of the different regimes is defined in terms of the normalized flux and aperture

A pore-scale hydro-mechanical coupled model for geomaterials

We present a model for fluid-saturated granular media coupled flow and mechanical deformation. The fluid is assumed to be incompressible and the solid part is assumed to be a cohesive granular material. Forces exerted by the fluid in motion are determinated and applied to solid particles. We derive a finite volumes formulation of the flow problem and we couple it to a discrete element method (DEM) formulation of the solid deformation. The ability of the algorithm to solve transient problems is tested by simulating an oedometer test on a soil sample. The numerical solution of our model is in good agreement with Terzaghi’s analytical solution

К вопросу применения комплексных систем контроля производственного процесса на урановых шахтах

Викладено технічні, технологічні й соціальні передумови застосування комплексних систем контролю виробничого процесу на уранових шахтах.Sets out technical, technological and social conditions of application of complex process control systems in the uranium mines

Investigation of internal erosion processes using a coupled DEM-fluid method

The evolution of granular beds subjected to upward seepage flow is investigated using a coupled DEM-fluid model implemented by Catalano et al. in the open-source software Yade-DEM. Firstly, filtration properties of a coarse narrowly graded material are analyzed by simulating the transport of smaller particles from a base layer through the coarse filter by gravitational loading or downward flow with uniform pressure gradient. The results are analysed on the basis of the constriction size distribution (CSD) of the filter which describes statistically the sizes of throats between pores in the material. Secondly, we examine the results obtained when, instead of two different layers, the coarse and fine materials are initially mixed in one unique layer and subjected to gravity. Thirdly, this mixture of coarse and fine particles is subjected to both gravity and a non-uniform pressure gradient, by injecting the fluid in one point below the layer, as inspired by previous experiments. Similar channeling patterns are obtained in both experiments and simulations when the boundary condition at the injection point is an imposed flux. This boundary condition results in a recirculation mechanism that remains confined in a finite zone around the injection point as long as the flux is below a threshold value. By simulating an imposed pressure condition, we finally show that instabilities can be triggered by the transport of small particles away from the injection point. This segregation process results in a lower porosity and an increased pressure gradient above the eroded zone, so that the instability-triggering pressure gradient in bi-dispersed mixtures is lower than in mono-dispersed mixtures

Numerical modeling of particle migration in granular soils

Suffusion is the process of internal erosion where fine particles migrate under water seepage through a coarser soil matrix. Relevant models of suffusive phenomena must reproduce the poromechanical effects that result from the two-way coupling between the deformation of the solid matrix, the fluid pressure and the flow. In this work, an advanced computational method is used to study the particle migration in granular soils. The so called coupled Discrete Element Method - Pore scale Finite Volume (DEM-PFV) is based on a microscopic hydromechanical approach. It couples the discrete element method that solves the equations of motion for the solid fraction, with a PFV method that solves the fluid flow equations. We use this method to study particle transport through coarser granular assemblies that do not evolve with time. These simulations allow us to obtain, for different cases, the parameters to include in a general advection-dispersion equation (ADE). We paid particular attention to the role played by the intermittent formation of blockages of transported particles in the constrictions of the granular assembly. These temporary and collective trapping events change local fluid flows and affect the particle transport on short time or length scales. As the transport time between consecutive blockages and the duration of blockages have exponential decays, sink and source terms can be added to the ADE

A pore-scale study on the drying kinetics and mechanical behavior of particle aggregates

[EN] A discrete thermo-mechanical drying model is developed to investigate the interaction between the porous structure and the drying characteristics of dense particle aggregates. The solid phase consists of polydisperse spherical particles in the micrometer range and the void space is constructed by a complementary network of tetrahedral pores. A modified version of the classical invasion percolation algorithm is set up to describe the preferential evaporation of the confined liquid in the pores. Thus, the evolution of the liquid distribution throughout the complex disordered medium can be simulated. In a one-way coupling scheme, capillary forces caused by both fluid pressure and surface tension are computed over time from the filling state of pores and they are applied as loads on each primary particle in the discrete element method. Based on this robust approach the drying kinetics and the mechanical behavior of several different aggregates with various fractions of small and large particles are simulated and quantified.Pham, TS.; Chareyre, B.; Tsotsas, E.; Kharaghani, A. (2018). A pore-scale study on the drying kinetics and mechanical behavior of particle aggregates. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 245-252. https://doi.org/10.4995/IDS2018.2018.7388OCS24525

Electrical Quality Assurance of the Superconducting Circuits during LHC Machine Assembly

Based on the LHC powering reference database, all-together 1750 superconducting circuits were connected in the various cryogenic transfer lines of the LHC machine. Testing the continuity, magnet polarity, and the quality of the electrical insulation were the main tasks of the Electrical Quality Assurance (ELQA) activities during the LHC machine assembly. With the assembly of the LHC now complete, the paper reviews the work flow, resources, and the qualification results including the different types of electrical non-conformities

Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC

The uncertainty on the calorimeter energy response to jets of particles is derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the calorimeter response to single isolated charged hadrons is measured and compared to the Monte Carlo simulation using proton-proton collisions at centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009 and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter response to specific types of particles (positively and negatively charged pions, protons, and anti-protons) is measured and compared to the Monte Carlo predictions. Finally, the jet energy scale uncertainty is determined by propagating the response uncertainty for single charged and neutral particles to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3% for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table, submitted to European Physical Journal

Standalone vertex finding in the ATLAS muon spectrometer

A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at √s = 7 TeV collected with the ATLAS detector at the LHC during 2011

Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H →γ γ, H → Z Z∗ →4l and H →W W∗ →lνlν. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV, corresponding to an integrated luminosity of about 25 fb−1. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson