Granular slumping in a fluid : focus on runout distances

We investigate the effect of an ambient fluid on the dynamics of collapse and spread of a granular column simulated by means of a recently developed model which takes into account both fluid forces that act on each grain and contacts between grains. The model couples the contact dynamics method for discrete element modeling of the grains and their interactions with the finite element method for the integration of Navier-Stokes equations in 2D. The coupling is based on the fictitious domain approach in which the fluid domain is extended to that of grains, and the rigid-body motion of the grains is imposed by means of distributed Lagrange multipliers. As in similar numerical and experimental works with dry grains, we focus here on the run-out distances and avalanche durations for different column aspect ratios (height vs width). We consider three options for the surrounding fluid: 1) no fluid, 2) water and 3) a viscous fluid that allows us to perform our simulations in the grain-inertial, fluid-inertial and viscous regimes, respectively. The run-out distance is found to increase as a power law with the aspect ratio of the column, and surprisingly, for a given aspect ratio and packing fraction, it may be similar in the grain-inertial regime and fluid inertial regimes but with considerably longer duration in the latter case. We show that the effect of the fluid in viscous and fluid-inertial regimes is both to reduce the kinetic energy during the collapse and enhance the flow by lubrication during the spread. Hence, the run-out distance in a fluid may be below or equal to that in the absence of fluid due to compensation between those effects

Failure in porous granular aggregates

We use a 3D Lattice Element Method, based on the discretization of the particles and binding matrix on a regular lattice, to investigate the particle-scale origins of the strength and failure of porous granular aggregates under tensile loading. Damage growth is analyzed by considering the evolution of stress probability density and the number of broken bonds in the particle phase. We show that the stress probability density functions are increasingly broader for a decreasing matrix volume fraction, the stresses being more and more concentrated in the interparticle contact zones with an exponential distribution as in cohesionless granular media [4]. We carried out a detailed parametric study in order to evaluate the combined influence of the matrix volume fraction and particlematrix adherence. Our findings are in agreement with 2D results previously reported in the literature [6]. Three regimes of crack propagation are evidenced, corresponding to no particle damage, particle abrasion and particle fragmentation, respectively. The crack morphology (tortuosity...) is another important feature that we investigate for different distributions of the particles and pores within porous granular aggregates

The triangular nasal notch sign in patients with Crohn's disease treated with tumor necrosis factor inhibitors

Tumor necrosis factor (TNF) inhibitors are used to treat a range of chronic inflammatory diseases, such as rheumatoid arthritis, inflammatory bowel disease and psoriasis. Some of the cutaneous side effects of these drugs are well documented, such as infections, skin carcinomas, palmoplantar and skinfold pustulosis, psoriasis-like or eczema-like lesions. We are not aware of TNF inhibitor-induced nasal lesions in the literature. We report a case series demonstrating a specific pattern of cicatricial nasal fissure (triangular nasal notch) following nasal dermatitis episodes in patients treated with TNF inhibitors. This article is protected by copyright. All rights reserved

Fissuration des matériaux à inclusions granulaires: effet de la microstructure

La morphologie d'une fissure dans un matériau hétérogène dépend bien évidemment des propriétés des phases en présence mais aussi de leur agencement spatial. Ce point, assez rarement étudié dans la littérature, est ici abordé sous l'angle numérique et statistique pour les matériaux à inclusions granulaires (type béton). Une méthode 3D sur réseau permet notamment de quantifier précisément l'effet microstructural des fractions volumiques et de la polydispersité des inclusions. Trois morphologies à la rupture, associées à trois régimes de fissuration, sont caractérisés

Comparative evaluation of the new xTAG GPP multiplex assay in the laboratory diagnosis of acute gastroenteritis. Clinical assessment and potential application from a multicentre Italian study.

Objective: Gastroenteritis caused by a single pathogen or multiple pathogens remains a major diagnostic challenge for the laboratory. The treatment of diarrhoea is based on microbiological results. Diagnosis is achieved using different laboratory techniques that have variable sensitivity and specificity. xTAG GPP is a new multiplex PCR assay that simultaneously detects 15 different pathogens responsible for diarrhoea. The results of the first multicentre study in Italy to evaluate the potential clinical application of the GPP assay in the laboratory diagnosis of diarrhoea are reported here. Methods: Faeces specimens (N = 664) from hospitalized patients were tested with the GPP assay using a Luminex 200 instrument. All specimens were run using comparator methods following a routine algorithm: culture for bacteria, enzyme immunoassay and PCR for viruses, and microscopy for parasites. Results: Of the samples tested with the GPP, 53.61% (356/664) gave positive results, as compared to 45.33% by routine testing. Of the positive specimens, 34.55% showed the presence of genomic DNA from multiple pathogens. The Luminex method showed an increase in the percentage of positivity of 8.28%. Conclusions: The GPP assay can be considered a helpful tool for the detection of gastrointestinal pathogens, with a hands-on time of 5 h; it provides accurate data for the clinical management of hospitalized patients and for epidemiological surveillance

Early psychological care of the French victims of the Costa Concordia shipwreck

Most of the French passengers who survived the shipwreck of the cruise ship Costa Concordia were repatriatedfrom Italy to Marseille, one of the stopovers of the cruise. The shipwreck happened during the nightof 13th–14th January 2012 and entailed the forced evacuation of 4195 passengers and crewmembers.Thirty-two persons died and 2 others are still reported missing. The massive and unexpected inflow of402 French citizens in the port of Marseille required the quick setting up of welcome facilities, not only tosolve logistical problems, but also to address psychological and sometimes even medical problems. ThePrehospital Psychological Emergency Service (CUMP) and the Prehospital Emergency Medical Service(SAMU) of Marseille examined 196 persons in total, and were able to avoid a great number of emergencyadmissions deemed necessary because of difficult psychological situations (death, missing or lost persons,acute stress). The objective of this report is to rapidly present the emergency committee as a whole andto describe in more detail the work that the CUMP accomplished during the 36 hours necessary to takecharge of the majority of the French passengers of the Costa Concordia.Most of the French passengers who survived the shipwreck of the cruise ship Costa Concordia were repatriatedfrom Italy to Marseille, one of the stopovers of the cruise. The shipwreck happened during the nightof 13th–14th January 2012 and entailed the forced evacuation of 4195 passengers and crewmembers.Thirty-two persons died and 2 others are still reported missing. The massive and unexpected inflow of402 French citizens in the port of Marseille required the quick setting up of welcome facilities, not only tosolve logistical problems, but also to address psychological and sometimes even medical problems. ThePrehospital Psychological Emergency Service (CUMP) and the Prehospital Emergency Medical Service(SAMU) of Marseille examined 196 persons in total, and were able to avoid a great number of emergencyadmissions deemed necessary because of difficult psychological situations (death, missing or lost persons,acute stress). The objective of this report is to rapidly present the emergency committee as a whole andto describe in more detail the work that the CUMP accomplished during the 36 hours necessary to takecharge of the majority of the French passengers of the Costa Concordia

Numerical Modeling of a Granular Collapse Immersed in a Viscous Fluid

The three-dimensional unsteady collapse of the granular column in a viscous fluid has been investigated with an IBM/DEM approach. Present numerical simulations allow one to confirm quantitatively several experimental observations of Rondon et al. regarding morphology, characteristic sizes of granular deposits and the basal pressure below the column. In the presented simulations, the collapse dynamics is controlled by the viscous time Tv. To our knowledge, a numerical approach, e.g. the IBM/DEM method, is able for the first time to capture the pore pressure feedback phenomenon in flowing fluid-grains mixture. The effect of the initial packing fraction has a great influence of the dynamics of granular collapse in the simulation results as in the experiments of Rondon et al. Furthermore, the IBM/DEM permits to investigate the inner state of the granular column during the collapse, in particular, the evolution of the pressure field inside the granular column can be analyzed which is difficult to do in experiments. Simulations of the collapse of a granular column immersed in a fluid can be performed in the inertial and free-fall regimes as well varying the nature of the fluid and/or the particles

Investigation of the structure of debris beds formed from fuel rods fragmentation

International audienceThis paper is a study of debris beds that can form in the core of a nuclear power plant under severe accident conditions. Such beds are formed of fragments of pellets and cladding remnants, as observed in the TMI-2 core. Many important issues are related with the morphology of those debris beds are they coolable in case of water injection and how does molten corium progress through them if they are not coolable? The answers to those questions depend on the structure of the debris bed porosity, number and arrangement of particles. In order to obtain relevant information, a numerical simulation of the formation of the debris bed is proposed. It relies on a granular approach of the type called “Contact Dynamics” to simulate the collapse of debris and their accumulation. Two different schemes of fuel pellet fragmentation are considered and simulations for different degrees of fragmentation of the pellets are performed. The results show that the number of axial cracks on fuel pellets strongly influences the final porosity of the debris bed. Porosities vary between 31% (less coolable cases) and 45% (similar to TMI-2 observations), with a most probable configuration around 41%. The specific surface of the bed is also evaluated. In the last part, a simple model is used to estimate the impact of the variation in geometry of the numeric debris beds on their flow properties. We show that the permeability and passability can vary respectively with a range of 30% and 15% depending on the number of fragment per pellet. The other benefits of the approach are finally discussed. Among them, the possibility to print 3D samples from the calculated images of debris beds appears as a promising perspective to perform experiments with realistic debris beds. © 2016 Elsevier B.V

Granular slumping in a fluid : focus on runout distances

We investigate the effect of an ambient fluid on the dynamics of collapse and spread of a granular column simulated by means of a recently developed model which takes into account both fluid forces that act on each grain and contacts between grains. The model couples the contact dynamics method for discrete element modeling of the grains and their interactions with the finite element method for the integration of Navier-Stokes equations in 2D. The coupling is based on the fictitious domain approach in which the fluid domain is extended to that of grains, and the rigid-body motion of the grains is imposed by means of distributed Lagrange multipliers. As in similar numerical and experimental works with dry grains, we focus here on the run-out distances and avalanche durations for different column aspect ratios (height vs width). We consider three options for the surrounding fluid: 1) no fluid, 2) water and 3) a viscous fluid that allows us to perform our simulations in the grain-inertial, fluid-inertial and viscous regimes, respectively. The run-out distance is found to increase as a power law with the aspect ratio of the column, and surprisingly, for a given aspect ratio and packing fraction, it may be similar in the grain-inertial regime and fluid inertial regimes but with considerably longer duration in the latter case. We show that the effect of the fluid in viscous and fluid-inertial regimes is both to reduce the kinetic energy during the collapse and enhance the flow by lubrication during the spread. Hence, the run-out distance in a fluid may be below or equal to that in the absence of fluid due to compensation between those effects