Comparison of multiphase SPH and LBM approaches for the simulation of intermittent flows

Smoothed Particle Hydrodynamics (SPH) and Lattice Boltzmann Method (LBM) are increasingly popular and attractive methods that propose efficient multiphase formulations, each one with its own strengths and weaknesses. In this context, when it comes to study a given multi-fluid problem, it is helpful to rely on a quantitative comparison to decide which approach should be used and in which context. In particular, the simulation of intermittent two-phase flows in pipes such as slug flows is a complex problem involving moving and intersecting interfaces for which both SPH and LBM could be considered. It is a problem of interest in petroleum applications since the formation of slug flows that can occur in submarine pipelines connecting the wells to the production facility can cause undesired behaviors with hazardous consequences. In this work, we compare SPH and LBM multiphase formulations where surface tension effects are modeled respectively using the continuum surface force and the color gradient approaches on a collection of standard test cases, and on the simulation of intermittent flows in 2D. This paper aims to highlight the contributions and limitations of SPH and LBM when applied to these problems. First, we compare our implementations on static bubble problems with different density and viscosity ratios. Then, we focus on gravity driven simulations of slug flows in pipes for several Reynolds numbers. Finally, we conclude with simulations of slug flows with inlet/outlet boundary conditions. According to the results presented in this study, we confirm that the SPH approach is more robust and versatile whereas the LBM formulation is more accurate and faster

LEPISME

We present a first version of a software dedicated to an application of a classical nonlinear control theory problem to the study of compartmental models in biology. The software is being developed over a new free computer algebra library dedicated to differential and algebraic elimination

Models of stochastic gene expression and Weyl algebra

International audienceThis paper presents a symbolic algorithm for computing the ODE systems which describe the evolution of the moments associated to a chemical reaction system, considered from a stochastic point of view. The algorithm, which is formulated in the Weyl algebra, seems more efficient than the corresponding method, based on partial derivatives. In particular, an efficient method for handling conservation laws is presented. The output of the algorithm can be used for a further investigation of the system behaviour, by numerical methods. Relevant examples are carried out

Degassing cascades in a shear-thinning viscoelastic fluid

International audienceWe report the experimental study of the degassing dynamics through a thin layer of shear-thinning viscoelastic fluid when a constant air flow is imposed at its bottom. The fluid is an aqueous solution of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal). Over a large range of parameters, the air is periodically released through a series of successive bubbles, hereafter named cascades. Each cascade is followed by a continuous degassing, lasting for several seconds, corresponding to an open channel crossing the fluid layer. The periodicity between two cascades does not depend on the injected flow rate. Inside one cascade, the properties of the overpressure signal associated with the successive bubbles vary continuously. The pressure threshold above which the fluid starts flowing, fluid deformation and pressure drop due to degassing through the thin fluid layer can be simply described by a Maxwell model

A Spitzer Search for Water in the Transiting Exoplanet HD189733b

We present Spitzer Space Telescope observations of the extrasolar planet HD189733b primary transit, obtained simultaneously at 3.6 and 5.8 microns with the Infrared Array Camera. The system parameters, including planetary radius, stellar radius, and impact parameter are derived from fits to the transit light curves at both wavelengths. We measure two consistent planet-to-star radius ratios, (Rp/Rs)[3.6$\mu$m] = 0.1560 +/- 0.0008(stat) +/- 0.0002(syst) and (Rp/Rs)[5.8$\mu$m] = 0.1541 +/- 0.0009(stat) +/- 0.0009(syst), which include both the random and systematic errors in the transit baseline. Although planet radii are determined at 1%-accuracy, if all uncertainties are taken into account the resulting error bars are still too large to allow for the detection of atmospheric constituants like water vapour. This illustrates the need to observe multiple transits with the longest possible out-of-transit baseline, in order to achieve the precision required by transmission spectroscopy of giant extrasolar planets.Comment: Accepted in The Astrophysical Journal Letter

A Spitzer Search for Water in the Transiting Exoplanet HD189733b

We present Spitzer Space Telescope observations of the extrasolar planet HD189733b primary transit, obtained simultaneously at 3.6 and 5.8 microns with the Infrared Array Camera. The system parameters, including planetary radius, stellar radius, and impact parameter are derived from fits to the transit light curves at both wavelengths. We measure two consistent planet-to-star radius ratios, (Rp/Rs)[3.6$\mu$m] = 0.1560 +/- 0.0008(stat) +/- 0.0002(syst) and (Rp/Rs)[5.8$\mu$m] = 0.1541 +/- 0.0009(stat) +/- 0.0009(syst), which include both the random and systematic errors in the transit baseline. Although planet radii are determined at 1%-accuracy, if all uncertainties are taken into account the resulting error bars are still too large to allow for the detection of atmospheric constituants like water vapour. This illustrates the need to observe multiple transits with the longest possible out-of-transit baseline, in order to achieve the precision required by transmission spectroscopy of giant extrasolar planets.Comment: Accepted in The Astrophysical Journal Letter

Microfracturing and microporosity in shales

Shales are ubiquitous rocks in sedimentary basins, where their low permeability makes them efficient seals for conventional oil and gas reservoirs and underground waste storage repositories (waste waters, CO2, nuclear fuels). Moreover, when they contain organic matter, they form source rocks for hydrocarbons that may escape towards a more porous reservoir during burial, a process referred to as primary migration. And when the hydrocarbons cannot escape, these rocks can be exploited as oil or shale gas reservoirs. While the presence of fractures at the outcrop scale has been described, the existence of fractures at smaller scales, their link with microporosity, the mechanisms that created them, their persistence over geological times, and their effect on the petrophysical properties of shales represent scientific challenges for which drillings in various sedimentary basins over the past decades may hold timely key data. Here, we review and synthetize the current knowledge on how microfractures and micropores in shales can be imaged and characterized and how they control their anisotropic mechanical properties and permeability. One question is whether such microfractures, when observed in outcrops or in drilled core samples extracted from boreholes, are related to decompaction and do not exist at depth. Another question is whether veins observed in shales represent microfractures that were open long enough to have acted as flow paths across the formation. The mechanisms of microfracture development are described. Some have an internal origin (fracturing by maturation of organic matter, dehydration of clays) while others are caused by external factors (tectonic loading). Importantly, the amount of microfracturing in shales is shown to depend strongly on the content in 1) organic matter, and 2) strong minerals. The nucleation of microfractures depends on the existence of mechanical heterogeneities down to the nanometer scale. Their propagation and linkage to create a percolating network will depend on the presence of heterogeneities at the meso- to macro-scales. Such percolating microfracture networks could control both the long-term sealing capabilities of cap rocks and the further propagation of hydraulic fracturing cracks. Finally, possible areas of research for describing the mechanism of microfracture formation in greater detail and how this impacts the transport and mechanical properties of shales are also discussed

Density-Dependent Prevalence of Francisella tularensis in Fluctuating Vole Populations, Northwestern Spain

Self Archiving; https://wwwnc.cdc.gov/eid/page/copyright-and-disclaimers J.J.L.L., F.M., and R.R.P. held official licenses for trapping wildlife in Spain. Capture permits were provided by the Dirección General del Medio Natural, Junta de Castilla y León. This study was supported by projects ECOVOLE (grant CGL2012-35348), ECOTULA (grant CGL2015-66962-C2-1-R), and RESERTULA (grant CLG2015-66962-C2-2-R), which were funded by the Ministerio de Economía y Competitividad MINECO/FEDER, Spain. R.R.P. was supported by a PhD studentship from the University of Valladolid (co-funded by Banco Santander).Peer reviewedPublisher PD

Heat storage efficiency, ground surface uplift and thermo-hydro-mechanical phenomena for high-temperature aquifer thermal energy storage

High-temperature aquifer thermal energy storage (HT-ATES) systems can help in balancing energy demand and supply for better use of infrastructures and resources. The aim of these systems is to store high amounts of heat to be reused later. HT-ATES requires addressing problems such as variations of the properties of the aquifer, thermal losses and the uplift of the surface. Coupled thermo-hydro-mechanical (THM) modelling is a good tool to analyse the viability and cost effectiveness of HT-ATES systems and to understand the interaction of processes, such as heat flux, groundwater flow and ground deformation. The main problem of this modelling is its high computational cost. We propose a dimensional and numerical analysis of the thermo-hydro-mechanical behaviour of a pilot HT-ATES. The results of this study have provided information about the dominant thermo-hydraulic fluxes, evolution of the energy efficiency of the system and the role of the hydraulic and thermal loads generated by the injection and extraction of hot water.We acknowledge the financial support received from the ERANET project HEATSTORE (170153–4401). This project has been subsidized through the ERANET cofund GEOTHERMICA (Project n. 731117), from the European Commission, RVO (the Netherlands), DETEC (Switzerland), FZJ-PTJ (Germany), ADEME (France), EUDP (Denmark), Rannis (Iceland), VEA (Belgium), FRCT (Portugal), and MINECO (Spain). We wish to thank the Department of Research and Universities of the Generalitat de Catalunya by supporting RV with a grant (2021 FI_B 00940).Peer ReviewedPostprint (published version