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International audience; A numerical method for longitudinal wave propagation in nonlinear elastic solids is presented. Here, we consider polynomial stress-strain relationships, which are widely used in nondestructive evaluation. The large-strain and infinitesimal-strain constitutive laws deduced from Murnaghan's law are detailed , and polynomial expressions are obtained. The Lagrangian equations of motion yield a hyperbolic system of conservation laws. The latter is solved numerically using a finite-volume method with flux limiters based on Roe linearization. The method is tested on the Riemann problem, which yields nonsmooth solutions. The method is then applied to a continuum model with one scalar internal variable, accounting for the softening of the material (slow dynamics).

International audience; Finer strategies of spacecraft fire mitigation require more experimental data related to fire detection. Fire detection systems developed on Earth rely massively on the optical detection of soot particles, which are present in the smoke. To detect the fire correctly, it is thus important to know how the optical properties of these particles are affected in reduced gravity. With different transport processes and increased residence time, soot in reduced gravity can be different from those produced at normal gravity. As their optical properties are related to their morphological properties, a better understanding about the evolution of soot particle morphology in flames under microgravity conditions is required. Within this context, a novel technique of soot sampling using electric field is applied to a spreading non-premixed flame at normal and micro-gravity. The soot particles sampled are observed subsequently under Transmission Electron Microscopy (TEM). Density, soot particle projected area, radius of gyration, fractal dimension, and primary particle size are extracted and the influence of gravity is investigated with the evolution of these morphological properties within the flame. Though the present study cannot be conclusive in itself, the similarity between the evolution of the optical density measured throughout the flame just before the electric perturbation required by the sampling technique and the evolution of the amount of soot deposited due to the electric perturbation along the sampling plates supports the future works that need to be devoted to further assess the consistency of the technique.

International audience; Flame spread over an insulated electrical wire is a major source of fire scenario in a space vehicle. In this work, an engineering model that predicts the creeping flame spread over cylindrical wires in microgravity is developed. The model is applied to interpret experimental data obtained in parabolic flights for wires composed by a 0.25 mm radius nickel-chromium (NiCr) metallic core coated by low-density polyethylene (LDPE) of different thicknesses ranging from 0.15 mm to 0.4 mm. The model relies on the assumption that, in the pyrolysis region, the NiCr and the LDPE are in thermal equilibrium. This assumption is supported by more detailed numerical simulations and the model reduces then to solving the heat transfer equations for both NiCr and LDPE in the pyrolysis region and in the region ahead of the flame front along with a simple degradation model for LDPE, an Oseen approximation of opposed oxidizer flow and an infinitely fast gas-phase chemistry. The flame spread rate (FSR) is controlled by two model parameters, which are measurable from intrinsic material and ambient gas properties: the convective flame heat flux transferred to the solid ahead from the flame front and the gaseous thermal heat length near the flame front. These parameters are then calibrated from experimental data for a given wire geometry and the calibrated model is validated against experimental data for other wire geometries and ambient conditions. The heat transfer mechanisms ahead of the pyrolysis front are investigated with a special emphasis on the LDPE thickness and the conductivity of the metallic core. In addition to NiCr, metallic cores of lower and higher conductivities are considered. The polymer is shown to be thermally thick for all tested wire geometries and core conductivities. The flame heat flux is found to dominate the heat transfer in the preheat zone where it applies. The core has nevertheless a significant impact in the heating of the LDPE with its contribution increasing with the core conductivity and when decreasing the LDPE thickness.

International audience; This work is about experimental study of a planar shock wave which slide over a water surface. The aim is to observe the air-water interface and the droplet entrainment which is associated. Experiments are performed at atmospheric pressure in a 200×200-mm²-square-cross-section shock tube for depths of 10, 20 and 30 mm and two incident planar shock waves having Mach number of 1.11 and 1.43. We recorded the pressure histories and high-speed visualization to study the flow patterns, surface waves and spray layers behind the shock wave. We observed two different flow patterns with ripples formed at the air-water interface for the weaker shock wave and the dispersion of a droplet mist for the stronger shock wave. We analyzed pressure signals both in the air and in the water at the same location. From these pressure signals we extracted the delay time between the arrival of the compression wave into the water and the shock wave in air at the same location. We show that the delay time evolves with the distance traveled over the water layer, the depth of the water layer and the Mach number of the incident shock wave.

International audience; Cable-in-Conduit Conductors (CICC) are made of several hundreds of superconducting and copper strands twisted together and gathered into multiple stages. To ensure safe and reliable operation of tokamaks, it is essential to take into account AC losses occurring in such conductors. Recently developed at CEA, the fully analytical model named COLISEUM (COupling Losses analytIcal Stages cablEs Unified Model) aims at predicting the coupling losses at various cable scales using only geometrical and electrical parameters. The most recent version of the COLISEUM model addresses the coupling losses for a full CICC, accounting contributions from the strand to the last stage of the cable. In this paper, we investigate the COLISEUM model in non-tangential conditions. On the other hand, we present a methodology to derive geometrical model inputs from tomographicimages.

International audience; Tokamaks coils are wound with long lengths of cables including hundreds of superconducting and copper strands twisted together into multiple stages. They refer to Cable In Conduit Conductors (CICC). Coupling losses induced by magnetic field variations dissipate power in the coils during machine operation. For several years, the CEA has been developing the analytical model COLISEUM (COupling Losses analytIcal Staged cablEs Unified Model) aiming at predicting coupling losses at various conductor scales. Geometrical (cabling radii, twist pitches) and electrical (inter-strand and inter-bundle conductances) parameters of each stage constitute the model inputs. In this article, we first present the raw 3D tomographic image treatment method that will serve to generate COLISEUM inputs with high level of reliability. We then define and extract several relevant effective geometric cable parameters from images data. These inputs are used along with the COLISEUM model to improve coupling losses prediction. A systematic study of six JT-60SA TF type samples has been realized and a geometric parameters database is constructed. The COLISEUM model is used in a 2-stage configuration with the two highest stages of the cable. First results are presented and discussed.

International audience; The separation efficiency and pressure drop of the dynamic separator of cement particles can be affected by many factors, like structural type, geometric parameters, and operating characteristics. In this paper, CFD modeling is applied to investigate the fluid flow behavior and the efficiency of the industrial dynamic separator with different heights of the inner cone called the vortex breaker. Simulations are based on the RSM and the DPM models. A CFD comparison of the original design and new designs has been performed. The simulation results showed that the fluid flow inside the industrial air separator is greatly dependent on the height of the vortex breaker. Interesting phenomena were observed by the numerical simulations and the results revealed that an increase in the height of the vortex breaker up to three-quarters of the magnitude of the fine powder outlet duct can improve the performances of particle separation not only by reducing 29% the cut size, and by 40% the bypassing of fine particles but also by increasing 30% the separation sharpness while keeping the pressure drop substantially unchanged.

International audience; In fusion facilities, the in-vessel wall receives high heat flux density up to 20 MW/m 2. The monitoring of in-vessel components is usually ensured by infra-red (IR) thermography but with all-metallic walls, disturbance phenomenon as reflections may lead to inaccurate temperature estimates, potentially endangering machine safety. A full predictive photonic simulation is then used to assess accurately the IR measurements. This paper investigates some reduced thermal models (semi-infinite wall, thermal quadrupole) to predict the surface temperature from the particle loads on components for a given plasma scenario. The results are compared with a reference 3D Finite Element Method (Ansys Mechanical) and used as input for simulating IR images. The performances of reduced thermal models are analysed by comparing the resulting IR images.

International audience; In this work, a method to estimate unsteady 2D heat sources is developed. The sources are estimated from Infra-Red (IR) temperature mapping on the front face of thermally thin material. A comparison of the estimation accuracy as well as the evaluation of time cost is also carried out between a direct method (coupled with filtering techniques) and an iterative method (of conjugate gradient type). The present work was realised on experimental data.

International audience; The present paper deals with the surface heat flux estimation with embedded thermocouples (TC) in a Plasma Facing Component (PFC) of the WEST Tokamak. A 2D nonlinear unsteady calculation combined with the Conjugate Gradient Method (CGM) and the adjoint state is achieved in order to estimate the time evolution of the heat flux amplitude and decay length lambda_q. The method is applied on different synthetic measurements in order to evaluate the accuracy of the method. The synthetic measurements are generated with realistic values of lambda_q and magnitudes as those expected for ITER.

International audience; An experimental study is carried out to investigate the different stages of the evaporation phenomenon of a methanol drop that exhibits a complex behavior because of its high volatility. An optical technique is employed with top and side view cameras; it allows to follow the drop shape evolution and determine the geometric parameters: contact angle and base diameter from which the volume of the droplet is computed. The outcomes of this study show three distinct stages. First, the evaporation kinetics is very fast (33% of the droplet lifetime) where 85% of the volume evaporates with a nearly pinned contact line. It is followed by a short stage (12% of lifetime) where 8% of the volume evaporates. In this stage, the drop forms a thin liquid film followed by a motion of the contact line in which the drop retracts. The wetting surface deforms and loses its quasi-circular shape. Then, the wetting area shrinks drastically to form a smaller droplet with a higher contact angle. In the third stage (55% of lifetime), the 7% remaining drop volume evaporates with a low evaporation rate accompanied by a strong decrease of contact angle and a slight decline of wetting area until total evaporation.

THe WEST Team: http://west.cea.fr/WESTteam; International audience; Plasma facing components temperature measurement is required to ensure safe high power for long pulse tokamak operation and for physics studies. During the WEST phase 1, a set of 20 thermocouples (TC) and 4 fibers Bragg grating (FBG) have been exposed to five experimental campaigns with 3889 plasmas for a total plasma duration of about 7h15 and 21.2 GJ of cumulated injected energy. This paper presents the performances in terms of response time and high temperature sustaining assess with high heat flux tests performed in the HADES facility. The response time of the TC remains at the same level as before their installation in the divertor. However, the FBG have shown clear increase of their response time depending on the location due to a degradation of the thermal contact of the graphite adhesive and the FBG or component. Finally, one regenerated FBG has been exposed to high temperature, showing that absolute temperature measurement is found reliable up to 1100 °C with the start of some spectrum degradations. Full erasure of the grating is obtained after 10 s at 1200 °C well above the stable temperature of 900 °C of the regenerated FBG.

International audience; The main objective of WEST is to study the behavior of the ITER-like divertor monobloc components, test their resistance and ageing under ITER relevant heat loads.For the upcoming phase 2 of WEST, the lower divertor is now fully equipped with the ITER-like actively cooled bulk tungsten Plasma Facing Units (PFU), designed to withstand 10MW/m2 in steady state. This divertor is also equipped with an enlarged set of ThermoCouples (TCs x 16) and Fiber Bragg Gratings (FBGs) probes (x5) with 14 measurement spots each to evaluate the heat loading during the experiments. This paper presents the new TC and FBG diagnostics as well as the associated inverse method used to estimate the surface heat flux from the embedded temperature measurements in the divertor. The performance of each diagnostic will be evaluated with synthetic measurements generated with realistic heat flux intensity and distribution. The results of a parametrical analysis shows that each diagnostic is able to estimate the spatial distribution of the expected heat fluxes in WEST

International audience; This paper explores the relationship between optimal control and Cosserat beam theory from the perspective of solving the forward and inverse dynamics (and statics as a subcase) of continuous manipulators and snake-like bio-inspired locomotors. By invoking the principle of minimum potential energy, and the Gauss principle of least constraint, it is shown that the quasi-static and dynamic evolution of these robots, are solutions of optimal control problems (OCPs) in the space variable, which can be solved at each step (of loading or time) of a simulation with the shooting method. In addition to offering an alternative viewpoint on several simulation approaches proposed in the recent past, the optimal control viewpoint \fred{allows us to improve some of them while providing a better understanding of their numerical properties}. The approach and its properties are illustrated through a set of numerical examples validated against a reference simulator.

Understanding the structural parameters of crystals during crystal growth is essential for the pharmaceutical and chemical industries. This study proposes a new method for 3D images of crystals obtained with micro X-ray computed tomography. This method aims to improve the crystal segmentation compared to the watershed methods. It is based on plane recognition at the surface of the crystals. The obtained segmentation is evaluated on a synthetic image and by considering the recognized particle number and convexity. The algorithm applied to three samples (potassium alum, chromium alum, and copper sulfate) reduced oversegmentation by 87% compared to watershed based on ultimate erosion while keeping the convexity of the recognized particle.

International audience; This study presents an experimental and numerical investigation into the efficiency of a two-stage heat recovery–storage system for reducing the thermal energy losses in the industry. The system is designed to recover and store waste thermal energy from residual fluids using heat pipes for recovery and an environmentally friendly phase change material for heat storage. Experimental investigation was conducted using water as the primary agent and varying the temperature between 60 °C, 65 °C, and 70 °C at a constant flow rate of 24 L/min. The secondary agent, also water, was used at an initial temperature of 10 °C and the flow rate was varied between 1 L/min, 2 L/min, and 3 L/min. The results show that the system had a peak efficiency of 78.1% and was able to recover a significant amount of thermal energy. This study demonstrates the potential of this system to reduce the thermal energy losses in the industry and highlight the importance of further research and development in this field, as the industry is responsible for approximately 14% of the total thermal energy losses and finding efficient ways to recover and store waste thermal energy is crucial to achieving sustainable energy consumption.

11th Region Workshop of the European-Microbeam-Analysis-Society (EMAS), Leoben, AUSTRIA, SEP 21-24, 2014; International audience; This work presents a series of three-dimensional computational methods with the objective of analyzing and quantifying some important structural characteristics in a collection of low-density polyolefin-based foams. First, the solid phase tortuosity, local thickness, and surface curvature, have been determined over the solid phase of the foam. These parameters were used to quantify the presence of wrinkles located at the cell walls of the foams under study. In addition, a novel segmentation technique has been applied to the continuous solid phase. This novel method allows performing a separate analysis of the constituting elements of this phase, that is, cell struts and cell walls. The methodology is based on a solid classification algorithm and evaluates the local topological dissimilarities existing between these elements. Thanks to this method it was possible to perform a separate analysis of curvature, local thickness, and corrugation ratio in the solid constituents that reveals additional differences that were not detected in the first analysis of the continuous structure. The methods developed in this work are applicable to other types of porous materials in fields such as geoscience or biomedicine.

28th Symposium on Fusion Technology (SOFT), San Sebastian, SPAIN, SEP 29-OCT 03, 2014; International audience; The assembly of W block with a CuCrZr block has been produced by adding compliant W-Cu layers. Firstly, three W-Cu powders (W80Cu20, W60Cu40 and W40Cu60) were sintered by spark plasma sintering (SPS) to investigate the influences of sintering temperature and pressure on relative density and microstructure. The experimental results indicated that the relative density increases with temperature and Cu concentration, achieving a value of 94.1% for the W40Cu60 sample sintered at 1000 degrees C and a value of 83.1% for the W80Cu20 sample sintered at the same temperature. Then, a three-layer W-Cu assembly between a W block and a CuCrZr block was fabricated using similar sintering conditions to the W-Cu powders. The sintering temperature was limited at 1000 degrees C due to the CuCrZr melting temperature (1083 degrees C). The experimental results indicated that loading time, when the right sintering temperature and pressure are applied, is the most important parameter. (C) 2015 Elsevier B.V. All rights reserved.

We consider the rotation of small neutrally buoyant axisymmetric particles in a viscous steady shear flow. When inertial effects are negligible the problem exhibits infinitely many periodic solutions, the "Jeffery orbits". We compute how inertial effects lift their degeneracy by perturbatively solving the coupled particle-flow equations. We obtain an equation of motion valid at small shear Reynolds numbers, for spheroidal particles with arbitrary aspect ratios. We analyse how the linear stability of the \lq log-rolling\rq{} orbit depends on particle shape and find it to be unstable for prolate spheroids. This resolves a puzzle in the interpretation of direct numerical simulations of the problem. In general both unsteady and non-linear terms in the Navier-Stokes equations are important., Comment: 5 pages, 2 figures

International audience; The rheology of dense colloidal suspensions, which may undergo discontinuous shear thickening or shear jamming, is particularly difficult to analyze with conventional rheometers. Here, we develop a rheometer adapted to colloidal suspensions: the "capillarytron," which uses the air-suspension capillary interface to impose particle (or osmotic) pressure during shear. The main virtues of this new device are that (i) it gives direct access to the suspension friction coefficient, (ii) it operates for very dense suspensions up to jamming, and, most importantly, (iii) it decouples the stresses developed within the suspension from the applied shear rate. We can, thus, smoothly move through the different frictional states of the system, precisely in the range of volume fractions where discontinuous shear thickening or shear jamming occur under volume-imposed conditions. Our results obtained with the capillarytron provide the first complete characterization of the dual frictional behavior of a model shear-thickening suspension, in agreement with the recently proposed frictional transition scenario. Based on a new concept in rheometry, the capillarytron unlocks the path to pressure-imposed rheology on colloidal and Brownian suspensions. Moreover, its fine control of the particle pressure via the soft capillary interface opens the possibility to explore the flow of "fragile" particles close to jamming, such as Brownian colloids, active particles, and living cells.

In this paper, numerical simulations have been performed to study the performance of a single fully activated flapping wing serving as energy harvester. The aims of the paper are predicting and maximizing the energy extraction efficiency by using optimization methodology. The metamodeling and the genetic algorithms are applied in order to find the optimal configuration improving the efficiency. A response surface method (RSM) based on Box–Behnken experimental design and genetic algorithm has been chosen to solve this problem. Three optimization factors have been manipulated, i.e. the dimensionless heaving amplitude h0, the pitching amplitude θ0 and the flapping frequency f. The ANSYS FLUENT 14 commercial software has been used to compute the governing flow equations at a Reynolds number of 1100, while the flapping movement combined from heaving and pitching of the NACA0015 foil has been carried out by using an in house user-defined function (UDF). A maximum predicted efficiency of 34.02% has been obtained with high accuracy of optimal kinematic factors of dimensionless heaving amplitude around the chord, high pitching amplitude and low flapping frequency of 0.304 hertz. Results have also showed that the interaction effect between optimization factors is important and the quadratic effect of the frequency is strong confirming the great potential of the applied optimization methodology.

We compute the full set of second-order inertial corrections to the instantaneous force and torque acting on a small spherical rigid particle moving unsteadily in a general steady linear flow. This is achieved by using matched asymptotic expansions and formulating the problem in a coordinate system co-moving with the background flow. Effects of the fluid-velocity gradients are assumed to be small, but to dominate over those of the velocity difference between the body and fluid, which makes the results essentially relevant to nearly neutrally buoyant particles. The outer solution (which at first order is responsible for the Basset-Boussinesq history force at short time and for shear-induced forces such as the Saffman lift force at long time) is expressed via a flow-dependent tensorial kernel. The second-order inner solution brings a number of different contributions to the force and torque. Some are proportional to the relative translational or angular acceleration between the particle and fluid, while others take the form of products of the rotation/strain rate of the background flow and the relative translational or angular velocity between the particle and fluid. Adding the outer and inner contributions, the known added-mass force or the spin-induced lift force are recovered, and new effects involving the rotation/strain rate of the background flow are revealed. The resulting force and torque equations provide a rational extension of the classical Basset-Boussinesq-Oseen equation incorporating all first- and second-order fluid inertia effects resulting from both unsteadiness and velocity gradients of the carrying flow., 39 pages, 3 figures

We propose in this paper a numerical strategy in order to compute a turbulence model for compressible flows, including a dynamical estimation of the jump of the turbulent kinetic energy across shock waves. The model is taken from [11], and the Finite Volume scheme applies for a specific interface Riemann solver. The whole procedure requires the detection of shock waves in unsteady flows.

International audience; With an increasing interest in hydrogen as an alternative fuel for transportation, there is a need to develop tools for the prediction of ignition events. A cost-effective passive scalar formulation has been recently developed to predict hydrogen auto-ignition. A single scalar advection-diffusion-reaction equation is used to reproduce the chain-branched ignition process, where the scalar represents the radical pool responsible of ignition (H, O, OH, HO2 , H2O2). The scalar reaction rate is analytically deduced from the Jacobian matrix associated to hydrogen ignition chemistry. This method was found to reproduce with good accuracy the ignition delays obtained by detailed chemistry for temperature where the branching is the leading process. For temperature close or below the crossover temperature, where other phenomenon such as the thermal runaway are important, the scalar approach fails to predict correctly ignition events. Thus, an extension of the scalar source term formulation is proposed to extend its validity over the entire temperature range. In addition, a simple way to approximate the diffusion properties of the scalar is introduced: the radical pool composition may vary drastically, with molecules having very different diffusion properties (e.g. H and HO2). The complete modified framework is presented and its capability is assessed in canonical scenarios and more complex simulations relevant to hydrogen safety.

International audience

Although multiple structural, mechanical, and molecular factors are definitely involved in osteoporosis, the assessment of subregional bone mineral density remains the most commonly used diagnostic index. In this study, we characterized bone quality in the femoral neck of one osteoporotic patients as compared to an age-matched control subject, and so used a multiscale and multimodal approach including X-ray computed microtomography at different spatial resolutions (pixel size: 51.0, 4.95 and 0.9 µm), microindentation and Fourier transform infrared spectroscopy. Our results showed abnormalities in the osteocytes lacunae volume (358.08 ± 165.00 for the osteoporotic sample vs. 287.10 ± 160.00 for the control), whereas a statistical difference was found neither for shape nor for density. The osteoporotic femoral head and great trochanter reported reduced elastic modulus (Es) and hardness (H) compared to the control reference (−48% (p < 0.0001) and −34% (p < 0.0001), respectively for Es and H in the femoral head and −29% (p < 0.01) and −22% (p < 0.05), respectively for Es and H in the great trochanter), whereas the corresponding values in the femoral neck were in the same range. The spectral analysis could distinguish neither subregional differences in the osteoporotic sample nor between the osteoporotic and healthy samples. Although, infrared spectroscopic measurements were comparable among subregions, and so regardless of the bone osteoporotic status, the trabecular mechanical properties were comparable only in the femoral neck. These results illustrate that bone remodeling in osteoporosis is a non-uniform process with different rates in different bone anatomical regions, hence showing the interest of a clear analysis of the bone microarchitecture in the case of patients’ osteoporotic evaluation. Nasl. z nasl. zaslona. Opis vira z dne 5. 1. 2023. Št. članka 8048. Bibliografija: str. 21-24. Abstract.

We experimentally revisite the flow down an inclined plane of dense granular suspensions, with particles of sizes in the micron range, for which thermal fluctuations cannot be ignored. Using confocal microscopy on a miniaturized set-up, we observe that, in contrast with standard granular rheology, the flow profiles strongly depend on the particles size. Also, suspensions composed of small enough particles flow at infinitesimal inclinations. From the velocity measurements, an effective rheology is extracted in terms of a friction coefficient as a fonction of the dimensionless shear rate (the viscous number), and of the particle pressure normalized by the thermal pressure. Inspired by a previous work [1], a phenomenological model based on the sum of a thermal contribution describing the glass transition and an athermal contribution capturing the jamming transition is developed, which reproduces well the experimental observations. The model predicts the existence of a glassy friction angle lower than the granular athermal friction angle, a signature of the glass transition in the framework of a pressure imposed rheology.

We investigate the transient dynamics of a sheared suspension of neutrally buoyant particles under pressure-imposed conditions, subject to a sudden change in shear rate or external pressure. Discrete Element Method simulations show that, depending on the flow parameters (particle and system size, initial volume fraction), the early stress response of the suspension may strongly differ from the prediction of the Suspension Balance Model based on the steady-state rheology. We show that a two-phase model incorporating the Reynolds-like dilatancy law of Pailha & Pouliquen (2009), which prescribes the dilation rate of the suspension over a strain scale $\gamma_0$, quantitatively captures the suspension dilation/compaction over the whole range of parameters investigated. Together with the Darcy flow induced by the pore pressure gradient during dilation or compaction, this Reynolds-like dilatancy implies that the early stress response of the suspension is nonlocal, with a nonlocal length scale $\ell$ which scales with the particle size and diverges algebraically at jamming. In regions affected by $\ell$, the stress level is fixed, not by the steady-state rheology, but by the Darcy fluid pressure gradient resulting from the dilation/compaction rate. Our results extend the validity of the Reynolds-like dilatancy flow rule, initially proposed for jammed suspensions, to flowing suspension below $\phi_\mathrm{c}$, thereby providing a unified framework to describe dilation and shear-induced migration. They pave the way for understanding more complex unsteady flows of dense suspensions, such as impacts, transient avalanches or the impulsive response of shear-thickening suspensions., Comment: 24 pages, 9 figures

The aim of the study is to develop a system for converting, accumulating, and delivering solar energy that is based on the development of an innovative solar panel with heat pipes and a heat storage wall, for the construction of passive structures. The novel aspect of this experiment is the utilization of concrete walls that have different recyclable materials added to their structure in various proportions. The solar energy from the sunny façades is transformed by this system into thermal energy, which is then transferred by integrated heat pipes in a massive element with high thermal inertia. Using insulated shutters, thermal energy can be stored during the day and released at night to keep the room at a comfortable temperature. In order to integrate the modules into the solar recovery system, four concrete samples were cast with a blend of standard and waste aggregates. Four heat fluxes of 100 W/m2, 150 W/m2, 200 W/m2, and 250 W/m2 were applied to each global system. Thermal imaging data and numerical simulations both supported the findings of temperature sensors. The most effective mixture, fly ash and chopped PET, delivered temperatures that were, on average, 3.3% higher at the end of the charging cycle than those measured for the control sample. The discharging cycle of the concrete block with fly ash and sawdust was the most effective, with an average temperature loss of 5.0 °C as compared to 5.5 °C for the control sample, on average.

When using Ion Cyclotron Range of Frequency (ICRF) heating, enhanced heat-fluxes are commonly observed on some plasma facing components close to the antennas. Experiments have recently been carried out on JET with the new ITER-Like-Wall (ILW) to characterize the heat flux to the JET ICRF antennas. Using Infra-Red thermography and thermal models of the tiles, heat-fluxes were evaluated from the surface temperature increase during the RF phase of L-mode plasmas. The maximum observed heat-flux intensity was ~ 4.5 MW/m2 when operating with -{\pi}/2 current drive strap phasing at power level of 2MW per antenna and with a 4 cm distance between the plasma and the outer limiters. Heat-fluxes are reduced when using dipole strap phasing. The fraction of ICRF power deposited on the antenna limiters or septa was in the range 2-10% for dipole phasing and 10-20% with +/-{\pi}/2 phasing., Comment: 22 pages, 6 figures

International audience; Structure and properties of laser beam welding zone of dissimilar materials, AZ31 magnesium alloy and A5754 Aluminum alloy, are investigated. The microstructure and quality of the Mg/Al weld were studied by metallography, microhardness and optical microscopy. Differences in physical and mechanical properties of both materials, magnesium and aluminum, affect weldability and resistance of this combination, and lead to the formation of intermetallic compounds in the welded metal.

International audience; Predicting analytically the coupling losses generated in a cable for fusion magnets is still a significant challenge. Difficulties are related to the complex geometry of the system: several multi-strand stages embedded in one another with different twist pitches length, difficulty to model multiplets of strands, including compaction to the final shape. A two-stage analytical geometry based model (COLISEUM) has previously been developed at CEA. We try to extend it to any n-stage cables We detail here an iterative enhancement method to an n-stage model. We validated it against experimental data and shown that it is robust enough to fit our measured coupling losses. Finally, this upgraded model can be used to assess coupling losses in fusion n-stage cables in a particularly precise way from only geometrical information and analytical tools.

Sessile drop creation in weightlessness is critical for designing scientific instruments for space applications and for manipulating organic or biological liquids, such as whole human blood or DNA drops. It requires perfect control of injection, spreading, and wetting; however, the simple act of creating a drop on a substrate is more complex than it appears. A new macroscopic model is derived to better understand this related behavior. We find that, for a given set of substrate, liquid, and surrounding gas properties, when the ratio of surface free energies to contact line free energy is on the macroscopic scale, the macroscopic contact angle can vary at static equilibrium over a broad volume range. It can increase or decrease against volume depending on the sign of this ratio up to an asymptotic value. Consequently, our model aims to explore configurations that challenge the faithful representativity of the classical Young’s equation and extends the present understanding of wetting.

International audience; In its original formulation by Forest & Sab (Math. Mech. Solids, 2017), stress gradient elastodynamics incorporate two inner-lengths to account for size effects in continuum theory. Here, an extended one-dimensional stress gradient model is developed by means of Lagrangian formalism, incorporating an additional inner-length and a fourth-order space derivative in the wave equation. Dispersive properties are characterised and hyperbolicity and stability are proven. Group velocity remains bounded in both original and extended models, proving causality is satisfied for both contrary to a usually-accepted postulate. By means of two-scale asymptotic homogeniza-tion, the high-order wave equation satisfied by the stress gradient model is shown to stand for an effective description of heterogeneous materials in the low-frequency range. An upscaling method is developed to identify the stress gradient material parameters and bulk forces on the parameters of elastic micro-structures. Application of the micro-macro procedure to periodic multi-laminates demonstrates the accuracy of the stress gradient continuum to account for the dispersive features of wave propagation. Frequency and time-domain simulations illustrate these properties.

International audience; A numerically effective approach was developed for the modeling of spray-drying of colloidal suspensions. This approach was based on the integration of two models. The first is a phenomenological and radially symmetric model accounting for the drying of single-droplets, while the second employs computational fluid dynamics (CFD) simulations to account for the gas flow conditions and atomization in a spray dryer. Experiments were also conducted on single suspension droplets trapped in an acoustic field as well as on droplets in a mini-spray dryer. The predictions of the models were found to be in reasonable agreement with the experimental data, in terms of droplet shrinking and buckling, particle yield, and spatial distribution in the spray dryer mockup.

International audience; In this article we propose a new solution to the forward dynamics of Cosserat beams with in perspective, its application to continuum and soft robotics manipulation and locomotion. In contrast to usual approaches, it is based on the non-linear parametrization of the beam shape by its strain fields and their discretization on a functional basis of strain modes. While remaining geometrically exact, the approach provides a minimal set of ordinary differential equations in the usual Lagrange matrix form that can be solved with standard explicit time-integrators. Inspired from rigid robotics, the calculation of the matrices of the Lagrange model is performed with a continuous inverse Newton-Euler algorithm. The approach is tested on several numerical benches of non-linear structural statics, as well as further examples illustrating its capabilities for dynamics.

International audience; The breakup of liquid threads into droplets is prevalent in engineering and natural settings. While drop formation in these systems has a long-standing history, existing studies typically consider axisymmetric systems. Conversely, the physics at play when multiple threads are involved and the interaction of a thread with a symmetry breaking boundary remain unexplored. Here, we show that the breakup of closely spaced liquid threads sequentially printed in an immiscible bath locks into crystal-like lattices of droplets. We rationalize the hydrodynamics at the origin of this previously unknown phenomenon. We leverage this knowledge to tune the lattice pattern via the control of injection flow rate and nozzle translation speed, thereby overcoming the limitations in structural versatility typically seen in existing fluid manipulations paradigms. We further demonstrate that these drop crystals have the ability to self-correct and propose a simple mechanism to describe the convergence toward a uniform pattern of drops.

A macroscopic model describing nonlinear viscoelastic waves is derived in Eulerian formulation, through the introduction of relaxation tensors. In the limiting case of small deformations, the governing equations recover those of the linear Zener model with memory variables, which is widely used in acoustics. The structure of the relaxation terms ensures that the model is dissipative. The chosen family of specific internal energies ensures also that the model is unconditionally hyperbolic. Numerical examples are proposed to illustrate the properties of viscoelastic waves, in small and large deformations.

International audience; The erosion and transport of particles by an impinging turbulent jet in air is observed in various situations, such as the cleaning of a surface or during the landing of a spacecraft. The presence of interparticle cohesive forces modifies the erosion threshold beyond which grains are transported. The cohesion also influences the resulting formation and shape of the crater. In this paper we characterize the role of the cohesive forces on the erosion of a flat granular bed by an impinging normal turbulent jet in air. We perform experiments using a cohesion-controlled granular material to finely tune the cohesion between particles while keeping the other properties constant. We investigate the effects of the cohesion on the erosion threshold and show that the results can be rationalized by a cohesive Shields number that accounts for the interparticle cohesion force. Despite the complex nature of a turbulent jet, we can provide a scaling law to correlate the jet erosion threshold, based on the outlet velocity at the nozzle, to a local cohesive Shields number. The presence of cohesion between the grains also modifies the shape of the resulting crater, the transport of grains, and the local erosion process.

International audience; As most classical fluidization technologies, Circulating Fluidized Beds (CFB) are widely employed in chemical and physical operations. However, CFB Reactors still have some disadvantages such as the non-uniform solid particles distribution and the backflow of the solid particles near the wall, which deteriorate the system mixing, and lead to low system conversion/heat and mass transfer rate. To improve the CFB performance, we propose in the current work to study the effect of the ring baffle configuration on the fluidization system hydrodynamics using a multifluid Eulerian CFD model, incorporating the Kinetic Theory of Granular Flow. In this approach, two different types of ring baffles, circular and trapezoidal, were considered and the corresponding results were compared. The results revealed that the incorporation of ring baffles improved the system mixing and reduced the backflow near the wall. Nevertheless, the shape of baffles had a limited impact on the system hydrodynamics.

International audience; The invariance theorems obtained in analytical mechanics and derived from Noether's theorems can be adapted to fluid mechanics. For this purpose, it is useful to give a functional representation of the fluid motion and to interpret the invariance group with respect to time in the quadri-dimensional reference space of Lagrangian variables. A powerful method of calculation uses Lie's derivative, and many invariance theorems and conservation laws can be obtained in fluid mechanics.

International audience; The motivation of this work is to better understand the dynamic behaviour of bistable structures presenting an analogy with regularized Ericksen bars. The archetype of such structures is the bistable tape spring, which exhibits a particular scenario of deployment, from the stable coiled configuration to the straight stable configuration: at each time of the deployment, the geometry of the tape is similar to a two-phase bar with a coiled part and a straight part separated by a transition zone that moves along the tape. One goal of this work is to show that a regularized and bistable Ericksen bar model contains all the properties to reproduce such a dynamic behaviour. The mathematical structure of this model presents a locally non-convex potential with two minima and a dependence of higher order terms. Some similarities exist between this model and the Euler-Korteweg system with a Van der Waals equation. To study numerically the dynamic behaviour of such models, it is necessary to solve a dispersive and conditionally hyperbolic system. For this purpose, the Lagrangian of the regularized bistable Ericksen model is extended and penalized. Variable boundary conditions are deduced from Hamilton's principle and are used to control the evolution of the system. Dispersion analysis allows to determine the numerical parameters of the model. The obtained non-homogeneous hyperbolic system can be solved by standard splitting strategy and finite-volume methods. Numerical simulations illustrate how the parameters of the model influence the width and the propagation speed of the transition zone. The effect of energy dissipation is also examined. Finally, comparisons with an exact kink wave solution indicate that the extended Lagrangian solution reproduces well the dynamics of the original Lagrangian.

ITER will operate with a tungsten divertor, a material featuring surface morphology changes when exposed to helium plasmas, in particular the formation of the so called tungsten fuzz under specific conditions. Investigating interactions between tungsten plasma facing components and helium plasmas in a tokamak environment is therefore a key point to consolidate predictions for the ITER divertor performance and lifetime. To this end, a dedicated helium campaign was performed in the full tungsten WEST tokamak, cumulating ∼2000 s of repetitive L mode discharges. It is shown that conditions for tungsten fuzz formation, as derived from linear devices experiments (incident helium energy E inc > 20 eV, helium fluence >1024 He/m2, surface temperature T surf > 700 °C), were met in the outer strike point (OSP) area of the inertially cooled tungsten divertor elements of WEST. Preliminary inspection of the components after the campaign did not show visible signs of surface modification, but points to significant net erosion in the OSP area. An extensive post mortem analysis is now ongoing to confirm these first indications. These results underline that the complex balance between erosion/redeposition (in particular linked to impurities) and tungsten fuzz formation needs to be taken into account in tokamak conditions.

It is well known that the reversibility of Stokes flow makes it difficult for small microorganisms to swim. Inertial effects break this reversibility, allowing new mechanisms of propulsion and feeding. Therefore it is important to understand the effects of unsteady and fluid inertia on the dynamics of microorganisms in flow. In this work, we show how to translate known inertial effects for non-motile organisms to motile ones, from passive to active particles. The method relies on a principle used earlier by Legendre and Magnaudet (1997) to deduce inertial corrections to the lift force on a bubble from the inertial drag on a solid sphere, using the fact that small inertial effects are determined by the far field of the disturbance flow. The method allows for example to compute the inertial effect of unsteady fluid accelerations on motile organisms, and the inertial forces such organisms experience in steady shear flow. We explain why the method fails to describe the effect of convective fluid inertia., 10 pages, revised version

International audience; This paper proposes a hybrid multiscale approach to evaluate the fire performance of large multicompartment structures. A probabilistic network model is at the core of the proposed approach, whose inputs, namely the mean durations of the fire phases and fire transmission through the barriers between compartments (e.g., walls or ventilation ducts), are determined beforehand by a zone model, which is detailed in a companion paper and a one-dimensional computational fluid dynamics code. Next, a proof of concept is developed by applying the hybrid approach to different fire scenarios in a full-scale generic military corvette and a four-story office building. The simulation results highlight the strengths and limitations of the proposed approach. Regarding the latter, a field model is used to evaluate how the hybrid approach performs depending on the interaction between the entire building system and its ventilation and the fire. Finally, a statistical study is carried out to produce fire vulnerability and risk maps, ranking the fire compartments according to their vulnerability or propensity to generate serious fires.

International audience; Smart concrete is a construction material designed to perform structural and self-sensing roles simultaneously. self-sensing behavior stems from the inclusion of conductive fibers within the cementitious matrix, reducing its electrical impedance and enabling piezoresistive behavior. good dispersion of fibers is essential to ensure good mechanical and sensing properties. this study assesses the efficiency of different mixing sequences and energies in dispersing fibers within the mortar. the efficiency is assessed with 0.1% and 0.5% carbon fiber volume, by measuring the ac impedance: those volume fractions correspond to two fiber percolation states: around the percolation threshold (0.1%), and in the saturation zone (0.5%). the study showed that the mixing sequence has a significant effect on the final impedance of the material, and that increasing mixing energy is relatively ineffective in enhancing the fiber dispersion. differences between different mixing sequences were evident with 0.1% carbon fibers, while, to a certain extent, saturating the system with conductive fibers reduced the gaps between different mixing sequences.

International audience; In this paper, we report an experimental study on an empty dryer. The device under is an indirect dryer electrically heated. The focus is made on the thermal and fluid behavior in such systems without considering the drying process. Thus, the temperature and fluid velocity profiles are presented in order to determine the fluid flow and the thermal profiles inside the different parts of the dryer in the situations of natural and mixed convection in order to describe and allow a better comprehension of the heat and fluid flow patterns inside a dryer. The enthalpy balances lead to the determination of the most efficient zone in the dryer, this latter is located at 2/3 of its length.

In microgravity, the extended time scales associated with the absence of buoyancy lead to peculiar flame features that are likely to affect the risk associated with flame spread in the case of a spacecraft fire. Investigating a non-buoyant flame spreading over the polyethylene coating of an electrical wire in an opposed laminar flow, recent studies especially evidenced and quantified the major role of soot in the radiative heat transfer, which affects local quenching at the flame tip as well as heat feedback from the flame to the coating. Consequently, the control of soot production in such a flame needs to be explored. In the present paper, the role of basic flow features, i.e. oxygen content, flow velocity, and ambient pressure, is documented. Conducted in parabolic flights, a set of 142 experiments spreads over 91 flow conditions, with oxygen content ranging from 18% to 21%, flow velocity kept between 100 mm s − 1 and 200 mm s − 1 , and pressure ranging from 51 kPa to 142 kPa. The implementation of the Broadband Modulated Absorption/Emission (B-MAE) technique allows the fields of soot temperature and volume fraction to be measured within the spreading flames. The flame spread rate is thus shown to be an increasing function of oxygen content, but is independent of flow velocity and pressure. Concomitantly, both oxygen content and flow velocity affect soot production residence time, while pressure has a marginal impact on it. Maximum soot volume fraction is a function of all three parameters. Complementing these results with a scaling analysis, soot production rate is third-order in pressure, and very sensitive to oxygen content. An increase in flow velocity promotes two competitive processes with respect to maximum soot volume fraction, i.e. a reduction in residence time and an increase in flame temperature. A numerical model supports the experimental finding that the latter phenomenon prevails, hence that maximum soot volume fraction increases with flow velocity. These conclusions will serve as basis for upcoming quenching and radiative heat feedback analysis.

International audience; Large Eddy Simulation (LES) of the lab-scale methane fire plumes investigated experimentally by McCaffrey are performed using the steady laminar flamelet/presumed beta filtered density function model on grids of different resolution ranging from the Taylor length scale to about six times the Kolmogorov length scale. This work focuses on investigating existing subgrid (SGS) mixing models for mixture fraction variance prediction. Three different models based on the local equilibrium assumption, the variance transport equation (VTE) and the second moment transport equation (STE) are assessed. In the non-equilibrium modeling (VTE and STE), the scalar dissipation rate is modeled with an algebraic expression involving a SGS mixing timescale. The comparison of the solutions is based on the convergence properties of LES statistics for mixture fraction, temperature and axial velocity with respect to the filter width. The simulations show that the equilibrium algebraic model is not suitable for purely buoyant flows. On the other hand, simulations performed with the transport models show that grids coarser than 1 cm cannot resolved adequately the natural laminar instability near the edge of the plume that governs the formation of large scale vortex and, therefore, underestimate the mixing process, especially in the lower part of the continuous flame. For grid resolutions finer than 1 cm, the STE model is less sensitive to grid refinement than the VTE formulation and differences between the two models are reduced with grid refinement. The STE model predicts also a stronger mixing, resulting in a slightly larger lateral expansion of the fire plume. Predicted solutions by the two models are in quantitative agreement with the experimental data in terms of axial temperature, velocity and temperature fluctuations.

International audience; Much has been stated about the potential risks of nasal lavages (NL) during the coronavirus disease 2019 (COVID-19) pandemic for COVID-19 patients and surrounding people. Several otolaryngological societies recommended to limit NL, supposing it may be associated with viral spread to lower airway.1 On the contrary, recent studies suggested that NL may be beneficial in upper viral respiratory infectious diseases. In order to take stock of this issue, we conducted a short literature review to address 4 main questions: - What Are the Potential Benefits of NL to COVID-19 Patients? - What Are the Potential Benefits of NL to Personal Contacts/Healthcare Workers Caring for COVID-19 Patients? - What Are the Potential Harms of NL to Patients With COVID-19? - What Are the Potential Harms of NL to Personal Contacts/HCWs Caring For COVID-19 Patients?