Direct modeling of material deposit and identification of energy transfer in gas metal arc welding

International audiencePurpose - The purpose of this paper is to present original methods related to the modeling of material deposit and associated heat sources for finite element simulation of gas metal arc welding (GMAW). Design/methodology/approach - The filler deposition results from high-frequency impingements of melted droplets. The present modeling approach consists of a time-averaged source term in the mass equation for selected finite elements in the fusion zone. The associated expansion of the mesh is controlled by means of adaptive remeshing. The heat input includes a volume source corresponding to the droplets energy, for which a model from the literature is expressed in coherency with mass supply. Finally, an inverse technique has been developed to identify different model parameters. The objective function includes the differences between calculations and experiments in terms of temperature, but also shape of the fusion zone. Findings - The proposed approach for the modeling of metal deposition results in a direct calculation of the formation of the weld bead, without any a priori definition of its shape. Application is shown on GMAW of steel 316LN, for which parameters of the model have been identified by the inverse method. They are in agreement with literature and simulation results are found quite close to experimental measurements. Originality/value - The proposed algorithm for material deposit offers an alternative to the element activation techniques that are commonly used to simulate the deposition of filler metal. The proposed inverse method for parameter identification is original in that it encompasses an efficient and convenient technique to take into account the shape of the fusion zone

Adaptive anisotropic mesh technique for coupled problems: application to welding simulation

International audienceA major problem arising in finite element analysis of coupled problems, such as welding for instance, is the control of the mesh, that is an appropriate mastering of the spatial discretization to get accurate results in a minimum computer time. The present anisotropic adaptation procedure is controlled by a directional error estimator based on local interpolation error and recovery of the second derivatives of different fields involved in the finite element calculation. Error indicators are derived to define an anisotropic mesh metric field, which is an input of the pre existing 3D remeshing procedure. The mesh metric consists of a combination of several metrics, each corresponding to the error estimation associated with a selected field of the solution produced (temperature, phase fraction, stress component). Mesh modifications are used to anisotropically and continuously adapt the mesh. We demonstrate the efficiency of the method by applying it to a coupled thermal-mechanical-metallurgical simulation of arc welding. We demonstrate that the use of an anisotropic adaptive finite element method can result in an order of magnitude reduction in computing time with no loss of accuracy compared to analyses obtained with isotropic meshes

New Numerical Technologies for the Simulation of Arc Welding Processes

International audienceThe paper presents the main concepts of a newly-developed numerical code for arc welding simulation and analysis. The new numerical technologies essentially consist first of original methods for the modeling of material deposit allowing a direct simulation of joint formation, instead of usual element birth techniques. Second, a dynamic mesh optimization procedure, allowing error control. And third, a multivariable finite element inverse method for identification of heat sources

A coupled approach for the modelling of arc welding processes

International audienceA 3D finite element model is presented, addressing some major phenomena arising in arc welding as well as their interaction: heat input, metal deposit, solidification, phase transformations in the solid state and material behavior. As a result of a simulation, the shape of the weld bead, the phase distribution, residual stresses and distortions are obtained. Some application and validation cases are discussed

Alterations in macrophage G proteins are associated with endotoxin tolerance

AbstractPrevious studies have suggested that endotoxin tolerance induces macrophage desensitization to endotoxin through altered guanine nucleotide regulatory (G) protein function. In the present study the binding characteristics of the nonhydrolyzable GTP analogue GTPγ[35S] to macrophage membranes from endotoxin tolerant and control rats were determined. Membranes were prepared from peritoneal macrophages harvested from rats 72 h after two sequential daily doses of vehicle or Salmonella enteritidis endotoxin (100 μg/kg on day 1 and 500 μg/kg on day 2). GTPγ[35S] bound to a single class of sites that were saturable and displaceable in control and endotoxin tolerant macrophage membranes. The maximum specific binding of GTPγ[35S] was significantly (P < 0.01) decreased in membranes from tolerant rats compared to control (Bmax = 39 ± 7 pmol/mg protein in control vs. 11 ± 2 pmol/mg protein in endotoxin tolerant; n = 5). There were no significant differences in the Kd values. To determine whether the reduced GTPγS binding was due to decreases in G proteins, macrophage membrane G protein content was determined by western blotting with specific antisera to Gi1,2 α, Gi3α, Gs α, and the β subunit of G. Scanning densitometric analysis demonstrated differential decreases in tolerant macrophage membrane G proteins. Gi3α was reduced the most to 48 ± 8% of controls (n = 3), and this reduction was significant compared to those of other G proteins. Gi1,2α and Gβ were reduced to 73 ± 5% (n = 3) and 65 ± 4% (n = 3) of control values, respectively. Gs α) (L) and Gs α(H) were reduced to 61 ± 5% (n = 3) and 68 ± 3% (n = 3) of control, respectively. These results demonstrate that endotoxin tolerant macrophages exhibit decreased membrane GTP binding capacity and differential reductions in the content of specific G proteins. The cellular mechanisms leading to such alterations in G proteins and their functional significance in the acquisition of endotoxin tolerance merit further investigation

Experimental validation of finite element codes for welding deformations

International audienceA single pass metal inert gas welding on an austenitic steel plate has been presented for the purpose of providing controlled experimental data against which numerical codes quantifying welding stresses can be validated. It includes a moving heat source with material deposit, and completes thus existing validation data. The experiment has been addressed by a numerical code, WeldSimS, reproducing qualitatively the distortion during welding quite well. Quantitative differences between the numerical and experimental results, however, indicate the need for more accurate modelling tools than those presently available, which are all based on commonly accepted modelling principles and input data

Signal transduction underlying the control of urinary bladder smooth muscle tone by muscarinic receptors and β-adrenoceptors

The normal physiological contraction of the urinary bladder, which is required for voiding, is predominantly mediated by muscarinic receptors, primarily the M3 subtype, with the M2 subtype providing a secondary backup role. Bladder relaxation, which is required for urine storage, is mediated by β-adrenoceptors, in most species involving a strong β3-component. An excessive stimulation of contraction or a reduced relaxation of the detrusor smooth muscle during the storage phase of the micturition cycle may contribute to bladder dysfunction known as the overactive bladder. Therefore, interference with the signal transduction of these receptors may be a viable approach to develop drugs for the treatment of overactive bladder. The prototypical signaling pathway of M3 receptors is activation of phospholipase C (PLC), and this pathway is also activated in the bladder. Nevertheless, PLC apparently contributes only in a very minor way to bladder contraction. Rather, muscarinic-receptor-mediated bladder contraction involves voltage-operated Ca2+ channels and Rho kinase. The prototypical signaling pathway of β-adrenoceptors is an activation of adenylyl cyclase with the subsequent formation of cAMP. Nevertheless, cAMP apparently contributes in a minor way only to β-adrenoceptor-mediated bladder relaxation. BKCa channels may play a greater role in β-adrenoceptor-mediated bladder relaxation. We conclude that apart from muscarinic receptor antagonists and β-adrenoceptor agonists, inhibitors of Rho kinase and activators of BKCa channels may have potential to treat an overactive bladder

Modélisation thermomécanique du soudage : apport de matière et adaptation de maillage

International audienceIn this paper, an adaptive remeshing strategy and a new technique for modelling of addition of filler material are presented. The anisotropic adaptation procedure is controlled by a directional error estimator based on local interpolation error. The material deposit is modelled as a source term in the conservation equation. We show that the use of an anisotropic adaptive finite element method can result in an order of magnitude reduction in computing time. It also allows modelling joint formation.Dans ce papier, une stratégie d'adaptation de maillage et une approche de modéli-sation de l'apport de matière sont présentées. Nous avons développé ici une stratégie de re-maillage adaptatif anisotrope basée sur l'estimateur d'erreur d'interpolation. Nous présentons aussi une approche qui permet de modéliser l'apport de métal comme un terme de source dans l'équation de conservation. Les résultats numériques obtenus montrent que l'adaptation de maillage permet à la fois le temps de calcul (à precision identique), et de suivre l'évolution de la surface du cordon au cours de l'apport et du refroidissement

A two parameter monthly water balance model for French watersheds

The performance of lumped monthly water balance models used for water resources assessment and management is considered. Because of the severe time lumping involved, these models could not be physically based and were at best conceptual or empirical. For this reason they were generally simple, with very few parameters to be calibrated. A new water balance model was developed with only 2 parameters to be calibrated or estimated using physical characteristics for use on a given catchment. In spite of its lack of sophistication the model generated results which compared favourably with those of other widely-used monthly water balance models. / Un modèle très simple de bilan hydrologique a été conçu pour l'évaluation et la gestion des ressources en eau. Seulement deux paramètres sont à caler ou à estimer à partir des caractéristiques physiques pour son utilisation sur un bassin versant donné. Les besoins modestes du modèle garantissent sa performance et, en dépit de sa nature élémentaire, ce modèle peut se comparer avec les autres modèles bien connus de bilan hydrologique mensuel