An ALE-FEM approach to the thermomechanics of solidification processes with application to prediction of pipe shrinkage

International audiencePurpose - The present paper addresses the computer modelling of pipe formation in metal castings. Design/methodology/approach - As a preliminary, a brief review of the current state-of-the-art in pipe shrinkage computation is presented. Then, in first part, the constitutive equations that have to be considered in thermomechanical computations are presented, followed by the main lines of the mechanical finite element resolution. A detailed presentation of an original arbitrary Lagrangian-Eulerian (ALE) formulation is given, explaining the connection between the Lagrangian and the quasi Eulerian zones, and the treatment of free surfaces. Findings - Whereas most existing methods are based on thermal considerations only, it is demonstrated in the current paper that this typical evolution of the free surface, originated by shrinkage at solidification front and compensating feeding liquid flow, can be effectively approached by a thermomechanical finite element analysis. Research limitations/implications - Future work should deal with the following points: identification of thermo-physical and rheological data, automatic and adaptive mesh refinement, calculation of the coupled deformation of mold components, development of a two-phase solid/liquid formulation. Practical implications - An example of industrial application is given. The proposed method has been implemented in the commercial software THERCAST® dedicated to casting simulation. Originality/value - The proposed numerical methods provide a comprehensive approach, capable of modelling concurrently all the main phenomena participating in pipe formation

Application of the arbitrary Eulerian Lagrangian finite element formulation to the thermomechanical simulation of casting processes, with focus on pipe shrinkage prediction

International audienceThe Arbitrary Lagrangian-Eulerian formulation (ALE) has become an indispensable component of finite element thermomechanical computations of casting processes. As it is an intermediate formulation between the Lagrangian formulation (material convected mesh) and the Eulerian one (fixed mesh), it allows the simultaneous computation of important phenomena: Deformation and stresses affecting solidified regions, yielding the computation of air gap evolution at part/mold interfaces. In such regions, the formulation is essentially Lagrangian. Thermosolutal convection flow in the non solidified regions; here the ALE formulation tends to a pure Eulerian one (stationary mesh). Free surface evolution at top of risers, leading to the prediction of pipe defects (macroshrinkage). In this case the ALE formulation allows the follow up of the free surface. After a brief reminder of the constitutive equations to be used in thermomechanical modeling of solidification, the mechanical equations are presented and their resolution in the context of FEM-ALE. We insist on the transport analysis, a key-point of ALE, and present a validation of the original scheme that is used here. Finally, we focus on the prediction of pipe shrinkage formation and show two industrial examples

The sex-specific factor SOA controls dosage compensation in <i>Anopheles</i> mosquitos

The Anopheles mosquito is one of thousands of species in which sex differences play a central role in their biology, as only females need a blood meal in order to produce eggs. Sex differentiation is regulated by sex chromosomes, but their presence creates a dosage imbalance between males (XY) and females (XX). Dosage compensation (DC) can re-equilibrate the expression of sex-chromosomal genes, but because DC mechanisms have only been fully characterized in a few model organisms, key questions about its evolutionary diversity and functional necessity remain unresolved 1. Here we report the discovery of a previously uncharacterized gene (SOA, for sex chromosome activation) as a master regulator of DC in the malaria mosquito Anopheles gambiae. Sex-specific alternative splicing prevents functional SOA protein expression in females. The male isoform encodes a DNA-binding protein that binds the promoters of active X chromosomal genes. Expressing male SOA is sufficient to induce DC in female cells. Male mosquitoes lacking SOA or female mosquitos ectopically expressing the male isoform exhibit X chromosome misregulation, which is compatible with viability but causes developmental delay. Thus, our molecular analysis of the first DC master regulator in a non-model organism elucidates the evolutionary steps leading to the establishment of a chromosome-specific fine-tuning mechanism

Relationship between physic-chemical properties, chemical properties and environmental condition production of Arabic Gum

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Relationship between physico-chemical properties, chemical properties, and environmental conditions production of arabic gum

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Sustainable development in Africa – Research and development openings

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Sustainable development in Africa – Research and development openings

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How flavor retention reflects the emulsifying properties of acacia gums

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New tools to predict the acacia gum efficacy for emulsion stabilization

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Mayotte Critical Zone Observatory: preliminary results on chemical weathering and erosion rates on volcanic edifices

Geochemistry of the Earth's Surface (GES) Meeting, Paris, FRANCE, AUG 18-23, 2014International audienceThis is the first multidisciplinary study on the critical zone of the French volcanic island of Mayotte to address chemical weathering rates. Here we present the first estimation of chemical weathering rates using element fluxes transported in surface and subsurface waters, ranging from 49 to 306 t/km(2)/yr for rivers and 113 to 1,382 t/km(2)/yr for groundwater. These results are consistent with the weathering pattern of other tropical volcanic islands and support the hypothesis that subsurface waters transport more solutes to the ocean than surface waters. In addition, a helicopter-borne resistivity survey was correlated to borehole geological data to understand the hydrogeological functioning of the ``deep critical zone''. (C) 2014 Published by Elsevier B.V