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Rhamnolipids as an eco-friendly corrosion inhibitor of rebars in simulated concrete pore solution: evaluation of conditioning and addition methods
No full textInternational audienceThe objective of this study was to evaluate the use of rhamnolipids (RLs) extracted from Pseudomonas aeruginosa as a possible eco-friendly inhibitor for the corrosion protection of rebars in concrete. Two application methods were tested: application of RLs as a coating on the steel (conditioning method) and addition of the RLs directly to the aggressive environment (addition method). Both methods were evaluated for their ability to protect steel in simulated concrete pore solution containing 0.5M NaCl. The results highlight a delay in the initiation of local corrosion followed by a rapid propagation rate of corrosion for conditioning method. This evolution is in relation with the heterogeneity of the formed RLs layers. The addition method provides a different film formation and better protection against corrosion. Using a 1gL concentration, the inhibition effect was observed at least for 24h of immersion
Efficient computation of optimal open-loop controls for stochastic systems
No full textInternational audienc
Models and Algorithms for the Product Pricing with Single-Minded Customers Requesting Bundles
No full textInternational audienceWe analyze a product pricing problem with single-minded customers, each interested in buying a bundle of products. The objective is to maximize the total revenue and we assume that supply is unlimited for all products. We contribute to a missing piece of literature by giving some mathematical formulations for this single-minded bundle pricing problem. We first present a mixed-integer nonlinear program with bilinear terms in the objective function and the constraints. By applying classical linearization techniques, we obtain two different mixed-integer linear programs. We then study the polyhedral structure of the linear formulations and obtain valid inequalities based on an RLT-like framework. We develop a Benders decomposition to project strong cuts from the tightest model onto the lighter models. We conclude this work with extensive numerical experiments to assess the quality of the mixed-integer linear formulations, as well as the performance of the cutting plane algorithms and the impact of the preprocessing on computation times
A low-diffusion self-adaptive flux-vector splitting approach for compressible flows
No full textInternational audienceA low-diffusion self-adaptive flux-vector splitting method is presented for the Euler equations. The flux-vector is here split into convective and acoustic parts following the formulation recently proposed by the authors. This procedure is based on the Zha-Bilgen (or previously Baraille et al. for the Euler barotropic system) approach enriched by a dynamic flow-dependent splitting parameter based on the local Mach number. As a consequence, in the present self-adaptive splitting, the convective and acoustic parts decouple in the low-Mach number regime whereas the complete Euler equations are considered for the sonic and highly subsonic regimes. The low diffusive property of the present scheme is obtained by adding anti-diffusion terms to the momentum and the energy components of the pressure flux in the acoustic part of the present splitting. This treatment results from a formal invariance principle preserving the discrete incompressible phase space through the pressure operator. Numerical results for several carefully chosen one- and two-dimensional test problems are finally investigated to demonstrate the accuracy and robustness of the proposed scheme for a wide variety of configurations from subsonic to highly subsonic flows
Hydrogen storage in two-dimensional and three-dimensional materials
No full textInternational audienc
A polynomial expansion based model for evaluating wear of thin surface coatings in fea
No full textInternational audienceIn the case of very thin soft surface coatings, the coating layer contribution is often discarded in a largescale Finite Element Analysis (FEA). This is mainly due to the extensive numerical cost involved. However, to avoid failure of contacting coated parts one has to consider wear of the coatings themselves. This adds additional layer of complexity to the problem. To overcome the excessive computational cost introduced by the full discretization of the layer an alternative approach needs to be considered. Inspired by the early work of Matthewson [1], using a polynomial expansion based approximation for the surface layer together with FEA can lead to an improved numerical framework. By proposing that the thin layer can be seen as a surface described by a dimensional variable ˆy, the displacement field in the coating layer can be approximated by a polynomial expansion as . where are the unknown displacement modes. By integrating over the layer dimensional variable ˆy the initial two phase problem is replaced by an interface problem. As the boundary of the substrate is discretized for FEA, the interface stiffness contribution can be directly added to the global FE-system. Thus, making the method easily suitable for usage with FEA. Furthermore, the only correction to KKT contact conditions is the modification of the gap function to include the displacements on the contacting interface. As there is no volumetric representation of the coating the removal of material due to wear can be described by the change of layer thickness. Making it straightforward to connect the abrasive/adhesive wear rate to a solution dependent field like shear stress or contact pressure as in case of Archard law. In addition, no remeshing routine is required as the thickness of the layer is a mesh independent parameter. The possibility of including the above mentioned methodology in a FEA based wear simulation is presented. This research work focuses on a specific tribology test (Cross-Cylinder) to investigate the abrasive wear of coated cylinders. The results of the numerical model are directly compared to Greenwood [2] and physical test results. It is shown that there exists a significant cost reduction by considering polynomial based approximation of thin layers without loss of accuracy. Furthermore, the inclusion of wear is straighforward as it scales down to controlling the evolution of just one internal paramater. Finally, the compatibility with FEA is adressed on the example of implementation in commercial FEA softwa
O -Allylated Pudovik and Passerini Adducts as Versatile Scaffolds for Product Diversification
No full textInternational audienc
Metal-Free Addition of Boronic Acids to Silylnitronates
No full textInternational audienceWe report for the first time a metal-free addition of boronic acids to silylnitronates to afford oxime derivatives through aryl transfer on the carbon nitrogen double bond. A reaction mechanism has been proposed in relation with a DFT study on the key aryl transfer. This arylation process is effective for cycloalkenyl nitro derivatives leading to oximes that may be oxidatively converted into 3-arylisoxazole derivatives
Combination of Hexahedral and Prismatic Solid-shell Finite Elements
No full text23rd International Conference on Material Forming (ESAFORM), ELECTR NETWORK, MAY 04-08, 2020International audienceIn most papers with solid-shell finite elements for non-linear calculation of thin structures, only one type of element is presented. Either prismatic solid-shell or hexahedral solid-shell element. However, it is well known that in industrial studies, where complex geometries are involved, it is very difficult to model with only hexahedral type of finite element. We will therefore propose a study where two recently formulated solid-shell finite elements (SB7 and SB9) are combined to solve a practical industrial problem. The SB7 and SB9 are two solid-shell finite elements of prismatic and hexahedral topologies. They contain respectively 6 and 8 vertex nodes plus one additional central node. This central node acts as an EAS parameter, but not only. From this additional degree of freedom (DOF), a new distribution is made on the applied pressure forces, generating a volume contribution. This allows to go beyond the EAS method, allowing to improve considerably the pinch stresses. These two elements work with three dimensional constitutive laws and are under integrated (reduced integration). The ANS method is also used to reduce transverse shear and trapezoidal locking. (C) 2020 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 23rd International Conference on Material Forming
Emulation of X-ray Light-Field Cameras
No full textInternational audienceX-ray plenoptic cameras acquire multi-view X-ray transmission images in a single exposure (light-field). Their development is challenging: designs have appeared only recently, and they are still affected by important limitations. Concurrently, the lack of available real X-ray light-field data hinders dedicated algorithmic development. Here, we present a physical emulation setup for rapidly exploring the parameter space of both existing and conceptual camera designs. This will assist and accelerate the design of X-ray plenoptic imaging solutions, and provide a tool for generating unlimited real X-ray plenoptic data. We also demonstrate that X-ray light-fields allow for reconstructing sharp spatial structures in three-dimensions (3D) from single-shot data