Parallel modeling of wildfires using efficient solvers for ill-conditioned linear systems

The Journal of Supercomputing - Numerical simulation of multi-physical processes requires a lot of processor time, especially when solving ill-conditional linear systems arising in fluid dynamics...     

Improvement of Staphylococcus xylosus lipase production through optimization of the culture conditions

The Staphylococcus xylosus strain produces without induction an original lipase named S. xylosus lipase (SXL). Since considerable interest has been given to microbial lipases for biotechnology applications like detergents, food, drugs and pharmaceutical products, improvement of their production is of great importance to reduce the final cost. This goal could be reached through the optimization of several physicochemical culture conditions. Indeed, an appropriate medium was formulated for SXL production. It was composed of 17 g/L pancreatic digest of casein, 2.5 g/L glucose, 6 g/L yeast extract, 0.75 g/L ammonium sulfate corresponding to a C/N ratio of 6, 1 g/L K₂HPO₄ and 1 g/L KH₂PO₄. In such a medium, SXL production reached 42 U/mL. Moreover, the usefulness of such a medium for large‐scale production of SXL was also evidenced in an automated fully controlled 2.6‐L fermenter. It was shown that aeration of the medium, which strongly affected the growth, regulated the lipase synthesis by the produced cells. It was found that when using a dissolved oxygen saturation of the medium of 50%, the SXL production reached 62 U/mL.     

Microstructure,Thermal and Mechanical Behavior of 3D Printed Acrylonitrile Styrene Acrylate

Fused deposition modeling (FDM) is one of the most popular additive manufacturing techniques for polymers. Despite the numerous works on the printability of various types of polymers, there is a lack in understanding the role of the microstructure on the mechanical performance of printed parts. This work aims at addressing this particular point for the case of a polymer that did not receive much attention, namely acrylonitrile styrene acrylate or ASA. This study emphasizes on the effect of the printing temperature on thermal and mechanical performance of printed ASA using differential scanning calorimetry, infra‐red measurements, mechanical testing, X‐ray micro‐tomography, and finite element computation. The experimental results demonstrate a narrow window of printability of ASA based on the thermal response of this polymer during the laying down process. In addition, both experimental and numerical results show an evident loss in the performance that represents one third of the performance of the raw material. Despite this loss, the limited amount of generated porosity and the level of tensile strength of ASA make it a good choice as a feedstock material for FDM compared to other polymers such as acrylonitrile butadiene styrene.     

New Computational Model Based on Finite Element Method to Quantify Damage Evolution Due to External Sulfate Attack on Self‐Compacting Concretes

Abstract: This work combines experimental and numerical investigations to study the mechanical degradation of self‐compacting concrete under accelerated aging conditions. Four different experimental treatments are tested among them constant immersion and immersion‐drying protocols allow an efficient external sulfate attack of the material. Significant damage is observed due to interfacial ettringite. A predictive analysis is then adopted to quantify the relationship between ettringite growth and mechanical damage evolution during aging. Typical 3D microstructures representing the cement paste‐aggregate structures are generated using Monte Carlo scheme. These images are converted into a finite element model to predict the mechanical performance under different criteria of damage kinetics. The effect of ettringite is then associated to the development of an interphase of lower mechanical properties. Our results show that the observed time evolution of Young's modulus is best described by a linear increase of the interphase content. Our model results indicate also that the interphase regions grow at maximum stress regions rather than exclusively at interfaces. Finally, constant immersion predicts a rate of damage growth five times lower than that of immersion‐drying protocol.     

The effect of cohesive forces on the fluidization of aeratable powders

The effects of cohesive forces of van der Waals type in the fluidization/defluidization of aeratable type A powders in the Geldart classification are numerically investigated. The effects of friction and particle‐size distribution (PSD) on some design‐significant parameters, such as minimum fluidization and bubbling velocities, are also investigated. For these types of particles, cohesive forces are observed as necessary to fully exhibit the role friction plays in commonly observed phenomena, such as pressure overshoot and hysteresis around minimum fluidization. This study also shows that a full‐experimental PSD consisting of a dozen particle sizes may be sufficiently represented by a few particle diameters. Reducing the number of particle types may benefit the continuum approach, which is based on the kinetic theory of granular flow, by reducing computational expense, while still maintaining the accuracy of the predictions. Published 2013 American Institute of Chemical Engineers AIChE J 60: 473–484, 2014