Numerical modelling of fluid-structure interactions

Fluid-structure interaction (FSI) problems occur when a potentially deformable solid interact with a surrounding fluid. The flow of the fluid deforms the solid and/or changes its position thus modifying the geometry of the fluid domain. In this paper, we present an Arbitrary Lagrangian Eulerian (ALE) formulation of FSI problems and we present a few numerical examples

Sensitivity study of a numerical model of heat and mass transfer involved during the medium-density fiberboard hot pressing process

The objective of this work was to estimate the impact of the variability of the mediumdensity fiberboard mat heat and moisture transfer properties on the results predicted by a numerical model of hot pressing. The three state variables of the model, temperature, air pressure, and vapor pressure, depend on parameters describing the material properties of the mat known with a limited degree of precision. Moreover, different moisture sorption models and initial moisture contents also have an impact on the numerically predicted results. In this sensitivity study, we determined the impact of variations of the mat properties, sorption models, boundary conditions, and initial MC on the state variables. Our study shows that mat thermal conductivity, convective mass transfer coefficient of the external boundary, and gas permeability have the most significant impact on temperature, gas pressure, and MC within the mat. On the other hand, the convective heat transfer coefficient of the external boundary has no impact on the state variables. The sorption model affects significantly mat MC predictions only. The initial MC of the mat has a strong influence on the internal gas pressure

Numerical modeling of the medium-density fiberboard hot pressing process. Part 1, Coupled heat and mass transfer model

A mathematical model describing heat and moisture transfer during hot pressing of mediumdensity fiberboard mats is presented. The model is based on conservation of energy, air mass, and water vapor mass, resulting in a three-dimensional unsteady-state problem in which mat properties and state variables vary in time and space. The conservation equations are expressed as functions of the three state variables: temperature, air pressure, and vapor pressure. The model includes conductive and convective heat transfer, phase change of water, and convective and diffusive mass transfer. Resin curing kinetics and latent heat associated with phase change of water are also taken into account. The closing of the batch press and development of the density profile are taken into account by imposing a predefined time- and space-dependent density profile. Calculations are carried out on reference geometry, and mathematical details relevant to the transfer from actual to reference geometry are presented. The system is discretized in space by the finite element method and in time by the Euler implicit scheme. The results exhibit good agreement with experimental measurements and provide information on variables of interest such as total gas pressure, temperature, moisture content, RH, and resin cure

Wood-Adhesive Interface Characterization And Modeling In Engineered Wood Flooring

Adhesive films used in layered wood-based composites have a significant impact on moisture movement and must be considered in models of such products. The objective of this study was to characterize the wood-adhesive interface and determine its impact on the hygromechanical behavior of engineered wood flooring (EWF). The radial water vapor diffusion coefficient and the coefficients of moisture expansion were determined for sugar maple wood, crosslinked polyviny1 acetate adhesive film (XPVAc), and the wood-adhesive interface. Sugar maple wood had the highest diffusion coefficient at 1.66 x 10-11 m2 · s-1 followed by the wood-adhesive interface at 5.73 x 10-12 m2 · s-1, and the free XPVAc film at 4.18 x 10-12 m2 · s-1. The coefficient of tangential moisture expansion of the sugar maple wood-adhesive interface was found to be 4 x 10-3 (%MC)-1 compared with 3 x 10-3 (%MC)-1 for sugar maple wood in the tangential direction, and 3 x 10-3 (%MC)-1 for the XPVAc film. Finite element modeling of EWF hygromechanical cupping did not show significant differences between hygromechanical cupping calculated with and without interface effects

Primary B-Cell Deficiencies Reveal a Link between Human IL-17-Producing CD4 T-Cell Homeostasis and B-Cell Differentiation

IL-17 is a pro-inflammatory cytokine implicated in autoimmune and inflammatory conditions. The development/survival of IL-17-producing CD4 T cells (Th17) share critical cues with B-cell differentiation and the circulating follicular T helper subset was recently shown to be enriched in Th17 cells able to help B-cell differentiation. We investigated a putative link between Th17-cell homeostasis and B cells by studying the Th17-cell compartment in primary B-cell immunodeficiencies. Common Variable Immunodeficiency Disorders (CVID), defined by defects in B-cell differentiation into plasma and memory B cells, are frequently associated with autoimmune and inflammatory manifestations but we found no relationship between these and Th17-cell frequency. In fact, CVID patients showed a decrease in Th17-cell frequency in parallel with the expansion of activated non-differentiated B cells (CD21lowCD38low). Moreover, Congenital Agammaglobulinemia patients, lacking B cells due to impaired early B-cell development, had a severe reduction of circulating Th17 cells. Finally, we found a direct correlation in healthy individuals between circulating Th17-cell frequency and both switched-memory B cells and serum BAFF levels, a crucial cytokine for B-cell survival. Overall, our data support a relationship between Th17-cell homeostasis and B-cell maturation, with implications for the understanding of the pathogenesis of inflammatory/autoimmune diseases and the physiology of B-cell depleting therapies