Homogenization of a Multiscale Viscoelastic Model with Nonlocal Damping, Application to the Human Lungs

International audienceWe are interested in the mathematical modeling of the deformation of the human lung tissue, called the lung parenchyma, during the respiration process. The parenchyma is a foam–like elastic material containing millions of air–filled alveoli connected by a tree– shaped network of airways. In this study, the parenchyma is governed by the linearized elasticity equations and the air movement in the tree by the Poiseuille law in each airway. The geometric arrangement of the alveoli is assumed to be periodic with a small period ε > 0. We use the two–scale convergence theory to study the asymptotic behavior as ε goes to zero. The effect of the network of airways is described by a nonlocal operator and we propose a simple geometrical setting for which we show that this operator converges as ε goes to zero. We identify in the limit the equations modeling the homogenized behavior under an abstract convergence condition on this nonlocal operator. We derive some mechanical properties of the limit material by studying the homogenized equations: the limit model is nonlocal both in space and time if the parenchyma material is considered compressible, but only in space if it is incompressible. Finally, we propose a numerical method to solve the homogenized equations and we study numerically a few properties of the homogenized parenchyma model

Convergence Analysis of a Projection Semi-Implicit Coupling Scheme for Fluid-Structure Interaction Problems

In this paper, we provide a convergence analysis of a projection semi-implicit scheme for the simulation of fluid-structure systems involving an incompressible viscous fluid. The error analysis is performed on a fully discretized linear coupled problem: a finite element approximation and a semi-implicit time-stepping strategy are respectively used for space and time discretization. The fluid is described by the Stokes equations, the structure by the classical linear elastodynamics equations and all changes of geometry are neglected. We derive an error estimate in finite time and we prove that the time discretization error for the coupling scheme is at least $\sqrt{\delta t}$. Finally, some numerical experiments that confirm the theoretical analysis are presented

Global existence of solutions to the incompressible Navier-Stokes-Vlasov equations in a time-dependent domain

International audienceIn this article, we prove the existence of global weak solutions for the in-compressible Navier-Stokes-Vlasov system in a three-dimensional time-dependent domain with absorption boundary conditions for the kinetic part. This model arises from the study of respiratory aerosol in the human airways. The proof is based on a regularization and approximation strategy designed for our time-dependent framework

Multiscale modelling of the respiratory tract

International audienceWe propose here a decomposition of the respiratory tree into three stages which correspond to different mechanical models. The resulting system is described by the Navier-Stokes equation coupled with an ODE (a simple spring model) representing the motion of the thoracic cage. We prove that this problem has at least one solution locally in time for any data and, in the special case where the spring stiffness is equal to zero, we obtain an existence result globally in time provided that the data are small enough. The behaviour of the global model is illustrated by three-dimensional simulations

Existence of Weak Solutions for the Unsteady Interaction of a Viscous Fluid with an Elastic Plate

International audienceWe consider a three--dimensional viscous incompressible fluid governed by the Navier--Stokes equations, interacting with an elastic plate located on one part of the fluid boundary. We do not neglect the deformation of the fluid domain which consequently depends on the displacement of the structure. The purpose of this work is to study the solutions of this unsteady fluid--structure interaction problem, as the coefficient modeling the viscoelasticity (resp. the rotatory inertia) of the plate tends to zero. As a consequence, we obtain the existence of at least one weak solution for the limit problem (Navier--Stokes equation coupled with a plate in flexion) as long as the structure does not touch the bottom of the fluid cavity

Existence and uniqueness for a quasi-static interaction problem between a viscous fluid and an active structure

We consider a quasi-static fluid-structure interaction problem where the fluid is modeled by theStokes equations and the structure is an active and elastic medium. More precisely, the displacementof the structure verifies the equations of elasticity with an active stress, which models the presenceof internal biological motors in the structure. Under smallness assumptions on the data, we provethe existence of a unique solution for this strongly coupled system

Convergence analysis of a projection semi-implicit coupling scheme for fluid-structure interaction problems.

International audienceIn this paper, we provide a convergence analysis of a projection semi- implicit scheme for the simulation of fluid-structure systems involving an incom- pressible viscous fluid. The error analysis is performed on a fully discretized linear coupled problem: a finite element approximation and a semi-implicit time-stepping strategy are respectively used for space and time discretization. The fluid is described by the Stokes equations, the structure by the classical linear elastodynamics equations (linearized elasticity, plate or shell models) and all changes of geometry are neglected. We derive an error estimate in finite time and we prove that the time discretization error of the coupling scheme is of order 1/2. Finally, some numerical experiments that confirm the theoretical analysis are presented

Convergence Analysis of a Projection Semi-Implicit Coupling Scheme for Fluid-Structure Interaction Problems

In this paper, we provide a convergence analysis of a projection semi-implicit scheme for the simulation of fluid-structure systems involving an incompressible viscous fluid. The error analysis is performed on a fully discretized linear coupled problem: a finite element approximation and a semi-implicit time-stepping strategy are respectively used for space and time discretization. The fluid is described by the Stokes equations, the structure by the classical linear elastodynamics equations and all changes of geometry are neglected. We derive an error estimate in finite time and we prove that the time discretization error for the coupling scheme is at least $\sqrt{\delta t}$. Finally, some numerical experiments that confirm the theoretical analysis are presented