Abstract. In this paper Fluid-structure interaction (FSI) simulations of artery aneurysms are carried out where both the fluid flow and the hyperelastic material are incompressible. We focus on time-dependent formulations adopting a monolithic approach, where the deformation of the fluid domain is taken into account according to an Arbitrary Lagrangian Eulerian (ALE) scheme. The exact Jacobian matrix is implemented by using automatic differentiation tools. The system is modeled using a specific equation shuffling that assures an optimal pivoting. We propose to solve the resulting linearized system at each nonlinear outer iteration with a GMRES solver preconditioned by a geometric multigrid algorithm with an Additive Schwarz Method (ASM) smoother.In order to test our numerical method on possible hemodynamics applications, we describe several benchmark settings. The configurations consist of realistic artery aneurysms where hybrid meshes are employed. Both two and three-dimensional benchmarks are considered. We show numerical results for the described aneurysm geometries focusing on pulsatile inflow conditions. Parallel implementation is addressed and a case of endovascular stent implantation on a cerebral aneurysm is presented. 955Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 955-974

We present fluid-structure interaction simulations of magnetic drug targeting (MDT) in blood flows. In this procedure, a drug is attached to ferromagnetic particles to externally direct it to a specific target after it is injected inside the body. The goal is to minimize the healthy tissue affected by the treatment and to maximize the number of particles that reach the target location. Magnetic drug targeting has been studied both experimentally and theoretically by several authors. In recent years, computational fluid dynamics simulations of MDT in blood flows have been conducted to obtain further insight on the combination of parameters that provide the best capture efficiency. However, to this day, no computational study addressed MDT in a fluid-structure interaction setting. With this paper, we aim to fill this gap and investigate the impact of the solid deformation on the capture efficiency.

The tracer equations are part of the primitive equations used in ocean modeling and describe the transport of tracers, such as temperature, salinity or chemicals, in the ocean. Depending on the number of tracers considered, several equations may be added to and coupled to the dynamics system. In many relevant situations, the time-step requirements of explicit methods imposed by the transport and mixing in the vertical direction are more restrictive than those for the horizontal, and this may cause the need to use very small time steps if a fully explicit method is employed. To overcome this issue, we propose an exponential time differencing (ETD) solver where the vertical terms (transport and diffusion) are treated with a matrix exponential, whereas the horizontal terms are dealt with in an explicit way. We investigate numerically the computational speed-ups that can be obtained over other semi-implicit methods, and we analyze the advantages of the method in the case of multiple tracers.

Venous valves are bicuspidal valves that ensure that blood in veins only flows back to the heart. To prevent retrograde blood flow, the two intraluminal leaflets meet in the center of the vein and occlude the vessel. In fluid-structure interaction (FSI) simulations of venous valves, the large structural displacements may lead to mesh deteriorations and entanglements, causing instabilities of the solver and, consequently, the numerical solution to diverge. In this paper, we propose an arbitrary Lagrangian-Eulerian (ALE) scheme for FSI simulations designed to solve these instabilities. A monolithic formulation for the FSI problem is considered, and due to the complexity of the operators, the exact Jacobian matrix is evaluated using automatic differentiation. The method relies on the introduction of a staggered in time velocity to improve stability, and on fictitious springs to model the contact force of the valve leaflets. Because the large structural displacements may compromise the quality of the fluid mesh as well, a smoother fluid displacement, obtained with the introduction of a scaling factor that measures the distance of a fluid element from the valve leaflet tip, guarantees that there are no mesh entanglements in the fluid domain. To further improve stability, a streamline upwind Petrov-Galerkin (SUPG) method is employed. The proposed ALE scheme is applied to a two-dimensional (2D) model of a venous valve. The presented simulations show that the proposed method deals well with the large structural displacements of the problem, allowing a reconstruction of the valve behavior in both the opening and closing phase.

In this paper we study convergence estimates for a multigrid algorithm with smoothers of successive subspace correction (SSC) type, applied to symmetric elliptic PDEs. First, we revisit a general convergence analysis on a class of multigrid algorithms in a fairly general setting, where no regularity assumptions are made on the solution. In this framework, we are able to explicitly highlight the dependence of the multigrid error bound on the number of smoothing steps. For the case of no regularity assumptions, this represents a new addition to the existing theory. Then, we analyze successive subspace correction smoothing schemes for a set of uniform and local refinement applications with either nested or non-nested overlapping subdomains. For these applications, we explicitly derive bounds for the multigrid error, and identify sufficient conditions for these bounds to be independent of the number of multigrid levels. For the local refinement applications, finite element grids with arbitrary hanging nodes configurations are considered. The analysis of these smoothing schemes is cast within the far-reaching multiplicative Schwarz framework. Now consider v ∈ V J , then a(E J v, v) = a(