Vascular fluid-structure-interaction using Fluent and Abaqus software (original) (raw)
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Numerical Simulation of Fluid Structure Interaction with Application to Aneurysm Hemodynamics
As an example for fluid-structure interaction in biomedical problems, the influence of endovascular stent implantation onto cerebral aneurysm hemodynamics is numerically investigated. The aim is to study the interaction of the elastic walls of the aneurysm with the geometrical shape of the implanted stent structure for prototypical 2D configurations. This study can be seen as a basic step towards the understanding of the resulting complex flow phenomena so that in future aneurysm rupture shall be suppressed by an optimal setting for the implanted stent geometry. From the mathematical side, numerical techniques for solving the problem of fluid-structure interaction with an elastic material in a laminar incompressible viscous flow are described. An Arbitrary Lagrangian-Eulerian (ALE) formulation is employed in a fully coupled monolithic way, considering the problem as one continuum. The mathematical description and the numerical schemes are designed in such a way that more complicated constitutive relations (and more realistic for biomechanics applications) for the fluid as well as the structural part can be easily incorporated. We utilize the well-known Q 2 P 1 finite element pair for discretization in space to gain high accuracy and perform as time-stepping the 2nd order Crank-Nicholson, resp., Fractional-Step-θ-scheme for both solid and fluid parts. The resulting nonlinear discretized algebraic system is solved by a Newton method which approximates the Jacobian matrices by the divided differences approach, and the resulting linear systems are solved by iterative solvers, preferably of Krylov-multigrid type. Preliminary results for the stent-assisted occlusion of cerebral aneurysm are presented. Since these results are currently restricted to 2D configurations, the aim is not to predict quantitatively the complex interaction mechanisms between stents and elastic walls of the aneurysm, but to analyse qualitatively the behaviour of the elasticity of the walls vs. the geometrical details of the stent for prototypical flow situations.
Fundamental Trends in Fluid-Structure Interaction
Numerical techniques for solving the problem of fluid-structure interaction with an elastic material in a laminar incompressible viscous flow are described. An Arbitrary Lagrangian-Eulerian (ALE) formulation is employed in a fully coupled monolithic way, considering the problem as one continuum. The mathematical description and the numerical schemes are designed in such a way that more complicated constitutive relations (and more realistic for biomechanics applications) for the fluid as well as the structural part can be easily incorporated. We utilize the well-known Q 2 P 1 finite element pair for discretization in space to gain high accuracy and perform as time-stepping the 2nd order Crank-Nicholson, resp., Fractional-Step-θ-scheme for both solid and fluid parts. The resulting nonlinear discretized algebraic system is solved by a Newton method which approximates the Jacobian matrices by a divided differences approach, and the resulting linear systems are solved by iterative solvers, preferably of Krylov-multigrid type. For validation and evaluation of the accuracy of the proposed methodology, we present corresponding results for a new set of FSI benchmarking configurations which describe the self-induced elastic deformation of a beam attached to a cylinder in laminar channel flow, allowing stationary as well as periodically oscillating deformations. Then, as an example for fluid-structure interaction (FSI) in biomedical problems, the influence of endovascular stent implantation onto cerebral aneurysm hemodynamics is numerically investigated. The aim is to study the interaction of the elastic walls of the aneurysm with the geometrical shape of the implanted stent structure for prototypical 2D configurations. This study can be seen as a basic step towards the understanding of the resulting complex flow phenomena so that in future aneurysm rupture shall be suppressed by an optimal setting for the implanted stent geometry.
Annals of Biomedical Engineering, 2011
Computational modeling is often used to quantify hemodynamic alterations induced by stenting, but frequently uses simplified device or vascular representations. Based on a series of Boolean operations, we developed an efficient and robust method for assessing the influence of current and next-generation stents on local hemodynamics and vascular biomechanics quantified by computational fluid dynamics. Stent designs were parameterized to allow easy control over design features including the number, width and circumferential or longitudinal spacing of struts, as well as the implantation diameter and overall length. The approach allowed stents to be automatically regenerated for rapid analysis of the contribution of design features to resulting hemodynamic alterations. The applicability of the method was demonstrated with patient-specific models of a stented coronary artery bifurcation and basilar trunk aneurysm constructed from medical imaging data. In the coronary bifurcation, we analyzed the hemodynamic difference between closed-cell and open-cell stent geometries. We investigated the impact of decreased strut size in stents with a constant porosity for increasing flow stasis within the stented basilar aneurysm model. These examples demonstrate the current method can be used to investigate differences in stent performance in complex vascular beds for a variety of stenting procedures and clinical scenarios.
Computer Methods in Applied Mechanics and Engineering, 2009
In this work, we present a computational fluid-structure interaction (FSI) study for a healthy patientspecific pulmonary arterial tree using the unified continuum and variational multiscale (VMS) formulation we previously developed. The unified framework is particularly well-suited for FSI, as the fluid and solid sub-problems are addressed in essentially the same manner and can thus be uniformly integrated in time with the generalized-α method. In addition, the VMS formulation provides a mechanism for large-eddy simulation in the fluid sub-problem and pressure stabilization in the solid sub-problem. The FSI problem is solved in a quasi-direct approach, in which the pressure and velocity in the unified continuum body are first solved, and the solid displacement is then obtained via a segregated algorithm and prescribed as a boundary condition for the mesh motion. Results of the pulmonary arterial FSI simulation are presented and compared against those of a rigid wall simulation.
2011
Cerebral aneurysms are abnormal focal dilatations of artery walls. The interest in virtual tools to help clinicians to value the effectiveness of different procedures for cerebral aneurysm treatment is constantly growing. This study is focused on the analysis of the influence of different stent deployment approaches on intra-aneurysmal haemodynamics using computational fluid dynamics (CFD). A self-expanding stent was deployed in an idealized aneurysmatic cerebral vessel in two initial positions. Different cases characterized by a progression of simplifications on stent modelling (geometry and material) and vessel material properties were set up, using finite element and fast virtual stenting methods. Then, CFD analysis was performed for untreated and stented vessels. Haemodynamic parameters were analysed qualitatively and quantitatively, comparing the cases and the two initial positions. All the cases predicted a reduction of average wall shear stress and average velocity of almost 50 per cent after stent deployment for both initial positions. Results highlighted that, although some differences in calculated parameters existed across the cases based on the modelling simplifications, all the approaches described the most important effects on intra-aneurysmal haemodynamics. Hence, simpler and faster modelling approaches could be included in clinical workflow and, despite the adopted simplifications, support clinicians in the treatment planning.
Three-Dimensional Numerical Simulation of Blood Flow in Two Coronary Stents
Numerical Heat Transfer Part A-applications, 2011
The aim of the present study is to carry out Computational Fluid Dynamics simulations in a realistic three dimensional geometry of two stent under physiological conditions. The two stent, similar to real coronary ones, are both made of 12 rings but are differing as far as the position of the struts is concerned. One type has parallel-connectors and the other transverse-ones. The artery is modeled as rigid cylinder and the fluid is assumed as incompressible Newtonian fluid in laminar flow with the average physical properties of blood. The commercial computational fluid dynamic code FLUENT is used with the mesh made of non-uniform tetrahedrons. The mesh independence is proved using the steady state results of the wall shear stress. The parameters correlated to neo-intimal hyperplasia, such as wall shear stress, magnitude of wall shear stress gradient, and oscillatory shear index, are investigated. Time variation of the parameters is investigated with the conclusion that the stent with parallel-connectors has a better fluid dynamic behavior.
On the necessity of modelling fluid–structure interaction for stented coronary arteries
Journal of the Mechanical Behavior of Biomedical Materials, 2014
Although stenting is the most commonly performed procedure for the treatment of coronary atherosclerotic lesions, in-stent restenosis (ISR) remains one of the most serious clinical complications. An important stimulus to ISR is the altered hemodynamics with abnormal shear stresses on endothelial cells generated by the stent presence. Computational fluid dynamics is a valid tool for studying the local hemodynamics of stented vessels, allowing the calculation of the wall shear stress (WSS), which is otherwise not directly possible to be measured in vivo. However, in these numerical simulations the arterial wall and the stent are considered rigid and fixed, an assumption that may influence the WSS and flow patterns. Therefore, the aim of this work is to perform fluid-structure interaction (FSI) analyses of a stented coronary artery in order to understand the effects of the wall compliance on the hemodynamic quantities. Two different materials are considered for the stent: cobalt-chromium (CoCr) and poly-L-lactide (PLLA). The results of the FSI and the corresponding rigid-wall models are compared, especially focusing on the analysis of the WSS distribution. Results showed similar trends in terms of instantaneous and time-averaged WSS between compliant and rigid-wall cases. In particular, the difference of percentage area exposed to TAWSS lower than 0.4 Pa between the CoCr FSI and the rigid-wall cases was about 1.5 % while between the PLLA cases 1.0 %.The results indicate that, for idealized models of a stented coronary artery, the rigidwall assumption for fluid dynamic simulations appears adequate when the aim of the study is the analysis of near-wall quantities like WSS.
Fluid-structure interaction within three-dimensional models of an idealized arterial wall
2014
The ascending branch of the aorta is one of the most stressed organ of the arterial system. We aim to design a biomechanical model for analysing the aorta dynamics under a shock. The model includes the aorta layers and the influence of the blood pressure. We undertake a three-dimensional modal analysis of the coupled aorta-blood system. We determine in the present work the coupled natural frequencies and the modes shapes of the system of the aorta and blood. Three models are presented in this study: three-layers model, twolayers model and one layer model. For the analytical solving a potential technique is used to obtain a general solution for an aorta domain. The finite element model is then validated by these original analytical solutions. The results from the proposed method are in good agreement with numerical solutions. combination of mechanisms including shear, torsion and stretching . These loadings are coupled with the blood pressure and propagation of wave within the aorta. To this end, it seems necessary to include the blood and the vessel undergoing deformation and interacting with the blood flow . In sum, there are still no definitive answers as to what the fundamental mechanisms are that cause this injury, though a great deal of speculation exists on what these might be. However, the high level of reproducibility of the site and nature of blunt traumatic rupture intuitively suggests that there is a reproducible mechanism of injury.
WIT Transactions on the Built Environment, 2005
Blood velocity and pressure fields in large arteries are greatly influenced by the deformability of the vessel. However, computational methods for simulating blood flow in three-dimensional models of arteries have either considered a rigid wall assumption for the vessel or significantly simplified or reduced geometries. Computing blood flow in deformable domains using standard techniques like the ALE method remains a formidable problem for large, realistic anatomic and physiologic models of the cardiovascular system. We have developed a new method to simulate blood flow in three-dimensional deformable models of arteries. The method couples the equations of the deformation of the vessel wall at the variational level as a boundary condition for the fluid domain. We consider a strong coupling of the degrees-of-freedom of the fluid and the solid domains. The effect of the vessel wall boundary is therefore added in a monolithic way to the fluid equations, resulting in a remarkably robust...
Fluid–structure interaction simulation of aortic blood flow
Computers & Fluids, 2011
The numerical tools to simulate blood flow in the cardiovascular system are constantly developing due to the great clinical interest and to scientific advances in mathematical models and computational power. The present work aims to address and validate new algorithms to efficiently predict the hemodynamics in large arteries. These algorithms rely on finite elements simulation of the fluid-structure interaction between blood flow and arterial wall deformation of a healthy aorta. Different sets of boundary conditions are devised and tested. The mean velocity and pressure time evolution is plotted on different sections of the aorta and the wall shear stress distribution is computed. The results are compared with those obtained with a rigid wall simulation. Pulse wave velocity is computed and compared with the values available from the literature. The flow boundary conditions used for the outlets are obtained using the solution of a one-dimensional model. The results of the simulations are in agreement with the physiological data in terms of wall shear stress, wall displacement, pressure waveforms and velocities.