Now showing1 - 3 of 3
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Simulation of fluid-structure interactions in arterial bypasses(Springer, 2017-09-18); ; ; Hintergrund Partitionierte Lösungsansätze für Probleme der Fluid-Struktur-Interaktion (FSI) stellen eine flexible Alternative zu monolithischen Ansätzen dar. Die Möglichkeit einer Kombination des klassischen dreidimensionalen (3D-)FSI-Problems mit reduzierten Modellen macht sie v. a. für die Simulation der Hämodynamik im arteriellen System attraktiv. Ziel der Arbeit Es wird entsprechend ein partitionierter Lösungsansatz vorgestellt, der eine solche Kombination und somit eine Untersuchung der Hämodynamik, z. B. im Anastomosenbereich arterieller Bypässe, ermöglicht. Material und Methoden Eine 3D-Simulation der FSI ist aufgrund begrenzter Rechenleistung nur für einen kleinen Ausschnitt des Herz-Kreislauf-Systems möglich. Umliegende Systemabschnitte müssen durch geeignete reduzierte Modelle beschrieben werden. Entsprechende Modelle werden im Rahmen des partitionierten Ansatzes mit dem 3D-FSI-Problem kombiniert. Dieses wird mithilfe der Finite-Elemente-Methode (Struktur bzw. Gefäßwand) und der Finite-Volumen-Methode (Fluid bzw. Blut) diskretisiert. Schlussfolgerung Durch die Verwendung der „quasi-newton least squares method“ können die Stabilitätsprobleme des partitionierten Ansatzes erfolgreich umgangen werden und das gekoppelte Problem effizient gelöst werden. Eine Simulation der Hämodynamik in einer End-zu-Seit-Anastomose zeigt die Möglichkeiten der Simulationsmethode auf.Publicationtype: Review Article81 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Anisotropic hierarchic solid finite elements for the simulation of passive–active arterial wall modelsA 3D anisotropic hierarchic solid finite element formulation is provided for the passive and active mechanical response of arteries. The artery is modeled as an anisotropic nearly incompressible hyperelastic tube consisting of two layers that correspond to the media and the adventitia. These layers are considered as a fiber-reinforced material consisting of two collagen fiber families that are symmetrically disposed and helically oriented around the tube's axis. The numerical analysis is based on a 3D anisotropic hierarchic solid finite element formulation, including the possibility of varying the polynomial degree in all local directions as well as for all displacement components. For the purpose of verification, analytical solutions are provided for different benchmarks focusing on the aspects of compressible and incompressible 3D stretch, plane strain and plane stress pure shear, as well as a mono-layer anisotropic incompressible circular cylindrical artery of Holzapfel–Gasser–Ogden material under inflation and extension. The resulting solutions, including stress and strain distribution through the arterial wall, are plotted to point out the passive response and different activation levels. In addition the effect of various compressibility levels, including nearly incompressibility, is studied by numerical examples. The robustness and accuracy of the proposed method is demonstrated by comparing the results of different ansatz spaces.Publicationtype: Journal Article112 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , The influence of geometric imperfections in cardiovascular FSI simulationsWe present a study of the fluid–structure interaction in an idealized end-to-end anastomosis of a vascular bypass-graft and an artery. Special attention is paid to the impact of geometric imperfections in the artery and the flow path of the upstream vessel segment on the hemodynamics. A partitioned solution approach is applied and developed further to solve the coupled problem in an implicit manner. To stabilize and accelerate the convergence of the staggered coupling iterations, an interface quasi-Newton least squares method is applied. While the finite volume method is used for the fluid mechanics subproblem, high-order finite elements serve to discretize the structural subproblem. A convergence study shows the efficiency of the high-order elements in the context of nearly incompressible, anisotropic materials used to model circular and irregular-shaped segments of an artery. The fluid–structure interaction simulations reveal a dominant influence of the upstream vessel’s curvature, which, however, decays rapidly in straight sections where the influence of geometric imperfections is dominant. Based on the proposed simulation approach, hemodynamic parameters such as the oscillating shear index can be directly linked to the shape and the intensity of the imperfections.Publicationtype: Journal Article110