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Item type:Publication, Access status: without files , Simulation of the fluid-structure interaction of a floating wind turbineIn this paper, we present a method for the analysis of the motion behaviour and also the structural response–stresses and deformations–of a floating wind turbine. A partitioned approach is chosen to solve the fluid-structure interaction problem. Therefore, our C++ library comana, developed to couple various solvers, is enhanced to couple the fluid solver pan MARE and the structural solver ANSYS. Initially, a simple elastic finite element model is used in the coupled analysis. This finite element model is described, and some results of the coupled simulation are presented. In order to use a more detailed finite element model without drastically increasing the computation time, superelements can be employed. This procedure is described and applied to an example, a floating buoy in waves, to demonstrate its applicability in fluid-structure interaction simulations.Publicationtype: Journal Article218 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Partitioned coupling of fluid-structure interaction for the simulation of floating wind turbines(Kassel University Press, 2019); ; ; ; Fluid-structure interaction problems appear in many different fields of application. An interesting and highly topical field is offshore renewable energy. An increasing energy demand, limited fossil energy sources and the climate change in combination with limited suitable and available space ashore lead to an increased relevance of offshore renewable energy. A promising offshore renewable energy concept is the use of floating wind turbines. For the simulation of floating wind turbines, the necessary and computationally expensive fluid-structure interaction coupling has to be combined with large domains, highly nonlinear and dynamic structural behavior and complex flow situations. This requires new and innovative techniques in the solution process. In this work, the partitioned solution utilizing existing field solvers is suitable for this type of problem due to the availability of well-developed fluid and structural solvers. To manage the partitioned coupling, the in-house C++ library comana is employed. This coupling framework is employed to control the iterative solution process and to perform the necessary exchange of surface quantities on the interface between the fluid and structural field of the fluid-structure interaction problem. Through this, comana enables the computation of complex strongly coupled fluid-structure interaction problems within a reasonable amount of time. Despite the necessary changes for the partitioned coupling, the modifications to the existing specialized high-fidelity fluid and structural solvers are minimized to maintain their sophisticated solution techniques. The partitioned coupling procedure is described and simulation results are presented. Different measures to accelerate, stabilize and improve the solution of this fluid-structure interaction problem are demonstrated. Among these measures are the prediction and the convergence acceleration in the implicit coupling of the fluid and structural field solvers. In the scope of a future research project, the presented method will be applied to develop the simulation of a point wave energy absorber used for the conversion of wave energy into electric energy.Publicationtype: Conference Paper257 171 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 261 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Adjoint shape optimization for fluid–structure interaction of ducted flows(2018-03-01); ; ; Based on the coupled problem of time-dependent fluid–structure interaction, equations for an appropriate adjoint problem are derived by the consequent use of the formal Lagrange calculus. Solutions of both primal and adjoint equations are computed in a partitioned fashion and enable the formulation of a surface sensitivity. This sensitivity is used in the context of a steepest descent algorithm for the computation of the required gradient of an appropriate cost functional. The efficiency of the developed optimization approach is demonstrated by minimization of the pressure drop in a simple two-dimensional channel flow and in a three-dimensional ducted flow surrounded by a thin-walled structure.Publicationtype: Review Article217 - 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 , 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 - 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 , A flexible C++ framework for the partitioned solution of strongly coupled multifield problems(2016-10-01); ; In this work, we present a flexible and generic C++ framework for the numerical solution of strongly coupled multifield problems, based on a partitioned approach. Coupled problems occur in a wide range of engineering applications, and their numerical treatment has recently gained much attention. We advocate a partitioned solution approach that enables the use of different discretization schemes and different solvers for the individual fields. Highly optimized, existing solvers can thus be reused—which enhances modularity, reusability, and performance. However, depending on the problem at hand, appropriate measures must be taken to stabilize the solution process and accelerate its convergence. In addition, the field quantities of interest need to be transferred between the solvers. To this end, we developed the software framework comana, which facilitates the implementation of different coupling strategies for a vast range of multifield problems. Interaction with the solvers is achieved through a uniform interface to the solvers’ databases. Interfaces for solvers for which there is no interface available yet can be implemented with minimum effort.Publicationtype: Journal Article215 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Convergence acceleration for partitioned simulations of the fluid-structure interaction in arteries(2016-06-01); ; ; We present a partitioned approach to fluid-structure interaction problems arising in analyses of blood flow in arteries. Several strategies to accelerate the convergence of the fixed-point iteration resulting from the coupling of the fluid and the structural sub-problem are investigated. The Aitken relaxation and variants of the interface quasi-Newton -least-squares method are applied to different test cases. A hybrid variant of two well-known variants of the interface quasi-Newton-least-squares method is found to perform best. The test cases cover the typical boundary value problem faced when simulating the fluid-structure interaction in arteries, including a strong added mass effect and a wet surface which accounts for a large part of the overall surface of each sub-problem. A rubber-like Neo Hookean material model and a soft-tissue-like Holzapfel-Gasser-Ogden material model are used to describe the artery wall and are compared in terms of stability and computational expenses. To avoid any kind of locking, high-order finite elements are used to discretize the structural sub-problem. The finite volume method is employed to discretize the fluid sub-problem. We investigate the influence of mass-proportional damping and the material model chosen for the artery on the performance and stability of the acceleration strategies as well as on the simulation results. To show the applicability of the partitioned approach to clinical relevant studies, the hemodynamics in a pathologically deformed artery are investigated, taking the findings of the test case simulations into account.Publicationtype: Journal Article65