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    Item type:Publication, Access status: with files ,
    Adjoint-assisted robust shape optimization of an idealized arterial bypass graft using the FOSM method
    (Springer, 2025-06-01)
    Bletsos, Georgios
    ;
    Radtke, Lars
    ;
    Rung, Thomas
    This paper presents the shape optimization of an idealized arterial bypass graft under uncertainties. The underlying blood flow problem is numerically solved using computational fluid dynamics (CFD) simulations, able to account for mechanical hemolysis and non-Newtonian viscosity properties of blood. The employed hemolysis and non-Newtonian models utilize a set of parameters that are considered uncertain in this work. To this end, the optimization problem is rendered robust and targets the minimization of the first two statistical moments of a hemolysis index. The propagation of the uncertainties to the hemolysis index is done through the first-order second-moment method (FOSM). The necessary derivatives are computed by the adjoint method and finite differences. Several steady-state robust shape optimization simulations of the idealized bypass graft are presented. Selected optimized shapes are further assessed by means of additional fluid–structure interaction (FSI) simulations under unsteady conditions.
    Publicationtype: Journal Article
      28  22
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    Item type:Publication, Access status: without files ,
    Hemodynamics in arterial bypass graft anastomoses with varying cuff sizes and proximal flow paths: a fluid–structure interaction study
    (Taylor & Francis, 2025)
    Bletsos, Georgios
    ;
    Rung, Thomas
    ;
    Radtke, Lars
    This article investigates the effect of the cuff size of arterial bypass grafts and the flow conditions on the hemodynamics in the anastomosis (connection) to the artery, using numerical simulations. We consider a fluid-structure interaction problem which is solved based on a partitioned scheme. Additionally, we employ computational fluid dynamics to investigate the effect of a rigid wall assumption. The work focuses on clinically relevant hemodynamic quantities associated with the development of intimal hyperplasia. We also include a model for the prediction of hemolysis into the simulation. The results show that even minor changes of the cuff size can result into significant differences in the corresponding quantities of interest. The importance of the inflow path is shown to be lower than that of the cuff size. The usually employed rigid wall assumption is found to be adequate to address wall shear stress oscillations but falls short on predicting maximum and minimum wall shear stress-related quantities of interest.
    Publicationtype: Journal Article
      29
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    Item type:Publication, Access status: with files ,
    Parameter-free shape optimization: Various shape updates for engineering applications
    (Multidisciplinary Digital Publishing Institute (MDPI), 2023-08-25)
    Radtke, Lars
    ;
    Bletsos, Georgios
    ;
    Kühl, Niklas
    ;
    Suchan, Tim
    ;
    Rung, Thomas
    In the last decade, parameter-free approaches to shape optimization problems have matured to a state where they provide a versatile tool for complex engineering applications. However, sensitivity distributions obtained from shape derivatives in this context cannot be directly used as a shape update in gradient-based optimization strategies. Instead, an auxiliary problem has to be solved to obtain a gradient from the sensitivity. While several choices for these auxiliary problems were investigated mathematically, the complexity of the concepts behind their derivation has often prevented their application in engineering. This work aims to explain several approaches to compute shape updates from an engineering perspective. We introduce the corresponding auxiliary problems in a formal way and compare the choices by means of numerical examples. To this end, a test case and exemplary applications from computational fluid dynamics are considered.
    Publicationtype: Journal Article
    Scopus© Citations 2  61  180