Cardiovascular Poster P-22 S395

INFLUENCE OF MODELLING PARAMETERS ON ABDOMINAL AORTIC ANEURYSM STENT-GRAFTS

David Molony, Anthony Callanan, Barry Doyle, Michael Walsh, Tim McGloughlin Centre for applied biomedical engineering research (CABER), Materials and Surface Science Institute and Department of Mechanical & Aeronautical Engineering, University of Limerick, Ireland

Introduction Computational modelling of abdominal aortic aneurysms has been used for a number of years. It has the ability to provide information regarding wall stresses which are complicit in aneurysm rupture and treatment device failure (Fillinger, 2003). Most studies are a simplification of the problem. These include neglecting the movement of the artery walls or the presence of the full aorta. This is commonly due to the increased computer demands with larger models. Recently more researchers have begun to use fluid structure interaction (FSI) (Li, 2006). The aim of this research was to investigate the significance of modelling parameters - namely FSI and the aortic arch - in computational models. Methods Models were reconstructed from CT scans using Mimics (Materialise, Belgium). They were then smoothed so they could be efficiently meshed. Several scenarios were investigated. The first case included a stent-graft by itself, with FSI and CFD simulations. The next model included the aortic arch (figure 1). The final model was the stent-graft with the artery attached upstream. All recreated fluid models were exported to Gambit (Fluent Europe), where a pave surface mesh was swept through the volume. For stand alone CFD models a velocity inlet and pressure outlet were assigned as boundary conditions (Scotti, 2006). The wall was modelled as rigid. Fluent v6.2.16 was used to model the flow. For the FSI models Abaqus v6.6-2 (Simulia, Rhode Island, USA) and Fluent were coupled together via a 3rd party software mesh based parallel code coupling interfcace (MpCCI v3.0.5, Fraunhofer SCAI, Germany). Again velocity inlet and pressure outlet boundary conditions were applied to the fluid model. In the structural model the inlet and outlet regions were rigidly held to simulate tethering to the aorta.

Results FSI of the aorta with the stent-graft results in a compliance mismatch due to the different stiffness’s of the aorta and the graft. This affects the stress patterns and also causes flow distortion. Inclusion of the aortic arch does not greatly affect drag force on the graft, resulting in a small difference (1%). The presence of the aortic arch does however have a stronger influence on the flow in the graft.

Figure 1 Aortic arch with stent-graft Discussion Incorporation of the aortic arch results in a large increase in the number of cells in the model, which has a significant increase in the computational time, but does alter the flow patterns. The additional cost of FSI is not as great. Generally structural meshes consist of a lot less elements than fluid meshes and this was the case here. The time step chosen will also have a large effect on the computational time. Other issues that could affect the results are inclusion of the branches of the aorta and the presence of the aneurysm. References Fillinger et al., J Vasc Surg, 37, 24-32, 2003 Li and Kleinstreuer, J Biomech, 39, 2573-2582, 2006 Scotti et al., Biomed Eng Online, 4:64, 2005

16th ESB Congress, Posters Journal of Biomechanics 41(S1)