Abstract

The aim of this study is to assess how the shape of the abdominal aortic aneurysms (AAA) affects the hemodynamic wall stresses. With this purpose, different AAAs are studied through simplified models based on geometrical parameters of the aneurism such as its maximum and minimum diameter, length and asymmetry. Then, a computational fluid dynamics analysis is performed on the simplified models in order to compute pressure and wall shear stresses on the aneurysm sac. The results obtained show that blood pressure is the main dynamic load acting on the artery wall, and that the morphology of the aneurysm could be a good indicator of risk of failure. Furthermore, the computational results are compared with patient-specific real models with the objective to assess the reliability of the proposed simplified approach.

Abstract

The aim of this work is the study of fluid dynamics models using the CFD software
OpenFOAM, an open source software allowing meshing, manipulation, simulation
and post-processing of many problems involving fluid mechanics.
The work consists of a study with OpenFOAM of a real engineering problem, namely
to analyze hemodynamics in the thoracic aorta in collaboration with CIMNE (Centre
Internacional de Metodes Numerics a l'Enginyeria) and LABSON-UPC (Laboratorio de
Sistemas Oleohidricos y Neumcos). Speci cally, the study aims to compute the
shear stress that blood causes to aorta walls.

Abstract

The immersed boundary method has attracted growing interest in CFD research community due to its simplicity in dealing with moving boundaries. In the diffused interface immersed boundary method, a discrete delta function is introduced to account for the boundary effects on the fluid, which causes the diffusion of the boundary interface. Therefore, the diffused interface immersed boundary method requires higher grid resolution in the vicinity of the immersed boundaries to get a better representation of the boundary. A strategy for the application of diffused interface immersed boundary-lattice Boltzmann method is introduced in the simulation of stenosis. The developed numerical method has been examined in the simulation of stenosis. Results show that the current solver is able to accurately predict the velocity profile within the stenosis.

Abstract

In the current clinical practice, the rupture risk prediction of fusiform aneurysms is based on maximum diameter. This approach does not account for the size and shape dependent cyclic stresses arising due to fluid-solid interaction (FSI). Previous fluid-structure interaction studies by the authors on model two dimensional fusiform aneurysms (abdominal aortic aneurysm (AAA)) has revealed that the maximum diameter to height ratio (DHr) could possibly be used as a critical parameter, since it can signify the hemodynamic and biomechanical stresses [7]. Hence the present study assesses whether the observations from the shape index based 2D simulations hold good in realistic 3D conditions as well. Based on the preliminary investigations, it is hypothesized, that a combination of Dmax and DHr would
be a better indicator of rupture risk.

Abstract

Abstract

Abstract

A comparison between the results of the CFD simulations and the in-vitro experiments carried out on a circulatory mock loop is presented. Both approaches integrate in-vivo measurements obtained from a patient-specific clinical data set. Three thoracic-aorta geometries are analyzed: a healthy aorta, an aneurysmatic aorta, and a coarctated aorta. The healthy geometry is obtained from Magnetic Resonance Imaging (MRI) acquisitions, together with the patient-specific flow-rate waveform, whereas the diseased ones are derived from the former geometry by locally morphing the vessel's wall. The open-source code Simvascular is used for simulations. The in-vitro results are measured in a fully controlled and sensorized circulatory mock loop for 3D-printed aortic models. Differently from in-vivo acquisitions, the experimental set-up eliminates some of the uncontrollable uncertainties that characterize MRI data. Indeed, perfect control of the flow rate and full knowledge of the wall model characteristics (rigid walls in the present case) is allowed in experiments and, thus, clear indications can be obtained to validate and improve the accuracy of numerical models. The numerical and experimental results are in good agreements for the three analyzed geometries and the flow-rate conditions. In-vivo data from the healthy case are in a satisfactory agreement with numerical/in-vitro results, and they can be ascribed to possible differences between MRI and numerical/in-vitro set-ups. The velocity fields obtained through CFD are consistent with the echographic results in in-vitro experiments, showing the same flow patterns in healthy and pathological cases.