Numerical Study on Fluid-Structure Interaction in a Patient-Specific Abdominal Aortic Aneurysm for Evaluating Wall Heterogeneity and Material Model Effects on its Rupture

Abdominal Aortic Aneurysm (AAA) is one of the main cardiovascular diseases, which threats human’s health while it appears, develops and in crucial cases ruptures and leads to hemorrhage. In the current work, we aim to investigate numerically the transient blood flow in a patient-specific AAA model, while effects of wall compliance is considered by employing the fluid-structure interaction method. The AAA model is reconstructed from acquired CT angiographic data of a patient diagnosed with AAA and an intraluminal thrombus (ILT). For the comparison purposes two different material models, i.e. isotropic and anisotropic are considered. Additionally, to have a better estimation, wall thickness variability is compared with simpler uniform wall thickness model. In this study Navier-Stokes equations along with elastodynamics equation are coupled through Arbitrary Lagrangian-Eulerian formulation method and solved numerically. Findings demonstrate that the isotropic material model with uniform wall thickness significantly underestimates wall stresses as compared to the anisotropic material model with variable wall thickness. Indeed, results emphasize that considering vessel wall as an anisotropic, heterogeneous (variable thickness) structure estimates much higher wall stresses comparing with isotropic, uniform thickness model. Therefore, given realistic vessel wall structure and the fact that the anisotropic, variable wall thickness model predicts higher wall stresses, it could be a more reliable model to give an accurate estimation to physicians to diagnose the stage of a disease and choosing an appropriate therapeutic procedure

Effects of Ageing on Aortic Circulation During Atrial Fibrillation; a Numerical Study on Different Aortic Morphologies

From Springer Nature via Jisc Publications RouterHistory: received 2020-11-09, registration 2021-02-01, accepted 2021-02-01, pub-electronic 2021-03-02, online 2021-03-02, pub-print 2021-09Publication status: PublishedAbstract: Atrial fibrillation (AF) can alter intra-cardiac flow and cardiac output that subsequently affects aortic flow circulation. These changes may become more significant where they occur concomitantly with ageing. Aortic ageing is accompanied with morphological changes such as dilation, lengthening, and arch unfolding. While the recognition of AF mechanism has been the subject of numerous studies, less focus has been devoted to the aortic circulation during the AF and there is a lack of such investigation at different ages. The current work aims to address the present gap. First, we analyse aortic flow distribution in three configurations, which attribute to young, middle and old people, using geometries constructed via clinical data. We then introduce two transient inlet flow conditions representative of key AF-associated defects. Results demonstrate that both AF and ageing negatively affect flow circulation. The main consequence of concomitant occurrence is enhancement of endothelial cell activation potential (ECAP) throughout the vascular domain, mainly at aortic arch and descending thoracic aorta, which is consistent with some clinical observations. The outcome of the current study suggests that AF exacerbates the vascular defects occurred due to the ageing, which increases the possibility of cardiovascular diseases per se

Feasibility and validation of trans-valvular flow derived by four-dimensional flow cardiovascular magnetic resonance imaging in patients with atrial fibrillation

Background: Four-dimensional (4D) flow cardiovascular magnetic resonance imaging (MRI) is an emerging technique used for intra-cardiac blood flow assessment. The role of 4D flow cardiovascular MRI in the assessment of trans-valvular flow in patients with atrial fibrillation (AF) has not previously been assessed. The purpose of this study was to assess the feasibility, image quality, and internal validity of 4D flow cardiovascular MRI in the quantification of trans-valvular flow in patients with AF. Methods: Patients with AF and healthy controls in sinus rhythm underwent cardiovascular MRI, including 4D flow studies. Quality assurance checks were done on the raw data and streamlines. Consistency was investigated by trans-valvular flow assessment between the mitral valve (MV) and the aortic valve (AV). Results: Eight patients with AF (88% male, mean age 62±13 years, mean heart rate (HR) 83±16 beats per minute (bpm)) were included and compared with ten healthy controls (70% male, mean age 41±20 years, mean HR 68.5±9 bpm). All scans were of either good quality with minimal blurring artefacts, or excellent quality with no artefacts. No significant bias was observed between the AV and MV stroke volumes in either healthy controls (–4.8, 95% CI –15.64 to 6.04; P=0.34) or in patients with AF (1.64, 95% CI –4.7 to 7.94; P=0.56). A significant correlation was demonstrated between MV and AV stroke volumes in both healthy controls (r=0.87, 95% CI 0.52 to 0.97; P=0.001) and in AF patients (r=0.82, 95% CI 0.26 to 0.97; P=0.01). Conclusions: In patients with AF, 4D flow cardiovascular MRI is feasible with good image quality, allowing for quantification of trans-valvular flow

The Numerical Study of the Gas-Solid Flow in a Conventional Cyclone Separator

This paper presents a numerical study of the gas–powder flow in a typical Lapple cyclone with division of gas and particle flow in a vortex finder. The Navier-Stokes equations along with the RNG k-ε turbulent model are solved numerically. The separation efficiency and the trajectory of particles are simulated and the effects of the particle size on the separation efficiency and the particle residence time are investigated. The effect of the particle density on the particle size in the range which results 100% cyclone separation efficiency and particle residence time is investigated. Large particles generally have a higher concentration in the wall region and small particles have a higher concentration in the inner vortex region. The particles enter from different sides give different separation efficiency and trajectory. A particle with a size exceeding a critical diameter or a critical density would stagnate on the wall of the cyclone’s cone. This phenomenon is regarded as a main reason for the deposition on the inner conical surface in such cyclones used in the cement industry