Papers by Adelia Sequeira
Applied Mathematics and Computation, Feb 1, 2011
The aim of this paper is to describe and discuss the results of numerical comparative study perfo... more The aim of this paper is to describe and discuss the results of numerical comparative study performed in order to demonstrate and quantify some of the most relevant non-Newtonian characteristics of blood flow in medium-sized blood vessels, namely its shear-thinning and viscoelastic behavior. The models studied in this work are the classical Newtonian and Oldroyd-B models, as well as their generalized (shear-thinning) modifications. Numerical tests are performed on three-dimensional geometries, namely an idealized axisymmetric stenosis and a realistic stenosed carotid bifurcation reconstructed from medical images. The numerical solution of the system of governing equations is obtained by a finite-volume method on a structured grid. Model sensitivity tests are achieved with respect to the characteristic flow rate to evaluate its impact on the observed non-Newtonian effects.
Journal of physics, Nov 1, 2022
This paper presents selected numerical simulations performed using Johnson–Segalman model with sp... more This paper presents selected numerical simulations performed using Johnson–Segalman model with specific setting of the convected derivative resulting in shear-thinning behavior of the model. The results are compared with the generalized Oldroyd-B model, which is typically used to simulate shear-thinning viscoelastic flows. Both models are solved using an in-house finite-volume solver on structured grid simulating steady flow in three-dimensional axisymmetric channel with smooth contraction. The results presented here focus on the flow recirculation behind the contraction and the structure of the forces emanating from the viscoelastic stress tensor.
Fluids, Jan 14, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
AIP Conference Proceedings, 2009
The present paper discusses the influence and importance of the application of generalized Newton... more The present paper discusses the influence and importance of the application of generalized Newtonian and generalized viscoelastic models to blood flow simulations. A simple shear-thinning viscosity model together with a Oldroyd-B model for the viscoelastic part of the stress was applied to a simplified test case of stenosed vessel. The direct comparison between results of Newtonian and non-Newtonian flows is
The main goal of this presentation is to demonstrate and discuss the differences between the resu... more The main goal of this presentation is to demonstrate and discuss the differences between the results of numerical simulations of blood flows obtained using generalized Newtonian and generalized Oldroyd-B models. Several idealized blood vessel geometries are assumed to simulate some of the representative blood flow conditions found in living organisms. Numerical solution of the corresponding governing systems of PDE's is carried out using an original numerical code based on finite-volume semi-discretization on structured grids. A simplified explicit Runge-Kutta multistage scheme is applied for time-integration.
Fluids, 2022
This paper presents a numerical comparison of viscoelastic shear-thinning fluid flow using a gene... more This paper presents a numerical comparison of viscoelastic shear-thinning fluid flow using a generalized Oldroyd-B model and Johnson–Segalman model under various settings. Results for the standard shear-thinning generalization of Oldroyd-B model are used as a reference for comparison with those obtained for the same flow cases using Johnson–Segalman model that has specific adjustment of convected derivative to assure shear-thinning behavior. The modeling strategy is first briefly described, pointing out the main differences between the generalized Oldroyd-B model (using the Cross model for shear-thinning viscosity) and the Johnson–Segalman model operating in shear-thinning regime. Then, both models are used for blood flow simulation in an idealized stenosed axisymmetric vessel under different flow rates for various model parameters. The simulations are performed using an in-house numerical code based on finite-volume discretization. The obtained results are mutually compared and dis...
Lecture Notes in Mathematics, 2018
The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Proceedings of the 3rd International Conference on Simulation and Modeling Methodologies, Technologies and Applications, 2013
This paper presents selected numerical results obtained using a macroscopic blood coagulation mod... more This paper presents selected numerical results obtained using a macroscopic blood coagulation model coupled with a non-linear viscoelastic model for blood flow. The governing system is solved using a central finitevolume scheme employing an explicit Runge-Kutta time-integration. An artificial compressibility method is used to resolve the pressure. A non-linear TVD filter is applied for stabilization. A simple test case of blood flow over a clotting surface in a straight 3D vessel is solved. This work merges and significantly extends our previous studies (Bodnár and Sequeira, 2008) and (Bodnár et al., 2011a).
Journal of Mechanics in Medicine and Biology, 2020
Aortic dilation is associated with congenital bicuspid aortic valve (BAV) disease, and its etiolo... more Aortic dilation is associated with congenital bicuspid aortic valve (BAV) disease, and its etiology is still not completely understood. The aim of this study is to provide further insight into aortic hemodynamics in a BAV population with different degrees of aortic dilation and regurgitation in comparison with a patient without pathology. A fluid–structure interaction (FSI) numerical approach is implemented regarding patient-specific geometries, where the aortic valves are defined by analytical orifices. Results show that, while the patient without pathology displays a typical hemodynamic behavior of flows in bends, BAV-related aortas present an accelerated flow along the outer aortic wall. Wall shear stress (WSS) overload in the outer curvature is observed, more marked in more dilated aortas. Moreover, helices in the ascending aorta are present in these patients, enhanced with greater dilation. These findings support the fact that hemodynamic factors play an important role in aorti...
Mathematical Modelling of Natural Phenomena, 2019
The review presents the state of the art in the atherosclerosis modelling. It begins with the bio... more The review presents the state of the art in the atherosclerosis modelling. It begins with the biological introduction describing the mechanisms of chronic inflammation of artery walls characterizing the development of atherosclerosis. In particular, we present in more detail models describing this chronic inflammation as a reaction-diffusion wave with regimes of propagation depending on the level of cholesterol (LDL) and models of rolling monocytes initializing the inflammation. Further development of this disease results in the formation of atherosclerotic plaque, vessel remodelling and possible plaque rupture due its interaction with blood flow. We review plaque-flow interaction models as well as reduced models (0D and 1D) of blood flow in atherosclerotic vasculature.
Lecture Notes in Mathematics, 2018
Experimental studies over many years have shown that blood flow exhibits non-Newtonian characteri... more Experimental studies over many years have shown that blood flow exhibits non-Newtonian characteristics such as shear-thinning, viscoelasticity, yield stress and thixotropy. The complex rheology of blood is influenced by numerous factors including plasma viscosity, hematocrit and in particular, the ability of erythrocytes to form aggregates when at rest or at low shear rates and to deform at high shear rates, storing and releasing energy. Hemodynamic analysis of blood flow in vascular beds and prosthetic devices requires the rheological behavior of blood to be characterized by phenomenological constitutive equations relating the stress to the rate of deformation and flow. The objective of this chapter is to present a short overview of some macroscopic constitutive models that can mathematically characterize the rheology of blood and describe their known phenomenological properties. Some test cases formulated in idealized and anatomically realistic vessels will be considered to investigate the impact of the most significant non-Newtonian characteristics of blood on its flow behavior, based on numerical simulations of different blood constitutive equation under given sets of physiological flow conditions.
Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2019
The analysis of medical image data currently requires the interpretation of a trained and experie... more The analysis of medical image data currently requires the interpretation of a trained and experienced user. The technological advances in imaging machinery and the understanding of disease onset, as well as medical planning, all favour the need for ever more automatic and robust methods for evaluating the health state of a subject. Here, we concentrate on methods for processing medical image data, as currently provided by existing imaging technologies, in particular the effectiveness of automatic image filtering in order to remove noise and improve the sharpness of distinct objects. The filtering approach is based on a partial differential equation, namely the Perona-Malik anisotropic diffusion equation. The approach adopted for terminating the iterative filtering procedure is based on image quality descriptors. In specific, we observe the rate of change of these to infer the transient effects of the filtering process. The entire pipeline is demonstrated to work effectively on different sets of medical image data, including MRI, CTA and CT, both in individual 2-D images in a stack, as well as treating the complete 3D volumetric dataset.
Computing and Visualization in Science, 2004
Applied Mathematics for Industrial Flow Problems (AMIF) is a five-year programme funded by the Eu... more Applied Mathematics for Industrial Flow Problems (AMIF) is a five-year programme funded by the European Science Foundation (ESF) (http://www.esf.org) which started in 1997 and ended in 2002. The overall goal of its scientific programme was to increase understanding of the mathematics underlying models of realistic flows and to improve methods and new approaches for their numerical solution in three main areas: fluid dynamics, nonlinear analysis and numerical analysis. These aims were attained by combining cooperation and expertise from different European research groups represented in the AMIF steering committee led by Pierre-Louis Lions (chairman) and Alfio Quarteroni (co-chairman). The AMIF programme included specialized workshops to discuss progress in particular topics. Tutorials and training sessions were organized for researchers from industry and universities and fellowships were offered to young researchers. Moreover three international conferences spanning the whole research field have been organized during the five-year programme to highlight recent advances, to stimulate discussions and to share ideas for future trends in research. The first conference took place in Spain, at San Feliu de Guixols (Barcelona) on
Fluids, 2019
The region where the vascular lumen meets the surrounding endothelium cell layer, hence the inter... more The region where the vascular lumen meets the surrounding endothelium cell layer, hence the interface region between haemodynamics and cell tissue, is of primary importance in the physiological functions of the cardiovascular system. The functions include mass transport to/from the blood and tissue, and signalling via mechanotransduction, which are primary functions of the cardiovascular system and abnormalities in these functions are known to affect disease formation and vascular remodelling. This region is denoted by the near-wall region in the present work, and we outline simple yet effective numerical recipes to analyse the near-wall flow field. Computational haemodynamics solutions are presented for six patient specific cerebral aneurysms, at three instances in the cardiac cycle: peak systole, end systole (taken as dicrotic notch) and end diastole. A sensitivity study, based on Newtonian and non-Newtonian rheological models, and different flow rate profiles, is effected for a s...
Computer Methods in Biomechanics and Biomedical Engineering, 2019
Bicuspid aortic valve (BAV) aortopathy remains of difficult clinical management due to its hetero... more Bicuspid aortic valve (BAV) aortopathy remains of difficult clinical management due to its heterogeneity and further assessment of related aortic hemodynamics is necessary. The aim of this study was to assess systolic hemodynamic indexes and wall stresses in patients with diverse BAV phenotypes and dilated ascending aortas. The aortic geometry was reconstructed from patient-specific images while the aortic valve was generated based on patient-specific measurements. Physiologic material properties and boundary conditions were applied and fully coupled fluid-structure interaction (FSI) analysis were conducted. Our dilated aortic models were characterized by the presence of abnormal hemodynamics with elevated degrees of flow skewness and eccentricity, regardless of BAV morphotype. Retrograde flow was also present. Both features, predicted by flow angle and flow reversal ratios, were consistently higher than those reported for non-dilated aortas. Right-handed helical flow was present, as well as elevated wall shear stress (WSS) on the outer ascending aortic wall. Our results suggest that the abnormal flow associated with BAV may play a role in aortic enlargement and progress it further on already dilated aortas.
SIAM Journal on Applied Mathematics, 2017
Some of the authors of this publication are also working on these related projects: Modélisation ... more Some of the authors of this publication are also working on these related projects: Modélisation mathématique des écoulements sanguins avec applications à l'athérosclérose et autre maladies View project Asymptotics and Simulation of Complex Fluids View project
Open Access Bioinformatics, 2016
Medical imaging provides a high-fidelity, noninvasive, or minimally invasive means for effective ... more Medical imaging provides a high-fidelity, noninvasive, or minimally invasive means for effective diagnostic and routine checks, and has become an established tool in both clinical and research settings. The interpretation of medical images commonly requires analysis by an experienced individual with the necessary skills. This dependence on an individual's evaluation in part limits the broader scope and widespread use of medical images that would be possible if performed automatically. The analysis of medical images by an individual may also influence reliability, with different users attaining alternative conclusions from the data set. It is thus beneficial to support the experienced user with robust and fast processing of the medical images for further analysis that relies as little as possible on user interaction. In the existing body of literature, a variety of methods have been proposed for medical image filtering and enhancement, which have been largely used in the context of improving image quality for both human visual perception and feature detection and object segmentation via a numerical algorithm. In this study, an analysis of some popular methodologies for image processing is presented. From the comparison of results, a robust and automatic pipeline procedure for medical image processing is put forward, and results for different imaging-acquisition techniques are given.
International Journal of Engineering Science, 2016
This paper presents an analysis of hyperelastic constitutive models for continuous bodies both fr... more This paper presents an analysis of hyperelastic constitutive models for continuous bodies both from a modeling and numerical point of view. Contributions are made within the context of finite element numerical simulations. Numerical results with relevance to flows in the cardiovascular system are outlined in the case of a sophisticated fluid-structure interaction problem, in specific complex geometries of anatomically accurate cerebral arteries in diseased state. In this regard, the work carefully outlines the numerical validation of constitutive models for healthy and unhealthy cerebral arterial tissues by means of simulations of static inflation tests on an idealized specimen of anterior cerebral artery (ACA). The healthy tissue is described by means of isotropic and anisotropic models that, are fitted with respect to experimental data describing the mechanical behavior of the ACA; the numerical results are presented highlighting the most important numerical aspects influencing the correct and efficient simulation of the mechanics of continuous bodies such as, for instance, the arterial wall. We further consider numerical simulations of unhealthy conditions of the tissue by taking into account different levels of weakening of its mechanical properties. Taking the cerebral cardiovascular system as a challenging test problem, we focus on the study of the effects of the imposed mechanical levels of degradation on kinematic quantities of interest by simulating static inflation tests for the different models. This work does not aim to propose a new mathematical model for the mechanical damage occurring at the onset of cardiovascular diseases such as cerebral aneurysms. The modelling and numerical techniques presented may be applied to a wide range of problems, equally challenging to that of the cardiovascular system with complex structural models and fluid-structure coupling.
Mathematical Modelling of Natural Phenomena, 2015
This review is devoted to recent developments in blood flow modelling. It begins with the discuss... more This review is devoted to recent developments in blood flow modelling. It begins with the discussion of blood rheology and its non-Newtonian properties. After that we will present some modelling methods where blood is considered as a heterogeneous fluid composed of plasma and blood cells. Namely, we will describe the method of Dissipative Particle Dynamics and will present some results of blood flow modelling. The last part of this paper deals with onedimensional global models of blood circulation. We will explain the main ideas of this approach and will present some examples of its application.
Computers & Mathematics with Applications, 1999
In this article, we present a new numerical method for solving the steady Oseen equations in an u... more In this article, we present a new numerical method for solving the steady Oseen equations in an unbounded plane domain. The technique consists in coupling the boundary integral and the finite element methods. An artificial smooth boundary is introduced separating an interior inhomogeneons region from an exterior homogeneous one. The solution in exterior region is represented by an integral equation over the artificial boundary. This integral equation is incorporated into a velocity-preseure formulation for the interior region, and a finite element method is used to approximate the resulting variational problem. Finally, the optimal error estimates of the numerical solution are derived. Computer results will be discussed in a forthcoming paper.
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Papers by Adelia Sequeira