Fluid-Structure Interaction in Biological Media / FSI
Alireza Hashemifard; Nasser Fatouraee; Malikeh Nabaei
Volume 17, Issue 3 , December 2023, , Pages 201-210
Abstract
The crucial responsibility of the aortic valve is to prevent returning of blood flow from the aorta back to the left ventricle. In-time and accurate opening and closing of the aortic valve can effectively produce the desired blood pressure and cardiac output. For this reason, aortic valve simulation ...
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The crucial responsibility of the aortic valve is to prevent returning of blood flow from the aorta back to the left ventricle. In-time and accurate opening and closing of the aortic valve can effectively produce the desired blood pressure and cardiac output. For this reason, aortic valve simulation can identify changes related to aortic valve hemodynamics and their relationship. Diagrams of the left ventricular pressure, the left ventricular pressure difference relative to the aortic artery, GOA, blood flow, the left ventricle pressure-to-volume, the left ventricular energy, kinematic energy density, viscous dissipation, valve resistance, fluid pressure difference in two The surface side of the leaflets, and the momentary pressure difference of the longitudinal axis of the aortic valve compared to the pressure of the aortic artery are reported in this research and based on these, the process of opening and closing of the aortic valve is analyzed using numerical methods named ALE. The moving of the aortic leaflet as the displacement of the solid boundary in the fluid-solid interaction method causes the fluid mesh to undergo displacement and change, which is repaired by the sequence of re-meshing in the fluid domain. In this process, problems occur, the details of which and the resolving method are explained in detail.
Computational Biomechanics
Faeze Jahani; Malikeh Nabaei; Zhenxiang Jiang; Seungik Baek
Volume 16, Issue 4 , March 2023, , Pages 20-30
Abstract
An abdominal aortic aneurysm is a gradual enlargement of the diameter of the aorta, which can threaten the patient's life if it ruptures. Several factors are effective in reducing aneurysm rupture risk and behavior. One of the important factors is the geometric characteristics of the aneurysm. It is ...
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An abdominal aortic aneurysm is a gradual enlargement of the diameter of the aorta, which can threaten the patient's life if it ruptures. Several factors are effective in reducing aneurysm rupture risk and behavior. One of the important factors is the geometric characteristics of the aneurysm. It is necessary to examine the geometric characteristics (shape and maximum diameter) of abdominal aortic aneurysms for each patient to predict the risk of aneurysm rupture and its behavior. Growth and remodeling models based on the finite element method are tools for describing biological characteristics and predicting the progression of diseases such as abdominal aortic aneurysms. In this article, a stress-mediated growth and remodeling model was used to simulate different geometries of abdominal aortic aneurysms with the help of elastin damage function and collagen turnover. The simulation results emphasized the role of elastin damage on the geometrical changes of the aneurysm and the sensitivity of collagen turnover on wall stress distribution and expansion rate, so that with the change of the collagen rate from 0.07 to 0.04, the wall stress increased up to 300 kPa. The results showed that the stress distribution and local expansion correspond to the amount of elastin damage. The elastin damage function plays a key role in determining the location of the maximum diameter and in creating different forms of abdominal aortic aneurysms. Furthermore, time changes have a direct impact on elastin degradation. The remodeling of collagen, which was caused by increasing stress, compensated for the loss of elastin and controlled the expansion rate of the aneurysm. In the future, this computational model will have the ability to depict patient-specific abdominal aortic aneurysm growth with the help of the geometrical changes of the aneurysm, the amount of elastin damage, and collagen remodeling.
Cardiovascular Biomechanics
Sara Barati; Nasser Fatouraee; Malikeh Nabaei
Volume 15, Issue 4 , March 2022, , Pages 355-366
Abstract
Transcatheter aortic valves have become the standard procedure for high-risk patients with severe aortic valve stenosis. This minimally invasive procedure can expand to a wider range of patients with a lower risk of surgery. The complications after the implantation and the structural malfunction of these ...
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Transcatheter aortic valves have become the standard procedure for high-risk patients with severe aortic valve stenosis. This minimally invasive procedure can expand to a wider range of patients with a lower risk of surgery. The complications after the implantation and the structural malfunction of these prostheses are the obstacles of this transition. Design optimization of the stents of these prostheses can improve their performance and reduce the post-operative complications associated with them. Since all prostheses are crimped before implantation, the designs should guarantee an acceptable structural performance after expansion, especially self-expandable stents for which the fatigue behavior strongly depends on the strain. This study applies a simple, cost-effective optimization framework to optimize the geometric parameters of these stents regarding the maximum strain during the crimping process. The design parameters include diameter profile, cell size, number of repeating components, and strut cross-section. The simplified models are evaluated and verified by the 3D simulations. The results show that the middle cells' height, number of cells, and strut width have the most prominent effect on the maximum crimping strain of the stent. The maximum strain of the optimized stent in the selected design space was 0.52. This stent had a width of 0.2 mm, thickness of 0.3 mm, the number of cells and patterns of 3 and 15, respectively, and the diameter profile associated with the diameter ratio of 1.05. This framework can be applied to a wide range of stent designs and tremendously reduce the cost of stent design and optimization.
Fluid-Structure Interaction in Biological Media / FSI
Saeid Siri; Malikeh Nabaei; Nasser Fatouraee
Volume 9, Issue 3 , December 2015, , Pages 229-241
Abstract
Every organ has its own metabolic and functional requirements and needs a variable amount of blood; hence, autoregulation is an important phenomenon. Shear stress induced autoregulation is defined as the innate ability of an organ to keep its hemodynamic conditions stable against changes in heart rate ...
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Every organ has its own metabolic and functional requirements and needs a variable amount of blood; hence, autoregulation is an important phenomenon. Shear stress induced autoregulation is defined as the innate ability of an organ to keep its hemodynamic conditions stable against changes in heart rate and perfusion pressure. For example, when heart rate changes arterial vessels undergo vasodilation or vasoconstriction in order to stabilize the hemodynamic forces and stresses with respect to the flow needed. The current study examines the local mechanisms employed in automatic control. Local regulatory mechanisms function independently of external control mechanisms, such as sympathetic nerves and endocrine hormones. Therefore, they can be considered isolated mechanisms. The application of boundary conditions in numerical modeling is of utmost importance, hence, using arterial tree modeling to achieve appropriate boundary conditions seems necessary. Thus, we have presented a zero-dimensional (lumped parameter) extensive model first. Then, we used this model to achieve boundary conditions for the common carotid artery. As one of the most important hemodynamic parameters, shear stress regulation will then be modeled in an axisymmetric model of this artery.
