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Computational modelling of blood flow in the carotid artery with serial stenosis
Lukáš, Petr ; Hájek, Petr (referee) ; Švancara, Pavel (advisor)
The aim of this bachelor's thesis is to analyse the effect of double stenosis on flow and stress characteristics in the carotid artery. First, based on the stated literature, a literature search is conducted regarding blood flow in the arterial system. Then, the procedure of creating idealized models of an artery with double stenosis and the procedure of mesh creation and numerical solution are described. The models have different size of the stenosis and different distance between stenosis. In the final stage, the results are analysed first for stationary flow, then one model is selected on which is performed the analysis for pulsating flow. Analytical calculation of pressure drop and comparison with numerical calculation is also part of this work.
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Comparison of Pulsating Flow of Newtonian and non-Newtonian Fluid in Complex Geometry
Kohút, Jiří ; Rudolf, Pavel (referee) ; Jagoš, Jiří (advisor)
This master's thesis deals with pulsating flow of Newtonian and non-Newtonian fluid. Theoretical part represents necessary theoretical knowledge for pulsating flow and understanding of non-Newtonian behaviour. Furthermore the thesis focus is directed on numerical simulation of pulsating flow in straight, ideally rigid tube and in patient-specific model of human artery, more precisely in carotid. Two methods are used: numerical solution based on finite volume method (FVM) and also analytical solution using Bessel functions by Womersley. Results are validated against experimental measurements of velocity profiles by particle image velocity method (PIV). The agreement between numerical and experimental data with consideration of PIV inaccuracy was was very good from both point of views - qualitative and quantitative. Numerical solution also compare influence of turbulence and non-Newtonian behaviour towards base (laminar flow, Newtonian fluid). Developed methodology is then applied on patient-specific model of carotid, which was renovated from computed tomography. Measurements in vivo in human arteries is very expensive and often invasive. Because of that measurement outputs are limited, most of the time on pressure and flow. Computational fluid dynamics (CFD) is non-invasive and outputs are through whole domain. Due to these advantages CFD significantly contributes to understanding of hemodynamics influence in cardiovascular diseases.
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Analysis of impact of mechanical properties of components of pathological arterial wall on its state of stress
Bartoňová, Petra ; Konvalinka, Jan (referee) ; Burša, Jiří (advisor)
The thesis deals with measurements of the atherosclerothic carotid plaques mechanical properties with wiew towards the improvements of their constitutive models and then towards the impact of application of those constitutive models in fibrous cap. The introductory part provides a brief summary of medical knowledge needed to understand atheroma formation and the risks involved. Next, there's a survey of plaque mechanical testing methods and the obtained results on tissue properties. The previously used constitutive models of atherosclerothic tissues are listed as well. Main body of the thesis describes the preparation of testing samples from obtained atheroma, methodology and course of experiments execution and subsequent processing of the experimental data to evaluate the behavior of the atheromatous tissue individual parts. Then the discussion and evaluation of our results and findings is given. Along with the evaluated mechanical properties, experimental data fitted to models are presented with respect to their predictive abilities. The final part is dedvoted to the finite element analysis of an idealized 2D model with emphasis on the effect of necrotic core and fibrous tissue properties on von Mises equivalent stress in the fibrous cap.
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Overview to arterial stents and possibilities of their computational modelling
Ondříšková, Tereza ; Lisický, Ondřej (referee) ; Turčanová, Michaela (advisor)
This bachelor thesis deals with arterial stents and possibilities of their computational modelling. The thesis contains a medical minimum, which is necessary to understand the principle of arterial stents. Furthermore, the thesis is focused on methods of a stent implantation, materials used for manufacturing and covering and the most used designs. There is a research study of analytical and numerical computational modelling of them with emphasis on the finite element method. In the last part of this thesis there was performed an analytical calculation of stress appeared in the carotid artery wall after stent implantation using a simplified model of stent-artery configuration. Then these stress functions were plotted and evaluated.
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Modelling of blood flow in a carotid artery with stenoses
Štefek, Martin ; Hájek, Petr (referee) ; Švancara, Pavel (advisor)
This bachelor's thesis deals with the analysis of blood flow in a carotid artery with stenoses in the area of the bifurcation. The current state of knowledge is presented in the theoretical part. As part of the practical part of the work, several 2D models of the artery with stenoses of dif-ferent sizes and distances were created. An ideal mesh of finite volumes was created and select-ed. Using the ANSYS Fluent program, basic hemodynamic parameters such as flow velocity, wall shear stress, pressure and fractional flow reserve (FFR) were evaluated for stationary flow. A time step was determined for the transient flow, and then the flow speed and shear stress on the walls at points were evaluated as a function of time.
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Computational modelling of the influence of stenoses on blood flow in the carotid artery
Lukáš, Petr ; Hájek, Petr (referee) ; Švancara, Pavel (advisor)
This diploma thesis deals with blood flow in carotid artery with tandem double stenosis. In the first part there is described cardiovascular system with emphasis on blood and arteries. In the practical part, geometric models of the carotid artery with 30% and 70% stenosis, as well as a model without stenosis, are created. The second stenosis is not included in the model of geometry but modeled using Windkessel effect. Blood is modeled as a non-Newtonian fluid using the Carreau model. After the calculations, the blood flow and arterial wall stress are evaluated, and the results are compared among the different geometry models. Critical values of shear stress, TAWSS, OSI, and FFR, as well as the mass flow rate in the internal carotid artery, are assessed.
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Impact of residual stresses and uncoiling of arterial specimen on its mechanical response
Sochor, Ondřej ; Lisický, Ondřej (referee) ; Burša, Jiří (advisor)
This thesis examines the impact of residual stresses in the carotid artery wall and the influence of specimen uncoiling on its mechanical response. The introductory part provides basic knowledge about the anatomy and the pathology of blood vessels, as well as overview of common methods used for testing artery samples. The main body of the thesis is divided into two sections. The first section focuses on the impact of specimen uncoiling on its mechanical response during the equibiaxial tensile test. It begins by describing the method used for sample testing and the method used for obtaining material constants from the mechanical response. These constants are then used as input for FEM simulation of the uncoiling and subsequent equibiaxial tensile test simulation on idealized model of geometry. The mechanical behaviour of the uncoiled model is compared to behaviour of the stress-free planar model to determine the influence of uncoiling. In the second section, the influence of residual stresses in the artery wall on its mechanical response is explored. This section includes a description of two methods used to show residual stress release, which are then used for specimen testing. The experiments are used to evaluate input parameters per layer for the model of geometry and subsequent FEM analysis. By comparing results from three levels of modeling, the impact of residual stresses on the artery’s mechanical response is determined.
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Design of a model of the human carotid artery based on an electrohydraulic analogy
Škrlová, Nikola ; Kohút, Jiří (referee) ; Jagoš, Jiří (advisor)
The carotid artery plays a crucial role in delivering blood to the cerebral system, which ensures the proper function of the human body. Mathematical models of the cardiovascular system have been proposed to understand vascular disease. The main aim of this study is to create mathematical model of the carotid artery, using an electrohydraulic analogy. The most basic or 0D modeling of cardiovascular system includes the two-element Windkessel model. Numerical modeling was carried out in the MATLAB environment. To make the model solvable, it was necessary to determine the initial flow parameters in the common carotid. It was necessary toadjust the resulting pressure curves on the common carotid to the ideal pressure range of a healthy person. A similar process was performed for the flow in the internal carotid. Then a comparison was made with the real measured flow curve. During the verification of the law of mass conservation of the flow, a 6% deviation was discovered. This discrepancy is attributed to the process of obtaining flow values from the equations assembled in Chapter 5, as well as the rounding error inherent in MATLAB itself. This breakthrough combination of science and medicine is primarily beneficial for doctors and patients who are dealing with the disease.
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Stress-strain Analysis of Carotid Arteries with Atheroma
Lisický, Ondřej ; Návrat, Tomáš (referee) ; Vimmr, Jan (referee) ; Burša, Jiří (advisor)
Kardiovaskulární příhody byly a jsou rozšířenou příčinou úmrtí ve většině zemí. Ateroskleróza karotických tepen mnohdy vedoucí k mrtvici je jejich nedílnou součástí. Včasná a vhodně mířená diagnostika rizikových lézí může vést ke snížení kritických příhod, a tím potenciálně snížit počet úmrtí. Porušení nestabilního aterosklerotického plátu je ovlivněno působením sil od proudící krve. V biomechanice měkkých tkání je využíváno výpočtového modelování jakožto potenciálního ukazatele, díky němuž by bylo možné odhalit nestabilitu plátu u pacientů podstupujících pravidelná kontrolní měření. Mechanické veličiny bývají spojovány s klinicky dostupnými ukazateli jako jsou například podstatné rozměry léze nebo přítomnost rizikových komponent. Komplexita a malé rozměry tkáně ovšem stále omezují možnosti tvorby výpočtových modelů a existuje tedy spousta faktorů, které je před možnou implementací do klinických postupů potřeba řádně vyšetřit. Tato práce je členěna do kapitol shrnujících aktuální stav řešené problematiky. Kapitoly jsou doplněny o komentář autorova příspěvku k dané problematice a odkaz na originální práci. Studium problematiky naznačilo velké množství potenciálních směrů výzkumu, což by ovšem nebylo možné zahrnout do jediné práce. Řešená témata se dají rozdělit na: (i) ověření možnosti tvorby 3D výpočtového modelu ze snímků aterosklerotického plátu s následným rozšířením na výpočtovou studii zahrnující řadu faktorů pro ověření vlivu na napjatost, (ii) studium mechanických vlastností aterosklerotických plátů odebíraných z endarterektomie během celé doby řešení, (iii) možnosti analýzy deformačního pole u experimentů zahrnujících měkké tkáně a (iv) experimentální a výpočtovou studii zbytkové deformace, potažmo napětí v souvislosti s karotickými tepnami. Výsledky jednotlivých částí jednoznačně poukázaly na problémy spojené s výpočtovým modelováním jako například časté opomíjení přítomnosti komponent stěny tepny při modelování aterosklerotického plátu, nutnost správného pochopení mechanického chování, ale také na způsob vyhodnocení experimentů s vyšším počtem vzorků. V neposlední řadě bylo ukázáno, že zbytkové napětí nemusí být podstatným faktorem u aterosklerotických plátů karotických tepen.
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Overview to arterial stents and possibilities of their computational modelling
Ondříšková, Tereza ; Lisický, Ondřej (referee) ; Turčanová, Michaela (advisor)
This bachelor thesis deals with arterial stents and possibilities of their computational modelling. The thesis contains a medical minimum, which is necessary to understand the principle of arterial stents. Furthermore, the thesis is focused on methods of a stent implantation, materials used for manufacturing and covering and the most used designs. There is a research study of analytical and numerical computational modelling of them with emphasis on the finite element method. In the last part of this thesis there was performed an analytical calculation of stress appeared in the carotid artery wall after stent implantation using a simplified model of stent-artery configuration. Then these stress functions were plotted and evaluated.
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