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Effect of fiber direction around the hole in longfiber composite on the stress distribution
Tulis, Vojtěch ; Majer, Zdeněk (referee) ; Polzer, Stanislav (advisor)
The bachelor thesis focuses on stress distribution of longfiber composite with a hole, mainly on the influence of fiber direction on the stress distribution around such a hole. To look into the problem closely some samples of common longfiber composites have been simulated in the software environment of Ansys. These samples were analyzed on the final stress distribution – first without any change of the direction of fibers and then with different models of control. Subsequently, all the data were processed and assessed.
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Stress-Strain Analysis of Aortic Aneurysms
Polzer, Stanislav ; Holeček, Miroslav (referee) ; Horný, Lukáš (referee) ; Burša, Jiří (advisor)
Tato práce se zabývá problematikou aneurysmat břišní aorty a možností využít konečnoprvkovou deformačně-napěťovou analýzu těchto aneurysmat ke stanovení rizika ruptury. První část práce je věnována úvodu do problematiky, popisu kardiovaskulární soustavy člověka s důrazem na abdominální aortu, anatomii, fyziologii a patologii stěny tepny s důrazem na procesy vedoucí ke vzniku aneurysmatu. Dále se práce věnuje rizikovým faktorům přispívajících ke vzniku aneurysmat spolu s analýzou současných klinických postupů ke stanovení rizika ruptury spolu se srovnáním navrhovaného kritéria maximálního napětí. Dominantní část této disertace je věnována identifikaci faktorů ovlivňujících napjatost a deformaci stěny aneurysmatu spolu s návrhem nových postupů, prezentací vlastních poznatků vedoucích ke zpřesnění určení rizika ruptury pomocí deformačně- napěťové analýzy a metody konečných prvků. Nejprve je analyzován vliv geometrie, vedoucí k závěru, že je nezbytné používání individuálních geometrií pacienta. Dále je pozornost zaměřena na odbočující tepny, které ve stěně působí jako koncentrátor napětí a mohou tedy ovlivňovat napjatost v ní. Jako další podstatný faktor byl identifikován vliv nezatížené geometrie a bylo napsáno makro pro její nalezení, které bylo opět zahrnuto jako standardní součást do výpočtového modelu. Mechanické vlastnosti jak stěny aneurysmatu, tak intraluminálního trombu jsou experimentálně testovány pomocí dvouosých zkoušek. Také je zde analyzován vliv modelu materiálu, kde je ukázáno, že srovnávání maximálních napětí u jednotlivých modelů materiálu není vhodné díky zcela rozdílným gradientům napětí ve stěně aneurysmatu. Dále je zdůrazněna potřeba znalosti distribuce kolagenních vláken ve stěně a navržen program k jejímu získání. Intraluminální trombus je analyzován ve dvou souvislostech. Jednak je ukázán vliv jeho ruptury na napětí ve stěně a jednak je analyzován vliv jeho poroelastické struktury na totéž. Posledním identifikovaným podstatným faktorem je zbytková napjatost ve stěně. Její významnost je demonstrována na několika aneurysmatech a i tato je zahrnuta jako integrální součást do našeho výpočtového modelu.Na závěr jsou pak navrženy další možné směry výzkumu.
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Computer simulations of biaxial tension tests of soft biological tissues
Slažanský, Martin ; Návrat, Tomáš (referee) ; Polzer, Stanislav (advisor)
Within the master thesis a computational model of biaxial tension test of soft biological tissues was developed. The tested specimen can be attached using clamps or hooks. The number and the size of clamps and hooks have a significant impact on the distribution of stress and strain in the centre of the specimen, where deformation is measured. Using the developed computational model, a sensitivity analysis of number and size of clamps and hooks and a sensitivity analysis of placement of clamps was elaborated. The number and size of clamps and hooks were optimized in such a way that the material’s parameters obtained by the tension test correspond to the utmost to the actual parameters of the material. By analyzing the placement of clamps, the influence of selected deviations on the outcome of the tension test was determined. Finally, a plan of the next course of action has been proposed.
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Deriving and Application of Analytical Design of Hammerspring in Firearms
Vobejda, Radek ; Polzer, Stanislav (referee) ; Slažanský, Martin (advisor)
The thesis deals with inference of analytic relations for calculation of pressure helical coil spring and considerates usage possibilities of simplified relations. In the thesis there is introduced analytic computation of slightly curvatured rod theory completed by finite element method calculations. The thesis describes two springs of firearm, which weren’t able to achieve required functionality. After this there was created a plan of concept particular spring on the base of derivated relations, which should be able to meet operative conditions.
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Proposal of a program for solving of problems of simple tension/compression of bars and strut frames
Martínek, Tomáš ; Kubík, Petr (referee) ; Polzer, Stanislav (advisor)
The aim of this work is a program that will solve problems from the simple tension /compression bars and strut frames in the range of bachelor. The work consists of two programs developed in the Borland Delphi development environment. The programs allow the user to define a bar (strut frames) on the basis of the geometrical parameters and constraints, determine the rate of statical indetermination, make the necessary calculations and, if necessary, indicate the condition of deformation (a program for solving bars). The written part of the work serves as a manual.
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Design of laminate handlebars for mountain bikes
Hanák, Jiří ; Ševeček, Oldřich (referee) ; Polzer, Stanislav (advisor)
This bachelor’s thesis describes design of laminate handlebars for mountain bikes. The first part describes the mechanical properties of composite materials, with the emphasis on fiber composites. The algorithm for acquiring material characteristics of fiber composite by analytical method is presented. In the next part, it is shown how to control the direction of fibers in lam-inate in the finite element calculations and its impact to resulting stresses in the material. The aim of the last part is design geometry model of laminate handlebars for mountain bikes with following stress – strain analysis by FEM and software ANSYS. The analysis is performed for static loading.
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Literature search of possibilities of computational modelling of brain aneurysms
Lipenský, Zdeněk ; Polzer, Stanislav (referee) ; Burša, Jiří (advisor)
This bachelor thesis is focused on gathering general information about a cerebrovascular disorder called Cerebral Aneurysm (or also Brain Aneurysm) which is a medical condition consisting in an abnormal bulging outward of one of the arteries in the brain. The initial attention is given to the human cardiovascular system, a description of which is fatal for understanding the problem of brain aneurysm. The next attention is focused on the solution of eliminating the tension within the aneurysm by using knowledge gained in lectures "Flexibility and Strength II" during the sixth semester. The last chapter shows a summary of three works dealing with computational modeling of cerebral aneurysm.
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Definition of principal material directions in the abdominal aortic aneurysms
Bartoňová, Petra ; Slažanský, Martin (referee) ; Polzer, Stanislav (advisor)
This bachelor thesis deals with definitions of principal material directions in idealized geometrical models. The theoretical part is particularly focused on general information of vascular system and abdominal aortic aneurysms in the field of anatomy, histology and surgery, afterwards it is concentrated on the biomechanical point of view. Consequently, the created algorithm is described and used to compare different definitions of principal directions considering the maximum principal stress. In conclusion, the results of FEM analyses are evaluated with respect to further study of this issue.
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Computational modelling of heart contraction
Vaverka, Jiří ; Polzer, Stanislav (referee) ; Burša, Jiří (advisor)
This thesis aims to determine the impact of slowed myocardial conduction velocity and depressed myocyte contractility on the duration of isovolumic contraction time (ICT) of the left ventricle by carrying out simulations using finite element method. A 3D finite element model enabling to simulate both physiological and pathological states of myocardium was created. The model is based on simplified ellipsoidal geometry and accounts for anisotropic behavior of myocardium, its asynchronous contraction and variations in the arrangement of muscle fibers. Slowing of conduction velocity to a half of its physiological value resulted in prolongation of ICT by 27 %; slowing of shortening velocity of myocytes by the same percentage prolonged ICT by 73 %. It is therefore concluded that ICT can be much more prolonged due to depressed contractility than due to conduction slowing. The presented results give an idea of the extent to which ICT can be prolonged due to depressed contractility and conduction slowing and therefore can be useful in identifying the causes of decreased myocardial performance in heart disease.
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Experimental estimation of arterial collagen waviness
Vávra, Jan ; Man, Vojtěch (referee) ; Polzer, Stanislav (advisor)
The bachelor thesis is focused on the experimental estimation of collagen waviness in arterial . The aim of this thesis is to get orientation of fibres from polarized light microscopy. This is possible thanks to phase correlation and image analysis in programe called MATLAB. After that, it is needed to vertify results in program called Hyperfit. Its done by estimating coefficients of constitutive model and comparing them with biaxial tests of porcine aortas.
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