Národní úložiště šedé literatury Nalezeno 5 záznamů.  Hledání trvalo 0.01 vteřin. 
Stress-Strain Analysis of Aortic Aneurysms
Polzer, Stanislav ; Holeček, Miroslav (oponent) ; Horný, Lukáš (oponent) ; Burša, Jiří (vedoucí práce)
This thesis deals with abdominal aortic aneurysms and the possibility of using finite element method in assessment of their rupture risk. First part of the thesis is dedicated to an introduction into the problem, description of human cardiovascular system where the abdominal aorta, its anatomy, physiology and pathology is emphasized. There Processes leading to formationing of abdominal aortic aneurysms are also discussed. Risk factors contributing to creation of aneurysms are discussed next. Finally, an analysis of current clinical criteria which determine rupture risk of an abdominal aortic aneurysm is presented and compared with the new maximum stress criterion being currently in development. Main part of the thesis deals with the identification of relevant factors which affect stress and deformation of aneurysmal wall. This is connected with proposals of new approaches leading to predicting the rupture risk more accurately by using finite element stress-strain analysis. The impact of geometry is analyzed first with the conclusion that patient-specific geometry is a crucial input in the computational model. Therefore its routine reconstruction has been managed. Attention is then paid to the branching arteries which were neglected so far although they cause a stress concentration in arterial wall. The necessity of knowing the unloaded geometry of aneurysm is then emphasized. Therefore a macro has been written in order to be able to find the unloaded geometry for any patient-specific geometry of aneurysm. Mechanical properties of both aneurysmal wall and intraluminal thrombus were also experimentally tested and their results were fitted by an isotropic material model. The effect of the material model itself has been also investigated by comparing whole stress fields of several aneurysms. It has been shown that different models predict completely different stresses due to different stress gradients in the aneurysmal wall. The necessity of known collagen fiber distribution in arterial wall is also emphasized. A special program is then presented enabling us to obtain this information. Effect of intraluminal thrombus on the computed wall stress is analyzed in two perspectives. First the effect of its failure on wall stress is shown and also the impact of its poroelastic structure is analyzed. Finally the residual stresses were identified as an important factor influencing the computed wall stress in aneurysmal wall and they were included into patient-specific finite element analysis of aneurysms. Further possible regions of investigation are mentioned as the last part of the thesis.
Deformačně-napěťová analýza aneurysmatu břišní aorty
Ryšavý, Pavel ; Janíček, Přemysl (oponent) ; Holeček, Miroslav (oponent) ; Burša, Jiří (vedoucí práce)
Tato práce se zabývá problematikou biomechaniky měkkých tkání, konkrétně se jedná o deformačně-napěťovou analýzu aneurysmatu abdominální aorty (AAA). V úvodu jsou stručně popsány možnosti výskytu aneurysmat se zaměřením na výdutě v oblasti břišní aorty.
Influence of Geometrical Parameters on Rupture Risk of Abdominal Aortic Aneurysm
Zemánek, Miroslav ; Janíček, Přemysl (oponent) ; Tonar,, Zbyněk (oponent) ; Holeček, Miroslav (oponent) ; Burša, Jiří (vedoucí práce)
The main objective of this thesis is finite element and experimental modeling of stress-strain states of the soft tissues specially focused on rupture risk of abdominal aortic aneurysm (AAA). The first chapter (chap. 1) summarizes the present state of the mentioned problematic and the major information published in the present-day literature. The key factors for AAA rupture risk decision are also summarized in this chapter. The next chapter (chap. 2) describe the artery wall histology, type of aneurysms and mechanical behavior of artery wall. The second part of the thesis (chap. 3) is focused on experimental modeling of stress-strain states of soft tissues which is necessary for reliable finite element modeling of this behavior. In this chapter a specially designed and produced experimental testing rig is described and the type of tests which is possible to realize with this testing rig. The key factors influencing the stress-strain behavior of the aortic tissue are also summarized and experimentaly tested on porcine thoracic aortas. The new knowledge resulting from experimental testing are summarized at the end of this chapter. The intention of third part (chap. 4) is the mathematical description of the stress-strain behavior of soft tissues, description of frequently used constitutive models and the parameter identification for these constitutive models based on the realized tension tests. The last chapter (chap. 5) is devoted to finite element modeling of the stress-strain states of AAA behavior. First the key factors and assumptions for finite element models creation and evaluation are summarized as well as the material parameters of the constitutive models which are implemented in ANSYS software. Several simulations were realized using hypothetical AAA geometry where the impact of some geometrical parameters change was tested. The backward incremental method using for evaluation of unloading state was designed and tested at real AAA geometry reconstructed from CT scans. Hypertension as one of the key factor for AAA rupture risk was tested using unloaded geometry. The new knowledge and possibilities of finite element modeling are summarized at the end of this thesis. The proposals to next research work is also summarized.
Vyhodnocení katastrofální povodně v srpnu 2002: Hydrologické a hydraulické posouzení povodně na tocích a úsecích toků nesledovaných pozorovací sítí ČHMÚ
Výzkumný ústav vodohospodářský T.G. Masaryka, v.v.i., Praha ; Šercl, Petr ; Müller, Michal ; Malíková, Petra ; Vránek, Tomáš ; Bouška, Petr ; Balvín, Pavel ; Matoušek, Václav ; Kašpárek, Jan ; Holeček, Miroslav ; Krátká, Martina ; Kašpárek, Ladislav
Byly hodnoceny kulminační průtoky v porovnání se srážkami v na vybraných tocích a úsecích toků . Byla hodnocena místa s extrémními naměřenými srážkami v povodí Berounky, v Krušných a Novohradských horách, v povodí Otavy a Polečnice.

Viz též: podobná jména autorů
12 Holeček, Martin
2 Holeček, Michal
5 Holeček, Milan
1 Holeček, Miloš
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