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A study of the vortex flow structures in heart compensation devices
Dokoupil, Michael ; Habán, Vladimír (referee) ; Fialová, Simona (advisor)
This master thesis is focused on study and description of flow in heart assistance devices. The aim was to evaluate the state of art for cardiac supports, selection of one device concept and improve the existing pump model. The types of heart replacements were evaluated in the research part of this work. Based on the research, an axial intraventricular pump was chosen for the simulation. The flow simulation was performed using computational fluid modeling. During the evaluation, special emphasis was placed on the description of vortex structures typical for cardiac support and analysis of hemolysis caused by the device.After selecting the optimization parameters, a design of a pump model was improved, which met the set optimization goals, especially the increase in efficiency and decrease of shear stresses. Towards the end of the work there was a discussion about the evaluation of hemolysis and vortex structures. In the end, particular possibilities for further improvement of the optimized pump were presented.
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Computational Fluid Dynamic Simulation of Intracranial Aneurysms : analysis of time-depend changes of hemodynamic parameters - the road to clinical use
Sejkorová, Alena ; Hejčl, Aleš (advisor) ; Vaverka, Miroslav (referee) ; Přibáň, Vladimír (referee)
Computational Fluid Dynamic Simulation of Intracranial Aneurysms Analysis of time-dependent changes of hemodynamic parameters - the road the clinical use Hemodynamics are involved in the genesis of intracranial aneurysms and time- dependent changes of their parameters lead to aneurysm growth, stabilization or rupture. Definition of these changes using computational fluid hemodynamics could significantly contribute to the understanding of aneurysmal development and rupture and could enable the routine use of mathematical simulations. In this study, computational fluid dynamics were performed for nine incidental aneurysms. Five aneurysms were monitored throughout time and factors leading to aneurysm rupture were analyzed. In four aneurysms the influence of the hemodynamics on the growth was defined. Major growth occurred in areas of low wall shear stress and oscillatory index. These areas increased in size during growth time. Contrary to this, neck shape remodeling occurred in areas with large wall shear stress and pressure. Throughout the follow-up of ruptured aneurysms, the minimal wall shear stress decreased, and the area of low wall shear stress increased significantly. The results indicate that decreasing values of minimal wall shear stress and increasing values of low wall shear stress area...
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Reologické vlastnosti smetany
Škopíková, Miroslava
This diploma thesis deals with rheological properties of cream in this theoretical part. The first part describes the composition of milk as a basic product in the production of cream, and the definition of cream according to legislation and its composition. Another part of the thesis is focused on the production of cream and its distribution by kind. In the next chapter, attention is paid to the rheological properties of food, esspecially viscosity and density. The practical part is focused on the measurement of rheological properties of 10 whipping cream samples available on market. The fat proportion of the samples ranged between 30 - 33 %. For all of these samples, viscosiy and density were measured. For chosen samples was also determined the dependency of shear stress to shear rate. This dependence, using Ostwald-de Waele model, determines what type of fluid is involved. Another observed parameter was the dependency of the dynamic viscosity on the shear rate and the relation of this viscosity to the temperature changes. All samples were subjected to analytical determination of cream (dry matter, fat, titration acidity, active acidity, electrical conductivity). From the analysis of the fat proportion proportion, we are able to compare our measured data to the projected data declared by producers.
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Reologické vlastnosti včelího medu
Klabenešová, Iveta
This diploma thesis was focused on the rheological properties of honey. In the theoretical part of the work, there I occupied with the honey from a wider point of view: its production, general characteristics, fabrication, classification and its physical and chemical properties. The last chapter of the theoretical part dealt with the general rheology of liquids and with the rheological properties of honey. The practical part was concentrated on the rheological properties of chosen honey samples bought from beekeepers, not from the market network. Amongs the nine samples represented by three kinds of honey (rape, linden, honey dew) there was spectophotometricaly determined the colour, measured the content of carbonhydrates, the viscosity and the shear stress depending on the shear rate. The Newton model was used to assemble the flow curves (Newton viscosity law) whose the grounds it was determined that the honey belongs thanks to its rheological properties to the Newtonian liquids. Moreover, the temporal dependence of viscosity, on whose basis should have been assessed the thixotropy of honey, was established. Formula clause:
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Use of finite element method for stress evaluation in layers for optical applications
Tesařová, Anežka ; Ohlídal, Miloslav (referee) ; Burša, Jiří (advisor)
This thesis is concerned with the mechanical stress generated in thin layers applied on a substrate. The application takes place at high temperatures and due to different coefficients of thermal expansion of materials, the sample is deformed, and thereby the stress is generated. The first part of the thesis includes the derivation of the Stoney formula for uniaxial and biaxial stress in a layer. Besides, analytical calculations of the normal stress in the layer for the simplified link model, and shear stress on the layer interface were evaluated. The main part of the work consists of solving the problem using FEM modeling. Because the actual temperature behavior during the application was not known, a fictitious temperature load was used as an input. For the samples, the coefficients of thermal expansion of the layer were then searched so that the thermal load resulting deflection corresponds to the experimental data. Three types of models were created, namely the link body model, the axisymmetric model, and the solid model. The axisymmetric model was used for the calculation of samples forming circular isolines during deformation and a volume model for samples forming elliptical isolines. The result of the FEM calculations was the normal stress in the applied layers, for which corresponding relationships were created using regression analysis.
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Rheological behaviour of alkali-activated aluminosilicates
Ševčík, Marek ; Vyšvařil, Martin (referee) ; Rovnaník, Pavel (advisor)
The bachelor thesis is focused on rheological properties of alkali activated materials, the main focus is on rheological behavior of geopolymers. The theoretical part describes the most commonly used materials for the preparation of geopolymers. Further, described rheology in general and rheological properties are described, types of behavior of substances and differences between rheological properties of different types of aluminosilicates are explained. In the experimental part, mechanical properties of geopolymer pastes based on metakaolin and fly ash with different silicate moduli of alkaline activator – water glass were investigated. For these materials, rheometric measurements and rheological behavior were also performed.
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Evaluation of accuracy of shear formula for chosen shapes of beams
Bolcek, Jan ; Kořista, Milan (referee) ; Burša, Jiří (advisor)
This bachelor thesis pursues the judgement of accuracy of Jourawski’s formula in short beams. Assumptions, on which is Jourawski’s formula derived, are described in the theoretical part, there is also a procedure how to derive the formula. In the theoretical part is also stated a literature search on inaccuracies which are made by using Jourawski’s formula. The accuracy of Jourawski’s formula is judged by example of simply supported beam loaded with force in the middle and with cross section in the shape I. Firstly there is analytic calculation of distribution of shear stress which is then compared with calculation acquired by finite element method. By the finite element method are simulated three models of beams with different edge conditions, which are those derived from rod assumptions and the real ones. In the conclusion are compared and evaluated results from both types of calculations.
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Numerical modeling of the prestress hollow core slabs Spiroll type on the flexural support and the evaluation of the stresses
Kršík, Jakub ; Vejvoda,, Stanislav (referee) ; Kaplan,, Věroslav (referee) ; Křiváková, Jarmila (advisor)
The doctoral thesis describes the possibilities of numerical modelling of hollow core concrete panels, SPIROLL type. The commercial finite element program ANSYS 13.0 is used for the modelling. The focus is on the specific flexural support of the panel and on the distribution of the shear stresses in the panel ribs near the support. The goal is to valid actually used method for homogenization of the panel’s foreheads and its influence on the shear resistance by using four numerical models. The numerical models are compared and verified with two experiments. The first experiment is vacuum loading on the hollow core slab. Second experiment is about shear loading by applying the loading blocks. Four methods for design of hollow core panels are evaluated. It is the method based on main stresses, design according EN 1992 and EN 1168 and Yang’s method of prestress effects transfer. Based on the results, a method of considering flexural support for the evaluation of hollow core panels is proposed.
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Influence of interference fit on Rolling Bearing life
Tetour, Stanislav ; Prokop, Aleš (referee) ; Řehák, Kamil (advisor)
Master thesis is focused on the influence of interference fit on rolling bearing life. The first part of thesis deals with the theoretical knowledge, that is necessary for the solution. The influence of interference fit was investigated of inner ring on shaft and outer ring in housing bore for recommended tolerance classes. Interference fit was solved on cylindrical roller bearing and tapered roller bearing. Analytical and numerical approach was used for the solution. A static analysis of bearing was made using program ANSYS Workbench in numerical section. The output of analysis was maximum shear stress under the contact surface, which result is contact fatigue of bearing. Bearing life was determined by life factor, which indicates bearing life with interference fit compared to bearing without interference fit.
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Reologické vlastnosti kravského, kozího a ovčího mléka
Písaříková, Veronika
This thesis is focused on the rheological properties of cow, goat and sheep milk. These kinds of milk are described and compared in the first part. The thesis describes physical properties and technology of milk transport. Next part deals with legislation about milk in the European Union and in the Czech Republic. Special attention is given to the requirements of warehouse equipment and heat treatment of milk. Another part deals with analytical properties of milk (dry matter, protein, fat, lactose, acidity of the milk, electrical conductivity and density). In the last part are monitored rheological properties of these three types of milk. Selected samples are measured with shear stress depending on the strain rate. It is important because it helps us to determine what type of fluid is milk. Then, there is monitored dependence of the dynamic viscosity at the shear stress and effect of temperature on viscosity. These experiments demonstrated that milk belongs to liquids with Newtonian behavior. To evaluation the results was used Newton's law of viscosity and Ostwald de Waele model.
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