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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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Torsion of bars with noncircular cross section
Votava, Ondřej ; Hájek, Petr (referee) ; Profant, Tomáš (advisor)
The aim of this bachelor's thesis is the problematics of twisting of bars with non-circular cross-section. In order to solve this problem, analytical and numerical methods are used. The theoretical part deals with the derivation of elementary relations, especially on the thin-walled open and closed section. This theoretical knowledge is further applied to solve specific tasks. In this thesis, the applicability of using individual methods for real parts is examined.
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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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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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Heat Transfer during Condensation of Steam-Air Mixture Flowing in Vertical Tube
Toman, Filip ; Masaryk, Michal (referee) ; Kořista, Milan (referee) ; Pospíšil, Jiří (advisor)
This thesis deals with the problem of condensation in the presence of non-condensable gases with a focus on heat and mass transfer inside a vertical pipe. The introductory part of the thesis is dedicated to the research analysis of the given issue. The attention is focused on the physically correct description of the events at the interface of the gas phase and the condensate film, as well as on the inclusion of the influence of the presence of non-condensable gases. Scientific hypotheses were developed based on this analysis. Subsequently, the objectives of the dissertation are formulated and the methods by which the objectives of the dissertation are solved, are presented. As part of the data evaluation, an analytical model was created enabling the quantification of heat and mass transfer for the measured conditions. This model was used to test variations of computational relationships published by various authors in the literature. The mathematical solution is supplemented by realized experimental measurements of the condensation coefficient of heat transfer and the total coefficient of heat transfer inside the pipe during the condensation of the steam-gas mixture in vertical pipes of three diameters, namely 16, 20 and 26 mm. At the end of the thesis, the most suitable combination of already published analytical relations is selected and is carried out as part of its refinement, using regression analysis.
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Reologické vlastnosti žloutků slepičích vajec v průběhu skladování
Pavková, Lucie
The thesis deals with the influence of storage time on particular physical and rheolo-gical properties of a yolk of chicken eggs. Monitored eggs were stored at 6 °C for 8 weeks. The thesis describes the influence of storage time on physical characteristics of a whole egg, such as weight and shape index. As expected, the weight loss of chicken eggs was demonstrated during eight weeks storing. Egg yolk (colour, height, width, weight, index and density) was also described and evaluated in detail. According to our estimates, there are no significant changes in weight during yolk storing. But yolk index is distinctly decreased. During the final part of monitoring rheological properties were evaluated - apparent viscosity, time dependence of viscosity and dependence of shear stress on the shear rate (flow curves). The experiments have proved Newtonian behaviour of egg yolk throughout the storage. The storage time has also clear impact on flow properties of yolk. The results of each experiment were modelled using the power law (Ostwald-de Waele) model.
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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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