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Slit flow rheometer for magnetic and non-magnetic fluids
Železník, Tomáš ; Vimmr, Jan (referee) ; Roupec, Jakub (advisor)
In this thesis was designed, manufactured and tested the fourth evolution of a slit-flow rheometer with another necessary parts, eg. rheometer`s holder, drive frame and important jig tools. The rheometer is able to measure rheological properties of magnetic and non-magnetic fluids at very high shear rates, which commercial rheometers can not reach. It is designed for 200 bar pressure and maximum load 15 kN. The construction of the slit-flow rheometer with it`s holder and drive frame improves user friendliness, accelerates change of the fluid sample and expands research opportunities thanks to a big space for additional adjustments. It is possible to use different length of the slit and thanks to a changeable inserts it is possible to change parameters of the slit (roughness of the walls, wall material, thickness of the slit). A part of this thesis was focused on illation of necessary equations for planning calibration measurements. Aim of these measurements is to obtain minor pressure losses dependence on Reynolds number for specific slit.
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Fluid-Structure Interaction between Structural Components of Hydraulic Turbine and Fluid Flow
Havlásek, Michal ; Malenovský, Eduard (referee) ; Vimmr, Jan (referee) ; Pochylý, František (advisor)
Tato dizertační práce se zabývá dvěma případy interakce tělesa s tekutinou (FSI). První z nich se zabývá analýzou vzájemné interakce mezi rotorem čerpadla a kapalinou uvnitř těsnící spáry. Vliv těsnící spáry na dynamiku celého stoje je popsán pomocí dynamických parametrů, které jsou také označovaný jako přídavné účinky. V současnosti používané modely těsnících spár používají pro stanovení dynamických parametrů řadu zjednodušujících předpokladů. V této práci je prezentováno pět různých analýz dynamických parametrů těsnící spáry čerpadla na okysličovadlo. Každá z těchto pěti analýz používá jinou míru zjednodušení výpočetního modelu. V případě největšího zjednodušení je modelován pouze objem kapaliny uvnitř těsnící spáry. Nejkomplexnější analýza pro stanovení dynamických parametrů těsnící spáry používá pro výpočet model celého čerpadla s excentrickou polohou rotoru. Druhá část této dizertační práce definuje novou metodu pro řešení interakce kapaliny s pružným tělesem. Tato metoda využívá řešení inverzního problému kmitání. Přímý problém kmitání, který je také označován jako problém vlastních hodnot, používá jako vstupy pro řešení matice hmotnosti, tuhosti a tlumení, které jsou dohromady označovány jako koeficientové matice, na základě kterých je v nejobecnějším případě stanovena Jordanovská matice a také modální matice pravostranných a levostranných vlastních vektorů. Při řešení inverzního problému kmitání jsou stanoveny koeficientové matice na základě Jordanovské matice a modálních matic pravostranných a levostranných vlastních vektorů. Existují dva případy inverzního problému kmitání. V případě, že jsou známy všechny vstupní vlastní čísla a vlastní vektory, pak se jedná o tzv. plný problém. Naopak v případě, že alespoň 1 mód kmitání soustavy není znám, tak se jedná o tzv. částečný problém. V této práci je prezentováno 5 algoritmů pro řešení inverzního problému v kmitání. Nicméně pro každý typ inverzního problému kmitání je prezentován jeden univerzální algoritmus. Algoritmus pro řešení plných problémů byl poprvé prezentován v roce 1979 Otakarem Daňkem. Algoritmy pro řešení částečných problémů, které jsou prezentovány v této práci, jsou vůbec prvními algoritmy pro řešení tohoto typu inverzního problému kmitání. Univerzální algoritmus pro řešení částečných problémů je označován jako algoritmus pro řešení částečných problémů s volbou doplňkových vlastních hodnot. Aplikace těchto dvou univerzálních algoritmů pro řešení inverzního problému kmitání pro případ plných i částečných problémů je ukázána na řešení dvou případů interakce pružného tělesa s kapalinou.
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Lubrication of plastic gears
Poledník, Radim ; Vimmr, Jan (referee) ; Šperka, Petr (advisor)
The purpose of this diploma thesis is to describe the influence of input parameters (rolling speed, load, temperature, dynamic viscosity and pressure coefficient of the lubricant) on film thickness in point and elliptical contacts using optical interferometry. Regression based film thickness formula has been obtained using universal form of non-dimensional parameters of entrainment speed U, load W and material G. Equations were also complemented by the function of ellipticity k. New regression formulas for central and minimum film thickness have been compared with existing EHL thickness equations. These film thickness measurement and new regression formulas have applicability to our understanding of the performance and more effective design of lubricated gears from polymeric materials.
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Enhancing of sedimentation stability using bentonit based clays
Michal, Lukáš ; Vimmr, Jan (referee) ; Roupec, Jakub (advisor)
The diploma thesis is focused on the issue of sedimentation stability of magnetorheological fluids, whis represents one of the most important characteristics determining the reliability of these fluids. Higher sedimentation stability can by achieved in several ways. Methods that are further examined in the thesis include particle polymerization and the addition of clay mineral additives. Both achieve positive results by schowing increased sedimentation stability. However, in the case of additives, the effect is much higher. In particular, the CLAYTONE 40 additive achieves a lower particle sedimentation rate while maintaining the same viscosity as the commercial LORD-122ED. The results provide significant knowledge in the field and can bring magnetorheological fluids closer to wider commercial use.
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The study of MR fluids sedimentation
Berka, Pavel ; Vimmr, Jan (referee) ; Roupec, Jakub (advisor)
This diploma thesis investigates the accelerated sedimentation of the magnetorheological fuids (MRFs) using centrifuge. Experiments are carried out at room temperature as well as at higher temperatures (40°C, 60°C and 80°C). The development of the new improved measuring device for the sedimentation evaulation is described. Magnetic components of the device were designed using FEM analysis. Newly designed device is verified. To accomplish the experiments at the high temperatures the new heated chamber for experimental centrifuge is designed and constructed. In the next part of the work full experiment of the accelerated sedimentation is performed. At final the empirical model of the sedimetation velocity for various accelerations and temperatures is synthesized.
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Behaviour of lubricated contacts under high-sliding conditions
Adam, Jakub ; Vimmr, Jan (referee) ; Omasta, Milan (advisor)
The aim of this diploma thesis is to describe the influence of individual operating parameters on thickness and temperature distribution of elastohydrodynamic contact under high slip ratio. In this work, the distribution of the lubricant film thickness is determined by optical interferometry and the temperature mapping in EHL contact is realized by infrared microscopy. Two optical filters were used to separate the radiation of contact surfaces and oil. Temperature of disk surface was measured using a sapphire disk with chromium layer that shielded radiation from ball and oil. The experimental device was modified to simulate the conditions of the various vectors between entrainment and sliding speed. The results extend existing information about behavior of EHL contact under high slip ratio conditions.
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Analysis of Influence of Collagen Organization on Mechanical Properties of Arteries
Novák, Kamil ; Daniel, Matej (referee) ; Vimmr, Jan (referee) ; Burša, Jiří (advisor)
This dissertation thesis concerns with Analysis of Influence of Collagen Organization on Mechanical Properties of Arteries and it is divided into three main parts. Motivation for this dissertation thesis was in a study reviewing effect of material model upon resulting stresses in AAA. The effect was calculated in 70 patient-specific geometries of AAA, which exceeds the number of geometries in other scientific papers by one order. Within this study, two material models were used, i.e. real one and 100× stiffer, and obtained stresses were mutually compared. It was quantified that peak stress difference can be higher than 20 % in 10% of patients and therefore the real material model should be preferred over the artificial one although operation with this model is more demanding. The second part of this thesis deals with an identification of structural parameters (orientation and dispersion of collagen fibres) of porcine aortic tissue by using adjusted Fast Fourier Transform based algorithm. The extracted structural parameters were inserted into two-layer structure-motivated constitutive model Martufi-Gasser. This model was validated and its predictive capabilities were also tested with fine results. The most important information obtained from the digital image processing of ~9000 micrographs is existence of only one family of dispersed collagen fibres which breaks the current dogma present in many scientific papers about two families of collagen fibres. The third part concerns with a proposal of an automated phase-correlation based algorithm for obtaining collagen fibre direction from polarized light microscopy images. The proposed algorithm was verified and validated and it yields histograms of collagen fibre directions with overall number of measured points larger than it would be possible to get from any manual measurement. The limitation of the original proposed algorithm is in 90° period of polarized light intensity, thus the method results in angles in the range of 0°–90. Therefore the end of the thesis is dedicated resolving this problem and obtaining real angles in a span of 0°–180°. To this end, the microscope set-up was changed and the algorithm was adjusted accordingly. The original and the adjusted algorithms are collagen-specific, fast and an operator independent. Despite all the author´s effort put into collagen fibre waviness quantification directly from the histograms, the waviness has not been quantified yet in this way and it remains at the stage of research.
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Surface tension measurements
Hála, Ondřej ; Vimmr, Jan (referee) ; Košťál, David (advisor)
The thesis deals with study of surface tension of liquids and measuring possibilities of this parameter. The paper is then focused on design of measuring apparatus based on pendant drop method. The apparatus is controlled with software written in Matlab. Several measurements are done at the end of this work, which confirm possibility to practical use of this apparatus for surface tension measurements. A part of this work is manual to use the apparatus and complete design documentation.
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Experimental study of journal bearings dynamics
Tkadlec, Josef ; Vimmr, Jan (referee) ; Omasta, Milan (advisor)
This work deals with experimental analysis of fluid film instability in rotor bearing systems stored in hydrodynamic plain bearings with focus on bearing surface modification. The experiments were performed on a journal bearing dynamics simulator. The aim was to determine the influence of individual operating parameters on the occurrence and course of turbulence instability. The emphasis here was on the effect of surface micro textures. The work also included the preparation of textured samples. Experiments were divided into experiments monitoring the influence of temperature, pressure, bearing geometry and surface modification. The output of the individual experiments were the values of the threshold speed of formation and termination of instability or the magnitude of the amplitude depending on the above described parameters. These values were plotted in graphs. This data was then confronted with previously published articles. The results showed that instabilityin rotor systems is very sensitive to temperature, pressure and bearing geometry changes. The fundamental influence on the unstable behavior of the rotor system has been demonstrated by the use of textured surfaces, where the threshold speed was significantly shifted to a higher speed range compared to the non-textured bearing.
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Study on wear of material in contact with MR fluid
Žáček, Jiří ; Vimmr, Jan (referee) ; Kubík, Michal (advisor)
This paper is focused on MR dampers and its critical parts in term of damper`s durability, which seems to be a piston-rod seals, and it should find an ideal material combination of seal and MR fluid for increasing the damper`s life. The tests were conducted in modified pin-on-flat configuration, which was supposed to be more suitable for laboratory testing. There was tested and compared a suitable material for seals, like PTFE, NBR, SBR of polyurethanes. The article is also focused on MR fluids and its contribution to seal`s wear. The impact of particle concentration, wear of MR fluid and effect of modification of MR fluid was tested. It showed up, that the best material for seal is H-PU95FDA. The effect of particle concentration is negligible on seal`s wear, while effect of modification and wear of MR fluids are significantly higher.
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