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Computational analysis of the dynamic behavior of the thrust bearings
Žatko, Miroslav ; Kos, Pavel (referee) ; Malenovský, Eduard (advisor)
This master´s thesis solves the problem of stationary viscous flow of incompressible fluids in thin layers of fluid film lubrication in fixed pad thrust bearings. The parametric computational model of oil domain was created for investigation the distribution of pressure, velocity and thermal fields together with the determination of the basic parameters as axial force, heating up and friction loss. Subsequently this model was applied for investigation influence of uneven bearing clearance. The problem task was solved by final volume method in Ansys CFX 12.0 software.
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Propagation of inclined cracks to the interface of ceramic laminates
Novotná, Lenka ; Trunec, Martin (referee) ; Chlup, Zdeněk (advisor)
Composite materials with laminated structure provide advantages which are utilised during component design. Low density, temperature and chemical stability are the profitable properties predetermining application of ceramic laminates. The main obstacle for wide spread of ceramic materials is their inherent brittleness. Therefore, in this thesis, the crack propagation in ceramics laminates has been extensively studied. Laminated structures with various volume fractions of components (alumina and zirconia) were prepared by electrophoretic deposition. Evaluation of crack propagation through the interface and determination of basic mechanical properties was conducted on the basis of extensive literature search. Crack deflection originated in both presence of internal stresses and differences in elastic modulus during the crack interface passing was monitored. A special type of specimen geometry was employed with the aim to set arbitrary angle between crack and interface. It was experimentally found that the degree of crack deflection is dependent on entering angle and volume fraction of components. Higher crack deflection was already found in the bulk of the test piece comparing to the test piece surface. The 3D fracture surface reconstruction generated using laser confocal microscopy was used in this detailed crack propagation study. Further basic elastic and strength characteristics of laminates were determined and compared to those obtained from monolithic materials. The validity of the mix rule for elastic characteristics was confirmed by comparing of elastics modulus. The most reliable method for elastic modulus determination was marked the dynamic resonance method due to low scatter and consistency in measurement. The flexural strength of all laminates tends to be close to the flexural strength of the weakest component. Therefore the mix rule is not applicable for flexural strength estimation on the contrary of elastic characteristics. The change of component volume fraction leads only to change of flexural strength scatter. Thanks to gained knowledge about crack propagation and basic characteristic determination will be possible to design ceramic laminates more efficiently for given needs of application.
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Atomistické simulace uspořádávání v niklových slitinách pod vlivem mechanického napětí
Buršík, Jiří
Systems containing up to six alloing elements typical of advanced Ni-based superalloys were modelled.their ordering was simulated at atomic level using a Monte Carlo approach with púeriodic boundary conditions and Kawasaki dynamics.molecular dynamics routines were embedded into standard kinetic Ising model to account for relaxing of local atomic positions.Straining computer experiments show that elastic parameters and bulk modulus undergo comparatively large changes at the beginning of ordering process.
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Clustering and regression analysis of micro panel data
Sobíšek, Lukáš ; Pecáková, Iva (advisor) ; Komárek, Arnošt (referee) ; Brabec, Marek (referee)
The main purpose of panel studies is to analyze changes in values of studied variables over time. In micro panel research, a large number of elements are periodically observed within the relatively short time period of just a few years. Moreover, the number of repeated measurements is small. This dissertation deals with contemporary approaches to the regression and the clustering analysis of micro panel data. One of the approaches to the micro panel analysis is to use multivariate statistical models originally designed for crosssectional data and modify them in order to take into account the within-subject correlation. The thesis summarizes available tools for the regression analysis of micro panel data. The known and currently used linear mixed effects models for a normally distributed dependent variable are recapitulated. Besides that, new approaches for analysis of a response variable with other than normal distribution are presented. These approaches include the generalized marginal linear model, the generalized linear mixed effects model and the Bayesian modelling approach. In addition to describing the aforementioned models, the paper also includes a brief overview of their implementation in the R software. The difficulty with the regression models adjusted for micro panel data is the ambiguity of their parameters estimation. This thesis proposes a way to improve the estimations through the cluster analysis. For this reason, the thesis also contains a description of methods of the cluster analysis of micro panel data. Because supply of the methods is limited, the main goal of this paper is to devise its own two-step approach for clustering micro panel data. In the first step, the panel data are transformed into a static form using a set of proposed characteristics of dynamics. These characteristics represent different features of time course of the observed variables. In the second step, the elements are clustered by conventional spatial clustering techniques (agglomerative clustering and the C-means partitioning). The clustering is based on a dissimilarity matrix of the values of clustering variables calculated in the first step. Another goal of this paper is to find out whether the suggested procedure leads to an improvement in quality of the regression models for this type of data. By means of a simulation study, the procedure drafted herein is compared to the procedure applied in the kml package of the R software, as well as to the clustering characteristics proposed by Urso (2004). The simulation study demonstrated better results of the proposed combination of clustering variables as compared to the other combinations currently used. A corresponding script written in the R-language represents another benefit of this paper. It is available on the attached CD and it can be used for analyses of readers own micro panel data.
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Ion attachment and ion emission of dust grains
Vyšinka, Marek ; Němeček, Zdeněk (advisor) ; Wild, Jan (referee)
Small dust grains could be found in many environments. Because of their size, their charge and the electric forces acting on them play an important role in their dynamics. The dust grain charge is influenced by many different processes. Among other methods, charging processes can be studied by trapping a single dust grain inside an electrodynamic quadrupole where it is put into specific environment (ion or electron beam, UV radiation). The progress of the charging process can be inferred from the changes in the grain charge. Our work contributed to the building of a new laboratory set-up for study of the charging processes. Specifically, a new Faraday cup for measurements and stabilization of the ion and electron gun currents is designed and its function verified. It solves the shortcomings of the previously used Faraday cups. Further, an amplifier for the ion gun current measurement is designed and constructed along with the design of digital stabilization of the current. The stabilization is neccesary for the interpretation of measurement results and its digitalization will allow more flexible adjustment and easier connection with the control computer. Finally, data acquired during the charging of dust grain with different ion species are evaluated in order to study the effect of different ions on surface...
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Dynamic Characteristics of Exhaust System and Noise Transmition to the Car Cocpit
Novotný, Václav ; Ramík, Pavel (referee) ; Svída, David (advisor)
This thesis deals with the complex analysis of dynamic characteristics of the exhaust system and the transmission of noise from exhaust system to the vehicle. In the first part is performed modal analysis, which is compared to experimentally measured data. Modal analysis of the complete exhaust system is made with focusing on the influence of temperature of the exhaust system. There is also performed an analysis of noise transmission from exhaust system to the car cockpit.
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Method of measurement parameters in metal forming.
Knebl, Martin ; Šlais, Miroslav (referee) ; Forejt, Milan (advisor)
This master’s thesis deals with the problem of measurement for thermomechanical parameters during metal forming under higher deformation rate. The first part works up general literary studies, comprising a summary of measurement methods for required parameters. There is described a principle of their function and usage. Further assessed the current situation and recommendation of appropriate methods for the dynamic processes of forming, especially their testing. The second part is devoted to the measurement for dynamic features of the material. This is a problem specified by Split Hopkinson preassure bar test. The test is described, including the mathematical evaluation process, in the theoretical part. In the practical part, there is a detailed description of the process and evaluation of the real test with aluminum alloy AlMg4, 5Mn ,07-EN AW 5083 performed within the framework of the junior project.
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Emergent properties of the G1/S network
Dražková, Jana ; Tomášek, Petr (referee) ; Palumbo,, Pasquale (advisor)
Tato práce se zabývá buněčným cyklem kvasinky Saccgaromyces cerevisiae. Oblastí našeho zájmu je přechod mezi G1 a S fází, kde je naším cílem identifikovat velikosti buňky v době počátku DNA replikace. Nejprve se věnujeme nedávno publikovanému matematickému modelu, který popisuje mechanismy vedoucí k S fázi. Práce poskytuje detailní popis tohoto modelu, stejně jako časový průběh některých důležitých proteinů či jejich sloučenin. Dále se zabýváme pravděpodobnostním modelem aktivace replikačních počátků DNA. Nově uvažujeme vliv šíření DNA replikace mezi sousedícími počátky a analyzujeme jeho důsledky. Poskytujeme také senzitivní analýzu kritické velikosti buňky vzhledem ke konstantám popisujícím dynamiku reakcí v modelu G1/S přechodu.
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