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Thunderstorms occurrence in the Czech Republic
Kovář, Jan ; Krška, Karel (referee) ; Jebáček, Ivo (advisor)
This bachelor thesis focuses on storm situations in the Czech Republic and their occurrence in the period 1961-2020. It analyses the conditions of occurrence and appearance of thunderstorms and describes the storm activity at Karlovy Vary, Prague-Ruzyně, Brno-Tuřany and Ostrava-Mošnov airports in the period between 2001-2020. Marginal mention is made of the phenomena accompanying the storm, conditions of its passage and methods of detection.
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Factors determining bad thermal conditions in the Czech Republic
Venclová, Markéta ; Chládová, Zuzana (advisor) ; Pešice, Petr (referee)
This presented work deals with a weak thermal convection over the Czech Republic. The main objective is to identify areas and meteorological conditions which determined weak thermal convection in the atmosphere. Another objective is to describe surfaces and situations that are characterized with occurrence of decreasing air currents. This work may be useful for non-motorized aircraft pilots for which the occurrence of weak thermal convection and decreasing air currents will be very dangerous during the flight. In the first part there are described different ways of spreading heat through the atmosphere, this is followed by a general description of thermal convection, its distribution, origin and course. The second part deals with weak thermal convection, describes the decreasing thermal current, meteorological conditions and factors causing weak thermal convection. The third part contains the results of a questionnaire, which was sent among aeroclubs in the Czech Republic. The results of the questionnaire were compared with the information reported in the literature and in most cases they coincide. The cases which differed from the literature are more detailed in the discussion.
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Precipitation nowcasting for the warm part of the year
Mejsnar, Jan ; Sokol, Zbyněk (advisor) ; Jaňour, Zbyněk (referee) ; Žák, Michal (referee)
Current precipitation nowcasting systems primarily use the extrapolation of observed radar reflectivity. I used the extrapolation and studied limits of the forecast using the concept of the decorrelation time (DCT). I used data from two radars covering the territory of the Czech Republic from warm parts of four years and calculated DCT in dependence on several selected conditions describing the state of the atmosphere. I found that the mean DCT for the extrapolation is 45.4 minutes. On average the increase of the DCT in comparison when the persistence forecast is employed is 13.4 minutes. However, in dependence on current conditions the DCT may increase or decrease in more than 40 %. I also explored time evolution of the DCT during two storm events. I found that the DCT may significantly change in time, which is the consequence of changing character of the atmosphere during the storm development.
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Convective environment indicies and their comparison
Marek, Lukáš ; Müller, Miloslav (advisor) ; Kašpar, Marek (referee)
In this work I created the overwiew of instability indices and other characteristics of convective environment which can be found in the literature. On the basis of variables, which the instability indices are calculated from, I suggested their categorization. It was created five groups of instability indices: (i) indices of isobaric levels differences, (ii) indices of rising air parcel, (iii) indices of potential temperatures, (iv) indices of the energy potential of convection and (v) indices of wind shear. In addition to these five categories it was created the sixth category consists of other thermodynamic characteristics. In the last chapter I used the upper air soundings data and values of instability indices of the University of Wyoming for one storm in Prague and I compared instability indices to each other. The group of the indices of potential temperatures was the most successful in the storm forecast, except the Rackliff index. The bulk Richardson number from the group of indices of wind shear forecasted a supercell storm correctly. The work could be used for creation of instability climatology of the Czech Republic on the basis of the selected instability indices. Keywords: instability index, convection, convective storm
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Adaptive methods for singularly perturbed partial differential equations
Lamač, Jan ; Knobloch, Petr (advisor)
This thesis deals with solving singularly perturbed convection- diffusion equations. Firstly, we construct a matched asymptotic expansion of the solution of the singularly perturbed convection-diffusion equation in 1D and derive a formula for the zeroth-order asymptotic expansion in several two- dimensional polygonal domains. Further, we present a set of stabilization meth- ods for solving singularly perturbed problems and prove the uniform convergence of the Il'in-Allen-Southwell scheme in 1D. Finally, we introduce a modification of the streamline upwind Petrov/Galerkin (SUPG) method on convection-oriented meshes. This new method enjoys several profitable properties such as the ful- filment of the discrete maximum principle. Besides the analysis of the method and derivation of a priori error estimates in respective energy norms we also carry out several numerical experiments verifying the theoretical results.
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Passive heat dissipation using carbon-based material
Genco, Ondřej ; Brázdil, Marian (referee) ; Pospíšil, Jiří (advisor)
The content of the diploma thesis is evaluation of the usability of carbon composites in the space industry. The aim of this work is to assess whether carbon composites can find application in mechanical systems of passive thermal protection of artificial objects. Model examples demonstrate the principle of operation of selected passive thermal protection. The evaluation is realized based on the results of thermal analysis. Analytical formulas from field theory of heat transfer are used as a calculation method. The diploma thesis consists from two parts. The theoretical part briefly describes the mechanisms of heat transfer, selected types of passive thermal protection and properties and applications of carbon composites. The practical part consists of the assignment, calculation and evaluation of three examples. The results show that carbon composites can compete with commonly used materials for specific requirements.
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Quantification of the thermohydraulic characteristics of the flexible element using experimental data
Sochorec, Rostislav ; Kilkovský, Bohuslav (referee) ; Jegla, Zdeněk (advisor)
The diploma thesis aims to establish thermo-hydraulic properties of a flexible tube described by its Darcy friction factor and film heat transfer coefficient respectively. A flexible tube (corrugated stainless steel tube) is an easily shapeable stainless steel component used to build various piping connections, in a place of more common copper or plastic made tubes. It can also be used to build heat exchangers thanks to its signature properties. The investigated product is the one developed and manufactured by the Czech company Flexira s.r.o. and sold under the brand name xConnect System. Its thermo-hydraulic properties are established by an experiment, which is based on real utilizations by Laboratory of Energy Intensive Processes in NETME (New Technologies for Mechanical Engineering) Centre at Brno University of Technology. The investigated case is a coil-shaped element serving a purpose of a water-to-water heat exchanger. The text contains a literature survey of the chosen flexible tube and a description of a draft and development of the specific experimental test based off the established theory. The obtained results are then analysed, for the purpose of establishing a functional dependence, which can then be used to calculate a film heat transfer coefficient.
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Thermal Losses of the Biomass Boiler
Suchánková, Lenka ; Milčák, Pavel (referee) ; Kracík, Petr (advisor)
The bachelor thesis focuses on the heat loss of the solid fuel boiler, especially on the loss of heat conduction and transfer to the surroundings. In order to minimalize thermal leaks through the boiler walls, materials with good isolation capabilities must be selected when designing. In Microsoft Excel, a universal mathematical model was created to calculate the heat flux flowing through the flat wall of the boiler, from which temperatures can be obtained on the inside of the wall. The work describes the calculation method on which the model is based and its correctness is verified on an experiment based on sensing of temperature fields of wall sur-faces of equipment burning biomass by thermal camera. The model can be used for a wall with up to 9 layers of material, where the wall can be cooled (heat loss) by air and water.
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Pulse flow of liquid in flexible tube
Komoráš, Miroslav ; Šedivý, Dominik (referee) ; Klas, Roman (advisor)
This master’s thesis is dealing with analysis of fluid flow pulse in a flexible tube representing e.g. an artery in a human body. In ANSYS program, 3D simulations were performed, and these are so-called interrelated FSI analysis. In Maple software, 1D simulations of fluid flow in the tube were performed for various thin-walled and thick-walled variants. The aim is using these programs to determine the flow rates and pressures in the tube, its wall deformation and stress. Therefore, the theoretical part deals mainly with basic equations of flow dynamics, linear and nonlinear models and rotationally symmetric vessels. In the computational part are described individual procedures in the mentioned programs.
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Precipitation nowcasting for the warm part of the year
Mejsnar, Jan ; Sokol, Zbyněk (advisor) ; Jaňour, Zbyněk (referee) ; Žák, Michal (referee)
Current precipitation nowcasting systems primarily use the extrapolation of observed radar reflectivity. I used the extrapolation and studied limits of the forecast using the concept of the decorrelation time (DCT). I used data from two radars covering the territory of the Czech Republic from warm parts of four years and calculated DCT in dependence on several selected conditions describing the state of the atmosphere. I found that the mean DCT for the extrapolation is 45.4 minutes. On average the increase of the DCT in comparison when the persistence forecast is employed is 13.4 minutes. However, in dependence on current conditions the DCT may increase or decrease in more than 40 %. I also explored time evolution of the DCT during two storm events. I found that the DCT may significantly change in time, which is the consequence of changing character of the atmosphere during the storm development.
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