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Numerical Simulation of Noise Generated by Shear Layer Instabilities
Šálený, Vratislav ; Kozubková, Milada (referee) ; Paur, František (referee) ; Tippner,, Jan (referee) ; Katolický, Jaroslav (advisor)
Predicting and inhibiting aerodynamically generated noise for fast moving vehicles such as cars, aircraft and trains is increasingly important. The tonal noise generated by the shear-layer instability of air flowing around the cavity opening is especially one of the most significant and most intense sources of aerodynamically generated noise. Computational aeroacoustics (CAA) based on the CFD simulations of compressible Navier-Stokes equations offers the most general approach to predicting those aerodynamically induced sounds. Aeroacoustics is practically always associated with turbulent flow and turbulence is the major challenge for CFD simulations. Four different turbulence modelling approaches are examined in this work. Three of them belong to the LES method category and one uses the URANS approach. Appropriate numerical discretization and iteration schemes have been identified for each of these approaches and implemented in the OpenFOAM open source CFD platform. The accuracy, computational performance and convergence reliability of those schemes have been subsequently studied during three-dimensional CFD simulations on a model of a suitable real object. The CFD simulation results are validated by a measurement. An organ pipe has been chosen as the object of this CAA research because it uses self-sustained oscillations, commonly referred as shear-layer (Rossiter) modes, as the source of its tone generation. The numerical simulation of the shear layer modes, respectively the noise generated by instability in the shear layer, is the subject of this work.
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Analysis of the Velocity and Pressure Fields of the Liquid Using Curvilinear Coordinates
Stejskal, Jiří ; Kozubková, Milada (referee) ; Kučera,, Radek (referee) ; Veselý, Jindřich (referee) ; Pochylý, František (advisor)
This work introduces a new method of hydraulic design of a centrifugal pump impeller. This method is based on a geometrical approach employing curvilinear coordinates that are used to formulate both the axisymmetrical flow model in a meridional shape and the final model of flow in a blade cascade taking into account the full 3D shape of the impeller blade. The solution to this model then directly provides the guidelines for shaping the impeller blade in order to suppress the secondary flows, thus increasing the impeller efficiency, which is demonstrated on a real impeller design case. The partial differential equations describing the flow in the blade cascade are numerically solved piecewise on each particular stream surface, which leads to a significant reduction of computational time.
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Analysis of the Fluid Flow in Pipes Circular and Not Circular Cross-Section With Methods Using Distribution of the Vorticity Density
Soukup, Lubomír ; Kozubková, Milada (referee) ; Matas, Jakub (referee) ; Štigler, Jaroslav (advisor)
The doctoral thesis deals with the analysis of the flow in the circular and not circular cross-section pipes by methods using the distribution of the vorticity density. This analysis is particularly focused on the derivation of the new velocity profiles formulas using the above mentioned method. In this work is presented a historical overview of the derived velocity profiles. This overview of already derived velocity profiles will be a fundamental benchmark for newly derived velocity profiles. These new velocity profiles are derived for the circular and not circular cross-section pipes and the derivation is based on the analogy of electromagnetic induction by using Biot-Savart law. It is necessary to apply this analogy at first on solitary vortex filament. By taking this step is possible to get the value of the induced velocity from one solitary vortex filament. Subsequently it is possible to obtain the value of the induced velocity from the vorticity wall and afterwards from the vorticity density distribution over the cross section. This work contains also the results of the experimental measurements of the velocity profiles, and of the CFD simulations. Experimentally measured results are used besides other for the selecting of the most suitable CFD computational model. Selected CFD model will be subsequently declared as a reference model and the valid velocity profiles for this model will serve with the experimentally measured data as a benchmark for the newly derived velocity profiles.
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Collection of Solved Problems of Business Intelligence for Students of the Faculty of Economics
KOZUBKOVÁ, Miroslava
The subject of the diploma thesis titled, "Collection of Solved Problems of Business Intelligence for Students of the Faculty of Economics" is a creation and description of a series of solved problems of Business Intelligence. The theoretical part is focused on basic terms associated with Business Intelligence. In the practical part, there is showed the usage of MS SQL Server and MS Server Data Tools for creation different parts of the Business Intelligence process.
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High Frequency Pulsation of Water Turbine in Operation
Kubálek, Jiří ; Kozubková, Milada (referee) ; Hružík, Lumír (referee) ; Haluza, Miloslav (advisor)
This thesis is concentrated on mathematical modeling of high frequency pulsations in pump turbines, which are the source of high-cycle continuous stress of the spiral casing cover, wicket gates and runner. There are proposed the solutions using the transfer matrix for the tube with a constant and conical cross-section. The paper compares variations of cylindrical and conical tubes, changes in boundary conditions. There are the models of PSPP Dlouhé Stráně made only of cylindrical tubes comparing to the model with cylindrical and conical tubes
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Modeling of Liquid Film Instabilities with Subsequent Entrainment of Droplets
Knotek, Stanislav ; Kozubková, Milada (referee) ; Čermák, Libor (referee) ; Jícha, Miroslav (advisor)
This dissertation deals with instabilities of thin liquid films up to entrainment of drops. Four types of instabilities have been classified depending on the type of structure and process on the liquid film surface: two-dimensional slow waves, two-dimensional fast waves, three-dimensional waves, solitary waves and entrainment of drops from the film surface. This thesis analyzes the physical principles of instabilities and deals with the mathematical formulation of the problem. Shear and pressure forces acting on the surface of the liquid film are identified as the cause of instabilities. Mathematical models for predicting instabilities are demonstrated using approaches based on solving the Orr-Sommerfeld equation and the equations of motion in integral form. Models of shear and pressure forces acting on the surface of the film and selected models of film thickness are presented. The work is focused on the prediction of the initiation of two-dimensional waves using the integral approach. Shear stress and pressure forces acting on the liquid film surface have been modeled using the simulation of air flow over a solid surface. Finally, criteria for drop entrainment are presented with their dependence on air velocity and film thickness.
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Solution of Non-Linear Hydraulic Networks
Himr, Daniel ; Kozubková, Milada (referee) ; Šklíba, Jan (referee) ; Abaid, Emhemmed (referee) ; Pochylý, František (advisor)
Thesis deals about solution of non-steady flow in hydraulic systems, which have one dominant component of velocity. Such systems can be arbitrarily structured and they are not limited by number of elements. Computation is based on Lax-Wendroff method and enables considering of variable sound peed as function of static pressure and properties of pipe material. It means, that hydraulic system can be very various. Numerical method is described in detail and description is also focused on sensitivity of method for time step and length step. It can be very imported for evaluation of numerical viscosity, which is compared with second viscosity of fluid. Hammer is working title of software, which was developed on the basis of written numerical procedures. This software enables fast computation of flow in pipe-line systems.
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The implementation of a server for communication in a corporate environment
KOZUBKOVÁ, Miroslava
The subject of the bachelor thesis "The implementation of a server for communication in a corporate environment" is a general description of server systems, selected products of Microsoft and IBM and an evaluation of their groupware features. Another part of this thesis is a qualitative research including information gained by interview in company ČD Cargo, where these products were used.
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Gas photoacoustic detection and its possible application in monitoring of foundry technologies
Herecová, L. ; Nevrlý, Václav ; Zelinger, Zdeněk ; Střižík, Michal ; Kozubková, M. ; Danihelka, P.
To improve occupational health & safety as well as process quality control, many foundry enterprises can be interested in application of new and effective techniques of gas monitoring due to a lot gaseous secondary compounds produced within such processes, e.g. during thermal degradation of organic binders in casting process. Generally, gas monitoring can just be performed as effective as possible when a sufficiently universal, sensitive and selective method of a broad dynamic range is available. The CO2-laser photoacoustic detection technique can represent such a monitoring tool, useful also for foundry industrial technologies. Its basic principles, description of instrumentation and possible applications in foundry technologies are discussed in our contribution.
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