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Modulated ultrasonic water jet cutting – optimization of the liquid wave guide shape
Veselý, Radek ; Foldyna, Josef (referee) ; Habán, Vladimír (advisor)
High speed water jets have un-substitutable place in unconventional technologies in the machining of materials. Indeed its larger spreading is limited above all by its really high purchase price and also high costs of the operation. Certain possibility is represented by high-speed pulsating jets, which don’t put such a high pretension on arrangement of generating the pressure during the comparable operation. Probably the most effective method of the generating of pulsating water jets is ultrasonic modulation. This work could benefit to understanding spreading of pressure impulses between ultrasonic generator and output nozzle. Pulsating is solved by the numerical calculation using transfer matrix method.
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Design of Acoustic Absorbers Using Perforated Boards
Jun, David ; Stejskal, Pavel (referee) ; Kalousek, Lubor (advisor)
Perforated boards are one of the most commonly used elements for the construction of acoustic resonators in the form of walls or ceilings. This diploma thesis focuses on some aspects of the design of these perforated resonators. The main factor considered was the shape of the holes in the plate and its influence on the measured course of the sound absorption coefficient and also on its prediction by commonly available methods. The first aspect of resonator design is to measure the sound absorption coefficient. Within the work, common measurement methods are thoroughly compared and the reverberation room method, which is further used for measuring the produced samples, is presented in more detail. For the purposes of this part, our own hardware and software solution of the measuring set is also developed. Service scripts were written in the Python programming language. The second aspect of the design treated in this work is the choice of the porous infill of the resonator based on its value of airflow resistivity. This value is determined here by the static airflow method and based on the relevant standards, our own measuring device was developed for these purposes. This device was made mainly by FDM 3D printing and was operated by scripts in Python. The third and last of the design aspects described here is the prediction of the course of the sound absorption coefficient of perforated resonators. In this part, the method of electro-acoustic analogy is presented together with the transfer matrix method as described in the literature, which is further supplemented by the introduction of an equivalent radius including the effect of hole elongation in the calculation. The results obtained by the calculation are finally compared with the measurement and the optimization of the calculation is proposed in the form of adjusting the relationship for the end correction factor and for the combination of acoustic impedances of individual layers.
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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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Pressure pulsation propagation in elastic hoses
Čapoš, Eduard ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
This thesis deals with propagation of pressure and flow pulsations, which are strongly affected by the tube flexibility. There are two mathematic models introduced, which are derived from basic physical relations. First model assumes velocity only in the axis direction. Second one assumes also non-zero radial velocity. Kelvin-Voigt model for viscoelasticity was used. Furthermore, experimental measurement was designed and evaluated. Measured data was used to calculate material properties. In addition, dynamic transfer was determined.
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Assessment of the second viscosity coefficient from measured pressure pulsations.
Černý, Ondřej ; Pochylý, František (referee) ; Habán, Vladimír (advisor)
Diploma thesis deals with problem of assessment of the second viscosity and acoustic velocity coefficients by the different liquid´s flow in pipe from measured pressure pulstation created by diaphragm pulsator. For the solution is used a transfer matrix model and for the data evaluation a genetic algorithm in „Facharp.exe“ program. Modal analysis in problematic part of the measured stand is realized to find a wave shapes and natural frequency of a pipe. The results are for the reason of clearness processed into „MS Excel“ program and fetched to the charts which shows depedence of a second viscosity and acoustic velocity coefficients on a various flow as the final result.
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High-Frequency Pulsations Modeling
Střecha, Ludvík ; Kubálek, Jiří (referee) ; Habán, Vladimír (advisor)
The diploma thesis deals with the mathematical modeling of high-frequency pressure pulsations in water turbines. Pulsations are caused by the interaction between stator a rotor blades. These high-frequency pressure pulsations then cause high cycle fatigue of the head cover, spiral casing, runner and distributor. The mathematical model is solved by transfer matrix method. Data are processed in F-A char and MS Excel programs. Final results are demonstrated by frequency amplitude characteristics and by pressure mode shapes, where comparison of the mathematical model with the measurement is shown.
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Laser coupling system
Dell, Roman ; Wilfert, Otakar (referee) ; Barcík, Peter (advisor)
This bachelor's thesis deals with the usage of a tunable pulsed laser for coupling to a single-mode fiber. At first, the thesis explains the principle of laser functioning, its basic technical components, properties of laser radiation and main types of tunable pulsed lasers. Next, it describes main types of optical fibres, their key properties and the methods for laser to fibre coupling. Finally, the thesis explains the basic concepts of matrix optics, its application to the Gaussian beam transformation and the calculation of coupling efficiency.
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Magneto-optic response of layered media
Kunt, Ota ; Ostatnický, Tomáš (advisor) ; Antoš, Roman (referee)
Optical response of materials strongly depends on their magnetic properties. This phenomenon is also used in materials in the form of thin layers and multi- layers. Using cited literature we summarize theory needed to calculate magneto- optical response of multilayers. The calculation is based on Maxwell equations and magnetic materials are described with effective permittivity tensor. Jones formalism is used to describe polarised light and Yeh formalism is used to de- scribe multilayer response. A program using presented theory was developed and calculations for concrete structure were made. Multilayer parameters were cho- sen to correspond with those of a sample whose magneto-optical response was measured at the Department of Chemical Physics and Optics, MFF UK. 1
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Light propagation in magnetic materials
Wagenknecht, David ; Ostatnický, Tomáš (advisor) ; Veis, Martin (referee)
Transparent magnetic materials, among the others semiconductors, have recently come to the focus of interest in both basic and applied research because they have great potential in optical applications and they can be used in optical spectroscopy to investigate fundamental physical phenomena. The theoretical calculations introduce that these materials have some extraordinary properties like asymmetric reflectance when light impact the sample from the opposite angles. In this bachelor thesis, transfer matrix formalism is derived based on Maxwell equations, taking into account special form of effective permittivity. The reflection coefficient for one layer demonstrates, that the asymmetric reflectance appears for transversal- magnetic polarization of light and transversal magnetization in the studied material. The derived formulae are used to calculate the difference in reflectivities for the waves impacting the structure from opposite angles. Ga1−xMnxAs with different concentrations of manganese is assumed to be the essential transparent magnetic layer in the sample. 1
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Optical response of magnetic materials
Wagenknecht, David ; Ostatnický, Tomáš (advisor)
David Wagenknecht: Abstract of a diploma thesis Optical response of magnetic materials, 2014 Magnetooptical properties of anisotropic semiconductors are studied to describe asymmetry of Ga1−xMnxAs, because theoretical calculations predict extraordinary behaviour of reflectivity. Analytical formulae to describe materials with non-diagonal permittivity are derived and they are used for the numerical calculations to describe the optical response of the samples available for the measurement. The transversal Kerr effect is calculated and it exhibits asymmetry in both rotation of the plane of polarization and ellipticity of circularly polarized light due to asymmetry in reflectivity. Moreover, longitudinal and polar magnetization are studied because of the influence on the observability of the phenomena. Results are not only used to discuss conditions, which must be satisfied to prove the asymmetry, but also the actual experimental setup is designed to prepare the measurement. 1
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