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Theoretical background for determining the fracture-mechanics parameters using the Boundary Element Method
Gröger, Roman
Boundary Element Method is a powerful tool for certain class of Solid Mechanics problems, where the fundamental solution of the governing differential equation is known. This article briefly outlines the theoretical background of BEM for plane problems as well as integral identities for calculation of internal stresses and displacements. Chapter 2 introduces the most useful contour integrals for calculation of fracture parameters in two-parameter linear elastic fracture mechanics. These coefficients are solved using the stress and strain tensor field calculated using BEM. All the proposed and discussed approaches are compared and the differences between FEM and BEM are discussed.
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Sborník semináře KŘEHKÝ LOM
Dlouhý, Ivo ; Chlup, Zdeněk
Contribution presented on one-day workshop paid to problems of mechanisms and mechanics of brittle fracture. Quantitative description of toughness transition behaviour. Problems of constraint indexing parameter and J-integral calculation at elastic plastic behaviour of material. Fracture mikromechanisms and their modelling.
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Vibratin of bridges under high speed trains
Frýba, Ladislav
The theoretical model explains the dynamic behaviour of railway bridges subjected to high speed trains. The method of integral transformations gives the deflections, stresses and vertical accelerations of the beam in a compact form. The numerical study presents a survey on the effect of several parameters.
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Forbidden Oxygen line emission from the traces of meteors
Habuda, Pavol ; Borovička, Jiří (advisor) ; Šolc, Martin (referee)
The aim of this diploma thesis was to study forbidden green oxygen line emission. It was found out that green line emit mainly in heights 100-110 kilometers, exceptionally below 90 kilometers. Time evolution of green line intensity with respect of heights was investigated in detail. There was suggested theoretical dependency and agreement with observed data was fulfilled. Dependency of integral intensity was investigated as well. Mechanisms of excitation and quenching of green line in emission was proposed in previous studies in 70. of previous century. This work discuss with its results. Efficiency of transformation of kinetic energy of meteoroid to forbidden green line's emission was discussed. The concentrations of atomic oxygen was estimated by several way in heights of green line emission.
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Mounting of leads by brazing on alumina substrate
Neradil, Petr ; Adámek, Martin (referee) ; Otáhal, Alexandr (advisor)
Bachelor´s thesis deals with the issue of implementation hybrid integrated circuit terminals for performance applications. It also states the advantages of each type of terminals and their technology. It discusses the materials used for brazing and describes problems of brazed in the electrical industry. The thesis also presents techniques for brazin of leads by brazers on the ceramic substrate. The conclusion contains the results of thermal and mechanical tests of the resulting connection.
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Gas and Vapour Transport and Mechanical Properties of Carbon Nanotube and Carbon Fibre-Reinforcement of Ethylene-Octene Copolymer Membranes
Sedláková, Zuzana ; Clarizia, G. ; Bernardo, P. ; Jansen, J.C. ; Slobodian, P. ; Svoboda, P. ; Kárászová, Magda ; Friess, K. ; Izák, Pavel
Helium, hydrogen, nitrogen, oxygen, methane and carbon dioxide were used for gas permeation rate measurements. Theoretical Maxwell’s model was used to predict and interpret gas transport properties in MMMs. Vapour transport properties were studied for aliphatic hydrocarbon (hexane), aromatic compound (toluene), alcohol (ethanol), as well as water. Organic vapours result more permeable than permanent gases in EOC-based membranes, with toluene and hexane permeabilities being about two orders of magnitude higher than permanent gas permeability. Carbon-filled membranes show that the EOC is an organophilic material that offers perspectives for application in gas/vapour separation with improved mechanical resistance.
Fulltext: content.csg -  PDF
Plný tet: SKMBT_C22014090110400 - PDF
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On the boundary conditions in the numerical simulation of stably stratified fluids flows
Bodnár, Tomáš ; Fraunié, P.
This paper presents the results of a numerical study of the stably stratified flow over a low smooth hill. The emphasize is on certain problems related to artificial boundary conditions used in the numerical simulations. The numerical results of three-dimensional simulations are shown for a range of Froude and Reynolds numbers in order to demonstrate the varying importance of these boundary issues in different flow regimes. The simulations were performed using the Boussinesq approximation model solved by a high-resolution numerical code. The in-house developed code is based on compact finite-difference discretization in space and Strong Stability Preserving Runge-Kutta time integration.
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Characterization of Turbulent Flow in a Breakup Cell.
Vejražka, Jiří ; Zedníková, Mária ; Stanovský, Petr
Our research focuses on breakup of bubbles and drops induced by a flow turbulence. In this contribution, we describe the experimental setup used for studying the breakup, and we characterize flow within it. The setup is a rectangular glass cell, in which a turbulent flow is generated by a set of coaxial nozzles. The flow within it is characterized by means of particle image velocimetry. From the velocity data, i) local dissipation rate (ε) is estimated using Large-Eddy PIV method, and ii) statistics of velocity difference in two points is evaluated. Estimation of ε is validated by integrating the total dissipation in the setup, which reasonably agrees with the injected kinetic energy. The probability density function of velocity difference is non-Gaussian and when properly normalized, it is universal within the setup.
Fulltext: content.csg - PDF
Plný tet: SKMBT_C22016120713100 - PDF
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Comparison of synthetic jet actuators based on sharp-edged and round-edged nozzles
Kordík, Jozef ; Trávníček, Zdeněk
Axisymmetric synthetic jet actuators based on a loudspeaker and on two types of flanged nozzles were tested and compared experimentally. The first type of the nozzle was a sharp-edged circular hole. The second one had a special design with fillets at inner and outer nozzle exit and with a small step in the middle of the nozzle. The function of the step was to prevent the flow reattachment during the extrusion stroke. The actuators with the two types of nozzles were operated at resonance and were compared first qualitatively using a simple phase locked flow visualization. Then the hot-wire anemometer was used to measure velocity \ndistributions along nozzle axis and velocity profiles at the nozzle exit. Comparison of the nozzles was based on evaluation of the characteristic velocity and integral quantities (volumetric, momentum, and kinetic energy fluxes). It was found out that these quantities, which were evaluated at the nozzle exit, differ substantially for both nozzles. On the other hand the velocity flow field in farther distances from the nozzle exit area did not exhibit such prominent differences.
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