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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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Waterjet cutting of material
Veselý, Radek ; Foldyna, Josef (referee) ; Habán, Vladimír (advisor)
This bachelor thesis describes principles of utilization of high-speed liquid jet for material machining. In the first part, basic classification of liquid jets and brief description of devices for generating high pressure liquid is presented. Next, using of continuous jets is discussed. Main scope of this work is oriented at the use of so-called pulsed jets, especially at ultrasonically modulated ones. Break-up of ultrasonically modulated high-speed pulsed jet into single pulses, impact of such pulse on the surface of disintegrated material and subsequent erosion in the impact area are described. The comparison of efficiency of modulated and continual water jets is summarized in the last part of the thesis.
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Elevation measurements in the northern area of mining areas Doubrava and Karvina Mines I in 2020
Kajzar, Vlastimil ; Staš, Lubomír ; Foldyna, Josef
In the northern area of the Doubrava and Karviná Mines I mining districts on the border of the cadastral district Dětmarovice and Doubrava, mining operations are underway. For this reason, in order to identify possible mining effects on the surface and surface objects, the stabilized points in this area are surveyed regularly twice a year. Since 2014 the Institute of Geonics AS CR, v.i., Ostrava has been selected as the contractor of these works. In June and November 2020, the surveying stages planned for this year were carried out, during which altogether 4 interconnected leveling routes, which are formed by these points, were carried out.
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Deformometric and leveling measurements in the cadastral area of Dětmarovice village in 2020
Kajzar, Vlastimil ; Staš, Lubomír ; Foldyna, Josef
Institute of Geonics AS CR, v.v.i. in Ostrava was in 2001 asked by the ČSA Mine, in connection with the considered underground mining of coal reserves and its possible impact on the cadastral district of Dětmarovice, to assess the possible effects of undermining on slope stability in selected parts of the cadastral district of Dětmarovice. Mining results in, among other things, surface subsidence, which, given the existing terrain morphology in the cadastral area, has raised concerns as to whether these subsidence will further induce slope movements. Thus, in November 2001, a monitoring monitoring network with four individual profiles was established in the area. On these lines it was recommended to perform deformometric (length) and leveling (height) measurements at the same intervals. The first of a pair of planned deformometric and height measurements in 2020 was carried out in May, the second during October.
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X-Ray CT inspection of subsurface areas of concretes exposed to fast flowing liquids
Sitek, Libor ; Hlaváček, Petr ; Souček, Kamil ; Bodnárová, L. ; Foldyna, Josef ; Zajícová, Vendula ; Berčáková, Andrea ; Foldyna, Vladimír
Concrete structures affected for a long time by flowing liquids are exposed to gradual erosion in surface layers caused by a combination of several degradation processes: abrasion, cavitation and chemical or bacterial impacts. Due to the complex phenomena and difficult-to-define initial and boundary conditions, the whole process cannot be easily simulated using the conventional computing tools. Laboratory experimental research is thus the most appropriate approach for the investigation of a suitable composition of concrete resistant to the flowing liquids. However, the methods used are often very time consuming and last even several years. High-speed water flows can be elegantly used for the acceleration of the mechanical simulation of a real situation. Several experiments on the effects of the high-speed water flows on concrete surfaces have been carried out. Using the X-Ray CT methods, subsurface structures of concretes exposed to the accelerated mechanical simulation of the erosion wear caused by fast flowing liquids were investigated and presented in the article. It has been shown that the simulation does not cause initiation of new fractures or cracks in the original concrete structure. The pure water flow mainly removes the hardened cement paste and reveals the aggregate grains. The water flow with abrasive particles disintegrates in greater depths and washes out entire aggregate grains, eventually amputates them and finally smoothens entire surface.
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Nanoscale phases on surface Fe-6Si magnetic sheets
Švábenská, Eva ; Roupcová, Pavla ; Král, Lubomír ; Bulín, Tomáš ; Vondráček, Martin ; Foldyna, Josef ; Čechal, J. ; Schneeweiss, Oldřich
Analysis of the nanoscale phases which appear on the surface Fe-6Si samples were carried out after the various treatments – grinding and etching, annealing, and water jet abrasion. The basic information on structure, chemical and phase composition was obtained by X-Ray Powder Diffraction (XRD), Scanning Electron Microscopy with EDX, Glow Discharge Optical Emission Spectrometry (GDOES), Mössbauer Spectroscopy and X-ray Photoelectron Spectrometry (XPS). The results show high stability of the surface phase composition after the mechanical and heat treatments. Results obtained from the surface analysis in micrometer depth (XRD, EDX, GDOES) do not show any changes after the different treatments. Iron oxides were detected in XPS and conversion electron Mössbauer spectra (CEMS) which analyze the surface composition in a nanometer scale. In addition to, fine changes in atomic ordering on the surface can be observed after mechanical and heat treatments in the CEMS spectra.
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Effects of Water Jets on CNTs/concrete composite
Foldyna, Vladimír ; Foldyna, Josef
Results of the resistance of carbon nanotubes concrete composite (CNTs/concrete\ncomposite) to the action of pulsating and continuous water jets are presented in\nthis paper. This work brings advanced results of fully hydrated CNTs/concrete\ncomposite (after 28 days) and it follows up the research of this composite\nhydrated 7 days. The experiments were focused at the determination of erosion\neffects of both types of water jets impinging the surface of reference (concrete) and\nCNTs/concrete composite samples. Erosion effects of water jets were evaluated in\nterms of material removal rate. Tests were performed at various operating\nparameters of continuous and pulsating water jets.
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Application of high speed water jet technology for concrete repair
Bodnárová, L. ; Sitek, Libor ; Foldyna, Josef ; Jarolím, T.
This article brings selected knowledge from the long-term cooperation between\nthe Brno University of Technology, the Faculty of Civil Engineering, the Institute of\nTechnology of Building Materials and Components, and the Academy of Sciences of\nthe Czech Republic, v.v.i., Institute of Geonics, Ostrava – Poruba in the field of\nthe interaction of high-speed water jets and concrete, especially with regard to\nthe use of high-speed water jet technology for the removal of surface layers of\nconcrete during repair of concrete.
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