Number of found documents: 14761
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On attempts to characterize facet-defining inequalities of the cone of exact games
Studený, Milan; Kroupa, Tomáš; Kratochvíl, Václav
2018 - English
The sets of balanced, totally balanced, exact and supermodular games play an important role in cooperative game theory. These sets of games are known to be polyhedral cones. The (unique) non-redundant description of these cones by means of the so-called facet-defining inequalities is known in cases of balanced games and supermodular games, respectively. The facet description of the cones of exact games and totally balanced games are not known and we present conjectures about what are the facet-defining inequalities for these cones. We introduce the concept of an irreducible min-balanced set system and conjecture that the facet-defining inequalities for the cone of totally balanced games correspond to these set systems. The conjecture concerning exact games is that the facet-defining inequalities for this cone are those which correspond to irreducible min-balanced systems on strict subsets of the set of players and their conjugate inequalities. A consequence of the validity of the conjectures would be a novel result saying that a game m is exact if and only if m and its reflection are totally balanced. Keywords: exact game; extremity; irreducible; balanced Fulltext is available at external website.
On attempts to characterize facet-defining inequalities of the cone of exact games

The sets of balanced, totally balanced, exact and supermodular games play an important role in cooperative game theory. These sets of games are known to be polyhedral cones. The (unique) non-redundant ...

Studený, Milan; Kroupa, Tomáš; Kratochvíl, Václav
Ústav teorie informace a automatizace, 2018

Tradiční opracování a kvalita dřeva při opravách dřevěných konstrukcí.
Kloiber, Michal; Růžička, Petr
2018 - Czech
Rozsáhlé terénní zkušenosti při opravách dřevěných konstrukcí ukazují na dva základní limitující faktory kvality odvedené práce, které se často různými obcházejí či zjednodušují. V první řadě je to kvalita dřeva při opravách (výměny, protézy) a z ní vyplývající problémy při nedodržení doporučených kritérií pro výběr vhodného materiálu, s ohledem na dlouhodobou koexistenci nového dřeva s původním materiálem. Ve druhém případě jsou velmi vlivným faktorem způsoby opracování dřeva, kdy se pro své výhody preferované tradiční způsoby z různých důvodů nahrazují podvrhem. V tomto článku se budeme vzhledem k jeho omezenému rozsahu věnovat pouze nejkřiklavějšímu případu, a tím je opracování kulatiny tesáním. Extensive field experience with repairing timber structures shows two main limiting factors for the quality of work that are often circumvented or simplified. First, it is the quality of the timber for the repairs (replacements, additions) and the resulting problem when the recommended criteria for the selection of suitable material are not met, with regard to the long-term coexistence of the new timber with the original material. Second, a critical factor is the way in which the timber is worked - the preferred traditional working is for various reasons replaced by counterfeits. Due to the limited scope of this paper, we can only pay attention to the most blatant case, which is working of logs by hewing. Keywords: wooden structures; old carpentry tools; timbers Available at various institutes of the ASCR
Tradiční opracování a kvalita dřeva při opravách dřevěných konstrukcí.

Rozsáhlé terénní zkušenosti při opravách dřevěných konstrukcí ukazují na dva základní limitující faktory kvality odvedené práce, které se často různými obcházejí či zjednodušují. V první řadě je to ...

Kloiber, Michal; Růžička, Petr
Ústav teoretické a aplikované mechaniky, 2018

Monitorování poruch reprezentačního sálu Fürstenberského paláce na Malé Straně v Praze
Drdácký, Miloš; Zíma, Pavel
2018 - Czech
Zpráva popisuje a analyzuje poruchy historických konstrukcí a vztahuje je k dlouhodobému monitorování změn teploty a pohybu trhlin. The report describes and analyses damage and failure of historic structures and relates them to a long term monitoring of movement in cracks and temperature fluctuations. Available at various institutes of the ASCR
Monitorování poruch reprezentačního sálu Fürstenberského paláce na Malé Straně v Praze

Zpráva popisuje a analyzuje poruchy historických konstrukcí a vztahuje je k dlouhodobému monitorování změn teploty a pohybu trhlin....

Drdácký, Miloš; Zíma, Pavel
Ústav teoretické a aplikované mechaniky, 2018

Combined coatings against mechanical wear and corrosion low carbon steel
Brožek, Vlastimil; Pokorný, P.; Kolísko, J.; Vokáč, M.; Mastný, L.; Stoulil, J.
2018 - English
In this study, special ceramic coatings were prepared on low carbon steel (1.0060 - EN 10027-2) via the plasma spraying technique using a WSP®-H plasma generator with output of up to 40 kg/h of aluminum oxide. Corundum coatings were deposited directly on the surface of steel plungers equipped with an anti-corrosion interlayer of zinc phosphate. Coating adhesion properties were tested using pin-off tests (modified ISO 4624) and reached a maximum value of 26 MPa. Corrosion resistance was evaluated by measurements of impedance spectra in the 100 kHz - 10 mHz range in a water solution of sodium sulfate. The capacity of electric double-layer varied depending on the porosity and thickness of the coating. Low-porosity coatings of >1.5 mm thickness had RCT 1.29·105 Ω·m2. The abrasive resistance of coatings was measured by rotary/machining test with SiC cutting knives, using a downforce of 50 kg·cm-2. Abrasion losses decreased with the quality of finish - starting at 0.00266 g cm-2 min-1 down to virtually zero losses after polishing the surface below Ra = 0.55 micro m. Keywords: Abrasion; Ceramic coatings; Corrosion resistance; Plasma spraying; Steel phosphating Available at various institutes of the ASCR
Combined coatings against mechanical wear and corrosion low carbon steel

In this study, special ceramic coatings were prepared on low carbon steel (1.0060 - EN 10027-2) via the plasma spraying technique using a WSP®-H plasma generator with output of up to 40 kg/h of ...

Brožek, Vlastimil; Pokorný, P.; Kolísko, J.; Vokáč, M.; Mastný, L.; Stoulil, J.
Ústav fyziky plazmatu, 2018

Suspension plasma spraying of sub-stoichiometric titania by hybrid water/argon stabilized plasma torch
Mušálek, Radek; Ctibor, Pavel; Medřický, Jan; Tesař, Tomáš; Kotlan, Jiří; Lukáč, František
2018 - English
In this study, suspension plasma spraying of sub-stoichiometric titania was attempted using hybrid water/argon stabilized plasma torch (WSP-H). Porous coatings with fine cauliflower-like columnar microstructure were successfully deposited in two separate experiments with different power levels of the plasma torch. In both cases, high solid-load content (40 wt. %) of the water-based suspension resulted in considerable coating thickness increase per deposition cycle. Coating annealing and partial remelting of the surface asperities were also achieved by additional pass of plasma torch in front of the coating surface. According to X-ray diffraction, all coatings consisted dominantly of rutile phase. Detailed microscopic observation of the as-sprayed and annealed deposits showed that the local coloration of the coating (ranging from dark blue to beige) was driven by the local overheating of the rough coating surface which could also promote the oxygen intake. Moreover, sample annealing was also observed to increase the sample reflectivity as observed by UV-VIS-NIR scanning spectrophotometry Keywords: Liquid feedstock; Plasma spraying; Suspension; Thermal spraying; Titania; WSP-H Available at various institutes of the ASCR
Suspension plasma spraying of sub-stoichiometric titania by hybrid water/argon stabilized plasma torch

In this study, suspension plasma spraying of sub-stoichiometric titania was attempted using hybrid water/argon stabilized plasma torch (WSP-H). Porous coatings with fine cauliflower-like columnar ...

Mušálek, Radek; Ctibor, Pavel; Medřický, Jan; Tesař, Tomáš; Kotlan, Jiří; Lukáč, František
Ústav fyziky plazmatu, 2018

Experimentální stanovení ventilačních ztrát ozubeného kola a tepelného zatížení zubu
Kordík, Jozef; Dobiáš, Jiří; Hrubý, Jan
2018 - Czech
Tato zpráva je sepsána v rámci čtvrté etapy řešení výzkumného úkolu TA04011656, „Vývoj rychloběžné planetové převodovky s pružným uložením satelitů pro extrémní obvodové rychlosti”. První část zprávy se věnuje ventilačním ztrátám a jsou zde uvedeny podrobnosti k experimentům, které byly uskutečněny s testovací převodovkou “Alfa II” na zkušebním pracovišti Wikov Gear. Experimenty zahrnovaly měření ventilačních ztrát a měření teplot zubu podél šířky kola. Při experimentech byly testovány tři konfigurace obvodového krytu převodového kola, které se lišily vzdáleností mezi krytem a kolem. Mimoto byl testován i případ bez krytu. V závěru této části je navrženo rozšíření modelu ventilačních ztrát z předešlé zprávy pro reálné geometrie převodového kola s krytem, který je otevřený v místě záběru s pastorkem a v místě odtoku oleje.\nDruhá část zprávy se věnuje tepelnému zatížení boku zubu a prezentuje výsledky experimentů, které se týkaly měření teplot zubu podél šířky kola. Jsou zde rovněž uvedeny detaily k numerickému modelování tepelného zatížení boku zubu. V rámci numerické analýzy (i) byla vyvinuta metodika modelování odvalování boků zubů kola a pastorku po sobě, (ii) byl vytvořen výpočetní model, (iii) byla vyvinuta metodika určování neznámých velikostí některých parametrů výpočetního modelu a (iv) byl vyvinut algoritmus a metodika výpočtu.\n The report is written for the needs of the project no. TA04011656 ("Research and development of new type of high-speed planetary gear unit with the flexible pin technology to support the planet wheels enabling the transmission of high outputs."). The first part of the report targets the topic of windage losses of a rotating toothed wheel, the experiments with testing gearbox “Alfa II” are introduced here, as well. The experiments included measurements of windage losses and temperature measurements along a wheel tooth width. Three geometrical configurations differing in wheel enclosure distance were tested, the case without the enclosure was tested too. The outcome of this part is an extension of the previous windage loss model for real geometry configuration: a wheel with an enclosure opened at place of oil outflow and at place of meshing with pinion.\nThe second part of the report targets the thermal load of a wheel tooth and presents experimental results of measurements of temperature distribution along the tooth. This part also contains the details concerning the numerical modeling of this problematic. The numerical analysis included (i) development of methodology for modeling of tooths meshing, (ii) development of the computational model, (iii) development of methodology for assessment of unknown values of some parameters of the model, (iv) development of algorithm. \n Keywords: widage loss; wheel enclosure; gear box Available at various institutes of the ASCR
Experimentální stanovení ventilačních ztrát ozubeného kola a tepelného zatížení zubu

Tato zpráva je sepsána v rámci čtvrté etapy řešení výzkumného úkolu TA04011656, „Vývoj rychloběžné planetové převodovky s pružným uložením satelitů pro extrémní obvodové rychlosti”. První část zprávy ...

Kordík, Jozef; Dobiáš, Jiří; Hrubý, Jan
Ústav termomechaniky, 2018

Running flutter waves in the model of turbine blades cascade
Půst, Ladislav; Pešek, Luděk
2018 - English
This contribution is connected with the paper on the previous conference, where the origin and properties of forced running waves produced by flowing steam through cascade of stationary and rotating wheels with different numbers of blades in the steam turbine were investigated. Due to the aero-elastic forces of this steam flow, these comparatively small vibrations can excite strong flutter running waves. Presented contribution is oriented on the analysis of dynamic properties of computational model of blades cascade, where the flutter is modelled by two types of Van der Pol self-excitation forces. Keywords: blades cascade; flutter; running waves; self-excitation; number of blades Available at various institutes of the ASCR
Running flutter waves in the model of turbine blades cascade

This contribution is connected with the paper on the previous conference, where the origin and properties of forced running waves produced by flowing steam through cascade of stationary and rotating ...

Půst, Ladislav; Pešek, Luděk
Ústav termomechaniky, 2018

Development, assessment and verification of finite element procedures for contact problems
Gabriel, Dušan; Kopačka, Ján; Masák, Jan; Plešek, Jiří
2018 - English
A frictionless three-dimensional contact algorithm based on the pre-discretization penalty formulation was proposed. The algorithm proved to be robust, accurate and symmetry preserving—no master/slave surfaces have been introduced. It was implemented in the finite element code PMD (Package for Machine Design) for the solution of complex engineering problems. The capability of the algorithm was demonstrated in creep analysis of T-piece of the steam distributor of the CHEMOPETROL heating plant T200. Material properties were described by the probabilistic exponential model with damage. The purpose of the analysis was to compare the original version and the proposed design modification applied to one of T-pieces of the distributor when the proposed contact algorithm was employed to simulate the interaction between the collar and the pipe. Keywords: FEM; contact algorithm; creep analysis; T-piece of the steam distributor Available at various institutes of the ASCR
Development, assessment and verification of finite element procedures for contact problems

A frictionless three-dimensional contact algorithm based on the pre-discretization penalty formulation was proposed. The algorithm proved to be robust, accurate and symmetry preserving—no master/slave ...

Gabriel, Dušan; Kopačka, Ján; Masák, Jan; Plešek, Jiří
Ústav termomechaniky, 2018

LOW CYCLE FATIGUE BEHAVIOR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C
Šulák, Ivo; Obrtlík, Karel; Hrbáček, K.
2018 - English
The second generation nickel-based superalloy MAR-M247 offers a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that are required for application at elevated temperatures in hostile environments. The microstructure consists mainly of the face centred cubic γ matrix and ordered γ´ strengthening precipitates (L12 crystal structure). The present work focuses on low cycle fatigue (LCF) behaviour of polycrystalline nickel-based superalloy MAR-M247 at high temperature. LCF tests were conducted on cylindrical specimens in a symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 700 °C in ambient air. Cyclic stress-strain curves and fatigue life curves in the representation of plastic strain amplitude vs. stress amplitude and stress amplitude vs. the number of cycles to failure, respectively, were plotted and compared with data obtained on Inconel 713LC. Special attention was paid to the investigation of crack initiation in MAR-M247 during low cycle fatigue. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). Specimens’ surface observations revealed the formation of pronounced surface relief indicating localisation of plastic deformation. Observations in transmission electron microscope (TEM) confirmed localisation of cyclic plastic deformation in persistent slip bands along {111} slip planes. Fractographic analysis revealed fatigue crack initiation sites. Fatigue crack propagation in stage I was typical of smooth facets up to 500 μm long. Keywords: Nickel-based superalloy; cyclic stress-strain curve; Fatigue life; fatigue crack initiation; focus ion beam Available at various institutes of the ASCR
LOW CYCLE FATIGUE BEHAVIOR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C

The second generation nickel-based superalloy MAR-M247 offers a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that are required for application at ...

Šulák, Ivo; Obrtlík, Karel; Hrbáček, K.
Ústav fyziky materiálů, 2018

Experimental and finite element analysis of composite gun barrels
Mochar, Dominik; Trnka, Jan; Chlada, Milan; Valeš, František; Gabriel, Dušan; Červ, Jan; Vtípil, J.
2018 - English
In this work experimental and numerical investigation of composite gun barrels was studied. The history of the stress-induced deformations located at the center of gun barrels on the outer surface generated by impact loading was measured for six types of barrels. The obtained signals were subsequently evaluated using wavelet transformation. Finally, the finite element analysis in Abaqus and MARC software for optimum composite material M46J was performed. Keywords: composite gun barrels; contact-impact analysis; drop weight tester; air cannon Available at various institutes of the ASCR
Experimental and finite element analysis of composite gun barrels

In this work experimental and numerical investigation of composite gun barrels was studied. The history of the stress-induced deformations located at the center of gun barrels on the outer surface ...

Mochar, Dominik; Trnka, Jan; Chlada, Milan; Valeš, František; Gabriel, Dušan; Červ, Jan; Vtípil, J.
Ústav termomechaniky, 2018

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