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Stanovení vlivu geometrie vzorku na rozvoj creepové deformace pomocí metody akustické emise
Dvořák, Jiří; Sklenička, Václav; Král, Petr; Kvapilová, Marie; Svobodová, M.; Šifner, J.; Koula, V.
2023 - Czech
Tato práce se zabývá stanovením vlivu geometrie tělesa na vývoj porušení v průběhu creepové expozice. Creepové testy byly provedeny při teplotě 600 °C a napětí 180 MPa v režimu ochranné atmosféry argonu. Pro zkušební testy byl zvoleny vzorky z oceli P92 s konvekčním hladkým povrchem a vzorky opatřené V-vrubem. Výsledky creepové odolnosti a lomového chování byly doplněny podrobnou mikrostrukturní charakterizací k posouzení iniciace a vývoje creepového poškození. Na základě naměřených výsledků byla creepová data vyhodnocena pomocí neuronových sítí, které systematicky vyhledávají a zpracovávají signál z akustické emise (AE). Akustická emise byla použita jako účinná nedestruktivní metoda pro včasnou predikci počátku možné havárie komponent energetických a chemických zařízení. This work deals with the determination of the influence of the sample geometry on the development of failure during creep exposure. Creep tests were carried out at temperature of 600 °C and a stress of 180 MPa in the protective atmosphere of argon. P92 steel samples with a conventional smooth surface and samples with a V-groove notch were chosen for the test tests. The results of creep resistance and fracture behaviour were complemented by detailed microstructural characterization to assess damage initiation and development. Based on the measured results, the creep data was evaluated using neural networks that systematically search for and process the signal from the acoustic emission (AE). Acoustic emission serves here as an effective non-destructive method for early prediction of the beginning of a possible accident of components of power and chemical plants.
Keywords:
creep specimen; creep deformation; acoustic emission
Available at various institutes of the ASCR
Stanovení vlivu geometrie vzorku na rozvoj creepové deformace pomocí metody akustické emise
Tato práce se zabývá stanovením vlivu geometrie tělesa na vývoj porušení v průběhu creepové expozice. Creepové testy byly provedeny při teplotě 600 °C a napětí 180 MPa v režimu ochranné atmosféry ...
Modřín v pomístních jménech v Čechách
Zirhutová, Martina
2023 - Czech
Příspěvek se zabývá apelativem modřín a jeho nářečními variantami v pomístních jménech v Čechách. Cílem výzkumu je zjistit, které nářeční varianty označující modřín se v anoikonymii Čech vyskytují, a určit jejich početní zastoupení, zeměpisné rozšíření a další charakteristiky. Analyzována jsou nejen anoikonyma vycházející z apelativ, která jsou v pomístních jménech na území Čech zastoupena ve větším množství (verpán, merfán, modřín, břím, dřín), ale pozornost je věnována i nářečním výrazům, které se v anoikonymii vyskytují spíše sporadicky (lerpán, relpán, tis, klenč, skřivánčí). The paper deals with the use of the common noun modřín (larch) and its dialectal variants in non-settlement place names in Bohemia. The focus of the research is to find out which dialectal words denoting a larch tree are included in the names, and to state their number, geographical occurrence and other characteristic features. Attention is paid not only to the common nouns which are used in non-settlement names frequently (verpán, merfán, modřín, břím, dřín), but also to the dialectal words which appear in names rather scarcely (lerpán, relpán, tis, klenč, skřivánčí).
Keywords:
onomastics; non-settlement names in Bohemia; the common noun modřín
Available at various institutes of the ASCR
Modřín v pomístních jménech v Čechách
Příspěvek se zabývá apelativem modřín a jeho nářečními variantami v pomístních jménech v Čechách. Cílem výzkumu je zjistit, které nářeční varianty označující modřín se v anoikonymii Čech vyskytují, a ...
Statistical Method Selection Matters: Vanilla Methods in Regression May Yield Misleading Results
Kalina, Jan
2023 - English
The primary aim of this work is to illustrate the importance of the choice of the appropriate methods for the statistical analysis of economic data. Typically, there exist several alternative versions of common statistical methods for every statistical modeling task\nand the most habitually used (“vanilla”) versions may yield rather misleading results in nonstandard situations. Linear regression is considered here as the most fundamental econometric model. First, the analysis of a world tourism dataset is presented, where the number of international arrivals is modeled for 140 countries of the world as a response of 14 pillars (indicators) of the Travel and Tourism Competitiveness Index. Heteroscedasticity is clearly recognized in the dataset. However, the Aitken estimator, which would be the standard remedy in such a situation, is revealed here to be very inappropriate. Regression quantiles represent a much more suitable solution here. The second illustration with artificial data reveals standard regression quantiles to be unsuitable for data contaminated by outlying values. Their recently proposed robust version turns out to be much more appropriate. Both\nillustrations reveal that choosing suitable methods represent an important (and often difficult) part of the analysis of economic data.
Keywords:
linear regression; assumptions; non-standard situations; robustness; diagnostics
Fulltext is available at external website.
Statistical Method Selection Matters: Vanilla Methods in Regression May Yield Misleading Results
The primary aim of this work is to illustrate the importance of the choice of the appropriate methods for the statistical analysis of economic data. Typically, there exist several alternative versions ...
PHYSICOCHEMICAL CHARACTERISTICS AND EVOLUTION OF AEROSOL FROM OPEN COMBUSTION OF BIOMASS DURING THE TRADITIONAL “BURNING OF THE WITCHES”
Mbengue, Saliou; Vodička, Petr; Komínková, Kateřina; Schwarz, Jaroslav; Zíková, Naděžda; Vítková, Gabriela; Windell, Laurence Christian; Suchánková, Lenka; Lhotka, Radek; Julaha, Kajal; Prokeš, Roman; Šmejkalová Holubová, A.; Ondráček, Jakub; Ždímal, Vladimír; Holoubek, Ivan
2023 - English
Open biomass burning (OBB) is a major source releasing large quantities of gaseous and particulate pollutants into the atmosphere, with global, regional and local impacts on air quality, public health and climate (Andreae, 2019, Chen et al., 2017). OBB aerosols mainly consist of carbonaceous matter, and a considerable amount of inorganic salts, which present distinctly different optical properties (Chen et al., 2017, Reid et al., 2005). In this study, we investigate the influence of OBB during the traditional Burning of the Witches (BoW), referred to in Czech as “Pálení čarodějnic”, on the physico-chemical properties of atmospheric aerosols collected at the National Atmospheric Observatory Košetice (NAOK). The BoW is a centuries-old pagan tradition very popular in the Czech Republic. Today, it is celebrated during the night from April 30 to May 1 by lighting bonfires made of woodpiles with fake witches.
Keywords:
biomass burning; air pollution; size distribution; atmospheric ageing
Available in digital repository of the ASCR
PHYSICOCHEMICAL CHARACTERISTICS AND EVOLUTION OF AEROSOL FROM OPEN COMBUSTION OF BIOMASS DURING THE TRADITIONAL “BURNING OF THE WITCHES”
Open biomass burning (OBB) is a major source releasing large quantities of gaseous and particulate pollutants into the atmosphere, with global, regional and local impacts on air quality, public health ...
PM1 UNDER THE MICROSCOPE: MULTI-ANNUAL AEROSOL OPTICAL PROPERTIES AND SIZE DISTIRBUTION OBSERVATION AT PERI-URBAN ATMOSPHERIC SITE ATOLL
Suchánková, Lenka; Bourrianne, E.; De Fillipi, R.; De Brito, J. F.; Riffault, V.; Prokeš, Roman; Holoubek, Ivan; Ždímal, V.; Crumeyrolle, S.
2023 - English
Atmospheric aerosols (AA) belong to short-lived climate forcers with high spatial and temporal variability. Although the radiative effects of AA are greatest on regional scales, changes in aerosol emissions can induce long-term global climate effects (Szopa et al., 2021). Thus, the measurement of aerosol properties is essential for better understanding of aerosol’s impact on health and climate. Although several international projects and platforms have been monitoring AA properties worldwide (GAW, WMO, ACTRIS, EMEP, EUCAARI, etc., Pandolfi et al., 2018), only PM10 or PM2.5 cutoff sizes have been used for measurements, and information about PM1 particles is missing. \nThe aim of this study is to present aerosol scattering properties with supporting data of absorption and particle number size distribution in PM1 in years 2018-2022 at peri-urban atmospheric site “Atmospheric Observations in LiLLE (ATOLL) in Lille, France. This study is the first to present results dedicated to aerosol scattering properties at this site.
Keywords:
pm1; scattering coefficient; nephelometer; fossil fuel and biomass burning contribution; aethalometer; smps
Available in digital repository of the ASCR
PM1 UNDER THE MICROSCOPE: MULTI-ANNUAL AEROSOL OPTICAL PROPERTIES AND SIZE DISTIRBUTION OBSERVATION AT PERI-URBAN ATMOSPHERIC SITE ATOLL
Atmospheric aerosols (AA) belong to short-lived climate forcers with high spatial and temporal variability. Although the radiative effects of AA are greatest on regional scales, changes in aerosol ...
Thermal and creep analysis of VVER-1000 reactor pressure vessel at high temperatures caused by fuel melting during severe accident
Gabriel, Dušan; Gál, P.; Kotouč, M.; Dymáček, Petr; Masák, Jan; Kopačka, Ján
2023 - English
Thermal and creep analysis of the VVER-1000 reactor pressure vessel (RPV) was performed at high temperatures caused by fuel melting during severe accident. First, the integral code ASTEC was applied simulating severe accident evolution since an initiating event up to a hypothetical radioactive release into the environment. The ASTEC outputs including the remaining RPV wall thickness, the heat flux achieved and the temperature profile in the ablated vessel wall served as boundary conditions for the consequent assessment of RPV integrity carried out with the aid of finite element method (FEM). The FEM analysis was performed including the creep behaviour of RPV material using a complex creep probabilistic exponential model with damage. The objective of the analysis was to computationally assess emergency condition and, on this basis, to propose a general methodology for evaluating the integrity of RPV at high temperatures due to fuel melting during severe accident.
Keywords:
integrity of reactor pressure vessel; severe accident; ASTEC; creep; FEM
Fulltext is available at external website.
Thermal and creep analysis of VVER-1000 reactor pressure vessel at high temperatures caused by fuel melting during severe accident
Thermal and creep analysis of the VVER-1000 reactor pressure vessel (RPV) was performed at high temperatures caused by fuel melting during severe accident. First, the integral code ASTEC was applied ...
Reduced modelling of aeroelastic instability in a turbine blade cascade
Pešek, Luděk; Šnábl, Pavel; Prasad, Chandra Shekhar
2023 - English
The contribution deals with the first results on flutter instability of the linear cascade triggered by impulse excitation. Together with experimental results, numerical results obtained by reduced modelling of the cascade using van der Pol model of self-excitation are presented and discussed.
Keywords:
flutter; blade cascade; self-excitation; Van der Pol
Available at various institutes of the ASCR
Reduced modelling of aeroelastic instability in a turbine blade cascade
The contribution deals with the first results on flutter instability of the linear cascade triggered by impulse excitation. Together with experimental results, numerical results obtained by reduced ...
Simulation of heterogeneously-catalyzed non-isothermal reactive flow in industrial packed beds
Hlavatý, Tomáš; Isoz, Martin; Khýr, M.
2023 - English
Packed bed reactors are the most frequently used devices to perform heterogeneously catalyzed reactions on industrial scales. An industrial real-life heterogeneous catalysis is complex process that combines fully three-dimensional mass, momentum and energy transport on several scales. In the present work, we leverage our previously developed CFD solver for non-isothermal heterogeneously catalyzed reactive flow based on the finite volume method and couple it with our\nin-house DEM-based method for preparation of random packed beds. The resulting framework is verified in the simplified cases against available analytical solutions and correlations and is used to study an industrially-relevant case of ethylene oxychlorination performed in a tubular packed bed comprising CuCl2-coated catalyst carrying particles. In particular, we compare properties of three different industrially used catalyst carrying particles: Raschig rings, Reformax, and Wagon wheels
Keywords:
CFD; OpenFOAM; non-isothermal flow
Available in a digital repository NRGL
Simulation of heterogeneously-catalyzed non-isothermal reactive flow in industrial packed beds
Packed bed reactors are the most frequently used devices to perform heterogeneously catalyzed reactions on industrial scales. An industrial real-life heterogeneous catalysis is complex process that ...
Numerical implementation of incremental minimization principle for materials with multiple rate-independent dissipative mechanisms
Frost, Miroslav; Moskovka, Alexej; Sedlák, Petr; Valdman, Jan
2023 - English
The incremental energy minimization approach is a compact variational formulation of the evolutionary boundary value problem for constitutive models of materials with a rate-independent response. Although it can be easily applied to many conventional models, its main advantages arise when applied to models with multiple strongly coupled dissipation mechanisms, where the direct construction of the coupled yield conditions and flow rules may be challenging. However, this usually requires a more complex numerical treatment of the resulting sequence of time-incremental boundary value problems resolved via the finite element method. This contribution presents, compares and discusses two genuine minimization approaches - the staggered solution procedure relying on alternating minimization and the monolithic approach employing global minimization - for an advanced constitutive model of shape memory alloys.
Keywords:
variational approach; constitutive modeling; numerical implementation
Fulltext is available at external website.
Numerical implementation of incremental minimization principle for materials with multiple rate-independent dissipative mechanisms
The incremental energy minimization approach is a compact variational formulation of the evolutionary boundary value problem for constitutive models of materials with a rate-independent response. ...
Astrophysical black holes embedded in organized magnetic fields
Karas, Vladimír
2023 - English
Large-scale magnetic fields pervade the cosmic environment where the astrophysical black holes are often embedded and influenced by mutual interaction. In thiscontribution, we outline the appropriate mathematical framework to describe magnetized black holes within General Relativity, and we show several examples of how these can be employed in the astrophysical context. In particular, we examine the magnetized black hole metric in terms of an exact solution of electro-vacuum Einstein-Maxwell equations under the influence of a non-vanishing electric charge. New effects emerge: the expulsion of the magnetic flux out of the black-hole horizon depends on the intensity of the imposed magnetic field.
Keywords:
black holes; electromagnetic fields; general relativity
Fulltext is available at external website.
Astrophysical black holes embedded in organized magnetic fields
Large-scale magnetic fields pervade the cosmic environment where the astrophysical black holes are often embedded and influenced by mutual interaction. In thiscontribution, we outline the appropriate ...
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