Computational and experimental assessment of natural frequencies in a bladed disk system
Mekhalfia, Mohammed Lamine; Procházka, Pavel; Maturkanič, Dušan; Voronova, Evgeniya; Hodboď, Robert
2024 - anglický
This paper examines the modal characteristics of a bladed disk in rotating machinery systems using a combination of analytical and experimental modal analysis methods. The analysis involves measuring natural frequencies and mode shapes under different operational conditions. A comparative analysis is conducted to assess modal properties obtained from both analytical and experimental approaches, while also considering the influence of rotation speed. Additionally, Finite Element Method (FEM) outputs are used to accurately position the strain gauge. Integrating these techniques provides a comprehensive understanding of the bladed disk's behaviour under varying rotational speeds, enhancing result accuracy and facilitating thorough investigation within rotating machinery systems.
Klíčová slova:
natural frequencies; FEM; LDV; strain gauge
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Computational and experimental assessment of natural frequencies in a bladed disk system
This paper examines the modal characteristics of a bladed disk in rotating machinery systems using a combination of analytical and experimental modal analysis methods. The analysis involves measuring ...
Numerické optimalizační metody
Lukšan, Ladislav
2024 - český
Tato zpráva popisuje teoretické i praktické vlastnosti numerických metod pro nepodmíněnou optimalizaci. Studují se metody pro obecné i speciální optimalizační úlohy, mezi které patří minimalizace součtu čtverců, součtu absolutních hodnot, maximní hodnoty a dalších nehladkých funkcí. Kromě metod pro standardní úlohy středních rozměrů jsou studovány i metody pro rozsáhlé řídké a strukturované úlohy. Velká pozornost je věnována soustavám nelineárních rovnic.\n
Klíčová slova:
Numerická optimalizace; nelineární aproximace; systémy nelineárních rovnic; algoritmy
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
Numerické optimalizační metody
Tato zpráva popisuje teoretické i praktické vlastnosti numerických metod pro nepodmíněnou optimalizaci. Studují se metody pro obecné i speciální optimalizační úlohy, mezi které patří minimalizace ...
Analýza příjmů státního rozpočtu 2024 ve světle předkrizového roku 2019
Janský, Petr; Kolář, Daniel
2024 - český
Tato analýza srovnává plánované příjmy státního rozpočtu na rok 2024 s výsledky státního rozpočtu v roce 2019. Mapuje období, během něhož na českou ekonomiku a veřejné rozpočty silně dopadly jak důsledky několika zásadních krizí (koronavirus, napadení Ukrajiny a válka, energetická krize a inflační vlna), tak výrazné parametrické změny českého daňového systému. Rok 2019 lze považovat za poslední předkrizový a rok 2024 za první pokrizový, takže odpovídají ‘normálním časům‘ lépe než roky mezi nimi. Tato analýza svým pojetím navazuje na předchozí analýzu vývoje výdajů státního rozpočtu mezi roky 2019 a 2024 a obsahuje i stručnou syntézu zjištění o vývoji příjmů a výdajů. This analysis compares planned state budget revenues in 2024 with the state budget outcomes of 2019. It charts a period in which the Czech economy and public budgets have been heavily impacted by the consequences of several major crises (coronavirus, the invasion of Ukraine and the war, an energy crisis, and an inflationary wave) as well as by significant parametric changes in the Czech tax system. 2019 can be considered the last pre-crisis year and 2024 the first post-crisis year, so they correspond to 'normal times' more closely than the years in between. This analysis builds on a previous analysis of the state budget expenditure development between 2019 and 2024 and includes a brief synthesis of findings on revenues and expenditures.
Klíčová slova:
budget proposal; budget revenues; Czech Republic
Dokument je dostupný na externích webových stránkách.
Analýza příjmů státního rozpočtu 2024 ve světle předkrizového roku 2019
Tato analýza srovnává plánované příjmy státního rozpočtu na rok 2024 s výsledky státního rozpočtu v roce 2019. Mapuje období, během něhož na českou ekonomiku a veřejné rozpočty silně dopadly jak ...
Zoologické dny Ostrava 2024: sborník abstraktů z konference 8.-9. února 2024.
Drozd, P.; Ožana, S.; Bryja, Josef
2024 - český
Klíčová slova:
zoology; conference
Dokument je dostupný na externích webových stránkách.
Zoologické dny Ostrava 2024: sborník abstraktů z konference 8.-9. února 2024.
Applying a two degree of freedom model for drive-by identification
Bayer, Jan
2024 - anglický
A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving spring-mass the second DOF. The response of the moving spring-mass is simulated on a bridge model using different road profiles and compared to parameters of the corresponding two DOF system. The focus is the spectral shift that can be observed on the moving spring-mass during its passage along the bridge and could possibly be applied for drive-by identification. The accuracy mainly depends on the relation of the moving spring-mass to the bridge mass and the relation between the natural frequency of the spring-mass and those of the bridge. The simulations showed that road profile can significantly reduce the accuracy of identified results, which imposes limits on practical applications.
Klíčová slova:
drive-by identification; structural health monitoring; finite element analysis; road roughness; two DOF system
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Applying a two degree of freedom model for drive-by identification
A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving ...
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Fischer, Cyril; Náprstek, Jiří
2024 - anglický
Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type nonlinear model. Determining the response probability density function involves solving the Fokker-Planck equation, which is generally a challenging task. Hence, semi-analytical and numerical methods come into play. This contribution reviews several possible techniques and spotlights the exponential-polynomial-closure method. The shown results are limited, as the paper reflects an early stage of the relevant research direction.
Klíčová slova:
Fokker-Planck equation; stochastic averaging; numerical solution; Galerkin approximation; van der Pol-type oscillator; partial amplitudes; exponential-polynomial-closure method
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type ...
Galloping of insulated bundled overhead line simplified analysis
Hračov, Stanislav; Macháček, Michael
2024 - anglický
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by polyethylene, and used for low-voltage power lines. The susceptibility to loss of stability is analyzed for cable without and with simulated icing observed on similar real conductors. In the first case, the proneness to galloping was excluded based on the results of CFD simulation and the Den Hartog criterion. In latter case, the possible occurrence of galloping was confirmed. The critical wind velocity for the ice-covered cable was calculated utilizing quasi-steady theory. Finally, the amplitudes of limit cycle oscillation for supercritical wind speeds were estimated based on simplified numerical analysis.
Klíčová slova:
aerial bundled cable; wind effects; galloping; limit cycle oscillation
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Galloping of insulated bundled overhead line simplified analysis
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by ...
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2024 - anglický
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The rectangle object was exposed to the airflow having a given velocity at different angles of the wind attack in the wind tunnel with the aim to obtain the curves of the aerodynamic coefficients and Strouhal number depending on the impact angle. The comparative numerical 3D simulations of the wind tunnel testing were performed using COMSOL Multiphysics and OpenFoam both incorporating the Large Eddy Simulation (LES) method.
Klíčová slova:
rectangle 2:1; wind tunnel; LES simulation; aerodynamic characteristics
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The ...
A New Hollow Fiber-Based Liquid-Phase Microextraction Method for the Determination of Antihypertensive Drug Lercanidipine in Biological Samples
Labzova, O.; Hrdlička, Vojtěch; Navrátil, Tomáš; Šelešovská, R.
2024 - anglický
A new hollow fiber-based liquid-phase microextraction (HF-LPME) method for the determination of antihypertensive drug lercandipine (LCN) in biological samples was developed. HF-LPME was\ncombined with optimized square wave voltammetry (SWV) on a cathodically pre-treated screenprinted boron-doped diamond electrode (SP-BDDE). Optimum HF-LPME conditions were:\nsupported liquid membrane (SLM) dodecane, 0.02 mol L-1 Britton-Robinson buffer (BRB, pH = 3) acceptor phase, BRB (pH = 7) donor phase, and time of extraction 30 min. Limits of quantification (LOQ) and detection (LOD) were 3.3 and 1.1 nmol L-1, respectively. The applicability of the developed method was verified on human urine, blood serum, and blood plasma with 20 and 100 nmol L-1 LCN addition.
Klíčová slova:
Lercanidipine hydrochloride; Hollow fiber liquid-phase microextraction; Screenprinted boron-doped diamond electrode
Plné texty jsou dostupné na vyžádání prostřednictvím repozitáře Akademie věd.
A New Hollow Fiber-Based Liquid-Phase Microextraction Method for the Determination of Antihypertensive Drug Lercanidipine in Biological Samples
A new hollow fiber-based liquid-phase microextraction (HF-LPME) method for the determination of antihypertensive drug lercandipine (LCN) in biological samples was developed. HF-LPME was\ncombined with ...
Gas sensors based on diamond heterostructures for air quality monitoring
Kočí, Michal; Szabó, Ondrej; Izsák, T.; Sojková, M.; Godzierz, M.; Wróbel, P.; Husák, M.; Kromka, Alexander
2024 - anglický
Currently, great emphasis is placed on air quality and the presence of pollutants. Attention is therefore focused on new gas-sensing materials enabling detection even at low (up to room) temperatures with sufficient response and short reaction time. Here, we investigate the suitability of H-NCD films and their heterostructures with MoS2, GO, rGO, SH-GO, or Au NPs for gas sensing applications. Electrical properties are measured for oxidizing gas NO2, reducing gas NH3, and chemical vapor of ethanol, and at temperatures varied from room temperature to 125 °C. In contrast to the individual forms of employed materials with limited response to the exposed gases, the HNCD heterostructures revealed better sensing properties. In particular, the Au NPs/H-NCD heterostructures revealed a higher response at 125 °C in contrast to H-NCD, MoS2/H-NCD had quite good response even at room temperature and GO/H-NCD revealed high sensitivity to chemical vapor, which further improved for the SH-GO/HNCD.
Klíčová slova:
gas sensors; nanocrystalline diamond; heterostructures; air quality monitoring
Dokument je dostupný na externích webových stránkách.
Gas sensors based on diamond heterostructures for air quality monitoring
Currently, great emphasis is placed on air quality and the presence of pollutants. Attention is therefore focused on new gas-sensing materials enabling detection even at low (up to room) temperatures ...
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