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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 ...
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 ...
Development of Polymeric Enantioselective Membranes
Čížek, Jan
2024 - anglický
Enantiomers are molecules that share the same chemical formula but in space form mirror images of each other. Their reactions with other chiral molecules can be remarkably different, which is crucial mainly for pharmaceuticals and agrochemicals. However, industrialscale synthetic production of enantiomerically pure compounds is not always available. Therefore, the need for pure enantiomeric compounds drives the development and research on various separation methods. However, most methods used on the industrial scale are limited to specific compounds (diastereomeric recrystallization) or generally difficult and/or expensive to scale up (chromatography-related methods). Separation of enantiomers using membranes is promising\nthanks to the easy scalability and continuous operation of membrane processes. Various ideas about how the enantioselective membranes should look like have been published in the last thirty years. The mechanism of enantiomeric separation on a membrane is, however, highly specific, and still requires extensive research. In this work, four types of enantioselective polymeric membranes are presented.
Plné texty jsou dostupné v digitálním repozitáři NUŠL
Development of Polymeric Enantioselective Membranes
Enantiomers are molecules that share the same chemical formula but in space form mirror images of each other. Their reactions with other chiral molecules can be remarkably different, which is crucial ...
Synthesis of Fluorinated Methyl β-Lactosides
Krčil, Aleš
2024 - anglický
In my contribution, I will describe the synthesis of a complete series of mono-deoxyfluorinated methyl β-lactosides (1–7). Their affinity towards hgals will be determined by analytical method ELISA. The synthesis relies on monosaccharide building blocks, which serves as key intermediates that are transformed into the target products through glycosylation followed by final deprotection steps.
Klíčová slova:
flurinated carbohydrates; galectin; deoxyfluorination
Plné texty jsou dostupné v digitálním repozitáři NUŠL
Synthesis of Fluorinated Methyl β-Lactosides
In my contribution, I will describe the synthesis of a complete series of mono-deoxyfluorinated methyl β-lactosides (1–7). Their affinity towards hgals will be determined by analytical method ELISA. ...
Investigation of Mechanical Processing of Solar Photovoltaic Panels
Šperlich, Antonín
2024 - anglický
This work aims to describe the possibilities of mechanical treatment of solar photovoltaic panels. In the first part, the shredding and milling process for the transformation of the product (whole panel) into material that can be further processed, was investigated. Milled material was sieved and analyzed. It was observed that this shredding also works as a selective grinding because three main products were produced. The second part of this work was aimed at the physical concentration of silver in real samples of milled solar photovoltaic panels by Knelson separator. This device (type of centrifugal separator) showed the ability to significantly increase the amount of silver in the outcome stream.
Klíčová slova:
solar photovoltaic panels; selective milling; Knelson
Plné texty jsou dostupné v digitálním repozitáři NUŠL
Investigation of Mechanical Processing of Solar Photovoltaic Panels
This work aims to describe the possibilities of mechanical treatment of solar photovoltaic panels. In the first part, the shredding and milling process for the transformation of the product (whole ...
Axial Dispersion and Mass Transfer in Bubble Column
Terentyak, Mark
2024 - anglický
The objective of the study is to experimentally investigate axial dispersion and mass transfer within a bubble column, examining their mutual interrelation\nand their correlation with operational parameters and AR1.
Klíčová slova:
bubble column; axial dispersion; mass transfer
Plné texty jsou dostupné v digitálním repozitáři NUŠL
Axial Dispersion and Mass Transfer in Bubble Column
The objective of the study is to experimentally investigate axial dispersion and mass transfer within a bubble column, examining their mutual interrelation\nand their correlation with operational ...
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