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Topical Problems of Fluid Mechanics 2022
Šimurda, David; Bodnár, T.
2022 - anglický
Proceedings consist of papers presented during the conference Topical Problems of Fluid Mechanics 2022. \n
Klíčová slova:
experimental fluid mechanics; mathematical modelling; CFD; turbulence; stratified fluid; multiphase flow; vortex structures; supersonic flow
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Topical Problems of Fluid Mechanics 2022
Proceedings consist of papers presented during the conference Topical Problems of Fluid Mechanics 2022. \n
Use of active power filter to reduce flicker caused by electric arc furnace operation
Čerňan, Martin; Bejvl, Martin; Šimek, Petr; Valouch, Viktor
2022 - anglický
Effectiveness of using a parallel active power filter to compensate for the flicker of an electric arc furnace,\nand mitigate the reactive power consumption and terminal\nvoltage variation in the grid is presented and evaluated in the contribution. The model of a power system with the electric arc furnace and parallel active power filter in the frequency domain has been developed. The selected results of simulation in the frequency domain using the data collected from the 60 t EAF are presented and evaluated.
Klíčová slova:
electric arc furnace; flicker mitigation; active power filter; power system model; simulation in frequency domain
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Use of active power filter to reduce flicker caused by electric arc furnace operation
Effectiveness of using a parallel active power filter to compensate for the flicker of an electric arc furnace,\nand mitigate the reactive power consumption and terminal\nvoltage variation in the grid ...
Identification of the blade tip possition and measurement techniques using the BTT method
Maturkanič, Dušan; Procházka, Pavel; Hodboď, Robert; Mekhalfia, Mohammed Lamine
2022 - anglický
This paper describes the existing practice in identifying and defining the position of the blade tips and the relevant technique for measuring their vibration during rotation. In connection with the effort to precisely define the position of the vibrating blade, the paper also analysed the possibilities of unambiguous determination of its position. This work creates a parallel branch to signal processing in the complex system of precision measurement and analysis of blade vibration, which was mentioned in previous papers.
Klíčová slova:
turbine blade; vibration; precision method; modification; harmonic function
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Identification of the blade tip possition and measurement techniques using the BTT method
This paper describes the existing practice in identifying and defining the position of the blade tips and the relevant technique for measuring their vibration during rotation. In connection with the ...
Measurement and analysis of vibration and acoustic emissions of a railway wheel under defined dynamic excitations
Pešek, Luděk; Prasad, Chandra Shekhar; Šnábl, Pavel
2022 - anglický
The paper deals with experimental vibro-acoustics of railway wheel. The methodology for evaluation of effect of vibrational plate dampers was elaborated. The four variants of the wheel was measured and analyse to achieve the optimal solution of the dampers.
Klíčová slova:
vibro-acoustics; railway wheel; dampers; noise
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Measurement and analysis of vibration and acoustic emissions of a railway wheel under defined dynamic excitations
The paper deals with experimental vibro-acoustics of railway wheel. The methodology for evaluation of effect of vibrational plate dampers was elaborated. The four variants of the wheel was measured ...
Study of the oscillation of a pendulum in a magnetic field
Zapoměl, Jaroslav; Kozánek, Jan; Košina, Jan; Cibulka, Jan
2022 - anglický
Realization of some technological processes requires application of rotating machines with a vertical rotor mounted in rolling element bearings. One of the requirements put on their operation is minimization of energy losses in the support elements. The proposed design variant consists in supporting the vertical rotor by one rolling element bearing placed at its upper part and by one axial magnetic bearing mounted in its lower end. The magnetic bearing is composed of an electric coil coupled with the stationary part and of a permanent magnet attached to the rotating part. The magnetic force attracts the permanent magnet, which reduces radial displacement of the lower end of the rotor. The magnetic field between the magnets represents a force coupling between the rotor and the stationary part, which shows some stiffness and affects the system natural frequencies. The controlled change of the stiffness makes it possible to reduce the rotor lateral oscillations in the resonance area. The investigated pendulum is coupled with the frame by a revolute joint at its upper end. The permanent magnet is attached to its lower end. The electric coil is coupled with the stationary part and placed under the pendulum. The system is excited by a moment of harmonic time history, which sets the pendulum into a seesaw motion.\n\n
Klíčová slova:
vertical rotor; pendulum; axial magnetic bearings; lateral oscillations; resonance
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Study of the oscillation of a pendulum in a magnetic field
Realization of some technological processes requires application of rotating machines with a vertical rotor mounted in rolling element bearings. One of the requirements put on their operation is ...
Localized formulation of bipenalty method in contact-impact problems
Kolman, Radek; González, J. A.; Dvořák, Radim; Kopačka, Ján; Park, K.C.
2022 - anglický
Often, the finite element method together with direct time integration is used for modelling of contact-impact problems of bodies. For direct time integration, the implicit or explicit time stepping are gen-\nerally employed. It is well known that the time step size in explicit time integration is limited by the stability limit. Further, the trouble comes with the task of impact of bodies with different critical time step sizes for each body in contact. In this case, this numerical strategy based on explicit time stepping with the same time step size for both bodies is not effective and is not accurate due to the dispersion behaviour and spurious stress oscillations. For that reason, a numerical methodology, which allows independent time stepping for each body with its time step size, is needed to develop. In this paper, we introduce the localized variant of the bipenalty method in contact-impact problems with the governing equations derived based on the Hamilton’s principle. The localized bipenalty method is applied into the impact problems of bars as an one-dimensional problem. The definition of localized gaps is presented and applied into the full concept of the localized bipenalty method.
Klíčová slova:
contact-impact problem; explicit time integration; bipenalty formulation; ocalized lagrange multipliers; stability analysis
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Localized formulation of bipenalty method in contact-impact problems
Often, the finite element method together with direct time integration is used for modelling of contact-impact problems of bodies. For direct time integration, the implicit or explicit time stepping ...
Aspects of Dosage from Short and Long Duration Emissions
Robins, A.; Hayden, P.; Gallacher, D.; Pace, S.; Chaloupecká, Hana
2022 - anglický
The objectives of this work were to use wind tunnel concentration measurements to describe the structure of dispersing clouds from an elevated source in a deep turbulent boundary layer and to develop scaling rules that reduce the results to a universal form. The experiments were carried out in the EnFlo meteorological wind tunnel at the University of Surrey. Ensembles of between 100 and 200\nrepeat emissions were used, emission durations between 0.067 and 1.02s and a reference flow speed of 2ms-1. The fetch studied extended to about six source heights downwind (about two boundary layer depths). The structure of the evolving clouds was analysed to determine time of flight, along-wind spread and dosage and to compare the dosage behaviour with the concentration field in a plume from the same source. This illustrated how the two were related and how cloud dosage statistics (mean and\nstandard deviation) could be derived from plume data. It also demonstrated that much larger ensembles were required to reduce the statistical uncertainty in the mean cloud properties. The next steps involve testing these conclusions in a wider range of flow and dispersion conditions, in the presence of obstacles or complex urban areas.
Klíčová slova:
wind tunnel; dose; dosage; gas releases
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Aspects of Dosage from Short and Long Duration Emissions
The objectives of this work were to use wind tunnel concentration measurements to describe the structure of dispersing clouds from an elevated source in a deep turbulent boundary layer and to develop ...
Numerical simulations of aeroelastic instabilities in turbine blade cascade by modified Van der Pol model at running excitation
Pešek, Luděk; Šnábl, Pavel; Prasad, Chandra Shekhar; Delanney, Y.
2022 - anglický
Apart from rotary test rig for evaluation of structural dynamics of the bladed wheels, the control flutter experiments has been performed on the linear cascade model in the subsonic wind tunnel in the Institute of Thermomechanics, of CAS, in Prague. These experiments are aimed at stability evaluation of the cascade at running waves or at stability limit testing by flow speed changes or by force impulses of blades. The onset of flutter and its spreading in the cascade are observed, too. The linear cascade model consists of five NACA010 blades. All the blades can be separately excited with electromagnetic torque excitation mechanism and all of them are instrumented to measure the aerodynamic moments which can be used to calculate the aerodynamic work. A more details about the linear blade cascade experimental set up can be found in [1-2]. To predict a dynamic behaviour in the blade cascade, we have been dealing with simplified theoretical modelling of the aeroelastic instability in turbine blade cascade [3-5]. Due to the application of the reduced cascade model consisting of simple elements – springs, rigid bodies, linear dampers – and aeroelastic forces introduced by analytical Van der Pol model, it facilitates to study the dangerous states of vibration of such complicated turbine parts [6-9]. This study is aimed at examination of aeroelastic instabilities of 10-blade cascade at running excitation that arises due to the wakes flowing from stator the blades to the rotating blades. They cause forced excitation in the narrow frequency range.
Klíčová slova:
rotary test; structural dynamics; bladed wheels
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Numerical simulations of aeroelastic instabilities in turbine blade cascade by modified Van der Pol model at running excitation
Apart from rotary test rig for evaluation of structural dynamics of the bladed wheels, the control flutter experiments has been performed on the linear cascade model in the subsonic wind tunnel in ...
Estimation of damping in human vocal folds vibration: measurements in vivo and on model
Horáček, Jaromír; Radolf, Vojtěch; Bula, Vítězslav; Košina, Jan; Geneid, A.; Laukkanen, A. M.
2022 - anglický
This study investigates the biomechanics of the end-part of phonation, i.e. the so-called phonation offset, experimentally. This information of vocal folds damping is important for testing and further development of mathematical modelling of phonation. The measurements of the damping ratio, based on high-speed videolaryngoscopic registrations, were realized in vivo on a male subject and in vitro using an originally developed silicon replica of the human vocal folds. In both cases the results show remarkable decrease of vibration frequency of the vocal folds and increase of damping ratio D in the phonation offset limiting to the values D=0.12 in vivo measurement and D=0.11 in vitro measurement. The results for vocal folds’ damping are in good agreement with previous measurements performed in humans using different methods.
Klíčová slova:
phonation offset; high-speed videolaryngoscopy
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Estimation of damping in human vocal folds vibration: measurements in vivo and on model
This study investigates the biomechanics of the end-part of phonation, i.e. the so-called phonation offset, experimentally. This information of vocal folds damping is important for testing and further ...
Experimental investigation of the frequency-modal properties of the measuring container for LUNA mission
Zolotarev, Igor; Bula, Vítězslav; Šnábl, Pavel; Snížek, Jan; Souček, Jan
2022 - anglický
This paper continues investigations of the measuring equipment for space missions. The frequency-modal properties of the measuring container for LUNA mission were obtained by experimental investigation.
Klíčová slova:
modal analysis; natural frequencies; modes of vibration
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Experimental investigation of the frequency-modal properties of the measuring container for LUNA mission
This paper continues investigations of the measuring equipment for space missions. The frequency-modal properties of the measuring container for LUNA mission were obtained by experimental ...
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