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Acoustic resonances can support self-oscillations of a dynamic system.
Horáček, Jaromír; Radolf, Vojtěch; Košina, Jan; Laukkanen, A. M.
2021 - English
Flutter instability of human vocal folds is a necessary condition for speaking, because airflow induced vibrations of the vocal folds create the voice source. The present study shows that the vocal fold self-oscillations can be strongly influenced by interaction with acoustic resonances of the human vocal tract.
Keywords:
biomechanics of voice; modelling of human voice
Available at various institutes of the ASCR
Acoustic resonances can support self-oscillations of a dynamic system.
Flutter instability of human vocal folds is a necessary condition for speaking, because airflow induced vibrations of the vocal folds create the voice source. The present study shows that the vocal ...
Identification of dynamic properties of built electrodynamic shaker
Šnábl, Pavel; Kozánek, Jan; Pešek, Luděk
2021 - English
Electrodynamic shaker was built in our institute for excitation of vibrating blade in a flow field. The shaker consists of permanent magnet and voice coil, 3D printed body, core and cover, and two at suspension rings laser-cutted from Pertinax. For simulation purposes of the whole system, identfication of shaker dynamic parameters was needed. Several identification methods in time or frequency domain were used, and it was shown that the shaker model must contain nonlinear stiffness in order to describe the real system more accurately.
Keywords:
identification; dynamics; shaker
Available at various institutes of the ASCR
Identification of dynamic properties of built electrodynamic shaker
Electrodynamic shaker was built in our institute for excitation of vibrating blade in a flow field. The shaker consists of permanent magnet and voice coil, 3D printed body, core and cover, and two at ...
Measurement of friction coefficient between damping wire and groove
Šnábl, Pavel; Pešek, Luděk; Bula, Vítězslav; Běhálek, V.; Boháč, T.; Tašek, H.
2021 - English
Damping wire is being used on railway wheels for noise suppression. It is inserted into a groove of the wheel and dry friction damping reduces vibrations and thus the noise transmitted by the wheel. For increase of durability of the wire, surface treatment of the groove and the ring must be applied to prevent corrosion. Three combinations of diferent surface treatments were studied during reciprocating motion in a set of measurements with diferent frequencies and normal forces to evaluate friction coeficient. Then, those measurements were repeated after a long-time run to evaluate the change of friction coeficient after the wear of the surfaces.
Keywords:
tribology; friction; damping wire
Available at various institutes of the ASCR
Measurement of friction coefficient between damping wire and groove
Damping wire is being used on railway wheels for noise suppression. It is inserted into a groove of the wheel and dry friction damping reduces vibrations and thus the noise transmitted by the wheel. ...
Use of Hydrogen Trains in Regional Rail Transportation
Gruber, Jan
2021 - Czech
The Czech Republic is among the countries with the highest density of non-electrified rail network. The alternative to electrification of small regional tracks is utilization of hydrogen fuel-cell trains. Such trains are much cleaner and quieter in comparison with diesel units. They also provide better range, faster refuelling, lower weight and ability to operate in adverse climatic conditions in comparison with solely battery units. There are successful examples of deployment of hydrogen trains in regional train transport in other countries. The presentation analyses possibilities of operating hydrogen trains in Moravian-Silesian region using various sources of hydrogen, including so-called green hydrogen and purple hydrogen. Česká republika patří k zemím s nejhustší sítí neelektrifikovaných tratí na světě. Jako alternativa k elektrizaci v oblastech malých regionálních tratí mohou sloužit vlaky využívající vodíkové palivové články. Oproti dieselovým jednotkám nabízejí vyšší ekologičnost, oproti jednotkám čistě bateriovým lepší dojezd, nižší hmotnost a odolnost proti klimatickým podmínkám. V zahraničí již existují úspěšné projekty provozu vodíkových vlaků na regionálních tratích. Prezentace se zabývá možnostmi provozu těchto vlaků v Moravskoslezském regionu při využití rozličných zdrojů vodíku, včetně vodíku tzv. zeleného, či purpurového.
Keywords:
hydrogen train; rail transport; green hydrogen; purple hydrogen
Available at various institutes of the ASCR
Use of Hydrogen Trains in Regional Rail Transportation
The Czech Republic is among the countries with the highest density of non-electrified rail network. The alternative to electrification of small regional tracks is utilization of hydrogen fuel-cell ...
Modelling approaches to the stress wave propagation in a cracked specimen
Kruisová, Alena; Kopačka, Ján; Kober, Jan
2021 - English
One of the essential tasks of non-destructive testing is to detect a crack in a specimen. It is well known that a component with a crack exposed to a harmonic excitation of a given frequency\nhas a nonlinear response as a function of the excitation amplitude. The focus of this paper is the numerical modelling of this phenomenon using the finite element method with the consideration\nof the contact constraint at the crack interface. In addition to the nonlinear transient dynamic problem solved by explicit time integration, a more efficient procedure based on the harmonic\nbalance method is developed. The results of numerical simulations are also compared with experimentally obtained data.
Keywords:
finite element method; contact; crack; harmonic balance method
Available at various institutes of the ASCR
Modelling approaches to the stress wave propagation in a cracked specimen
One of the essential tasks of non-destructive testing is to detect a crack in a specimen. It is well known that a component with a crack exposed to a harmonic excitation of a given frequency\nhas a ...
Development of autonomous experimental setup to investigate directional distortional hardening under biaxial loading
Svárovský, Jiří; Parma, Slavomír; Štefan, Jan; Ciocanel, C.; Feigenbaum, H. P.; Klepač, Vilém; Marek, René; Plešek, Jiří
2021 - English
Plastic deformations alter the shape of the yield surface in the stress space. Models for predicting the shape of the yield surface according to the direction of loading are being developed. Experimental data are the key factor in development and validation of phenomenological models, such as the model of directional distortional hardening cited in this study. The objective of this paper is to present the experimental setup for investigation of the directional distortional hardening. A new autonomous method was developed using an axial-torsional testing machine and the Labivew 2017 graphical programming environment to monitor the yield surface in axial stress – shear stress space. A suitable yield condition in form of effective plastic strain was used for the determination of the yield points. Initial yield surface obtained by this method shows promising agreement with von Mises model of the yield surface. Several outstanding yield points were measured which disrupt the assumption of the yield surface convexity. Therefore, possible shortcomings caused by the methodology are being investigated.
Keywords:
directional distortional hardening; yield surface; strain hardening; Labview
Available at various institutes of the ASCR
Development of autonomous experimental setup to investigate directional distortional hardening under biaxial loading
Plastic deformations alter the shape of the yield surface in the stress space. Models for predicting the shape of the yield surface according to the direction of loading are being developed. ...
Recent improvements in CFD solver for fully coupled particle-laden flows
Šourek, M.; Isoz, Martin
2021 - English
While new methods combining the computational fluid dynamics (CFD) and the discrete element method (DEM) have been developed to simulate freely moving solid particles, they tend to be focused on simulations with spherical particles only. Here, we present a strongly coupled CFD-DEM solver capable of simulating movement of arbitrarily-shaped particles dispersed in a fluid. The particles are assumed to be large enough to affect the fluid flow and distributed densely enough to come into contact with both the boundaries of the computational domain and with each other. In this paper, we will focus on the recent improvements of our solver, specifically, in the areas of (i) inclusion of solid bodies into the computational domain, (ii) general CFD-DEM coupling algorithm, and (iii) code parallelization and practical usability.
Keywords:
CFD; DEM; HFDIB-DEM; OpenFOAM
Available at various institutes of the ASCR
Recent improvements in CFD solver for fully coupled particle-laden flows
While new methods combining the computational fluid dynamics (CFD) and the discrete element method (DEM) have been developed to simulate freely moving solid particles, they tend to be focused on ...
Numerical estimation of blade displacement due to air excitation
Mekhalfia, Mohammed Lamine; Procházka, Pavel; Tchawou Tchuisseu, Eder Batista; Hodboď, Robert; Maturkanič, Dušan
2021 - English
For the last few years, vibration measurement has taken an intense interest from research activities. For this reason, this article considers, besides vibration measurements, the impact of air forced excitation on blade motion, displacement and vibration through both simulation analysis and The Transformation of mathematical analysis that explain the interaction between fluid (Air) and the structure (Blade) into numerical setup along with FEM analysis through ANSYS Software. 3D Blade was created to meet the same characteristics of the real blade to enable real environment criteria for the simulation.
Keywords:
displacement; Fluid structure interaction (FSI); air; blade
Available at various institutes of the ASCR
Numerical estimation of blade displacement due to air excitation
For the last few years, vibration measurement has taken an intense interest from research activities. For this reason, this article considers, besides vibration measurements, the impact of air forced ...
Study of aeroacoustics noise of high-speed aircraft propellers and mitigation of the cause
Prasad, Chandra Shekhar
2021 - English
The project deals with the study of aeroacoustics noise generated by high-speed turboprop propellers and methods to minimize its causes. A reduced order flow solver with aeroacaustic noise capturing characteristics is developed for fast numerical analysis purpose. The acoustical performance will be also studied using flow visualization using article image velocimetry under rotation and acoustics noise will be measured by microphones for both conventional as well as unconventional propeller designs at diferent rotational speeds.
Keywords:
aeroacoustics; aircraft propellers; tip-vortex interaction; low noise propeller; ROM-CFD/CAA
Available at various institutes of the ASCR
Study of aeroacoustics noise of high-speed aircraft propellers and mitigation of the cause
The project deals with the study of aeroacoustics noise generated by high-speed turboprop propellers and methods to minimize its causes. A reduced order flow solver with aeroacaustic noise capturing ...
The new HPC results of 3D FE modelling of dry-friction damping at tie-boss couplings of bladed wheel - 6nd resonant mode
Pešek, Luděk; Šnábl, Pavel; Bula, Vítězslav
2021 - English
The paper is a direct continuation of our study published in the last colloquium DYMAMESI. This paper deals with the new results of dry-friction damping calculation of the bladed wheel with tie-boss couplings vibrating at a higher resonant mode, i.e. mode with 6 nodal diameters (ND). The numerical solution of the wheel based on 3D finite element method with surface-to-surface dry friction contact model is applied. Due to dry friction contacts and non-linear solution, it leads to HPC computations and long computation times. Therefore, the earlier proposed computational strategy for damping evaluation where the resonant attenuation is computed directly from the defined resonant initial conditions given by the 6ND mode is used. Comparison of experimental and numerical results of dynamical behaviour of the bladed wheel yields a reasonable agreement for the studied vibration mode.
Keywords:
bladed wheel; dry-friction contacts; damping; tie-boss couplings
Available at various institutes of the ASCR
The new HPC results of 3D FE modelling of dry-friction damping at tie-boss couplings of bladed wheel - 6nd resonant mode
The paper is a direct continuation of our study published in the last colloquium DYMAMESI. This paper deals with the new results of dry-friction damping calculation of the bladed wheel with tie-boss ...
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