Number of found documents: 2944
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Finite element modeling of the signal propagation in a thin tube and comparison with experimental data
Kruisová, Alena; Kolman, Radek; Trnka, Jan; Mračko, Michal
2018 - English
In finite element modeling of wave propagation problems, both the spatial and temporal discretization lead to dispersion errors. It means that the phase velocity of propagated wave is related to its frequency. In framework of temporal-spatial dispersion analysis, the time step size for implicit time integration method based on the Newmark method is proposed for linear and quadratic serendipity plane finite elements. In this paper, we verify the theoretical dispersion analysis by elastic wave propagation in thin tube, where experimental results are known. Such time step size was used in finite element modeling of the stress wave propagating in this thin steel tube, the results of simulations were compared with experimental results. Keywords: wave propagation; finite element method; dispersion errors Available at various institutes of the ASCR
Finite element modeling of the signal propagation in a thin tube and comparison with experimental data

In finite element modeling of wave propagation problems, both the spatial and temporal discretization lead to dispersion errors. It means that the phase velocity of propagated wave is related to its ...

Kruisová, Alena; Kolman, Radek; Trnka, Jan; Mračko, Michal
Ústav termomechaniky, 2018

Experimental investigation of fault tolerant converter connected to unbalanced grid
Valouch, Viktor; Šimek, Petr; Škramlík, Jiří
2018 - English
A model of the three-phase voltage converter for simulation of its modes of operation in standard as wellas fault states is presented. The presented model can be used to simulate steady-states and also transients at dc and ac side of the grid-connected converter. Based on simulation, an algorithm was designed to identify and localize a fault in some phase of the three-phase converter. Rules how to modify hardware, and control and modulation strategies to hold the converter in operation after the fault are presented and tested. the algorithm was experimentally verified. Keywords: grid-connected converter; fault identification and localization; reconfiguration Available at various institutes of the ASCR
Experimental investigation of fault tolerant converter connected to unbalanced grid

A model of the three-phase voltage converter for simulation of its modes of operation in standard as wellas fault states is presented. The presented model can be used to simulate steady-states and ...

Valouch, Viktor; Šimek, Petr; Škramlík, Jiří
Ústav termomechaniky, 2018

Influence of excitation frequency and pulse width on blade vibration
Voronova, Evgeniya; Maturkanič, Dušan
2018 - English
The paper describes results of measuring of blade vibration characteristics excitation by one electromagnet at harmonic regime.The measurements were performed in the laboratory of rotational laser vibrometry originated at the Institute of Thermomechanics AS CR, v.v.i.\n Keywords: vibration; blade; laser; turbine Available at various institutes of the ASCR
Influence of excitation frequency and pulse width on blade vibration

The paper describes results of measuring of blade vibration characteristics excitation by one electromagnet at harmonic regime.The measurements were performed in the laboratory of rotational laser ...

Voronova, Evgeniya; Maturkanič, Dušan
Ústav termomechaniky, 2018

Generation of Intermittent Jet by Pulse-Modulated Synthetic Jets
Broučková, Zuzana
2018 - English
An axisymmetric air jet was excited using a pair of counter synthetic jets running in opposed direction. First, the control synthetic jets were measured alone. The driving signal was pulse modulated sinusoidal signal. After an adjustment, the primary axisymmetric jet was excited to the bifurcating mode, and its behavior was studied experimentally. For comparison purposes, a reference steady (unforced) jet from the same nozzle was also measured (Reynolds number was approximately 1300). The flow visualization and hot-wire anemometry techniques were used. Keywords: synthetic jet; pulse modulation; flow control Available at various institutes of the ASCR
Generation of Intermittent Jet by Pulse-Modulated Synthetic Jets

An axisymmetric air jet was excited using a pair of counter synthetic jets running in opposed direction. First, the control synthetic jets were measured alone. The driving signal was pulse modulated ...

Broučková, Zuzana
Ústav termomechaniky, 2018

The 2nd International Conference on Advanced Modelling of Wave Propagation in Solids
Kolman, Radek; Berezovski, A.; Kruisová, Alena
2018 - English
The 2nd International Conference on Advanced Modelling of Wave Propagation in Solids aims to bring together scientists and engineers with interest in advanced modelling of wave propagation in solids. The Conference on Advanced Modelling of Wave Propagation in Solids will concentrate on topics related to analytical, numerical and experimental studies of linear and non-linear waves in conventional, advanced and modern materials like metamaterials and auxetic materials, to strongly dispersive wave propagation in inhomogeneous solids and to waves in materials with microstructure, etc. Attention will also be devoted to up-to-date formulations of non-linear constitutive equations in the description of material response under thermomechanical loading, dynamic fracture and damage, phase transformations, shock waves, and to dissipative effects. The recent advances and properties of analytical and numerical approaches and strategies should also be discussed. The main purpose of the Conference on Advanced Modelling of Wave Propagation in Solids is to discuss novel and recent methods of wave propagation modelling and to consider expected credibility of results especially in cases when comparison with those of experiment is not available. Theoretical, computational as well as experimental contributions on the wave propagation are welcome. Keywords: wave propagation; advanced materials; numerical methods; experimental methods; dynamic behaviour of materials Available at various institutes of the ASCR
The 2nd International Conference on Advanced Modelling of Wave Propagation in Solids

The 2nd International Conference on Advanced Modelling of Wave Propagation in Solids aims to bring together scientists and engineers with interest in advanced modelling of wave propagation in solids. ...

Kolman, Radek; Berezovski, A.; Kruisová, Alena
Ústav termomechaniky, 2018

Spatial and temporal correlations in turbulent boundary layers
Jurčáková, Klára; Kellnerová, Radka
2018 - English
The experimental data from time-resolved particle image velocimetry measurement of the boundary-layer flows over various aerodynamically rough surfaces are presented. Temporal, spatial, and time-space correlation are analyzed and used for calculation of integral length and time scales. Temporal and spatial integral scales are connected via convection velocity. Taylor's hypothesis on frozen turbulence says that the convection velocity is equal to the local mean velocity. The experimental data shows that the convection velocity is larger than local mean velocity in the lower third of the boundary layer and greater in the upper two thirds. The cross-over line is higher over surfaces with higher roughness. Keywords: wind tunnel; time-resolved particle image velocimetry; aerodynamically rough surfaces; integral length scales Available at various institutes of the ASCR
Spatial and temporal correlations in turbulent boundary layers

The experimental data from time-resolved particle image velocimetry measurement of the boundary-layer flows over various aerodynamically rough surfaces are presented. Temporal, spatial, and time-space ...

Jurčáková, Klára; Kellnerová, Radka
Ústav termomechaniky, 2018

XXIV Biennial Symposium on Measuring Techniques in Turbomachinery
Šimurda, David
2018 - English
Aim of the symposium is to bring together researchers from the field of experimental research in turbomachines who can share and are interested in experience with the development of new experimental measurement techniques, new techniques for monitoring engine operation and performance, and application of new analysis techniques to experimental data. Keywords: turbomachines; experiment; measurement techniques; data analysis Available at various institutes of the ASCR
XXIV Biennial Symposium on Measuring Techniques in Turbomachinery

Aim of the symposium is to bring together researchers from the field of experimental research in turbomachines who can share and are interested in experience with the development of new experimental ...

Šimurda, David
Ústav termomechaniky, 2018

Numerical simulation of flow in superpak family packings
Smutek, J.; Isoz, Martin
2018 - English
The distillation is currently the most energy-intensive technology of the chemical industry. Commonly, the distillation is performed in the columns lled with a structured packing. Structured packings are complex structures used to increase the size of the interface available for the mass transfer. Because of the high complexity of both the packings and the physical phenomena occurring during the distillation, the design of the distillation columns is still based mostly on empirical data. In this work, we concentrate on modeling the gas ow in the SuperPak family of structured packings. First, we propose an algorithm for automatic generation\nof the packing geometry. Next, we construct and validate a three-dimensional computational uid dynamics (CFD) model of gas ow through SuperPak 250.Y and SuperPak 350.Y packings. The model validation is done by comparing experimental data of dry pressure losses to the values computed by our model. The obtained di erence between the CFD estimates and experiments is bellow 10 %. Finally, we present a parametric study of the SuperPak 250.Y packing geometry. The devised modeling approach may be easily automated and used for optimization of the SuperPak type packing geometry with respect to the gas ow. Furthermore,\nthe proposed CFD model may be extended to account for the multiphase ow. Keywords: CFD; OpenFOAM; structured packing; distillation; absorption Fulltext is available at external website.
Numerical simulation of flow in superpak family packings

The distillation is currently the most energy-intensive technology of the chemical industry. Commonly, the distillation is performed in the columns lled with a structured packing. Structured packings ...

Smutek, J.; Isoz, Martin
Ústav termomechaniky, 2018

Model order reduction technique for large scale flow computations
Isoz, Martin
2018 - English
Current progress in numerical methods and available computational power combined with industrial needs promote the development of more and more complex models. However, such models are, due to their complexity, expensive from the point of view of the data storage and the time necessary for their evaluation. The model order reduction (MOR) seeks to reduce the computational complexity of large scale models. We present an application of MOR to the problems originating in the finite volume (FV) discretization of incompressible Navier-Stokes equations. Our approach to MOR is based on the proper orthogonal decomposition (POD)\nwith Galerkin projection. Moreover, the problems arising from the nonlinearities present in the original model are adressed within the framework of the discrete empirical interpolation method (DEIM). We provide a link between the POD-DEIM based MOR and OpenFOAM, which is an open-source CFD toolbox capable of solving even industrial scale problems. The availability of a link between OpenFOAM and POD-DEIM based MOR enables a direct order reduction for large scale systems originating in the industrial practice. Keywords: proper orthogonal decomposition; discrete empirical interpolation method; computational fluid dynamics; OpenFOAM Fulltext is available at external website.
Model order reduction technique for large scale flow computations

Current progress in numerical methods and available computational power combined with industrial needs promote the development of more and more complex models. However, such models are, due to their ...

Isoz, Martin
Ústav termomechaniky, 2018

Aerodynamic transfer of energy to vibrating vocal folds for different driving mechanisms
Valášek, J.; Sváček, P.; Horáček, Jaromír
2018 - English
This paper studies the mutual energy transfer between the fluid flow, described by incompressible Navier-Stokes equations, and the elastic body represented by vocal folds. The aerodynamic energy transfer function describes the amount and more importantly the sign of the energy exchange. It determines if the vocal fold vibrations are self-excited or prescribed.The energy transfer function is studied for three different driving mechanisms introduced by different inlet boundary conditions (BC). The most frequently used inlet BCs for incompressible model of fluid flow approximated by the finite element method are either Dirichlet BC giving the inlet velocity or do-nothing type of BC prescribing the pressure difference between the inlet and the outlet. Since the numerical simulations with both aforementioned BCs do not provide results observed experimentally the newly introduced BC based on the penalization approach seems as remedy. The numerical model consists of strongly coupled partitioned scheme based on the stabilized finite element method.\n\n Keywords: inlet boundary conditions; weakly imposed Dirichlet boundary condition; energy transfer function; finite element method Available at various institutes of the ASCR
Aerodynamic transfer of energy to vibrating vocal folds for different driving mechanisms

This paper studies the mutual energy transfer between the fluid flow, described by incompressible Navier-Stokes equations, and the elastic body represented by vocal folds. The aerodynamic energy ...

Valášek, J.; Sváček, P.; Horáček, Jaromír
Ústav termomechaniky, 2018

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