Number of found documents: 2874
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An explicit time scheme with local time stepping for one-dimensional wave propagation in a bimaterial bar
Kolman, Radek; Cho, S.S.; Gonzalez, J.G.; Park, K.C.; Berezovski, A.
2017 - English
In this paper, we test a two-time step explicit scheme with local time stepping. The standard explicit time scheme in finite element analysis is not able to keep accuracy of stress distribution through meshes with different local Courant numbers for each finite element. The used two-time step scheme with the diagonal mass matrix is based on the modification of the central difference method with pullback interpolation. We present a numerical example of one-dimensional wave propagation in a bimaterial elastic bar. Based on numerical tests, the employed time scheme with pullback interpolation and local stepping technique is able to eliminate spurious oscillations in stress distribution in numerical modelling of shock wave propagation in heterogeneous materials. Keywords: wave propagation in heterogeneous materials; explicit time integration; finite element method; local stepping; spurious oscillations Available at various institutes of the ASCR
An explicit time scheme with local time stepping for one-dimensional wave propagation in a bimaterial bar

In this paper, we test a two-time step explicit scheme with local time stepping. The standard explicit time scheme in finite element analysis is not able to keep accuracy of stress distribution ...

Kolman, Radek; Cho, S.S.; Gonzalez, J.G.; Park, K.C.; Berezovski, A.
Ústav termomechaniky, 2017

Investigation of droplet nucleation in CCS relevant systems – design and testing of the expansion chamber
Čenský, Miroslav; Hrubý, Jan; Vinš, Václav; Hykl, Jiří; Šmíd, Bohuslav
2017 - English
A unique in-house designed experimental apparatus for investigation of nucleation of droplets in CCS relevant systems is being developed by the present team. The apparatus allows simulating various processes relevant to CCS technologies. Gaseous mixtures with CO2 are prepared in a Mixture Preparation\nDevice (MPD) based on accurate adjustment of flow rates of individual components [EPJ Web of Conferences 143, 02140 (2017)]. The mixture then flows into an expansion chamber, where it undergoes a rapid adiabatic expansion. As a consequence of adiabatic cooling, the mixture becomes supersaturated and nucleation and simultaneous growth of droplets occurs. In this study, we describe the design and testing of the expansion part of the experimental setup. The rapid expansion was realized using two valve systems, one for low pressures (up to 0.7 MPa) and the other for high pressures (up to 10 MPa). A challenge for a proper design of the expansion system is avoiding acoustic oscillations. These can occur either in the mode of Helmholtz resonator, where the compressible gas in the chamber acts as a spring and the rapidly moving\ngas in the valve system as a mass, or in the “flute” mode, where acoustic waves are generated in a long outlet tubing.\n Keywords: carbon capture and storage; expansion chamber; experiment Available at various institutes of the ASCR
Investigation of droplet nucleation in CCS relevant systems – design and testing of the expansion chamber

A unique in-house designed experimental apparatus for investigation of nucleation of droplets in CCS relevant systems is being developed by the present team. The apparatus allows simulating various ...

Čenský, Miroslav; Hrubý, Jan; Vinš, Václav; Hykl, Jiří; Šmíd, Bohuslav
Ústav termomechaniky, 2017

Physical modelling axisymmetric diffusors by plane models
Uruba, Václav
2017 - English
Diffusers with axisymmetric geometry are used very often in technical applications, they are characterized by circular cross-section along the flow axis. Such geometry is not suitable for application of optical methods, so the plane model with rectangular cross-section is used instead very often. However the flow inside such model could be significantly different as for velocity and pressure fields. The physical similarity of 1D flow in axisymmetric diffusers and plane models will be studied in details. The plane model opening angle is suggested to optimize velocity and pressure distributions in the model. Keywords: diffusor; pressure gradient; axisymmetric geometry; plane model Available at various institutes of the ASCR
Physical modelling axisymmetric diffusors by plane models

Diffusers with axisymmetric geometry are used very often in technical applications, they are characterized by circular cross-section along the flow axis. Such geometry is not suitable for application ...

Uruba, Václav
Ústav termomechaniky, 2017

Mapping of problematic regions in AE source location
Chlada, Milan; Převorovský, Zdeněk
2017 - English
Similarly to Global Positioning System, location of material defects by acoustic emission method meets the geometrical dilution of precision (GDOP) phenomena. Besides the several attitudes how to mathematically express its measure and compare particular sensor configurations in accordance with desired location precision, recently proposed method brings extended possibilities for detection of critical regions characterized by strong sensitivity of location results to signal arrival time changes or errors. Analogically to GDOP parameter it yields the sensitivity map available even for non-continuous or anisotropic materials. During the computation it uses the algorithm for finding the shortest ways in discretely defined bodies, which furthermore enables to view the problem through the so-called similarity and ambiguity maps. Keywords: acoustic emission; source location; geometrical dilution of precision Available at various institutes of the ASCR
Mapping of problematic regions in AE source location

Similarly to Global Positioning System, location of material defects by acoustic emission method meets the geometrical dilution of precision (GDOP) phenomena. Besides the several attitudes how to ...

Chlada, Milan; Převorovský, Zdeněk
Ústav termomechaniky, 2017

On finite element modelling in time reversal problems
Mračko, Michal; Kober, Jan; Kolman, Radek; Převorovský, Zdeněk; Plešek, Jiří; Masák, Jan; Kruisová, Alena
2017 - English
In this paper we analyse suitability and accuracy of computational techniques in time reversal applications based on finite element method (FEM) for detection and localization of defects, cracks or other acoustic emission sources in bodies and structures. As it is known, a classical explicit integration scheme - central difference is reversible. The central difference scheme as a time integrator is widely used for linear and nonlinear finite element analyses and it is also implemented in commercial and open-source finite element software. In the paper properties of the explicit FEM in time reversal problems are studied and analysed. We use the standard Galerkin FEM formulation with linear shape functions, one-point Gauss integration and lumped mass matrix. Loading by the Ricker pulse was applied for modelling of the acoustic source in an elastic square domain. A special attention is paid to the choice of boundary conditions in reverse problem which keep the reversibility of problems of interest. Finally, we show the quality of refocusing of the original acoustic source. Keywords: time reversal; explicit finite element analysis; elastic wave propagation; non-destructive testing; source reconstruction; refocusing Available at various institutes of the ASCR
On finite element modelling in time reversal problems

In this paper we analyse suitability and accuracy of computational techniques in time reversal applications based on finite element method (FEM) for detection and localization of defects, cracks or ...

Mračko, Michal; Kober, Jan; Kolman, Radek; Převorovský, Zdeněk; Plešek, Jiří; Masák, Jan; Kruisová, Alena
Ústav termomechaniky, 2017

NDT in additive manufacturing of metals
Převorovský, Zdeněk; Krofta, Josef; Kober, Jan
2017 - English
In this study we tested possibilities of nonlinear elastic wave spectroscopy (NEWS) methods to classify two types of artificially created defects in Ti-6Al-4V prismatic samples fabricated by Electron Beam Melting (EBM) system. Two series of samples with variable internal defects were tested: samples with central circular defects (missing material gaps), and samples with gradually growing stochastic porosity. Each group of samples contained also fully compact sample for a comparison. Five ultrasonic NEWS procedures were used to classify defects variability. Relatively simple experimental facility with two piezoelectric transducers allows interrogate samples and record their response. The best results, documented in this paper, were obtained by two modifications of NWMS procedure. Results of NEWS tests indicate that selected NEWS procedures can be used also for online AM monitoring. Keywords: additive manufacturing; 3D printing of metals; nondestructive testing; nonlinear elastic wave spectroscopy Available at various institutes of the ASCR
NDT in additive manufacturing of metals

In this study we tested possibilities of nonlinear elastic wave spectroscopy (NEWS) methods to classify two types of artificially created defects in Ti-6Al-4V prismatic samples fabricated by Electron ...

Převorovský, Zdeněk; Krofta, Josef; Kober, Jan
Ústav termomechaniky, 2017

A MODIFIED MATHEMATICAL MODEL OF HUMAN VENTRICULAR CARDIOMYOCYTE INCORPORATING SEPARATE T-TUBULAR AND SURFACE DYADS AND SUBMEMBRANE SPACES
Pásek, Michal; Bébarová, M.; Christé, G.
2017 - English
Intracellular Ca2+ load and Ca2+ transient are considerably dependent on distribution of sarcolemmal Ca2+ pump and Na+-Ca2+ exchanger between the t-tubular and surface membranes in the presence of separate dyadic and subsarcolemmal spaces in rat ventricular cell model. To explore analogical phenomenon in human, we modified our previously published model of human ventricular myocyte. When the t-tubular fractions of Na+-Ca2+ exchanger and of sarcolemmal Ca2+ pump were increased to the newly proposed value of 0.95 in the modified model, the following changes were observed at 1 Hz steady-state stimulation: a shortening of the action potential duration at 90% repolarisation by 6% and an increase of the cytosolic Ca2+ transient by 22%. Further analysis revealed a critical role of Ca2+ concentration changes in the subsarcolemmal spaces and consequent change in cellular Ca2+ cycling in this effect. Keywords: human ventricular cell model; t-tubules; dyads; subsarcolemmal spaces; calcium cycling Available at various institutes of the ASCR
A MODIFIED MATHEMATICAL MODEL OF HUMAN VENTRICULAR CARDIOMYOCYTE INCORPORATING SEPARATE T-TUBULAR AND SURFACE DYADS AND SUBMEMBRANE SPACES

Intracellular Ca2+ load and Ca2+ transient are considerably dependent on distribution of sarcolemmal Ca2+ pump and Na+-Ca2+ exchanger between the t-tubular and surface membranes in the presence of ...

Pásek, Michal; Bébarová, M.; Christé, G.
Ústav termomechaniky, 2017

A short wave limit of the frequency equation for plane-stress nonaxisymmetric disc motions
Červ, Jan; Valeš, František; Adámek, V.
2017 - English
It is proved that the general frequency equation for plane-stress nonaxisymmetric disc motions tends for the first mode of propagation and for wavelengths very short when compared with the disc radius to the secular equation for Rayleigh waves. Keywords: frequency equation; elastic disc; Rayleigh waves Available at various institutes of the ASCR
A short wave limit of the frequency equation for plane-stress nonaxisymmetric disc motions

It is proved that the general frequency equation for plane-stress nonaxisymmetric disc motions tends for the first mode of propagation and for wavelengths very short when compared with the disc radius ...

Červ, Jan; Valeš, František; Adámek, V.
Ústav termomechaniky, 2017

Transition Modelling on Separated Flow in Turbine Cascade
Louda, Petr; Příhoda, Jaromír; Kozel, K.
2017 - English
The work deals with numerical simulation of turbulent ow through turbine cascade by RANS model with model of transition to turbulence. Performance of two transition models is compared. First one is gamma-zeta model based on transition criteria, second one algebraic transition model based on the concept of laminar uctuations energy (Kubacki, Dick 2016). The criterion for transition in separated state is re-formulated in order to remove stream-wise non-local formulation. The performance of the transition models is observed on the shock wave - boundary layer interaction on turbine blade. Keywords: turbine cascade; transition model; separation bubble; shock wave-boundary layer interaction Fulltext is available at external website.
Transition Modelling on Separated Flow in Turbine Cascade

The work deals with numerical simulation of turbulent ow through turbine cascade by RANS model with model of transition to turbulence. Performance of two transition models is compared. First one is ...

Louda, Petr; Příhoda, Jaromír; Kozel, K.
Ústav termomechaniky, 2017

Modelling of running waves in turbine blades cascade
Půst, Ladislav; Pešek, Luděk
2017 - English
Dynamic properties of blades in the blade cascade excited by steam flow from the stationary bladed disk are investigated with the aim to explain origin and behaviour of running waves. It is shown that one of the most important reasons for existence of running waves is the running periodic forces from steam wakes due to different numbers of blades of stationary and rotating wheels. On a simplified computational model of disk with closed 10-blades bundle are presented resulting velocities, theirs directions and modes of forced running waves. The effect of these forced running waves on the existence of flutter waves will be shortly mentioned as well. Keywords: blade cascade; turbine disk; delay of excitation forces; forward; backward running waves Available at various institutes of the ASCR
Modelling of running waves in turbine blades cascade

Dynamic properties of blades in the blade cascade excited by steam flow from the stationary bladed disk are investigated with the aim to explain origin and behaviour of running waves. It is shown that ...

Půst, Ladislav; Pešek, Luděk
Ústav termomechaniky, 2017

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