Number of found documents: 2618
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On the 3D Dynamics of the Wake Behind a Circular Cylinder
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2020 - English
Flow in the wake of a circular cylinder is studied experimentally using time-resolved stereo PIV method. Special attention is paid to 3D topology of dynamical structures. While the distribution of statistic quantities along the cylinder is uniform, and i.e. 2D, the instantaneous flow structure is fully 3D. Within the velocity fluctuating flow field the structures containing streamwise vorticity and velocity components are dominant. The POD modes connected with von Kármán vortex street are identified. Keywords: circular cylinder; wake; 3D structure; POD Fulltext is available at external website.
On the 3D Dynamics of the Wake Behind a Circular Cylinder

Flow in the wake of a circular cylinder is studied experimentally using time-resolved stereo PIV method. Special attention is paid to 3D topology of dynamical structures. While the distribution of ...

Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
Ústav termomechaniky, 2020

Contribution to hpc fem calculations of bladed disk dynamics with dry-friction contacts
Pešek, Luděk; Šnábl, Pavel; Bula, Vítězslav
2020 - English
The experimental set-up for studying dynamical behaviour of the bladed wheel with pre-stressed dry-friction contacts in tie-bosses was built. The numerical solution of the turbine bladed wheel with tiebosses based on 3D finite element method with surface to surface dry friction contact model is proposed. Comparison of experimental and preliminary numerical results of dynamical behaviour and damping estimation of our bladed wheel design yielded a reasonable agreement. Due to dry friction contacts and non-linear solution of 3D FE model it, however, leads to HPC computations and long computation times. The contribution deals with description of computational strategy for damping evaluation and achieved results, too. Keywords: bladed wheel; dry-friction contacts; damping; tie-boss couplings Available at various institutes of the ASCR
Contribution to hpc fem calculations of bladed disk dynamics with dry-friction contacts

The experimental set-up for studying dynamical behaviour of the bladed wheel with pre-stressed dry-friction contacts in tie-bosses was built. The numerical solution of the turbine bladed wheel with ...

Pešek, Luděk; Šnábl, Pavel; Bula, Vítězslav
Ústav termomechaniky, 2020

Design of experiment for temperature dependence of rubber samples under torsional harmonic load
Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Košina, Jan; Cibulka, Jan
2020 - English
This work deals with the preparation and methodology of temperature measurement inside the rubber sample. There is a design of a rubber sample with placed temperature sensors and a description with a scheme of temperature measurement under torsional dynamic stress. The reason for these measurements is to determine the temperature dependence and sensitivity of the parameters of the thermal outputs. Keywords: heat flow; temperature; Fourier equation Available at various institutes of the ASCR
Design of experiment for temperature dependence of rubber samples under torsional harmonic load

This work deals with the preparation and methodology of temperature measurement inside the rubber sample. There is a design of a rubber sample with placed temperature sensors and a description with a ...

Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Košina, Jan; Cibulka, Jan
Ústav termomechaniky, 2020

Comparison of power control method for B4 converter connected to unbalanced grid
Šimek, Petr; Valouch, Viktor
2020 - English
The aim of the paper is to present a power control of a three-phase inverter with only four inverter legs (connections B4) connected to an unbalanced grid. The results obtained by the predictive power control with a finite set of control values, the results obtained using a modified direct power control strategy, and the results obtained using a generalized predictive control are compared and discussed.\n Keywords: power control; B4 converter; unbalanced grid Available at various institutes of the ASCR
Comparison of power control method for B4 converter connected to unbalanced grid

The aim of the paper is to present a power control of a three-phase inverter with only four inverter legs (connections B4) connected to an unbalanced grid. The results obtained by the predictive power ...

Šimek, Petr; Valouch, Viktor
Ústav termomechaniky, 2020

Experimental modelling of vibroacoustics of the human vocal tract with compliant walls
Radolf, Vojtěch; Horáček, Jaromír; Košina, Jan
2020 - English
Experimental model of human vocal tract cavities with hard walls has been modified to take into account the compliance of the soft tissue of the human vocal tract. The paper presents the studied acoustic-structural interaction of the vocal tract cavities with a dynamical system originated in vibration of the soft tissue. The experimental results are in qualitative agreement with the results of mathematical modelling. Compliant walls of acoustic cavities generate additional low frequency acoustical-mechanical resonances of the system and increase acoustic resonance frequencies. Keywords: biomechanics of voice; vocal tract acoustics; acoustic-structural interaction. Available at various institutes of the ASCR
Experimental modelling of vibroacoustics of the human vocal tract with compliant walls

Experimental model of human vocal tract cavities with hard walls has been modified to take into account the compliance of the soft tissue of the human vocal tract. The paper presents the studied ...

Radolf, Vojtěch; Horáček, Jaromír; Košina, Jan
Ústav termomechaniky, 2020

Laminar-Turbulent Transition in View of Flow Separation from Isothermal and Heated Cylinder
Pech, Jan
2020 - English
This work presents insight to the laminar-turbulent transition in flow around cylinder through a numerical simulation, both in isothermal and heated case. The flow is modelled directly as a solution to the Navier-Stokes and Navier-Stokes-Fourier system. Reynolds numbers are considered in range 100-20000, ratio of cylinder-wall and upstream temperature is up to 1.5. Curves representing evolution of separation positions in time provide novel insight to vortex formation. Various regimes are recognized and some of them can be assigned to phenomena described formerly in experiment. Keywords: transition to turbulence; heated flow; cylinder flow; separation angle; Navier-Stokes- Fourier; spectral/hp element method Fulltext is available at external website.
Laminar-Turbulent Transition in View of Flow Separation from Isothermal and Heated Cylinder

This work presents insight to the laminar-turbulent transition in flow around cylinder through a numerical simulation, both in isothermal and heated case. The flow is modelled directly as a solution ...

Pech, Jan
Ústav termomechaniky, 2020

A simple algorithm for probes positioning in BTT systems
Tchawou Tchuisseu, Eder Batista; Procházka, Pavel; Maturkanič, Dušan
2020 - English
The Blade Tip Timing (BTT), a non-contact method for measuring the blade tip displacement through the time of arrival, is studied in this article. This work proposes a simple algorithm based on the minimization of the coherence and the condition number of the sensingmatrix for defining the best probe positioning in the case of synchronous and asynchronous vibrations. Keywords: BTT systems; probe positioning; condition number; coherence Available at various institutes of the ASCR
A simple algorithm for probes positioning in BTT systems

The Blade Tip Timing (BTT), a non-contact method for measuring the blade tip displacement through the time of arrival, is studied in this article. This work proposes a simple algorithm based on the ...

Tchawou Tchuisseu, Eder Batista; Procházka, Pavel; Maturkanič, Dušan
Ústav termomechaniky, 2020

Creep behaviour of 316L stainless steel prepared by 3D printing
Dymáček, Petr; Kloc, Luboš; Gabriel, Dušan; Masák, Jan; Pagáč, M.; Halama, R.
2020 - English
The 3D printed 316L stainless steel produced by selective laser melting (SLM) was subjected to short term creep testing at 700 °C. Two directions of printing: i) horizontal and ii) vertical, were selected to test the creep performance of the steel. Comparison with the open literature data shows very good short-term creep properties of 3D printed steel that are superior to conventional steel. Both studied directions of printing show similar results so the steel can be considered from creep point of view as isotropic. The solution annealing prior to the creep testing slightly, but not substantially, lowers the creep performance of the steel. Keywords: 3D print; selective laser melting; 316L Stainless steel; creep Available at various institutes of the ASCR
Creep behaviour of 316L stainless steel prepared by 3D printing

The 3D printed 316L stainless steel produced by selective laser melting (SLM) was subjected to short term creep testing at 700 °C. Two directions of printing: i) horizontal and ii) vertical, were ...

Dymáček, Petr; Kloc, Luboš; Gabriel, Dušan; Masák, Jan; Pagáč, M.; Halama, R.
Ústav termomechaniky, 2020

Effect of the controllable bearings lubricated by magnetically sensitive oil on vibration of rigid rotors
Zapoměl, Jaroslav; Ferfecki, P.
2020 - English
Dynamical properties of hydrodynamic bearings depend of the Sommerfeld number. To avoid rupture of the oil film of heavily loaded bearings or inducing self-excited oscillation of rotors operating at high angular velocities the Sommerfeld number should remain in a certain interval that depends of the bearing size and design. The only parameter that can be changed during the rotor running to adapt the Sommerfeld number and thus the bearing performance to the current operating conditions is the dynamical viscosity. This is offered by application of magnetic fluids as lubricants. This paper reports on a new design concept of a controllable hydrodynamic bearings lubricated by composite liquid. The research is focused on investigation of the possibilities of the control process on the load capacity of the bearings and on the rotor vibration amplitude attenuation. Keywords: controllable hydrodynamic bearing; composite magnetic fluids; increase of the load capacity; vibration attenuation; rigid rotors Fulltext is available at external website.
Effect of the controllable bearings lubricated by magnetically sensitive oil on vibration of rigid rotors

Dynamical properties of hydrodynamic bearings depend of the Sommerfeld number. To avoid rupture of the oil film of heavily loaded bearings or inducing self-excited oscillation of rotors operating at ...

Zapoměl, Jaroslav; Ferfecki, P.
Ústav termomechaniky, 2020

Inverse mass matrix for higher-order finite element method in linear free-vibration problems
Kolman, Radek; González, J.G.; Cimrman, Robert; Kopačka, Ján; Cho, S.S.; Park, B.G.
2020 - English
In the paper, we present adirect inverse mass matrix in the higher-orderfinite element method forsolid mechanics. The direct inverse mass matrix is sparse, has the same structure as the consistent mass matrixand preserves the total mass. The core of derivation of the semi-discrete mixed form is based on the Hamilton’s principle of leastaction. The cardinal issue is finding the relationship between discretized velocities and discretized linear momentum. Finally, the simple formula for the direct inversemass matrix is presented as well as thechoice of density-weighted dual shape functions for linear momentum with respect to the displacement shape functionwith achoice of the lumping mass method for obtaining the correct and positive definitive velocity-linear momentum operator. The application of Dirichlet boundaryconditions into the direct inversemass matrix forafloating system is achieved usingthe projection operator. The suggested methodology is tested on a free-vibration problem of heterogeneous bar for different ordersof shape functions. Keywords: higher-order finite element method; direct inverse mass matrix; consistent and lumped massmatrix; free vibration problem; heterogeneous bar Available at various institutes of the ASCR
Inverse mass matrix for higher-order finite element method in linear free-vibration problems

In the paper, we present adirect inverse mass matrix in the higher-orderfinite element method forsolid mechanics. The direct inverse mass matrix is sparse, has the same structure as the ...

Kolman, Radek; González, J.G.; Cimrman, Robert; Kopačka, Ján; Cho, S.S.; Park, B.G.
Ústav termomechaniky, 2020

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