Počet nalezených dokumentů: 3051
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Laminar-Turbulent Transition in View of Flow Separation from Isothermal and Heated Cylinder
Pech, Jan
2020 - anglický
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. Klíčová slova: transition to turbulence; heated flow; cylinder flow; separation angle; Navier-Stokes- Fourier; spectral/hp element method Dokument je dostupný na externích webových stránkách.
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 - anglický
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. Klíčová slova: BTT systems; probe positioning; condition number; coherence Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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

Rázy v potrubí
Luxa, Martin
2020 - český
Zpráva se zabývá problematikou rázových vln potrubí, které vznikají při jeho náhlém uzavření. Jsou popsány tři možné teoretické přístupy k řešení a jsou uvedena i řešení praktických úloh. The report deals with shock waves in ducts, which originate as a consequence of sudden closing of quick acting valve. Three methods of solving are described. Selected actual problems of czech power plants are solved. Klíčová slova: water hammer; hydrodynamics; shock wave; aerodynamics Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Rázy v potrubí

Zpráva se zabývá problematikou rázových vln potrubí, které vznikají při jeho náhlém uzavření. Jsou popsány tři možné teoretické přístupy k řešení a jsou uvedena i řešení praktických úloh....

Luxa, Martin
Ústav termomechaniky, 2020

Contribution to HPC FEM calculations of bladed disk dynamics with dry-friction contacts
Pešek, Luděk; Šnábl, Pavel; Bula, Vítězslav
2020 - anglický
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 tie-bosses 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. Klíčová slova: bladed wheel; dry-friction contacts; damping; tie-boss couplings Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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. Klíčová slova: heat flow; temperature; Fourier equation Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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 Klíčová slova: power control; B4 converter; unbalanced grid Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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. Klíčová slova: biomechanics of voice; vocal tract acoustics; acoustic-structural interaction. Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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

On the 3D Dynamics of the Wake Behind a Circular Cylinder
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2020 - anglický
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. Klíčová slova: circular cylinder; wake; 3D structure; POD Dokument je dostupný na externích webových stránkách.
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

Dependence of signal strangth on the radial distance and different types of magnets
Procházka, Pavel; Voronova, Evgeniya; Maturkanič, Dušan
2020 - anglický
The paper describes dependence of signal strength on the radial distance between the sensor and the measured object and dependence of signal strength on the different types of magnets. The measurements were performed in the laboratory of the rotational laser vibrometry originated at the Institute of Thermomechanics AS CR, v.v.i. Klíčová slova: vibration; diagnostics; sensor; laser; blade; turbine Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Dependence of signal strangth on the radial distance and different types of magnets

The paper describes dependence of signal strength on the radial distance between the sensor and the measured object and dependence of signal strength on the different types of magnets. The ...

Procházka, Pavel; Voronova, Evgeniya; Maturkanič, Dušan
Ústav termomechaniky, 2020

POD-DEIM-based model order reduction for four-way coupled fluid-solid flows
Isoz, Martin; Šourek, M.
2020 - anglický
Proper orthogonal decomposition (POD) and discrete empirical interpolation method (DEIM) have become established tools for model order reduction in simulations of fluid flows. However, including moving solid bodies in the computational domain poses additional issues with respect to the fluid-solid coupling and to the solution of the movement of the solids. Still, it seems that if the hybrid ctitious domain-immersed boundary method is used to include the solids in the flow domain, POD-DEIM based approaches may be extended for four-way coupled particleladen flows. The present work focuses on the construction of POD-DEIM based reduced order models for the aforementioned flows. Klíčová slova: CFD; POD; DEIM; HFDIB-DEM; OpenFOAM Dokument je dostupný na externích webových stránkách.
POD-DEIM-based model order reduction for four-way coupled fluid-solid flows

Proper orthogonal decomposition (POD) and discrete empirical interpolation method (DEIM) have become established tools for model order reduction in simulations of fluid flows. However, including ...

Isoz, Martin; Šourek, M.
Ústav termomechaniky, 2020

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