No (383)
Yes (30)
Number of found documents:
413
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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 ...
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 ...
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 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.
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 ...
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 ...
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 ...
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 ...
Shock waves in ducts
Luxa, Martin
2020 - Czech
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. 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.
Keywords:
water hammer; hydrodynamics; shock wave; aerodynamics
Available at various institutes of the ASCR
Shock waves in ducts
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 ...
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 ...
Dependence of signal strangth on the radial distance and different types of magnets
Procházka, Pavel; Voronova, Evgeniya; Maturkanič, Dušan
2020 - English
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.
Keywords:
vibration; diagnostics; sensor; laser; blade; turbine
Available at various institutes of the ASCR
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 ...
Software Implementation of Lowest Level Control for FB-MMC Converter
Kokeš, Petr
2020 - Czech
For FB-MMC converter (Full Bridge Cell, Modular Multilevel Converter), the software implementation of SA-PWM modulation (Sampled Average PWM) and SORT-BAL sorting type balancing of cell voltages have been designed. The report deals with the specifics of realizing control methods using the Beckhoff TwinCAT 3 system. The control structure was divided into explicitly defined function blocks for the Master controller as well as for the distributed EPX Slave units. Data transfer timing between the Master and the Slave units has been designed and the synchronization of EtherCAT link communication has been tested in practice. \n Pro měnič FB-MMC (Full Bridge Cell, Modular Multilevel Converter) byla rozpracována softwarová implementace pro modulaci SA-PWM (Sampled Average PWM) a pro balancování napětí buněk pomocí třídění SORT-BAL. Práce se zabývá specifikou realizace tohoto řízení se systémem Beckhoff TwinCAT 3. Řízení bylo rozděleno do jasně definovaných funkčních bloků pro hlavní počítač (Master) a pro distribuované jednotky EPX (Slave). Bylo navrženo časování přenosu dat mezi Master a Slave a byla prakticky testována synchronizace komunikace v síti EtherCat.
Keywords:
modular multilevel converter; full bridge cell; sampled average modulation; TwinCat
Available at various institutes of the ASCR
Software Implementation of Lowest Level Control for FB-MMC Converter
For FB-MMC converter (Full Bridge Cell, Modular Multilevel Converter), the software implementation of SA-PWM modulation (Sampled Average PWM) and SORT-BAL sorting type balancing of cell voltages have ...
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