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Analysis of Three-Phase Delta-Connected Converter for Compensation of Unsymmetrical Loads
Bejvl, Martin; Šimek, Petr; Valouch, Viktor; Hauptmann, R.
2020 - English
The paper presents possibilities of compensation of general single-phase load connected to the three-phase grid. The compensation is to ensure a symmetrical and pure active load of the three-phase grid. It is documented that after the proposed compensation it is possible to draw symmetrical and pure active current from all phases. A set of multi-level voltage converters is considered as a compensation device. The paper presents a way of determining the reference currents for the converter in its two branches and proposes a method of controlling the converter so that the active power from the grid is equal to the active load of the load. This methodology is documented by the results of a series of simulations for static and dynamic modes of the system.
Keywords:
three-phase grid; single-phase load; unbalance compensation
Available at various institutes of the ASCR
Analysis of Three-Phase Delta-Connected Converter for Compensation of Unsymmetrical Loads
The paper presents possibilities of compensation of general single-phase load connected to the three-phase grid. The compensation is to ensure a symmetrical and pure active load of the three-phase ...
Classification of Czech sign language alphabet letters using cnn – preliminary study
Krejsa, Jiří; Věchet, Stanislav
2020 - English
Abstract: The paper deals with the classification of Czech sign language single hand alphabet letters from static images using convolutional neural network (CNN). Proposed CNN architecture exhibits about 71% successful rate of classifying the letters signed by the person not included in the training data set.
Keywords:
classification; sign language; convolution neural network
Available at various institutes of the ASCR
Classification of Czech sign language alphabet letters using cnn – preliminary study
Abstract: The paper deals with the classification of Czech sign language single hand alphabet letters from static images using convolutional neural network (CNN). Proposed CNN architecture exhibits ...
Human vocal tract models with yielding walls – preliminary experimental results
Radolf, Vojtěch; Horáček, Jaromír; Košina, Jan
2020 - English
Yielding walls of acoustic cavities cause an additional low frequency acoustical – mechanical resonance of the system. This resonance changes also the higher acoustic resonance frequencies. Experimental model of human vocal tract cavities with hard walls has been modified to take into account the compliance of the soft tissue of human vocal tract. The unique experimental set-up has been assembled to study in detail 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.
Keywords:
biomechanics of voice; vocal tract acoustics; acoustic-structural interaction
Available at various institutes of the ASCR
Human vocal tract models with yielding walls – preliminary experimental results
Yielding walls of acoustic cavities cause an additional low frequency acoustical – mechanical resonance of the system. This resonance changes also the higher acoustic resonance frequencies. ...
Modelling and simulation of self-balanced vertical rigid rotors
Zapoměl, Jaroslav; Kozánek, Jan; Košina, Jan; Cibulka, Jan
2020 - English
Unbalance of rotors of rotating machines is mostly caused by the manufacturing and assembling inaccuracies. In some cases it can be induced by the rotor operation or can be variable during the rotor running. In these cases the classical approach based on attaching the balancing weights to the rotor surface is not efficient. The technological solution is offered by application of a self-balancing device. This paper deals with its design, modelling, and investigation of its functionality in dependence of the rotor operation parameters.
Keywords:
vertical rotors; unbalance; self-balancing device
Available at various institutes of the ASCR
Modelling and simulation of self-balanced vertical rigid rotors
Unbalance of rotors of rotating machines is mostly caused by the manufacturing and assembling inaccuracies. In some cases it can be induced by the rotor operation or can be variable during the rotor ...
Simple model for investigation of aerodynamic coupling in linear blade cascades
Chládek, Štěpán; Pešek, Luděk; Procházka, Pavel P.
2020 - English
Simple viscous-elastic model has been proposed for investigation of aerodynamic coupling in linear blade cascades. One blade is connected with both adjacent blades using idealized springs and dampers which represent viscous fluid. All blades may oscillate with one degree of freedom represented by vertical translation. Energy method using travelling waves model was utilized for aerodynamic damping coefficient derivation. The proposed model does not compute the damping values quantitatively, nevertheless it provides the damping shape analysis. Interesting results are presented within zero and low subsonic flow velocities, where the experiment included velocity flow field measurement.
Keywords:
linear cascade stability; aerodynamic damping; PIV
Available at various institutes of the ASCR
Simple model for investigation of aerodynamic coupling in linear blade cascades
Simple viscous-elastic model has been proposed for investigation of aerodynamic coupling in linear blade cascades. One blade is connected with both adjacent blades using idealized springs and dampers ...
Influencing of the Pile-Up and the Sink-In by the Coefficient of Friction in the Nanoindentation Test
Kovář, J.; Fuis, Vladimír; Čtvrtlík, Radim
2020 - English
The influence of the coefficient of friction between an indenter and a specimen on the height of the pile-up or depth of the sink-in during the nanoindentation test is discussed in this paper. When the indenter is pressed into the hard material, the sink-in behavior causes the bending of the specimen’s surface under the indenter. When the indenter is pressed into the soft material, the deformed material accumulates under the sides of the indenter and makes a pile-up region. The pile-up or sink-in behavior influences the contact area. In this paper, the finite element method was used for calculation of the dependency between the depth of the sink-in or height of the pile-up and the coefficient of friction. The results showed that while there is not any dependency between the friction and the depth of the sink-in, there is a strong dependency between the friction and the height of the pile-up until a specific value of the coefficient of friction. When the pile-up behavior occurs, the friction influences the contact area and should be included into the calculation of the contact area.
Keywords:
nanoindentation; pile-up; sink-in; coefficient of friction; FEM
Available at various institutes of the ASCR
Influencing of the Pile-Up and the Sink-In by the Coefficient of Friction in the Nanoindentation Test
The influence of the coefficient of friction between an indenter and a specimen on the height of the pile-up or depth of the sink-in during the nanoindentation test is discussed in this paper. When ...
Analysis of measurement of temperature dependence inside rubber sample under dynamic harmonic load
Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Šnábl, Pavel; Cibulka, Jan; Košina, Jan
2020 - English
This work deals with the preparation and methodology of temperature measurement inside a rubber sample. In this paper, a rubber sample with temperature sensors is described and a description with a temperature measurement scheme under torsional dynamic stress with the possibility of measurement in a temperature chamber is proposed. Large torsional deformations are considered for harmonic torsional loads. The reason for these measurements is to determine the temperature dependence and sensitivity of the heat output parameters.
Keywords:
heat flow; temperature; Fourier equation; heat conduction
Available at various institutes of the ASCR
Analysis of measurement of temperature dependence inside rubber sample under dynamic harmonic load
This work deals with the preparation and methodology of temperature measurement inside a rubber sample. In this paper, a rubber sample with temperature sensors is described and a description with a ...
Applicability of the deterministic methods in blade tip-timing analyses
Maturkanič, Dušan; Procházka, Pavel; Hodboď, Robert; Tchawou Tchuisseu, Eder Batista
2020 - English
The paper describes the possible use of the deterministic methods for analyses of blade vibration. In this respect, the main attention is focused on turbine rotor speed instabilities which could cause inaccuracy of results. The initial method and approach were presented in previous works. The measurements were performed in the Laboratory of the rotational laser vibrometry in the Institute of Thermomechanics, Academy of Sciences of the Czech Republic.
Keywords:
turbine rotor blade vibration; rotating speed instability; vibration diagnostics; blade tip-timing
Available at various institutes of the ASCR
Applicability of the deterministic methods in blade tip-timing analyses
The paper describes the possible use of the deterministic methods for analyses of blade vibration. In this respect, the main attention is focused on turbine rotor speed instabilities which could cause ...
Experimentální vyšetřování vhodné poréznosti protiprašné stěny
Nosek, Štěpán
2019 - Czech
Článek seznamuje čtenáře se základními principy fyzikálního modelování atmosférické mezní vrstvy ve větrných tunelech a jejich aplikací na řešení prašnosti. Je uveden praktický příklad použití těchto metod v rámci řešení šíření prašnosti z pásových dopravníků do bezprostředního okolí protiprašnou stěnou. The paper introduces the reader to the basic principles of physical modelling of the atmospheric boundary layer in wind tunnels and their application to the solution of dustiness. A practical example elucidates the use of these methods in the solution of dustiness from conveying belts to immediate surroundings.
Keywords:
atmospheric boundary layer; physical modelling; porosity; dustiness; wind tunnel
Available at various institutes of the ASCR
Experimentální vyšetřování vhodné poréznosti protiprašné stěny
Článek seznamuje čtenáře se základními principy fyzikálního modelování atmosférické mezní vrstvy ve větrných tunelech a jejich aplikací na řešení prašnosti. Je uveden praktický příklad použití těchto ...
Vyšetřování proudění uvnitř přirozeně větraného kravína: předběžné výsledky z experimentů v aerodynamickém tunelu
Nosek, Štěpán; Kluková, Zuzana; Kellnerová, Radka; Jakubcová, Michala; Jaňour, Zbyněk
2019 - Czech
V této studii byly kvalitativně porovnány střední vektorové (složky podélné a vertikální rychlosti) a skalární pole (intenzita turbulence) v měřítkovém (1:50) modelu přirozeně větraného kravína. Tato kvalitativní srovnání jasně poukazují na účinek simulované mezní vrstvy atmosféry (MVA) a konfiguraci otvorů na proudové charakteristiky uvnitř kravína. MVA mírně drsného terénu vytváří vyšší rychlosti jak u vstupních a výstupních otvorů, tak uvnitř kravina, než MVA velmi drsného terénu. Intenzita turbulence je však více závislá na konfiguraci otvoru. Například, ačkoli MVA byla velmi drsná, a tedy turbulentnější, byly v případě středních otvorů pozorovány nižší intenzity turbulence než u středně drsné MVA. The mean vector (longitudinal and vertical velocity components) and scalar (turbulence intensity) fields within a scale (1:50) model of naturally ventilated cattle barn were qualitatively compared in this study. These qualitative comparisons clearly show the effect of the simulated atmospheric boundary layer (ABL) and the opening configuration on the flow characteristics within the barn. ABL of moderately rough terrain produces higher velocities at both the inlet and the outlet openings and inside the barn than that ABL of very rough terrain. However, the intensity of the turbulence is more dependent on the configuration of the opening. For instance, although ABL was very rough and therefore more turbulent, lower turbulence intensities were observed for that ABL than for the moderately rough ABL in the case of middle openings.
Keywords:
atmospheric boundary layer; livestock building; natural ventilation; wind-tunnel
Available at various institutes of the ASCR
Vyšetřování proudění uvnitř přirozeně větraného kravína: předběžné výsledky z experimentů v aerodynamickém tunelu
V této studii byly kvalitativně porovnány střední vektorové (složky podélné a vertikální rychlosti) a skalární pole (intenzita turbulence) v měřítkovém (1:50) modelu přirozeně větraného kravína. Tato ...
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