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Souvislost mezi principem nejmenší akce a termodynamickou podmínkou stability
Maršík, František; Trávníček, Zdeněk; Antošová, Zuzana
2023 - anglický
The extended principle is formulated for a material point (M.P.) X, which has nonzero mass, temperature, and trajectory x(X,t). The Lagrangian of this variation principle is equal to the kinetic energy from which, the internal energy of the material point (which depends on the entropy) and the additional energy caused by the frictional force are subtracted. The relation between the inertial force and the entropy gradient is found and the gravitational force is completely replaced by the entropy gradient. Thanks to the mentioned properties of the total enthalpy, the Thermodynamic criterion of stability of the state of M.P., is formulated.
Klíčová slova:
principle of the least action; thermodynamic stability condition; annular swirl flow
Dokument je dostupný na externích webových stránkách.
Souvislost mezi principem nejmenší akce a termodynamickou podmínkou stability
The extended principle is formulated for a material point (M.P.) X, which has nonzero mass, temperature, and trajectory x(X,t). The Lagrangian of this variation principle is equal to the kinetic ...
Statistical Approach for BTT probes distribution
Mekhalfia, Mohammed Lamine; Procházka, Pavel; Šmíd, R.; Tchawou Tchuisseu, Eder Batista
2023 - anglický
Blade tip timing (BTT) system is a non-invasive method used for measuring the blade tip timing of rotating machinery. The BTT system typically consists of sensor probes, signal conditioning system, and data acquisition unit. The sensor probes are placed in proximity to the rotating blade tips, Sensors measure the time at which each blade passes by the probe. By measuring the blade tip timing, the BTT system can detect changes in the blade tip vibration, which is an important for the health monitoring and performance optimization of rotating machinery [1]. To ensure accurate measurement of blade tip timing, the probe arrangement is crucial. The placement of the probe relative to the blade tips can affect the measurement accuracy, and thus, several arrangement algorithms have been developed to optimize the placement of the probes. Instead of considering the condition number, a statistical algorithms is followed to optimize the placement of probes for accurate measurement of blade tip timing in turbo-machinery. The statistical approach will be employed to determine the optimal locations for probes, with the aim of reducing errors in the measurement of blade tip timing. \n
Klíčová slova:
blade tip timing principle; RMSE; blade´s dynamics
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Statistical Approach for BTT probes distribution
Blade tip timing (BTT) system is a non-invasive method used for measuring the blade tip timing of rotating machinery. The BTT system typically consists of sensor probes, signal conditioning system, ...
Střední úroveň řízení měniče FB-MMC s topologií Delta
Kokeš, Petr
2023 - český
Regulace modulárního vícehladinového měniče (Modular Multilevel Converter, MMC) je technicky podstatně komplikovanější, než měniče klasického, a to nejen kvůli velkému počtu jednotlivých buněk. Na rozdíl od klasického měniče se zde musíme zabývat další úrovní řízení, která představuje balancování napětí mezi větvemi měniče a řízení kruhových proudů uvnitř měniče. Ve zprávě je analyzována vhodná metoda a navržena regulační struktura pro balancování napětí mezi všemi třemi větvemi MMC v zapojení do trojúhelníku (Delta) s buňkami typu úplného můstku (Full H-bridge, FB). Následně byla ověřována činnost tohoto balancování pomocí počítačových simulací a praktických zkoušek na dvou fyzikálních modelech MMC pro sítě 400V a 6kV s implementovanou funkcí aktivního filtru. Control of a modular multilevel converter (MMC) is technically far more complicated than control of a standard 2-level converter. It is not only because of a great number of series-connected cells. For a MMC converter we need to cope with another control level (mentioned here as the middle-level control), which means balancing of voltages among MMC branches and the control of currents circulating inside this converter. For the Delta connected MMC with full H–bridge (FH) cells a convenient method for voltage balancing among all three MMC branches has been analysed and the appropriate control structure has been designed. Then the functionality of this balancing method has been verified using computer simulations and also tested with two MMC physical models operating as active power filters on 400V and 6kV grids.
Klíčová slova:
Modular Multilevel Converter (MMC); voltage balancing; control; Delta connection
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Střední úroveň řízení měniče FB-MMC s topologií Delta
Regulace modulárního vícehladinového měniče (Modular Multilevel Converter, MMC) je technicky podstatně komplikovanější, než měniče klasického, a to nejen kvůli velkému počtu jednotlivých buněk. Na ...
The design of Bayesian diagnostic expert system Querix and it’s engineering application
Věchet, Stanislav; Krejsa, Jiří; Chen, K.-S.
2023 - anglický
Expert systems have gained attention over the last two decades as they bring the possibility of using expert knowledge in various control systems. However, it has lost attraction in favor of artificial neural networks in recent years, which is mostly influenced by the availability of data to train neural network models and the availability of various frameworks to achieve fast time-to-market applications for given solutions.
Klíčová slova:
expert system; decision making; advanced diagnostic; autonomous navigation; RPA
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
The design of Bayesian diagnostic expert system Querix and it’s engineering application
Expert systems have gained attention over the last two decades as they bring the possibility of using expert knowledge in various control systems. However, it has lost attraction in favor of ...
A short study on self-balancing of vertical rotors mounted in passive contactless bearings
Zapoměl, Jaroslav; Kozánek, Jan
2023 - anglický
Energy losses and wear of the support elements of high-speed rotors can be reduced by mounting the rotors in stable passive contactless bearings, the operation of which is based on magnetic levitation. The goal of the conducted research was to investigate applicability of selfbalancing device added to vertical rotors supported by bearings showing low stiffness and damping, which is a specific property of passive magnetic bearings. This paper deals with applicability and efficiency of self-balancing devices added to vertical rotors supported by bearings having very low stiffness and damping, which corresponds to the properties of magnetic frictionless bearings.
Klíčová slova:
self-balancing of rotors; passive contactless bearings; the influence of external damping
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
A short study on self-balancing of vertical rotors mounted in passive contactless bearings
Energy losses and wear of the support elements of high-speed rotors can be reduced by mounting the rotors in stable passive contactless bearings, the operation of which is based on magnetic ...
Dynamic tensile experiments of hard rubber on instron test machine under finite deformations
Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Šnábl, Pavel
2023 - anglický
This paper deals with the first experimental tests of hard rubbers under tensile harmonic loading on the axial-torsional servohydraulic Instron 8852 test machine. The objective of these experiments on cylindrical rubber specimens on this machine is to obtain stress-strain curves of rubber specimens, first considering uniaxial finite longitudinal strains for a single load cycle. Next, the hysteresis loops and their skeleton curves are compared for two selected strain measures as a function of their conjugate stress. It is shown how to obtain the dependence between elongation in the axial direction and constriction in the radial direction, which is used to determine the Cauchy stress in this configuration.
Klíčová slova:
uniaxial harmonic loading; finite deformation; second Piola-Kirchhoff stress; hysteresis loop; Green-Lagrange strain tensor
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Dynamic tensile experiments of hard rubber on instron test machine under finite deformations
This paper deals with the first experimental tests of hard rubbers under tensile harmonic loading on the axial-torsional servohydraulic Instron 8852 test machine. The objective of these experiments on ...
Deep learning methods for the acoustic emission methods to evaluate an onset of plastic straining
Parma, Slavomír; Kovanda, Martin; Chlada, Milan; Štefan, Jan; Kober, Jan; Feigenbaum, H. P.; Plešek, Jiří
2023 - anglický
Development of phenomenological plasticity models, hardening rules, and plasticity theories relies on experimental data of plastic straining. The experimental data are usually measured as the stress–strain response of the material being loaded and do not provide any clues or information about the local response of\nmaterial. In this paper, we analyze the plastic deformation of the material using the acoustic emission method and current state-of-the-art neural network models such as the InceptionTime architecture.
Klíčová slova:
metal plasticity; strain hardening; acoustic emission; neural networks
Dokument je dostupný na externích webových stránkách.
Deep learning methods for the acoustic emission methods to evaluate an onset of plastic straining
Development of phenomenological plasticity models, hardening rules, and plasticity theories relies on experimental data of plastic straining. The experimental data are usually measured as the ...
Model order reduction for particle-laden flows: systems with rotations and discrete transport operators
Kovárnová, A.; Isoz, Martin
2023 - anglický
In the present work, we concentrate on particle-laden flows as an example of industry-relevant transport-dominated systems. Our previously-developed framework for data-driven model order reduction (MOR) of such systems, the shifted proper orthogonal decomposition with interpolation via artificial neural networks, is further extended by improving the handling of general transport operators. First, even with intrusive MOR approaches, the underlying numerical solvers can provide only discrete realizations of transports linked to the movement of individual particles in the system. On the other hand, our MOR methodology requires continuous transport operators. Thus, the original framework was extended by the possibility to reconstruct continuous approximations of known discrete transports via another artificial neural network. Second, the treatment of rotation-comprising transports was significantly improved.
Klíčová slova:
model order reduction; shifted POD; artificial neural networks; CFD-DEM; Open- FOAM
Dokument je dostupný na externích webových stránkách.
Model order reduction for particle-laden flows: systems with rotations and discrete transport operators
In the present work, we concentrate on particle-laden flows as an example of industry-relevant transport-dominated systems. Our previously-developed framework for data-driven model order reduction ...
Aerodynamic Measurements on Subsonic Compressor Blade Cascades KR-D-7 and KR-D-8
Šimurda, David; Hála, Jindřich; Luxa, Martin; Radnic, Tomáš
2023 - anglický
This report contains results and evaluation of aerodynamic measurements conducted on two variant subsonic compressor blade cascades with MCA profile (KR-D-7) and DCA profile (KR-D-8) at transonic flow regimes.
Klíčová slova:
compressor blade cascade; experiment; transonic flow; subsonic flow; MCA profile; DCA profile
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Aerodynamic Measurements on Subsonic Compressor Blade Cascades KR-D-7 and KR-D-8
This report contains results and evaluation of aerodynamic measurements conducted on two variant subsonic compressor blade cascades with MCA profile (KR-D-7) and DCA profile (KR-D-8) at transonic flow ...
Aerodynamic Measurements on Transonic Compressor Blade Cascades KR-D-9 and KR-D-10
Šimurda, David; Hála, Jindřich; Luxa, Martin
2023 - anglický
This report contains results and evaluation of aerodynamic measurements conducted on two variant transonic compressor blade cascades with MCA profile (KR-D-10) and DCA profile (KR-D-9) at transonic flow regimes.
Klíčová slova:
compressor blade cascade; experiment; transonic flow; MCA profile; DCA profile
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Aerodynamic Measurements on Transonic Compressor Blade Cascades KR-D-9 and KR-D-10
This report contains results and evaluation of aerodynamic measurements conducted on two variant transonic compressor blade cascades with MCA profile (KR-D-10) and DCA profile (KR-D-9) at transonic ...
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