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There are linear dynamical systems with Multiple Eigenvectors?
Kozánek, Jan; Zapoměl, Jaroslav
2020 - anglický
The steady-state response of non-damped linear and discrete dynamical systems on harmonic excitation can be expressed as the linear combination of independent eigenvectors. For special damped dynamical systems, there are some case, where the same eigenvector corresponds to the different eigenvalues.
Klíčová slova:
non-damped and damped dynamical systems; classical eigenvalue problem; non-linear eigenvalue problem; eigenvectors
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
There are linear dynamical systems with Multiple Eigenvectors?
The steady-state response of non-damped linear and discrete dynamical systems on harmonic excitation can be expressed as the linear combination of independent eigenvectors. For special damped ...
Dynamic and heat transfer analysis of a container with measuring instruments for space probes
Zolotarev, Igor; Bula, Vítězslav; Šnábl, Pavel; Gabriel, Dušan; Dobiáš, Jiří; Masák, Jan; Snížek, Jan; Souček, Jan
2020 - anglický
Rocket boosters and spacecraft are subject to intense acoustic environments during launch, which induce high levels of vibration in structural elements and equipment. In addition, elastic structural interactions with propulsion systems and flight control systems can produce low-frequency, high-deflection flight instabilities. Natural vibration of the container with measuring equipment were studied by numerical and experimental methods in the laboratory of Institute termomechanics CAS. Heat transfer analysis inside the container was made by FEM with respect to the conditions during start of the rocket and work in space.\n
Klíčová slova:
vibrations; modal analysis; natural frequencies; FEM thermal analysis; finite element model; radiative heat transfer
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Dynamic and heat transfer analysis of a container with measuring instruments for space probes
Rocket boosters and spacecraft are subject to intense acoustic environments during launch, which induce high levels of vibration in structural elements and equipment. In addition, elastic structural ...
The Effect of Angle of Attack on a Blade Cascade with Overlap
Procházka, Pavel P.; Uruba, Václav; Pešek, Luděk
2020 - anglický
This experimental study was carried out to study an aeroelastic coupling in the case of a blade cascade with overlap exposed to tunnel freestream of different angle of attack (AoA). Three of five blades were constructed to allow vertical position changing by the effect of three shakers. Particle Image Velocimetry was used to measure averaged velocity and dynamical parameters of the flow. Mainly, the effect of AoA will be discussed as well as the influence of blade enlargement and Re number. The influence of potential endplates will be indicated.
Klíčová slova:
blade cascade; time-resolved PIV; FFT; leakage
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
The Effect of Angle of Attack on a Blade Cascade with Overlap
This experimental study was carried out to study an aeroelastic coupling in the case of a blade cascade with overlap exposed to tunnel freestream of different angle of attack (AoA). Three of five ...
Creep behaviour of 316L stainless steel prepared by 3D printing
Dymáček, Petr; Kloc, Luboš; Gabriel, Dušan; Masák, Jan; Pagáč, M.; Halama, R.
2020 - anglický
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.
Klíčová slova:
3D print; selective laser melting; 316L Stainless steel; creep
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Optical and Pneumatic Measurement on TR-U-10 Cascade
Luxa, Martin; Šimurda, David
2020 - anglický
The report contains results and evaluation of conducted optical (interferometry and schlierren technique) and pneumatic measurements on the third variant of the new tip section, intended for long rotor blade.
Klíčová slova:
transonic flow; tip section; steam turbine
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Optical and Pneumatic Measurement on TR-U-10 Cascade
The report contains results and evaluation of conducted optical (interferometry and schlierren technique) and pneumatic measurements on the third variant of the new tip section, intended for long ...
Optical and Pneumatic Measurements on TR-U-9A Cascade
Luxa, Martin; Šimurda, David
2020 - anglický
The report contains results and evaluation of conducted optical (interferometry and schlieren technique) and pneumatic measurements on the eroded variant of the new tip section, intended for long rotor blade.
Klíčová slova:
transonic flow; experimental aerodynamic; steam turbine
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Optical and Pneumatic Measurements on TR-U-9A Cascade
The report contains results and evaluation of conducted optical (interferometry and schlieren technique) and pneumatic measurements on the eroded variant of the new tip section, intended for long ...
A hybrid boundary element based aeroelastic model for flexible wing.
Prasad, Chandra Shekhar; Pešek, Luděk
2020 - anglický
The paper describes development of medium delity aeroelastic numerical model for fast aeroelastic analysis of the flexible aeronautical structures e.g. wings, rotor blades etc. The numerical model is developed particularly for the incompressible low subsonic flow regime application. For the flow field modeling boundary element based hybrid panel method flow solver with viscous-inviscid coupling strategy have been successfully developed and implemented here.The unsteady flow field is modeled using hybrid/modi ed panel method where, integral boundary layer theory (vis-cous part), surface panel method (potential flow inviscid part) and vortex particle method (separated shear layer modeling) are coupled together. The proposed model can simulate both attached and separated flow fields. The estimated aerodynamic lift coefficients and the pressure coefficient are compared with experimental results for static and dynamic stall flow conditions. Furthermore, the results from new aeroelastic model will be compared with classical CFD-CSD based aeroelastic models for efficiency and accuracy check. The proposed methodology for the aeroelastic analysis of long exible aeronautical structure will provide researchers and engineers a fast, cost effective and efficient tool for aeroelastic analysis for different design at preliminary design stage where large numbers of design iteration are required within short time frame.
Klíčová slova:
aeroelsticity; panel method; vortex particle method; boundary layer method; reduce order model; flutter
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
A hybrid boundary element based aeroelastic model for flexible wing.
The paper describes development of medium delity aeroelastic numerical model for fast aeroelastic analysis of the flexible aeronautical structures e.g. wings, rotor blades etc. The numerical model is ...
Aeroacoustic simulation of human phonation with the wale sub-grid scale model
Šidlof, Petr; Lasota, M.
2020 - anglický
The paper reports on an aeroacoustic model of voice generation in human larynx, based on Large Eddy Simulation with the Wall-Adapting Local Eddy-Viscosity (WALE) sub-grid scale (SGS) model. The simulation uses a three-step hybrid approach, with an incompressible finite volume CFD computation providing the filtered velocity and pressure, evaluation of the aeroacoustic sources, and simulation of the sound propagation by finite element discretization of the Acoustic Perturbation Equations. The WALE SGS model is used to overcome the limitation of the classical Smagorinski SGS model, which overpredicts the SGS viscosity in regions of high shear, especially within the boundary layer in the glottal constriction. Results of the 3D CFD simulation, location of the aeroacoustic sources and the spectra of the radiated sound for two vowels are presented.
Klíčová slova:
large eddy simulation; turbulence modelling; voice generation; aeroacoustics
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Aeroacoustic simulation of human phonation with the wale sub-grid scale model
The paper reports on an aeroacoustic model of voice generation in human larynx, based on Large Eddy Simulation with the Wall-Adapting Local Eddy-Viscosity (WALE) sub-grid scale (SGS) model. The ...
Analysis of Three-Phase Delta-Connected Converter for Compensation of Unsymmetrical Loads
Bejvl, Martin; Šimek, Petr; Valouch, Viktor; Hauptmann, R.
2020 - anglický
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.
Klíčová slova:
three-phase grid; single-phase load; unbalance compensation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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.
Klíčová slova:
classification; sign language; convolution neural network
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
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