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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 ...
On the problem of singular limit
Caggio, Matteo; Ducomet, B.; Nečasová, Šárka; Tang, T.
2023 - anglický
We consider the problem of singular limit of the compressible Euler system confined to a straight layer Ωδ = (0, δ)×R², δ > 0. In the regime of low Mach number limit and reduction of dimension the convergence to the strong solution of the 2D incompressible Euler system is shown.
Klíčová slova:
compressible Euler equations; dissipative measure-valued solutions; low Mach number; thin domain
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
On the problem of singular limit
We consider the problem of singular limit of the compressible Euler system confined to a straight layer Ωδ = (0, δ)×R², δ > 0. In the regime of low Mach number limit and reduction of dimension the ...
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 ...
Can extended bodies follow geodesic trajectories?
Lukes-Gerakopoulos, Georgios; Mukherjee, Sajal
2023 - anglický
We provide an extension of the analysis on whether an extended test body can follow a geodesic trajectory given by Mukherjee et al. (2022). In particular, we consider a test body in a pole-dipole-quadrupole approximation under the Ohashi-Kyrian-Semer´ak spin supplementary condition moving in the Schwarzschild and Kerr background. Using orbital setups under which a pole-dipole body can follow geodesic motion, we explore under which conditions this can also take place in the pole-dipole-quadrupole approximation when only the mass quadrupole is taken into account. For our analysis, we employ the assumption that the dipole contribution and the quadrupole contribution vanish independentlly.
Klíčová slova:
Mathisson–Papapetrou–Dixon equations; particle dynamics; black holes; chaos
Dokument je dostupný na externích webových stránkách.
Can extended bodies follow geodesic trajectories?
We provide an extension of the analysis on whether an extended test body can follow a geodesic trajectory given by Mukherjee et al. (2022). In particular, we consider a test body in a ...
Underground Spaces In Bosonožský Hájek Nature Reserve And Their Geoeducation Importance
Kirchner, Karel; Kuda, František; Baldík, V.; Kubalíková, Lucie
2023 - anglický
Bosonožský hájek Natural Reserve (Brno, South Moravia) is a very important site from the Earth Science point of view, however, its geodiversity values have been rather overlooked and omitted in the past (the object of legal protection is the occurrence of well-preserved forest ecosystems and endangered species). In the last decades, a series of field work and geophysical measurements has been carried out and the Earth Science phenomena have been identified and described here. These are represented by a dense network of gullies that developed in Pleistocene loess and that are both of natural and anthropogenic origin (some gullies probably developed along the old paths) and specific underground spaces (so called dugouts). Until now, the dugouts in South Moravia have been investigated mainly by archaeologists and those in Bosonožský hájek NR have not been described in detail yet. This brief contribution brings new information about three underground landforms and their possible relationship to the age and development of the gullies. The possibility of different interpretations of the origin of these specific landforms can be considered an opportunity in the field of Earth Science (geosciences) education and as an interesting complement of tourist and recreational activities on site.
Klíčová slova:
gully network; loess; dugouts; Earth Science education
Dokument je dostupný na externích webových stránkách.
Underground Spaces In Bosonožský Hájek Nature Reserve And Their Geoeducation Importance
Bosonožský hájek Natural Reserve (Brno, South Moravia) is a very important site from the Earth Science point of view, however, its geodiversity values have been rather overlooked and omitted in the ...
Identification of quasiperiodic processes in the vicinity of the resonance
Fischer, Cyril; Náprstek, Jiří
2023 - anglický
In nonlinear dynamical systems, strong quasiperiodic beating effects appear due to combination of self-excited and forced vibration. The presence of symmetric or asymmetric beatings indicates an exchange of energy between individual degrees of freedom of the model or by multiple close dominant frequencies. This effect is illustrated by the case of the van der Pol equation in the vicinity of resonance. The approximate analysis of these nonlinear effects uses the harmonic balance method and the multiple scale method.
Klíčová slova:
dynamical systems; quasiperiodic response; van der Pol equation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Identification of quasiperiodic processes in the vicinity of the resonance
In nonlinear dynamical systems, strong quasiperiodic beating effects appear due to combination of self-excited and forced vibration. The presence of symmetric or asymmetric beatings indicates an ...
Laboratory X-ray imaging in material sciences
Koudelka_ml., Petr; Kytýř, Daniel; Jiroušek, O.
2023 - anglický
In recent decades, X-ray imaging and computed (micro)tomography (XCT) in particular have become common tools for volumetric inspection, visualization, and analysis of internal structure in materials from various fields [1]. In this lecture, we will explore various applications of laboratory X-ray imaging chains utilizing the combination of tomographical imaging with mechanical, thermal, or chemical loading of the irradiated sample in a so-called time-resolved imaging allowing for unprecedented insight into different phenomena driving fundamental processes encountered in various fields of material science. We will show that failure processes in engineering or geological materials [2] can be thoroughly studied by synergy of information from radiographical imaging and other methods including acoustic emission detection and optical measurements via high-speed visible-spectrum and thermal-imaging cameras, where the radiography provides important spatial information regarding deformation processes evolving within the tested samples that could not be obtained otherwise. The state-of-the-art the laboratory based imaging chains for investigation of dynamic response of materials under loading will be also discussed including high speed X-ray radiography utilizing a powerful X-ray source during high velocity impact as an approach suitable for inspection of an impacted sample. As an alternative to both conventional high-power sources and accelerator facilities, capabilities of a flash X-ray system developed primarily for in-situ ballistics research providing very short bursts of an extremely powerful intermittent X-ray radiation with a typical duration of dozens of nanoseconds will be shown.
Klíčová slova:
X-ray imaging; material characterization; mechanical properties
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Laboratory X-ray imaging in material sciences
In recent decades, X-ray imaging and computed (micro)tomography (XCT) in particular have become common tools for volumetric inspection, visualization, and analysis of internal structure in materials ...
Interpolation with restrictions -- role of the boundary conditions and individual restrictions
Valášek, Jan; Sváček, P.
2023 - anglický
The contribution deals with the remeshing procedure between two computational finite element meshes. The remeshing represented by the interpolation of an approximate solution onto a new mesh is needed in many applications like e.g. in aeroacoustics, here we are particularly interested in the numerical flow simulation of a gradual channel collapse connected with a~severe deterioration of the computational mesh quality. Since the classical Lagrangian projection from one mesh to another is a dissipative method not respecting conservation laws, a conservative interpolation method introducing constraints is described. The constraints have form of Lagrange multipliers enforcing conservation of desired flow quantities, like e.g. total fluid mass, flow kinetic energy or flow potential energy. Then the interpolation problem turns into an error minimization problem, such that the resulting quantities of proposed interpolation satisfy these physical properties while staying as close as possible to the results of Lagrangian interpolation in the L2 norm. The proposed interpolation scheme does not impose any restrictions on mesh generation process and it has a relatively low computational cost. The implementation details are discussed and test cases are shown.
Klíčová slova:
interpolation; Lagrange multiplier; Lagrange projection
Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Interpolation with restrictions -- role of the boundary conditions and individual restrictions
The contribution deals with the remeshing procedure between two computational finite element meshes. The remeshing represented by the interpolation of an approximate solution onto a new mesh is needed ...
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