No (7623)
Yes (1652)
Number of found documents:
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Self-balancing of vertical disc rotors supported by contactless bearings
Zapoměl, Jaroslav; Kozánek, Jan; Košina, Jan
2023 - English
Article discusses the self-balancing of the vertical disc rotors supported by contactless bearings on principle of diamagnetic levitation. There are three possibilities of contactless supports: permanent magnet levitation with the help of bismuth, graphite and pyrolitic graphite.
Keywords:
self balancing; vertical disc rotors; contactless bearings
Available at various institutes of the ASCR
Self-balancing of vertical disc rotors supported by contactless bearings
Article discusses the self-balancing of the vertical disc rotors supported by contactless bearings on principle of diamagnetic levitation. There are three possibilities of contactless supports: ...
Dynamics of a cantilever beam with piezoelectric sensor: Finite element modeling
Cimrman, Robert; Kolman, Radek; Musil, Ladislav; Kotek, Vojtěch; Kylar, Jaromír
2023 - English
An elastodynamical model of a cantilever beam coupled with a piezoelectric sensor is introduced and its discretization using the finite element method is presented. The mathematical model includes additional terms that enforce the floating potential boundary condition for keeping a constant charge on an electrode of the sensor. The behaviour of the model is illustrated using a numerical example corresponding to an experimental setup, where vibrations of the beam and the potential on the sensor are measured.
Keywords:
finite element method; piezo-electricity; floating potential; dynamic simulation
Fulltext is available at external website.
Dynamics of a cantilever beam with piezoelectric sensor: Finite element modeling
An elastodynamical model of a cantilever beam coupled with a piezoelectric sensor is introduced and its discretization using the finite element method is presented. The mathematical model includes ...
Topical Problems of Fluid Mechanics 2023
Šimurda, David; Bodnár, T.
2023 - English
Proceedings contain collection of papers presented during the conference Topical Problems of Fluid Mechanics 2023. Majority of papers is concerned with numerical simulations covering wide range of applications in fluid mechanics.\n
Keywords:
experimental fluid mechanics; mathematical modelling; CFD; turbulence; stratified fluid; multiphase flow; vortex structures; supersonic flow
Available at various institutes of the ASCR
Topical Problems of Fluid Mechanics 2023
Proceedings contain collection of papers presented during the conference Topical Problems of Fluid Mechanics 2023. Majority of papers is concerned with numerical simulations covering wide range of ...
Effect of the long-term storage methods on the stability of cartilage biomechanical parameters
Žaloudková, Blanka; Sekorová, Š.; Kopecká, B.; Kytýř, Daniel
2023 - English
Long-term stability of the tissue product in terms of mechanical parameters is a key factor for its expiration date. For the investigation of storage effects on the cartilage tissues the experimental mechanical loading test combined with XCT scanning for the irregular shape inspection was performed. The samples were preserved according to three different protocols using the deep-freezing and two types of saline solution preservation. The stability of the biomechanical parameters was tested within annual intervals. All samples were subjected to uni-axial compression loading using the in-house developed compact table top loading device in displacement-driven mode. Based on the measurements, the results are represented in the form of stress-strain curves and quantified as elastic modulus and ultimate compression stress. It can be concluded that no significant difference was found in neither the mechanical properties of the samples nor in the effects of each preservational method.
Keywords:
stability study; cartilage; biomechanical characterisation; compression loading; XCT imaging
Available at various institutes of the ASCR
Effect of the long-term storage methods on the stability of cartilage biomechanical parameters
Long-term stability of the tissue product in terms of mechanical parameters is a key factor for its expiration date. For the investigation of storage effects on the cartilage tissues the experimental ...
Damage detection study for a pedestrian cable-stayed bridge using ANSYS
Bayer, Jan; Kawulok, Marek; Urushadze, Shota
2023 - English
In connection to development of new testing techniques for bridges at ITAM, a theoretical damage detection case study was performed for a cable stayed bridge over the Vltava River at Lužec. The results recognise the most susceptible loading modes which should be identified exactly during the in-situ measurements.
Keywords:
cable stayed bridges; structural health monitoring; ANSYS
Available at various institutes of the ASCR
Damage detection study for a pedestrian cable-stayed bridge using ANSYS
In connection to development of new testing techniques for bridges at ITAM, a theoretical damage detection case study was performed for a cable stayed bridge over the Vltava River at Lužec. The ...
Technological challenges in the fabrication of MoS.sub.2./sub./diamond heterostructures
Varga, Marián; Sojková, M.; Hrdá, J.; Hutar, P.; Parsa Saeb, S.; Vanko, G.; Pribusova Slusna, L.; Ondič, Lukáš; Fait, Jan; Kromka, Alexander; Hulman, M.
2023 - English
Nowadays, 2D materials are one of the most studied classes of materials. In addition to the most famous graphene, progress has been achieved in studying and using fundamental properties of transition metal dichalcogenides (TMD). Complementary, diamond as a representative of 3D materials has gained a reputation as an extremely versatile material due to its extraordinary combination of physical/chemical/electrical/optical properties. Besides these particular forms of 2D and 3D materials, their heterostructures have become very attractive due to new phenomena and functions (bandgap engineering, enhanced charge transport, optical interaction, etc.). However, individual technological procedures are still minimally investigated and described. Here, we will demonstrate a proof-of-concept for the preparation of MoS2/diamond heterostructures, where two different strategies were employed: a) growth of MoS2 layers on diamond films, and b) growth of diamond films on Si/MoS2 substrates.
Keywords:
transition metal dichalcogenides; molybdenum disulfide; diamond; heterostructures
Available at various institutes of the ASCR
Technological challenges in the fabrication of MoS.sub.2./sub./diamond heterostructures
Nowadays, 2D materials are one of the most studied classes of materials. In addition to the most famous graphene, progress has been achieved in studying and using fundamental properties of transition ...
Good vs. Bad Volatility in Major Cryptocurrencies: The Dichotomy and Drivers of Connectedness
Šíla, Jan; Kočenda, Evžen; Kukačka, Jiří; Krištoufek, Ladislav
2023 - English
Cryptocurrencies exhibit unique statistical and dynamic properties compared to those of traditional financial assets, making the study of their volatility crucial for portfolio managers and traders. We investigate the volatility connectedness dynamics of a representative set of eight major crypto assets. Methodologically, we decompose the measured volatility into positive and negative components and employ the time-varying parameters vector autoregression (TVP-VAR) framework to show distinct dynamics associated with market booms and downturns. The results suggest that crypto connectedness reflects important events and exhibits more variable and cyclical dynamics than those of traditional financial markets. Periods of extremely high or low connectedness are clearly linked to specific events in the crypto market and macroeconomic or monetary history. Furthermore, existing asymmetry from good and bad volatility indicates that information about market downturns spills over substantially faster than news about comparable market surges. Overall, the connectedness dynamics are predominantly driven by fundamental crypto factors, while the asymmetry measure also depends on macro factors such as the VIX index and the expected inflation.
Keywords:
Volatility; Dynamic connectedness; Asymmetric effects; Cryptocurrency
Fulltext is available at external website.
Good vs. Bad Volatility in Major Cryptocurrencies: The Dichotomy and Drivers of Connectedness
Cryptocurrencies exhibit unique statistical and dynamic properties compared to those of traditional financial assets, making the study of their volatility crucial for portfolio managers and traders. ...
Direct construction of reciprocal mass matrix and higher order fininite element method
Cimrman, Robert; Kolman, Radek; González, J. A.; Park, K. C.
2023 - English
When solving dynamical problems of computational mechanics, such as contact-impact problems or cases involving complex structures under fast loading conditions, explicit time-stepping algorithms are usually preferred over implicit ones. The explicit schemes are normally combined with the lumped (diagonal) mass matrix so that the calculations are efficient and moreover dispersion errors in wave propagation are partially eliminated. As an alternative to lumping with advantageous properties, the reciprocal mass matrix is an inverse mass matrix that has the same sparsity structure as the original consistent mass matrix, preserves the total mass, captures well the desired frequency spectrum and leads thus to efficient and accurate calculations. In the contribution we comment on the usability of the reciprocal mass matrix in connection with higher order FEM.
Keywords:
higher-order finite element method; reciprocal mass matrix; transient problems; explicit time integration; lumping process
Fulltext is available at external website.
Direct construction of reciprocal mass matrix and higher order fininite element method
When solving dynamical problems of computational mechanics, such as contact-impact problems or cases involving complex structures under fast loading conditions, explicit time-stepping algorithms are ...
Reduced basis solver for stochastic Galerkin formulation of Darcy flow with uncertain material parameters
Béreš, Michal
2023 - English
In this contribution, we present a solution to the stochastic Galerkin (SG) matrix equations coming from the Darcy flow problem with uncertain material coefficients in the separable form. The SG system of equations is kept in the compressed tensor form and its solution is a very challenging task. Here, we present the reduced basis (RB) method as a solver which looks for a low-rank representation of the solution. The construction of the RB consists of iterative expanding of the basis using Monte Carlo sampling. We discuss the setting of the sampling procedure and an efficient solution of multiple similar systems emerging during the sampling procedure using deflation. We conclude with a demonstration of the use of SG solution for forward uncertainty quantification.
Keywords:
stochastic Galerkin method; reduced basis method; Monte Carlo method; deflated conjugate gradient method
Fulltext is available at external website.
Reduced basis solver for stochastic Galerkin formulation of Darcy flow with uncertain material parameters
In this contribution, we present a solution to the stochastic Galerkin (SG) matrix equations coming from the Darcy flow problem with uncertain material coefficients in the separable form. The SG ...
Numerical realization of the Bayesian inversion accelerated using surrogate models
Bérešová, Simona
2023 - English
The Bayesian inversion is a natural approach to the solution of inverse problems based on uncertain observed data. The result of such an inverse problem is the posterior distribution of unknown parameters. This paper deals with the numerical realization of the Bayesian inversion focusing on problems governed by computationally expensive forward models such as numerical solutions of partial differential equations. Samples from the posterior distribution are generated using the Markov chain Monte Carlo (MCMC) methods accelerated with surrogate models. A surrogate model is understood as an approximation of the forward model which should be computationally much cheaper. The target distribution is not fully replaced by its approximation. Therefore, samples from the exact posterior distribution are provided. In addition, non-intrusive surrogate models can be updated during the sampling process resulting in an adaptive MCMC method. The use of the surrogate models significantly reduces the number of evaluations of the forward model needed for a reliable description of the posterior distribution. Described sampling procedures are implemented in the form of a Python package.
Keywords:
Bayesian inversion; delayed-acceptance Metropolis-Hastings; Markov chain Monte Carlo; surrogate model
Fulltext is available at external website.
Numerical realization of the Bayesian inversion accelerated using surrogate models
The Bayesian inversion is a natural approach to the solution of inverse problems based on uncertain observed data. The result of such an inverse problem is the posterior distribution of unknown ...
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