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Random response of a dynamic system under polynomial of a white noise
Náprstek, Jiří; Fischer, Cyril
2020 - English
Many types of external additive random excitation of dynamic systems admit to be modelled as a combination of powers of a Gaussian noise. Such a type of excitation produces a non-Gaussian response even if the dynamic system is linear and the excitation is additive only. Although the excitation as a whole is non-Gaussian, the problem can be transformed into the form of a linear system with an additive and multiplicative white noise excitation which _nally produces a non-Gaussian response. The general method of transformation, the respective FPK equation, basic stochastic moments of the response, and a demonstrative example are discussed.
Keywords:
non-Gaussian excitation; nonlinear filtering; Kronecker algebra
Available at various institutes of the ASCR
Random response of a dynamic system under polynomial of a white noise
Many types of external additive random excitation of dynamic systems admit to be modelled as a combination of powers of a Gaussian noise. Such a type of excitation produces a non-Gaussian response ...
Region of interest tomography
Vopálenský, Michal; Kumpová, Ivana
2020 - English
During standard tomographic process, the acquisition of tomographic data (projections) is performed with geometric adjustment of the tomographic assembly ensuring that the projection of the entire width of the examined object fits onto the detector during the full object rotation. Because of the limited width of the detector, this approach has a limited maximum achievable resolution for the given specimen diameter. It is possible to make higher magnification, but then the projections do not fit onto the detector, which causes certain problems during the reconstruction, but allows achieving of higher resolution in the always-visible region of the object (the region of interest). The research was focused on evaluation of ROI tomography approach on the TORATOM tomograph.
Keywords:
X-ray computed tomography; resolution; Region-of-Interest tomography
Available at various institutes of the ASCR
Region of interest tomography
During standard tomographic process, the acquisition of tomographic data (projections) is performed with geometric adjustment of the tomographic assembly ensuring that the projection of the entire ...
Damage detection using a cogwheel load - numerical case study
Bayer, Jan
2020 - English
A moving impulse load generated by a heavy cogwheel (CW) can be used as a testing excitation for bridges. This proposed type of dynamic load acts along the entire driving path, its intensity is adjustable, and it can be very efficient in the case of resonance. However, higher harmonic components are an inevitable effect of this type of loading, complicating the vibration analysis. The present study investigates suitable procedures to detect and locate damage in structures using a cogwheel load and only one or a few transducers mounted on the bridge. This arrangement seems to be sensitive to early damage indication. Damage localization is also possible, but further research will be required to increase its credibility.
Keywords:
bridge testing; damage detection; impulse loading; vibration analysis; bridge health monitoring
Available at various institutes of the ASCR
Damage detection using a cogwheel load - numerical case study
A moving impulse load generated by a heavy cogwheel (CW) can be used as a testing excitation for bridges. This proposed type of dynamic load acts along the entire driving path, its intensity is ...
Multifold stationary solutions of an auto-parametric non-linear 2DOF system
Fischer, Cyril; Náprstek, Jiří
2020 - English
A non-linear 2DOF model of a bridge girder with a bluff cross-section under wind loading is used to describe the heave and pitch self-excited motion. Existence conditions of stationary auto-parametric response for both the self-excited case and an assumption of a harmonic load form a non-linear algebraic system of equations. Number of distinct solutions to this algebraic system depends on the frequencies of two principal aero-elastic modes and other system parameters. Thus, the system may possess none, one, or several stationary solutions, whose stability has to be checked using the Routh-Hurwitz conditions. If all quantities entering the system are continuous functions, individual solutions may exhibit (piecewise) continuous dependence on selected system parameters. Thus, multiple identified solutions to the system for a given set of parameters may actually belong to a single solution branch and their values can be determined from the knowledge of the solution branch. Such a situation may significantly simplify assessment of stability of the particular solutions and/or provides an applicable overall description of the system response.
Keywords:
multifold solution; algebraic system; aero-elastic system; stationary vibration
Available at various institutes of the ASCR
Multifold stationary solutions of an auto-parametric non-linear 2DOF system
A non-linear 2DOF model of a bridge girder with a bluff cross-section under wind loading is used to describe the heave and pitch self-excited motion. Existence conditions of stationary auto-parametric ...
Distribution of hydration products in the microstructure of cement pastes
Hlobil, Michal
2020 - English
This case study focuses on the quantification of the amorphous hydrate distribution in the microstructure of hardened cement paste. Microtomographic scans of the hardenend cement paste were thresholded based on histogram image analysis combined with microstructural composition obtained from CEMHYD3D hydration model, to separate unhydrated cement grains, crystalline and amorphous hydrates, and capillary pores. The observed spatial distribution of the amorphous hydrate exhibited a strong spatial gradient as the amorphous gel tended to concentrate around dissolving cement grains rather than precipitate uniformly in the available space. A comparative numerical study was carried out to highlight the effect of the spatially (non)uniform hydrate distribution on the compressive strength of the hardened cement paste.
Keywords:
cement paste; hydration products; microstructure; modelling
Available at various institutes of the ASCR
Distribution of hydration products in the microstructure of cement pastes
This case study focuses on the quantification of the amorphous hydrate distribution in the microstructure of hardened cement paste. Microtomographic scans of the hardenend cement paste were ...
A system approach to medieval ruins management
Novotný, Jakub; Bláha, Jiří
2019 - English
The aim of this paper is to briefly discuss the complexity of monument care and the young heritage science disciplines on the example of historical ruins management. There is an empirical reflection on problems connected with historical ruins management presented as an introduction. The following part then presents a possible methodological interconnection of a systems approach and cultural heritage management. The next part of the paper first introduces the RUINS project in general and then one of its methodological outputs—rules and model forms for ruins. Based on practical experience, the paper concludes that the more general methodological basis and foundation of cultural heritage sites management may be general systems theory and a systems approach.
Keywords:
historical ruins; heritage science; systems approach; RUINS project
Fulltext is available at external website.
A system approach to medieval ruins management
The aim of this paper is to briefly discuss the complexity of monument care and the young heritage science disciplines on the example of historical ruins management. There is an empirical reflection ...
Probability density determination by means of Gibbs entropy probability density
Náprstek, Jiří; Fischer, Cyril
2019 - English
A method of random response investigation of a nonlinear dynam-ical system is discussed. In particular, the solution of the probability density of a single/multi-degree of freedom (SDOF/MDOF) system response is investigated. Multiple stable equilibrium states with possible jumps of the snap-through type among them are considered. The system is Hamiltonian with weak damping excited by a set of non-stationary Gaussian white noises. The solution, which is based on the Gibbs principle of the maximum entropy of probability, can be employed in various branches of engineering. The search for the extreme of the Gibbs entropy functional is formulated as a constrained optimization problem. The secondary constraints follow from the Fokker-Planck equation (FPE) for the system considered or from the system of ordinary di_erential equations for the stochastic moments of the response derived from the relevant FPE
Keywords:
Fokker-Planck equation; Gibbs entropy functional; maximum entropy; probability density principle
Available at various institutes of the ASCR
Probability density determination by means of Gibbs entropy probability density
A method of random response investigation of a nonlinear dynam-ical system is discussed. In particular, the solution of the probability density of a single/multi-degree of freedom (SDOF/MDOF) system ...
Moving dynamic test loads for road bridges - a case study
Bayer, Jan; Urushadze, Shota
2019 - English
Two types of dynamic testing load for bridges - driving sprung mass and driving impulse load - areexamined from the drive-by identification point of view. Numerical studies in ANSYS using contact elements and in MATLAB using a modal solution together with coupling force were performed. Equations for the estimation of the impulse load caused by a rolling cogwheel were suggested. The experiments confirmed that a driving impulse load is more efficient in exciting bridge vibrations. This, together with the fact that impulse loading is not sensitive to surface roughness, leads to the conclusion that, as a method for bridge health monitoring, impulse loading is more promising than using a driving sprung mass
Keywords:
drive-by identification; bridge testing; moving sprung mass; impulse loading; vibration measurements; laboratory experiments
Available at various institutes of the ASCR
Moving dynamic test loads for road bridges - a case study
Two types of dynamic testing load for bridges - driving sprung mass and driving impulse load - areexamined from the drive-by identification point of view. Numerical studies in ANSYS using contact ...
System response with random imperfections in coefficients on the space of realizations
Náprstek, Jiří; Fischer, Cyril
2019 - English
The contribution is concerned with the analysis of the simultaneous effect of a random perturbation and a white noise in the coefficient of the system. The excitation of the system of the 1-st order is described by the sum of a deterministic signal and an additive white noise which is partly correlated with the parametric noise. The random perturbation in the parameter is considered as a statistics in a set of realizations. It reveals that the density of probability of perturbations must be limited in the phase space, otherwise the system would lose the stochastic stability in probability. The width of the permissible zone depends heavily on the intensity of the parametric noise, the extent of correlation with the additive excitation noise and the type of probability density. The general explanation is demonstrated on cases of normal, uniform and truncated normal densities of probability.
Keywords:
noisy signal; filtration; random imperfections
Available at various institutes of the ASCR
System response with random imperfections in coefficients on the space of realizations
The contribution is concerned with the analysis of the simultaneous effect of a random perturbation and a white noise in the coefficient of the system. The excitation of the system of the 1-st order ...
Deformation response of polydimethylsiloxane substrates subjected to uniaxial quasi-static loading
Vinařský, V.; Martino, F.; Forte, G.; Šleichrt, Jan; Rada, Václav; Kytýř, Daniel
2019 - English
To investigate cellular response of cardiomyocytes to substrate mechanics, biocompatible material with stiffness in physiological range is needed. PDMS based material is used for construction of microfluidic organ on chip devices for cell culture due to ease of device preparation, bonding, and possibility of surface functionalization. However it has stiffness orders of magnitude out of physiological range. Therefore, we adapted recently available protocol aiming to prepare substrates which offer stiffness in physiological range 5−100 kPa using various mixtures of Sylgard. An in-house developer loading device with single micron position tracking accuracy and sub-micron position sensitivity was adapted for this experimental campaign. All batches of the samples were subjected to uniaxial loading. During quasi-static experiment the samples were compressed to minimally 40% deformation. The results are represented in the form of stress-strain curves calculated from the acquired force and displacement data and elastic moduli are estimated.
Keywords:
quasi-static loading; hyperelasticity; polydimethylsiloxane substrates; in-situ loading device
Available at various institutes of the ASCR
Deformation response of polydimethylsiloxane substrates subjected to uniaxial quasi-static loading
To investigate cellular response of cardiomyocytes to substrate mechanics, biocompatible material with stiffness in physiological range is needed. PDMS based material is used for construction of ...
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