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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 ...
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 ...
Wind tunnel tests for lifetime estimation of bridge and mast cables exposed to vortex induced vibrations
Trush, Arsenii; Pospíšil, Stanislav; Kuznetsov, Sergeii
2019 - English
A significant number of TV and radio broadcasting masts in the Czech Republic was built in the 70-80s of the last century. At the moment is an actual issue is the reconstruction and determination of residual life of these structures. Guyed masts and particularly guy ropes have significant dimensions and comparatively low mass and damping with high flexibility. Therefore, aerodynamic and aeroelastic loads, such as vortex induced vibrations, galloping, wind gusts, etc., are key for them. As a tensile construction elements (guy ropes) for guyed masts the traditional open wire spiral strand cables are used. This type of cable has a characteristic helical surface roughness pattern that can act as vortex suppressor, high fatigue endurance, although somewhat lower corrosion resistance comparing to modern locked coil cables with non-circular shaped wires of outer layer and cables with protective polymer coatings. At the same time, on numerous bridges with the above-mentioned modern cable types the fatigue damage to wires in anchorage zones and destruction of protective coatings was detected. Present paper provides results of wind tunnel testing of three models of helical strake cable in order to evaluate separately impact of lay angle and surface roughness factors and reference smooth cylinder model in flow with grid generated turbulence of different intensities. The reduction of the lock-in range of helical strand cables comparing to reference smooth model was observed whereby the greatest impact was an increase of lay angle.
Keywords:
bridge cable; wind tunnel; vortex shedding
Available at various institutes of the ASCR
Wind tunnel tests for lifetime estimation of bridge and mast cables exposed to vortex induced vibrations
A significant number of TV and radio broadcasting masts in the Czech Republic was built in the 70-80s of the last century. At the moment is an actual issue is the reconstruction and determination of ...
In-situ compression test of artificial bone foams in controlled environment using X-Ray micro-computed tomography
Glinz, J.; Kytýř, Daniel; Fíla, Tomáš; Šleichrt, Jan; Schrempf, A.; Fürst, D.; Kastner, J.; Senck, S.
2019 - English
In this study, we investigated specimens of artificial bone foams, developed by the research group for surgical simulators at the UAS Linz, which are used to mimic the haptic feedback of physiologic and pathologic bone for more realistic surgery training. Specimens with two kinds of mineral filler material as well as different amounts of foaming agent were tested in an environmental in-situ loading stage developed by the ITAM CAS and scanned via X-ray micro-computed tomography. In this in-situ stage, specimens can be immersed in liquid and tested under temperature-controlled conditions. Consequently, a total amount of 12 specimens was subjected to compression loading, half of them immersed in water at 36.5 °C and half in dry condition. Results showed that there is no significant influence of liquid immersion to the compression outcome. However, foams with less amount of foaming agent appeared to have smaller pores resulting in higher compression strength.
Keywords:
x-ray micro-computed tomography; artificial bone foams; in-situ testing
Available at various institutes of the ASCR
In-situ compression test of artificial bone foams in controlled environment using X-Ray micro-computed tomography
In this study, we investigated specimens of artificial bone foams, developed by the research group for surgical simulators at the UAS Linz, which are used to mimic the haptic feedback of physiologic ...
Local stabilization of the quasiperiodic response of the generalized van der Pol oscillator
Fischer, Cyril; Náprstek, Jiří
2019 - English
The generalized van der Pol equation is often used for description of various effects originating in the aero-elasticity of large slender engineering structures. This applies mainly to the quasiperiodic beatings that can be encountered especially in lock-in regimes when the vortex frequency becomes close to the structure eigenfrequency with a small detuning. The current paper presents numerical analysis of influence of the subor superharmonic excitation on the character of the response of a generalized van der Pol oscillator. This way it complements two previous papers of the authors dealing with stability analysis of certain types of the stationary periodic or quasiperiodic response of the system under study.
Keywords:
generalized van der Pol equation; quasiperiodic response; sub- and superharmonic synchronization; beating effect; numerical simulation
Available at various institutes of the ASCR
Local stabilization of the quasiperiodic response of the generalized van der Pol oscillator
The generalized van der Pol equation is often used for description of various effects originating in the aero-elasticity of large slender engineering structures. This applies mainly to the ...
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