Number of found documents: 564
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Applying a two degree of freedom model for drive-by identification
Bayer, Jan
2024 - English
A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving spring-mass the second DOF. The response of the moving spring-mass is simulated on a bridge model using different road profiles and compared to parameters of the corresponding two DOF system. The focus is the spectral shift that can be observed on the moving spring-mass during its passage along the bridge and could possibly be applied for drive-by identification. The accuracy mainly depends on the relation of the moving spring-mass to the bridge mass and the relation between the natural frequency of the spring-mass and those of the bridge. The simulations showed that road profile can significantly reduce the accuracy of identified results, which imposes limits on practical applications. Keywords: drive-by identification; structural health monitoring; finite element analysis; road roughness; two DOF system Available in digital repository of the ASCR
Applying a two degree of freedom model for drive-by identification

A new concept of drive-by identification is examined applying the analogy with a Two Degree Of Freedom (DOF) system where the bridge is considered the ground-supported spring-mass and the moving ...

Bayer, Jan
Ústav teoretické a aplikované mechaniky, 2024

Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Fischer, Cyril; Náprstek, Jiří
2024 - English
Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type nonlinear model. Determining the response probability density function involves solving the Fokker-Planck equation, which is generally a challenging task. Hence, semi-analytical and numerical methods come into play. This contribution reviews several possible techniques and spotlights the exponential-polynomial-closure method. The shown results are limited, as the paper reflects an early stage of the relevant research direction. Keywords: Fokker-Planck equation; stochastic averaging; numerical solution; Galerkin approximation; van der Pol-type oscillator; partial amplitudes; exponential-polynomial-closure method Available in digital repository of the ASCR
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation

Assessing responses in slender engineering structures facing both deterministic harmonic and stochastic excitation is often based on an approximation by the single-degree-of-freedom van der Pol-type ...

Fischer, Cyril; Náprstek, Jiří
Ústav teoretické a aplikované mechaniky, 2024

Galloping of insulated bundled overhead line simplified analysis
Hračov, Stanislav; Macháček, Michael
2024 - English
Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by polyethylene, and used for low-voltage power lines. The susceptibility to loss of stability is analyzed for cable without and with simulated icing observed on similar real conductors. In the first case, the proneness to galloping was excluded based on the results of CFD simulation and the Den Hartog criterion. In latter case, the possible occurrence of galloping was confirmed. The critical wind velocity for the ice-covered cable was calculated utilizing quasi-steady theory. Finally, the amplitudes of limit cycle oscillation for supercritical wind speeds were estimated based on simplified numerical analysis. Keywords: aerial bundled cable; wind effects; galloping; limit cycle oscillation Available in digital repository of the ASCR
Galloping of insulated bundled overhead line simplified analysis

Our paper provides an analysis of the susceptibility of a particular bundled overhead line to galloping. It presents a case study of an aerial bundled cable, consisting of four conductors insulated by ...

Hračov, Stanislav; Macháček, Michael
Ústav teoretické a aplikované mechaniky, 2024

LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2024 - English
Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The rectangle object was exposed to the airflow having a given velocity at different angles of the wind attack in the wind tunnel with the aim to obtain the curves of the aerodynamic coefficients and Strouhal number depending on the impact angle. The comparative numerical 3D simulations of the wind tunnel testing were performed using COMSOL Multiphysics and OpenFoam both incorporating the Large Eddy Simulation (LES) method. Keywords: rectangle 2:1; wind tunnel; LES simulation; aerodynamic characteristics Available in digital repository of the ASCR
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments

Our contribution is focused on the comparison of the experimental investigations and of the numerical 3D LES simulations of the airflow around sharply edged rectangle with side ratio 2:1. The ...

Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
Ústav teoretické a aplikované mechaniky, 2024

Galloping of insulated bundled overhead line - nonlinear numerical analysis in time domain
Macháček, Michael; Hračov, Stanislav
2024 - English
Our contribution focuses on a 3D numerical nonlinear analysis of galloping in a specific bundled overhead line with ice accretion. We studied the susceptibility to this self-excited oscillation, critical onset wind speeds, and global dynamic response of a very low-tensioned line with simulated icing observed on similar real conductors. Due to the highly nonlinear mechanical behavior of such a flexible cable, we employed the Newmark integration method combined with the iterative Newton-Raphson method. We analyzed two numerical models of the overhead line loaded by the wind: one assuming nonlinearity only in the wind load, while retaining the linearity of the mechanical system itself, and the other representing a fully nonlinear system including geometrical nonlinearity. Our analysis revealed that the determined critical wind speeds for the onset of galloping are in relatively close ranges for both models. However, numerical simulations with the fully nonlinear system indicated significantly lower amplitudes of limit cycle oscillations, especially at higher wind speeds, compared to the linear model of the line. This underscores the necessity of using fully nonlinear models during the design stage of such low-tensioned aerial conductors. Keywords: aerial bundled conductors; wind effects; galloping; limit cycle oscillation Available in digital repository of the ASCR
Galloping of insulated bundled overhead line - nonlinear numerical analysis in time domain

Our contribution focuses on a 3D numerical nonlinear analysis of galloping in a specific bundled overhead line with ice accretion. We studied the susceptibility to this self-excited oscillation, ...

Macháček, Michael; Hračov, Stanislav
Ústav teoretické a aplikované mechaniky, 2024

Stochastic version of the arc-length method
Náprstek, Jiří; Fischer, Cyril
2024 - English
The solution of a nonlinear algebraic system using the incremental method, based on pre-defined loading steps, fails in the vicinity of local extrema as well as around bifurcation points. The solution involved the derivation of the so-called ’Arc-Length’ method. Its essence lies in not incrementing the system parameter or any of the independent variables but rather the length of the response curve. The stochastic variant of this method allows for working with a system where system parameters include random imperfections. This contribution presents a variant that tracks the first two stochastic moments. Even in this simple case, interesting phenomena can be observed, such as the disappearance of the energy barrier against equilibrium jump due to random imperfections in the system. Keywords: random imperfection; stochastic arc-length method; continuation; numerical method Available in digital repository of the ASCR
Stochastic version of the arc-length method

The solution of a nonlinear algebraic system using the incremental method, based on pre-defined loading steps, fails in the vicinity of local extrema as well as around bifurcation points. The solution ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2024

Acoustic emission methods in steel bridge degradation identification and monitoring
Šorm, Filip
2024 - English
Acoustic emission methods proved to be an effective diagnostic tool in many industrial sectors. The potential of this method in the field of steel bridge diagnostics is explored in this article. The goal is to find the most effective use of this method. Keywords: steel bridges; diagnostics; acoustic emission Available in digital repository of the ASCR
Acoustic emission methods in steel bridge degradation identification and monitoring

Acoustic emission methods proved to be an effective diagnostic tool in many industrial sectors. The potential of this method in the field of steel bridge diagnostics is explored in this article. The ...

Šorm, Filip
Ústav teoretické a aplikované mechaniky, 2024

Adaptation of methods for cyclo-stationary processes for noisy structural health data
Fischer, Cyril; Bayer, Jan; Náprstek, Jiří; Urushadze, Shota
2023 - English
In structural health analysis, various techniques, including indirect measurement via monitoring vehicles, often yield data with significant randomness and insufficient frequency separation. Conversely, the desired attributes under scrutiny are periodic in nature. Thus, methodologies designed to identify cyclo-stationary properties within noisy data can be adapted for such scenarios, assuming an adequate length of the recorded data. Keywords: data analysis; cyclo-stationary processes; structural health monitoring Available at various institutes of the ASCR
Adaptation of methods for cyclo-stationary processes for noisy structural health data

In structural health analysis, various techniques, including indirect measurement via monitoring vehicles, often yield data with significant randomness and insufficient frequency separation. ...

Fischer, Cyril; Bayer, Jan; Náprstek, Jiří; Urushadze, Shota
Ústav teoretické a aplikované mechaniky, 2023

Consistency of mathematical and experimental model of the autoparametric system
Fischer, Cyril; Náprstek, Jiří
2023 - English
This paper presents a long-overdue comparison of data obtained from experimental investigation of a spherical vibration absorber with the results of two mathematical models of the motion of a heavy sphere in a spherical surface. It shows that the danger posed by the potentially unstable self-parametric nature of the mathematical system is not too great in the case of realistic configurations, and that the values of the parameters describing the realistic structures remain within intervals corresponding to the stable behaviour of the absorber. Keywords: vibration absorber; rolling sphere; spherical surface; autoparametric system; structural health monitoring Available at various institutes of the ASCR
Consistency of mathematical and experimental model of the autoparametric system

This paper presents a long-overdue comparison of data obtained from experimental investigation of a spherical vibration absorber with the results of two mathematical models of the motion of a heavy ...

Fischer, Cyril; Náprstek, Jiří
Ústav teoretické a aplikované mechaniky, 2023

Stereolithography for manufacturing of advanced porous solids
Drechslerová, V.; Neuhäuserová, M.; Falta, J.; Šleichrt, J.; Kytýř, Daniel
2023 - English
The aim of this paper is focused on benefits of stereolithography (SLA) technology for the fabrication of the lightweight lattice structures with potential for load-bearing function and high absorption of impact energy. SLA is an additive manufacturing technology employing the principle of liquid resins curing moderated by radiation of a wavelength from ultra-violet band where resulting material parameters are tunable by setting of the curing process. The batches of samples manufactured using three different resins were subjected to quasi-static uni-axial tensile and compression tests. Acquired data were processed to derive deformation behaviour expressed as stress-strain diagrams and fundamental material properties. Based on the knowledge obtained from the mechanical tests, the setup of the fabrication parameters, the most suitable resin for manufacturing of the lattice structures and the overall suitability of SLA technology for the fabrication of advanced porous materials, were determined. Keywords: stereolithography; advanced porous materials; quasi-static testing; resin; mechanical characteristics Available at various institutes of the ASCR
Stereolithography for manufacturing of advanced porous solids

The aim of this paper is focused on benefits of stereolithography (SLA) technology for the fabrication of the lightweight lattice structures with potential for load-bearing function and high ...

Drechslerová, V.; Neuhäuserová, M.; Falta, J.; Šleichrt, J.; Kytýř, Daniel
Ústav teoretické a aplikované mechaniky, 2023

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