2024-05-25
00:04 |
Segmentation of Hippocampus in MRI Data
Kodym, O.
This project deals with application of graph-based methods in segmentation of low contrast image data, specifically hippocampus in MRI data. Using graph cuts for the segmentation allows the software to utilize high accuracy, robustness and an ability to interact with the user.
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2024-05-25
00:00 |
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2024-05-25
00:00 |
Stochastic version of the arc-length method
Náprstek, Jiří ; Fischer, Cyril
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.
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2024-05-25
00:00 |
Galloping of insulated bundled overhead line - nonlinear numerical analysis in time domain
Macháček, Michael ; Hračov, Stanislav
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.
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2024-05-25
00:00 |
LES simulations of airflow around rectangle with side ratio 2:1 and their comparison with experiments
Ledvinková, Blanka ; Hračov, Stanislav ; Macháček, Michael
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.
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2024-05-25
00:00 |
Galloping of insulated bundled overhead line simplified analysis
Hračov, Stanislav ; Macháček, Michael
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.
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2024-05-25
00:00 |
Solution methods for an aeroelastic problem with combined harmonic and stochastic excitation
Fischer, Cyril ; Náprstek, Jiří
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.
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2024-05-25
00:00 |
Applying a two degree of freedom model for drive-by identification
Bayer, Jan
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.
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2024-05-12
00:03 |
Continuous Welded Rail Track on Tramway Bridges
Křečková, Magdalena
The issues related to the continuous welded rail remain a debated topic, especially in connection with bridge structures. The issues are relevant not only to railway tracks where bridge structures with long expansion lengths are becoming more and more common but also to tramway tracks. This article presents the continuous welded rail theory on tramway bridges, including an example of a structure on which the monitoring of expansion displacements in rail expansion joints has been initiated.
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2024-05-12
00:03 |
Examining the Impact of Demand-Side Management Through Dynamic Simulation: Integrating Smart-Grid-Ready Control of Residential Heat Pumps
Horváth, Miklós ; Takács, Zoltán ; Gergely, László Zsolt
This paper investigates the suitability of air-to-water heat pumps for smart grids, with a particular focus on load shifting. The research uses dynamic building energy simulations to show that the utilisation of these features effectively addresses the energy consumption challenges of heat pumps while ensuring that heating and domestic hot water demands are met. The implemented control system successfully shifts the morning and evening peaks to the daytime period, resulting in a modest 2% increase in total energy demand.
These results not only demonstrate the balancing of heat pump energy consumption, but also provide insights for the development of objective functions. Such functions can play a key role in supporting the smooth integration of renewables into the wider energy framework.
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