Number of found documents: 973
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Conductive open-cell silicone foam for modulatable damping and impact sensing applications
Preuer, R.; Šleichrt, Jan; Kytýř, Daniel; Graz, I.
2023 - English
Nature has long served as a source of inspiration for the development of new materials, with foam-like structures in fruits such as oranges and pamelos serving as examples of efficient energy dissipation. In this study, we present the synthesis and characterization of a conductive silicone foam for potential impact sensing applications. By blending Sylgard 184 and Carbon Black, we create a highly porous structure capable of dissipating energy and modulating its resistance. To investigate the properties of the foam, we utilized both micro-computer tomography (μCT) and scanning electron microscopy (SEM) imaging techniques. The μCT imaging revealed the intricate pore network of the foam, reminiscent of the complex structure found in natural sponges. SEM imaging allowed for observation of the uniform distribution of Carbon Black particles within the foam, enabling the conductive properties of the foam. The foam’s mechanical behavior was characterized by a compression test under μCT imaging to measure the deformation behavior and changes in the foam’s resistance. Additionally, a ball drop test was conducted to investigate the foam’s damping behavior while simultaneously measuring the impact location by the local change in resistance. Remarkably, our results demonstrate the exceptional damping capabilities of the conductive silicone foam, with the damping ratio modulated by adjusting the degree of compression-induced deformation. This is attributed to the collapse of the foam’s porous structure, resulting in a significant increase in the foam’s contact area. Overall, our study provides valuable insights into the behavior of conductive silicone foams and their potential as an impact sensing material. The use of both CT and SEM imaging techniques allows for a comprehensive understanding of the foam’s properties, which can be optimized for a variety of applications. The foam’s ability to modulate its damping properties by adjusting the degree of deformation provides a promising avenue for future research in the field of materials science and engineering. Keywords: silicone foam; conductive properties; deformation behaviour; damping Available at various institutes of the ASCR
Conductive open-cell silicone foam for modulatable damping and impact sensing applications

Nature has long served as a source of inspiration for the development of new materials, with foam-like structures in fruits such as oranges and pamelos serving as examples of efficient energy ...

Preuer, R.; Šleichrt, Jan; Kytýř, Daniel; Graz, I.
Ústav teoretické a aplikované mechaniky, 2023

Innovative device for the simulation of environmental conditions and testing of building materials
Cacciotti, Riccardo; Wolf, Benjamin; Macháček, Michael; Frankl, Jiří
2022 - English
Excessive humidity influences the performance of building envelopes and the safety of their occupants. Moisture related problems can indeed impose significant health risks for buildings’ users and even lead, under extreme scenarios, to structural failures. This paper investigates an innovative experimental setup for evaluating the influence of changing environmental conditions on the performance of building materials. It stems out from a broader ongoing research aimed at studying the trends of mould growth on wooden building components. The presented results include the design, construction and numerical validation of a small-scale climatic wind tunnel (2m x 1.8m ca.) to be used for the simulation of natural ventilation and daily humidity and temperature fluctuations. Key findings include the final design of a low cost, modular construction which allows gathering reliable data on the response of building materials exposed to changing boundary conditions, intended for improving current mould growth models. Future work is also suggested. Keywords: building envelope; moisture; building material; wind tunnel; performance Available in digital repository of the ASCR
Innovative device for the simulation of environmental conditions and testing of building materials

Excessive humidity influences the performance of building envelopes and the safety of their occupants. Moisture related problems can indeed impose significant health risks for buildings’ users and ...

Cacciotti, Riccardo; Wolf, Benjamin; Macháček, Michael; Frankl, Jiří
Ústav teoretické a aplikované mechaniky, 2022

Application of first integrals in the construction of the Lyapunov function for the random response stability testing
Náprstek, Jiří; Fischer, Cyril
2022 - English
The paper deals with a possibility of using the properties of first integrals for the construction of Lyapunov function for the analysis of a dynamic system stability in the stochastic domain. It points out certain characteristics of first integrals resulting in the necessity to introduce additional constraints to assure the principal properties of the Lyapunov function. A number of these constraints has their physical interpretation with reference to system stability. The advantage of this method constructing the Lyapunov function consists in the fact that the Lyapunov function itself contains information on the examined system and, consequently, it is not merely a positive definite function without any relation to the actual case concerned. The presented theory finds application in many dynamical systems. The procedure is illustrated by a nonlinear SDOF example. Keywords: stochastic stability; Lyapunov function; first integrals; cyclic coordinates Available in digital repository of the ASCR
Application of first integrals in the construction of the Lyapunov function for the random response stability testing

The paper deals with a possibility of using the properties of first integrals for the construction of Lyapunov function for the analysis of a dynamic system stability in the stochastic domain. It ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2022

Determination of aerodynamic coefficients for air flow around U-profiles with different flange porosities
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2022 - English
Our contribution presents the comparison of the experimental investigations and of the numerical 2D simulations of the air flow around U –profiles having different flange porosities. The U-shaped beams were exposed to the air flow having a given velocity at different angles of the wind attack for obtaining the curves of the aerodynamic coefficients depending on the impact angle. The numerical simulations of the wind tunnel testing were performed using the Unsteady Reynolds Averaged Navier-Stokes (RANS) method, k-ω SST turbulence model was assumed. Keywords: U-shaped beams; porosity; wind tunnel; RANS simulation; k-ω SST model Available in digital repository of the ASCR
Determination of aerodynamic coefficients for air flow around U-profiles with different flange porosities

Our contribution presents the comparison of the experimental investigations and of the numerical 2D simulations of the air flow around U –profiles having different flange porosities. The U-shaped ...

Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
Ústav teoretické a aplikované mechaniky, 2022

Theoretical analysis of selected trajectories inscribed by a ball freely rolling in a spherical cavity
Náprstek, Jiří; Fischer, Cyril
2022 - English
Indirect monitoring of structures is significantly complicated when an artificial vibration absorber has to be taken into account. Knowledge of the absorber’s behaviour is necessary in order to correctly distinguish the response types obtained during an drive-by measurement. In this work, the mathematical model of the ball-type vibration absorber is used, which is based on the Lagrangian formalism. Three first integrals are identified when no external excitation nor damping is assumed. The paper illustrates the power of this approach, which enables a detailed analysis of free movement of the ball in the spherical cavity. Properties of several particular trajectories depending on initial conditions are presented. Keywords: slender structure; vibration absorber; first integral; rolling sphere; structural health monitoring Available in digital repository of the ASCR
Theoretical analysis of selected trajectories inscribed by a ball freely rolling in a spherical cavity

Indirect monitoring of structures is significantly complicated when an artificial vibration absorber has to be taken into account. Knowledge of the absorber’s behaviour is necessary in order to ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2022

Long term optical monitoring technique of displacement fields based on ArUco markers
Kunecký, Jiří
2022 - English
In structural engineering it is often needed to measure tiny displacements of parts of the structure extremely precisely. For such a purpose it is often needed to use some type of sensor attached to the surface of the structure. This paper presents a new technique which simply uses computer vision libraries to measure displacement of markers originally developed for robotics. Such analysis can be under specific circumstances (2D planar movement) valid if we compare two images taken at different times with the same camera. Main advantage of this method is simplicity of use and low cost of markers, which can be printed in a standard office laser printer. The resolution (error) can be for standard cameras around 0.1 pixel. The method is especially developed for research of timber frames/joints behavior in real structures, because displacements of joints in creep or under load can reach an amplitude which is perfectly detectable by this method. Keywords: displacement measurement; long-term monitoring; ArUco markers Available at various institutes of the ASCR
Long term optical monitoring technique of displacement fields based on ArUco markers

In structural engineering it is often needed to measure tiny displacements of parts of the structure extremely precisely. For such a purpose it is often needed to use some type of sensor attached to ...

Kunecký, Jiří
Ústav teoretické a aplikované mechaniky, 2022

Analysis of van der Pol equation on slow time scale for combined random and harmonic excitation
Náprstek, Jiří; Fischer, Cyril
2022 - English
Vortex shedding represents one of the most important processes that constantly attract the attention of experimental and theoretical research. A number of non-linear effects arise from the fluid-structure interaction. The non-stationary response in the vicinity of the lock-in region has a quasi-periodic character, beating frequency of which varies considerably with the distance from the lock-in frequency. This property is significantly affected by the assumption of combined random and harmonic excitation. This paper describes several details that contribute to the probabilistic characteristics of the system on a time-slow scale using partial response amplitudes. Keywords: SDOF oscillator; slow-time system; Fokker-Planck equation Available at various institutes of the ASCR
Analysis of van der Pol equation on slow time scale for combined random and harmonic excitation

Vortex shedding represents one of the most important processes that constantly attract the attention of experimental and theoretical research. A number of non-linear effects arise from the ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2022

Construction of the Lyapunov function reflecting the physical properties of the model
Náprstek, Jiří; Fischer, Cyril
2022 - English
Practical experience shows that the random excitation component can affect the system response and its dynamic stability not only negatively but also positively. Such mechanisms are usually developed heuristically and are often not sufficiently justified theoretically. The paper presents a possibility of using the properties of first integrals for the construction of a Lyapunov function for the analysis of a dynamic system stability in the stochastic domain. In such case, the Lyapunov function itself contains information on the examined system and, consequently, it is able to provide a more detailed insight into the system stability properties. The procedure is illustrated by a nonlinear SDOF example. Keywords: Lyapunov function; stability; spherical pendulum Available at various institutes of the ASCR
Construction of the Lyapunov function reflecting the physical properties of the model

Practical experience shows that the random excitation component can affect the system response and its dynamic stability not only negatively but also positively. Such mechanisms are usually developed ...

Náprstek, Jiří; Fischer, Cyril
Ústav teoretické a aplikované mechaniky, 2022

Zřícenina středověkého hradu a moderní technologie pro bezpečnou správu
Novotný, Jakub
2022 - Czech
Tématem příspěvku je vztah torzální architektury a moderních technologií. Nejprve je stručně představen dokument Report assessing innovative restoration techniques, technologies and materials used in conservation, který poskytuje přehled nejpoužívanějších technik, technologií a materiálů pro průzkumu a ochranu tohoto typu památek. Dále příspěvek přibližuje průběh a výsledky projektu regionální spolupráce Technologický výzkum zříceniny hradu Štamberk v širším kontextu regionu s důrazem na použití moderních technologií. The topic of the paper is the relationship between torsional architecture and modern technologies. First, the Report assessing innovative restoration techniques, technologies and materials used in conservation is briefly presented, which provides an overview of the most used techniques, technologies and materials for the exploration and protection of this type of monuments. Furthermore, the paper provides an overview of the progress and results of the regional cooperation project Technological research of the Štamberk castle ruins in the wider context of the region with an emphasis on the use of modern technologies. Keywords: ruin; modern technologies; Štamberk Castle; conservation Available at various institutes of the ASCR
Zřícenina středověkého hradu a moderní technologie pro bezpečnou správu

Tématem příspěvku je vztah torzální architektury a moderních technologií. Nejprve je stručně představen dokument Report assessing innovative restoration techniques, technologies and materials used in ...

Novotný, Jakub
Ústav teoretické a aplikované mechaniky, 2022

Analytical model of joint loaded perpendicular to wooden grain
Hataj, M.; Pošta, J.; Hasníková, Hana; Kunecký, Jiří
2022 - English
Computing models for structural behaviour and determination of traditional timber butt joints using analytical relations are presented in this paper. A component method is the base of the computing technique introduced herein. This method is usually used for steel joint design. The component method is based on dividing a joint into individual components. These are defined by partial joint component stiffness. An analytical solution includes a subsidence effect of wooden material close to compressive loading. Analytical computation results are compared with the experimental outputs. A design procedure according to Eurocode 5 for a load capacity determination of perpendicularly loaded structural elements is stated in the paper. Keywords: analytical models; load capacity; butt joint; carpentry; timber structures Available at various institutes of the ASCR
Analytical model of joint loaded perpendicular to wooden grain

Computing models for structural behaviour and determination of traditional timber butt joints using analytical relations are presented in this paper. A component method is the base of the computing ...

Hataj, M.; Pošta, J.; Hasníková, Hana; Kunecký, Jiří
Ústav teoretické a aplikované mechaniky, 2022

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