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Distribution of the external wind pressure coefficients on the surface of the façade of the high‐rise building "KINEUM" determined from the wind tunnel measurements
Hračov, Stanislav; Macháček, Michael
2019 - anglický
The report describes the procedure and results of the measurements of aerodynamic model of the planned high-rise building in Gothenburg in Sweden. The determined wind pressure distribution on individual surfaces of the building for several wind directions are presented in the form of external pressure coefficients. The obtained pressure coefficients are subsequently used by the client for the design of façade elements loaded by the wind.
Klíčová slova:
external pressure coefficient; wind load; high-rise building
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Distribution of the external wind pressure coefficients on the surface of the façade of the high‐rise building "KINEUM" determined from the wind tunnel measurements
The report describes the procedure and results of the measurements of aerodynamic model of the planned high-rise building in Gothenburg in Sweden. The determined wind pressure distribution on ...
Inspection of endangered cultural heritage assets in Iran
Drdácký, Miloš
2019 - anglický
Findings and comments based on visual inspection of damaged historical buildings – cultural heritage monuments - by Professor Miloš Drdácký. lt seems that there is a lack of an advanced documentation and especially diagnostics of condition of historical buildings and monuments. Namely, long term monitoring of defects in their relation to loadings is missing. Further, laboratories and know how for determination of material characteristics has a potential for improvement.
Klíčová slova:
cultural heritage; Iran; visual inspection; ICOMOS ISCARSAH mission
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Inspection of endangered cultural heritage assets in Iran
Findings and comments based on visual inspection of damaged historical buildings – cultural heritage monuments - by Professor Miloš Drdácký. lt seems that there is a lack of an advanced documentation ...
Wind tunnel tests for lifetime estimation of bridge and mast cables exposed to vortex induced vibrations
Trush, Arsenii; Pospíšil, Stanislav; Kuznetsov, Sergeii
2019 - anglický
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.
Klíčová slova:
bridge cable; wind tunnel; vortex shedding
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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.
Klíčová slova:
x-ray micro-computed tomography; artificial bone foams; in-situ testing
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 - anglický
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.
Klíčová slova:
generalized van der Pol equation; quasiperiodic response; sub- and superharmonic synchronization; beating effect; numerical simulation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
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 ...
Rapid research with computer algebra systems
Fischer, Cyril
2019 - anglický
Computer algebra systems (CAS) are gaining popularity not only among young students and scholars but also as a tool for serious work. These highly complicated software systems, which used to just be regarded as toys for computer enthusiasts, have reached maturity. Nowadays such systems are available on a variety of computer platforms, starting from freely-available on-line services up to complex and expensive software packages. The aim of this review paper is to show some selected capabilities of CAS and point out some problems with their usage from the point of view of 25 years of experience.
Klíčová slova:
computer algebra system; methodology; Wolfram Mathematica
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Rapid research with computer algebra systems
Computer algebra systems (CAS) are gaining popularity not only among young students and scholars but also as a tool for serious work. These highly complicated software systems, which used to just be ...
Strategies for computation of Lyapunov exponents estimates from discrete data
Fischer, Cyril; Náprstek, Jiří
2019 - anglický
The Lyapunov exponents (LE) provide a simple numerical measure of the sensitive dependence of the dynamical system on initial conditions. The positive LE in dissipative systems is often regarded as an indicator of the occurrence of deterministic chaos. However, the values of LE can also help to assess stability of particular solution branches of dynamical systems. The contribution brings a short review of two methods for estimation of the largest LE from discrete data series. Two methods are analysed and their freely available Matlab implementations are tested using two sets of discrete data: the sampled series of the Lorenz system and the experimental record of the movement of a heavy ball in a spherical cavity. It appears that the most important factor in LE estimation from discrete data series is quality of the available record.
Klíčová slova:
dynamical system; Lyapunov exponents; stability; data analysis
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Strategies for computation of Lyapunov exponents estimates from discrete data
The Lyapunov exponents (LE) provide a simple numerical measure of the sensitive dependence of the dynamical system on initial conditions. The positive LE in dissipative systems is often regarded as an ...
Sensitivity of the generalized van der Pol equation to sub- or super-harmonic resonance
Fischer, Cyril; Náprstek, Jiří
2019 - anglický
Vortex induced vibrations in aeroelasticity of slender structures are often described using the generalized van der Pol equation. This equation provides a good analytical model which is able to reproduce the complex non-stationary behaviour of the structure. Due to the non-linear character of the underlying physical system, the effect of sub- or super-harmonic synchronization can be encountered. The contribution presents results of a numerical study aimed at detailed identification of sub- or super-harmonic resonance effects in the model. This way it supplements the previous works by the authors.
Klíčová slova:
generalized van der Pol equation; sub-/super-harmonic resonance; stationary response
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Sensitivity of the generalized van der Pol equation to sub- or super-harmonic resonance
Vortex induced vibrations in aeroelasticity of slender structures are often described using the generalized van der Pol equation. This equation provides a good analytical model which is able to ...
Study of aeroelastic interference effect among four cylinders arranged in rectangular configuration
Hračov, Stanislav; Macháček, Michael; Michálek, Petr
2019 - anglický
The paper describes the analysis of the destructive oscillation of a skewed steel rod with the length 21 m. The steel rod is a part of roof supporting bundle (rectangular array) of cylindrical hangers at the airport building; it is therefore exposed to frequent moderate and sometimes strong winds with the low turbulence. The vibration is analyzed from the aeroelastic perspective, i.e. the cause of the oscillation is analyzed as wake-induced vibration because the collapse was observed at the bottom downwind hanger in that array configuration. The normalized distance of hangers in horizontal and vertical directions is equal to 3.15D, and 3.8D, respectively, where D is the diameter of the hanger cross section. Experimental testing of 1:1 scaled sectional model of four-cylinder array in the wind tunnel indicates, that the cause of the high level vibration is most probably the interference galloping. The unstable behavior was detected both for the downwind hanger as a part of rectangular array and for the hanger as a part of a two hangers in a row only. The results indicate the strong influence of the top pair of the hangers on the decrease of the critical wind velocity, which is even below the value of the critical wind velocity obtained for two hangers only. The strong hysteresis effect resulting in the preservation of the high vibration amplitudes even after the decrease of wind speed far below the critical one, was observed.
Klíčová slova:
aeroelastic interference; flow structure interaction
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Study of aeroelastic interference effect among four cylinders arranged in rectangular configuration
The paper describes the analysis of the destructive oscillation of a skewed steel rod with the length 21 m. The steel rod is a part of roof supporting bundle (rectangular array) of cylindrical hangers ...
Book of abstracts. XVIIth Youth symposium on experimental solid mechanics
Kytýř, Daniel; Doktor, Tomáš; Zlámal, Petr
2019 - anglický
The YSESM symposium provides a forum for young researchers and engineers, PhD students and students dealing with subjects of experimental mechanics. The Symposium concentrates on current work in all areas of experimental research and its application in solid and fluid mechanics.
Klíčová slova:
mechanics of solids; fluid mechanic; non-destructive testing (NDT); optical methods; measurements in biomechanics
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Book of abstracts. XVIIth Youth symposium on experimental solid mechanics
The YSESM symposium provides a forum for young researchers and engineers, PhD students and students dealing with subjects of experimental mechanics. The Symposium concentrates on current work in all ...
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