National Repository of Grey Literature 4 records found  Search took 0.00 seconds. 
Wind tunnel tests for lifetime estimation of bridge and mast cables exposed to vortex induced vibrations
Trush, Arsenii ; Pospíšil, Stanislav ; Kuznetsov, Sergeii
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.
Measurements of dynamic wind pressures on gable roofs – comparison with ČSN EN 1991-1-4
Pospíšil, Stanislav ; Macháček, Michael ; Hračov, Stanislav ; Kuznetsov, Sergeii ; Trush, Arsenii
The contribution is dealing with the wind tunnel measurements of dynamic pressures on the canopy roofs. It compares experimentally determined pressure coefficients Cp with the values in ČSN EN 1991-1-4 and former code ČSN 73 0035 as well. The pressures are expressed by the dynamic values. Thus, the averaged values are presented together with the fluctuating part, which significantly contributes to the overall loading. The measurement is carried out at two roof models, two basic directions, and two turbulence intensities.
Visualization methods of flow in the climatic wind tunnel
Kuznetsov, Sergeii ; Trush, Arsenii ; Král, Radomil ; Pospíšil, Stanislav
Visualization of wind tunnel flow around the test model - one of the most informative and demonstrative techniques used in the study of aerodynamics models. Most fluids, gaseous or liquid, are transparent media, and their motion remains invisible to the human eye during direct observation. The visualisation of complex flows has been played a unique role in the improvement of understanding of fluid dynamic phenomena. Flow visualization has been used to verify existing physical principles and has to led the discovery of numerous flow phenomena. In addition to obtaining qualitative global pictures of the flow, the possibility of acquring quantitative measurements without introducing probes, which invariably disturb the flow. A great variety of such methods is known that enable one to make fluid flows visible.
Stochastic resonance of cylinder induced wind flow
Pospíšil, Stanislav ; Kuznetsov, Sergeii ; Trush, Arsenii ; Král, Radomil
The response of a dynamic nonlinear single degree of freedom system to combination of addtive random Gaussian white noise and external deterministic periodic force applied to the aerodynamic phenomena is studied. It is coming to light that under certain circumstances the jumping between wells of the bistable elastic potential can occur leading to internal hopping. The frequency of this hopping can be for certain combination of input parameters nearly the constant and corresponding to external periodic force frequency. This state leads to high ratio of periodic component amplitude and intensity of the random component of the response proces. As the object was chosen in tubulent flow.

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