 
 
 

Finite element solution of the nonlinear 2DOFs dynamic system under random Gaussian excitation using the FokkerPlanck equation
Král, Radomil ; Náprstek, Jiří
Papers published until now are dealing with single degree of freedom (SDOF) systems. So the respective FP equation includes two independent space variables only (x1, x2). Nevertheless stepping over this limit and entering into a true multidimensionality a number of specific problems must be overcome. While in usual FEM practice the number of space variables is two or three, investigating FP equation, so 2n independent space variables emerges. It means for instance 12 space variables when random motion of a rigid body in space with six degrees of freedom is studied. Many requirements should be respected which are out of a conventional practice of Finite Element employment.

 

Transient heat transfer coefficient on precooled circular cylinder at various reynolds numbers
Král, Radomil ; Beran, Pavel ; Kuznetsov, Sergeii
In this work, the experimental investigation of unsteady averaged heat transport coefficient is carried out. Using precooled concrete circular cylinder being immersed into the air crossflow at constant temperature level, the heat convection for various wind speed ranging from 5 to 15 m/s is determined. The attention is also given to the temperature distribution over the circular crosssection with respect the time evolution. Instantaneous energy lost is evaluated in average together with its distribution over the cylinder. The heat transfer effect expressed by the nondimensional Nusselt numvber is identified and graphically interpreted.


Stability of a Ushaped profile and combination of wind flow velocity 018 m/s
Král, Radomil ; Kuznetsov, Sergeii ; Pospíšil, Stanislav ; Buljac, Andrija
The report presents experimental results regarding the aeroelastic stability of a Ushaped profile withan aspectratio (along wind length B, frontal height H) of B/H = 4.65. In the literature it can be found that a square prism (B/H =1) can perform galloping oscillations. However, this is not the case for a flat rectangular prism (B/H = 10). The aspect ratio of the Ubeam under consideration here lies between these two values. Additionally, the asymetry of the profile possibly introduces interesting effects. In a comprehensive study of B/H = 4 rectangulsr prism, it is shown experimentally that vortexinduced as well as selfexcited onedegree of freedom vibrations are possible. Our investigation aims at understanding the excitation mechanism and estimate critical velocities. Simulations and, more recently wind tunnel experiments are used in our investigations.


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.
