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PROBLEM OF IDENTIFICATION OF DETERMINISTIC CHAOS IN THE INTERACTIVE DRIVE SYSTEMS
Kratochvíl, Ctirad ; Švéda, P. ; Houfek, Martin ; Houfek, Lubomír
Chaos and chaos theory is a field of study in mathematics, computer sciences, electronics, physics and also engineering too. In our article will be explored chaotic behaviour and numerical solutions of the models of drive systems with electric DC motors. These solutions are also bounded like equilibrium, periodic and quasiperiodic solution. There is no precise definition for a chaotic solution because it cannot be represented through standard mathematical functions. However, a chaotic solution is aperiodic solution, which is endowed with some special identifiable characteristics, for example attractors, bifurcations or one-and two dimensional maps.
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Computational aeroacoustics of human phonation
Šidlof, Petr ; Zörner, S.
The current paper presents a CFD model of flow past vibrating vocal folds coupled to an acoustic solver, which calculates the sound sources from the flow field in a hybrid approach. The CFD model is based on the numerical solution of 3D Navier-Stokes equations on a time-dependent domain, solved by cell-centered finite volume method. To capture the fine turbulent scales important for the acoustic source calculations, the equations are discretized and solved on large computational meshes up to 3.2M elements. The CFD simulations were run in parallel using domain decomposition method and OpenMPI implementation of the MPI standard. Aeroacoustic simulations are calculated in a separate step by Lighthill’s acoustic analogy, which determines the acoustic sources based on the fluid field. This is done with the research code CFS++ which employs the finite element method (FEM).
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Aeroelastic experiments with the structural properties variation
Chládek, Štěpán ; Zolotarev, Igor ; Uruba, Václav
The paper measurements on a model of the airfoil NACA0012. Usually there is a limit range of the flow velocity in the wind tunnel. The chosen wind tunnel is usually fixed, the only one possibility is to modify the structural properties of the experimental stand. There are presented two kinds of modifications, one is based on the geometry variation, the other one on the added mass approach. Both of them have been verified experimentally.
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3D Micromodels of Porous Structures
Pražák, Josef
Speaking about modeling in technical sciences, we have in mind an analysis of mathematical (computational) or physical analogies of objects to be studied. Physical modeling means a systematic building of physical objects heaving some analogy with the studied physical reality. For the models of porous structures, the notion micromodels has been introduced. The micro- means that the model represents only a small fraction of real porous structure and that some essential schematization of reality is included. The difference between a micromodel and a simple probe of a natural porous material (a small volume of soil, sand, etc.) consist in the fact that some exact geometrical information is ahead. Very often, the real porous space is schematized into a regular graph network. The Lenormand´s micromodels are 2D objects where a random square network has been cut in a sophisticated way into a layer of resin between two layers of plexiglass.
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Holographic interferometry as a tool for visualization of temperature fields in fluids
Dančová, Petra ; Vít, Tomáš ; Lédl, V. ; Trávníček, Zdeněk ; Doleček, R.
Measurement of temperature field in moving fluids is connected with many difficulties. Usage of point temperature measurement methods, such as Constant Current Anemometry (CCA), is limited to frequencies up to 3kHz. This frequency should be the limiting factor for using the CCA in fluid when fast change of temperature occurs. This shortcoming of CCA measurements should be overcome by using of optical methods such as digital holographic interferometry. It is necessary to employ a special holographic setup with double sensitivity instead of the commonly used Mach-Zehnder type of holographic interferometer in order to attain the parameters sufficient for the studied case. This setup is not light efficient like the Mach-Zehnder type but has double sensitivity. The special technique of acquiring and phase averaging of results from holographic interferometry is presented.
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