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1
Vibration characteristic of the femoral bone
Vosynek P., Navrat T., Houfek L.
Modelling and Optimization of Physical Systems
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2012
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z. 11
31--34
EN
The mechanical properties of the bone tissue are still important theme in many fields of the science. We can remind the problem of bone loss of astronauts in space, or osteoporosis, or quality of the bone remodelling after some trauma. So therefore the contribution deals with the different experimental method based on the vibrations, which could be useful for the investigation of the global mechanical properties of the bone tissue and the bone itself.
CS
Článek uvádí v souvislosti potřebu řešení biomechanických problémů v lidské společnosti. Konkrétně je zaměřena na oblast vibračnich charakteristik kostní tkáně, které mohou být nápomocny při určování její kvality v návaznosti na osteoporózu, připadně výsledek remodelačního procesu po traumatu. V článku jsou uvedeny dva přístupy k stanovení vibračních charakteristik. Pomocí rázového kladívka a budiče kmitů. Dále je vyšetřován vliv předzatižení a přenos vibrací přes závitové vložky, případně vruty.
2
Comparison of experimentally identified modal properties of components using experimental modal analysis and acoustic holography
Houfek L., Klapka M.
Modelling and Optimization of Physical Systems
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2012
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z. 11
19--22
EN
This paper is a comparison of experimental investigation of modal properties of two different methods - experimental modal analysis and acoustic holography (SoNAH method). Comparison is made for a simple system. Good agreement between both methods has been found.
3
Computational simulation of rod cutting process
Petruska J, Hulka J, Houfek L
Modelling and Optimization of Physical Systems
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2009
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z. 8
91--96
EN
The paper deals with computational Simulation of rod cutting process and its experimental verifícation. Two ductile fracture criteria - Strain Limit and the Johnson-Cook criterion - are applied to cutting of cylindrical rods. The criteria are used in explicit FEM codes to simulation of fast processes. Numerical analysis of the problem was realized by the ABAQUS-Explicit FEM package and the experimental verifícation was realized in semi industrial conditions by our industrial partner, the company J-VST Brno.
4
Chaos in drive system
Houfek L., Kratochvil C, Krejsa J., Navrat Τ.
Modelling and Optimization of Physical Systems
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2009
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z. 8
55--58
EN
The paper is focused on analysis of dynamic properties of drive systems. It deseribes the possible ways of stability analysis and possible ways of analysis of bifurcation of steady states and possible oceurrence of chaotic behavior.
5
Comparative analysis of SOCON CS screws in treatment of osteoporotic vertebral fractures
Navrat T, Cernohousova I, Florian Z, Kocis J, Houfek L
Modelling and Optimization of Physical Systems
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2008
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z. 7
75--78
EN
The article focuses on the effect of transpedicular cemented and non-cemented screws applied in osteoporotic vertebrae and on the stability of connection between the bone and screw when subjected to extraction test. Cemented and non-cemented screws were inserted in experimental vertebral samples and extracted using a standard testing device. The obtained results prove that the extraction force in cemented screws is significantly higher than in non-cemented screws (t-test, p-value = 0.007).
CS
Příspěvek se zabývá posouzením transpedikulárních cementovaných a necementovaných šroubů aplikovaných do kadaverózního osteoporotického obratle; pevnost spojení kost - šroub jsme hodnotili při vytrhávací zkoušce. Do zkušebních vzorků obratlů byly aplikovány cementované a necementované šrouby a na zkušebním stroji vytrženy. Naměřené výsledky potvrzují, že vytrhávací síla je pro cementované šrouby statisticky významně vyšší než pro necementované (t-test, p-value = 0,007).
6
Bifurcation diagram for drive system
Houfek L., Kratochvil C., Krejsa J., Navrat T
Modelling and Optimization of Physical Systems
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2008
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z. 7
43--46
EN
The paper is focused on analysis of dynamic properties of drive systems. It describes the possible ways of stability analysis and possible ways of analysis of bifurcation of steady states and possible occurrence of chaotic behavior.
7
Bifurcation and chaos in electromechanical drive systems with small motors
Kratochvil C., Houfek L., Houfek M., Krejsa J.
Modelling and Optimization of Physical Systems
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2008
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z. 7
55--58
EN
The purpose of this article is to provide an elementary introduction to the subject of chaos in the electromechanical drive systems. In this article, we explore chaotic solutions of maps and continuous time systems. These solutions are also bounded like equilibrium, periodic and quasiperiodic solutions.
8
Chaotic behavior description in technical systems
Houfek L., Kratochvil C., Krejsa J., Houfek M., Navrat Τ.
Modelling and Optimization of Physical Systems
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2007
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z. 6
77--80
EN
Chaotic behavior of technical systems is lately under great interest of researchers. The paper describes a possibility to analyze system which exhibits chaotic oscillations. For simplicity the model of Duffing oscillator was selected as analyzed case, as the chaotic oscillations occur in this model. Bifurcation diagram and phase plane analysis are used as analysis tool.
9
Singular cases of parallel and serial mechanism
Houfek L., Brezina L., Krejsa J.
Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska
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2006
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z. 31
59-62
EN
The paper describes the methodology for calculation of singular cases in mechanisms. The singular cases have been defined as those positions in the working space, where the system loses the univocal solution. The solution of two mechanisms - serial and parallel - is presented.
10
Identification of shock absorber nonlinear model characteristics
Krejsa J., Houfek L.
Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska
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2006
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z. 31
99-102
EN
The paper shows the possible way of identification of shock absorber nonlinear model characteristics using genetic algorithm. 2 DOF quarter car model is used with nonlinear characteristics of main spring and damping forces defined as piecewise functions. Using time courses of position, velocity and acceleration of both masses under kinematic excitation the characteristics are found. Simulation results are satisfactory.
11
Bifurcation and chaos in drive systems
Kratochvil C., Houfek L., Houfek M., Krejsa J.
Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska
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2006
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z. 31
89-94
EN
The paper is focused on analysis of dynamic properties of controlled drive systems. It describes the possible ways of stability analysis. Paper is also focused on bifurcation of steady states and possible oceurence of chaotic behavior.
12
Using of the long squeeze film dampers in rotor systems
Hlavon P., Houfek L.
Zeszyty Naukowe Katedry Mechaniki Stosowanej / Politechnika Śląska
|
2003
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nr 21
79-84
EN
The present paper focuses on the issues of rotor systems with hydrodynamic dampers known as sąueeze film dampers (SFD), which are non-linear hydraulic binding elements between the rotor and stator. The hydrodynamic dampers, with maximum discharged layer, have recently been applied more and more often thanks to their favourable characteristics, mainly in the rotor systems of aircraft engines. In principal, the dampers decrease amplitude of the actuated oscillations, primarily when crossing the critical speed. They tend to shift the amplitude-frequency characteristic of the whole system to lower values due to the supplementary material of oil film, preventing thus the transmission of vibrations on to the machine frame and, in fact, reducing noisiness of the whole equipment.
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