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Self-excited oscillations of elastic tubes induced by fluid-structure interactin
Štembera, Vítězslav ; Maršík, František (advisor) ; Okrouhlík, Miloslav (referee) ; Žitný, Rudolf (referee)
1 Introduction The aim of this thesis was to develop a mathematical model that could describe the phe- nomenon of self-excited oscillations of flexible tubes induced by fluid-structure interaction between the tube wall and the inner fluid flow. The term self-excited means that the studied system has no oscillatory inner sources or bound- ary conditions, the harmonic motion originates in the system itself. Let us show some examples for the occurrence of this phenomenon in the human body: Pedley ([?]) mentions that vessel collapse is most readily seen in veins, such as in the veins of a hand raised above the level of the heart or in the jugular vein when a person is standing erect ([?]). In arteries1 , such a collapse can be observed only in some special cases, for example in the case when additional outer pressure is applied to the artery. One example is blood pressure measurement using a sphygmomanometer cuff. During this measurement, the so- called Korotkoff sounds, which are strongly believed to be connected to these self-excited oscillations of the brachial artery wall, appear. These Korotkoff sounds are used by medical doctors for pressure diagnostics and are known from the beginning of the 20th century2 . They disappear when the cuff is removed. Artery collapse is also probable if an artery is filled with...
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Self-excited oscillations of elastic tubes induced by fluid-structure interactin
Štembera, Vítězslav ; Maršík, František (advisor) ; Okrouhlík, Miloslav (referee) ; Žitný, Rudolf (referee)
1 Introduction The aim of this thesis was to develop a mathematical model that could describe the phe- nomenon of self-excited oscillations of flexible tubes induced by fluid-structure interaction between the tube wall and the inner fluid flow. The term self-excited means that the studied system has no oscillatory inner sources or bound- ary conditions, the harmonic motion originates in the system itself. Let us show some examples for the occurrence of this phenomenon in the human body: Pedley ([?]) mentions that vessel collapse is most readily seen in veins, such as in the veins of a hand raised above the level of the heart or in the jugular vein when a person is standing erect ([?]). In arteries1 , such a collapse can be observed only in some special cases, for example in the case when additional outer pressure is applied to the artery. One example is blood pressure measurement using a sphygmomanometer cuff. During this measurement, the so- called Korotkoff sounds, which are strongly believed to be connected to these self-excited oscillations of the brachial artery wall, appear. These Korotkoff sounds are used by medical doctors for pressure diagnostics and are known from the beginning of the 20th century2 . They disappear when the cuff is removed. Artery collapse is also probable if an artery is filled with...
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Dispersion properties of finite element method: review
Kolman, Radek ; Okrouhlík, Miloslav ; Plešek, Jiří ; Gabriel, Dušan
Review of the dispersion properties of plane square bilinear finite element used in plane elastic wave propagation problems is presented. It is assumed the grid (spatial) dispersion analysis and, further, the temporal-spatial dispersion analysis for explicit direct time integration based on the central difference method. In this contribution, the dispersion surfaces, polar diagrams and error dispersion graphs for bilinear finite element are depicted for different Courant numbers in explicit time integration. Finally, recommendation for setting the mesh size and the time step size for the explicit time integration of discretized equations of motion by the bilinear finite element method is provided.
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EUROMECH Colloquium 540 - Advanced Modelling of Wave Propagation in Solids
Kolman, Radek ; Berezovski, A. ; Okrouhlík, Miloslav ; Plešek, Jiří
The Euromech Colloquium 540 - Advanced Modelling of Wave Propagation in Solids took place at the Institute of Thermomechanics in Prague from 1st to 3rd October 2012. It aimed at bringing together engineers and scientists interested in modelling of wave propagation in solids. The Colloquium focused on topics related to effects in linear and non-linear wave propagation in solids. Recent advances in numerical and analytical approaches and strategies were discussed. The main purpose of the Colloquium was to discuss novel methods of wave propagation modelling and to assess the credibility of results especially in cases when experiment validation had not been available.
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Stress wave propagation in the Institute of Thermomechanics
Okrouhlík, Miloslav
The paper is devoted to a survey of old, recent and contemporary stress wave propagation tasks having been studied in the Institute of Thermomechanics (IT) within the period of the last sixty years. Scientific deeds as well as people who deserve admirations for achieving them are mentioned.achieving them are mentioned. Problems and employed analytical and numerical methods are shortly listed.
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SIGA 2011
Kolman, Radek ; Linkeová, I. ; Okrouhlík, Miloslav ; Pařík, Petr
The conference SIGA 2011 aimed to bring together mathematicians, physicists, computer designers and engineers dealing with splines who are using them for the numerical solutions of partial differential equations of various problems in mechanics and physics. In computational mechanics, it is isogeometric analysis (IGA) which is being dynamically developed. This numerical method employs shape functions based on different types of splines (B-splines, NURBS, T-splines and many others), and the fields of unknown quantities are consequently described the same way as the geometry of the studied domain. In addition, this approach provides a higher degree of continuity than that offered by the classical finite element (FE) method based on Lagrangian polynomials. Isogeometric analysis aims to integrate FE ideas in CAD systems without necessity to regenerate mesh. The conference intends to create a forum for further discussion in multidisciplinary scientific areas involving mathematics, computer graphics, geometry, physics, engineering and software engineering, respectively.
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Analysis of classical and spectral finite element spatial discretization in one-dimensional elastic wave propagation
Kolman, Radek ; Plešek, Jiří ; Okrouhlík, Miloslav ; Gabriel, Dušan
The spatial discretization of continuum by finite element method introduces the dispersion error to numerical solutions of stress wave propagation. For higher order finite elements there are the optical modes in the spectrum resulting in spurious oscillations of stress and velocity distributions near the sharp wavefront. Spectral finite elements are of h-type finite element, where nodes have special positions along the elements corresponding to the numerical quadrature schemes, but the displacements along element are approximated by Lagrangian interpolation polynomials. In this paper, the classical and Legendre and Chebyshev spectral finite elements are tested in the one-dimensional wave propagation in an elastic bar.
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