Volume 4, number 1 (2010)
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Item Numerical solution of gas exhaustion from a reciprocating engine(University of West Bohemia, 2010) Žaloudek, Milan; Fořt, Jaroslav; Deconinck, H.This paper presents the numerical simulations of a flow around an exhaust valve, inside the cylinder of a fourstroke combustion engine. The different flow models have been tested. Besides, the impact of the dimensionality and geometry detailness has been studied. Fixed (i.e. non-moving) geometry and steady boundary conditions have been assumed for all simulations. All the results presented have been obtained by a newly developed CFD package, based on finite volume method (FVM) with an AUSM-family numerical scheme.
Item Finite element modeling of airflow during phonation(University of West Bohemia, 2010) Šidlof, Petr; Lunéville, Eric; Chambeyron, Colin; Doaré, Olivier; Chaigne, Antoine; Horáček, JaromírIn the paper a mathematical model of airflow in human vocal folds is presented. The geometry of the glottal channel is based on measurements of excised human larynges. The airflow is modeled by nonstationary incompressible Navier-Stokes equations in a 2D computational domain, which is deformed in time due to vocal fold vibration. The paper presents numerical results and focuses on flow separation in glottis. Quantitative data from numerical simulations are compared to results of measurements by Particle Image Velocimetry (PIV), performed on a scaled self-oscillating physical model of vocal folds.Item Effects of manufacturing process in crash simulations(University of West Bohemia, 2010) Šašek, Jakub; Pašek, Miloslav; Beneš, Karel; Glac, VojtěchThis article describes an impact of a manufacturing, which can significantly change real parts behavior. The influence of technology process is neglected in regular simulations. However, advanced finite elements solvers make possible to involve themanufacturing process in final simulations. It brings distortions and initial distribution of stress and strain into simulations. The possibilities are demonstrated on a crash simulation of a simple box-beam, where stamping and welding processes and spring-back are considered. All mentioned operations are performed in Virtual Performance Solution. The effects of manufacturing process are discussed with a respect to common simulation practice at the end of the paper.Item Comments on the thermodynamical background to the growth and remodelling theory applied to a model of muscle fibre contraction(University of West Bohemia, 2010) Rosenberg, Josef; Svobodová, MiroslavaMuscle fibre contraction is a complex thermomechanical process. The change in muscle fibre length (isotonic contraction) and tension (isometric contraction) may be regarded as muscle fibre growth (change in length) and remodelling (change in stiffness). In this study a general mathematical model based on the growth and remodelling theory and the theory of irreversible thermodynamics is proposed. The isometric contraction of muscle fibre is treated as an isothermal process. The relevance of chemical agents diffusion is also discussed.Item On acoustic band gaps in homogenized piezoelectric phononic materials(University of West Bohemia, 2010) Rohan, Eduard; Cimrman, RobertWe consider a composite medium made of weakly piezoelectric inclusions periodically distributed in the matrix which ismade of a different piezoelectricmaterial. Themediumis subject to a periodic excitation with an incidence wave frequency independent of scale ε of the microscopic heterogeneities. Two-scale method of homogenization is applied to obtain the limit homogenized model which describes acoustic wave propagation in the piezoelectric medium when ε → 0. In analogy with the purely elastic composite, the resulting model allows existence of the acoustic band gaps. These are identified for certain frequency ranges whenever the so-called homogenized mass becomes negative. The homogenized model can be used for band gap prediction and for dispersion analysis for low wave numbers. Modeling such composite materials seems to be perspective in the context of Smart Materials design.Item Ultrasonic horn design for ultrasonic machining technologies(University of West Bohemia, 2010) Naď, MilanMany of industrial applications and production technologies are based on the application of ultrasound. In many cases, the phenomenon of ultrasound is also applied in technological processes of the machining of materials. The main element of equipments that use the effects of ultrasound for machining technology is the ultrasonic horn – so called sonotrode. The performance of ultrasonic equipment, respectively ultrasonic machining technologies depends on properly designed of sonotrode shape. The dynamical properties of different geometrical shapes of ultrasonic horns are presented in this paper. Dependence of fundamental modal properties (natural frequencies, mode shapes) of various sonotrode shapes for various geometrical parameters is analyzed. Modal analyses of the models are determined by the numerical simulation using finite element method (FEM) design procedures. The mutual comparisons of the comparable parameters of the various sonotrode shapes are presented.Item Strain-stress analysis of lower limb with applied fixator(University of West Bohemia, 2010) Mrázek, Michal; Florian, Zdeněk; Veselý, Radek; Borák, LiborThis paper compares physiological state of tibia before and after application of an external fixator. The fixator systems’ models but also model of tibia are loaded in the direction of body axis. The paper is focused on the examination of differences in stiffness before and after the application of fixation. Two types of axial external fixators are compared. Both fixators differ in their construction. The first fixator is two-frame and fixation rods are used for fixing the bone tissue (variant I). The second one is fixed into tibia with screws (variant II). We have found out that the two-frame external fixator has much bigger stiffness during limb fixation than the fixator with one body. Much higher deformations compared to physiological state of tibia occur in the variant II.Item A comparison of flow field characteristics from PIV experiment measurement to numerical simulation behind a spacer in a vertical pipe(University of West Bohemia, 2010) Lávička, DavidThis paper describes the topic of measurement using a modern laser method (PIV) in an annular channel of very small dimensions. The annular channel simulates the flow area around a model of a fuel rod in the VVER nuclear reactor. The annular channel holds spacers which create obstacles to fluid flow. The spacers serve a number of important purposes. In the real nuclear reactor, the spacer holds a fuel rod in the fuel rod bundle. Another important function of the spacer is to influence the flow field characteristics, especially turbulence size, by the shape of the spacer. The value of the turbulence regulates the intensity of heat transfer between the fuel rod and the fluid. Therefore, it is very important to provide a correct description and analysis of the flow field behind the obstacle the spacer generates. The paper further looks into the solution of the same task using numerical simulation. The solution of this task consisted of setting the suitable boundary conditions and of setting the turbulence model for the numerical simulation. The result is a comparison of the flow field characteristics from the experimental measurement and the findings of the numerical simulation. The numerical simulation was carried out using commercial CFD software package, FLUENT.Item Prediction of brittle fracture of epoxy-aluminum flanging(University of West Bohemia, 2010) Korbel, Jakub; Schmidt, Lars; Singh, Bandeep; Zant, Nikolaus; Klusák, Jan; Knésl, ZdeněkThis paper presents a fracture mechanical approach for estimation of critical bending load of different types of aluminum-epoxy flanging and comparison with experimental measurements. For this purpose, several designs of the flanges were investigated. The flanges were glued to the epoxy bars and adhesive-epoxy interface was considered as a bi-material notch. Prediction of the failure is based on generalized stress intensity factor and generalized fracture toughness.Item Modelling of the bladed disk vibration with damping elements in blade shroud(University of West Bohemia, 2010) Kellner, Josef; Zeman, VladimírThe requirement for wide operation range of steam turbine can cause, that the blades work close to resonant frequency. For decreasing of blade’s vibration there are placed damping elements in the blade shroud. These elements are calculated for dissipation of the vibration energy. The analytical method of blade and bladed disk modal analysis is introduced. The method enables to include blades both with and without damping elements in shroud. The mathematical model of the bladed disk is prepared for including damping effects in contact planes.Item Acoustic emission source modeling(University of West Bohemia, 2010) Hora, Petr; Červená, OlgaThe paper deals with the acoustic emission (AE) source modeling by means of FEM system COMSOL Multiphysics. The following types of sources are used: the spatially concentrated force and the double forces (dipole). The pulse excitation is studied in both cases. As a material is used steel. The computed displacements are compared with the exact analytical solution of point sources under consideration.Item Shape optimization of supersonic ejector for supersonic wind tunnel(University of West Bohemia, 2010) Dvořák, VáclavThe article deals with the shape optimization of a supersonic ejector for propulsion of an experimental supersonic wind tunnel. This ejector contains several primary nozzles arranged around the mixing chamber wall. CFD software Fluent was used to compute the flow in the ejector. A dynamic mesh method was applied to find an optimal shape of the three-dimensional geometry. During the work it was found out that the previously developed optimization method for subsonic ejectors must be modified. The improved method is more stable and the solution requires fewer optimization steps. The shapes of the mixing chamber, the diffuser, inlet parts and the optimal declination of the primary nozzles are obtained as the optimization results.Item Thin viscoelastic disc subjected to radial non-stationary loading(University of West Bohemia, 2010) Adámek, Vítězslav; Valeš, FrantišekThe investigation of non-stationary wave phenomena in isotropic viscoelastic solids using analytical approaches is the aim of this paper. Concretely, the problem of a thin homogeneous disc subjected to radial pressure load nonzero on the part of its rim is solved. The external excitation is described by the Heaviside function in time, so the nonstationary state of stress is induced in the disc. Dissipative material behaviour of solid studied is represented by the discrete material model of standard linear viscoelastic solid in the Zener configuration. After the derivation of motion equations final form, the method of integral transforms in combination with the Fourier method is used for finding the problem solution. The solving process results in the derivation of integral transforms of radial and circumferential displacement components. Finally, the type of derived functions singularities and possible methods for their inverse Laplace transform are mentioned.
