Volume 10, number 1 (2016)
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Item Mathematical modelling of friction-vibration interactions of nuclear fuel rods(University of West Bohemia, 2016) Zeman, Vladimír; Hlaváč, ZdeněkNuclear fuel rods (FRs) are transverselly linked to each other by three spacer grid cells at several vertical levels inside a fuel assembly (FA). Vibration of FA components, caused by the motion of FA support plates in the reactor core, generates variable contact forces between FRs and spacer grid cells. Friction effects in contact surfaces have an influence on the expected lifetime period of nuclear FA in terms of FR cladding fretting wear. This paper introduces an original approach to mathematical modelling and simulation analysis of FR nonlinear vibrations and fretting wear taking into consideration friction forces at all levels of spacer grids.
Item Vibration modes of a single plate with general boundary conditions(University of West Bohemia, 2016) Phamová, Lucie; Vampola, TomášThis paper deals with free flexural vibration modes and natural frequencies of a thin plate with general boundary conditions — a simply supported plate connected to its surroundings with torsional springs. Vibration modes were derived on the basis of the Rajalingham, Bhat and Xistris approach. This approach was originally used for a clamped thin plate, so its adaptation was needed. The plate vibration function was usually expressed as a single partial differential equation. This partial differential equation was transformed into two ordinary differential equations that can be solved in the simpler way. Theoretical background of the computations is briefly described. Vibration modes of the supported plate with torsional springs are presented graphically and numerically for three different values of stiffness of torsional springs.Item Using Fourier and Taylor series expansion in semi-analytical deformation analysis of thick-walled isotropic and wound composite structures(University of West Bohemia, 2016) Jiran, Lukáš; Mareš, TomášThick-walled tubes made from isotropic and anisotropic materials are subjected to an internal pressure while the semi-analytical method is employed to investigate their elastic deformations. The contribution and novelty of this method is that it works universally for different loads, different boundary conditions, and different geometry of analyzed structures. Moreover, even when composite material is considered, the method requires no simplistic assumptions. The method uses a curvilinear tensor calculus and it works with the analytical expression of the total potential energy while the unknown displacement functions are approximated by using appropriate series expansion. Fourier and Taylor series expansion are involved into analysis in which they are tested and compared. The main potential of the proposed method is in analyses of wound composite structures when a simple description of the geometry is made in a curvilinear coordinate system while material properties are described in their inherent Cartesian coordinate system. Validations of the introduced semi-analytical method are performed by comparing results with those obtained from three-dimensional finite element analysis (FEA). Calculations with Fourier series expansion show noticeable disagreement with results from the finite element model because Fourier series expansion is not able to capture the course of radial deformation. Therefore, it can be used only for rough estimations of a shape after deformation. On the other hand, the semi-analytical method with Fourier Taylor series expansion works very well for both types of material. Its predictions of deformations are reliable and widely exploitable.Item Usage of the particle swarm optimization in problems of mechanics(University of West Bohemia, 2016) Hajžman, Michal; Bulín, Radek; Svatoš, Petr; Šika, ZbyněkThis paper deals with the optimization method called particle swarm optimization and its usage in mechanics. Basic versions of the method is introduced and several improvements and modifications are applied for better convergence of the algorithms. The performance of the optimization algorithm implemented in an original in-house software is investigated by means of three basic and on complex problems of mechanics. The goal of the first problem is to find optimal parameters of a dynamic absorber of vibrations. The second problem is about the tunning of eigenfrequencies of beam bending vibrations. The third problem is to optimize parameters of a clamped beam with various segments. The last complex problem is the optimization of a tilting mechanism with multilevel control. The presented results show that the particle swarm optimization can be efficiently used in mechanical tasks.Item Design of the blisk of an aircraft turbojet engine and verification of its resonance free operation(University of West Bohemia, 2016) Chromek, LukášIntegral turbine wheels belong to one of the most stressed parts of jet aircraft engines. In addition to high rotational speeds and temperatures, they are also subjected to dynamic forces from a non-uniform pressure field in the flow path. Dynamic forces even at a relatively small amplitude can cause failure by fatigue, which leads to fracture of blades and crash of the machine. These adverse conditions, called resonance, should be avoided already in the design stage when a suitable choice of stator vanes and the number of blades can move the critical speed of the blisk beyond the operating speed or at least reduce their influence. In the case of a small jet engine produced by the První brněnská strojírna (PBS) Velká Bíteš, the operating speed is of nearly half of the entire speed range of the machine. This makes the design of a proposed turbine wheel very complicated. A higher harmonic order of aerodynamic excitation is almost always present, its influence was therefore tested experimentally by vibration tests in the test station PBS Velká Bíteš.
