Articles (MDP)
Permanent URI for this collection
Browse
Recent Submissions
Item Modelling of the three-dimensional friction contact of vibrating elastic bodies with rough surfaces(University of West Bohemia, 2009) Voldřich, JosefFriction contact appears to be an intricate nonlinear coupling in modelling engineering structures. With vibration systems, it can serve as a dampening element for reducing the stress range. The contribution deals with the modelling of the 3D dry friction elastic contact. The influence of surface roughness on its normal and tangential stiffness, both of nonlinear nature, is being considered. The model also allows a change of the normal contact force and of the applied moment of force in the course of a vibration cycle. The equations of the proposed mathematical model have been solved using direct integration.
Item Influence of the terminal muffler geometry with three chambers and two tailpipes topology on its attenuation characteristics(University of West Bohemia, 2009) Matas, Richard; Kňourek, Jindřich; Voldřich, JosefAimed at describing the harmonic acoustic waves passage through an exhaust system, the two-tailpipes terminal muffler may be seen as an acoustic element defined by eight quantities (usually arranged in a 2 by 4 matrix). The quantities make up a complex functions depending on the frequency of the wave motion. The engine speed is a variable that can be regarded as another parameter. This contribution presents a procedure how to establish the quantities coming from the suggested mathematical model and using the finite element method. In addition, formulae are derived for calculation of the terminal muffler attenuation based on the indicated characteristics. Finally, the attenuation haracteristics of the terminal muffler are presented and mutually compared for several design options of the mufflers which indeed are different with respect to their geometry but have identical topology of the chambers and tailpipes.Item Mathematical modelling of biogenous filter cake and identification of oilseed material parameters(University of West Bohemia, 2009) Očenášek, Jan; Voldřich, JosefMathematical modeling of the filtration and extrusion process inside a linear compression chamber has gained a lot of attention during several past decades. This subject was originally related to mechanical and hydraulic properties of soils (in particular work of Terzaghi) and later was this approach adopted for the modeling of various technological processes in the chemical industry (work of Shirato). Developed mathematical models of continuum mechanics of porousmaterials with interstitial fluid were then applied also to the problem of an oilseed expression. In this case, various simplifications and partial linearizations are introduced in models for the reason of an analytical or numerical solubility; or it is not possible to generalize the model formulation into the fully 3D problem of an oil expression extrusion with a complex geometry such as it has a screw press extruder. We proposed a modified model for the oil seeds expression process in a linear compression chamber. The model accounts for the rheological properties of the deformable solid matrix of compressed seed, where the permeability of the porous solid is described by the Darcy’s law. A methodology of the experimental work necessary for a material parameters identification is presented together with numerical simulation examples.Item The proper filling confirmation of the cavities in massive concrete structures of nuclear power plants by impact-echo method(University of West Bohemia, 2007) Morávka, ŠtefanNuclear power plants (NPP) are duty to certify their security for renewal of operating license. Security can be significantly affected by defects of ageing concrete reinforced structures. The methods, how to do in-service inspections of these aging structures of NPP more quickly, cheaply and reliably, are still being looking for. Advanced Impact-Echo method seams to be very hopeful. This paper is a part of extensive project and continues a number of papers published in Czech as well as in foreign. It brings a method description and a main results survey of the numerical modeling of the detection of grouted (repaired) voids in massive concrete structures. Cavities are filled by grouting polyurethan compound CarboPur WF. We try to find out if it is possible or impossible to confirm simply, by Impact-Echo method, if cavities have been filled properly. Consequently, these numerical predictions will be verified on real (scaled 1:1) specimens in NRI Řež as a part of this project as well.Item Separation of contact in a sliding system with frictionally excited thermoelastic instability(University of West Bohemia, 2007) Voldřich, JosefThe first phase of the thermoelastic instability, which is characterized by a full contact regime, can be modelled using Fourier decomposition and application of an analytical description. However, in case of further increase of instability, a separation of the contact occurs which is more difficult to cover by mathematical means. The contribution deals with numerical simulations of the separation. The problems are topical in connection with the disk brakes design, should we give an example.Item Numerical simulation of the detection of crack in reinforced concrete structures of NPP due to expansion of reinforcing corrosive products using impact-echo method(University of West Bohemia, 2008) Morávka, ŠtefanNuclear energy boom is starting nowadays. But also current nuclear power plants (NPP) are duty to certify their security for regular renewal of their operating licenses. NPP security can be significantly affected by defects of large amount of ageing reinforced concrete structures. Advanced Impact-Echo method seams to be very hopeful to cooperate at performing in-service inspections such structures. Just these in-service inspections are included in the first priority group of specific technical issues according to the recommendations of OECD-Nuclear Energy Agency, Commission on Safety of Nuclear Installation in the field of ageing management. This paper continues of extensive project dealing with Impact-Echo method application. It will present a method description and main results of numerical modeling of detection and localization of crack caused by corrosive product expansion. Steel reinforcing rods are subjected to corrosion due to diffusion of corrosive agents from structure surface. Corrosive products have up to 7-times larger volume than pure steel. Raised strain can cad lead up to concrete failure and crack development. We investigate whether it is possible to detect these growing cracks by Impact-Echo method in time. Experimental verification of our numerical predictions is prepared on Civil Faculty in Brno.Item A viscoelastic orthotropic Timoshenko beam subjected to general transverse loading(University of West Bohemia, 2008) Adámek, Vítězslav; Valeš, FrantišekThe investigation of lateral vibrations of a simply supported thin beam is the aim of this work. The analytical solution of the problem is derived based on the approximate Timoshenko beam theory for a general continuous loading acting on the upper beam face over the whole beam width and perpendicular to the beam axis. The material of the beam studied is assumed linear orthotropic viscoelastic. The generalized standard viscoelastic solid is chosen for representing of viscoelastic beam behaviour. Final system of partial integro-differential equations is solved by the standard method of integral transforms and resulting relations describing beam deflection, slope of the beam and corresponding stress and strain components are presented. Moreover, the derivation of final functions of beam deflection and slope of the beam for a specific impulse loading is presented and analytical results are compared with results obtained using numerical simulation in 2D (FEM). This confrontation shows very good agreement between results obtained. Furthermore, it was shown that the measure of agreement depends not only on the beam geometry.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.
