Volume 3, number 1 (2009)
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Item Static and modal analysis of the brake stand(University of West Bohemia, 2009) Švantner, Michal; Klepáček, Jan; Lang, VladislavTesting and development of braking systems belong to significant technical problems solved in automotive industry. The braking systems testing could be carried out directly on a car or using a special testing device — a brake stand. The brake stand developed at the workplace of the University of West Bohemia is introduced in this paper. Its function and usage characterisation are described. Static and modal analyses, which were performed for adjustments of the final design of the brake stand, are presented. The results of the computer modelling are commented and discussed.
Item Buoyancy driven flow in reactor safety(University of West Bohemia, 2009) Vaibar, Roman; Höhne, ThomasBuoyancy driven flow is often found in many engineering applications such as the mixing process of fluids, which have different densities. The aim of this study is to simulate mixing of borated and unborated water, an issue which is relevant to the analysis of the safety of nuclear reactors. The degree of mixing of weakly and highly borated coolant is a critical issue with respect to reactivity of the reactor core. Therefore, a combined numerical and experimental study of buoyant mixing processes has been performed. The numerical studies on different types of grid show, that the main influence to the discription of the mixing processes is the simplifacation of the flow domain. In the case when the proper flow domain is used, a better agreement between the numerical and experimental results can be achieved.Item Tool center position determination of deformable sliding star by redundant measurement(University of West Bohemia, 2009) Vampola, Tomáš; Valášek, Michael; Šika, ZbyněkThis paper deals with the procedures for the determination of TCP (tool center position) of machine tool of PKM (parallel kinematical machines) structure in the case that PKM must be considered as compliant mechanism. Two different approaches are described and investigated. The first approach is based on the model of compliant mechanism of PKM. The second approach is based on the redundant measurement that can replace the stiffness knowledge and force balance computation by pure geometric consideration. These procedures are described on PKM Sliding Star.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 Problem of the gyroscopic stabilizer damping(University of West Bohemia, 2009) Šklíba, JanThe gyroscopic stabilization of the vibro-isolation system of an ambulance couch is analyzed. This paper follows several previous papers, which concern the derivation of the complete system of appropriate differential equations and some analyses were provided there, as well. It was supposed that mass matrix, stiffness matrix and gyroscope impulse-moment remain constant and the stability of equilibrium state was solved according to different alternatives of the damping and of the radial correction. Little known theorems of the stability were used there. With respect to these theorems, vibro-isolation systems can be classified according to odd or even number of generalized coordinates.Item Crack propagation in the vicinity of the interface in layered materials(University of West Bohemia, 2009) Šestáková, Lucie; Náhlík, Luboš; Hutař, Pavel; Knésl, ZdeněkThe paper deals with the problem of crack propagation in the vicinity of the interface in layered materials. Layered materials are often used in practice, primarily because of their better mechanical properties in comparison with the properties of individual materials components. The configuration of a crack with its tip at the bi-material interface can be created during crack propagation in the structure. It is important to decide if the crack propagates into the second material in this case. The step change of material properties at the bi-material interface means that classical linear elastic fracture mechanics are not appropriate. A generalized approach has to be applied. In this paper, two criteria are applied for the determination of the critical value of an applied load. Knowledge of these values is important for the estimation of the service life time of such structures. The results obtained can be used especially for multi-layer polymer composites designs. On the basis of the procedures presented, suitable materials combinations can be suggested for new composite structures.Item Dynamic model of stirling engine crank mechanism with connected electric generator(University of West Bohemia, 2009) Sikora, Michal; Vlach, RadekThis paper treats of a numerical dynamic model of Stirling engine crank mechanism. The model is included in the complex model of combined heat and power unit. The unit is composed of the Stirling engine and of attached threephase synchronous generator. This generator should start the Stirling engine in motor mode as well. It is necessary to combine the crank shaft dynamic model and the complete thermal model of Stirling engine for simulations and analyses of engine run. Our aim is to create a dynamics model which takes into account the parameters of crankshaft, piston rods, pistons, and attached generator. For unit working, the electro-mechanical behaviour of generator is also important. That is why we experimentally verified the parameters of generator. The measured characteristics are used in a complex model of heat and power unit. Moreover, it is also possible to determine the Stirling engine torque by the help of these electro-mechanical characteristics. These values can be used e. g. for determination of optimal engine working point or for unit control.Item Connection between inlet velocity field and diffuser flow instability(University of West Bohemia, 2009) Rudolf, PavelSimulations of the flow in a straight diffuser were carried out for different inlet velocity profiles equivalent to the real turbine operating points. Frequencies and magnitudes of pressure pulsations of the rotating vortex rope were recorded. Two types of vortices were detected. The first one is a thin vortex with higher frequency and relatively low pressure amplitudes corresponding to higher part load turbine operation. For lower loads, further from best efficiency point, a huge vortex rotating on higher diameter appears, which is accompanied by massive pressure pulsations, but with lower frequency. Connections of these two regimes with inlet circumferential velocity component are discussed in the paper.Item Dynamical analysis of machining tool body with reinforced inner core of circular shape(University of West Bohemia, 2009) Naď, MilanThe vibration analysis of a clamped beam structure representing vibrating machining body tool is solved in this paper. The required modal properties of beam are obtained by application the reinforcing core with circular cross section. The perfect adhesion between core material and basic beam material is considered. The different material properties of beam and core are considered. The fundamental mathematical formulations describing the bending vibrations of this composite beam structure are presented. The effect of material properties and geometrical parameters of reinforcing core on natural frequencies of cantilever composite beam structure with circular and rectangular cross section is presented. This form of composite beam structure provides effective tool to modification of its dynamical properties.Item Numerical computing of elastic homogenized coefficients for periodic fibrous tissue(University of West Bohemia, 2009) Moravec, Fanny; Roman, SophieThe homogenization theory in linear elasticity is applied to a periodic array of cylindrical inclusions in rectangular pattern extending to infinity in the inclusions axial direction, such that the deformation of tissue along this lastdirection is negligible. In the plane of deformation, the homogenization scheme is based on the average strain energy whereas in the third direction it is based on the average normal stress along this direction. Namely, these average quantities have to be the same on a Repeating Unit Cell (RUC) of heterogeneous and homogenized media when using a special form of boundary conditions forming by a periodic part and an affine part of displacement. It exists an infinity of RUCs generating the considered array. The computing procedure is tested with different choices of RUC to control that the results of the homogenization process are independent of the kind of RUC we employ. Then, the dependence of the homogenized coefficients on the microstructure can be studied. For instance, a special anisotropy and the role of the inclusion volume are investigated. In the second part of this work, mechanical traction tests are simulated. We consider two kinds of loading, applying a density of force or imposing a displacement. We test five samples of periodic array containing one, four, sixteen, sixty-four and one hundred ofRUCs. The evolution of mean stresses, strains and energy with the numbers of inclusions is studied. Evolutions depend on the kind of loading, but not their limits, which could be predicted by simulating traction test of the homogenized medium.Item Static and dynamic analysis of 1 220 mm steel last stage blade for steam turbine(University of West Bohemia, 2009) Míšek, Tomáš; Kubín, ZdeněkThe 3 000 rpm 1 220 mm blade for a steam turbine was developed with application of new design features. The last stage moving blade is designed with an integral cover, a mid-span tie-boss connection and a fir-tree dovetail. With this configuration the blades are continuously coupled by the blade untwist due to the centrifugal force when the blades rotate at high speed, so that vibration control and increased structural damping are provided. Blade was tuned in order to eigen-frequencies were safely far from possible excitation. Because of connection members, the number of the resonant vibration modes can be reduced by virtue of the vibration characteristics of the circumferentially continuous blades. The last stage airfoil was optimalized from view of minimalization of its centrifugal force. In order to develop the 3 000 rpm 1 220 mm blade, the advanced analysis methods to predict dynamics behavior of the bladed structure were applied. Coupled rotor-blade analysis was also aim of the attention. To validate calculated results the verification measurement such as rotational vibration tests was carried out in the high-speed test rig. Relation of the friction damping of the bladed structure on amount of excitation level was also monitored and evaluated.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 Smoothed particle hydrodynamics modelling in continuum mechanics: fluid-structure interaction(University of West Bohemia, 2009) Lobovský, Libor; Groenenboom, Paul H. L.Mathematical 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 Probability and sensitivity analysis of machine foundation and soil interaction(University of West Bohemia, 2009) Králik, Juraj; Králik, Juraj jr.This paper deals with the possibility of the sensitivity and probabilistic analysis of the reliability of the machine foundation depending on variability of the soil stiffness, structure geometry and compressor operation. The requirements to design of the foundation under rotating machines increased due to development of calculation method and computer tools. During the structural design process, an engineer has to consider problems of the soil-foundation and foundation-machine interaction from the safety, reliability and durability of structure point of view. The advantages and disadvantages of the deterministic and probabilistic analysis of the machine foundation resistance are discussed. The sensitivity of the machine foundation to the uncertainties of the soil properties due to longtime rotating movement of machine is not negligible for design engineers. On the example of compressor foundation and turbine fy. SIEMENS AG the affectivity of the probabilistic design methodology was presented. The Latin Hypercube Sampling (LHS) simulation method for the analysis of the compressor foundation reliability was used on program ANSYS. The 200 simulations for five load cases were calculated in the real time on PC. The probabilistic analysis gives us more complex information about the soil-foundation-machine interaction as the deterministic analysis.Item Sensitivity analysis for the optimal perforation problem in acoustic transmission(University of West Bohemia, 2009) Rohan, Eduard; Lukeš, VladimírThe paper deals with the acoustic transmission through perforated interface and its sensitivity w.r.t. the perforation design. The homogenized transmission conditions are imposed on an interface plane separating two halfspaces occupied by the acoustic medium. The conditions were obtained recently as the two-scale homogenization limit of the standard acoustic problem imposed in the layer perforated by a sieve-like obstacle with periodic structure. The limit model involves some homogenized impedance coefficients depending on the so-called microscopic problems; these are imposed in the reference computational cell, Y embedding obstacle S the shape of which can be designed. This homogenization approach allows for an efficient treatment of complicated perforation designs of perforations. Acoustic response to the global acoustic problem involving the transmission conditions is subject to the sensitivity analysis. Namely the total variation of an objective function depending on the acoustic pressure w.r.t. shape of S at the “microlevel” is derived.Item Computational analysis of acoustic transmission through periodically perforated interfaces(University of West Bohemia, 2009) Lukeš, Vladimír; Rohan, EduardThe objective of the paper is to demonstrate the homogenization approach applied to modelling the acoustic transmission on perforated interfaces embedded in the acoustic fluid. We assume a layer, with periodically perforated obstacles, separating two half-spaces filled with the fluid. The homogenizationmethod provides limit transmission conditions which can be prescribed at the homogenized surface representing the “limit” interface. The conditions describe relationship between jump of the acoustic pressures and the transversal acoustic velocity, on introducing the “in-layer pressure” which describes wave propagation in the tangent directions with respect to the interface. This approach may serve as a relevant tool for optimal design of devices aimed at attenuation of the acoustic waves, such as the engine exhaustmufflers or other structures fitted with sieves and grillages. We present numerical examples of wave propagation in a muffler-like structure illustrating viability of the approach when complex 3D geometries of the interface perforation are considered.Item Orientation of smooth muscle cells with application in mechanical model of gastropod tissue(University of West Bohemia, 2009) Kochová, Petra; Cimrman, Robert; Rohan, EduardIn this paper, we determine the spatial orientation of smooth muscle cells of gastropod tissue. This together with volume fractions of smooth muscle cells and other tissue components obtained using stereological methods serves as input data for our mechanical model of gastropod tissue. The mechanical model is a composite model consisting of various components chosen to describe key features of the tissue like elasticity and viscoelasticity and preferential directions of muscle fibres. The elastic and viscoelastic constitutive parameters are identified by an automatic identification procedure based on nonlinear least squares. Numerical examples of the identification using real experimental data from uniaxial tension tests are shown.Item Contribution to the gas flow and heat transfer modelling in microchannels(University of West Bohemia, 2009) Klášterka, Hynek; Vimmr, Jan; Hajžman, MarekThis study is focused on the mathematical modelling of gas flow and heat transfer in a microchannel with the rectangular cross-section. The gas flow is considered to be steady, laminar, incompressible, hydrodynamically and thermally fully developed. The main objective is the application of the slip flow boundary conditions — the velocity slip and the temperature jump at microchannel walls. The analytical solution of both flow and heat transfer is derived using the Fourier method and it is also compared with the numerical solution based on the finite difference method applied on the Poisson’s equations describing gas flow and heat transfer in the microchannel.Item Diffusion and the self-measurability(University of West Bohemia, 2009) Holeček, MiroslavThe familiar diffusion equation, ∂g/∂t = DΔg, is studied by using the spatially averaged quantities. A non-local relation, so-called the self-measurability condition, fulfilled by this equation is obtained. We define a broad class of diffusion equations defined by some “diffusion inequality”, ∂g/∂t ·Δg ≥ 0, and show that it is equivalent to the self-measurability condition. It allows formulating the diffusion inequality in a non-local form. That represents an essential generalization of the diffusion problem in the case when the field g(x, t) is not smooth. We derive a general differential equation for averaged quantities coming from the self-measurability condition.Item Optimization of the railway vehicle bogie in term of dynamics(University of West Bohemia, 2009) Hlaváč, Zdeněk; Zeman, VladimírThe paper deals with parameter optimization method of a railway vehicle bogie. Wheelsets are subjected to stochastic excitation caused by irregularities of the track geometry and/or caused by deterministic excitation from polygonalized running surface of the wheels, respectively. Stochastic irregularities are understood as stationary stochastic process described by spatial power spectral density functions. The polygonalization process forms radial irregularities of the running surface which can be described by of a harmonic function depending on order of the wheel polygonalization. The optimization method is based on minimization of several types of objective functions suitable for optimization from the dynamic load point of view of exposed linkage
