# Volume 1, number 2 (2007)

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Item Study of coupling between bending and torsional vibration of cracked rotor system supported by radial active magnetic bearings(University of West Bohemia, 2007) Ferfecki, PetrShow more The coupling of bending and torsional vibration due to the presence of transverse fatigue crack in a rotor system supported by radial active magnetic bearings (AMB) is investigated. For this purpose the modified stiffness matrix with six degrees of freedom per node is used and takes into account all the coupling phenomena that exists in a cracked rotor. The partial opening and closing of crack is considered by means of status of stress intensity factor along the crack edge. The equation of motion of rotor system is nonlinear due to response dependent non-linear breathing crack model and nonlinear force coupling introduced by AMB. A response of the rotor system is obtained by direct integration of nonlinear equation of motion. When the torsional harmonic excitation is applied to the rotor system with the crack then the sum and difference of torsional frequency around a bending natural frequency is observed in the lateral vibration spectrum. Influence of different values of crack parameters for two different speeds of rotor is investigated with help of frequency spectra.Show more Item Vehicle dynamic effects in the course of passing over turnouts(University of West Bohemia, 2007) Zelenka, Jaromír; Hába, Aleš; Kohout, MartinShow more For the quantification of vehicle dynamic effects at passing over turnouts at a higher speed there was developed a methodology for evaluating of acceleration measured on vehicle axle boxes in the year 2003. The methodology is based on statistical evaluation of lateral and vertical acceleration measured values at passing over both critical parts of a turnout (tongue, frog). The created methodology was used for investigation of vehicle dynamic effects by running at speed up to 230 km/h in the year 2004 in terms of high-speed tests of tilting-body unit class 680 CD. There was found relatively high values of dynamic effects already at a speed 160 km/h. In terms of tilting-body unit class 680 tests at a higher speed in curves of chosen track lines of 1st and 2nd corridor of Czech Railways there was carried out also verification of curved turnouts state according to methodology mentioned above with a view to possibility of speed increasing at curved throats of chosen stations. Lateral vehicle dynamic effects at passing over a curved turnout frog area were evaluated. There were carried out simulation calculations of vehicle passing over a turnout based on measured geometric parameters of wheelset as well as chosen turnouts. Results of the calculations were compared with measurements. The increased vehicle dynamic effects found in pulsed beats character influence negatively the turnouts part (not only wheel contacting parts) as well as operating life all unsuspended parts of vehicles.Show more Item System model reduction for MBS optimization(University of West Bohemia, 2007) Zavřel, Jan; Valášek, MichaelShow more A disadvantage of optimization of flexible multibody systems (MBS) is a computing time, mainly for large systems, especially designed by FEM. The computing time rises with the complexity of the model significantly. A reduction techniques allow decreasing of degrees of freedom and it contributes to the reduction of the computing time. These techniques can be used for the reduction from thousands and more degrees of freedom to tens, but some limits exist. A reduction degree (ratio between number of DOFs before and after the reduction) is the most important feature because it predicts the final accuracy of the model. The next one is the selection of master and slave degrees of freedom that play an important role in connecting all bodies together within the MBS (e.g. by joints). There are many reduction methods, but they differ in available accuracy, speed, efficiency and suitability for the same reduction degree. A dimension of the original system is decisive for the reduction method suitability, many methods require an inversion matrix from the part of the stiffness matrix. The inversion matrix are than large and the computing time grows up. This paper deals with the reduction techniques, their disadvantages, suitability and applicability.Show more Item Analysis of blood flow through a three-dimensional bypass model(University of West Bohemia, 2007) Vimmr, Jan; Jonášová, AlenaShow more The purpose of this study is to analyze the steady laminar blood flow through a complete idealized threedimensional bypass model with regard to the bypass hemodynamics and to compare the obtained results with the ones from the two-dimensional model. The type of flow restriction in the native artery is represented by either an occlusion or a 75% symmetric stenosis. In both cases, the blood is considered to be an incompressible Newtonian fluid. The walls are assumed to be impermeable and rigid. In order to solve the non-linear system of incompressible Navier-Stokes equations, the pseudo-compressibility method and the finite volume formulation of the central explicit fourth order Runge-Kutta scheme are applied using own computational software developed for unstructured hexahedral grids.Show more Item Reconstruction of the material parameters of the homogenous isotropic or orthotropic 2D continuum(University of West Bohemia, 2007) Vampola, Tomáš; Šika, Zbyněk; Valášek, MichaelShow more The paper describes the way how to find the material parameters of the homogenous isotropic or orthotropic 2D continuum from measurements of deformation of selected nodes. The FE method is used for reconstruction of the stiffness matrix. The developed method enables to determine the angle between the material axes of the continuum and the local coordinate system of the used elements.Show more Item Buoyancy driven turbulent flow and experimental validation at the VeMix test facility(University of West Bohemia, 2007) Vaibar, Roman; Da Silva, Marco Jose; Sühnel, TobiasShow more Buoyancy driven flow is often found in many engineering application 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. As nuclear reactor geometries are complex, a vertical mixing (VeMix) test facility was used to validate the numerical models used with optical and surface wire mesh measurements. Good agreement was found between the physicality of the flow phenomena of the observed experiments and numerical calculations. Fourier analysis of the vortical oscillations in both the experiments and simulations also show good agreement for several flow conditions.Show more Item Form of growth law(University of West Bohemia, 2007) Tringelová, MiroslavaShow more Our aim in future is to computer simulate the mechanical stimulated postnatal heart development (normal growth, heart hypertrophy, etc.). We are now interested in the study of the form of growth law [1], which we could use for the simulation. We follow the theory of volumetric growth in [1]. This theory is based on the theory of generalized continuum [2] and describes the volumetric growth of tissue from macroscopic point of view.Show more Item A thin rectangular viscoelastic orthotropic plate under transverse impuls loading(University of West Bohemia, 2007) Soukup, Josef; Volek, JanShow more An analytical solution of stress wave propagation in a thin rectangular viscoelastic plate with special orthotropy under transverse impulse loading is presented. The solution is based on the approximate theory of thin plates using the Kirchhoff and the Rayleigh corrections. Constitutive equations for two-dimensional linear viscoelastic Maxwell model of solid are derived using the superposition principle. Transverse impulse loading has been allowed to effect on an arbitrary point of the plate surface and it has general behaviour in time. Results in the form of displacement, velocities and stress components are obtained.Show more Item The geometry of surfaces contact(University of West Bohemia, 2007) Siegl, Jaroslav; Švígler, JaromírShow more This contribution deals with a geometrical exact description of contact between two given surfaces which are defined by the vector functions. These surfaces are substituted at a contact point by approximate surfaces of the second order in accordance with the Taylor series and consequently there is derived a differential surface of these second order surfaces. Knowledge of principal normal curvatures, their directions and the tensor (Dupin) indicatrix of this differential surface are necessary for description of contact of these surfaces. For description of surface geometry the first and the second surface fundamental tensor and a further methods of the differential geometry are used. A geometrical visualisation of obtained results of this analysis is made. Method and results of this study will be applied to contact analysis of tooth screw surfaces of screw machines.Show more Item Homogenization method for elastic materials(University of West Bohemia, 2007) Seifert, FrantišekShow more In the paper we study the homogenization method and its potential for research of some phenomenons con- nected with periodic elastic materials. This method will be applied on partial differential equations that describe the deformation of a periodic composite material. The next part of the paper will deal with applications of the homogenization method. The importance of the method will be discussed more detailed for the exploration of the so called bandgaps. Bandgap is a phenomenon which may appear during vibrations of some periodically heteroge- neous materials. This phenomenon is not only observable during vibrations for the aforementioned materials, but we may also observe similar effects by propagation of electromagnetic waves of heterogeneous dielectric medias.Show more Item Use of elastic stresses for a multiaxial fatigue prediction(University of West Bohemia, 2007) Růžička, Milan; Papuga, Jan; Hrubý, Zbyněk; Doubrava, KarelShow more A new computational method derived from Papuga PCr multiaxial criterion is presented in the paper. While the PCr criterion is suitable for a comparison of a local multiaxial loading with a fatigue limit, the PCF criterion derived is focused on computation within a finite life. Its use is intended for a variable amplitude multiaxial loading, where the Palmgren-Miner damage cumulation law is applied. The PCF method is based on local elastic stresses and their action within the standard S-N curves of smooth specimens. No arrangement concerning the stress gradient effect was applied, since the experiments serving for comparison were carried on smooth and unnotched specimens. The experimental set covers different load paths applied to specimens manufactured of CSN 41 1523 structural steel. Computational results are promising for cases with load paths formed from single unclosed lines, but for the cases with load paths related to closed constructs it provides too conservative solution. A need for a further term counting for the multiaxial hardening is discussed.Show more Item Growing and remodeling material as a dynamical system(University of West Bohemia, 2007) Rosenberg, Josef; Hynčík, LuděkShow more Contribution contains the short description of the general theory of growth and remodeling based on Di’Carlo’s approach. This theory is applied to the one dimensional continuum using the quadratic form of the free energy function. Two different forms of loading are dealt – isometric and isotonic one. For both cases the corresponding equations describe the dynamical system. Its properties are analyzed using the methods of nonlinear dynamics. It’s shown the influence of the constant growth and remodeling parameters on the stability of the equilibrium pointShow more Item Comparison of optimization methods for human vocal tract resonance properties tuning(University of West Bohemia, 2007) Radolf, VojtěchShow more The paper deals with the two various optimization processes finding such geometrical form of acoustical cavities which leads to excitation of predefined acoustic resonance. A computing times and accuracy of a solutions are compared. The attention is focused both on the first two formants that are important for vowel production, and on a domain between the third and the fifth formant. This frequency domain is important for voice timbre, namely for singing voice. The problem is solved by the help of transfer matrix method using conic acoustic elements. The results should help to have a physical background for voice rehabilitation, for teaching of opera singers at musical faculties and for better understanding of biomechanics of voice production.Show more Item Nonlinear effects on the rotor driven by a motor with limited power(University of West Bohemia, 2007) Půst, LadislavShow more Rotating machines are complicated systems consisting of rotor, stator, driving motor, electric feeding system, etc. Such structures contain many kinds of nonlinearities, both in mechanical and electrical parts. Computing model of the studied system has 4 DOF and the main nonlinearities that are considered are those generated by the driving properties of limited power source and nonlinearities of electric part of motor. Effect of non-ideal source of excitation energy was studied e.g. in [1–5]. Nonlinearities of rotor supports were investigated e.g. in [3, 6]. Here we focus on the influence of nonlinear magnetic flux, with weak smooth nonlinear characteristics. Rotor and its supports are considered as linear. After derivation of differential equations of motion, the effect of different values of nonlinearity of magnetic flux on the mechanical vibration of rotor, on fluctuation of angular velocity and on variation of driving current at constant feeding voltage and at constant loading moment is studied by numerical solutions. Results are presented in the form of time histories and of plane trajectories of main motion variables.Show more Item The patellofemoral joint and the total knee replacement(University of West Bohemia, 2007) Pokorný, Jiří; Křen, JiříShow more The biomechanical investigation of the entire knee joint is essential in understanding the joint function and interaction between various components in both intact and perturbed condition. In the most clinically successful cases many patients treated by total knee replacement (TKR) cannot achieve normal joint function over time. The knee joint is the most complicated joint in the human body. The model of the knee joint with total knee replacement is based on the finite element method. The attention of present study was focused on the patellofemoral joint and the patella tracking with different Q-angle and condylar twist angle. The patellofemoral joint is frequently the source of the knee anterior pain related to disturbances in normal tracking.Show more Item Coverage of multiaxial fatigue criteria in fatigue limit region(University of West Bohemia, 2007) Papuga, JanShow more There is a power of methods aimed at calculation of equivalent fatigue limit for arbitrary multiaxial loading. Although there are so many ways of computation, their thorough mutual comparison in a larger scale is missing. The database project presented in this paper comprise of several databases crowned with the FatLim database, which comprise of a huge number of experimental results and of 18 computational method working in the category mentioned before. The great block of data was acquired using in-house fatigue software PragTic, which is offered as a freeware application. The FatLim database follows its philosophy of a simple and non-paid accessibility. Its query tool written in MySQL and PhP allows to users to evaluate a practical usability of tested methods on load cases, which the users define. All the issues covered within this paper are available on the website www.pragtic.com, structure of which is described here.Show more Item Multicompartment/CFD modelling of transport and reaction processes in Couette-Taylor photobioreactor(University of West Bohemia, 2007) Papáček, Štepán; Štýs, Dalibor; Dolínek, Pavel; Petera, KarelShow more A hybrid multicompartment/CFD modelling approach, introduced by Bezzo et al. (2003), describing processes with much faster fluid dynamics time-scale than the reaction rate, is used to characterise microalgal growth in a photobioreactor. Our system of interest, the Couette-Taylor bioreactor (CTBR), is divided into a network of wellmixed compartments. Photosynthetic reactions and other related phenomena are described in each compartment by an ordinary differential equation (ODE). The flow of neutrally-buoyant particles, representing a continuous mass flow of microalgal cells inside CTBR, is simulated by a steady-state computational fluid dynamics (CFD) computations. The flow rates between adjacent compartments are derived from several thousand predicted trajectories, post-processed using MATLABr, accordingly to our original method. The resulting governing equations are formed as a system of nc (total number of compartments) ODE’s, which are easier to handle than the large system of equations rising from a reaction phenomena incorporated in CFD models.Show more Item Influence of media mixing rates in T-joints upon their damage(University of West Bohemia, 2007) Nekvasil, Richard; Neterda, ZdeněkShow more Mixing of media having different temperatures and velocities of separate streams often takes place in the industry. Being heated material of a pipe acquires no nuniform volume expansion as well as cyclic load, which causes pipeline lifetime decreasing. Damaged zones are to some degree dependant on the rates of mixed streams, which determine mixing process after thermo-hydraulic values are stabilized. These analyses will help to predict more effectively appearing of damaged zones.Show more Item Parametric studies in elastic stability of nonconservative beams(University of West Bohemia, 2007) Nánási, TiborShow more In this paper the nonconservative Beck`s column loaded with follower compressive force is generalized by introduction of the possibility to be subjected to subtangential follower force with excentric point of action. For corresponding boundary eigenvalue problem the frequency equation is derived. Results of parametric studies are presented for the lowest eigencurves, which describe the relation between the compressive load magnitude and the eigenfrequencies and indicate whether stability loss by divergence or by flutter occurs.Show more Item Parallel algorithm of trigonometric collocation method in nonlinear dynamics of rotors(University of West Bohemia, 2007) Musil, Tomáš; Jakl, OndřejShow more A parallel algorithm of a numeric procedure based on a method of trigonometric collocation is presented for investigating an unbalance response of a rotor supported by journal bearings. After a condensation process the trigonometric collocation method results in a set of nonlinear algebraic equations which is solved by the Newton-Raphson method. The order of the set is proportional to the number of nonlinear bearing coordinates and terms of the finite Fourier series. The algorithm, realized in the MATLAB parallel computing environment (DCT/DCE), uses message passing technique for interacting among processes on nodes of a parallel computer. This technique enables portability of the source code both on parallel computers with distributed and shared memory. Tests, made on a Beowulf cluster and a symmetric multiprocessor, have revealed very good speed-up and scalability of this algorithm.Show more