# Volume 6, number 1 (2012)

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Item Constitutive modelling of an arterial wall supported by microscopic measurements(University of West Bohemia, 2012) Vychytil, Jan; Kochová, Petra; Tonar, Zbyněk; Kuncová, Jitka; Švíglerová, JitkaShow more An idealized model of an arterial wall is proposed as a two-layer system. Distinct mechanical response of each layer is taken into account considering two types of strain energy functions in the hyperelasticity framework. The outer layer, considered as a fibre-reinforced composite, is modelled using the structural model of Holzapfel. The inner layer, on the other hand, is represented by a two-scale model mimicing smooth muscle tissue. For this model, material parameters such as shape, volume fraction and orientation of smooth muscle cells are determined using the microscopic measurements. The resulting model of an arterial ring is stretched axially and loaded with inner pressure to simulate the mechanical response of a porcine arterial segment during inflation and axial stretching. Good agreement of the model prediction with experimental data is promising for further progress.Show more Item Energy transformation and flow topology in an elbow draft tube(University of West Bohemia, 2012) Štefan, David; Rudolf, Pavel; Skoták, Aleš; Motyčák, LukášShow more Paper presents a computational study of energy transformation in two geometrical configurations of Kaplan turbine elbow draft tube. Pressure recovery, hydraulic efficiency and loss coefficient are evaluated for a series of flow rates and swirl numbers corresponding to operating regimes of the turbine. These integral characteristics are then correlated with local flow field properties identified by extraction of topological features. Main focus is to find the reasons for hydraulic efficiency drop of the elbow draft tube.Show more Item Design of a large deformable obstacle for railway crash simulations according to the applicable standard(University of West Bohemia, 2012) Špirk, Stanislav; Kemka, Vladislav; Kepka, Miloslav; Malkovský, ZdeněkShow more This article discusses the design of a deformable obstacle to be used in simulated rail and road vehicle collisions as prescribed by scenario 3 specified by standard ČSN EN 15227. To approve a vehicle in accordance with this standard, it is necessary to carry out numeric simulations of its collision with a large obstacle, following the standard’s specification. A simulated impact of a rigid ball into the obstacle is used to calibrate the obstacle’s properties, and the standard specifies limit deformation characteristics for that collision. The closer are the deformation characteristics observed in the test to the limit characteristics prescribed by the standard, the more favorable results can be expected when using the obstacle in actual numeric simulations of frontal impacts of rail vehicles. There are multiple ways to design a FEM model of the obstacle; this article discusses one of those. It shows that given a suitable definition of material properties, this particular approach yields quite favorable deformation characteristics.Show more Item Bending and free vibration analysis of thick isotropic plates by using exponential shear deformation theory(University of West Bohemia, 2012) Sayyad, Atteshamuddin Shamshuddin; Ghugal, Yuwaraj M.Show more This paper presents a variationally consistent an exponential shear deformation theory for the bi-directional bending and free vibration analysis of thick plates. The theory presented herein is built upon the classical plate theory. In this displacement-based, refined shear deformation theory, an exponential functions are used in terms of thickness co-ordinate to include the effect of transverse shear deformation and rotary inertia. The number of unknown displacement variables in the proposed theory are same as that in first order shear deformation theory. The transverse shear stress can be obtained directly from the constitutive relations satisfying the shear stress free surface conditions on the top and bottom surfaces of the plate, hence the theory does not require shear correction factor. Governing equations and boundary conditions of the theory are obtained using the dynamic version of principle of virtual work. The simply supported thick isotropic square and rectangular plates are considered for the detailed numerical studies. Results of displacements, stresses and frequencies are compared with those of other refined theories and exact theory to show the efficiency of proposed theory. Results obtained by using proposed theory are found to be agree well with the exact elasticity results. The objective of the paper is to investigate the bending and dynamic response of thick isotropic square and rectangular plates using an exponential shear deformation theory.Show more Item Periodically stimulated remodelling of a muscle fibre: perturbation analysis of a simple system of first-order ODEs(University of West Bohemia, 2012) Rosenberg, Josef; Byrtus, MiroslavShow more The paper deals with the dynamical analysis of the system of first-order ODE’s describing the isometric stimulation of the muscle fibre. This system is considered to be a non-autonomous one having the periodical excitation. For the analysis of dynamical behaviour the system the multiple scale method (MSM) is employed. The main goal of this contribution is to show the application of MSM to the non-autonomous dynamical system using the first order approximation of the solution. The existence of the degenerated Hopf’s bifurcation of the gained solution is presented.Show more Item Dynamic behavior of Jeffcott rotors with an arbitrary slant crack orientation on the shaft(University of West Bohemia, 2012) Ramezanpour, Reza; Ghayour, Mostafa; Ziaei-Rad, SaeedShow more Dynamic behaviour of a Jeffcott rotor system with a slant crack under arbitrary crack orientations is investigated. Using concepts of fracture mechanics, flexibility matrix and stiffness matrix of the system are calculated. The system equations motion is obtained in four directions, two transversal, one torsional and one longitudinal, and then solved using numerical method. In this paper a symmetric relation for global stiffness matrix is presented and proved; whereas there are some literatures that reported nonsymmetrical form for this matrix. The influence of crack orientations on the flexibility coefficients and the steady-state response of the system are also investigated. The results indicate that some of the flexibility coefficients are greatly varied by increasing the crack angle from 30◦ to 90◦ (transverse crack). It is also shown that some of the flexibility coefficients take their maximum values at (approximately) 60◦ crack orientation.Show more Item Springback analysis of thermoplastic composite plates(University of West Bohemia, 2012) Padovec, Zdeněk; Růžička, Milan; Stavrovský, VladimírShow more Residual stresses, which are set in the fiber reinforced composites during the laminate curing in a closed form, lead to dimensional changes of composites after extracting from the form and cooling. One of these dimensional changes is called “springback” of the angle sections. Other dimensional changes are warpage of flat sections of composite or displacement of single layers of composite for example. In our case four different lay-ups were analysed (three symmetrical and one unsymmetrical). An analytical model which covers temperature changes, chemical shrinkage during curing and moisture change was used. Also a FEM analysis was done for predicting the springback, and both calculations were compared with the measured data from manufacturer.Show more Item FEM simulation of the size and constraining effect in lead free solder joints(University of West Bohemia, 2012) Lederer, Martin; Khatibi, Golta; Weiss, BrigitteShow more Due to the ongoing miniaturization in microelectronics, the influence of dimensional constraining effects on the strength of solder joints becomes increasingly important. Detailed investigations show a strong dependence of tensile strength and ductility on solder geometry. This paper focuses on FEM simulations of the thickness effect of Sn-3.5Ag solder gaps under tensile load. Solder joints and copper base material are simulated with an elasto-plastic material model in the framework of von Mises plasticity. Within the solder material a pronounced triaxiality of stress is observed. In consequence, the von Mises stress inside the solder material is considerably smaller than the longitudinal stress along the tensile axis. This leads to increased tensile strength of thin solder joints. However, the increase of strength also depends on the yield stress of the copper base material. The FEM simulations were compared with experimental results of tensile tests and satisfactory coincidence was found. The remaining deviation between experiment and simulation is explained by pressure dependency of the flow stress. In conclusion, a new pressure dependent plasticity model is suggested.Show more Item Determination of Lamb wave dispersion curves by means of Fourier transform(University of West Bohemia, 2012) Hora, Petr; Červená, OlgaShow more This work reports on methods for determination of Lamb wave dispersion curves by means of Fourier transform (FT). Propagating Lamb waves are sinusoidal in both the frequency domain and the spatial domain. Therefore, the temporal FT may be carried out to go from the time to the frequency domain, and then the spatial FT may be carried out to go to the frequency–wave-number domain, where the amplitudes and the wave-numbers of individual modes may be measured. The result of this transform will be a 2D array of amplitudes at discrete frequencies and wave-numbers. Other method of determination of dispersion curves is based on the solution of FEM task in frequency domain. The frequency spectrum of a time-dependent excitation is defined using FT. Since a small number of frequencies are sufficient to achieve a correct representation of a wide variety of temporal excitations, this approach considerably speeds up the computation by avoiding the temporal FT and by decreasing the number of calculation steps.Show more Item Investigation of the effect of controllable dampers on limit states of rotor systems(University of West Bohemia, 2012) Zapomněl, Jaroslav; Ferfecki, Petr; Liberdová, JanaShow more The unbalance and time varying loading are the principal sources of lateral vibrations of rotors and of increase of forces transmitted through the coupling elements into the stationary part. These oscillations and force effects can be considerably reduced if damping devices are added to the coupling elements placed between the rotor and its casing. The theoretical studies and practical experience show that to achieve their optimum performance their damping effect must be controllable. This article focuses on investigation of influence of controlled damping in the rotor supports on its limit state of deformation, fatigue failure and on magnitude of the forces transmitted into the stationary part. The analysed system is a flexible rotor with one disc driven by an electric DC motor and loaded by the disc unbalance and by technological forces depending on the rotor angular position. In the computational model the system vibration is governed by a set of nonlinear differential equations of the first and second orders. To evaluate the fatigue failure both the flexural and torsional oscillations are taken into account. The analysis is aimed at searching for the intervals of angular speeds, at which the rotor can be operated without exceeding the limit states.Show more