Volume 5, number 2 (2011)
Permanent URI for this collection
Browse
Recent Submissions
Item Stress analysis of finite length cylinders of layered media(University of West Bohemia, 2011) Desai, Payal; Kant, TaruntIn this paper, we analyze an orthotropic, layered (0/90) and (0/core/0) sandwich cylinders under pressurized load with a diaphragm supported boundary conditions which is considered as a two dimensional (2D) plane strain boundary value problem of elasticity in (r, z) direction. A simplified numerical cum analytical approach is used for the analysis. Boundary conditions are satisfied exactly by using an analytical expression in longitudinal (z) direction in terms of Fourier series expansion. Resulting first order simultaneous ordinary differential equations (ODEs) with boundary conditions prescribed at r = ri, ro defines a two point boundary value problem (BVP), whose equations are integrated in radial direction through an effective numerical integration technique by first transforming the BVP into a set of initial value problems (IVPs). Numerical solutions are first validated for their accuracy with 1D solution of an infinitely long cylinder. Stresses and displacements in cylinders of finite lengths having various l/R and h/R ratios are presented for future reference.
Item Car impact to pedestrian - fast 2D numerical analysis(University of West Bohemia, 2011) Hynčík, Luděk; Čechová, HanaThe paper concerns a modelling approach for fast 2D car to pedestrian impact analysis. The pedestrian model is composed using the Lagrange equations with multipliers. The model consists of rigid bodies defining the major human body segments. The bodies are connected by rotational joints with non-linear response. The model is scalable based on the age and the gender. The car model is multi-segment composed as an open polygon. Between the pedestrian and the car, there are contacts defined and modelled explicitly by force-penetration dependence. For a given car profile design and a given human gender, age and percentile, the pedestrian impact consequences can be evaluated quickly by means of virtual numerical analysis.Item A time stepping method in analysis of nonlinear structural dynamics(University of West Bohemia, 2011) Gholampour, Ali Akbar; Ghassemieh, Mehdi; Razavi, HadiIn this paper a new method is proposed for the direct time integration method for structural dynamics problems. The proposed method assumes second order variations of the acceleration at each time step. Therefore more terms in the Taylor series expansion were used compared to other methods. Because of the increase in order of variations of acceleration, this method has higher accuracy than classical methods. The displacement function is a polynomial with five constants and they are calculated using: two equations for initial conditions (from the end of previous time step), two equations for satisfying the equilibrium at both ends of the time step, and one equation for the weighted residual integration. Proposed method has higher stability and order of accuracy than the other methods. c 2011 University of West Bohemia. All rights reserved.Item Contact of screw surfaces with displaced axes(University of West Bohemia, 2011) Machulda, Vladimír; Švígler, JaromírA couple of conjugate screw surfaces, which create a three-member mechanism with a higher kinematic pair, constitutes an important part of mechanical systems. One of these surfaces is created as an envelope of the second surface. In an ideal arrangement surface axes are parallel and the contact between both surfaces is curvilinear. After displacement of the surface axes, which is induced in technical equipments by force and heat loading, the original parallel arrangement of the surface axes is changed into an incorrect, spatial or alternatively parallel displaced, position. Consequently the original curvilinear contact changes into a contact at a point. This change is significant from the view of contact analysis. Determination of the contact point of conjugate surfaces, which are in the incorrect position, based on the kinematic way is presented in this contribution.Item Biomechanical study of the bone tissue with dental implants interaction(University of West Bohemia, 2011) Marcián, Petr; Borák, Libor; Florian, Zdeněk; Bartáková, Sonia; Konečný, Ondřej; Navrátil, PetrThe article deals with the stress-strain analysis of human mandible in the physiological state and after the dental implant application. The evaluation is focused on assessing of the cancellous bone tissue modeling-level. Three cancellous bone model-types are assessed: Non-trabecular model with homogenous isotropic material, nontrabecular model with inhomogeneous material obtained from computer tomography data using CT Data Analysis software, and trabecular model built from mandible section image. Computational modeling was chosen as the most suitable solution method and the solution on two-dimensional level was carried out. The results show that strain is more preferable value than stress in case of evaluation of mechanical response in cancellous bone. The non-trabecular model with CT-obtained material model is not acceptable for stress-strain analysis of the cancellous bone for singularities occurring on interfaces of regions with different values of modulus of elasticity.Item Reduction of lateral forces between the railway vehicle and the track in small-radius curves by means of active elements(University of West Bohemia, 2011) Michálek, Tomáš; Zelenka, JaromírThis paper deals with a possibility of reduction of guiding forces magnitude in small-radius curves by means of active elements. These guiding forces characterize the lateral force interaction between the rail vehicle and the track and influence the wear of wheels and rails in curves. Their magnitudes are assessed in the framework of vehicle authorization process. However, in case of new railway vehicles with axleload of approximately 20 t and more it is problematic to meet the condition of maximum value of the quasistatic guiding force which acts on the outer wheel of the 1st wheelset in small-radius curves. One of the possible ways how to reduce these forces is using the system of active yaw dampers. By means of computer simulations of guiding behaviour of a new electric locomotive, comparison of reached values of the quasistatic guiding forces in case of locomotive equipped with active yaw dampers and without them was performed. Influences of magnitude of force generated by the active yaw dampers, friction coefficient in wheel/rail contact and curve radius were analysed in this work, as well.Item A design influence on the mechanical compliance and fracture resistance of railway wheel(University of West Bohemia, 2011) Navrátil, Petr; Janíček, Přemysl; Brabenec, Ladislav; Matug, Michal; Marcián, PetrA fracture mechanics approach is used to determinate crack behaviour in a railway wheel which is working under different operating conditions with consideration of different types of railway wheel discs. Reliability of the railway wheel is related to a material failure. This paper is focused on failure of the material which is connected with violation consistency of the wheel material. The fracture mechanic approach is applied with consideration of influence of mechanical compliance. The topology optimization is used to define the shape of one disc type. Obtained results show fracture behaviour and the mechanical compliance of used railway wheel discs. From these results, comparison of separated railway wheel discs is obtained.Item Vibration of imperfect rotating disk(University of West Bohemia, 2011) Půst, Ladislav; Pešek, LuděkThis study is concerned with the theoretical and numerical calculations of the flexural vibrations of a bladed disk. The main focus of this study is to elaborate the basic background for diagnostic and identification methods for ascertaining the main properties of the real structure or an experimental model of turbine disks. The reduction of undesirable vibrations of blades is proposed by using damping heads, which on the experimental model of turbine disk are applied only on a limited number of blades. This partial setting of damping heads introduces imperfection in mass, stiffness and damping distribution on the periphery and leads to more complicated dynamic properties than those of a perfect disk. Calculation of FEM model and analytic—numerical solution of disk behaviour in the limited (two modes) frequency range shows the splitting of resonance with an increasing speed of disk rotation. The spectrum of resonance is twice denser than that of a perfect disk.Item Comparison of various refined beam theories for the bending and free vibration analysis of thick beams(University of West Bohemia, 2011) Sayyad, Atteshamuddin ShamshuddinIn this paper, unified shear deformation theory is used to analyze simply supported thick isotropic beams for the transverse displacement, axial bending stress, transverse shear stress and natural frequencies. This theory enables the selection of different in-plane displacement components to represent shear deformation effect. The numbers of unknowns are same as that of first order shear deformation theory. The governing differential equations and boundary conditions are obtained by using the principle of virtual work. The results of displacement, stresses, natural bending and thickness shear mode frequencies for simply supported thick isotropic beams are presented and discussed critically with those of exact solution and other higher order theories. The study shows that, while the transverse displacement and the axial stress are best predicted by the models 1 through 5 whereas models 1 and 2 are overpredicts the transverse shear stress. The model 4 predicts the exact dynamic shear correction factor (π2/12 = 0.822) whereas model 1 overpredicts the same.Item Adaptive calibration method with on-line growing complexity(University of West Bohemia, 2011) Skopec, Tomáš; Šika, ZbyněkThis paper describes a modified variant of a kinematical calibration algorithm. In the beginning, a brief review of the calibration algorithm and its simple modification are described. As the described calibration modification uses some ideas used by the Lolimot algorithm, the algorithm is described and explained. Main topic of this paper is a description of a synthesis of the Lolimot-based calibration that leads to an adaptive algorithm with an on-line growing complexity. The paper contains a comparison of simple examples results and a discussion. A note about future research topics is also included.Item Possibility of identification of elastic properties in laminate beams with cross-ply laminae stacking sequences(University of West Bohemia, 2011) Zajíček, Martin; Dupal, JanThe goal of this work is to show the possibility of the identification of laminate beam specimens elastic properties with cross-ply laminae stacking sequences using prescribed eigenfrequencies. These frequencies are not determined experimentally in this paper but they are calculated numerically by means of the finite element (FE) software MSC.Marc. The composite material properties of the FE model based on Euler-Bernoulli theory have been subsequently tuned to correlate the determined frequencies in cross-ply laminate beams with the eigenfrequencies obtained by the software package. A real-coded genetic algorithm (GA) and a micro-genetic algorithm (μGA) are applied as the inverse technique for the identification problem. Because a small efficiency of the GAs in searching for Poisson’s ratio values was found, this parameter and the in-plane shear modulus have been estimated by using the law of mixtures. Some numerical examples are given to illustrate the proposed technique.Item Modelling and modal properties of nuclear fuel assembly(University of West Bohemia, 2011) Zeman, Vladimír; Hlaváč, ZdeněkThe paper deals with the modelling and modal analysis of the hexagonal type nuclear fuel assembly. This very complicated mechanical system is created from the many beam type components shaped into spacer grids. The cyclic and central symmetry of the fuel rod package and load-bearing skeleton is advantageous for the fuel assembly decomposition into six identical revolved fuel rod segments, centre tube and skeleton linked by several spacer grids in horizontal planes. The derived mathematical model is used for the modal analysis of the Russian TVSA-T fuel assembly and validated in terms of experimentally determined natural frequencies, modes and static deformations caused by lateral force and torsional couple of forces. The presented model is the first necessary step for modelling of the nuclear fuel assembly vibration caused by different sources of excitation during the nuclear reactor VVER type operation.
