Volume 2, number 2 (2008)
Permanent URI for this collection
Browse
Recent Submissions
Item Dynamical properties of the growing continuum using multiple-scale method(University of West Bohemia, 2008) Rosenberg, Josef; Hynčík, LuděkThe theory of growth and remodeling is applied to the 1D continuum. This can be mentioned e.g. as a model of the muscle fibre or piezo-electric stack. Hyperelastic material described by free energy potential suggested by Fung is used whereas the change of stiffness is taken into account. Corresponding equations define the dynamical system with two degrees of freedom. Its stability and the properties of bifurcations are studied using multiple-scale method. There are shown the conditions under which the degenerated Hopf’s bifurcation is occuring.
Item Impact injury prediction by FE human body model(University of West Bohemia, 2008) Číhalová, Lenka; Hynčík, LuděkThe biomechanical simulations as powerful instruments are used in many areas such as traffic, medicine, sport, army etc. The simulations are often performed with models, which are based on the Finite Element Method. The great ability of FE deformable models of human bodies is to predict the injuries during accidents. Due to its modular implementation of thorax and abdomen FE models, human articulated rigid body model ROBBY, which was previously developed at the University of West Bohemia in cooperation with ESI Group (Engineering Simulation for Industry), can be used for this purpose. ROBBY model representing average adult man is still being improved to obtain more precise model of human body with the possibility to predict injuries during accidents. Recently, new generated thoracic model was embedded into ROBBY model and this was subsequently satisfactorily validated. In this study the updated ROBBY model was used and injury of head and thorax were investigated during frontal crashes simulated by virtue of two types of sled tests with various types of restraint system (shoulder belt, lap belt and airbag). The results of the simulation were compared with the experimental ones.Item Thermo-mechanical transient analysis of concrete structure around the nuclear reactor(University of West Bohemia, 2008) Žmindák, Milan; Novák, Pavol; Nozdrovický, JurajThis paper deals with transient thermal — stress analysis of concrete structure around the nuclear reactor loaded by dead load and thermal loads. The FEM simulations were performed for various input materials characteristic of concrete based on experimentally obtained physical-mechanical properties and measuring of temperatures. The proposed calculation model, procedures of numerical simulation have been describing conclusions of analysis. The numerical simulation has been performed by means of the finite element method (FEM) using a commercially available ANSYS code.Item Linear elastic analysis of thin laminated beams with uniform and symmetric cross-section(University of West Bohemia, 2008) Zajíček, MartinThis paper deals with analyses of linear elastic thin beams which are consisted of the homogeneous orthotropic layers. The cross-sections of these beams are assumed uniform and symmetric. Governing equations of onedimensional model are derived on the base of the Timoshenko’s beam theory. An evaluation of shear correction factor consists in conservation of the shear strain energy. This factor is calculated in this paper but only in the cases of the static problem. The general static solution for the flexural and axial displacement and for the slope of the cross-section is found. Further, the possibility of calculation of the free vibrations of beams are also presented. The obtained results for the static solution are compared with the results of numerical solution based on the finite element method. The numerical model is prepared in software package MARC. As a tested example is used the uniformly loaded simply supported beam with various cross-sections.Item Numerical models for evaluation thermal conductivity of coatings(University of West Bohemia, 2008) Šroub, Jan; Honner, Milan; Švantner, MichalThis paper is dealing with simulation and model development for the evaluation of thermal conductivity of coatings by the Laser Quasistatic Thermography (LQT) method. The main principles of the measurement method are introduced and the process of thermal conductivity evaluation based on numerical simulation is presented. The evaluation requires special procedure to simulate thermal process induced by laser pulse in coating on some substrate. The thickness of the coating is manifold less than the thickness of the substrate and total sample surface. In numerical system Cosmos/M there are created two suitable models: “Shell-Clink-Solid” model and model based on physical similarity. In this paper there are also described characteristics of both models and their comparison with classical axisymmetric and volume models.Item Active integral vibration control of elastic bodies(University of West Bohemia, 2008) Smrž, Martin; Valášek, MichaelThis paper deals with the design and analysis of active integral vibration control of elastic beam using piezoactuator. The concept of integral control means that multiple distributed piezoapatches are controlled using one integral feedback signal. This concept has been verified by simulations. However, it was detected that the dual concept of integral sensing, i.e. to integrate the signals from multiple piezopatches as sensors, fails in the case of position feedback due to the mutual interaction of piezopatches as sensors and actuators.Item Tracking optimization for propagation of electromagnetic waves for multiple wavelengths(University of West Bohemia, 2008) Seifrt, František; Leugering, Günter; Rohan, EduardThe purpose of our work is to design dielectric composite structures with specific qualities. In this paper we construct interfaces of given material components such that the originated structure attains desired properties. Propagation of the electromagnetic waves in the composite is described by the Helmholtz equation. Quality of the structure for a given set of wavelengths is enumerated by the tracking functionals that are to be minimized. Interfaces of the given materials are parametrized by the cubic B-spline curves. The design variables are afterwards the positions of B-spline control points. For cost functional evaluation one forward computation of the Helmholtz equation for each wavelength is needed. To get the sensitivity of the objective function we solve the backward (adjoint) equation. Several numerical simulations are presented. Finally three different designs are discussed.Item Numerical simulations of pipeline bending tests(University of West Bohemia, 2008) Rojíček, Jaroslav; Halama, RadimThe paper compares numerical solution with results of experimental solution of pipeline under cyclic loading in elastoplastic domain. The pipeline was subjected to internal pressure and bending moment. Firstly material parameters were estimated (for Besseling model, Chaboche model and Modified AbdelKarim-Ohno model) on the basis of uniaxial loading. The possibility of parameter identification of assumed models using multiaxial tests was tested too. FE program ANSYS was used for all computations. Modified AbdelKarim-Ohno model was implemented by writing own user subrutin in FORTRAN language. Chaboche model usually overpredicts ratcheting under multiaxial stress state in confrontation with experiments, when it is calibrated by uniaxial tests only. Modified AbdelKarim-Ohnomodelmakes possible better calibration for both uniaxial and multiaxial loading cases.Item Nonlinear vibrations and stability of aerostatic bearing(University of West Bohemia, 2008) Půst, Ladislav; Kozánek, JanBearings based on aerostatic principle belong to the new machine elements advantageous for low- and high-speed applications, but their dynamic and stability properties are not yet sufficiently known. This paper presents a new elaborated method and gained results of theoretical investigation of dynamic properties of aerostatic bearing in general dimensionless form. It is aimed also as a supporting tool for diagnostic and identification methods used at developing of new bearings proposed by TECHLAB, Prague for industrial applications. Mathematical model expresses nonlinear and evolutive properties in the entire area of bearing clearance, contains sufficient number of free parameters in functions of restoring and damping forces and can therefore describe all types of motions occurring in gas bearings as periodic, quasi-periodic, including beats and instability, which can leads to chaotic and self-excited vibrations. The influence of non-diagonal elements of stiffness and dampingmatrices of linearized model on the spectral properties and the stability of system is investigated, too.Item The influence of the excitation pulse shape on the stress wave propagation in a bcc iron crystal(University of West Bohemia, 2008) Pelikán, Vladimír; Hora, Petr; Machová, Anna; Červená, OlgaThis article presents a large-scale molecular dynamic simulations of wave propagation in a cracked bcc (body centered cubic) iron crystal based on an N-body potential model which gives a good description of an anisotropic elasticity. The crystal is loaded by a stress pulse on its front face and the response is detected on its opposite face. The various shapes, amplitudes, and widths of stress pulse are considered. The simulations are performed also for a central pre-existing Griffith crack. The crack is embedded in a bcc iron crystal having a basic cubic orientation. The acquired results bring important information for further analysis oriented to new NDT nanoscale methods.Item Computability limits within the scope of computational mechanics(University of West Bohemia, 2008) Okrouhlík, MiloslavThe contribution deals with limits of computational mechanics as they unreel from those of physics, instrumental limits of computers and experimental instruments. It is shown that, more than on the above limits, our ability to predict the behavior of investigated phenomena depends on validity of models being employed. Author ponders about limits of applicability of continuum model as well as about limits of finite element approaches when applied to approximate solutions of fast transient tasks in solid continuum mechanics.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 Mechanical behavior of fabric-reinforced elastomer straight flexible hoses(University of West Bohemia, 2008) Manach, Pierre YvesThis paper presents a model applicable to large strain analysis of composite materials such as flexible hoses. A three-dimensional constitutive law, which uses the concept of convected coordinate frame, is developed for materials presenting non linear elastic and linear orthotropic behaviors in the large deformation field. The proposed model is implemented in a finite element home code and the formulation of both the hyperelastic and the orthotropic constitutive laws is presented. Finally, in order to validate our numerical results, an experimental device is developed to exhibit the mechanical behavior of straight flexible hoses in the case of elementary tests. The model is then compared to these experimental results.Item The influence of loading direction on micro-crack behaviour in polymer composite(University of West Bohemia, 2008) Majer, Zdeněk; Hutař, Pavel; Náhlík, Luboš; Knésl, ZdeněkIn this paper polymeric particulate composites are studied. Especially on polypropylene (PP) matrix and mineral fillers was focused. Polymeric particulate composites are frequently used in many engineering applications. The composite was modeled as a three-phase continuum — matrix, interphase and particle. The properties of the particles and interphase (size, shape, material properties) have a significant effect on the global behaviour of the composite. On the basis of fracture mechanics methodology the interaction of micro-crack propagation in the matrix filled by rigid particles covered by the interphase was analyzed. Effect of the loading direction on mechanical properties of polymeric particulate composites is studied here.Item Mean velocity profiles in a boundary layer under the joint action of surface roughness and external turbulent flow(University of West Bohemia, 2008) Jonáš, PavelThis paper considers the knowledge of the individual action and joint action of surface roughness and external flow turbulence on the mean flow in boundary layer. The experimental evidence of this problem has been reviewed. A lack of results has been ascertain of the investigation on the joint action of the mentioned influences on the development of a boundary layer from the state with laminar flow up to a turbulent boundary layer. The knowledge on the actions of individual effects has been gathered with the regard to the improvement of the evaluation and analysis of the mean flow characteristics of the zero pressure gradient boundary layer developing under the joint action of the uniform roughness of the surface and homogeneous, close to isotropy, free stream turbulence.Item Stiffness reconstruction of 3D frame by reduced redundant measurements(University of West Bohemia, 2008) Gráf, Stanislav; Vampola, Tomáš; Valášek, MichaelThe paper describes the way how the recently publishedmethod of redundant measurements is suitable for reducing the number of measured parameters. The developedmethod enables to determine the deformation and the stiffness of a truss that is equipped with redundant measurements during varying loading which is partially measured. The paper is focus on ability to help to provide better comfort during measurements.Item Vehicle lateral dynamics stabilization using active suspension(University of West Bohemia, 2008) Drobný, Vladislav; Valášek, MichaelThe paper deals with the investigation of active nonlinear suspension control in order to stabilize the lateral vehicle motion in similar way as systems like ESP do. The lateral stabilization of vehicle based on braking forces can be alternatively provided by the different setting of suspension forces. The basis of this control is the nonlinear property of the tyres. The vehicle has at least four wheels and it gives one or more redundant vertical forces that can be used for the different distribution of vertical suspension forces in such a way that resulting lateral and/or longitudinal forces create the required correction moment for lateral dynamic vehicle stabilization.Item NI LabView - Matlab SimMechanics Stewart platform design(University of West Bohemia, 2008) Březina, Lukáš; Andrš, Ondřej; Březina, TomášThe article deals with approach of using NI Labview and Matlab SimMechanics for the designing of Stewart platform model of dynamics and its control. Matlab SimMechanics was used as a tool for the multi body dynamics modeling of the mechanism. The advantage of working within this computational environment is the possibility of the model linearization at a specified operating point and receiving linear state space model. Another benefit is the option of designing of the machine control and also the control simulations may be performed in the same environment. On the other hand NI LabView seems to be better for the real-time control implementation because of the possibility of real-time computer communication and possibility of FPGA chipset direct configuration. NI LabView has also ability to work with Matlab commands, thus possibility of Matlabmodels importing. Advantages of using both of environments are presented on the example of Stewart platform. The presented approach is quite complex and seems to be suitable for a dynamics modeling and a control designing of mechatronic systems.Item Input shaping control with reentry commands of prescribed duration(University of West Bohemia, 2008) Beneš, Petr; Valášek, MichaelControl of flexible mechanical structures often deals with the problem of unwanted vibration. The input shaping is a feedforwardmethod based on modification of the input signal so that the output performs the demanded behaviour. The presented approach is based on a finite-time Laplace transform. It leads to no-vibration control signal without any limitations on its time duration because it is not strictly connected to the system resonant frequency. This idea used for synthesis of control input is extended to design of dynamical shaper with reentry property that transform an arbitrary input signal to the signal that cause no vibration. All these theoretical tasks are supported by the results of simulation experiments.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.
