Volume 8, number 1 (2014)
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Item Dry friction damping couple at high frequencies(University of West Bohemia, 2014) Půst, Ladislav; Pešek, Luděk; Košina, Jan; Radolfová, AlenaThe contribution deals with the application of dry friction couples for noise and vibration damping at high fre- quency of several kHz what brings new problems connected with the small amplitudes of relative slipping motion of contact surfaces. The most important information from the experimental results is knowledge that the value of evaluated friction coefficient can have different physical sense according to the magnitude of excitation force and to the frequency of applied vibrations. If amplitudes of motion are very small, then the external harmonic force produces only elastic micro-deformations of contacting bodies, where no slip occurs and then the traction contact force is proportional only to elastic deformation of the sample.
Item Application of the Monte Carlo method for investigation of dynamical parameters of rotors supported by magnetorheological squeeze film damping devices(University of West Bohemia, 2014) Zapoměl, Jaroslav; Ferfecki, Petr; Kozánek, JanA flexible suspension with damping devices is an efficient technological tool for reducing forces transmitted be- tween the rotor and its frame. To achieve optimum performance of the damping elements, their damping effect must be adaptable to the current operating conditions. In practical rotordynamic applications this is offered by magnetorheological squeeze film dampers. Some of parameters, which determine behaviour of rotors, may have uncertain character. Then a probabilistic approach is needed for analysis of such systems. In this paper there is investigated the vibration amplitude of a rigid rotor damped by two magnetorheological squeeze film dampers and magnitude of the force transmitted to the stationary part during the steady state operating regime. The uncertain parameters of the studied system are the rotor unbalance and speed of its rotation. The Monte Carlo method was employed for this analysis.Item Double pendulum contact problem(University of West Bohemia, 2014) Špička, Jan; Hynčík, Luděk; Hajžman, MichalThe work concerns contact problems focused on biomechanical systems modelled by a multibody approach. The example is modelling of impact between a body and an infrastructure. The paper firstly presents algorithm for minimum distance calculation. An analytical approach using a tangential plain perpendicular to an initial one is applied. Contact force generated during impact is compared by three different continuous force models, namely the Hertz’s model, the spring-dashpot model and the non-linear damping model. In order to identify contact parameters of these particular models, the method of numerical optimization is used. Purpose of this method is to find the most corresponding results of numerical simulation to the original experiment. Numerical optimization principle is put upon a bouncing ball example for the purpose of evaluation of desirable contact force parameters. The contact modelling is applied to a double pendulum problem. The equation of motion of the double pendulum system is derived using Lagrange equation of the second kind with multipliers, respecting the contact phenomena. Applications in biomechanical research are hinted at arm gravity motion and a double pendulum impact example.Item Development of aerodynamic bearing support for application in air cycle machines(University of West Bohemia, 2014) Šimek, Jiří; Lindovský, P.Air cycle machines (ACM) are used in environmental control system of aircrafts to manage pressurization of the cabin. The aim of this work is to gain theoretical and experimental data enabling replacement of rolling bearings, which require lubrication and have limited operating speed, with aerodynamic bearing support. Aerodynamic bearings do not pollute process air and at the same time allow achieving higher operating speed, thus enabling to reduce machine mass and dimensions. A test stand enabling the verification of aerodynamic bearing support properties for prospective ACM was designed, manufactured and tested with operating speeds up to 65 000 rpm. Some interesting features of the test stand design and the test results are presented. A smaller test stand with operating speed up to 100 000 rpm is in design stage.Item Influence of the mass of the weight on the dynamic response of the asymmetric laboratory fibre-driven mechanical system(University of West Bohemia, 2014) Polach, Pavel; Hajžman, Michal; Šika, Zbyněk; Červená, Olga; Svatoš, PetrExperimental measurements focused on the investigation of a fibre behaviour are performed on an assembled weigh-fibre-pulley-drive mechanical system. The fibre is driven with one drive and it is led over a pulley. On its other end there is a prism-shaped steel weight, which moves in a prismatic linkage on an inclined plane. The position of the weight is asymmetric with respect to the vertical plane of drive-pulley symmetry. Drive exciting signals can be of a rectangular, a trapezoidal and a quasi-sinusoidal shape and there is a possibility of variation of a signal rate. Dynamic responses of the weight and the fibre are measured. The same system is numerically investigated by means of a multibody model. The influence of the mass of the weight and the influence of the weight asymmetry on the coincidence of results of experimental measurements and the simulations results are evaluated. The simulations aim is to create a phenomenological model of a fibre, which will be utilizable in fibre modelling in the case of more complicated mechanical or mechatronic systems.Item Using the Neumann series expansion for assembling Reduced Order Models(University of West Bohemia, 2014) Nasisi, Salvatore; Valášek, Michael; Vampola, TomášAn efficient method to remove the limitation in selecting the master degrees of freedom in a finite element model by means of a model order reduction is presented. A ma jor difficulty of the Guyan reduction and IRS method (Improved Reduced System) is represented by the need of appropriately select the master and slave degrees of freedom for the rate of convergence to be high. This study approaches the above limitation by using a particular arrangement of the rows and columns of the assembled matrices K and M and employing a combination between the IRS method and a variant of the analytical selection of masters presented in (Shah, V. N., Raymund, M., Analytical selection of masters for the reduced eigenvalue problem, International Journal for Numerical Methods in Engineering 18 (1) 1982) in case first lowest frequencies had to be sought. One of the most significant characteristics of the approach is the use of the Neumann series expansion that motivates this particular arrangement of the matrices’ entries. The method shows a higher rate of convergence when compared to the standard IRS and very accurate results for the lowest reduced frequencies. To show the effectiveness of the proposed method two testing structures and the human vocal tract model employed in (Vampola, T., Horacek, J., Svec, J. G., FE modeling of human vocal tract acoustics. Part I: Prodution of Czech vowels, Acta Acustica United with Acustica 94 (3) 2008) are presented.Item Optimization methodology for beam gauges of the bus body for weight reduction(University of West Bohemia, 2014) Jain, Richa; Tandon, Punnet; Vasantha Kumar, MahadevappaDuring service, a bus is subjected to various loads that cause stresses, vibrations and noise in the different components of its structure. It requires appropriate strength, stiffness and fatigue properties of the components to be able to stand these loads. Besides, quality and optimum weight of the vehicle, for efficient energy consumption, safety and provision of the comfort to the user are highly desired. The present work proposes a methodology to minimize the bus weight by modifying its beam gauges to optimum thickness. The bus performance is evaluated by multiple iterations on the basis of parameters like frequency, distortion, stress and stiffness. The algorithm performs gauge optimization of the bus by analyzing and satisfying its structural strength through linear static analysis on a laden bus. It also performs structural stiffness analysis and vibration analysis for safety of the bus structure. This work unfolds an integrated methodology to the bus manufacturers to optimize the structural weight for improving the fuel efficiency, static and dynamic safety, and robust design. The work is implemented by creating a finite element model of the bus and optimizing in HyperWorks environment. The results are verified for a full length 11 m, 65 seats bus. The methodology helps in weight reduction along with improvement in performance parameters.Item Seismic response of nuclear fuel assembly(University of West Bohemia, 2014) Hlaváč, Zdeněk; Zeman, VladimírThe paper deals with mathematical modelling and computer simulation of the seismic response of fuel assembly components. The seismic response is investigated by numerical integration method in time domain. The seismic excitation is given by two horizontal and one vertical synthetic accelerograms at the level of the pressure vessel seating. Dynamic response of the hexagonal type nuclear fuel assembly is caused by spatial motion of the support plates in the reactor core investigated on the reactor global model. The modal synthesis method with condensation is used for calculation of the fuel assembly component displacements and speeds on the level of the spacer grid cells.Item A numerical study of planar discharge motion(University of West Bohemia, 2014) Benkhaldoun, Fayssal; Fořt, Jaroslav; Hassouni, Khaled; Karel, Jan; Trdlička, DavidPresented paper describes a numerical study of discharge plasma motion. This non-stationary phenomenon with steep gradients and sharp peaks in unknowns is described as a coupled problem of convection-diffusion equation with source term for electron, ion densities and Poisson’s equation for electric potential. The numerical method is 2nd order of accuracy in space and time and it uses dynamical adaptation of unstructured triangular mesh. Results of numerical studies included size of computational domain, type of boundary conditions and numerical convergence test are presented.Item Thermal analysis of both ventilated and full disc brake rotors with frictional heat generation(University of West Bohemia, 2014) Belhocine, Ali; Cho, Chong Du; Nouby, Mahdy; Yi, Yun Bo; Abu Bakar, Abd RahimIn automotive engineering, the safety aspect has been considered as a number one priority in development of a new vehicle. Each single system has been studied and developed in order to meet safety requirements. Instead of having air bags, good suspension systems, good handling and safe cornering, one of the most critical systems in a vehicle is the brake system. The objective of this work is to investigate and analyze the temperature distribution of rotor disc during braking operation using ANSYS Multiphysics. The work uses the finite element analysis techniques to predict the temperature distribution on the full and ventilated brake discs and to identify the critical temperature of the rotor. The analysis also gives us the heat flux distribution for the two discs.
