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Szabo Z.,Budapest University of Technology and Economics | Stepan G.,Budapest University of Technology and Economics | Zelei A.,HAS BUTE Research Group on Dynamics of Machines and Vehicles
21st International Congress on Sound and Vibration 2014, ICSV 2014 | Year: 2014

Flutter instability is a typical aerodynamic vibration phenomenon of slender elastic bridges. The sensitivity for flutter can be predicted by determining the so-called nutter derivatives from the small-scale model of the bridge. This work investigates an elastic supported two d.o.f. bridge section model which can move vertically and rotate around a horizontal axis. These movements correspond to the bending and torsional vibrations of the bridge. The linearised equations of motion is assumed to be known, thus, the aerodynamic forces can be determined from wind-tunnel experiments. These forces are assumed as linear functions of the generalised coordinates and their time-derivatives. The coefficients of the linear terms called also as flutter derivatives depend on the flow (wind) velocity. These coefficients are to be determined by the Monte Carlo method using the measured acceleration data. The obtained results are compared to the results determined by curve-fitting on the acceleration time-signal. The original (structural) damping and stiffness matrices can be modified by using the flutter derivatives since the equations of motion form a homogeneous linear differential equation system. Thus, we get effective damping and stiffness matrices. Flutter instability occurs when a harmonic solution satisfies the equations. The critical flow velocity which the system loses its stability at is also compared to the stability boundary of the analytical model based on Theodorsen's approach. Source

Bachrathy D.,HAS BUTE Research Group on Dynamics of Machines and Vehicles | Stepan G.,Budapest University of Technology and Economics
Periodica Polytechnica, Mechanical Engineering | Year: 2012

Several engineering applications need a robust method to find all the roots of a set of nonlinear equations automatically. The proposed method guarantees monotonous convergence, and it can determine whole submanifolds of the roots if the number of unknowns is larger than the number of equations. The critical steps of the multidimensional bisection method are described and possible solutions are proposed. An efficient computational scheme is introduced. The efficiency of the method is characterized by the box-counting fractal dimension of the evaluated points. The multidimensional bisection method is much more efficient than the brute force method. The proposed method can also be used to determine the fractal dimension of the submanifold of the solutions with satisfactory accuracy. © Periodica Polytechnica 2012. Source

Palmai Z.,Budapest University of Technology and Economics | Csernak G.,HAS BUTE Research Group on Dynamics of Machines and Vehicles
Journal of Sound and Vibration | Year: 2013

Built-up edge (BUE) is the accumulation of the cut material on the rake face that is close to the tip of the cutting tool. As the BUE periodically develops and breaks off, the thickness of the cut layer changes, which leads to poor surface quality. We developed a thermo-mechanical model for the description of the chip formation during turning that takes into account the variation of the depth of the cut. The model comprises a set of delay-differential equations; thus, the phase-space of the system has an infinite dimension. The formation of the BUE provides an excitation for the cutting dynamics. According to our experimental and numerical investigations, the resulting vibrations can be chaotic. To prove the occurrence of chaos, we determined the largest Lyapunov exponent using two different methods. © 2012 Elsevier Ltd. All rights reserved. Source

Beda P.B.,HAS BUTE Research Group on Dynamics of Machines and Vehicles
Materials Science Forum | Year: 2010

There are several self-sustained oscillatory phenomena observed at plastic deformation of metals. One of them happens at the beginning of plastic behavior and leads to appearance of the famous Lüders-Hartmann bands. However, it can also be found self-sustained oscillations well beyond the yield stress like Portevin and Le Chatelier did in the early 20th century. This paper presents a simple model of that by using continuum approach and the theory of dynamical systems. © (2010) Trans Tech Publications. Source

Licsko G.,Budapest University of Technology and Economics | Csernak G.,HAS BUTE Research Group on Dynamics of Machines and Vehicles
Mathematics and Computers in Simulation | Year: 2014

In this paper we investigate an early and yet simple model used for the analysis of mechanical systems incorporating Coulomb-type friction. We show an interesting non-smooth bifurcation of the crossing-sliding type that causes symmetry breaking. In its simplicity it was not obvious for a long time to find chaos in the simple one degree-of-freedom sliding block model with dry-friction. With the introduction of static coefficient of friction besides the dynamic one we found chaotic bands over a wide range of parameters. In this work we also highlight the possibility of transient chaos for a narrow range of parameters. © 2013 IMACS. Source

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