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Ilmar Santos - One of the best experts on this subject based on the ideXlab platform.

  • vibration control of a Flexible Rotor suspended by shape memory alloy wires
    Journal of Intelligent Material Systems and Structures, 2018
    Co-Authors: Marco Tulio Santana Alves, Valder Steffen, Marina Castro Santos, Marcelo A Savi, Soren Enemark, Ilmar Santos
    Abstract:

    The present contribution is devoted to the study of the influence of shape memory alloys on the dynamic behavior of Flexible Rotors. In this sense, a suspension composed by pseudoelastic shape memo...

  • lateral vibration control of a Flexible overcritical Rotor via an active gas bearing theoretical and experimental comparisons
    Journal of Sound and Vibration, 2016
    Co-Authors: Fabian G Pierart, Ilmar Santos
    Abstract:

    Abstract The lack of damping of radial gas bearings leads to high vibration levels of a Rotor supported by this type of bearing when crossing resonant areas. This is even more relevant for Flexible Rotors, as studied in this work. In order to reduce these high vibration levels, an active gas bearing is proposed. The control action of this active bearing is selected based on two different strategies: a simple proportional integral derivative controller and an optimal controller. Both controllers are designed based on a theoretical model previously presented. The dynamics of the Flexible Rotor are modelled aided by the finite element method and the Rotor–fluid interaction in the gas bearing is included using the solution of a modified version of the Reynolds equation for compressible fluids, taking into account the piezoelectrically controlled jet action. Performance and accuracy of both model-based controllers are compared against experimental results, showing good agreement. Theoretical and experimental results show a significant increase in the damping ratio of the system, enabling the Flexible Rotor to run safely across the critical speeds and up to 12,000 rev/min, i.e. 50 percent over the second critical speed without any instability problems.

  • adjustable hybrid gas bearing influence of piezoelectrically adjusted injection on damping factors and natural frequencies of a Flexible Rotor operating under critical speeds
    Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, 2016
    Co-Authors: Fabian G Pierart, Ilmar Santos
    Abstract:

    Damping factors and natural frequencies of a Flexible Rotor supported by a gas bearing with piezoelectrically adjusted flow, are theoretically determined using a Rotor finite element model coupled with the modified Reynolds equation. An extra term is added to the standard formulation of Reynolds equation aiming at incorporating the effect of the adjustable external pressurized inlet flow. Two different configurations are theoretically as well as experimentally studied: (a) the air is injected from a single orifice positioned at the bottom of the bearing and (b) the air is injected through four radial injectors equally pressurized. For the two configurations, the theoretical results are experimentally validated as a function of the piezoactuators input voltage and the journal angular velocity. Results show a good agreement for natural frequencies and damping factors. Theoretical and experimental results show qualitatively as well as quantitatively that the injectors position and the injection flow (depende...

Chengchi Wang - One of the best experts on this subject based on the ideXlab platform.

  • bifurcation and nonlinear analysis of a Flexible Rotor supported by a relative short spherical gas bearing system
    Communications in Nonlinear Science and Numerical Simulation, 2010
    Co-Authors: Chengchi Wang
    Abstract:

    Abstract This paper employs a hybrid numerical method combining the differential transformation method and the finite difference method to study the bifurcation and nonlinear dynamic behavior of a Flexible Rotor supported by a relative short spherical gas bearing (RSSGB) system. The analytical results reveal a complex dynamic behavior comprising periodic, sub-harmonic, quasi-periodic, and chaotic responses of the Rotor center and the journal center. Furthermore, the results reveal the changes which take place in the dynamic behavior of the bearing system as the Rotor mass and bearing number are increased. The current analytical results are found to be in good agreement with those of other numerical methods. Therefore, the proposed method provides an effective means of gaining insights into the nonlinear dynamics of RSSGB systems.

  • application of a hybrid method to the nonlinear dynamic analysis of a Flexible Rotor supported by a spherical gas lubricated bearing system
    Nonlinear Analysis-theory Methods & Applications, 2009
    Co-Authors: Chengchi Wang
    Abstract:

    Abstract This paper employs a hybrid numerical method combining the differential transformation method and the finite difference method to study the nonlinear dynamic behavior of a Flexible Rotor supported by a spherical gas-lubricated bearing system. The analytical results reveal a complex dynamic behavior comprising periodic, sub-harmonic, and quasi-periodic responses of the Rotor center and the journal center. Furthermore, the results reveal the changes which take place in the dynamic behavior of the bearing system as the Rotor mass and bearing number are increased. The current analytical results are found to be in good agreement with those from other numerical methods. Therefore, the proposed method provides an effective means of gaining insights into the nonlinear dynamics of spherical gas film Rotor–bearing systems.

  • theoretical and nonlinear behavior analysis of a Flexible Rotor supported by a relative short herringbone grooved gas journal bearing system
    Physica D: Nonlinear Phenomena, 2008
    Co-Authors: Chengchi Wang
    Abstract:

    Abstract This paper considers the bifurcation and nonlinear behavior of a Flexible Rotor supported by a relative short herringbone-grooved gas journal bearing system. A numerical method is employed to a time-dependent mathematical model. A finite difference method with successive over relation method is employed to solve the Reynolds’ equation. The system state trajectory, Poincare maps, power spectra, and bifurcation diagrams are used to analyze the dynamic behavior of the Rotor and journal centers in the horizontal and vertical directions under different operating conditions. The analysis reveals a complex dynamic behavior comprising periodic and quasi-periodic response of the Rotor and journal centers. It further shown the dynamic behavior of this type of system varies with changes in bearing number and Rotor mass. The results of this study contribute to a better understanding of the nonlinear dynamics of herringbone-grooved gas journal bearing systems.

  • bifurcation and nonlinear dynamic analysis of a Flexible Rotor supported by relative short gas journal bearings
    Chaos Solitons & Fractals, 2007
    Co-Authors: Chengchi Wang, Ming-jyi Jang, Yenliang Yeh
    Abstract:

    This paper studies the bifurcation and nonlinear behaviors of a Flexible Rotor supported by relative short gas film bearings. A time-dependent mathematical model for gas journal bearings is presented. The finite difference method with successive over relation method is employed to solve the Reynolds’ equation. The system state trajectory, Poincare maps, power spectra, and bifurcation diagrams are used to analyze the dynamic behavior of the Rotor and journal center in the horizontal and vertical directions under different operating conditions. The analysis reveals a complex dynamic behavior comprising periodic and subharmonic response of the Rotor and journal center. This paper shows how the dynamic behavior of this type of system varies with changes in Rotor mass and rotational velocity. The results of this study contribute to a further understanding of the nonlinear dynamics of gas film Rotor-bearing systems.

  • theoretical analysis of the non linear behavior of a Flexible Rotor supported by herringbone grooved gas journal bearings
    Tribology International, 2007
    Co-Authors: Chengchi Wang, Ming-jyi Jang, Herterng Yau, Yenliang Yeh
    Abstract:

    This paper studies the behavior of a Flexible Rotor supported by a herringbone-grooved gas journal-bearing system. A hybrid method is employed to develop a time-dependent mathematical model of the bearing system. The finite difference method is employed with the successive over relaxation technique to solve the Reynolds equation. The system state trajectories, Poincare maps, power spectra, and bifurcation diagrams are used to analyze the dynamic behavior of the Rotor and the journal center in the horizontal and vertical directions under different operating conditions. The analysis reveals a complex dynamic behavior comprising periodic and quasi-periodic responses of the Rotor and the journal center. The present numerical study illustrates the relationship between the dynamic behavior of this type of system and the Rotor mass and bearing number. As such, the present results provide a deeper understanding of the non-linear dynamics of gas film Rotor-bearing systems.

L. J. Mclean - One of the best experts on this subject based on the ideXlab platform.

  • Stability and Bifurcation of Unbalanced Response of a Squeeze Film Damped Flexible Rotor
    Journal of Tribology, 1994
    Co-Authors: J. Y. Zhao, I. W. Linnett, L. J. Mclean
    Abstract:

    The stability and bifurcation of the unbalance response of a squeeze film damper-mounted Flexible Rotor are investigated based on the assumption of an incompressible lubricant together with the short bearing approximation and the “π” film cavitation model. The unbalanced Rotor response is determined by the trigonometric collocation method and the stability of these solutions is then investigated using the Floquet transition matrix method. Numerical examples are given for both concentric and eccentric damper operations. Jump phenomenon, subharmonic, and quasi-periodic vibrations are predicted for a range of bearing and unbalance parameters. The predicted jump phenomenon, subharmonic and quasi-periodic vibrations are further examined by using a numerical integration scheme to predict damper trajectories, calculate Poincare maps and power spectra. It is concluded that the introduction of unpressurized squeeze film dampers may promote undesirable nonsynchronous vibrations.

Nenad Mihajlovic - One of the best experts on this subject based on the ideXlab platform.

  • interaction between torsional and lateral vibrations in Flexible Rotor systems with discontinuous friction
    Nonlinear Dynamics, 2007
    Co-Authors: Nenad Mihajlovic, Van De N Nathan Wouw, Pcjn Nick Rosielle, Henk Nijmeijer
    Abstract:

    In this paper, we analyze the interaction between friction-induced vibrations and self-sustained lateral vibrations caused by a mass-unbalance in an experimental Rotor dynamic setup. This study is performed on the level of both numerical and experimental bifurcation analyses. Numerical analyses show that two types of torsional vibrations can appear: friction-induced torsional vibrations and torsional vibrations due to the coupling between torsional and lateral dynamics in the system. Moreover, both the numerical and experimental results show that a higher level of mass-unbalance, which generally increases the lateral vibrations, can have a stabilizing effect on the torsional dynamics, i.e. friction-induced limit cycling can disappear. Both types of analysis provide insight in the fundamental mechanisms causing self-sustained oscillations in Rotor systems with flexibility, mass-unbalance and discontinuous friction which support the design of such Flexible Rotor systems.

  • Friction-induced limit cycling in Flexible Rotor systems: An experimental drill-string set-up
    Nonlinear Dynamics, 2006
    Co-Authors: Nenad Mihajlovic, N. Wouw, M. P. M. Hendriks, Henk Nijmeijer
    Abstract:

    Friction-induced limit cycling deteriorates system performance in a wide variety of mechanical systems. In this paper, we study the way in which essential friction characteristics affect the occurrence and nature of friction-induced limit cycling in an experimental drill-string set-up. This study is performed on the level of a Lyapunov-based stability analysis and on the level of both numerical and experimental bifurcation analyses. The synthesis of these results confirms that friction-induced limit cycling is due to a subtle balance between negative damping at lower velocities and viscous friction at higher velocities. Moreover, it is shown how these essential friction characteristics depend on physical conditions such as temperature and normal forces in the frictional contact in the experimental set-up.

  • Friction-Induced Limit Cycling in Flexible Rotor Systems: An Experimental Drill-String System
    Volume 1: 20th Biennial Conference on Mechanical Vibration and Noise Parts A B and C, 2005
    Co-Authors: N. Van De Wouw, H Henk Nijmeijer, Nenad Mihajlovic
    Abstract:

    Friction-induced limit cycling deteriorates system performance in a wide variety of mechanical systems. In this paper, we study the way in which essential friction characteristics affect the occurrence and nature of friction-induced limit cycling in Flexible Rotor systems. This study is performed on the level of both numerical and experimental bifurcation analyses. Hereto, an experimental drill-string set-up is used. The synthesis of these numerical and experimental results confirms that friction-induced limit cycling is due to a subtle balance between a velocity weakening characteristic of the friction (Stribeck effect) at lower velocities and viscous friction at higher velocities. Moreover, it is shown how these essential friction characteristics depend on physical conditions such as temperature and normal forces in the frictional contact in the experimental set-up.Copyright © 2005 by ASME

  • torsional and lateral vibrations in Flexible Rotor systems with friction
    2005
    Co-Authors: Nenad Mihajlovic
    Abstract:

    Self-sustained vibrations which can appear in mechanical systems often limit the performance of such systems or can even cause failure or damage to such systems. Moreover, different types of vibration can appear in dynamical systems. In order to gain an improved understanding and to predict different types of vibrations which appear in mechanical systems, it is important to understand the causes for such vibrations and the interaction between those vibrations. In this thesis, we address on the one hand friction-induced vibrations in flex- ible mechanical systems, and on the other hand lateral vibrations caused by mass- unbalance in Rotor systems, and the interaction between those two types of vibrations. Although a lot of theoretical research has been done on vibrations in Flexible Rotor systems, a limited number of papers is available which include experimental results on the friction-induced vibrations and on the interaction between different types of vibrations. For this purpose, we have designed and constructed an experimental drill-string set-up which exhibits both types of vibration. The set-up consists of a DC-motor, two rotating (upper and lower) discs, a low-stiffness string, which connects the two discs, and an additional brake at the lower disc. The lower disc can rotate around its geometric center and is also free to move in lateral direction. The configuration of the experimental set-up is representative for many other mechanical systems, in which friction or unbalance can deteriorate the system performance by the appearance of vibrations. For example, when the lower disc is fixed in lateral direction (i.e. when the lower disc only rotates), the system forms a configuration of two masses, coupled by a flexibility, of which one is subject to friction and the other is driven by an actuator. In this context, one can think of set-ups such as printers, pick and place machines, industrial and domestic robots, braking mechanisms and many others. Moreover, when mass-unbalance is present at the lower disc and the disc can move in lateral direction, this configuration can be recognized in drilling systems which are used for exploration of oil and gas, in electrical shavers, in various turbines, pumps, fans and so on. The drill-string set-up is modelled and the parameters of the model are estimated. The comparison between responses of the experimental set-up and estimated model indicates a high accuracy of the obtained parameter estimates. The steady-state behaviour of the drill-string system has been analyzed when various constant input voltages are applied to the DC motor; first, when only torsional and no lateral vi- brations occur and, second, when both torsional and lateral vibrations appear in the system. When analyzing the friction-induced vibrations a discontinuous static friction model is used. We have chosen such a model and not a more complicated dynamical friction model since it accounts for the friction characteristics which are crucial for the global dynamics of the system but avoids unnecessary complexity. A discontin- uous friction model leads to a discontinuous model of the system dynamics which exhibits both friction-induced vibrations and the interaction between friction-induced vibrations and vibrations due to mass-unbalance. As a result of the analysis on a theoretical, numerical and experimental level the following conclusions are drawn. When analyzing the set-up with only friction-induced torsional vibrations and no lateral vibrations, the main conclusion is that a subtle interplay of negative damping characteristics at low velocities and viscous friction at higher velocities determines the occurrence and nature of friction-induced limit cycling. It also determines the range of parameters for which these limit cycles sustain. Furthermore, the level of posi- tive damping at very low velocities relative to the negative damping level at slightly higher velocities determines whether torsional vibrations with or without stick-slip can occur. Then, both model-based and experimental bifurcation analysis confirm that discontinuous bifurcations play a crucial role in the creation and disappearance of these limit cycles. Also, the way in which such friction characteristics are influ- enced by physical conditions such as temperature and normal forces on the frictional contact is experimentally studied. An important observation is that the normal force in the frictional contact influences the friction force in a rather complex way and can induce a higher negative damping level (for larger normal forces), which in turn can give rise to limit cycles of a larger amplitude for a larger range of constant input voltages to the DC motor. The analysis of the set-up, when both torsional and lateral vibrations are present, leads to the main conclusion that two types of torsional vibrations can appear. Firstly, friction-induced torsional vibrations and, secondly, torsional vibrations due to cou- pling between torsional and lateral dynamics may appear. Furthermore, if mass- unbalance is present at the lower disc, the amplitude of friction-induced vibrations and the region in which these vibrations occur, both decrease compared to the situ- ation without mass-unbalance. Moreover, it is shown that if the mass-unbalance is large enough then torsional vibrations can disappear entirely. Next, on a simulation level it is shown that torsional vibrations due to coupling between torsional and lateral modes appear for input voltages to the DC motor which are higher than the so-called critical voltage, which is related to the critical angular velocity inducing resonance in lateral direction. Due to limitations in the available DC motor, those vibrations are studied only at a simulation level. Finally, the knowledge obtained in this thesis provides a better understanding of the causes for torsional and lateral vibrations. Moreover, based on this knowledge, various control strategies may be designed and tested on the designed set-up in or- der to eliminate torsional and lateral vibrations. Furthermore, the results presented here can support the design of various braking mechanisms, pumps and fans in pre- venting the occurrence of or in decreasing the amplitude of friction-induced torsional vibrations and lateral vibrations due to mass-unbalance.

Marco Tulio Santana Alves - One of the best experts on this subject based on the ideXlab platform.