References of "Kerschen, Gaëtan"
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See detailIdentifying Triggering Mechanisms and Suppressing Aeroelastic Instabilities by Passive Targeted Energy Transfers: Nonlinear System Identification, Modal Interactions and Resonance Captures
Lee, Young S; Vakakis, Alexander F.; McFarland, D. M. et al

in 44th Aeroelasticity and Fluid/Structure Interaction Symposium, College Station, 2007 (2007)

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See detailNonlinear MDOF System Characterization and Identification using the Hilbert- Huang Transform: Experimental Demonstration
Kerschen, Gaëtan ULg; Vakakis, Alexander F.; Lee, Young.S et al

in 25th International Modal Analysis Conference, Orlando, 2007 (2007)

The Hilbert transform is one of the most successful approaches to tracking the varying nature of vibration of a large class of nonlinear systems, thanks to the extraction of backbone curves from ... [more ▼]

The Hilbert transform is one of the most successful approaches to tracking the varying nature of vibration of a large class of nonlinear systems, thanks to the extraction of backbone curves from experimental data. Because signals with multiple frequency components do not admit a well-behaved Hilbert transform, this transform is inherently limited to the analysis of single-degree-of-freedom systems; this shortcoming is potentially overcome by the Hilbert-Huang transform (HHT). In this study, the joint application of the complexification-averaging method and the HHT enables us to develop a new technique, the slow-flow model identification method. Through an experimental application, we demonstrate that the proposed method is adequate for characterizing and identifying multi-degreeof-freedom nonlinear systems. [less ▲]

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See detailSuppression of limit cycle oscillations with a nonlineart energy sink: theoretical basis
Lee, Young S.; Vakakis, Alexander F.; McFarland, D. Michael et al

in 47th AIAA Structural Dynamics and Materials Conference, Newport, 2006 (2006, May)

Limit cycle oscillations (LCOs) commonly require restrictions on the operation of high- performance aircraft and have the potential to cause structural damage or failure. This paper summarizes recent ... [more ▼]

Limit cycle oscillations (LCOs) commonly require restrictions on the operation of high- performance aircraft and have the potential to cause structural damage or failure. This paper summarizes recent theoretical findings on the application of passive and targeted nonlinear energy transfer (\nonlinear energy pumping") for the reduction or elimination of LCOs in self-excited systems. This NES has been used successfully to suppress LCOs of an elastically mounted, rigid airfoil in flow. The theoretical results are in agreement with experimental studies of a practical airfoil with an attached NES. These experimental results, presented in full in a separate paper, verify the capacity of the NES to reduce or even eliminate these undesired oscillations and to extend the operating speed range of the wing. [less ▲]

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See detailPast, present and future of nonlinear system identification in structural dynamics
Kerschen, Gaëtan ULg; Worden, Keith; Vakakis, Alexander F. et al

in Mechanical Systems & Signal Processing (2006), 20(3), 505-592

This survey paper contains a review of the past and recent developments in system identification of nonlinear dynamical structures. The objective is to present some of the popular approaches that have ... [more ▼]

This survey paper contains a review of the past and recent developments in system identification of nonlinear dynamical structures. The objective is to present some of the popular approaches that have been proposed in the technical literature, to illustrate them using numerical and experimental applications, to highlight their assets and limitations and to identify future directions in this research area. The fundamental differences between linear and nonlinear oscillations are also detailed in a tutorial. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailExperimental demonstration of transient resonance capture in a system of two coupled oscillators with essential stiffness nonlinearity
Kerschen, Gaëtan ULg; McFarland, D. Michael; Kowtko, Jeffrey J. et al

in Journal of Sound & Vibration (2006), 299(4-5), 822-838

The purpose of this paper is to report an experimental study of transient resonance capture that may occur in a system of two coupled oscillators with essential (i.e., nonlinearizable) nonlinearity. It is ... [more ▼]

The purpose of this paper is to report an experimental study of transient resonance capture that may occur in a system of two coupled oscillators with essential (i.e., nonlinearizable) nonlinearity. It is shown that during transient resonance capture the two oscillators are in a state of resonance, the frequency of which varies with time, which leads to targeted nonlinear energy transfer. Further evidence of resonance capture is a non-time-like behavior of the phase difference between the oscillators; this quantity is monitored using the Hilbert transform or the Huang Hilbert transform in the case of multifrequency response signals. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

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See detailSuppression of limit cycle oscillations with a nonlinear energy sink: experimental results
Hill, W. Joel; Strganac, Thomas W.; Lee, Young S. et al

in 47th AIAA Structural Dynamics and Materials Conference, Newport, 2006 (2006)

The presence of limit cycle oscillations within the flight envelopes of existing aircraft is well documented. Future air vehicle designs are also likely to encounter limit cycle oscillations under certain ... [more ▼]

The presence of limit cycle oscillations within the flight envelopes of existing aircraft is well documented. Future air vehicle designs are also likely to encounter limit cycle oscillations under certain loading conditions. These steady-state constant amplitude oscillations are detrimental to mission effectiveness and lead to increased fatigue of aircraft structures. Previous efforts to suppress limit cycle oscillations have focused primarily on active control methods. These efforts have been effective but require significant measurement and control resources. In this study the investigators test a passive method for suppressing limit cycle behavior. A nonlinear energy sink, based on the principle of nonlinear energy pumping, is shown to be effective for increasing the stability threshold of a nonlinear two degree of freedom aeroelastic system. [less ▲]

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See detailToward a fundamental understanding of the HHT in nonlinear structural dynamics
Kerschen, Gaëtan ULg; Vakakis, Alexander F.; Lee, Y. S. et al

in 24th International Modal Analysis Conference, Saint-Louis, 2006 (2006)

The Hilbert-Huang transform (HHT) has been shown to be effective for characterizing a wide range of nonstationary signals in terms of elemental components through what has been called the empirical mode ... [more ▼]

The Hilbert-Huang transform (HHT) has been shown to be effective for characterizing a wide range of nonstationary signals in terms of elemental components through what has been called the empirical mode decomposition. The HHT has been utilized extensively despite the absence of a serious analytical foundation, as it provides a concise basis for the analysis of strongly nonlinear systems. In this paper, we attempt to provide the missing link, showing the relationship between the EMD and the slow-flow equations of the system. The slow-flow model is established by performing a partition between slow and fast dynamics using the complexification-averaging technique, and a dynamical system described by slowly-varying amplitudes and phases is obtained. These variables can also be extracted directly from the experimental measurements using the Hilbert transform coupled with the EMD. The comparison between the experimental and analytical results forms the basis of a nonlinear system identification method, termed the slow-flow model identification method, which is demonstrated using numerical examples. [less ▲]

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See detailIrreversible passive energy transfer in coupled oscillators with essential nonlinearity
Kerschen, Gaëtan ULg; Lee, Young Sup; Vakakis, Alexander F. et al

in SIAM Journal on Applied Mathematics (2006), 66(2), 648-679

We study numerically and analytically the dynamics of passive energy transfer from a damped linear oscillator to an essentially nonlinear end attachment. This transfer is caused by either fundamental or ... [more ▼]

We study numerically and analytically the dynamics of passive energy transfer from a damped linear oscillator to an essentially nonlinear end attachment. This transfer is caused by either fundamental or subharmonic resonance capture, and in some cases is initiated by nonlinear beat phenomena. It is shown that, due to the essential nonlinearity, the end attachment is capable of passively absorbing broadband energy at both high and low frequencies, acting, in essence, as a passive broadband boundary controller. Complicated transitions in the damped dynamics can be interpreted based on the topological structure and bifurcations of the periodic solutions of the underlying undamped system. Moreover, complex resonance capture cascades are numerically encountered when we increase the number of degrees of freedom of the system. The ungrounded essentially nonlinear end attachment discussed in this work can find application in numerous practical settings, including vibration and shock isolation of structures, seismic isolation,. utter suppression, and packaging. [less ▲]

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See detailNonlinear MDOF system characterization and identi cation using the Hilbert-Huang transform
Kerschen, Gaëtan ULg; Vakakis, Alexander F.; Lee, Young.S et al

in International Conference on Noise and Vibration Engineering, Leuven, 2006 (2006)

The Hilbert transform is one of the most successful approaches to tracking the varying nature of vibration of a large class of nonlinear systems thanks to the extraction of backbone curves from ... [more ▼]

The Hilbert transform is one of the most successful approaches to tracking the varying nature of vibration of a large class of nonlinear systems thanks to the extraction of backbone curves from experimental data. Because signals with multiple frequency components do not admit a well-behaved Hilbert transform, it is inherently limited to the analysis of single-degree-of-freedom systems. In this study, the joint application of the complexification-averaging method and the empirical mode decomposition enables us to develop a new technique, the slow-flow model identification method. Through numerical and experimental applications, we demonstrate that the proposed method is adequate for characterizing and identifying multi-degree-offreedom nonlinear systems. [less ▲]

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See detailDevelopment of Numerical Algorithms for Practical Computation of Nonlinear Normal Modes
Peeters, Maxime ULg; Georgiades, Fotios; Viguié, Régis ULg et al

in International Conference on Noise and vibration Engineering, Leuven, 2006 (2006)

When resorting to numerical algorithms, we show that nonlinear normal mode (NNM) computation is possible with limited implementation effort, which paves the way to a practical method for determining the ... [more ▼]

When resorting to numerical algorithms, we show that nonlinear normal mode (NNM) computation is possible with limited implementation effort, which paves the way to a practical method for determining the NNMs of nonlinear mechanical systems. The proposed method relies on two main techniques, namely a shooting procedure and a method for the continuation of NNM motions. In addition, sensitivity analysis is used to reduce the computational burden of the algorithm. A simplified discrete model of a nonlinear bladed disk is considered to demonstrate the developments. [less ▲]

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See detailNonlinear energy pumping: a new paradigm for vibration mitigation
Kerschen, Gaëtan ULg; Lee, Young-Sup; McFarland, D. M. et al

in 7ème congrès national de Mécanique Th. et App., Mons, 2006 (2006)

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See detailEnergy Transition from a Linear Oscillator to an Attached Mass through an Essential Nonlinearity
Quinn, D. Dane; Kerschen, Gaëtan ULg; Vakakis, Alexander F. et al

in 11th Nonlinear Vib., Stability and Dynamics of Structures Conf., Blacksburg, 2006 (2006)

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See detailExperimental modal analysis using blind source separation techniques
Poncelet, Fabien ULg; Kerschen, Gaëtan ULg; Golinval, Jean-Claude ULg

in International Conference on Noise and Vibration Engineering, Leuven, 2006 (2006)

Recently, statistical and empirical signal processing techniques such as the proper orthogonal decomposition and the Hilbert-Huang transform have shown promise for structural system identification. In the ... [more ▼]

Recently, statistical and empirical signal processing techniques such as the proper orthogonal decomposition and the Hilbert-Huang transform have shown promise for structural system identification. In the present study, experimental modal analysis is carried out by employing blind source separation techniques and by interpreting the response of a mechanical system as a static mixture of sources. Specifically, it is shown under which circumstances the normal coordinates of the vibration modes may be interpreted as virtual sources. The advantages and limitations of the proposed method will be discussed, and the procedure will be demonstrated using numerical applications. [less ▲]

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See detailTHEORETICAL AND EXPERIMENTAL STUDY OF MULTIMODAL TARGETED ENERGY TRANSFER IN A SYSTEM OF COUPLED OSCILLATORS
Kerschen, Gaëtan ULg; Kowtko, J. J.; McFarland, D. M. et al

in 2nd International Conf. on NNMs and Localization in Vibrating Systems, Samos, 2006 (2006)

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See detailAn Overview of Targeted Energy Transfer Phenomena in Coupled Oscillators: Theoretical and Experimental Results and System Identification
Lee, Young S.; Kerschen, Gaëtan ULg; McFarland, D. M. et al

in 11th Nonlinear Vib., Stability and Dynamics of Structures Conf., Blacksburg, 2006 (2006)

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See detailTARGETED ENERGY TRANSFERS AND SUPPRESSION OF AEROELASTIC INSTABILITIES
Lee, Young S; Vakakis, Alexander F.; Bergman, Lawrence A. et al

in 2nd International Conf. on NNMs and Localization in Vibrating Systems, Samos, 2006 (2006)

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See detailPARTICIPATION OF UNDERGRADUATE STUDENTS TO THE SOLAR PANELS DESIGN OF THE EDUCATIONAL SPACECRAFT ESEO
Bolland, M.; Collignon, G.; Vandenplas, X. et al

Conference (2006)

The objective of this presentation is to discuss the participation of students at the University of Liège to the educational spacecraft project SSETI-ESEO proposed by the European Space Agency.

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See detailTriggering mechanisms of limit cycle oscillations due to aeroelastic instability
Lee, Y. S.; Vakakis, Alexander F.; Bergman, Lawrence A. et al

in Journal of Fluids & Structures (2005), 21

We show that a cascade of resonance captures constitutes the triggering mechanism of limit cycle oscillations (LCOs) due to aeroelastic instability of rigid wings in flow. We consider a two-degree-of ... [more ▼]

We show that a cascade of resonance captures constitutes the triggering mechanism of limit cycle oscillations (LCOs) due to aeroelastic instability of rigid wings in flow. We consider a two-degree-of-freedom (2-dof) wing model in subsonic flow with cubic nonlinear stiffnesses at the support. Under the assumption of quasi-steady aerodynamics, we apply a complexification/averaging technique to express the dynamics of fluid-structure interactions in terms of three fast-frequency components; these are the two linear natural frequencies corresponding to heave and pitch, and a superharmonic at three times the pitch frequency. Bifurcation analysis of the resulting set of modulation equations governing the slow dynamics is carried out via the method of numerical continuation, and reveals the different types of steady state motions realized as parameters vary. It turns out that the LCO triggering mechanism consists of a combination of different dynamic phenomena, taking place at three main stages or regimes: attraction to transient resonance captures (TRCs), escapes from these captures and, finally, entrapments into permanent resonance captures (PRCs). We examine numerically and analytically the dynamics at each of these stages by means of wavelet transform analysis, study of the evolution of appropriately defined phase variables in projections of the phase space of the dynamics, and analysis of instantaneous energy exchanges between the various nonlinear modes involved. The general conclusion is that an initial excitation of the heave mode by the flow acts as the triggering mechanism for the excitation of the pitch mode through nonlinear interactions resulting from the resonance captures and escapes. The eventual excitation of the pitch mode signifies the appearance of an LCO of the in-flow wing. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailEnergy transfers in a system of two coupled oscillators with essential nonlinearity: 1 : 1 resonance manifold and transient bridging orbits
Kerschen, Gaëtan ULg; Vakakis, Alexander F.; Lee, Young S. et al

in Nonlinear Dynamics (2005), 42(3), 283-303

The purpose of this study is to highlight and explain the vigorous energy transfers that may take place in a linear oscillator weakly coupled to an essentially nonlinear attachment, termed a nonlinear ... [more ▼]

The purpose of this study is to highlight and explain the vigorous energy transfers that may take place in a linear oscillator weakly coupled to an essentially nonlinear attachment, termed a nonlinear energy sink. Although these energy exchanges are encountered during the transient dynamics of the damped system, it is shown that the dynamics can be interpreted mainly in terms of the periodic orbits of the underlying Hamiltonian system. To this end, a frequency-energy plot gathering the periodic orbits of the system is constructed which demonstrates that, thanks to a 1:1 resonance capture, energy can be irreversibly and almost completely transferred from the linear oscillator to the nonlinear attachment. Furthermore, it is observed that this nonlinear energy pumping is triggered by the excitation of transient bridging orbits compatible with the nonlinear attachment being initially at rest, a common feature in most practical applications. A parametric study of the energy exchanges is also performed to understand the influence of the parameters of the nonlinear energy sink. Finally, the results of experimental measurements supporting the theoretical developments are discussed. [less ▲]

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