References of "Kerschen, Gaëtan"
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See detailBLIND SOURCE SEPARATION TECHNIQUES FOR MODAL ANALYSIS: EXPERIMENTAL DEMONSTRATION
Poncelet, Fabien ULg; Kerschen, Gaëtan ULg; Golinval, Jean-Claude ULg et al

in International Conference on Engineering Dynamics, Carvoeiro, 2007 (2007)

The present study carries out output-only modal analysis using two blind source separation (BSS) techniques, namely independent component analysis and second-order based identification. It is shown under ... [more ▼]

The present study carries out output-only modal analysis using two blind source separation (BSS) techniques, namely independent component analysis and second-order based identification. It is shown under which circumstances the normal coordinates of the vibration modes may be interpreted as virtual sources, which renders the application of these BSS techniques possible. To support the theoretical findings, numerical experiments are first carried out using a discrete system of three masses. Secondly the method is applied to a real-life structure which is a blade extracted from a turbojet engine stator. The results are compared with the stochastic subspace identification method. [less ▲]

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See detailBlind source separation techniques - Another way of doing operational modal analysis
Poncelet, Fabien ULg; Kerschen, Gaëtan ULg; Golinval, Jean-Claude ULg et al

in International Operational Modal Analysis Conference, Copenhague, 2007 (2007)

In many practical applications, it is difficult or even impossible to measure the force applied to a structure. This is especially the case in civil engineering applications. Therefore, this paper ... [more ▼]

In many practical applications, it is difficult or even impossible to measure the force applied to a structure. This is especially the case in civil engineering applications. Therefore, this paper proposes to explore the utility of blind source separation (BSS) techniques for operational modal analysis. The basic idea of BSS is to recover unobserved source signals from their observed mixtures. The feasibility and practicality of the proposed method are demonstrated using an experimental application. [less ▲]

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See detailLEODIUM project and student space activities at the University of Liege
Vandenrijt, Jean-François ULg; Rochus, Pierre ULg; Kerschen, Gaëtan ULg et al

Conference (2007)

the origin of the LEODIUM project which stands for Low Earth Orbit Demonstration of Innovations in University Mode. This project aims to create student pico- or nano-satellites. There is a strong ... [more ▼]

the origin of the LEODIUM project which stands for Low Earth Orbit Demonstration of Innovations in University Mode. This project aims to create student pico- or nano-satellites. There is a strong motivation coming from the students and from the academic members to promote space. Being unexperienced in complete satellite design, as a first step in this direction, we started working with the ESA funded SSETI association. At the moment, two teams of students are working on SSETI satellites. One is working as the MECH team which is in charge of the design of the sun-pointing solar panels of the European Student Earth Orbiter (ESEO) satellite mechanisms, the other team is working on the phase-A studies of the Narrow Angle Camera (NAC) which will be the core payload of the European Student Moon Orbiter (ESMO) satellite, both in collaboration with local industrials. The students are mainly working on ESEO and ESMO as part of their master thesis. In addition to that, two PhD students are in charge of the coordination of the teams (one for the ESEO team and another for the ESMO team). They will also be the link between previous and new students every times an overlap will occur and ensure that information is not lost during the transition. In this paper, we will describe the current design and the achievements on the ESEO solar panels and the ESMO NAC camera. Explanation will also be given on how the collaboration between the local student and the SSETI association is managed. Finally, we will briefly introduce the prospective for the LEODIUM project. [less ▲]

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See detailPractical Computation of Nonlinear Normal Modes Using Numerical Continuation Techniques
Peeters, Maxime ULg; Viguié, Régis ULg; Kerschen, Gaëtan ULg et al

in International Workshop: Advancements in Design Optimization of Materials, Structures and Mechanical Systems, Xi'An, 2007 (2007)

The concept of nonlinear normal modes (NNMs) is considered in the present paper. One reason of the still limited use of NNMs in structural dynamics is that their computation is often regarded as ... [more ▼]

The concept of nonlinear normal modes (NNMs) is considered in the present paper. One reason of the still limited use of NNMs in structural dynamics is that their computation is often regarded as impractical. However, when resorting to numerical algorithms, we show that the 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 algorithm relies on two main techniques, namely a shooting procedure and a method for the continuation of NNM motions. The algorithm is demonstrated using two different mechanical systems, a nonlinear two-degree-of-freedom system and a nonlinear cantilever beam discretized by the finite element method. [less ▲]

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See detailPARTICIPATION OF ULG STUDENTS TO THE SSETI MICROSATELLITE PROGRAMME USING SAMCEF
Bolland, M.; COLLIGNON, G.; VANDENPLAS, X. et al

Conference (2007)

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. SSETI ... [more ▼]

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. SSETI students are now mainly involved in the ESEO satellite for which the University of Liège is in charge of the MECH work package. The students have to propose a design for the structure of the solar panels (including the geometry and materials) and their deployment and pointing mechanisms (including electrical circuits, motors, hinges and actuators). Through detailed finite element computations in the SAMCEF software, they have to verify the structural integrity of the panels during the launch phase and to guarantee a safe deployment once on-orbit. Another task is to ensure an appropriate orientation of the solar panels to collect the maximum power from the sun. An industrial partner specialized in the development of computer-aided engineering solutions, SAMTECH, and a research center, Liège Space Center (CSL), also bring their expertise to the project. [less ▲]

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See detailPASSIVE SUPPRESSION OF AEROELASTIC INSTABILITIES OF IN-FLOW WINGS BY TARGETED ENERGY TRANSFERS TO LIGHTWEIGHT ESSENTIALLY NONLINEAR ATTACHMENTS
lee, Young S.; Vakakis, Alexander F.; Bergman, Lawrence A. et al

in International Forum on Aerolasticity and Strucural Dynamics, Stockholm, 2007 (2007)

Theoretical and experimental suppression of aeroelastic instabilities by means of broadband passive targeted energy transfers has been recently studied. A single-degree-offreedom (SDOF) nonlinear energy ... [more ▼]

Theoretical and experimental suppression of aeroelastic instabilities by means of broadband passive targeted energy transfers has been recently studied. A single-degree-offreedom (SDOF) nonlinear energy sink (NES) was coupled to a 2-DOF rigid wing modeled in the low-speed, subsonic regime with quasi-steady aerodynamic theory. The nonlinear attachment was designed and optimized to suppress the critical nonlinear modal energy exchanges between the flow and the (pitch and heave) wing modes, thus suppressing the (transient) triggering mechanism of aeroelastic instability. We performed bifurcation analysis to find regions of robust passive aeroelastic suppression in parameter space. Then, we employed multi-degreeof-freedom nonlinear energy sinks (MDOF NESs) to improve robustness of the aeroelastic instability suppression. Bifurcation analysis by a numerical continuation technique demonstrated that controlling the occurrence of a limit point cycle (LPC or saddle-node) bifurcation point above a Hopf bifurcation point is crucial to enhancing suppression robustness. MDOF NESs not only can enhance robustness of suppression against even strong gust-like disturbances, but they require lower NES mass compared to SDOF NES designs. The validity of the theoretical findings was proven by a series of wind tunnel experiments. [less ▲]

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See detailSystem Identification in Structural Dynamics Using Blind Source Separation Techniques
Poncelet, Fabien ULg; Kerschen, Gaëtan ULg; Golinval, Jean-Claude ULg et al

in 7th International Conference on ICA and Signal, Londres, 2007 (2007)

This paper proposes to explore the potential of Blind Source Separation (BSS) techniques for the estimation of modal parameters, namely the resonant frequencies, vibration modes and damping ratios. The ... [more ▼]

This paper proposes to explore the potential of Blind Source Separation (BSS) techniques for the estimation of modal parameters, namely the resonant frequencies, vibration modes and damping ratios. The concept of virtual sources, which was introduced in recent publications, allows to consider BSS as a simple way of doing output-only modal analysis. This work illustrates the proposed methodology using free and random responses of an experimental truss structure. [less ▲]

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See detailNonlinear System Identification in Structural Dynamics: A Short (and Biased) History
Worden, K.; Kerschen, Gaëtan ULg; Vakakis, Alexander F. et al

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

Although linear systems are now very well-understood in the context of structural dynamics, this is not at all the case for nonlinear systems. In particular, despite huge advances in the mathematical ... [more ▼]

Although linear systems are now very well-understood in the context of structural dynamics, this is not at all the case for nonlinear systems. In particular, despite huge advances in the mathematical theory of nonlinear dynamical systems, progress in the difficult field of nonlinear system identification (learning of models from measured input/output data) has largely remained fairly slow and incremental. This is not to say that there have been no major successes in the field in its comparatively short history, and the objective of this paper is to present some of the highlights, as perceived by the authors, and to pave the way for a second paper discussing new developments and possibilities for the future. [less ▲]

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See detailNonlinear System Identification in Structural Dynamics: Current Status and Future Directions
Kerschen, Gaëtan ULg; Worden, K.; Vakakis, Alexander F. et al

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

Nonlinear system identification aims at developing high-fidelity mathematical models in the presence of nonlinearity from input and output measurements performed on the real structure. The present paper ... [more ▼]

Nonlinear system identification aims at developing high-fidelity mathematical models in the presence of nonlinearity from input and output measurements performed on the real structure. The present paper is a discussion of the recent developments in this research field. Three of the latest approaches are presented, and application examples are considered to illustrate their fundamental concepts, advantages and limitations. Another objective of this paper is to identify future research needs, which would make the identification of structures with a high modal density in abroad frequency range viable. [less ▲]

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See detailThe slow-flow method of identification in nonlinear structural dynamics
Kerschen, Gaëtan ULg; Vakakis, Alexander F.; Lee, Young.S et al

in Smart Str. and Mat. & Nondestructive Eval. and Health Mon., San Diego, 2007 (2007)

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-flowmodel identification method, which is demonstrated using numerical examples. [less ▲]

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See detailTOWARDS MULTI-SCALE NONLINEAR (AND LINEAR) SYSTEM IDENTIFICATION IN STRUCTURAL DYNAMICS
Kerschen, Gaëtan ULg; Lee, Young-Sup; Vakakis, Alexander F. et al

in 8th HSTAM International Congress on Mechanics, Patras, 2007 (2007)

The Hilbert-Huang transform (HHT) has been shown to be effective for characterizing a wide range of nonstationary signals in terms of elemental oscillatory components, termed the intrinsic mode functions ... [more ▼]

The Hilbert-Huang transform (HHT) has been shown to be effective for characterizing a wide range of nonstationary signals in terms of elemental oscillatory components, termed the intrinsic mode functions (IMFs). In this presentation, we describe a combination of methods involving numerical integral transforms and theoretical analysis that cumulate to a new nonparametric method for nonlinear system identification based on multiple slow-fast partitions of the dynamics. This method can find wide applicability to linear and (weakly or strongly) nonlinear systems with various damping and/or stiffness nonlinearities. Moreover, through this method we can systematically examine transient resonance captures in the responses of dynamically interacting nonlinear structures, hence, decomposing and identifying the underlying multimodal nonlinear modal interactions that give rise to complex phenomena. [less ▲]

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See detailTARGETED ENERGY TRANSFER PHENOMENA FROM PRIMARY STRUCTURES TO GEOMETRICALLY NONLINEAR LIGHTWEIGHT ATTACHMENTS: AN OVERVIEW
Vakakis, Alexander F.; Kerschen, Gaëtan ULg; Bergman, Lawrence A. et al

in EUROMECH Colloquium 483 Geometrically Non-linear Vibrations of Structures, Porto, 2007 (2007)

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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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