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See detailModal testing using nonlinear normal modes: experimental demonstration
Peeters, Maxime ULg; Kerschen, Gaëtan ULg; Golinval, Jean-Claude ULg

in Proceedings of the International Conference on Noise and Vibration Engineering (2010)

Modal testing and analysis is well-established for linear vibrating structures. While the common practice is to assume linear behavior, nonlinearity is a frequent occurrence in engineering applications ... [more ▼]

Modal testing and analysis is well-established for linear vibrating structures. While the common practice is to assume linear behavior, nonlinearity is a frequent occurrence in engineering applications and can drastically alter the behavior of mechanical systems. In this paper, an attempt is made to extend experimental modal analysis methodology to a practical nonlinear analog. In this context, nonlinear normal modes (NNMs) offer a solid theoretical and mathematical tool for interpreting a wide class of nonlinear dynamical phenomena, yet they have a clear and simple conceptual relation to the classical linear normal modes. Based on a nonlinear extension of phase resonance testing (also called force appropriation), the proposed methodology excites the structure to isolate one single NNM during the experiments. Thanks to the invariance principle, the energy dependence of that nonlinear mode (i.e., the NNM modal curves and their frequencies of oscillation) can be extracted from the resulting free decay response using time-frequency analysis. The proposed method is demonstrated using an experimental cantilever beam with a geometrical nonlinearity. [less ▲]

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See detailOrbital dynamics characteristics of a QB50 CubeSat performing atmospheric reentry
Asma, C.; Naviaux, J.; Kerschen, Gaëtan ULg et al

in Proceedings of the AIAA Atmospheric Flight Mechanics Conference (2010)

The QB50 mission has the scientific objective to study the temporal and spatial variations of a number of key parameters in the lower thermosphere with a network of 50 CubeSats, each performing identical ... [more ▼]

The QB50 mission has the scientific objective to study the temporal and spatial variations of a number of key parameters in the lower thermosphere with a network of 50 CubeSats, each performing identical in-situ measurements. One of these 50 CubeSats, the von Karman Institute Atmospheric Re-Entry CubeSat, will further be equipped by a thermal protection system and a dedicated sensor pack to study the atmospheric re-entry. This paper is devoted to the orbital dynamics analysis performed for the QB50 mission and the atmospheric re-entry trajectory analysis for a double unit CubeSat. The main focus is on the sensitivity of the results on atmospheric models, drag coefficient and the launch date. Typical atmospheric re-entry trajectories, including the stagnation point heat flux values are calculated using three different methods for three different scenarios. The predicted heat flux values will be used in the preliminary design of the thermal protection system of the VKI atmospheric re-entry CubeSat, which is to be the first CubeSat to be used as an atmospheric re-entry demonstrator. [less ▲]

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See detailDetection and quantification of non-linear dynamic behaviour of space structures
Hot, A.; Kerschen, Gaëtan ULg; Cogan, S. et al

in 28th International Modal Analysis Conference, Jacksonville, 2010 (2010)

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See detailDesign procedure of a nonlinear vibration absrober: enhancement of the amplitude robustness
Viguié, R.; Kerschen, Gaëtan ULg

in Proceedings of the International Conference on Noise and Vibration Engineering (2010)

Nonlinear vibration absorbers are known as being frequency-robust but not amplitude-robust devices. This lack of amplitude robustness is due to the frequency-energy dependence of their related nonlinear ... [more ▼]

Nonlinear vibration absorbers are known as being frequency-robust but not amplitude-robust devices. This lack of amplitude robustness is due to the frequency-energy dependence of their related nonlinear oscillations. This feature makes the design of nonlinear vibration absorbers a particulary challenging problem. In this paper an innovative design procedure of a nonlinear vibration absorber is proposed so that a nonlinear mode of a nonlinear primary structure can be controlled in a frequency and amplitude robustness fashion. [less ▲]

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See detailOn the functional form of a nonlinear vibration absorber
Viguié, V; Kerschen, Gaëtan ULg

in Journal of Sound & Vibration (2010), 329

Due to the frequency–energy dependence of nonlinear oscillations, nonlinear dynamical absorbers present interesting properties for mitigating unwanted vibrations in mechanical systems. Unlike the tuned ... [more ▼]

Due to the frequency–energy dependence of nonlinear oscillations, nonlinear dynamical absorbers present interesting properties for mitigating unwanted vibrations in mechanical systems. Unlike the tuned mass damper, the functional form of a nonlinear absorber is not known a priori and must be determined. This short note addresses this issue when a light-weight nonlinear absorber is attached to a nonlinear primary structure. Numerical simulations demonstrate that the determination of an adequate functional form may be directly linked to the frequency–energy dependence of the primary structure. [less ▲]

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See detailAdvanced Strategies for Nonlinear System Identification
Kerschen, Gaëtan ULg

in Vakakis, A. F. (Ed.) Advanced Nonlinear Strategies for Vibration Mitigation and System Identification (2010)

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See detailExperimental modal analysis of nonlinear vibrating structures using nonlinear normal modes
Peeters, Maxime ULg; Kerschen, Gaëtan ULg; Golinval, Jean-Claude ULg

in IV European Conference on Computational Mechanics, Paris, 2010 (2010)

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See detailDamping material characterization and modeling: an industrial case-study
Poncelet, Fabien ULg; Bernay, Bruno; Kerschen, Gaëtan ULg et al

in International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE 2009), San Diego, 2009 (2009, August)

Turbojet engines contain potential nonlinearity sources such as geometric nonlinearities due to the slenderness and the length of modern blades, contacts between the blades and the shrouds, friction in ... [more ▼]

Turbojet engines contain potential nonlinearity sources such as geometric nonlinearities due to the slenderness and the length of modern blades, contacts between the blades and the shrouds, friction in the connections, and material nonlinearities. This paper focuses on the damping material which can be found in some stator stages of low-pressure compression parts. This material makes the shroud and all the blades of the stage interdependent, providing damping and fluid vein airtightness. The objective is to propose a characterization and a numerical modeling methodology that could easily be integrated within an industrial process. Nonlinearity characterization tests, based on the Restoring Force Surface method, are presented as well as viscoelastic characterization. Finally the proposed viscoelastic modeling, based on the Modal Strain Energy method, is validated against experimental data. [less ▲]

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See detailEfficiency of targeted energy transfers in coupled nonlinear oscillators associated with 1:1 resonance captures:Part II, analytical study
Sapsis, T. P.; Vakakis, Alexander F.; Gendelman, O. V. et al

in Journal of Sound & Vibration (2009)

We study targeted energy transfer in a two degree-of-freedom damped system under the conditionof1:1transient resonance capture. The system consists of a linear oscillator strongly coupled to an ... [more ▼]

We study targeted energy transfer in a two degree-of-freedom damped system under the conditionof1:1transient resonance capture. The system consists of a linear oscillator strongly coupled to an essentially nonlinear attachment or nonlinear energy sink. In a companion paper[ Quinnetal., Efficiency of targeted energy transfers in coupled nonlinear oscillators associated with1:1resonance captures: part I, Journal of Sound and Vibration 311 (2008)1228–1248]we studied the under lying structure of the Hamiltonian dynamics of this system ,and showed that for sufficiently small values of viscous damping , nonlinear damped transitions are strongly influenced by the under lying topological structure of periodic and quasi periodic or bits of the Hamiltonian system. In this work direct analytical treatment of the governing strongly nonlinear damped equations of motion is performed through slow/fast partitions of the transient responses, in order to investigate analytically the parameter region of optimal targeted energy transfer .To this end, we determine the characteristic time scales of the dynamics that influence the capacity of the nonlinear attachment to passively absorb and locally dissipate broad band energy from the linear oscillator. Then, we prove that optimal targeted energy transfer is realized for initial energies close to the neighbourhood of a homo clinic or bit of the under lying Hamiltonian system. We study analytically transient orbits resulting as perturbations of the homo clinic or bit in the weak lydamped system, and show that this yields an additional slow-time scale in the averaged dynamics, and leads to optimal targeted energy transfer from the linear oscillator to the nonlinear energy sink in a single ‘‘super-slow’’ half-cycle. We show that at higher energies, this ‘‘super-slow’’ half-cycle is replaced by strong nonlinear beats, which lead to significant but suboptimal targeted energy transfer efficiency. Finally, we investigate numerically targeted energy transfer efficiency in this system over a wide range of system parameter sand verify the analytical predictions. 2009 Elsevier Ltd .All rights reserved. [less ▲]

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See detailAnalyse dynamique du phénomène d'auto-blocage dans les charnières de type Carpentier
Hoffait, Sébastien ULg; Bruls, Olivier ULg; Granville, D. et al

in Colloque National en Calcul des Structures, Giens, 2009 (2009)

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See detailEnergy Transfer and Dissipation in a Duffing Oscillator Coupled to a Nonlinear Attachment
Viguié, Régis ULg; Peeters, Maxime ULg; Kerschen, Gaëtan ULg et al

in Journal of Computational and Nonlinear Dynamics (2009), 4(4),

The dynamics of a two-degree-of-freedom nonlinear system consisting of a grounded Duffing oscillator coupled to an essentially nonlinear attachment is examined in the present study. The underlying ... [more ▼]

The dynamics of a two-degree-of-freedom nonlinear system consisting of a grounded Duffing oscillator coupled to an essentially nonlinear attachment is examined in the present study. The underlying Hamiltonian system is first considered, and its nonlinear normal modes are computed using numerical continuation and gathered in a frequency-energy plot. Based on these results, the damped system is then considered, and the basic mechanisms for energy transfer and dissipation are analyzed. [DOI: 10.1115/1.3192130] [less ▲]

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See detailNonlinear vibration absorber coupled to a nonlinear primary system: A tuning methodology
Viguié, Régis ULg; Kerschen, Gaëtan ULg

in Journal of Sound & Vibration (2009), 326(3-5), 780-793

This paper addresses the problem of mitigating the vibration of nonlinear mechanical systems using nonlinear dynamical absorbers. One particular feature of the proposed absorber is that it is effective in ... [more ▼]

This paper addresses the problem of mitigating the vibration of nonlinear mechanical systems using nonlinear dynamical absorbers. One particular feature of the proposed absorber is that it is effective in a wide range of forcing amplitudes. A qualitative tuning methodology is developed and validated using numerical simulations. (C) 2009 Elsevier Ltd. All rights reserved. [less ▲]

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See detailNonlinear Targeted Energy Transfer in Mechanical and Structural Systems II
Vakakis, Alexander F.; Gendelman, O. V.; Bergman, L. A. et al

Book published by Springer (2009)

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See detailNonlinear normal modes, Part 1: Useful framework for the structural dynamicist
Kerschen, Gaëtan ULg; Peeters, Maxime ULg; Golinval, Jean-Claude ULg et al

in Mechanical Systems & Signal Processing (2009), 23

The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartII.BecausethereisvirtuallynoapplicationoftheNNMstolarge-scale engineeringstructures ... [more ▼]

The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartII.BecausethereisvirtuallynoapplicationoftheNNMstolarge-scale engineeringstructures,thesepapersareanattempttohighlightseveralaspectsthat mightdrivetheirdevelopmentinthefuture.Specifically,wesupportthat(i)numerical methodsforthecontinuationofperiodicsolutionspavethewayforaneffectiveand practical computationofNNMs,and(ii)time–frequencyanalysisisparticularlysuitable fortheanalysisoftheresultingdynamics.Anotherobjectiveofthepresentpaperisto describe,insimpleterms,andtoillustratethefundamentalpropertiesofNNMs.Thisis achievedtoconvincethestructuraldynamicistnotnecessarilyacquaintedwiththemthat theyareausefulframeworkfortheanalysisofnonlinearvibratingstructures. & 2008ElsevierLtd.Allrightsreserved [less ▲]

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See detailNonlinear Targeted Energy Transfer in Mechanical and Structural Systems I
Vakakis, Alexander F.; Gendelman, O. V.; Bergman, L. A. et al

Book published by Springer (2009)

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See detailTargeted energy transfer for suppressing aeroelastic instability due to unsteady lift
Lee, Y. S.; Vakakis, Alexander F.; Bergman, L. A. et al

in Targeted energy transfer for suppressing aeroelastic instability due to unsteady lift, Palm Springs, 2009 (2009)

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See detailModal Analysis of a Nonlinear Periodic Structure with Cyclic Symmetry
Georgiades, Fostios; Peeters, Maxime ULg; Kerschen, Gaëtan ULg et al

in AIAA Journal (2009), 47

The objective of this paper is to examine nonlinear normal modes and their bifurcations in cyclic periodic structures. The nonlinear normal modes are computed using a numerical technique that combines ... [more ▼]

The objective of this paper is to examine nonlinear normal modes and their bifurcations in cyclic periodic structures. The nonlinear normal modes are computed using a numerical technique that combines shooting and pseudoarclength continuation. Unlike perturbation techniques, the resulting algorithm can investigate strongly nonlinear regimes of motion. This study reveals that modal interactions may occur without necessarily having commensurate natural frequencies in the underlying linear system. In addition, a countable infinity of such modal Q2 interactions are shown to exist in the system. [less ▲]

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See detailNonlinear normal modes, Part 2: Toward a pratical computation using numerical continuation techniques
Peeters, Maxime ULg; Viguié, Régis ULg; Sérandour, Guillaume ULg et al

in Mechanical Systems & Signal Processing (2009), 23

The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartI.OnereasonofthestilllimiteduseofNNMsinstructuraldynamicsis that theircomputationisoftenregardedasimpractical ... [more ▼]

The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartI.OnereasonofthestilllimiteduseofNNMsinstructuraldynamicsis that theircomputationisoftenregardedasimpractical.However,whenresortingto numericalalgorithms,weshowthattheNNMcomputationispossiblewithlimited implementationeffort,whichpavesthewaytoapracticalmethodfordeterminingthe NNMsofnonlinearmechanicalsystems.Theproposedalgorithmreliesontwomain techniques,namelyashootingprocedureandamethodforthecontinuationofNNM motions. Thealgorithmisdemonstratedusingfourdifferentmechanicalsystems,a weakly andastronglynonlineartwo-degree-of-freedomsystem,asimplifieddiscrete modelofanonlinearbladeddiskandanonlinearcantileverbeamdiscretizedbythefinite elementmethod. [less ▲]

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