References of "Kerschen, Gaëtan"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailPassive Linearization of Nonlinear System Resonances
Habib, Giuseppe ULg; Grappasonni, Chiara ULg; Kerschen, Gaëtan ULg

Conference (2016, August 22)

In this work we demonstrate that the addition of properly-tuned nonlinearities to a nonlinear system can increase the range over which a specific resonance responds linearly. Specifically, we seek to ... [more ▼]

In this work we demonstrate that the addition of properly-tuned nonlinearities to a nonlinear system can increase the range over which a specific resonance responds linearly. Specifically, we seek to enforce two important properties of linear systems, namely the force-displacement proportionality and the invariance of resonance frequencies. Theoretical findings are validated through numerical simulations and experiments. [less ▲]

Detailed reference viewed: 15 (0 ULg)
Full Text
Peer Reviewed
See detailPassive linearization of nonlinear resonances
Habib, Giuseppe ULg; Grappasonni, Chiara ULg; Kerschen, Gaëtan ULg

in Journal of Applied Physics (2016), 120

The objective of this paper is to demonstrate that the addition of properly-tuned nonlinearities to a nonlinear system can increase the range over which a speci c resonance responds linearly. Speci cally ... [more ▼]

The objective of this paper is to demonstrate that the addition of properly-tuned nonlinearities to a nonlinear system can increase the range over which a speci c resonance responds linearly. Speci cally, we seek to enforce two important properties of linear systems, namely the force-displacement proportionality and the invariance of resonance frequencies. Numerical simulations and experiments are used to validate the theoretical ndings. [less ▲]

Detailed reference viewed: 8 (0 ULg)
Full Text
See detailPassive flutter suppression using a nonlinear tuned vibration absorber
Verstraelen, Edouard ULg; Gourc, Etienne ULg; Kerschen, Gaëtan ULg et al

Poster (2016, July)

A recent study showed that the addition of a linear tuned vibration absorber could increase the flutter speed of a rigid wing with pitch and flap degrees of freedom by about 35%. However, the absorber was ... [more ▼]

A recent study showed that the addition of a linear tuned vibration absorber could increase the flutter speed of a rigid wing with pitch and flap degrees of freedom by about 35%. However, the absorber was turning the initial super-critical bifurcation into a sub-critical one. This work shows numerically that adding a nonlinear restoring force to the absorber can restore the su- percritical behaviour of the bifurcation and further reduce the post-instability limit cycle amplitude. [less ▲]

Detailed reference viewed: 35 (8 ULg)
Full Text
See detailIdentification of nonlinear frequency responses and bifurcations from experimental data
Noël, Jean-Philippe ULg; Gourc, Etienne ULg; Grappasonni, Chiara ULg et al

in Actes de CFA/VISHNO 2016 (2016, April)

The objective of the paper is to obtain the frequency response curves of nonlinear mechanical systems from broadband testing. The proposed approach consists in coupling an identification method with a ... [more ▼]

The objective of the paper is to obtain the frequency response curves of nonlinear mechanical systems from broadband testing. The proposed approach consists in coupling an identification method with a continuation method. Specifically, the frequency-domain nonlinear subspace identification (FNSI) method is first used to derive an experimental model of the structure in state-space from broadband measurements. The harmonic balance method coupled with arclength continuation then utilizes this experimental model to compute the frequency response curves of the system. The method is demonstrated using a numerical example. [less ▲]

Detailed reference viewed: 37 (2 ULg)
Full Text
See detailA nonlinear state-space solution to a hysteretic benchmark in system identification
Noël, Jean-Philippe ULg; Esfahani, Alireza; Kerschen, Gaëtan ULg et al

Conference (2016, April)

Detailed reference viewed: 21 (2 ULg)
Full Text
See detailObtaining nonlinear frequency responses from broadband testing
Gourc, Etienne ULg; Grappasonni, Chiara ULg; Noël, Jean-Philippe ULg et al

in Proceedings of the International Modal Analysis Conference (IMAC) XXXIV (2016, January)

The objective of the paper is to obtain the frequency response curves of nonlinear mechanical systems from broadband testing. The proposed approach consists in coupling an identification method with a ... [more ▼]

The objective of the paper is to obtain the frequency response curves of nonlinear mechanical systems from broadband testing. The proposed approach consists in coupling an identification method with a continuation method. Specifically, the frequency-domain nonlinear subspace identification (FNSI) method is first used to derive an experimental model of the structure in state space from broadband measurements. The harmonic balance method coupled with arclength continuation then utilizes this experimental model to compute the frequency response curves of the system. The method is demonstrated using a numerical example. [less ▲]

Detailed reference viewed: 52 (6 ULg)
Full Text
See detailHysteresis identification using nonlinear state-space models
Noël, Jean-Philippe ULg; Esfahani, Alireza; Kerschen, Gaëtan ULg et al

in Proceedings of the International Modal Analysis Conference (IMAC) XXXIV (2016, January)

Most studies tackling hysteresis identification in the technical literature follow white-box approaches, i.e. they rely on the assumption that measured data obey a specific hysteretic model. Such an ... [more ▼]

Most studies tackling hysteresis identification in the technical literature follow white-box approaches, i.e. they rely on the assumption that measured data obey a specific hysteretic model. Such an assumption may be a hard requirement to handle in real applications, since hysteresis is a highly individualistic nonlinear behaviour. The present paper adopts a black-box approach based on nonlinear state-space models to identify hysteresis dynamics. This approach is shown to provide a general framework to hysteresis identification, featuring flexibility and parsimony of representation. Nonlinear model terms are constructed as a multivariate polynomial in the state variables, and parameter estimation is performed by minimising weighted least-squares cost functions. Technical issues, including the selection of the model order and the polynomial degree, are discussed, and model validation is achieved in both broadband and sine conditions. The study is carried out numerically by exploiting synthetic data generated via the Bouc-Wen equations. [less ▲]

Detailed reference viewed: 75 (9 ULg)
Full Text
See detailExperimental study of isolated response curves in a two-degree-of-freedom nonlinear system
Detroux, Thibaut ULg; Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg et al

in Proceedings of the International Modal Analysis Conference (IMAC) XXXIV (2016, January)

In the present paper, the observation and characterization of isolated response curves (IRCs) are experimentally reported in the case of a nonlinear system consisting of two masses sliding on an ... [more ▼]

In the present paper, the observation and characterization of isolated response curves (IRCs) are experimentally reported in the case of a nonlinear system consisting of two masses sliding on an horizontal guide. Transverse springs are attached to one mass to provide the nonlinear restoring force, and a harmonic motion of the complete system is imposed by prescribing the displacement of their supports. The existence of an IRC is related to a 3:1 internal resonance between the two modes of the system. The observed IRC is studied in detached and merged conditions using swept-sine excitations and system perturbations. [less ▲]

Detailed reference viewed: 46 (14 ULg)
Full Text
See detailRobust Subspace Identification of a Nonlinear Satellite Using Model Reduction
Dossogne, Tilàn ULg; Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg

in Proceedings of the International Modal Analysis Conference (IMAC) XXXIV (2016, January)

The frequency-domain nonlinear subspace identification (FNSI) method has recently been successfully applied to large-scale nonlinear structures. One of the key features of FNSI is the nonlinear ... [more ▼]

The frequency-domain nonlinear subspace identification (FNSI) method has recently been successfully applied to large-scale nonlinear structures. One of the key features of FNSI is the nonlinear generalisation of the stabilisation diagram. However, as in linear system identification, the selection of the model order in the diagram is complicated by the presence of spurious poles, resulting from noise and modelling errors. Spurious poles have been shown to strongly perturb the estimation of the nonlinear coefficients. The present paper establishes a constructive procedure to discriminate between spurious and genuine poles. This procedure is derived in modal space and is based on a dominancy index and on model reduction techniques. It is demonstrated on a complete satellite structure possessing nonsmooth nonlinearities and high modal density. Spurious frequency variations in the nonlinear coefficients are proved to be effectively removed, significantly improving the quality of the overall identified model. [less ▲]

Detailed reference viewed: 54 (4 ULg)
Full Text
Peer Reviewed
See detailA principle of similarity for nonlinear vibration absorbers
Habib, Giuseppe ULg; Kerschen, Gaëtan ULg

in Physica D: Nonlinear Phenomena (2016), 332

This paper develops a principle of similarity for the design of a nonlinear absorber, the nonlinear tuned vibration absorber (NLTVA), attached to a nonlinear primary system. Specifically, for effective ... [more ▼]

This paper develops a principle of similarity for the design of a nonlinear absorber, the nonlinear tuned vibration absorber (NLTVA), attached to a nonlinear primary system. Specifically, for effective vibration mitigation, we show that the NLTVA should feature a nonlinearity possessing the same mathematical form as that of the primary system. A compact analytical formula for the nonlinear coefficient of the absorber is then derived. The formula, valid for any polynomial nonlinearity in the primary system, is found to depend only on the mass ratio and on the nonlinear coefficient of the primary system. When the primary system comprises several polynomial nonlinearities, we demonstrate that the NLTVA obeys a principle of additivity, i.e., each nonlinear coefficient can be calculated independently of the other nonlinear coefficients using the proposed formula. [less ▲]

Detailed reference viewed: 10 (1 ULg)
Full Text
See detailExperimental Passive Flutter Mitigation Using a Linear Tuned Vibrations Absorber
Verstraelen, Edouard ULg; Habib, Giuseppe ULg; Kerschen, Gaëtan ULg et al

in Proceedings of the IMAC XXXIV Conference (2016)

The current drive for increased efficiency in aeronautic structures such as aircraft, wind turbine blades and helicopter blades often leads to weight reduction. A consequence of this tendency can be ... [more ▼]

The current drive for increased efficiency in aeronautic structures such as aircraft, wind turbine blades and helicopter blades often leads to weight reduction. A consequence of this tendency can be increased flexibility, which in turn can lead to unfavourable aeroelastic phenomena involving large amplitude oscillations and nonlinear effects such as geometric hardening and stall flutter. Vibration mitigation is one of the approaches currently under study for avoiding these phenomena. In the present work, passive vibration mitigation is applied to an experimental aeroelastic system by means of a linear tuned vibration absorber. The aeroelastic apparatus is a pitch and flap wing that features a continuously hardening restoring torque in pitch and a linear one in flap. Extensive analysis of the system with and without absorber at subcritical and supercritical airspeeds showed an improvement in flutter speed around 34%, a suppression of a jump due to stall flutter, and a reduction in LCO amplitude. Mathematical modelling of the experimental system showed that optimal flutter delay can be obtained when two of the system modes flutter simultaneously. However, the absorber quickly loses effectiveness as it is detuned. The wind tunnel measurements showed that the tested absorbers were much slower to lose effectiveness than those of the mathematical predictions. [less ▲]

Detailed reference viewed: 16 (1 ULg)
Full Text
See detailExperimental nonlinear identification of an aircraft with bolted connections
De Filippis, Giovanni; Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg et al

in Proceedings of the International Modal Analysis Conference (IMAC) XXXIII (2016)

Aircraft structures are known to be prone to nonlinear phenomena, especially as they constantly become lighter and hence more flexible. One specific challenge that is regularly encountered is the modeling ... [more ▼]

Aircraft structures are known to be prone to nonlinear phenomena, especially as they constantly become lighter and hence more flexible. One specific challenge that is regularly encountered is the modeling of the mounting interfaces between aircraft subcomponents. Indeed, for large amplitudes of vibration, such interfaces may loosen and, in turn, trigger complex mechanisms such as friction and clearances. In this context, the present work intends to investigate the nonlinear dynamics of the Morane–Saulnier Paris aircraft, accessible at ONERA. This aircraft possesses multiple bolted connections between two external fuel tanks and wing tips. The objective of the paper is specifically to carry out an adequate identification of the numerous nonlinearities affecting the dynamics of this full-scale structure. Nonlinearity detection and the subsequent subspace-based parameter estimation have been performed on experimental data, collected during an on-ground test campaign. Nonlinearity detection is first achieved by the comparison of frequency response functions estimated at low excitation level, with those obtained at high amplitude level, yielding insight towards accurately characterizing the behavior of the bolted connections. Then, a nonlinear subspace identification method is applied to measured data to estimate the linear and nonlinear parameters of the structure and novel strategies and tools that overcome specific arisen problems are developed. [less ▲]

Detailed reference viewed: 100 (6 ULg)
Full Text
Peer Reviewed
See detailIdentification of nonlinear normal modes of engineering structures under broadband forcing
Noël, Jean-Philippe ULg; Renson, Ludovic ULg; Grappasonni, Chiara ULg et al

in Mechanical Systems & Signal Processing (2016)

The objective of the present paper is to develop a two-step methodology integrating system identification and numerical continuation for the experimental extraction of nonlinear normal modes (NNMs) under ... [more ▼]

The objective of the present paper is to develop a two-step methodology integrating system identification and numerical continuation for the experimental extraction of nonlinear normal modes (NNMs) under broadband forcing. The first step processes acquired input and output data to derive an experimental state-space model of the structure. The second step converts this state-space model into a model in modal space from which NNMs are computed using shooting and pseudo-arclength continuation. The method is demonstrated using noisy synthetic data simulated on a cantilever beam with a hardening-softening nonlinearity at its free end. [less ▲]

Detailed reference viewed: 24 (4 ULg)
Full Text
Peer Reviewed
See detailDirection and surface sampling in ray tracing for spacecraft radiative heat transfer
Jacques, Lionel ULg; Masset, Luc ULg; Kerschen, Gaëtan ULg

in Aerospace Science and Technology (2015), 47

This paper addresses the computation of radiative exchange factors through Monte Carlo ray tracing with the aim of reducing their computation time when dealing with the finite element method. Both ... [more ▼]

This paper addresses the computation of radiative exchange factors through Monte Carlo ray tracing with the aim of reducing their computation time when dealing with the finite element method. Both direction and surface samplings are studied. The recently-introduced isocell method for partitioning the unit disk is applied to the direction sampling and compared to other direction sampling methods. It is then combined to different surface sampling schemes with either one or multiple rays traced per surface sampling point. Two promising approaches present better performances than standard spacecraft thermal analysis software. The first approach combines a Gauss surface sampling strategy with a local isocell direction sampling, whereas the second approach fires one ray per surface points using a global isocell direction sampling scheme. The advantages and limitations of the two methods are discussed, and they are benchmarked against a standard thermal analysis software using the entrance baffle of the Extreme Ultraviolet Imager instrument of the Solar Orbiter mission. [less ▲]

Detailed reference viewed: 47 (19 ULg)
Full Text
See detailFinite Element Model Reduction for Spacecraft Thermal Analysis
Jacques, Lionel ULg; Masset, Luc ULg; Kerschen, Gaëtan ULg

Scientific conference (2015, November 03)

The finite element method (FEM) is widely used in mechanical engineering, especially for space structure design. However, FEM is not yet often used for thermal engineering of space structures where the ... [more ▼]

The finite element method (FEM) is widely used in mechanical engineering, especially for space structure design. However, FEM is not yet often used for thermal engineering of space structures where the lumped parameter method (LPM) is still dominant. Both methods offer advantages and disadvantages and the proposed global approach tries to combine both methods: - The LPM conductive links are error-prone and still too often computed by hand. This is incompatible with the increasing accuracy required by the thermal control systems (TCS) and associated thermal models. Besides offering the automatic and accurate computation of the conductive links, the FEM also provides easy interaction between mechanical and thermal models, allowing better thermo-mechanical analyses. - On another hand, due to the large number of elements composing a FE model, the computation of the radiative exchange factors (REFs) is prohibitively expensive. New methods to accelerate the REFs computation by ray-tracing are necessary. Ray-tracing enhancement methods were presented in the previous editions, providing at least a 50% reduction of the number of rays required for a given accuracy. Another way to speed up the REF computation consists in grouping the FE external facets into super-faces. Surfaces in FEM are approximated where primitives are used in the LPM. In parallel to super-faces, quadric surface fitting of selected regions in the FE mesh is therefore performed where high surface accuracy is required for the computation of the radiative links and environmental heat loads. Last year’s presentation focused solely on the first point. Developments of super-face ray-tracing with quadrics fitting will be presented. In addition to REFs, orbital heat loads computation is also implemented with significant improvement. The presentation will also address the global process involving first the detailed FE model conductive reduction, then the super-faces generation with selective quadric fitting for the computation of REFs and orbital heat loads and finally the computation of the reduced model temperatures. Detailed FE model temperature field can then be computed back from the reduced ones and the reduction matrices for potential thermo-mechanical analyses. [less ▲]

Detailed reference viewed: 22 (3 ULg)
Full Text
Peer Reviewed
See detailThe harmonic balance method for bifurcation analysis of large-scale nonlinear mechanical systems
Detroux, Thibaut ULg; Renson, Ludovic ULg; Masset, Luc ULg et al

in Computer Methods in Applied Mechanics and Engineering (2015), 296

The harmonic balance (HB) method is widely used in the literature for analyzing the periodic solutions of nonlinear mechanical systems. The objective of this paper is to exploit the method for bifurcation ... [more ▼]

The harmonic balance (HB) method is widely used in the literature for analyzing the periodic solutions of nonlinear mechanical systems. The objective of this paper is to exploit the method for bifurcation analysis, i.e., for the detection and tracking of bifurcations of nonlinear systems. To this end, an algorithm that combines the computation of the Floquet exponents with bordering techniques is developed. A new procedure for the tracking of Neimark–Sacker bifurcations that exploits the properties of eigenvalue derivatives is also proposed. The HB method is demonstrated using numerical experiments of a spacecraft structure that possesses a nonlinear vibration isolation device. [less ▲]

Detailed reference viewed: 46 (12 ULg)
Full Text
Peer Reviewed
See detailGrey-box nonlinear state-space modelling for mechanical vibrations identification
Noël, Jean-Philippe ULg; Schoukens, Johan; Kerschen, Gaëtan ULg

in Proceedings of the 17th IFAC Symposium on System Identification (2015, October)

In the present paper, a flexible and parsimonious model of the vibrations of nonlinear mechanical systems is introduced in the form of state-space equations. It is shown that the nonlinear model terms can ... [more ▼]

In the present paper, a flexible and parsimonious model of the vibrations of nonlinear mechanical systems is introduced in the form of state-space equations. It is shown that the nonlinear model terms can be formed using a limited number of output measurements. A two-step identification procedure is derived for this grey-box model, integrating nonlinear subspace initialisation and maximum likelihood optimisation. The complete procedure is demonstrated on the Silverbox benchmark, which is an electrical mimicry of a single-degree-of-freedom mechanical system with one displacement-dependent nonlinearity. [less ▲]

Detailed reference viewed: 20 (2 ULg)
Full Text
Peer Reviewed
See detailNonlinear normal modes, modal interactions and isolated resonance curves
Kuether, Robert J.; Renson, Ludovic ULg; Detroux, Thibaut ULg et al

in Journal of Sound and Vibration (2015), 351

The objective of the present study is to explore the connection between the nonlinear normal modes of an undamped and unforced nonlinear system and the isolated resonance curves that may appear in the ... [more ▼]

The objective of the present study is to explore the connection between the nonlinear normal modes of an undamped and unforced nonlinear system and the isolated resonance curves that may appear in the damped response of the forced system. To this end, an energy balance technique is used to predict the amplitude of the harmonic forcing that is necessary to excite a specific nonlinear normal mode. A cantilever beam with a nonlinear spring at its tip serves to illustrate the developments. The practical implications of isolated resonance curves are also discussed by computing the beam response to sine sweep excitations of increasing amplitudes. [less ▲]

Detailed reference viewed: 44 (7 ULg)
Full Text
See detailArchitecture of educational OUFTI-1 nanosatellite of University of Liège, as tested in preparation for space flight
Werner, Xavier ULg; De Dijcker, Sébastien ULg; Broun, Valery ULg et al

Poster (2015, September)

Overview of the OUFTI-1 nanosatellite space segment. The OUFTI-1 project was initiated in September 2007. The nanosatellite is a one-unit (1U) CubeSat. Its main payload is - in essence - a D-STAR repeater ... [more ▼]

Overview of the OUFTI-1 nanosatellite space segment. The OUFTI-1 project was initiated in September 2007. The nanosatellite is a one-unit (1U) CubeSat. Its main payload is - in essence - a D-STAR repeater in space, potentially the first one ever. D-STAR is an amateur-radio (“ham”), digital radio communication - protocol (with associated equipment) allowing the simultaneous transmission of voice and data, such as GPS coordinates and call-signs. [less ▲]

Detailed reference viewed: 83 (2 ULg)
Full Text
See detailOverview of the ground facilities for controlling the OUFTI-1 nanosatellite and for routing its radio-communications through the worldwide D-STAR repeater network
Werner, Xavier ULg; De Dijcker, Sébastien ULg; Broun, Valery ULg et al

Poster (2015, September)

Overview of the current state and upgrade plan of the OUFTI-1 nanosatellite ground segment. The OUFTI-1 project was initiated in September 2007. The OUFTI-1 nanosatellite is a one-unit (1U) CubeSat. Its ... [more ▼]

Overview of the current state and upgrade plan of the OUFTI-1 nanosatellite ground segment. The OUFTI-1 project was initiated in September 2007. The OUFTI-1 nanosatellite is a one-unit (1U) CubeSat. Its main payload is - in essence - a D-STAR repeater in space, potentially the first one ever. D-STAR is an amateur-radio (“ham”), digital radio-communication protocol (with associated equipment) allowing the simultaneous transmission of voice and data, such as GPS coordinates and call-signs. The satellite was tested in 2014 and 2015 within the ESA’s Education Office Fly Your Satellite! (FYS) project, and it is now fully qualified and ready for launch and operation in space. [less ▲]

Detailed reference viewed: 58 (2 ULg)