References of "Kerschen, Gaëtan"
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See detailExperimental passive flutter suppression using a linear tuned vibration absorber
Verstraelen, Edouard ULg; Habib, Giuseppe ULg; Kerschen, Gaëtan ULg et al

in AIAA Journal (in press)

The current drive for increased efficiency in aeronautic structures such as aircraft, wind turbine blades and helicopter blades often leads to weight reduction. A con- sequence 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 con- sequence of this tendency can be increased flexibility, which in turn can lead to un- favourable aeroelastic phenomena involving large amplitude oscillations and non- linear 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 a nonlinear 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 restoring torque in flap. Extensive analysis of the sys- tem with and without absorber at pre-critical and post-critical airspeeds showed an improvement in flutter speed of around 36%, a suppression of a jump due to stall flutter, and a reduction in LCO amplitude. Mathematical modelling of the exper- imental system is used to demonstrate that optimal flutter delay is achieved when two of the system modes flutter at the same flight condition. Nevertheless, even this optimal absorber quickly loses effectiveness as it is detuned. The wind tunnel mea- surements showed that the tested absorbers were much slower to lose effectiveness than those of the mathematical predictions. [less ▲]

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See detailFinite element model reduction for space thermal analysis
Jacques, Lionel ULg; Béchet, Eric ULg; Kerschen, Gaëtan ULg

in Finite Elements in Analysis and Design (2017), 127

To alleviate the computational burden of the nite element method for thermal analyses involving conduction and radiation, this paper proposes an automatic conductive-radiative reduction process based on ... [more ▼]

To alleviate the computational burden of the nite element method for thermal analyses involving conduction and radiation, this paper proposes an automatic conductive-radiative reduction process based on the clustering of a detailed mesh coming from a structural model for instance. The proposed method leads to a signi cant reduction of the number of radiative exchange factors (REFs) to compute and size of the corresponding matrix. It further keeps accurate conduction information by introducing the concept of physically meaningful super nodes. The REFs between the super nodes are computed through Monte Carlo ray-tracing on the partitioned mesh, preserving the versatility of the method. The resulting conductive-radiative reduced model is solved using standard iterative techniques and the detailed mesh temperatures can be recovered from the super nodes temperatures for further thermo-mechanical analysis. The proposed method is applied to a structural component of the Meteosat Third Generation mission and is benchmarked against ESATAN-TMS, the standard thermal analysis software used in the European aerospace industry. [less ▲]

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See detailFlutter and limit cycle oscillation suppression using linear and nonlinear tuned vibration absorbers
Verstraelen, Edouard ULg; Kerschen, Gaëtan ULg; Dimitriadis, Grigorios ULg

in Proceedings of the SEM IMAC XXXV (2017, February)

Aircraft are more than ever pushed to their limits for performance reasons. Consequently, they become increasingly nonlinear and they are more prone to undergo aeroelastic limit cycle oscillations ... [more ▼]

Aircraft are more than ever pushed to their limits for performance reasons. Consequently, they become increasingly nonlinear and they are more prone to undergo aeroelastic limit cycle oscillations. Structural nonlinearities affect aircraft such as the F-16, which can undergo store-induced limit cycle oscillations (LCOs). Furthermore, transonic buzz can lead to LCOs because of moving shock waves in transonic flight conditions on many aircraft. This study presents a numerical investigation of passive LCO suppression on a typical aeroelastic system with pitch and plunge degrees of freedom and a hardening stiffness nonlinearity. The absorber used is made of a piezoelectric patch glued to the plunge springs and connected to a resistor and an inductance forming a RLC circuit. A mechanical tuned mass damper absorber of similar configuration is also considered. The piezoelectric absorber features significant advantages in terms of size, weight and tuning convenience. The results show that both types of absorber increase the linear flutter speed of the system in a similar fashion but, when optimal, they lead to a sub-critical bifurcation while a super-critical bifurcation was observed without absorber. Finally, it is shown that the addition of a properly tuned nonlinear spring (mechanical absorber) or capacitor (piezo- electric absorber) can restore the super-criticality of the bifurcation. The tuning of the nonlinearity is carried out using numerical continuation. [less ▲]

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See detailNonlinear Robust Control for Satellite Formation Flying via Adaptive Second-Order Sliding Modes
Cho, Hancheol ULg; Kerschen, Gaëtan ULg

in 27th AAS/AIAA Space Flight Mechanics Meeting, San Antonio 5-9 February 2017 (2017, February)

This paper presents a robust adaptive control methodology based on the concept of second-order sliding modes for satellite formation control in the presence of unknown, but bounded uncertainties. By ... [more ▼]

This paper presents a robust adaptive control methodology based on the concept of second-order sliding modes for satellite formation control in the presence of unknown, but bounded uncertainties. By introducing two sliding variables to achieve the concept of second-order sliding modes, a robust controller is designed so that it forces the first sliding variable to converge to a desired error box in a finite time. Then, the second sliding variable is automatically bounded in a much smaller region by sliding mode control theory, thereby considerably improving the control accuracy. The proposed control scheme is of a smooth form and effectively alleviates chattering. An adaptive law that updates the control gain is also presented without a priori knowledge of the uncertainties. Numerical simulations, in which a desired formation configuration is required to be precisely maintained under uncertain mass and external disturbances, are carried out to validate the efficiency and the accuracy of the proposed robust adaptive control scheme developed herein. [less ▲]

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See detailIdentification of complex nonlinearities using cubic splines with automatic discretization
Dossogne, Tilàn ULg; Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg

in Proceedings of the International Modal Analysis Conference (IMAC) XXXV (2017, January)

One of the major challenges in nonlinear system identification is the selection of appropriate mathematical functions to model the observed nonlinearities. In this context, piecewise polynomials, or ... [more ▼]

One of the major challenges in nonlinear system identification is the selection of appropriate mathematical functions to model the observed nonlinearities. In this context, piecewise polynomials, or splines, offer a simple and flexible representation basis requiring limited prior knowledge. The generally-adopted discretization for splines consists in an even distribution of their control points, termed knots. While this may prove successful for simple nonlinearities, a more advanced strategy is needed for nonlinear restoring forces with strong local variations. The present paper specifically introduces a two-step methodology to select automatically the location of the knots. It proposes to derive an initial model, using nonlinear subspace identification, and incorporating cubic spline basis functions with fixed and equally-spaced abscissas. In a second step, the location of the knots is optimized iteratively by minimizing a least-squares cost function. A single-degree-of-freedom system with a discontinuous stiffness characteristic is considered as a case study. [less ▲]

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See detailNonlinear system identification in structural dynamics: 10 more years of progress
Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg

in Mechanical Systems & Signal Processing (2017), 83

Nonlinear system identification is a vast research field, today attracting a great deal of attention in the structural dynamics community. Ten years ago, in an MSSP paper reviewing the progress achieved ... [more ▼]

Nonlinear system identification is a vast research field, today attracting a great deal of attention in the structural dynamics community. Ten years ago, in an MSSP paper reviewing the progress achieved until then, it was concluded that the identification of simple continuous structures with localised nonlinearities was within reach. The past decade witnessed a shift in emphasis, accommodating the growing industrial need for a first generation of tools capable of addressing complex nonlinearities in larger-scale structures. The objective of the present paper is to survey the key developments which arose in the field since 2006, and to illustrate state-of-the-art techniques using a real-world satellite structure. Finally, a broader perspective to nonlinear system identification is provided by discussing the central role played by experimental models in the design cycle of engineering structures. [less ▲]

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See detailA nonlinear state-space approach to hysteresis identification
Noël, Jean-Philippe ULg; Esfahani, Alireza; Kerschen, Gaëtan ULg et al

in Mechanical Systems & Signal Processing (2017), 84

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 ▲]

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See detailOUFTI-1 : comment les étudiants belges ont envoyé un satellite en orbite
Verly, Jacques ULg; Kerschen, Gaëtan ULg; Werner, Xavier ULg et al

Conference given outside the academic context (2016)

Detailed reference viewed: 44 (6 ULg)
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See detailRobust mission design using invariant manifolds
Dell'Elce, Lamberto ULg; Baresi, Nicola; Kerschen, Gaëtan ULg et al

in Proceedings of the 67th International Astronautical Congress (2016, September 26)

Uncertainties in the dynamical system affect all real-life applications in astrodynamics. This is particularly true for satellites orbiting about small bodies owing to their irregular shapes and to the ... [more ▼]

Uncertainties in the dynamical system affect all real-life applications in astrodynamics. This is particularly true for satellites orbiting about small bodies owing to their irregular shapes and to the difficulties in characterizing their physical properties at the early stages of a dedicated spacecraft mission. Hence, accommodating uncertainty in the orbital design process may be extremely beneficial for the success of the mission. Here, in a Lyapunov stability perspective, the properties of the invariant manifolds are exploited to generate regions of the phase space where the motion is guaranteed to evolve despite the uncertainties in the system parameters and navigation errors. Specifically, the scenario approach is applied to tackle a semi-infinite optimization problem that locates these robust regions. The methodology is illustrated with the robust design of a inner retrograde orbit about the primary of (65803) Didymos as well as with a ballistic landing on the smaller secondary body. [less ▲]

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See detailSatellite Formation Control Using Continuous Adaptive Sliding Mode Controller
Cho, Hancheol ULg; Kerschen, Gaëtan ULg

in AIAA/AAS Astrodynamics Specialist Conference (2016, September)

The focus of this study is on the development of a robust controller with a simple gain adaptation for satellite formation control. The complete nonlinear dynamics of the motion of the follower satellite ... [more ▼]

The focus of this study is on the development of a robust controller with a simple gain adaptation for satellite formation control. The complete nonlinear dynamics of the motion of the follower satellite relative to the leader satellite is considered and the rigorous proof for the stability of the controlled formation system is given in the presence of unknown external disturbances and unknown mass of the follower satellite. Although the controller design is based on the concept of sliding mode control, the proposed control strategy is free from chattering and guarantees a finite-time convergence of the controlled system to the target area. Furthermore, a simple adaptive law to automatically update the control gain is suggested that does not require a priori knowledge of the uncertainties of the system. In addition, to guarantee the robustness from the beginning and to improve the transient performance, a new sliding surface is also constructed. Numerical simulations are carried out to demonstrate the effectiveness of the proposed adaptive controller to maintain a desired formation configuration by compensating for the initial offset errors and external disturbance effects including gravitational perturbations and atmospheric drag. [less ▲]

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See detailNonlinear vibration analysis of the SmallSat spacecraft: From identification to design
Detroux, Thibaut ULg; Noël, Jean-Philippe ULg; Masset, Luc ULg et al

Conference (2016, September)

The objective of the present contribution is to introduce nonlinear experimental and numerical tools and methods applicable to real-life structures. The study is illustrated using the SmallSat spacecraft ... [more ▼]

The objective of the present contribution is to introduce nonlinear experimental and numerical tools and methods applicable to real-life structures. The study is illustrated using the SmallSat spacecraft developed by Airbus Defence and Space, which possesses several localized nonlinearities. The computation of nonlinear normal modes and bifurcations reveals that the satellite possesses complex dynamics including modal interactions, quasiperiodic oscillations and isolated resonances. [less ▲]

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See detail10 years of advances in nonlinear system identification in structural dynamics: A review
Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg

in Proceedings of ISMA 2016 - International Conference on Noise and Vibration Engineering (2016, September)

Nonlinear system identification is a vast research field, today attracting a great deal of attention in the structural dynamics community. Ten years ago, an MSSP paper reviewing the progress achieved ... [more ▼]

Nonlinear system identification is a vast research field, today attracting a great deal of attention in the structural dynamics community. Ten years ago, an MSSP paper reviewing the progress achieved until then concluded that the identification of simple continuous structures with localised nonlinearities was within reach. The past decade witnessed a shift in emphasis, accommodating the growing industrial need for a first generation of tools capable of addressing complex nonlinearities in larger-scale structures. The objective of the present paper is to survey the key developments which arose in the field since 2006 towards developing these tools. [less ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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 ▲]

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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: 26 (2 ULg)