References of "Kerschen, Gaëtan"
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See detailExperimental study of isolas in nonlinear systems featuring modal interactions
Detroux, Thibaut ULiege; Noël, Jean-Philippe ULiege; Virgin, Lawrence et al

in PLoS ONE (in press)

The objective of the present paper is to provide experimental evidence of isolated resonances in the frequency response of nonlinear mechanical systems. More specifically, this work explores the presence ... [more ▼]

The objective of the present paper is to provide experimental evidence of isolated resonances in the frequency response of nonlinear mechanical systems. More specifically, this work explores the presence of isolas, which are periodic solutions detached from the main frequency response, in the case of a nonlinear set-up consisting of two masses sliding on a horizontal guide. A careful experimental investigation of isolas is carried out using responses to swept-sine and stepped-sine excitations. The experimental findings are validated with advanced numerical simulations combining nonlinear modal analysis and bifurcation monitoring. In particular, the interactions between two nonlinear normal modes are shown to be responsible for the creation of the isolas. [less ▲]

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See detailNonlinearities of an aircraft Piccolo tube: Identification and modeling
Dossogne, Tilàn ULiege; Trillet, Pierre; Schoukens, Maarten et al

in Proceedings of the International Modal Analysis Conference (IMAC) XXXV (2018, February)

Piccolo tubes are parts of aircraft wings anti-icing system and consist of titanium pipes inserted into the internal structure of the slat. Due to differential thermal expansion, clearances between the ... [more ▼]

Piccolo tubes are parts of aircraft wings anti-icing system and consist of titanium pipes inserted into the internal structure of the slat. Due to differential thermal expansion, clearances between the tube and its support are unavoidable and cause the overall system to exhibit highly nonlinear behavior, resulting from impacts and friction. This paper addresses the identi cation and modeling of the nonlinearities present in the slat-Piccolo tube connection. The complete identi cation procedure, from nonlinearity detection and characterization to parameter estimation, is carried out based upon sine-sweep measurements. The use of several techniques, such as the acceleration surface method, enables to understand the complex dynamics of the Piccolo tube and build a reliable model of its nonlinearities. In particular, the parameters of nonsmooth nonlinear stiffness and damping mechanisms are estimated. The nonlinear model is finally validated on standard quali cation tests for airborne equipments. [less ▲]

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See detailSubspace-based identification of a distributed nonlinearity in time and frequency domains
Anastasio, Dario; Marchesiello, Stefano; Noël, Jean-Philippe ULiege et al

in Proceedings of the International Modal Analysis Conference (IMAC) XXXV (2018, February)

Nonlinear system identification has become of great interest during the last decades. However, a common and shared framework is not present yet, and the identification may be challenging, especially when ... [more ▼]

Nonlinear system identification has become of great interest during the last decades. However, a common and shared framework is not present yet, and the identification may be challenging, especially when real engineering structures are considered with strong nonlinearities. Subspace methods have proved to be effective when dealing with local nonlinearities, both in time domain (TNSI method) and in frequency domain (FNSI method). This study reports an improvement for both methods, as a first attempt to account for distributed nonlinearities, which is still an open question in the research community. A numerical beam under moderately large oscillations that exhibits geometric nonlinearity is considered. The object of the identification process is to exploit its behavior through the correct identification of the parameters that define the nonlinearity. Results show a high level of confidence between the two methods, and suggest that a more complete analysis of distributed nonlinear phenomena can be conducted based on these approaches. [less ▲]

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See detailModel updating of a wing-engine structure with nonlinear connections
Song, Mingming; Renson, Ludovic; Noël, Jean-Philippe ULiege et al

in Proceedings of the International Modal Analysis Conference (IMAC) XXXV (2018, February)

This paper investigates the performance of a Bayesian model updating approach using nonlinear normal modes (NNMs). The proposed approach is applied to a wing-engine structure tested in the laboratory. The ... [more ▼]

This paper investigates the performance of a Bayesian model updating approach using nonlinear normal modes (NNMs). The proposed approach is applied to a wing-engine structure tested in the laboratory. The structure response to a broadband input excitation is measured experimentally. The structure NNMs are then extracted from the measured data by combining a frequency-domain nonlinear subspace identification method with numerical continuation technique. An initial finite element model of the wing-engine structure is built in Matlab and its linear stiffness parameters and the coefficients of the local nonlinearities are selected as the updating parameters. The joint posterior probability distribution of the model parameters is estimated based on their prior distribution and the likelihood function which is defined as a Gaussian distribution of error function. The error function in this study is defined as the difference between model-predicted and identified NNMs at different energy levels. The calibrated model is then used to predict the structure response (NNMs and time history), taking into account model parameters uncertainties and modeling errors. The model predictions are compared with a set of experimental results that were not used in the calibration process and only considered for validation purpose. [less ▲]

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See detailVers l'identification non-linéaire des structures industrielles au moyen de sinus balayés
Dossogne, Tilàn ULiege; Noël, Jean-Philippe ULiege; Kerschen, Gaëtan ULiege

Poster (2017, November 16)

Les phénomènes vibratoires non-linéaires sont fréquemment rencontrés dans les structures mécaniques et aérospatiales. La division de ces structures en sous-systèmes assemblés ou l’usage de nouveaux ... [more ▼]

Les phénomènes vibratoires non-linéaires sont fréquemment rencontrés dans les structures mécaniques et aérospatiales. La division de ces structures en sous-systèmes assemblés ou l’usage de nouveaux matériaux favorisent l’apparition de mécanismes non-linéaires tels que le frottement, les impacts ou l'hystérésis. Il existe donc un besoin croissant en industrie de pouvoir détecter et identifier ces phénomènes non-linéaires sur des structures complexes et à grande échelle. L’ objectif de ce travail est d'établir une méthodologie d’identification des non-linéarités dans les structures industrielles, allant de la détection à la caractérisation et l’estimation de paramètres non-linéaires. Le processus d’identification est basé uniquement sur des mesures obtenues en sinus balayé, afin d’ obtenir une séparation naturelle des modes ainsi qu’une excitation suffisante des mécanismes non-linéaires. La première étape, la détection, permet de localiser spatialement les sources de non-linéarités dans une structure au moyen d’un indice de non-linéarité. La seconde étape, la caractérisation, offre une visualisation qualitative des comportements non-linéaires locaux en utilisant la méthode dite ASM (Acceleration Surface Method). Cette méthode repose sur l’approximation des forces de rappel non-linéaires au moyen de signaux d’accélération représentés dans l’espace d’état. La dernière étape a recours à la méthode x-ASM (eXtended Acceleration Surface Method) afin d’estimer la valeur de chaque paramètre linéaire du modèle grâce à des procédés d’optimisation couplés à des modèles éléments finis. L’ensemble de la méthodologie est validée sur un avion F-16 Fighting Falcon possédant des non-linéarités au niveau des connexions entre les ailes et la charge utile. [less ▲]

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See detailModel reduction and frequency residuals for a robust estimation of nonlinearities in subspace identification
De Filippis, Giovanni; Noël, Jean-Philippe ULiege; Kerschen, Gaëtan ULiege et al

in Mechanical Systems & Signal Processing (2017), 93

The introduction of the frequency-domain nonlinear subspace identification (FNSI) method in 2013 constitutes one in a series of recent attempts toward developing a realistic, first-generation framework ... [more ▼]

The introduction of the frequency-domain nonlinear subspace identification (FNSI) method in 2013 constitutes one in a series of recent attempts toward developing a realistic, first-generation framework applicable to complex structures. If this method showed promising capabilities when applied to academic structures, it is still confronted with a number of limitations which needs to be addressed. In particular, the removal of nonphysical poles in the identified nonlinear models is a distinct challenge. In the present paper, it is proposed as a first contribution to operate directly on the identified state-space matrices to carry out spurious pole removal. A modal-space decomposition of the state and output matrices is examined to discriminate genuine from numerical poles, prior to estimating the extended input and feedthrough matrices. The final state-space model thus contains physical information only and naturally leads to nonlinear coefficients free of spurious variations. Besides spurious variations due to nonphysical poles, vibration modes lying outside the frequency band of interest may also produce drifts of the nonlinear coefficients. The second contribution of the paper is to include residual terms, accounting for the existence of these modes. The proposed improved FNSI methodology is validated numerically and experimentally using a full-scale structure, the Morane-Saulnier Paris aircraft. [less ▲]

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See detailHARMONIC BALANCE COMPUTATION OF THE NONLINEAR FREQUENCY RESPONSE OF A THIN PLATE
Lee, Jongsuh ULiege; Kerschen, Gaëtan ULiege; Detroux, Thibaut ULiege

Conference (2017, July 24)

The harmonic balance method (HBM) is used to investigate the dynamical behavior of the geometrical nonlinear plate. The middle plane displacements are included in the plate in which the equations of ... [more ▼]

The harmonic balance method (HBM) is used to investigate the dynamical behavior of the geometrical nonlinear plate. The middle plane displacements are included in the plate in which the equations of motion are developed by the principle virtual work. Moreover, the nonlinear frequency response curves, or NFRCs, are obtained by a continuation method. [less ▲]

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See detailFreeplay-induced limit cycle oscillation mitigation using linear and nonlinear tuned vibration absorbers
Verstraelen, Edouard ULiege; Kerschen, Gaëtan ULiege; Dimitriadis, Grigorios ULiege

in Proceeding of the IFASD 2017 Conference (2017, June 27)

Structural nonlinearities such as freeplay in control surface bearings and actuators or in connections between wings and external payloads sometimes lead to aeroelastic limit cycle oscillations at ... [more ▼]

Structural nonlinearities such as freeplay in control surface bearings and actuators or in connections between wings and external payloads sometimes lead to aeroelastic limit cycle oscillations at airspeeds lower than the linear flutter speed of the aircraft. In parallel, numerous studies demonstrated the potential of linear and nonlinear tuned vibration absorbers to increase the flutter speed of linear and continuously hardening aeroelastic systems such as two-degree- of-freedom wings or long span bridges. In this work, the effect of linear and nonlinear tuned vibration absorbers is studied on a wing with pitch plunge and control surface deflection degrees of freedom and with freeplay in pitch. Depending on the tuning of the linear absorber, the linear flutter speed of the system can be increased by 10% or the onset of limit cycle oscillations due to the freeplay can be delayed by 7.7% and their amplitude can be significantly decreased. The addition of cubic hardening forces on the absorber can further decrease the limit cycle amplitude in a limited airspeed range at the cost of an increase in limit cycle amplitude in another airspeed range. Conversely, the addition of a freeplay hardening force on the absorber can decrease the limit cycle amplitude without any detrimental effect. [less ▲]

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See detailCubesats activities at the University of Liège
Werner, Xavier ULiege; Broun, Valery ULiege; De Dijcker, Sébastien ULiege et al

Conference given outside the academic context (2017)

Detailed reference viewed: 22 (4 ULiège)
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See detailExperimental passive flutter suppression using a linear tuned vibration absorber
Verstraelen, Edouard ULiege; Habib, Giuseppe ULiege; Kerschen, Gaëtan ULiege et al

in AIAA Journal (2017), 55(5), 1707-1722

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 ULiege; Béchet, Eric ULiege; Kerschen, Gaëtan ULiege

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 ULiege; Kerschen, Gaëtan ULiege; Dimitriadis, Grigorios ULiege

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 ULiege; Kerschen, Gaëtan ULiege

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 ULiege; Noël, Jean-Philippe ULiege; Kerschen, Gaëtan ULiege

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 phase separation testing of an experimental wing-engine structure
Renson, Ludovic; Noël, Jean-Philippe ULiege; Barton, David et al

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

Modal testing of nonlinear engineering structures is currently a research area that attracts substantial attention. Recently, a nonlinear generalisation of phase separation testing has been proposed for ... [more ▼]

Modal testing of nonlinear engineering structures is currently a research area that attracts substantial attention. Recently, a nonlinear generalisation of phase separation testing has been proposed for identifying nonlinear normal modes (NNMs) based on input and output measurements. The nonlinear phase separation (NPS) method integrates identification and continuation tools to calculate multiple NNMs from broadband data. The present contribution reports the first experimental application of the NPS method. The structure of interest is a model inspired by a wing with two engines connected by means of nonlinear pylons with softening-hardening stiffness characteristics. The frequency-energy dependences of four NNMs in the 0-100 Hz range are estimated, including modal interactions. NNMs identified using the NPS method are also compared to free-decay testing results. [less ▲]

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See detailBayesian FE model updating using nonlinear normal modes: Application to a cantilever beam
Song, Mingming; Renson, Ludovic; Noël, Jean-Philippe ULiege et al

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

This paper investigates the performance of a probabilistic finite element (FE) model updating approach using the Bayesian inference and nonlinear normal mode (NNM) error functions. The considered beam is ... [more ▼]

This paper investigates the performance of a probabilistic finite element (FE) model updating approach using the Bayesian inference and nonlinear normal mode (NNM) error functions. The considered beam is the European COST Action F3 benchmark and its response in this study is simulated when subjected to a broadband excitation. The simulated response is then contaminated with different levels of Gaussian white noise to represent noisy measurements. The NNMs of the beam are identified from the noisy data by integrating a nonlinear subspace identification method and numerical continuation in a phase separation approach. An initial FE model of the beam is created in Matlab and its parameters are probabilistically updated. The considered updating parameters are the Young’s modulus of the main beam and coefficients of the local geometric nonlinearity. In the proposed FE model updating approach, error functions are defined as the difference between model-predicted and identified NNMs at different energy levels. Posterior probability distributions of the updating parameters are estimated for different levels of measurement noise. The error function is assumed to have a Gaussian distribution. Performance of the updating results are studied for two cases, namely (1) when the error mean is assumed to be zero and the error covariance is known, and (2) when both the error mean and covariance are updated. [less ▲]

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

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 ULiege; Esfahani, Alireza; Kerschen, Gaëtan ULiege 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 ULiege; Kerschen, Gaëtan ULiege; Werner, Xavier ULiege et al

Conference given outside the academic context (2016)

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See detailAnalysis of the Nonlinear Dynamics of an F-16 Aircraft Using the NI2D Toolbox
Detroux, Thibaut ULiege; Dossogne, Tilàn ULiege; Masset, Luc ULiege et al

Conference (2016, October)

Detailed reference viewed: 38 (10 ULiège)