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See detailNonlinear ground vibration identification of an F-16 aircraft - Part 2: Parameter estimation using a frequency-domain subspace method
Dossogne, Tilàn ULg; Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg et al

in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics (2015, June)

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic ... [more ▼]

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic nonlinearity, is the modelling of the wing-to-payload mounting interfaces. For large amplitudes of vibration, friction and gaps may be triggered in these connections and markedly impact the dynamic behaviour of the complete structure. In this series of two papers, the nonlinear dynamics of an F-16 aircraft is investigated using rigorous methods applied to real data collected during a ground vibration test campaign. The present work focuses on the construction of an experimental mathematical model of the F-16 structural dynamics. A nonlinear generalisation in the frequency domain of the so-called subspace identification algorithms, termed FNSI method, is exploited to this end. The frequency response functions of the underlying linear aircraft and the coefficients of the nonlinearities are reliably estimated by this approach based on periodic random data. The use of stabilisation diagram in nonlinear system identification is also discussed. The application of the FNSI method is made challenging by the high modal density of the structure, and the complexity of the nonlinear stiffness and damping mechanisms involved within the wing-to-payload connections. [less ▲]

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See detailA frequency-domain method for identifying nonlinear vibrating structures
Noël, Jean-Philippe ULg; Dossogne, Tilàn ULg; Kerschen, Gaëtan ULg

Conference (2015, June)

System identification, which refers to the construction of mathematical models from experimental data, plays a key role in the design process of engineering systems. In structural dynamics, the ... [more ▼]

System identification, which refers to the construction of mathematical models from experimental data, plays a key role in the design process of engineering systems. In structural dynamics, the theoretical and experimental aspects of linear system identification have been successfully addressed since the early seventies, and mature analytical, computational and testing tools have emerged. Nonlinear system identification of vibrating structures has also enjoyed significant advances during the past few years. However, the common practice in industry is to ignore nonlinearities, arguably because their analysis is still regarded as impractical. The present work describes a rigorous nonlinear generalisation in the frequency domain of the classical subspace identification algorithms, termed FNSI method. This method is applicable to large-scale systems comprising strong nonlinearities, closely-spaced modes and potentially high, nonproportional damping. Another distinct advantage of the approach is that it offers a convenient way to select an appropriate order for the nonlinear model by means of stabilisation diagrams. The FNSI method is demonstrated in this study using a complete satellite structure with nonsmooth nonlinearities, and a solar panel assembly exhibiting complex nonlinear stiffness and damping mechanisms. [less ▲]

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See detailNonlinear ground vibration identification of an F-16 aircraft - Part 1: Fast nonparametric analysis of distortions in FRF measurements
Vaes, Mark; Schoukens, Johan; Peeters, Bart et al

in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics (2015, June)

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic ... [more ▼]

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic nonlinearity, is the modelling of the wing-to-payload mounting interfaces. For large amplitudes of vibration, friction and gaps may be triggered in these connections and markedly impact the dynamic behaviour of the complete structure. In this series of two papers, the nonlinear dynamics of an F-16 aircraft is investigated using rigorous methods applied to real data collected during a ground vibration test campaign. The present work focuses on the detection, qualification and quantification of nonlinear distortions affecting frequency response function (FRF) measurements. The key idea of the approach is to excite the structure using a random signal with a user-defined amplitude spectrum, where only a set of well-selected frequencies is different from zero in the band of interest. It is demonstrated that this careful choice of the input frequencies allows, without any further user interaction, to quantify the importance of odd and even nonlinear distortions in the output spectra with respect to the noise level. At high excitation amplitude, the F-16 dynamics is found to exhibit substantial odd nonlinearities and less significant, yet not negligible, even nonlinearities. [less ▲]

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See detailNonlinear model updating by means of identified nonlinear normal modes
Song, Mingming; Renson, Ludovic ULg; Noël, Jean-Philippe ULg et al

Conference (2015, June)

Modal parameters are the most common features used for linear model updating. Although the modal analysis theory does not hold for nonlinear dynamic systems, its popularity encouraged researchers to come ... [more ▼]

Modal parameters are the most common features used for linear model updating. Although the modal analysis theory does not hold for nonlinear dynamic systems, its popularity encouraged researchers to come up with an equivalent version of normal modes for nonlinear systems, i.e., nonlinear normal modes (NNMs). A nonlinear system vibrates in NNMs when all masses have periodic motions of the same period, and at any time, the position of all the masses is uniquely defined by the position of any one of them. This paper investigates the feasibility of nonlinear model updating by minimizing the difference between the model-predicted and measured/identified nonlinear normal modes. A two degree-of-freedom mass-spring system with three linear springs and a cubic nonlinear spring is considered as the case study. The energy-dependent natural frequency and NNM of the first vibration mode of the system are identified at three different levels of energy. The stiffness parameters of the system are estimated by minimizing an objective function which is defined as the discrepancy between model-predicted natural frequency and NNM of the first mode, and their identified counterparts at the three measured energy levels. Performance of the proposed updating approach is evaluated at different levels of noise and different levels of modeling errors (i.e., nonlinear model classes). [less ▲]

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See detailLe dosage du cobalt dans le sang par ICP-MS : application aux patients porteurs de prothèses de hanche en métal
MISTRETTA, Virginie ULg; Charlier, Corinne ULg

in Toxicologie Analytique & Clinique (2015), 27(2), 91-98

Objectif Les patients porteurs de prothèse de hanche à couple métal-métal (PHM) présentent un taux de cobalt circulant supérieur à celui de la population générale. Chez ces patients, le dosage du cobalt ... [more ▼]

Objectif Les patients porteurs de prothèse de hanche à couple métal-métal (PHM) présentent un taux de cobalt circulant supérieur à celui de la population générale. Chez ces patients, le dosage du cobalt permet d’apprécier le risque toxique éventuel de l’implant et peut servir d’indicateur de révision ou de remplacement de cette prothèse. A cette fin, une méthode de dosage a été validée et appliquée à des patients porteurs de PHM. Méthode Le dosage du cobalt est réalisé sur 500 μL de sang total, après dilution dix fois dans une solution aqueuse acide et après ajout de 100 μL d’une solution de standard interne titrée à 500 μg/L de germanium. L’échantillon est ensuite analysé par un spectromètre de masse avec source d’ionisation par plasma induit haute fréquence (ICP-MS). La méthode décrite a été validée par l’approche de l’erreur totale au moyen du logiciel e•noval (Arlenda®). Résultats La méthode de dosage a été validée avec succès. Elle est linéaire de 0,5 à 50 μg/L. L’inexactitude et l’imprécision intra- et inter-essais sont inférieures à 5 % et 8 %, respectivement. L’incertitude de mesure est inférieure à 17 %. La concentration sanguine moyenne de cobalt estimée sur une période de 1 an à partir de 107 prélèvements de patients porteurs de PHM est de 2,61 μg/L (nombre de patients : 98 ; âge moyen : 60 ans ; ratio hommes/femmes : 38/60). Ce résultat est inférieur au seuil recommandé dans ces populations, fixé à 7 μg/L de cobalt sanguin. Conclusion La méthode analytique présentée permet de doser le cobalt sanguin, notamment chez les patients porteurs de PHM. Ce dosage est recommandé pour le suivi de ces patients, en association avec un examen clinique et radiologique. [less ▲]

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See detailGroupes délinquants juvéniles, quelle méthode pour une recherche « ethno-criminologique » ? La loi des 4 C
Witvrouw, Line ULg; Glowacz, Fabienne ULg

in Revue Internationale de Criminologie et de Police Technique et Scientifique [= RICPTS] (2015), LXVIII(Avril-Juin), 196-209

La criminologie nous amène à travailler avec des populations difficiles d’accès et requiert une démarche méthodologique structurée et prenant en compte les caractéristiques du milieu de rencontre. A ... [more ▼]

La criminologie nous amène à travailler avec des populations difficiles d’accès et requiert une démarche méthodologique structurée et prenant en compte les caractéristiques du milieu de rencontre. A partir de notre recherche portant sur les groupes de jeunes délinquants ou déviants, une spécificité est apparue dès le début des démarches empiriques. En effet, une notion d’exclusivité est entendue entre chaque membre du groupe, rendant l’accès à l’information difficile tant les frontières de ce groupe vis-à-vis de l’extérieur sont imperméables. Le chercheur se trouve alors confronté à différents obstacles: la difficulté de prise de contacts avec les groupes, la difficulté d’intégration du chercheur au sein de ceux-ci et la difficulté de récolte de données suffisantes pour la recherche. Au vu des constats de terrain, nous avons développé une méthodologie spécifique inspirée de modèles ethnologiques. En prenant en compte les jeunes en tant qu’experts de leur vécu et les intervenants médiateurs d’inclusion sur un terrain, ce processus méthodologique relève d’une co-construction de trois pôles et partenaires et s’apparente à une approche ethno-criminologique. Ce processus par étapes se décline en séquences temporelles successives. Tout d’abord, le positionnement du chercheur comme non-détenteur du savoir, la triangulation de la relation, l’acceptation de la temporalité de la démarche et de l’instrumentalisation de la relation sont autant d’éléments constituant l’étape préalable de ce processus méthodologique. Les étapes suivantes se construisent sur la base de l’évolution du lien entre le chercheur et les jeunes. La loi des 4 C réunit ces étapes, la relation évoluant de la confiance, à la confidence, ensuite à la communication pour aboutir à la coopération [less ▲]

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See detailThe Mars discrete aurora: Mars Express observations and modeling.
Gérard, Jean-Claude ULg

Scientific conference (2015, June)

Summary of earlier work Detection of additional ultraviolet auroral events (nadir and limb) Concurrent SPICAM-­‐ASPERA 3 observations Model results Perspectives

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See detailIntroduction: vegetal, animal and mineral residues
Rots, Veerle ULg

Scientific conference (2015, June)

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See detailIntroduction: Palaeolithic stone tool hafting
Rots, Veerle ULg

Scientific conference (2015, June)

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See detailLes prix de traduction fabriquent-ils une image régulatrice du traducteur ?
Mogollon Zapata, Juan Manuel ULg; Valéry, Plouhinec

in Convergences francophones (2015), 2

Les prix de traduction participent à la fois aux luttes pour la détention d’un capital de consécration et à la construction de l’image publique du traducteur. Ils sont une excellente entrée pour mesurer ... [more ▼]

Les prix de traduction participent à la fois aux luttes pour la détention d’un capital de consécration et à la construction de l’image publique du traducteur. Ils sont une excellente entrée pour mesurer les discours qui circulent dans l’espace du livre sur le traducteur et sa pratique. Comment ces prix construisent-ils une image légitimante du traducteur ? Quels critères guident le choix des jurys et quels dispositifs discursifs les justifient ? Quelles retombées pour les traducteurs et l’image de la traduction en général ? À travers l’analyse de nombreux exemples, cet article cherche à établir la manière dont les prix de traduction produisent un discours légitimant sur la figure du traducteur qui contribue à la fabrication de son image. [less ▲]

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See detailGènes candidats dans un modèle de développement de l'inflorescence de tomate
Périlleux, Claire ULg

Scientific conference (2015, June)

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See detailModeling inflorescence development in tomato
Périlleux, Claire ULg; Lobet, Guillaume ULg; Tocquin, Pierre ULg

Conference (2015, June)

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See detailA forecasting method using a wavelet-based mode decomposition and application to the ENSO index
Deliège, Adrien ULg; Nicolay, Samuel ULg; Fettweis, Xavier ULg

Conference (2015, June)

This work consists of a presentation and applications of a forecasting methodology based on a mode decomposition performed through a continuous wavelet transform. The idea is comparable to the Fourier ... [more ▼]

This work consists of a presentation and applications of a forecasting methodology based on a mode decomposition performed through a continuous wavelet transform. The idea is comparable to the Fourier series decomposition but where the amplitudes of the components are not constant anymore: the signal is written as a sum of periodic components with smooth time-varying amplitudes. This leads to a drastic decrease in the number of terms needed to decompose and rebuild the original signal without loss of precision. Once the decomposition is performed, the components are separately extrapolated, which leads to an extrapolation of the reconstructed signal that stands for a forecast of the original one. The quality of the forecast is assessed through a hindcast procedure (running retroactive probing forecasts) and Pearson correlations and root mean square errors are computed as functions of the lead time. This technique is first illustrated in details with a toy example, then with the El Niño Southern Oscillation (ENSO) time series. This signal consists of monthly-sampled sea surface temperature (SST) anomalies in the Eastern Pacific Ocean and is well-known to be one of the most influential climate patterns on the planet, inducing many consequences worldwide (hurricanes, droughts, flooding,…) and affecting human activities. Therefore, short-term predictions are of first importance in order to plan actions before the occurrence of these phenomena. As far as the ENSO time series is concerned, the wavelet-based mode decomposition leads to four components corresponding to periods of about 20, 31, 43 and 61 months respectively and the reconstruction recovers 97% of the El Niño/La Niña events (anomalous warming/cooling of the SST) of the last 65 years. Also, it turns out that more than 78% of these extreme events can be retrieved up to three years in advance. Finally, a forecast of the ENSO index is issued: the next La Niña event should start early in 2018 and should be followed soon after by a strong El Niño event in the second semester of 2019. [less ▲]

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See detailAdjusted Equivalent Static Wind Loads for non-Gaussian linear static analysis
Blaise, Nicolas ULg; Denoël, Vincent ULg

Conference (2015, June)

In this paper, we propose a parametric bi-cubic model for the joint probability distribution of wind aerodynamic pressures and structural responses. This non-Gaussian model is a bivariate extension of the ... [more ▼]

In this paper, we propose a parametric bi-cubic model for the joint probability distribution of wind aerodynamic pressures and structural responses. This non-Gaussian model is a bivariate extension of the well-known Hermite polynomial transformation. It offers a new way to determine Equivalent Static Wind Loads, with the embedded feature to –at least partly– capture the non-Gaussianity of the aerodynamic pressures and responses. In a second step, based on the observation that this model as well as the usual LRC method or the conditional sampling technique, fail in reproducing structural responses that do not overestimate the extreme values resulting from a complete structural analysis, we propose a two-step adjustment procedure that restores the non-overestimation condition and the recovery of the considered structural response. With the example of a boundary layer flow around a duo-pitched roof, it is demonstrated that the Equivalent Static Wind Loads, adjusted or not, obtained with the proposed model of non-Gaussian joint probability density function reconstruct the envelope of structural response more efficiently than with the other two techniques. [less ▲]

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See detailOxidative stress or not in healthy older subjects?
PINCEMAIL, Joël ULg; CHRISTELBACH, Sophie ULg; RICOUR, Céline ULg et al

in OCC2015 (2015, June)

Detailed reference viewed: 12 (1 ULg)