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See detailA Frequency-domain Approach to Subspace Identification of Nonlinear Systems, Application to Aerospace Structures
Noël, Jean-Philippe ULg

Doctoral thesis (2014)

The construction of mathematical models from experimental data is an essential step in the design process of engineering systems. The different tasks involved in this activity, from the measurement and ... [more ▼]

The construction of mathematical models from experimental data is an essential step in the design process of engineering systems. The different tasks involved in this activity, from the measurement and processing of data to the validation of the model, fall into the general field of system identification. 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 objective of this doctoral thesis is precisely to progress towards the development of a practical system identification methodology dedicated to real-life nonlinear structures. The first facet of the thesis is to introduce a nonlinear generalisation in the frequency domain of the so-called subspace identification methods. The proposed frequency-domain nonlinear subspace identification (FNSI) approach yields accurate models of large-scale systems comprising strong nonlinearities, closely-spaced modes and high damping. Because it can also estimate a large number of parameters while maintaining an acceptable computational burden, the second facet of this research is to investigate the utilisation of cubic splines as a very flexible means to model complex nonlinearities. Finally, the third facet of the present work is to derive nonlinear models with optimal statistical properties in the presence of measurement noise. This is achieved by embedding the FNSI method into the maximum likelihood identification framework. The scope of the identification and modelling tools developed in this thesis encompasses nonlinear structural systems originating from the various areas of vibration engineering, including the aerospace, mechanical or civil fields, amongst others. Throughout the dissertation, these tools are illustrated using numerical and experimental structures of increasing complexity, mainly related to aerospace applications. [less ▲]

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See detailA Frequency-Domain Processor for Maximum Resolution and Quicklook Processing of Wide-Swath ASAR Images
Barbier, Christian ULg; Piette, François; Renson, Luc et al

in Proc. EUSAR'96 Conference (1996)

Detailed reference viewed: 8 (1 ULg)
See detailA Frequency-Domain Processor for ScanSAR Images
Barbier, Christian ULg; Rosello-Guasch, Josep

in Preparing for the Future (1995), 5(4), 6-7

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See detailFrequency-domain subspace identification for nonlinear mechanical systems
Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg

in Mechanical Systems & Signal Processing (2013), 40

This paper introduces a new frequency-domain subspace-based method for the identification of nonlinear mechanical systems. The technique exploits frequency-domain data and interprets nonlinearities as ... [more ▼]

This paper introduces a new frequency-domain subspace-based method for the identification of nonlinear mechanical systems. The technique exploits frequency-domain data and interprets nonlinearities as feedback forces exciting the underlying linear system. It is first demonstrated using two academic examples, namely a Duffing oscillator and a five-degree-of-freedom system comprising two nonlinearities. The identification of an experimental beam exhibiting geometrically nonlinear behaviour is then addressed. [less ▲]

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See detailFrequency-domain subspace identification of nonlinear mechanical systems
Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg

in Proceedings of the 5th International Operational Modal Analysis Conference (2013, May)

The objective of the present paper is to address the identification of a real-life strongly nonlinear space structure, the EADS-Astrium SmallSat spacecraft. To this end, a new nonlinear subspace ... [more ▼]

The objective of the present paper is to address the identification of a real-life strongly nonlinear space structure, the EADS-Astrium SmallSat spacecraft. To this end, a new nonlinear subspace identification method formulated in the frequency domain is exploited, referred to as the FNSI method. The frequency response functions of the underlying linear spacecraft and the amplitudes of the nonlinear internal forces are estimated based on a periodic-random data set corrupted by noise. This application is challenging for several reasons, including high modal density, highly non-proportional damping and the non-smooth nature of the nonlinearities. [less ▲]

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See detailFrequency-domain subspace identification of nonlinear mechanical systems - Application to a solar array structure
Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg; Foltête, Emmanuel et al

in Proceedings of the International Modal Analysis Conference (IMAC) XXXI (2013)

The present paper addresses the experimental identification of a simplified realisation of a solar array structure in folded configuration. To this end, a nonlinear subspace identification technique ... [more ▼]

The present paper addresses the experimental identification of a simplified realisation of a solar array structure in folded configuration. To this end, a nonlinear subspace identification technique formulated in the frequency domain, referred to as the FNSI method, is exploited. The frequency response functions of the underlying linear structure and the nonlinear coefficients are estimated by this approach. Nonlinearity is caused by impacts between adjacent panels and friction and gaps appearing in their clamping interfaces. This application is challenging for several reasons, which include high modal density and the complicated nature of the involved nonlinear mechanisms. [less ▲]

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See detailLa fréquentation des massifs forestiers à des fins récréatives et de détente pour la population wallonne et bruxelloise
Colson, Vincent ULg

in Forêt Wallonne (2006), (81), 26-38

Une enquête téléphonique menée auprès de 1 005 personnes habitant les régions bruxelloise et wallonne a tenté de caractériser le type de public qui se rend en forêt, les périodes recherchées ou encore les ... [more ▼]

Une enquête téléphonique menée auprès de 1 005 personnes habitant les régions bruxelloise et wallonne a tenté de caractériser le type de public qui se rend en forêt, les périodes recherchées ou encore les activités pratiquées. Les destinations choisies et le consentement à payer pour ce type de loisir ont également été abordés. [less ▲]

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See detailLa fréquentation des massifs forestiers wallons: le public, ses activités et sa perception de la forêt
Colson, Vincent ULg

in Forêt Wallonne (2007), (87), 20-35

Une enquête a été menée entre octobre 2005 et août 2006 au sein de quarante massifs forestiers afin de pouvoir dresser l’image la plus fidèle de la fréquentation de la forêt wallonne. Les questions posées ... [more ▼]

Une enquête a été menée entre octobre 2005 et août 2006 au sein de quarante massifs forestiers afin de pouvoir dresser l’image la plus fidèle de la fréquentation de la forêt wallonne. Les questions posées ont permis de caractériser le profil du public, les activités pratiquées et la façon dont est perçue la forêt. [less ▲]

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See detailLa fréquentation des promenades balisées en forêt wallonne. Résultat d'une enquête menée avec la collaboration de huit organismes touristiques wallons
Colson, Vincent ULg

in Les Echos du Tourisme (2006), (44), 7-8

Dans le cadre d’une étude portant sur l’évaluation de la fonction récréative de la forêt wallonne, une enquête a été réalisée entre le 1er mai et le 7 novembre 2005 auprès des utilisateurs de cartes de ... [more ▼]

Dans le cadre d’une étude portant sur l’évaluation de la fonction récréative de la forêt wallonne, une enquête a été réalisée entre le 1er mai et le 7 novembre 2005 auprès des utilisateurs de cartes de promenades de 8 organismes touristiques (Florenville, Spa, Saint-Hubert, Nassogne, Assesse, Viroinval, Lobbes et Villersla- Ville). Les personnes acquérant une carte de promenades étaient invitées à répondre à un questionnaire à renvoyer au moyen d’une enveloppe « port payé par le destinataire ». Malgré un faible taux de réponse (196 soit 6,3%), des informations intéressantes ont pu être obtenues sur le profil des promeneurs et sur leurs desiderata. Cet article reprend quelques-uns des principaux résultats obtenus. [less ▲]

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See detailFrequently Relapsing Crohn's Disease Is Characterized by Persistent Elevation in Interleukin-6 and Soluble Interleukin-2 Receptor Serum Levels During Remission
Van Kemseke, Catherine ULg; Belaiche, Jacques ULg; Louis, Edouard ULg

in International Journal of Colorectal Disease (2000), 15(4), 206-10

We examined immune and inflammatory activation during remission in patients with Crohn's disease who presented with various clinical profiles (prolonged remission vs. relapsing disease). Thirty-six ... [more ▼]

We examined immune and inflammatory activation during remission in patients with Crohn's disease who presented with various clinical profiles (prolonged remission vs. relapsing disease). Thirty-six patients with at least 3 years' follow-up starting from a remission period were studied retrospectively. Relapses were defined by a retrospective calculation of the Crohn's disease activity index or by the clinical judgement of the physicians in charge of the patients. Disease course over the study period was assessed by the mean number of annual relapses. Analysis used measurements during remission of the following: erythrocytes sedimentation rate, relative lymphocytosis, acid alpha1-glycoprotein, interleukin-6 (IL-6), and soluble interleukin-2 receptor (sIL-2R) serum levels. During the study period 21 patients experienced at least one relapse and 15 did not. Mean serum levels of sIL-2R and mean relative lymphocytosis in remission significantly discriminated between relapsing and nonrelapsing patients. Only the mean sIL-2R serum level was selected by multivariate analysis, with a cutoff value of 82 pM/1 (sensitivity of 76% and specificity of 80%). The only features correlated with mean number of annual relapses in the relapsing patients were mean serum levels of sIL-2R (r=0.58, P=0.015) and IL-6 in remission (r=0.45, P=0.039). Multivariate analysis demonstrated statistical significance only for the mean serum level of IL-6 (P=0.014). In Crohn's disease the persistent elevation in sIL-2R serum levels during remission corresponds to chronic active disease, while high serum levels of IL-6 in these patients is associated with a high frequency of relapse. [less ▲]

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See detailFrères et soeurs pour la vie? : Les relations fraternelles à l'épreuve du temps
Favart, Evelyne ULg

Book published by Cortext (2007)

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See detailA fresh look on confidence marking
Leclercq, Dieudonné ULg; De Brogniez, Philippe

(1990)

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See detailFresnel rhombs as achromatic phase shifters for infrared nulling interferometry
Mawet, D.; Hanot, Charles ULg; Lenaers, C. et al

in Optics Express (2007), 15

We propose a new family of achromatic phase shifters for infrared nulling interferometry. These key optical components can be seen as optimized Fresnel rhombs, using the total internal reflection ... [more ▼]

We propose a new family of achromatic phase shifters for infrared nulling interferometry. These key optical components can be seen as optimized Fresnel rhombs, using the total internal reflection phenomenon, modulated or not. The total internal reflection indeed comes with a phase shift between the polarization components of the incident light. We propose a solution to implement this vectorial phase shift between interferometer arms to provide the destructive interference process needed to disentangle highly contrasted objects from one another. We also show that, modulating the index transition at the total internal reflection interface allows compensating for the intrinsic material dispersion in order to make the subsequent phase shift achromatic over especially broad bands. The modulation can be induced by a thin film of a well-chosen material or a subwavelength grating whose structural parameters are thoroughly optimized. We present results from theoretical simulations! together with preliminary fabrication outcomes and measurements for a prototype in Zinc Selenide. [less ▲]

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See detailFresnel rhombs as achromatic phase shifters for infrared nulling interferometry: first experimental results
Hanot, Charles ULg; Mawet, D.; Loicq, Jerôme ULg et al

in Coulter, Daniel R (Ed.) "Techniques and Instrumentation for Detection of Exoplanets III" Proceedings of the SPIE, Volume 6693, Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series (2007, September 01)

One of the most critical units of nulling interferometers is the Achromatic Phase Shifter. The concept we propose here is based on optimized Fresnel rhombs, using the total internal reflection phenomenon ... [more ▼]

One of the most critical units of nulling interferometers is the Achromatic Phase Shifter. The concept we propose here is based on optimized Fresnel rhombs, using the total internal reflection phenomenon, modulated or not. The total internal reflection induces a phase shift between the polarization components of the incident light. We present the principles, the current status of the prototype manufacturing and testing operations, as well as preliminary experiments on a ZnSe Fresnel rhomb in the visible that have led to a first error source assessment study. Thanks to these first experimental results using a simple polarimeter arrangement, we have identified the bulk scattering as being the main error source. Fortunately, we have experimentally verified that the scattering can be mitigated using spatial filters and does not decrease the phase shifting capabilities of the ZnSe Fresnel rhomb. [less ▲]

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See detailFret ferroviaire : vue prospective
Arda, Yasemin ULg; Nondonfaz, Robert ULg

Article for general public (2009)

Livre blanc de la Commission Européenne. Faiblesses du transport ferroviaire de fret : interopérabilité, ferroutage

Detailed reference viewed: 9 (2 ULg)
See detailFreud et Binswanger
Gyemant, Maria ULg

in Terquem, Sarah (Ed.) Dictionnaire Sigmund Freud (2014)

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See detailFreud et Brentano
Gyemant, Maria ULg

in Terquem, Sarah (Ed.) Dictionnaire Sigmund Freud (2014)

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See detailFreud et Brücke
Gyemant, Maria ULg

in Terquem, Sarah (Ed.) Dictionnaire Sigmund Freud (2014)

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See detailFreud et Hjelmslev : Métapsychologie et métalinguistique
Badir, Sémir ULg

in Arrivé, Michel; Normand, Claudine (Eds.) Linguistique et psychanalyse (2013)

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