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See detailRegression-based modelling of a fleet of gas turbine engines for performance trending
Borguet, Sébastien ULg; Léonard, Olivier ULg; Dewallef, Pierre ULg

in Proceedings of ASME Turbo Expo 2015 (2015, June)

Module performance analysis is a well-established framework to assess changes in the health condition of the components of the engine gas-path. The primary material of the technique is the so-called ... [more ▼]

Module performance analysis is a well-established framework to assess changes in the health condition of the components of the engine gas-path. The primary material of the technique is the so-called vector of residuals, which are built as the difference between actual measurement taken in the gas-path and values predicted by means of an engine model. Obviously, the quality of the assessment of the engine condition depends strongly on the accuracy of the engine model. The present paper proposes a new approach for data-driven modelling of a fleet of engines of a given type. Such black-box models can be designed by operators such as airlines and thirdparty companies. The fleet-wide modelling process is formulated as a regression problem that provides a dedicated model for each engine in the fleet, while recognising that all engines are of the same type. The methodology is applied to a virtual fleet of engines generated within the ProDiMES environment. The set of models is assessed quantitatively through the coefficient of determination and is further used to perform anomaly detection. [less ▲]

Detailed reference viewed: 25 (0 ULg)
See detail“Pourquoi écrivez-vous ?” Création et sacralisation
Saint-Amand, Denis ULg

Conference (2015, June)

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See detailThe Pedagogical and Political Roots of Belgian Design
Prina, Daniela ULg

in Simon Thomas, Mienke; Huygens, Frank (Eds.) Design Derby: Netherlands-Belgium (1815-2015), exh.cat. (2015)

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See detailLes leviers de l'inovation pédagogique: contraintes externes vs régulations internes
Scheffers, Patricia ULg

in Scheffers, Patricia (Ed.) Actes du colloque (2015, June)

Depuis les années 60, la fréquence de mutations organisationnelles de l'enseignement supérieur et universitaire en Belgique s'amplifie et adopte même un rythme frénétique ces dix dernières années. Les ... [more ▼]

Depuis les années 60, la fréquence de mutations organisationnelles de l'enseignement supérieur et universitaire en Belgique s'amplifie et adopte même un rythme frénétique ces dix dernières années. Les causes sont tour à tour l'évolution des professions et la volonté politique et/ou économique de restructuration. Deux niveaux de régulations pédagogiques sont amenés à s'articuler. D'une part, celui de l'enseignant acteur-réflexif de son enseignement et d'autre part, des injonctions externes qui réorganise le cadre général. Retour d'expérience sur les innovations en Faculté d'Architecture à Liège. [less ▲]

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See detailInvestigation of Demagnetization in HTS Stacked Tapes Implemented in Electric Machines as a Result of Crossed Magnetic Field
Baghdadi, M.; Ruiz, H. S.; Fagnard, Jean-François ULg et al

in IEEE Transactions on Applied Superconductivity (2015), 25(3), 6602404

This paper investigates the practical effectiveness of employing superconducting stacked tapes to superconducting electric machinery. The use of superconducting bulks in various practical applications has ... [more ▼]

This paper investigates the practical effectiveness of employing superconducting stacked tapes to superconducting electric machinery. The use of superconducting bulks in various practical applications has been addressed extensively in the literature. However, in practice, dramatic decrease in magnetization would occur on superconducting bulks due to the crossed field effect. In our study, we employed the superconducting stacked tapes in a synchronous superconducting motor, which was designed and fabricated in our laboratory, aiming to lessen demagnetization due to crossed field effect in comparison with superconducting bulks. Applying the transverse AC field, the effects of frequency, amplitude, and number of cycles of the transverse magnetic field are discussed. Furthermore, a stack of 16 layers of superconducting tapes is modelled and the consequences of applying the crossed magnetic field on the sample are evaluated. The confrontation between experiments and simulation allows us to thoroughly understand the crossed field effects on stacked tapes. At the end, a preventive treatment, based on the shielding characteristic of superconductor and materials with high permeability, i.e. $mu$-metal and metalic glass, is suggested. On the other hand, the shielding feature of aforementioned materials will hinder the penetration of magnetic field and, consequently, reduction of the demagnetization will be attained. [less ▲]

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See detailSemiótica de la acción: textualización y notación
Dondero, Maria Giulia ULg

in Tópicos del seminario (2015), 31

Our essay focuses on some methodological issues concerning the semiotic analysis of practice. We will initially retrace the debate about the epistemological relationship between text and action, outlining ... [more ▼]

Our essay focuses on some methodological issues concerning the semiotic analysis of practice. We will initially retrace the debate about the epistemological relationship between text and action, outlining the forms of enunciative praxis through different levels of pertinence analysis. Secondly, we propose the concept of ‘textualization’ as a mediation between text and action: textualizations (photographs, videos, notes) organize and represent practices which are in themselves ephemeral and elusive. Finally, we will consider the textual diagrammatization that we call ‘notation’: this analytical form of mediation between text and practice does not have the same status of in-vivo textualisations, but it works like an ex-post reconstruction which highlights the main gestures and exchanges while performing their grammaticalization. A more general aim of this essay is an enquiry into the legitimate objects of textual semiotics: what are the objects that it can analyze without betraying its principle of immanence, but also without being confined to it and, as a consequence, being unable to analyze practices and respond to topical questions on social issues and on the research in the human sciences? [less ▲]

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See detailWhat are the determinants of the operational losses severity distribution ? A multivariate analysis based on a semiparametric approach.
Hambuckers, julien ULg; Heuchenne, Cédric ULg; Lopez, Olivier

Poster (2015, June)

In this paper, we analyse a database of around 41,000 operational losses from the European bank UniCredit. We investigate three kinds of covariates: firm-specific, fi- nancial and macroeconomic covariates ... [more ▼]

In this paper, we analyse a database of around 41,000 operational losses from the European bank UniCredit. We investigate three kinds of covariates: firm-specific, fi- nancial and macroeconomic covariates and we study their relationship with the shape parameter of the severity distribution. To do so, we introduce a semiparametric approach to estimate the shape parameter of the severity distribution, conditionally to large sets of covariates. Relying on a single index assumption to perform a dimension reduction, this approach avoids the curse of dimensionality of pure multivariate nonparametric techniques as well as too restrictive parametric assumptions. We show that taking into account variables measuring the economic well being of the bank could cause the required Operational Value-at-Risk to vary drastically. Especially, high pre-tax ROE, efficiency ratio and stock price are associated with a low shape parameter of the severity distribution, whereas a high market volatility, leverage ratio and unemployment rate are associated with higher tail risks. Finally, we discuss the fact that the considered approach could be an interesting tool to improve the estimation of the parameters in a Loss Distribution Approach and to offer an interesting methodology to study capital requirements variations throughout scenario analyses. [less ▲]

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See detailThe International Journal of Learning in Higher Education
Noiroux, Kevin ULg

in International Journal of Learning in Higher Education (2015), 22

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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 ▲]

Detailed reference viewed: 24 (1 ULg)
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 detailCardiac Biomarkers and Cycling Race
LE GOFF, Caroline ULg; Kaux, Jean-François ULg; Goffaux, Sébastien et al

in Journal of Sports Science & Medicine (2015), 14(2), 475-476

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See detailNumerical study of intrinsic features of isolas in a 2-dof nonlinear system
Detroux, Thibaut ULg; Noël, Jean-Philippe ULg; Masset, Luc ULg et al

in Proceedings of the ICEDyn conference (2015, June)

In the present paper, isolated response curves in a nonlinear system consisting of two masses sliding on a horizontal guide are examined. Transverse springs are attached to one mass to provide the ... [more ▼]

In the present paper, isolated response curves in a nonlinear system consisting of two masses sliding on a horizontal guide are examined. 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. Numerical simulations are carried out to study the conditions of existence of isolated solutions, their bifurcations, their merging with the main response branch and their basins of attraction. This is achieved using tools including nonlinear normal modes, energy balance, harmonic balance-based continuation and bifurcation tracking, and global analysis. [less ▲]

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See detailA process to address electricity distribution sector challenges: the GREDOR project approach
Cornélusse, Bertrand ULg; Vangulick, David; Glavic, Mevludin ULg et al

in Proceedings of the International Conference on Electricity Distribution, CIRED 2015 (2015, June)

This paper presents a general process set in the GREDOR (French acronym for “Gestion des Réseaux Electriques de Distribution Ouverts aux Renouvelables”) project to address the challenges in distribution ... [more ▼]

This paper presents a general process set in the GREDOR (French acronym for “Gestion des Réseaux Electriques de Distribution Ouverts aux Renouvelables”) project to address the challenges in distribution systems posed by the integration of renewable generation, changing load patterns, and the changes in the electricity market sector. A use case describing interactions among different players that fits the process is also presented. A pseudo-dynamic approach to Global Capacity Announcement as a way to increase penetration of Renewable Energy Sources in a distribution system is elaborated in more details. [less ▲]

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See detailGraph matching for reconciling SCADA and GIS of a distribution network
Cornélusse, Bertrand ULg; Leroux, Amandine; Glavic, Mevludin ULg et al

in Proceedings of the International Conference on Electricity Distribution, CIRED 2015 (2015, June)

This article deals with the problem of automatically es- tablishing a correspondence between two databases popu- lated independently over the years by a distribution com- pany, for instance a SCADA system ... [more ▼]

This article deals with the problem of automatically es- tablishing a correspondence between two databases popu- lated independently over the years by a distribution com- pany, for instance a SCADA system and a geographical information system. This problem is abstracted as a graph matching problem, well known in the combinatorial op- timisation community. It is then casted as an integer quadratic program. An idea of achievable results on a real system is provided, and needs for approximation or decom- position algorithms are discussed. [less ▲]

Detailed reference viewed: 20 (1 ULg)