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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 ▲]

Detailed reference viewed: 16 (1 ULg)
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 ▲]

Detailed reference viewed: 17 (3 ULg)
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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Peer Reviewed
See detailCyber-pédopornographes : fixation pédophilique et Internet, une alternative à risque ?
Glowacz, Fabienne ULg; Galligani, Lucas; Hennen, Clarisse

Poster (2015, June)

La consommation de pédopornographie est un thème de recherche récent faisant suite à l’intérêt scientifique et clinique porté à la délinquance sexuelle. La question des rapports entre l’existence d’une ... [more ▼]

La consommation de pédopornographie est un thème de recherche récent faisant suite à l’intérêt scientifique et clinique porté à la délinquance sexuelle. La question des rapports entre l’existence d’une fixation pédophilique, la consommation de pédopornographie et les passages à l’acte pédophilique a été abordée par plusieurs études (Bourke et Hernandez, 2009 ; Babchishin, Hanson et Herman, 2010 ; Corriveau et Fortin, 2014) et reste en débat. Selon l’article 383bis du code pénal belge, la pédopornographie consiste en des « emblèmes, objets, films, photos, diapositives ou autres supports visuels présentant des mineurs d’âge dans des positions à caractère sexuel ». Cependant, le point de vue légal ne permet pas de prendre en considération tous les supports que peuvent utiliser les pédopornographes. En effet, certains amateurs trouveront satisfaction dans des contenus non-pornographiques. Dès lors, une typologie des images utilisées par les amateurs de pornographie enfantine a été mise en place par Taylor, Holland et Quayle (2001), sous le nom de COPINE Scale, reprenant dix catégories d’images pouvant être consultées ou téléchargées par les amateurs. Il existe différents lieux sur l’Internet sur lesquels ces supports se trouvent, le plus important étant les groupes de nouvelles, mais aussi plusieurs systèmes, comme que le peer-to-peer, dans lesquels les échanges de telles images s’opèrent. Plusieurs typologies ont été élaborées (Fortin et Roy, 2003 ; Delmonico et Griffin, 2008 ; Davidson, 2008 ; Corriveau et Fortin, 2011) identifiant divers profils : collectionneurs, distributeurs, abuseurs, producteurs et commerçants. Dans le cadre de notre recherche, à partir d’entrevues menées avec 9 sujets consommateurs de pédopornographie (âgés entre 29 et 60 ans) consultant au centre de santé mentale SYGMA, équipe de santé spécialisée, (8 d’entre eux dans le cadre d’une mesure judiciaire), nous avons exploré plusieurs dimensions pouvant être associées aux conduites de consommation de pédopornographie : l’addiction à internet, la présence d’une fixation pédophilique, la tendance à l’ennui, l’impulsivité et la recherche de sensation, la présence d’un soutien social ainsi que le rôle de sous-cultures pédopornograhiques. Au niveau méthodologique, nous avons adopté une approche mixte basée sur un entretien semi-structuré et la passation de tests (Echelle de provision sociale, Caron, 1996 ; Echelle de disposition à l’ennui, Gana et Akrmi, 1988 ; Implusive Behavior Scale, Whiteside et Lynam, 2001 ; Mesure de l’intensité des conduites addictives appliquée à l’internet, Décamps, Battaglia, et Idier, 2010) et sur une analyse du dossier clinique comprenant les jugements, les avis motivés et les entretiens cliniques. Nos résultats indiquent que la fixation pédophilique pouvait être un moteur de la consommation sans pour autant être présente chez tous les sujets. La tendance à l’ennui est une dimension peu signifiante dans la dynamique de consommation. Ce sont le manque de soutien social et l’insatisfaction affective et sexuelle qui se retrouvent au centre des dynamiques de la consommation pédopornographique de nos sujets. Isolés socialement et présentant un développement problématique sur le plan sexuel et affectif, c’est notamment par la consommation de pédopornographie que les sujets disent avoir trouvé une alternative. Cette consommation renvoie par ailleurs à un manque de contrôle social, offrant l’opportunité de consommer, ainsi qu’une impossibilité d’identifier un partenaire sexuel. L’Internet sera alors vu comme un outil permettant de répondre à ces difficultés sexuelles, sans pour autant qu’il n’y ait de comportement addictif. [less ▲]

Detailed reference viewed: 8 (0 ULg)
See detailTime and aspect: what the academic grammars say, and what the texts actually show
Winand, Jean ULg

Scientific conference (2015, May 29)

Detailed reference viewed: 27 (0 ULg)
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See detailFragmentation urbaine à travers les réseaux techniques
Cabrera Quispe, Juan Edson ULg

Doctoral thesis (2015)

Since about three decades ago, the networking services (water, energy, transport and telecommunications) are the subject of studies and mainly reforms (liberalization, privatization and concessions to ... [more ▼]

Since about three decades ago, the networking services (water, energy, transport and telecommunications) are the subject of studies and mainly reforms (liberalization, privatization and concessions to private companies, etc.) and also an important economic policy issue. However the possible effects of these reforms on the fragmentation or integration of urban societies are still poorly studied, although some studies (mainly on developing cities) support the thesis that there would be a growing urban fragmentation, reinforced by the dominant modes of implementing reforms network services. One of the most important theses about the subject is in a relatively recent development of the English authors Stephen Graham and Simon Marvin (2001). Their work generalizes the motion of fragmentation (splintering Urbanism) to all network services and a set of economic regions in the world. While this thesis presents consistency and validity - since it is known that the application of models of decentralization and liberalization of services has an effect on the fragmentation - the position of fragmentation due to centralized networks is inside a new analysis framework and still incomplete considering the absence of more empirical evidence. The thesis of fragmentation from centralized networks suggests that powerful factors are contributing to the disintegration of infrastructure, favoring the fragmentation of the social structure and material of cities. In fact, this breakdown of infrastructures makes possible many strategies of evasion; they are addressed to connect powerful users and valorized spaces, preventing the connection with less powerful users and poor spaces. These processes lead to the creation of spaces from different social networks, resulting in social elites living every day in places disconnected from the urban structure of the set (in gated communities, new complex people and other planned communities), as well as the lower classes, but the latter with the worst conditions. The main hypothesis of the "splintering Urbanism" argues that network services have an integrated character and are precisely the privatization and liberalization of services that contribute to the breakdown of network infrastructure and urban fragmentation feed. The control of networks from powerful coalitions of actors, separation and segmentation boost infrastructure in different network elements and service pack (2001: 141). This separation would occur across strategies "bypass" or "wrap" seeking to connect users, valuable or powerful places, and through discarding or dodge weaker users and worthless places. Our thesis "Urban Fragmentation through technical networks," confirms and reinforces the thesis made by Graham & Marvin, across expounding on the Cochabamba Bolivian context, a set of technical networks of small-scale or micro decentralized networks which are managed by autonomous social organizations that also fragment the territory without the need for "by pass" and the socio-spatial differentiation, but through the realization of strategies linked to autonomous administration and management of common and basic goods like water. This thesis demonstrates the existence of processes of spatial dislocation and loss of solidarity (main evils of urban fragmentation) across the dynamics of technical devices and decentralized networks infrastructure services from private-community water and small scale. However, our work describes in its urban development, territorial and environmental problems inside the phenomenon. The paper first presents a set of theories that attempt to explain the fragmentation and its particularities, then describes the socio-spatial formation of the study area whose characteristics allow this type of phenomenon, to arrive to a section that exposes all the particularities of the management water from public and local actors, analyzed from the environmental logic of urban water cycle, including the specifics of the main stage of study of this thesis, the municipality of Quillacollo in Cochabamba. From a spatial perspective, the thesis exhibits the characteristics of urban fragmentation across technical networks, exposing the details related to the organization of urban space as a result of processes of spatial dislocation, loss of solidarity and exercise of territoriality in small networks. It is concluded in a discussion about the validity of the strategies in terms of access to the resource, the possibilities of intervention and reflections about the power relationships among fragments and for water control. Finally, as a supplement, urban fragmentation through small technical networks, also allows to display the tensions between two ways of managing the territory (centralized view from the public sector and decentralized vision from local communities) highlighting the uncomfortable and marginalized urban planning position, but challenging the urbanism to recover to action on the highly fragmented contemporary cities with complex scenarios of governance and sometimes rare or endangered resources. [less ▲]

Detailed reference viewed: 24 (3 ULg)
See detailLe donné phénoménal de Tim Crane
Gauvry, Charlotte ULg

Conference (2015, May 28)

Detailed reference viewed: 9 (0 ULg)
Peer Reviewed
See detailPsychopathy and emotions: would emotional distancing make more efficient in cognitive tasks?
Grandjean, Sylvie; Dehon, Hedwige ULg; Blavier, Adelaïde ULg et al

Poster (2015, May 28)

Detailed reference viewed: 13 (0 ULg)
Peer Reviewed
See detailBorderline Personality Disorder through the Rorschach test
Rommes, Jennifer; Englebert, Jérôme ULg; Blavier, Adelaïde ULg

Poster (2015, May 28)

Detailed reference viewed: 13 (0 ULg)
Peer Reviewed
See detailWork incapacity and chronic pain patients: Is there an impact of work incapacity on anxiety and depression?
Beaumel, Alexia; Vanootighem, Valentine ULg; Gillet, Aline ULg et al

Poster (2015, May 28)

In 2011, a report of the Federal Public Service have shown that 8.5% of the Belgian population suffers from chronic pains, which represents 938 300 belgian people (Berquin et al., 2011). These persistent ... [more ▼]

In 2011, a report of the Federal Public Service have shown that 8.5% of the Belgian population suffers from chronic pains, which represents 938 300 belgian people (Berquin et al., 2011). These persistent pains may result in functional limitations on both domestic and professional domains which may lead to temporary or permanently work incapacity (Faymonville et al., 2014). These incapacities may in turn cause a social withdrawal and a tendency to focus on pain (Berquin et al., 2011). Additionally, patients are prone to emotional modifications due to persistent pain (Ossipov et al., 2010). All of these factors may contribute in the emergence of anxiety and depressive symptoms. The present study examines the impact of type of work incapacities (at work, temporary incapacity and permanent incapacity) on anxiety and depression scores as a function of diagnoses (fibromyalgia, chronic pain syndrome, back pain, polyalgia). 123 patients suffering from chronic pain completed a measure of anxiety and depression (HADS), and a self-reported questionnaire of psychological and physical disability at work. We did not found any significant effect of type of work incapacities on anxiety and depression scores. Results present tables of frequencies to illustrate the social and professional situations of patients as a function of chronic pain diagnoses. [less ▲]

Detailed reference viewed: 19 (0 ULg)
See detailDétecteurs de candidats au djihad - 150 travailleurs sociaux ont commencé une formation en "déradicalisation"
Ponciau, Ludivine; Garcet, Serge ULg

Article for general public (2015)

L'article propose une analyse de la politique de formation du secteur de l'aide à la jeunesse en matière de "déradicalisation" et un entretien dans lequel nous donnons notre point de vue d'expert.

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See detailGestion des déchets nucléaires en France et en Belgique: Quelle place pour la critique ?
Parotte, Céline ULg

Conference (2015, May 25)

Depuis les années 1970, avec la multiplication des controverses scientifiques (Callon, Lascoumes et Barthe 2001), souvent liées à des mouvements pacifistes en environnementalistes ; nous assistons à la ... [more ▼]

Depuis les années 1970, avec la multiplication des controverses scientifiques (Callon, Lascoumes et Barthe 2001), souvent liées à des mouvements pacifistes en environnementalistes ; nous assistons à la naissance d’un flux d’incertitude et de critique politico-sociale, dirigée principalement vers le monde scientifique, sa production et ses hésitations. Il est malaisé de prévoir si cela mènera à une réelle désolidarisation des notions de science, technologie et progrès, mais il reste à supposer que cette critique permettra une gestion plus réflexive des effets majeurs du développement scientifique et technologique (Schot et Rip 2009). En d’autres termes, bien que les liens entre les idéologies du progrès et de la technologie restent très souvent puissants et non remis en question, on assiste au même moment à une critique sociale des conséquences sur le processus de gestion des choix technologiques qui s’y rapportent. Cette contribution propose de s’attarder sur le cas de la gouvernance socio technique de la gestion des déchets hautement radioactifs depuis le « tournant participatif » opéré dans les années 90 en France et en Belgique. Il s’agit de poser un regard critique sur l’apparition d’un nouveau mode de gouvernance plus participatif (au travers de l’inclusion de nouveaux acteurs) et ses conséquences. Dans quelle mesure ceux-ci redéfinissent-ils les positionnements du monde scientifique au sein du processus décisionnel ? Comment le monde scientifique reçoit-il les critiques qui lui sont adressées ? Plutôt que des tendances globales, cette contestation témoigne le plus souvent d’une mosaïque d’activités critiques dynamiques, concurrentes ou complémentaires dont les effets semblent faire vaciller — ou à tout le moins mettre sous tension — l’organisation, les routines et les institutions des sociétés modernes (Delvenne 2011). Cette mosaïque reflète le dynamisme des acteurs sociaux qui propagent leurs agendas et défendent leurs intérêts à travers la négociation de concessions, l’enchevêtrement de décisions et la cristallisation de rapports de force. En d’autres termes, les avancées d’un projet comme la gestion des déchets nucléaires ne sont pas la progression inéluctable d’un processus uniformément accepté par toutes les tendances de la société. En réalité, il existe une multitude d’acteurs qui influencent sans cesse la nature de ses contours. Ces acteurs sociaux bénéficient d’espaces politiques et institutionnels divers pour exprimer leurs préférences et tenter de transformer durablement les critiques qu’ils formulent en actions politiques qui trouvent un écho plus large au sein de la société. [less ▲]

Detailed reference viewed: 5 (1 ULg)
See detailLa culture industrielle de microalgues
Franck, Fabrice ULg

Conference given outside the academic context (2015)