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See detailOperational Modal Analysis using Second-Order Blind Identification
Poncelet, Fabien ULg; Kerschen, Gaëtan ULg; Golinval, Jean-Claude ULg

in 26th International Modal Analysis Conference, Orlando, 2008 (2008)

For modal analysis of large structures, it is unpractical and expensive to use artificial excitation (e.g., shakers). However, engineering structures are most often subject to ambient loads (e.g., traffic ... [more ▼]

For modal analysis of large structures, it is unpractical and expensive to use artificial excitation (e.g., shakers). However, engineering structures are most often subject to ambient loads (e.g., traffic and wind) that can be exploited for modal parameter estimation. One difficulty is that the actual loading conditions cannot generally be measured, and output-only measurements are available. This paper proposes to explore the utility of blind source separation (BSS) techniques for operational modal analysis. The basic idea of BSS is to recover unobserved source signals from their observed mixtures. The feasibility and practicality of the proposed method are demonstrated using an experimental application. [less ▲]

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See detailEfficiency of Targeted Energy Transfers in Coupled Nonlinear Oscillators Associated with 1:1 Resonance Captures
Sapsis, T.; Vakakis, Alexander F.; Gendelman, O. V. et al

in 45th Technical Meeting of the Society of Engineering Science, Urbana Champaign, 2008 (2008)

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See detailElectrophysiologic contribution to cervical pain
WANG, François-Charles ULg; TOMASELLA, Marco ULg

in Revue du Rhumatisme et des Maladies Osteo-Articulaires (2008)

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See detailLateral-torsional buckling of stainless steel I-beam in case of fire
Vila Real, P. M. M.; Lopes, N.; Simoes da Silva, L. et al

in Journal of Constructional Steel Research (2008), 64

This work presents a numerical study of the behaviour of stainless steel I-beams subjected to lateral–torsional buckling in case of fire and compares the obtained results with the beam design curves of ... [more ▼]

This work presents a numerical study of the behaviour of stainless steel I-beams subjected to lateral–torsional buckling in case of fire and compares the obtained results with the beam design curves of Eurocode 3. New formulae for lateral–torsional buckling, that approximate better the real behaviour of stainless steel structural elements in case of fire are proposed. These new formulae were based on numerical simulations using the program SAFIR, which was modified to take into account the material properties of the stainless steel. [less ▲]

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See detailPlastic analysis of continuous beams
Franssen, Jean-Marc ULg; Riva, P.

in Fire design of concrete structures - structural behaviour and assessment. State-of-art report. (2008), Bulletin 46

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See detailNonlinear Normal Modes, Part I: An Attempt To Demystify Them
Kerschen, Gaëtan ULg; Peeters, Maxime ULg; Golinval, Jean-Claude ULg et al

in 26th International Modal Analysis Conference, Orlando, 2008 (2008)

The concept of nonlinear normal modes (NNMs) is discussed in the present paper and its companions, Parts II and III. Because there is virtually no application of the NNMs to large-scale engineering ... [more ▼]

The concept of nonlinear normal modes (NNMs) is discussed in the present paper and its companions, Parts II and III. Because there is virtually no application of the NNMs to large-scale engineering structures, these papers are an attempt to highlight several aspects that might drive their development in the future. Specifically, we support that (i) numerical methods for the continuation of periodic solutions pave the way for an effective and practical computation of NNMs, and (ii) time-frequency analysis is particularly suitable for the analysis of the resulting dynamics. Another objective of the present paper is to describe, in simple terms, and to illustrate the fundamental properties of NNMs. This is achieved to convince the structural dynamicist not necessarily acquainted with them that they are a useful framework for the analysis of nonlinear vibrating structures. [less ▲]

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See detailComputation of Nonlinear Normal Modes using Numerical Continuation Techniques
Peeters, Maxime ULg; Viguié, Régis ULg; Serandour, Guillaume et al

in International Confernce on Advanced Computational Methods in Engineering, Liège, 2008 (2008)

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See detailImpacts of alien invasive plants on soil nutrients are correlated with initial site conditions in NW Europe
Dassonville, Nicolas; Vanderhoeven, SONIA ULg; Vanparys, Valerie et al

in Oecologia (2008), 157(1), 131-140

Alien invasive plants are capable of modifying ecosystem function. However, it is difficult to make generalisations because impacts often appear to be species- and site-specific. In this study, we ... [more ▼]

Alien invasive plants are capable of modifying ecosystem function. However, it is difficult to make generalisations because impacts often appear to be species- and site-specific. In this study, we examined the impacts of seven highly invasive plant species in NW Europe (Fallopia japonica, Heracleum mantegazzianum, Impatiens glandulifera, Prunus serotina, Rosa rugosa, Senecio inaequidens, Solidago gigantea) on nutrient pools in the topsoil and the standing biomass. We tested if the impacts follow predictable patterns, across species and sites or, alternatively, if they are entirely idiosyncratic. To that end, we compared invaded and adjacent uninvaded plots in a total of 36 sites with widely divergent soil chemistry and vegetation composition. For all species, invaded plots had increased aboveground biomass and nutrient stocks in standing biomass compared to uninvaded vegetation. This suggests that enhanced nutrient uptake may be a key trait of highly invasive plant species. The magnitude and direction of the impact on topsoil chemical properties were strongly site-specific. A striking finding is that the direction of change in soil properties followed a predictable pattern. Thus, strong positive impacts (higher topsoil nutrient concentrations in invaded plots compared to uninvaded ones) were most often found in sites with initially low nutrient concentrations in the topsoil, while negative impacts were generally found under the opposite conditions. This pattern was significant for potassium, magnesium, phosphorus, manganese and nitrogen. The particular site-specific pattern in the impacts that we observed provides the first evidence that alien invasive species may contribute to a homogenisation of soil conditions in invaded landscapes. [less ▲]

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See detailClinal differentiation during invasion: Senecio inaequidens (Asteraceae) along altitudinal gradients in Europe.
Monty, Arnaud ULg; Mahy, Grégory ULg

Poster (2008)

Plant population differentiation may play a role in decreasing the ability to predict whether, where, and when an introduced species will invade. However, few studies have addressed the level of genetic ... [more ▼]

Plant population differentiation may play a role in decreasing the ability to predict whether, where, and when an introduced species will invade. However, few studies have addressed the level of genetic change an alien species may undergo during range expansion, e.g. in response to climatic variation with altitude. In the present study, we tested the hypothesis that invasive populations of Senecio inaequidens (Asteraceae) differentiated during migration from two independent introduction sites into divergent altitudinal and climatic zones. We carried out two years of common garden experiments with eight populations from a Belgian altitudinal transect and ten populations from similar French transect. Climatic analysis revealed that the Belgian transect followed a temperature and precipitation gradient. A temperature and summer drought gradient characterized the French study site. We evaluated differentiation and clinal variation in the following characters: days to germination, days to flowering, height at maturity, final plant height and aboveground biomass. Results showed that S. inaequidens populations differentiated in growth traits during invasion. First year of experiment, regressing population growth trait means against source population altitude indicated the presence of clinal variation along both transects. Second year, similar results were found along the French transect, i.e. a reduction in height at maturity, plant height and aboveground biomass with increasing altitude. Including seed mass as a covariate did not change the outcome of the analysis. The possible evolutionary causes for the differentiation observed are discussed. [less ▲]

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See detailRelationships between C respiration and fine particulate organic matter (250-50 mu m) weight
Koutika, L *-Stella; Dassonville, Nicolas; Vanderhoeven, SONIA ULg et al

in European Journal of Soil Biology (2008), 44(1), 18-21

Soil organic matter (SOM) status was evaluated using the relationships between two independent soil variables, i.e., C respiration and the weight of particulate organic matter POM (4000-50 mu m) under ... [more ▼]

Soil organic matter (SOM) status was evaluated using the relationships between two independent soil variables, i.e., C respiration and the weight of particulate organic matter POM (4000-50 mu m) under different vegetation covers and ecosystems of central Belgium. A positive relationship was found between the weight of the finest POM fraction, i.e., fine POM fraction (250-50 mu m) and C respiration after 1 week (R-2 = 0.34, n = 120, p < 0.0001) and 2 weeks (R-2 = 0.28, n = 120, p < 0.0001) of incubation. Therefore, we assumed that the C respiration and the weight of fine POM might be used to evaluate the SOM status under different vegetation covers and ecosystems. (C) 2007 Elsevier Masson SAS. All rights reserved. [less ▲]

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See detailCarnet de pédiatrie en Afrique: Notes de chirurgie et imagerie
Battisti, Oreste ULg

Learning material (2008)

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See detailTheoretical Understanding of Targeted Energy Transfers for Suppressing Aeroelastic Instabilities in a Nonlinear Aeroelastic Test Apparatus
Lee, Young S.; McFarland, D. Michael; Kerschen, Gaëtan ULg et al

in 45th Technical Meeting of the Society of Engineering Science, Urbana Champaign, 2008 (2008)

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See detailEmpirical Mode Decomposition in the Reduced-Order Modeling of Aeroelastic Systems
Lee, Young S; McFarland, D. Michael; Vakakis, Alexander F. et al

in 49th AIAA Structural Dynamics and Materials Conference, Shaumberg, 2008 (2008)

A relationship between IntrinsicMode Functions (IMFs), derived from the Empirical Mode Decomposition (EMD), and the slow-flow model of a nonlinear dynamical system has been exploited in the development of ... [more ▼]

A relationship between IntrinsicMode Functions (IMFs), derived from the Empirical Mode Decomposition (EMD), and the slow-flow model of a nonlinear dynamical system has been exploited in the development of the Slow Flow Model Identification (SFMI) method for strongly nonlinear systems, in which the physical parameters of such systems are identified from experimental data. Both the slow flows and IMFs provide the means to expand a general multicomponent signal in terms of a series of simpler, dominant, monocomponent signals. The slow flows are obtained analytically, for example through application of the method of complexification and averaging (CxA), which transforms the equations of motion into a set of approximate equations in amplitude and phase for each modeled frequency component. In contrast, the EMD characterizes a signal through the envelope and phase of its elemental components, the IMFs. Thus, between nonlinear transitions, the equations derived using the CxA method govern the amplitude and phase of the modeled IMFs. Application of SFMI has, until now, been limited to low-dimensional systems subjected to impulsive excitation. Herein, the method is extended to identification of a planar rigid airfoil [less ▲]

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See detailVibration Mitigation of Nonlinear Vibrating Structures using Nonlinear Energy Sinks
Viguié, Régis ULg; Peeters, Maxime ULg; Kerschen, Gaëtan ULg et al

in 26th International Modal Analysis Conference, Orlando, 2008 (2008)

The tuned mass damper (TMD) is a simple and efficient device, but it is only effective when it is precisely tuned to the frequency of a vibration mode. Because nonlinear vibrating structures have resonant ... [more ▼]

The tuned mass damper (TMD) is a simple and efficient device, but it is only effective when it is precisely tuned to the frequency of a vibration mode. Because nonlinear vibrating structures have resonant frequencies that vary with the amount of total energy in the system, the efficiency of a TMD is questionable in this case. In the present study, the performance of an essentially nonlinear attachment, termed a nonlinear energy sink (NES), is assessed. It is shown that, unlike the TMD, an NES has no preferential resonant frequency, which makes it a good candidate for vibration mitigation of nonlinear vibrating structures. [less ▲]

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See detailIdentification of the Slow-Flow Dynamics of Transonic Aeroelastic Response from Time-Series Data
Lee, Y. S.; Vakakis, Alexander F.; McFarland, D. M. et al

in 45th Technical Meeting of the Society of Engineering Science, Urbana Champaign, 2008 (2008)

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